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  • 251.
    De Rosa, Horacio
    et al.
    Laboratorio de metulografia, Facultad de Ingenieria UBA, Buenos Aries, Argentina.
    Cardus, Gustavo
    Laboratorio de metulografia, Facultad de Ingenieria UBA, Buenos Aries, Argentina.
    Broitman, Esteban
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Zimmerman, Rosa
    Laboratorio de Peliculas Delgudas, Facultad de IngenieriLaboratorio de Peliculas Delgadas, Facultad de Ingenieria UBA, Buenos Aries, Argentina.
    Propiedades Tribológicas de Películas de AlSn Depositadas por Magnetron Sputtering [Tribological Properties of AlSn Thin Films Deposited by Magnetron Sputtering]2000In: Anales AFA, Vol. 11, no 1, p. 195-198Article in journal (Refereed)
    Abstract [en]

    In this paper structural and tribological properties of thin films, made with the bimetal 20AlSn used as solid lubricant in the automotive industry, were studied. Films with thicknesses in the range 150 nm to 3μm were deposited by magnetron sputtering. It is found that in the thinner films predominates a diffusion growth mechanism, while for larger thicknesses it is observed an aggregation growth mechanism. A finely dispersed structure of uniform particle size and shape, vital for good tribological behavior, is obtained.

  • 252.
    Diliegros-Godines, C. J.
    et al.
    CINVESTAV, Querétaro, Mexico.
    Flores-Ruiz, Francisco
    CINVESTAV, Querétaro, Mexico.
    Castanedo-Pérez, R.
    CINVESTAV, Querétaro, Mexico.
    Torres-Delgado, G.
    CINVESTAV, Querétaro, Mexico.
    Espinoza-Beltrán, F. J.
    CINVESTAV, Querétaro, Mexico.
    Broitman, Esteban
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Mechanical and tribological properties of CdO + SnO2 thin films prepared by sol–gel2015In: Journal of Sol-Gel Science and Technology, ISSN 0928-0707, E-ISSN 1573-4846, Vol. 74, no 1, p. 114-120Article in journal (Refereed)
    Abstract [en]

    We report the mechanical and tribological properties of transparent conductive oxide CdO + SnO2 coatings. The films were deposited on glass substrates by the sol–gel technique using, as precursor solution, a mixture of CdO and SnO2 solutions obtained at room temperature. Depending on the Sn atomic concentration percentage values the X-ray diffraction patterns show three types of films constituted of (1) CdO + Cd2SnO4, (2) Cd2SnO4 and (3) Cd2SnO4 + CdSnO3 crystals. Reciprocal microfriction tests revealed that films with Cd2SnO4 phase have friction values in the range 0.48–0.51 and a low wear rate of ~5 × 10−5 mm3 N−1 m−1. Nanoindentation tests have shown an increment of the elastic modulus from 50 GPa for CdO + Cd2SnO4 films to 90 GPa for Cd2SnO4 films, while the hardest coating was the one constituted by Cd2SnO4 crystals with H = 5.7 GPa, comparable to the hardness and elastic modulus reported for ITO films.

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  • 253.
    Dobrovolskiy, Alexander
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, The Institute of Technology.
    Persson, Per O. Å
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Sukrittanon, Supanee
    Graduate Program of Materials Science and Engineering, University of California, La Jolla, California 92093, United States.
    Kuang, Yanjin
    Department of Physics, University of California, La Jolla, California 92093, United States.
    Tu, CHarles W.
    Department of Electrical and Computer Engineering, University of California, La Jolla, California 92093, United States.
    Chen, Weimin
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, The Institute of Technology.
    Buyanova, Irina
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, The Institute of Technology.
    Effects of Polytypism on Optical Properties and Band Structure ofIndividual Ga(N)P Nanowires from Correlative Spatially Resolved Structural and Optical Studies2015In: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 15, no 6, p. 4052-4058Article in journal (Refereed)
    Abstract [en]

    III-V semiconductor nanowires (NWs) have gained significant interest as building blocks in novel nanoscale devices. The one-dimensional (1D) nanostructure architecture allows one to extend band structure engineering beyond quantum confinement effects by utilizing formation of different crystal phases that are thermodynamically unfavorable in bulk materials. It is therefore of crucial importance to understand the influence of variations in the NWs crystal structure on their fundamental physical properties. In this work we investigate effects of structural polytypism on the optical properties of gallium phosphide and GaP/GaNP core/shell NW structures by a correlative investigation on the structural and optical properties of individual NWs. The former is monitored by transmission electron microscopy, whereas the latter is studied via cathodoluminescence (CL) mapping. It is found that structural defects, such as rotational twins in zinc blende (ZB) GaNP, have detrimental effects on light emission intensity at low temperatures by promoting nonradiative recombination processes. On the other hand, formation of the wurtzite (WZ) phase does not notably affect the CL intensity neither in GaP nor in the GaNP alloy. This suggests that zone folding in WZ GaP does not enhance its radiative efficiency, consistent with theoretical predictions. We also show that the change in the lattice structure have negligible effects on the bandgap energies of the GaNP alloys, at least within the range of the investigated nitrogen compositions of <2%. Both WZ and ZB GaNP are found to have a significantly higher efficiency of radiative recombination as compared with that in parental GaP, promising for potential applications of GaNP NWs as efficient nanoscale light emitters within the desirable amber-red spectral range.

  • 254.
    Dorri, Samira
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering. Linköpings universitet.
    Growth and Characterization of CrB2/TiB2 Superlattices by Magnetron Sputtering2019Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    In the present work, growth and structural characterization of CrB2/TiB2 superlattices on (0001) Al2O3 substrate is studied. The superlattices are grown using a direct current magnetron sputtering (DCMS) system with a base pressure of <9E-7 Torr.

    For structural characterization X-ray diffraction (XRD), X-ray reflectivity (XRR), transmission electron microscopy (TEM), selected area electron diffraction (SAED), energy dispersive X-ray spectroscopy (EDX), and scanning transmission electron microscopy (STEM) are used. Hardness is measured using nanoindentation technique.

    For growth of CrB2/TiB2 superlattices it is shown that the sputtering gas pressure of PAr= 4 mTorr, and substrate temperature of T= 600 °C are optimized parameters for growing well-structured superlattices with good interface quality. Superlattices with a layer thickness ratio of Γ= 0.43 (Γ= DTiB2/DCrB2+DTiB2) and a total thickness of 1 μm are deposited with different modulation periods Λ=1, 2, 6, 8, and 10 nm to see the layer-thickness affect on the quality of the structures. XRD and TEM results show that by increasing the modulation period, the quality of superlattices with smooth interfaces increases. The superlattices with modulation period Λ=8 nm is shown to be the best structure having coherent lattice and smooth interfaces up to ~20 periods. The STEM analysis shows that after about 20 periods, grains started to grow at slightly different orientations. A superlattice of TiB2/CrB2(having TiB2 as the first deposited layer) with modulation period Λ=8 nm shows an epitaxial growth of TiBon Al2O3 (0001) substrate, however, no big difference between the structure of TiB2/CrBand CrB2/TiB2 superlattices is seen.

    EDX maps and line profiles show that there is a diffusion of CrB2 into TiB2 layers which is a serious problem for obtaining sharp interfaces. STEM also shows that for a small modulation period of Λ=1 nm, there is a faint layered structure, whereas EDX, SAED and XRD indicates a homogenous textures Ti-Cr-B film in this sample.

    Finally, the hardness measurement shows a hardness value of 29-34 GPa for different modulation periods. The lowest hardness value is related to the sample with modulation period of Λ=1 nm with about 29 GPa, and the highest hardness is related to the sample with Λ=8 nm ith around 34 GPa.

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  • 255.
    dos Santos, R. B.
    et al.
    University of Federal Bahia, Brazil.
    Rivelino, R.
    University of Federal Bahia, Brazil.
    de Brito Mota, F.
    University of Federal Bahia, Brazil.
    Kostov Gueorguiev, Gueorgui
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Kakanakova-Gueorguie, Anelia
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Dopant species with Al-Si and N-Si bonding in the MOCVD of AlN implementing trimethylaluminum, ammonia and silane2015In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 48, no 29, article id 295104Article in journal (Refereed)
    Abstract [en]

    We have investigated gas-phase reactions driven by silane (SiH4), which is the dopant precursor in the metalorganic chemical vapor deposition (MOCVD) of aluminum nitride (AlN) doped by silicon, with prime focus on determination of the associated energy barriers. Our theoretical strategy is based on combining density-functional methods with minimum energy path calculations. The outcome of these calculations is suggestive for kinetically plausible and chemically stable reaction species with Al-Si bonding such as (CH3)(2)AlSiH3 and N-Si bonding such as H2NSiH3. Within this theoretical perspective, we propose a view of these reaction species as relevant for the actual MOCVD of Si-doped AlN, which is otherwise known to be contributed by the reaction species (CH3)(2)AlNH2 with Al-N bonding. By reflecting on experimental evidence in the MOCVD of various doped semiconductor materials, it is anticipated that the availability of dopant species with Al-Si, and alternatively N-Si bonding near the hot deposition surface, can govern the incorporation of Si atoms, as well as other point defects, at the AlN surface.

  • 256.
    dos Santos, Renato B.
    et al.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, Faculty of Science & Engineering. University of Federal Bahia, Brazil.
    de Brito Mota, F.
    University of Federal Bahia, Brazil.
    Rivelino, R.
    University of Federal Bahia, Brazil.
    Kakanakova-Gueorguie, Anelia
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Gueorguiev, Gueorgui Kustov
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Van der Waals stacks of few-layer h-AlN with graphene: an ab initio study of structural, interaction and electronic properties2016In: Nanotechnology, ISSN 0957-4484, E-ISSN 1361-6528, Vol. 27, no 14, p. 145601-Article in journal (Refereed)
    Abstract [en]

    Graphite-like hexagonal AlN (h-AlN) multilayers have been experimentally manifested and theoretically modeled. The development of any functional electronics applications of h-AlN would most certainly require its integration with other layered materials, particularly graphene. Here, by employing vdW-corrected density functional theory calculations, we investigate structure, interaction energy, and electronic properties of van der Waals stacking sequences of few-layer h-AlN with graphene. We find that the presence of a template such as graphene induces enough interlayer charge separation in h-AlN, favoring a graphite-like stacking formation. We also find that the interface dipole, calculated per unit cell of the stacks, tends to increase with the number of stacked layers of h-AlN and graphene.

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  • 257.
    dos Santos, Renato B.
    et al.
    University of Federal Bahia, Brazil.
    Rivelino, R.
    University of Federal Bahia, Brazil.
    de Brito Mota, F.
    University of Federal Bahia, Brazil.
    Kakanakova-Gueorguie, Anelia
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Gueorguiev, Gueorgui Kostov
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Feasibility of novel (H3C)(n)X(SiH3)(3-n) compounds (X = B, Al, Ga, In): structure, stability, reactivity, and Raman characterization from ab initio calculations2015In: Dalton Transactions, ISSN 1477-9226, E-ISSN 1477-9234, Vol. 44, no 7, p. 3356-3366Article in journal (Refereed)
    Abstract [en]

    We employ ab initio calculations to predict the equilibrium structure, stability, reactivity, and Raman scattering properties of sixteen different (H3C)(n)X(SiH3)(3-n) compounds (X = B, Al, Ga, In) with n = 0-3. Among this methylsilylmetal family, only the (H3C)(3)X members, i.e., trimethylboron (TMB), trimethylaluminum (TMA), trimethylgallium (TMG), and trimethylindium (TMI), are currently well-studied. The remaining twelve compounds proposed here open up a two-dimensional array of new possibilities for precursors in various deposition processes, and evoke potential applications in the chemical synthesis of other compounds. We infer that within the (H3C)(n)X(SiH3)(3-n) family, the compounds with fewer silyl groups (and consequently with more methyl groups) are less reactive and more stable. This trend is verified from the calculated cohesive energy, Gibbs free energy of formation, bond strength, and global chemical indices. Furthermore, we propose sequential reaction routes for the synthesis of (H3C)(n)X(SiH3)(3-n) by substitution of methyl by silyl groups, where the silicon source is the silane gas. The corresponding reaction barriers for these chemical transformations lie in the usual energy range typical for MOCVD processes. We also report the Raman spectra and light scattering properties of the newly proposed (H3C)(n)X(SiH3)(3-n) compounds, in comparison with available data of known members of this family. Thus, our computational experiment provides useful information for a systematic understanding of the stability/reactivity and for the identification of these compounds.

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  • 258.
    dos Santos, Renato B
    et al.
    Instituto de Física, Universidade Federal da Bahia, Salvador, Bahia, Brazil.
    Rivelino, R
    Instituto de Física, Universidade Federal da Bahia, Salvador, Bahia, Brazil.
    de Brito Mota, F
    Instituto de Física, Universidade Federal da Bahia, Salvador, Bahia, Brazil.
    Kostov Gueorguiev, Gueorgui
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Effects of N doping on the electronic properties of a small carbon atomic chain with distinct sp(2) terminations: A first-principles study2011In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 84, no 7, p. 075417-Article in journal (Refereed)
    Abstract [en]

    arbon nanostructures consisting of corannulene/coronene-like pieces connected by atomic chains and doped with nitrogen atoms have been addressed by carrying out first-principles calculations within the framework of the spin-polarized density functional theory. Our results show that the conformation, charge distributions, and spin states are significantly influenced by the nitrogen incorporation in comparison to these characteristics of similar pure carbon structures. Higher concentration of incorporated nitrogen leads to a smaller highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) gap and different conductive states near the Fermi level. In turn the different location of the N-incorporation sites allows switching on and off of the pi-electron magnetism in these systems. We found that the rotational deformation of the terminations with respect to the carbon chain depends on the number and the location of the incorporated N atoms. The most stable N-doped structures exhibit a relative rotation of the terminations of approximately 90 degrees. These findings indicate that by controllable N doping one can tune the conducting channel of carbon chains connected to sp(2) terminations; thus obtaining low band-gap nano-units.

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  • 259.
    dos Santos, Renato B.
    et al.
    University of Federal Bahia, Brazil .
    Rivelino, Roberto
    University of Federal Bahia, Brazil .
    de B. Mota, Fernando
    University of Federal Bahia, Brazil .
    Gueorguiev, Gueorgui Kostov
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Exploring Hydrogenation and Fluorination in Curved 2D Carbon Systems: A Density Functional Theory Study on Corannulene2012In: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 116, no 36, p. 9080-9087Article in journal (Refereed)
    Abstract [en]

    Corannulene has been a useful prototype for studying C-based nanostructures as well as surface chemistry and reactivity of sp(2)-hybridized carbon-based materials. We have investigated fluorination and hydrogenation of corannulene carrying out density functional theory calculations. In general, the fluorination is energetically more favorable than hydrogenation of corannulene. The substitution of the peripheral H atoms in the corannulene molecule by F atoms leads to a larger cohesive energy gain than when F (or H) atoms are bonded to the hub carbon and bridge carbon sites of this molecule. As expected for doped C-based nanostructures, the hydrogenation or fluorination significantly changes the HOMO-LUMO gap of the system. We have obtained HOMO-LUMO gap variations of 0.13-3.46 eV for F-doped and 0.38-1.52 eV for H-doped systems. These variations strongly depend on the concentration and position of the incorporated F/H atoms, instead of the structural stability of the doped systems. Considering these calculations, we avoid practical difficulties associated with the addition/substitution reactions of larger curved two-dimensional (2D) carbon nanostructures, and we obtain a comprehensive and systematic understanding of a variety of F/H 2D doped systems.

  • 260.
    Du, Yong
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering. Shanghai Inst Technol, Peoples R China.
    Chen, Jiageng
    Shanghai Inst Technol, Peoples R China.
    Liu, Xin
    Shanghai Inst Technol, Peoples R China.
    Lu, Chun
    Shenyang Aerosp Univ, Peoples R China.
    Xu, Jiayue
    Shanghai Inst Technol, Peoples R China.
    Paul, Biplab
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Eklund, Per
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Flexible n-Type Tungsten Carbide/Polylactic Acid Thermoelectric Composites Fabricated by Additive Manufacturing2018In: Coatings, ISSN 2079-6412, Vol. 8, no 1, article id 25Article in journal (Refereed)
    Abstract [en]

    Flexible n-type tungsten carbide/polylactic acid (WC/PLA) composites were fabricated by additive manufacturing and their thermoelectric properties were investigated. The preparation of an n-type polymer-based thermoelectric composite with good stability in air atmosphere via additive manufacturing holds promise for application in flexible thermoelectric devices. For WC/PLA volume ratios varying from similar to 33% to 60%, the electrical conductivity of the composites increased from 10.6 to 42.2 S/cm, while the Seebeck coefficients were in the range -11 to -12.3 V/K. The thermal conductivities of the composites varied from similar to 0.2 to similar to 0.28 Wamp;lt;boldamp;gt;mamp;lt;/boldamp;gt;-1amp;lt;boldamp;gt;Kamp;lt;/boldamp;gt;-1 at similar to 300 K.

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  • 261.
    Du, Yong
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering. Shanghai Inst Technol, Peoples R China.
    Chen, Jiageng
    Shanghai Inst Technol, Peoples R China.
    Meng, Qiufeng
    Shanghai Inst Technol, Peoples R China.
    Xu, Jiayue
    Shanghai Inst Technol, Peoples R China.
    Paul, Biplab
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Eklund, Per
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Flexible ternary carbon black/Bi2Te3 based alloy/polylactic acid thermoelectric composites fabricated by additive manufacturing2020In: JOURNAL OF MATERIOMICS, ISSN 2352-8478, Vol. 6, no 2, p. 293-299Article in journal (Refereed)
    Abstract [en]

    Flexible ternary carbon black/Bi2Te3 based alloy/polylactic acid (CB/BTBA/PLA) composites were fabricated by additive manufacturing and their thermoelectric properties were investigated from 300 K to 360 K. At 300 K, as the mass ratios of BTBAs in the composites increased from 38.5% to 71.4%, both the electrical conductivity and Seebeck coefficient of the composites increased from 5.8 S/cm to 13.3 S/cm, and from 60.2 mV/K to 119.9 mV/K, respectively, and the thermal conductivity slightly increased from 0.15 W m(-1)K(-1) to 0.25 W m(-1)K(-1), as a result, the ZT value of the composites increased from 0.004 to 0.023. As the temperature increased from 300 K to 360 K, the electrical conductivity of all the composites slightly decreased, while the thermal conductivity slowly increased, and a highest ZT value of 0.024 was achieved for the composites with 71.4% BTBAs at 320 K. Unlike traditional sterolithography, fused deposition modeling, selective laser melting, etc., this additive manufacturing process can directly print the solutions which contain inorganic fillers and polymer matrixes into almost any designed intricate geometries of thermoelectric composites, therefore this process has great potential to be used for fabrication of flexible polymer based thermoelectric composites and devices. (C) 2020 The Chinese Ceramic Society. Production and hosting by Elsevier B.V.

  • 262.
    Du, Yong
    et al.
    Shanghai Inst Technol, Peoples R China.
    Li, Haixia
    Shanghai Inst Technol, Peoples R China.
    Jia, Xuechen
    Shanghai Inst Technol, Peoples R China.
    Dou, Yunchen
    Shanghai Inst Technol, Peoples R China.
    Xu, Jiayue
    Shanghai Inst Technol, Peoples R China.
    Eklund, Per
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Preparation and Thermoelectric Properties of Graphite/poly(3,4-ethyenedioxythiophene) Nanocomposites2018In: Energies, ISSN 1996-1073, E-ISSN 1996-1073, Vol. 11, no 10, article id 2849Article in journal (Refereed)
    Abstract [en]

    Graphite/poly(3,4-ethyenedioxythiophene) (PEDOT) nanocomposites were prepared by an in-situ oxidative polymerization process. The electrical conductivity and Seebeck coefficient of the graphite/PEDOT nanocomposites with different content of graphite were measured in the temperature range from 300 K to 380 K. The results show that as the content of graphite increased from 0 to 37.2 wt %, the electrical conductivity of the nanocomposites increased sharply from 3.6 S/cm to 80.1 S/cm, while the Seebeck coefficient kept almost the same value (in the range between 12.0 V/K to 15.1 V/K) at 300 K, which lead to an increased power factor. The Seebeck coefficient of the nanocomposites increased from 300 K to 380 K, while the electrical conductivity did not substantially depend on the measurement temperature. As a result, a power factor of 3.2 Wm(-1) K-2 at 380 K was obtained for the nanocomposites with 37.2 wt % graphite.

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  • 263.
    Du, Yong
    et al.
    Shanghai Inst Technol, Peoples R China.
    Li, Jia
    Shanghai Inst Technol, Peoples R China.
    Xu, Jiayue
    Shanghai Inst Technol, Peoples R China.
    Eklund, Per
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Thermoelectric Properties of Reduced Graphene Oxide/Bi2Te3 Nanocomposites2019In: Energies, ISSN 1996-1073, E-ISSN 1996-1073, Vol. 12, no 12, article id 2430Article in journal (Refereed)
    Abstract [en]

    Reduced graphene oxide (rGO)/Bi2Te3 nanocomposite powders with different contents of rGO have been synthesized by a one-step in-situ reductive method. Then, rGO/Bi2Te3 nanocomposite bulk materials were fabricated by a hot-pressing process. The effect of rGO contents on the composition, microstructure, TE properties, and carrier transportation of the nanocomposite bulk materials has been investigated. All the composite bulk materials show negative Seebeck coefficient, indicating n-type conduction. The electrical conductivity for all the rGO/Bi2Te3 nanocomposite bulk materials decreased with increasing measurement temperature from 25 degrees C to 300 degrees C, while the absolute value of Seebeck coefficient first increased and then decreased. As a result, the power factor of the bulk materials first increased and then decreased, and a power factor of 1340 mu Wm(-1)K(-2) was achieved for the nanocomposite bulk materials with 0.25 wt% rGO at 150 degrees C.

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  • 264.
    Du, Yong
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering. Shanghai Inst Technol, Peoples R China.
    Xu, Jiayue
    Shanghai Inst Technol, Peoples R China.
    Paul, Biplab
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Eklund, Per
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Flexible thermoelectric materials and devices2018In: APPLIED MATERIALS TODAY, ISSN 2352-9407, Vol. 12, p. 366-388Article, review/survey (Refereed)
    Abstract [en]

    Thermoelectric generators (TEGs) can directly convert waste heat into electrical power. In the last few decades, most research on thermoelectrics has focused on inorganic bulk thermoelectric materials and corresponding devices, and their thermoelectric properties have been significantly improved. An emerging topic is flexible devices, where the use of bulk inorganic materials is precluded by their inherent rigidity. The purpose of this paper is to review the research progress on flexible thermoelectric materials and generators, including theoretical principles for TEGs, conducting polymer TE materials, nanocomposites comprised of inorganic nanostructures in polymer matrices and fully inorganic flexible TE materials in nanostructured thin films. Approaches for flexible TEGs and components are reviewed, and remaining challenges discussed. (C) 2018 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).

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  • 265.
    Duc Tran, Thien
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Pozina, Galia
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Amano, Hiroshi
    Department of Electrical Engineering and Computer Science, Nagoya University, Chikusa-ku, Nagoya, Japan.
    Monemar, Bo
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Janzén, Erik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Hemmingsson, Carl
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Deep level study of Mg-doped GaN using deep level transient spectroscopy and minority carrier transient spectroscopy2016In: Physical Review B, ISSN 2469-9950, Vol. 94, no 4, article id 045206Article in journal (Refereed)
    Abstract [en]

    Deep levels in Mg doped GaN have been studied using deep level transient spectroscopyand minority charge carrier transient spectroscopy. Two traps are revealed in the investigatedtemperature range. In the substrate, one electron trap labelled ET1 (EC – 0.158 eV) is observedand in the Mg-doped layer, one hole trap labelled HT1 has been revealed. By varying theelectric field, it is found that the hole trap HT1 exhibits an electric field enhanced hole emissionrate. Using four theoretical models based on 3-dimensional Coulombic Poole-Frenkel effect, 3-dimensional square well Poole-Frenkel effect, phonon assisted tunneling, and 1-dimensionalCoulombic Poole-Frenkel effect including phonon assisted tunneling, the experimental data arefitted in order to justify the field enhanced emission process. It is found that the 1-dimensionalCoulombic Poole-Frenkel model including phonon assisted tunneling is consistent with theexperimental data. Since the trap exhibits Poole-Frenkel effect, we suggest it is acceptor like.From the theoretical model, the zero field activation energy of HT1 and an estimate of the holecapture cross section have been determined as Ev+0.57 eV and 1.9x10-15 cm2, respectively.Since the level is only observed in Mg-doped material, it is suggested that the trap can beassociated with a Mg related defect.

  • 266.
    Duc Tran, Thien
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Pozina, Galia
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Janzén, Erik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Hemmingsson, Carl
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Investigation of deep levels in bulk GaN material grown by halide vapor phase epitaxy2013In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 114, no 15Article in journal (Refereed)
    Abstract [en]

    Electron traps in thick free standing GaN grown by halide vapor phase epitaxy were characterized by deep level transient spectroscopy. The measurements revealed six electron traps with activation energy of 0.252 (E1), 0.53 (E2), 0.65 (E4), 0.69 (E3), 1.40 (E5), and 1.55 eV (E6), respectively. Among the observed levels, trap E6 has not been previously reported. The filling pulse method was employed to determine the temperature dependence of the capture cross section and to distinguish between point defects and extended defects. From these measurements, we have determined the capture cross section for level E1, E2, and E4 to 3.2 × 10−16 cm2, 2.2 × 10−17 cm2, and 1.9 × 10−17 cm2, respectively. All of the measured capture cross sections were temperature independent in the measured temperature range. From the electron capturing kinetic, we conclude that trap E1, E2, and E3 are associated with point defects. From the defect concentration profile obtained by double correlated deep level transient spectroscopy, we suggest that trap E4 and E6 are introduced by the polishing process.

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  • 267.
    Duc Tran, Thien
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Pozina, Galia
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Nguyen, Tien Son
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Janzén, Erik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Kordina, Olle
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Ohshima, Takeshi
    Japan Atomic Energy Agency, Takasaki, Japan.
    Hemmingsson, Carl
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Thermal behavior of irradiation-induced-deep levels in bulk GaN2015Manuscript (preprint) (Other academic)
    Abstract [en]

    Bulk GaN grown by halide vapor phase epitaxy and irradiated by 2 MeV electrons at a fluence of 5×1016 cm-2 were studied by deep level transient spectroscopy. After irradiation, two new peaks labelled D0 (EC – 0.18 eV) and D1 (EC – 0.13 eV) are observed. From isochronal annealing studies in the temperature range of 350 - 600 K, it is observed that peak D0 is completely annealed out already at 550 K while the broad peak D1 has a more complex annealing behavior. The concentration of D1 is decreasing during annealing and its peak position is shifted to higher temperatures, until a relatively stable peak labelled D2 (EC – 0.24 eV) is formed. From an isothermal annealing study of D2, it is concluded that the annealing process can be described by a first order annealing process with an activation energy and prefactor of 1.2 eV and 6.6 × 105 s-1, respectively. From the large pre-factor it is concluded that the annihilation of D2 is governed by a long-range migration process. From its annealing behavior, it is suggested that trap D2 may be related to the VGa.

  • 268.
    Duc Tran, Thien
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Pozina, Galia
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Nguyen, Tien Son
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Kordina, Olle
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Janzén, Erik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Ohshima, Takeshi
    Japan Atomic Energy Agency, Takasaki, Japan.
    Hemmingsson, Carl
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Deep levels in as-grown and electron-irradiated n-type GaN studied by deep level transient spectroscopy and minority carrier transient spectroscopy2016In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 119, no 9Article in journal (Refereed)
    Abstract [en]

    By minority carrier transient spectroscopy on as-grown n-type bulk GaN produced by halide vapor phase epitaxy (HVPE) one hole trap labelled H1 (EV + 0.34 eV) has been detected. After 2 MeV-energy electron irradiation, the concentration of H1 increases and at fluences higher than 5×1014 cm-2, a second hole trap labelled H2 is observed. Simultaneously, the concentration of two electron traps, labelled T1 (EC - 0.12 eV) and T2 (EC - 0.23 eV) increases. By studying the increase of the concentration versus electron irradiation fluences, the introduction rate of T1 and T2 using 2 MeV-energy electrons was determined to 7X10-3 cm-1 and 0.9 cm-1, respectively. Due to the low introduction rate of T1 and the low threading dislocation density in the HVPE bulk GaN material, it is suggested that the defect is associated with a primary defect decorating extended structural defects. The high introduction rate of the trap H1 suggests that the H1 defect is associated with a primary intrinsic defect or a complex.

  • 269.
    Duc Tran, Thien
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Pozina, Galia
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Nguyen, Tien Son
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Ohshima, Takeshi
    Japan Atomic Energy Agency, Takasaki, Japan.
    Janzén, Erik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Hemmingsson, Carl
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Electronic properties of defects in high-fluence electron irradiated bulk GaN2016In: Physica status solidi. B, Basic research, ISSN 0370-1972, E-ISSN 1521-3951, Vol. 253, no 3, p. 521-526Article in journal (Refereed)
    Abstract [en]

    Using deep level transient spectroscopy, deep levels and capture cross sections of defects introduced by high-fluence electron irradiation of thick halide vapour phase epitaxy grown GaN has been studied. After irradiation with 2 MeV electrons to a high-fluence of 5×1016 cm-2, four deep trap levels, labelled T1 (EC – 0.13 eV), T2 (EC – 0.18 eV), T3 (EC – 0.26 eV) T4 and a broad band of peaks consisting of at least two levels could be observed. These defects, except T1 and T3, were annealed out after annealing at 650 K for 2 hours. The capture cross section is found to be temperature independent for T2 and T3, while T1 shows an decresing capture cross section with increasing temperature, suggesting that electron capturing to this deep level is governed by a cascade capturing process.

  • 270.
    Duc, Tran Thien
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Pozina, Galia
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Son, Nguyen Tien
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Janzén, Erik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Ohshima, Takeshi
    Japan Atomic Energy Agency (JAEA), Takasaki, Japan.
    Hemmingsson, Carl
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Capture cross section of electron-irradiation-induced defects in bulk GaN grown by halide vapor phase epitaxy2014Manuscript (preprint) (Other academic)
    Abstract [en]

    Electron-irradiation-induced defects in GaN grown by halide vapor phase epitaxy is studied by deep level transient spectroscopy in which the capture cross section and its temperature dependence of the deep levels was determined by the filling pulse method. Before irradiation, one trap level, labelled ET4 (EC – 0.244 eV), was observed. After performing electron irradiation with an energy of 2 MeV at a fluence of 5 × 1016 cm-2, four deep trap levels, labelled ET1 (EC – 0.178 eV), ET2 (EC – 0.181 eV), ET3 (EC – 0.256 eV) and ET5 appeared. After annealing at 650K for 2 hours, only two irradiation induced deep levels, ET1 and ET3, were observed. By varying the rate windows, the temperature dependence of the capture cross section of the two deep levels ET1 and ET2 and ET3 was studied. The temperature behavior of ET2 and ET3 capture cross section is independent on temperature whereas the capture cross section of the deep level ET1 depends strongly on the temperature. It is suggested that electron capturing is govern by a multiphonon process to the level ET1.

  • 271.
    Duc, Tran Thien
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Pozina, Galia
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Son, Nguyen Tien
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Janzén, Erik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Ohshima, Takeshi
    Japan Atomic Energy Agency (JAEA), Takasaki, Japan.
    Hemmingsson, Carl
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Radiation-induced defects in GaN bulk grown by halide vapor phase epitaxy2014In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 105, no 10, p. 102103-Article in journal (Refereed)
    Abstract [en]

    Defects induced by electron irradiation in thick free-standing GaN layers grown by halide vapor phase epitaxy were studied by deep level transient spectroscopy. In as-grown materials, six electron traps, labeled D2 (E-C-0.24 eV), D3 (E-C-0.60 eV), D4 (E-C-0.69 eV), D5 (E-C-0.96 eV), D7 (E-C-1.19 eV), and D8, were observed. After 2MeV electron irradiation at a fluence of 1 x 10(14) cm(-2), three deep electron traps, labeled D1 (E-C-0.12 eV), D5I (E-C-0.89 eV), and D6 (E-C-1.14 eV), were detected. The trap D1 has previously been reported and considered as being related to the nitrogen vacancy. From the annealing behavior and a high introduction rate, the D5I and D6 centers are suggested to be related to primary intrinsic defects.

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  • 272. Duteil, F.
    et al.
    Du, Chun-Xia
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology.
    Joelsson, K.B.
    Persson, Per
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics.
    Hultman, Lars
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics.
    Pozina, Galia
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Ni, Wei-Xin
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics .
    Hansson, Göran
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics .
    Luminescence and microstructure of Er/O co-doped Si structures grown by MBE using Er and SiO evaporation2000In: Materials Science in Semiconductor Processing, ISSN 1369-8001, E-ISSN 1873-4081, Vol. 3, no 5-6, p. 523-528Article in journal (Refereed)
    Abstract [en]

    Er and O co-doped Si structures have been prepared using molecular-beam epitaxy (MBE) with fluxes of Er and O obtained from Er and silicon monoxide (SiO) evaporation in high-temperature cells. The incorporation of Er and O has been studied for concentrations of up to 2×1020 and 1×1021 cm-3, respectively. Surface segregation of Er can take place, but with O co-doping the segregation is suppressed and Er-doped layers without any indication of surface segregation can be prepared. Si1-xGex and Si1-yCy layers doped with Er/O during growth at different substrate temperatures show more defects than corresponding Si layers. Strong emission at 1.54µm associated with the intra-4f transition of Er3+ ions is observed in electroluminescence (EL) at room temperature in reverse-biased p-i-n-junctions. To optimize the EL intensity we have varied the Er/O ratio and the temperature during growth of the Er/O-doped layer. Using an Er-concentration of around 1×1020 cm-3 we find that Er/O ratios of 1:2 or 1:4 give higher intensity than 1:1 while the stability with respect to breakdown is reduced for the highest used O concentrations. For increasing growth temperatures in the range 400-575 °C there is an increase in the EL intensity. A positive effect of post-annealing on the photoluminescence intensity has also been observed.

  • 273.
    Dyatkin, Boris
    et al.
    Drexel Univ, PA 19104 USA; Drexel Univ, PA 19104 USA; US Army, MD 20783 USA; US Naval Res Lab, DC 20375 USA.
    Halim, Joseph
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering. Drexel Univ, PA 19104 USA; Drexel Univ, PA 19104 USA.
    Read, Jeffrey A.
    US Army, MD 20783 USA.
    Electrode Surface Composition of Dual-Intercalation, All-Graphite Batteries2017In: C-JOURNAL OF CARBON RESEARCH, ISSN 2311-5629, Vol. 3, no 1, article id 3010005Article in journal (Refereed)
    Abstract [en]

    Dual-intercalation batteries implement graphite electrodes as both cathodes and anodes and offer high specific energy, inexpensive and environmentally sustainable materials, and high operating voltages. Our research investigated the influence of surface composition on capacities and cycling efficiencies of chemically functionalized all-graphite battery electrodes. We subjected core-shell spherical particles and synthetic graphite flakes to high-temperature air oxidation, and hydrogenation to introduce, respectively, -OH, and -H surface functional groups. We identified noticeable influences of electrode surface chemistry on first-cycle efficiencies and charge storage densities of anion and cation intercalation into graphite electrodes. We matched oxidized cathodes and hydrogenated anodes in dual-ion batteries and improved their overall performance. Our approach provides novel fundamental insight into the anion intercalation process and suggests inexpensive and environmentally sustainable methods to improve performance of these grid-scale energy storage systems.

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  • 274.
    Edman Jönsson, Gustav
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics.
    Sputtring av Ti-Si-C-Ag beläggningar från sammansatta sputterkällor2009Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Today gold is used as contact material on electric contacts for low current applications. Gold, however,has low wear resistance, is expensive and environmentally stressful to produce. An alternative contactmaterial to gold is nano composite Ti-Si-C-Ag deposited with DC-magnetron sputtering. Nanocomposite Ti-Si-C-Ag has so far been deposited by a compound Ti-Si-C sputter source with a separateAg source.

    In this work films have been deposited by three different compound Ti-Si-C-Ag sources with threedifferent carbon contents. The films have been deposited in two separate PVD systems: Oneconventional batch loaded and one sequential with a load-lock.

    The phase- and elemental composition of the films has been studied with XRD and EDX respectively.Thickness and microstructure have been analysed with SEM. Adhesion and resistivity has beenanalysed with Rockwell indentation and surface resistivity measurement with four point probe. Contactresistance has also been studied to a limited extent.

    The work shows that the increment of carbon content in the source yields more carbon rich films withlarger titanium carbide crystallites. The resistivity is increasing due to an increased amorphous phasebetween the crystallites but the contact resistance is decreasing due to a more ductile film.

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  • 275.
    Edström, Daniel
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    A theoretical study of mass transport processes on TiN(001) and mechanical properties of TiN- and VN-based ternaries2014Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis concerns computer simulations, using classical molecular dynamics, of transport processes related to TiN(001) growth. It is motivated from the challenge to understand transport processes at the atomic scale responsible for crystal and film growth and their different growth modes. Not even the most advanced experimental techniques are capable of resolving the sub ps time and sub-Ångström length-scales required. TiN belongs to an important class of transition metal nitrides, and is chosen here as a model system for such fundamental studies of surface transport. The simulations show that on terraces, Ti adatoms exhibit much higher migration rates than N adatoms. For TiNx complexes, as x increases from 1 to 3, rotation becomes increasingly more prevalent than translation. This leads to surprisingly high mobilities of TiN2 trimers, higher than that of N adatoms. On islands, Ti adatoms experience a significant funneling effect, resulting in short residence times. TiN dimers and TiN2 trimers exhibit surprisingly high diffusivities and residence times even shorter than Ti adatoms. TiN3 trimers, however, are essentially stationary on both terraces and islands and serve as nucleation clusters. Overall, Ti adatoms and TiN2 trimers are the most efficient carriers of Ti and N atoms with and between TiN(001) surface layers. These results indicate that Ti/N flux ratios close to one promote layer-by-layer TiN(001) growth, whereas lower ratios result in surface roughening. Understanding of these phenomena enables experimentalists to tune  the growth processes to optimize material properties.

    In this thesis I also carry out theoretical calculations to investigate the role of configurational order on the metallic sublattice in relation to toughness enhancement. My studies set out from the recent understanding that the toughness of transition metal nitrides can be enhanced by tuning the valence electron concentration. My results show that ordered alloys exhibit lower resistance to shear deformations than disordered alloys, and higher resistance to tensile deformation. The lower resistance to shear deformations is explained by the formation of fully bonding electronic states perpendicular to the applied stress. Using the Pugh-Pettifor criterion, it is shown that while configurational order has an effect on the ductility of the material, this is primarily governed by the valence electron concentration.

    List of papers
    1. Dynamics of Ti, N, and TiNx (x=1-3) admolecule transport on TiN(001) surfaces
    Open this publication in new window or tab >>Dynamics of Ti, N, and TiNx (x=1-3) admolecule transport on TiN(001) surfaces
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    2012 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 86, no 15, p. 155443-Article in journal (Refereed) Published
    Abstract [en]

    We use classical molecular dynamics and the modified embedded atom method formalism to investigate the dynamics of atomic-scale transport on a low-index model compound surface, TiN(001). Our simulations, totaling 0.25 mu s for each case study, follow the pathways and migration kinetics of Ti and N adatoms, as well as TiNx complexes with x = 1-3, which are known to contribute to the growth of TiN thin films by reactive deposition from Ti, N-2, and N precursors. The simulations are carried out at 1000 K, within the optimal range for TiN(001) epitaxial growth. We find Ti adatoms to be the highest-mobility species on TiN(001), with the primary migration path involving jumps of one nearest-neighbor distance d(NN) between adjacent fourfold hollow sites along in-plane andlt; 100 andgt; channels. Long jumps, 2d(NN), are also observed, but at much lower frequency. N adatoms, which exhibit significantly lower migration rates than Ti, diffuse along in-plane andlt; 110 andgt; directions and, when they intersect other N atoms, associatively form N-2 molecules, which desorb at kinetic rates. As expected, TiN and TiN3 complexes migrate at even lower rates with complex diffusion pathways involving rotations, translations, and rototranslations. TiN2 trimers, however, are shown to have surprisingly high diffusion rates, above that of N adatoms and almost half that of Ti adatoms. TiN3 motion is dominated by in-place rotation with negligible diffusion.

    Place, publisher, year, edition, pages
    American Physical Society, 2012
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-86129 (URN)10.1103/PhysRevB.86.155443 (DOI)000310130800008 ()
    Note

    Funding Agencies|Swedish Research Council (VR)|2008-6572|Swedish Government Strategic Research Area Grant in Materials Science|Mat-LiU 2009-00971|

    Available from: 2012-12-07 Created: 2012-12-07 Last updated: 2019-06-28
    2. Ti and N adatom descent pathways to the terrace from atop two-dimensional TiN/TiN(001) islands
    Open this publication in new window or tab >>Ti and N adatom descent pathways to the terrace from atop two-dimensional TiN/TiN(001) islands
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    2014 (English)In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 558, p. 37-46Article in journal (Refereed) Published
    Abstract [en]

    We use classical molecular dynamics and the modified embedded atom method to determine residence times and descent pathways of Ti and N adatoms on square, single-atom-high, TiN islands on TiN(001). Simulations are carried out at 1000 K, which is within the optimal range for TiN(001) epitaxial growth. Results show that the frequency of descent events, and overall adatom residence times, depend strongly on both the TiN(001) diffusion barrier for each species as well as the adatom island-edge location immediately prior to descent. Ti adatoms, with a low diffusion barrier, rapidly move toward the island periphery, via funneling, where they diffuse along upper island edges. The primary descent mechanism for Ti adatoms is via push-out/exchange with Ti island-edge atoms, a process in which the adatom replaces an island edge atom by moving down while pushing the edge atom out onto the terrace to occupy an epitaxial position along the island edge. Double push-out events are also observed for Ti adatoms descending at N corner positions. N adatoms, with a considerably higher diffusion barrier on TiN(001), require much longer times to reach island edges and, consequently, have significantly longer residence times. N adatoms are found to descend onto the terrace by direct hopping over island edges and corner atoms, as well as by concerted push-out/exchange with N atoms adjacent to Ti corners. For both adspecies, we also observe several complex adatom/island interactions, before and after descent onto the terrace, including two instances of Ti islandatom ascent onto the island surface.

    Place, publisher, year, edition, pages
    Elsevier, 2014
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-91377 (URN)10.1016/j.tsf.2014.02.053 (DOI)000334314100006 ()
    Available from: 2013-04-23 Created: 2013-04-23 Last updated: 2019-06-28Bibliographically approved
    3. The dynamics of TiNx (x = 1 – 3) admolecule interlayer and intralayer transport on TiN/TiN(001) islands
    Open this publication in new window or tab >>The dynamics of TiNx (x = 1 – 3) admolecule interlayer and intralayer transport on TiN/TiN(001) islands
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    2015 (English)In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 589, p. 133-144Article in journal (Refereed) Published
    Abstract [en]

    It has been shown both experimentally and by density functional theory calculations that the primary diffusing species during the epitaxial growth of TiN/TiN(001) are Ti and N adatoms together with TiNx complexes (x = 1, 2, 3), in which the dominant N-containing admolecule species depends upon the incident N/Ti flux ratio. Here, we employ classical molecular dynamics (CMD) simulations to probe the dynamics of TiNx (x = 1–3) admolecules on 8 × 8 atom square, single-atom-high TiN islands on TiN(001), as well as pathways for descent over island edges. The simulations are carried out at 1000 K, a reasonable epitaxial growth temperature. We find that despite their lower mobility on infinite TiN(001) terraces, both TiN and TiN2 admolecules funnel toward descending steps and are incorporated into island edges more rapidly than Ti adatoms. On islands, TiN diffuses primarily via concerted translations, but rotation is the preferred diffusion mechanism on infinite terraces. TiN2 migration is initiated primarily by rotation about one of the N admolecule atoms anchored at an epitaxial site. TiN admolecules descend from islands by direct hopping over edges and by edge exchange reactions, while TiN2 trimers descend exclusively by hopping. In contrast, TiN3 admolecules are essentially stationary and serve as initiators for local island growth. Ti adatoms are the fastest diffusing species on infinite TiN(001) terraces, but on small TiN/TiN(001) islands, TiN dimers provide more efficient mass transport. The overall results reveal the effect of the N/Ti precursor flux ratio on TiN(001) surface morphological evolution and growth modes.

    Place, publisher, year, edition, pages
    Elsevier, 2015
    Keywords
    Titanium nitride; Molecular dynamics; Film growth simulations; TiNx admolecule diffusion on TiN/TiN(001) islands; TiNx admolecule descent from TiN/TiN(001) islands
    National Category
    Physical Sciences
    Identifiers
    urn:nbn:se:liu:diva-111948 (URN)10.1016/j.tsf.2015.05.013 (DOI)000360320000023 ()
    Available from: 2014-11-11 Created: 2014-11-11 Last updated: 2019-06-28
    4. Effects of atomic ordering on the elastic properties of TiN- and VN-based ternary alloys
    Open this publication in new window or tab >>Effects of atomic ordering on the elastic properties of TiN- and VN-based ternary alloys
    2014 (English)In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 571, no Part 1, p. 145-153Article in journal (Refereed) Published
    Abstract [en]

    Improved toughness is one of the central goals in the development of wear-resistant coatings. Previous studies of toughness in transition metal nitride alloys have addressed the effects of chemical composition in these compounds. Herein, we use density functional theory to study the effects of various metal sublattice configurations, ranging from fully ordered to fully disordered, on the mechanical properties of VM2N and TiM2N (M2 = W, Mo) ternary alloys. Results show that all alloys display high incompressibility, indicating strong M-N bonds. Disordered atomic arrangements yield lower values of bulk moduli and C11 elastic constants, as well as higher values of C44 elastic constants, compared to ordered structures. We attribute the low C44 values of ordered structures to the formation of fully-bonding states perpendicular to the applied stress. We find that the ductility of these compounds is primarily an effect of the increased valence electron concentration induced upon alloying.

    Place, publisher, year, edition, pages
    Elsevier, 2014
    Keywords
    Nitrides, Density functional theory, Elastic properties, Ductility, Toughness
    National Category
    Physical Sciences
    Identifiers
    urn:nbn:se:liu:diva-111949 (URN)10.1016/j.tsf.2014.09.048 (DOI)000346053900024 ()
    Available from: 2014-11-11 Created: 2014-11-11 Last updated: 2019-06-28Bibliographically approved
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    A theoretical study of mass transport processes on TiN(001) and mechanical properties of TiN- and VN-based ternaries
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  • 276. Order onlineBuy this publication >>
    Edström, Daniel
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Growth and Mechanical Properties of Transition Metal Nitrides and Carbides2016Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The atomic-scale dynamical processes at play during film growth cannot be resolved by even the most advanced experimental methods. As such, computational methods, and chiefly classical molecular dynamics, are the only available research tools to study these processes. The investigation of key dynamical processes during thin film growth yields a deeper understanding of the film growth evolution, ultimately allowing for the optimization of experimental parameters and tailoring of film properties. This thesis details the study of fundamental surface dynamics processes, and the role played by primary diffusing species, during TiN film growth, here employed as a model system for transition metal nitrides in general. It is found that Ti adatoms and TiN2 admolecules are the fastest diffusing species, and the species which most rapidly descend from islands onto the growing film. Thus, they are the main contributors and players in driving the layer-by-layer growth mode. TiN3 admolecules, in contrast, are essentially stationary and thereby promote multilayer growth. Large-scale growth simulations reveal that tailoring the incident N/Ti ratio and N kinetic energy significantly affects the growth mode and film microstructure.

    The mechanical properties of ternary transition metal nitride and carbide alloys, investigated using density functional theory, are also discussed herein, in comparison to recent experimental results. By optimizing the valence electron concentration in these compounds, the occupation of shear-compliant d‑t2g electronic states can be maximized. The investigation of M1M2N alloys, where M1 = Ti or V and M2 = W or Mo, with different structures demonstrates that this optimization leads to enhanced ductility, and thereby toughness, in transition metal nitride alloys regardless of the degree of ordering on the metal sublattice. Estimations based on the calculation of the mechanical properties of the corresponding M1M2C transition metal carbide alloys indicate that these materials remain brittle. However, charge density analysis and calculations of stress/strain curves reveal features commonly associated with ductile materials.

    List of papers
    1. Dynamics of Ti, N, and TiNx (x=1-3) admolecule transport on TiN(001) surfaces
    Open this publication in new window or tab >>Dynamics of Ti, N, and TiNx (x=1-3) admolecule transport on TiN(001) surfaces
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    2012 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 86, no 15, p. 155443-Article in journal (Refereed) Published
    Abstract [en]

    We use classical molecular dynamics and the modified embedded atom method formalism to investigate the dynamics of atomic-scale transport on a low-index model compound surface, TiN(001). Our simulations, totaling 0.25 mu s for each case study, follow the pathways and migration kinetics of Ti and N adatoms, as well as TiNx complexes with x = 1-3, which are known to contribute to the growth of TiN thin films by reactive deposition from Ti, N-2, and N precursors. The simulations are carried out at 1000 K, within the optimal range for TiN(001) epitaxial growth. We find Ti adatoms to be the highest-mobility species on TiN(001), with the primary migration path involving jumps of one nearest-neighbor distance d(NN) between adjacent fourfold hollow sites along in-plane andlt; 100 andgt; channels. Long jumps, 2d(NN), are also observed, but at much lower frequency. N adatoms, which exhibit significantly lower migration rates than Ti, diffuse along in-plane andlt; 110 andgt; directions and, when they intersect other N atoms, associatively form N-2 molecules, which desorb at kinetic rates. As expected, TiN and TiN3 complexes migrate at even lower rates with complex diffusion pathways involving rotations, translations, and rototranslations. TiN2 trimers, however, are shown to have surprisingly high diffusion rates, above that of N adatoms and almost half that of Ti adatoms. TiN3 motion is dominated by in-place rotation with negligible diffusion.

    Place, publisher, year, edition, pages
    American Physical Society, 2012
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-86129 (URN)10.1103/PhysRevB.86.155443 (DOI)000310130800008 ()
    Note

    Funding Agencies|Swedish Research Council (VR)|2008-6572|Swedish Government Strategic Research Area Grant in Materials Science|Mat-LiU 2009-00971|

    Available from: 2012-12-07 Created: 2012-12-07 Last updated: 2019-06-28
    2. Ti and N adatom descent pathways to the terrace from atop two-dimensional TiN/TiN(001) islands
    Open this publication in new window or tab >>Ti and N adatom descent pathways to the terrace from atop two-dimensional TiN/TiN(001) islands
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    2014 (English)In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 558, p. 37-46Article in journal (Refereed) Published
    Abstract [en]

    We use classical molecular dynamics and the modified embedded atom method to determine residence times and descent pathways of Ti and N adatoms on square, single-atom-high, TiN islands on TiN(001). Simulations are carried out at 1000 K, which is within the optimal range for TiN(001) epitaxial growth. Results show that the frequency of descent events, and overall adatom residence times, depend strongly on both the TiN(001) diffusion barrier for each species as well as the adatom island-edge location immediately prior to descent. Ti adatoms, with a low diffusion barrier, rapidly move toward the island periphery, via funneling, where they diffuse along upper island edges. The primary descent mechanism for Ti adatoms is via push-out/exchange with Ti island-edge atoms, a process in which the adatom replaces an island edge atom by moving down while pushing the edge atom out onto the terrace to occupy an epitaxial position along the island edge. Double push-out events are also observed for Ti adatoms descending at N corner positions. N adatoms, with a considerably higher diffusion barrier on TiN(001), require much longer times to reach island edges and, consequently, have significantly longer residence times. N adatoms are found to descend onto the terrace by direct hopping over island edges and corner atoms, as well as by concerted push-out/exchange with N atoms adjacent to Ti corners. For both adspecies, we also observe several complex adatom/island interactions, before and after descent onto the terrace, including two instances of Ti islandatom ascent onto the island surface.

    Place, publisher, year, edition, pages
    Elsevier, 2014
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-91377 (URN)10.1016/j.tsf.2014.02.053 (DOI)000334314100006 ()
    Available from: 2013-04-23 Created: 2013-04-23 Last updated: 2019-06-28Bibliographically approved
    3. Effects of atomic ordering on the elastic properties of TiN- and VN-based ternary alloys
    Open this publication in new window or tab >>Effects of atomic ordering on the elastic properties of TiN- and VN-based ternary alloys
    2014 (English)In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 571, no Part 1, p. 145-153Article in journal (Refereed) Published
    Abstract [en]

    Improved toughness is one of the central goals in the development of wear-resistant coatings. Previous studies of toughness in transition metal nitride alloys have addressed the effects of chemical composition in these compounds. Herein, we use density functional theory to study the effects of various metal sublattice configurations, ranging from fully ordered to fully disordered, on the mechanical properties of VM2N and TiM2N (M2 = W, Mo) ternary alloys. Results show that all alloys display high incompressibility, indicating strong M-N bonds. Disordered atomic arrangements yield lower values of bulk moduli and C11 elastic constants, as well as higher values of C44 elastic constants, compared to ordered structures. We attribute the low C44 values of ordered structures to the formation of fully-bonding states perpendicular to the applied stress. We find that the ductility of these compounds is primarily an effect of the increased valence electron concentration induced upon alloying.

    Place, publisher, year, edition, pages
    Elsevier, 2014
    Keywords
    Nitrides, Density functional theory, Elastic properties, Ductility, Toughness
    National Category
    Physical Sciences
    Identifiers
    urn:nbn:se:liu:diva-111949 (URN)10.1016/j.tsf.2014.09.048 (DOI)000346053900024 ()
    Available from: 2014-11-11 Created: 2014-11-11 Last updated: 2019-06-28Bibliographically approved
    4. The dynamics of TiNx (x = 1 – 3) admolecule interlayer and intralayer transport on TiN/TiN(001) islands
    Open this publication in new window or tab >>The dynamics of TiNx (x = 1 – 3) admolecule interlayer and intralayer transport on TiN/TiN(001) islands
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    2015 (English)In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 589, p. 133-144Article in journal (Refereed) Published
    Abstract [en]

    It has been shown both experimentally and by density functional theory calculations that the primary diffusing species during the epitaxial growth of TiN/TiN(001) are Ti and N adatoms together with TiNx complexes (x = 1, 2, 3), in which the dominant N-containing admolecule species depends upon the incident N/Ti flux ratio. Here, we employ classical molecular dynamics (CMD) simulations to probe the dynamics of TiNx (x = 1–3) admolecules on 8 × 8 atom square, single-atom-high TiN islands on TiN(001), as well as pathways for descent over island edges. The simulations are carried out at 1000 K, a reasonable epitaxial growth temperature. We find that despite their lower mobility on infinite TiN(001) terraces, both TiN and TiN2 admolecules funnel toward descending steps and are incorporated into island edges more rapidly than Ti adatoms. On islands, TiN diffuses primarily via concerted translations, but rotation is the preferred diffusion mechanism on infinite terraces. TiN2 migration is initiated primarily by rotation about one of the N admolecule atoms anchored at an epitaxial site. TiN admolecules descend from islands by direct hopping over edges and by edge exchange reactions, while TiN2 trimers descend exclusively by hopping. In contrast, TiN3 admolecules are essentially stationary and serve as initiators for local island growth. Ti adatoms are the fastest diffusing species on infinite TiN(001) terraces, but on small TiN/TiN(001) islands, TiN dimers provide more efficient mass transport. The overall results reveal the effect of the N/Ti precursor flux ratio on TiN(001) surface morphological evolution and growth modes.

    Place, publisher, year, edition, pages
    Elsevier, 2015
    Keywords
    Titanium nitride; Molecular dynamics; Film growth simulations; TiNx admolecule diffusion on TiN/TiN(001) islands; TiNx admolecule descent from TiN/TiN(001) islands
    National Category
    Physical Sciences
    Identifiers
    urn:nbn:se:liu:diva-111948 (URN)10.1016/j.tsf.2015.05.013 (DOI)000360320000023 ()
    Available from: 2014-11-11 Created: 2014-11-11 Last updated: 2019-06-28
    5. Large-scale molecular dynamics simulations of TiN/TiN(001) epitaxial film growth
    Open this publication in new window or tab >>Large-scale molecular dynamics simulations of TiN/TiN(001) epitaxial film growth
    Show others...
    2016 (English)In: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films, ISSN 0734-2101, E-ISSN 1520-8559, Vol. 34, no 4, p. 041509-1-041509-9Article in journal (Refereed) Published
    Abstract [en]

    Large-scale classical molecular dynamics simulations of epitaxial TiN/TiN(001) thin film growth at 1200K are carried out using incident flux ratios N/Ti -1, 2, and 4. The films are analyzed as a function of composition, island size distribution, island edge orientation, and vacancy formation. Results show that N/Ti-1 films are globally understoichiometric with dispersed Ti-rich surface regions which serve as traps to nucleate 111-oriented islands, leading to local epitaxial breakdown. Films grown with N/Ti=2 are approximately stoichiometric and the growth mode is closer to layer-by-layer, while N/Ti-4 films are stoichiometric with N-rich surfaces. As N/Ti is increased from 1 to 4, island edges are increasingly polar, i. e., 110-oriented, and N-terminated to accommodate the excess N flux, some of which is lost by reflection of incident N atoms. N vacancies are produced in the surface layer during film deposition with N/Ti-1 due to the formation and subsequent desorption of N-2 molecules composed of a N adatom and a N surface atom, as well as itinerant Ti adatoms pulling up N surface atoms. The N vacancy concentration is significantly reduced as N/Ti is increased to 2; with N/Ti-4, Ti vacancies dominate. Overall, our results show that an insufficient N/Ti ratio leads to surface roughening via nucleation of small dispersed 111 islands, whereas high N/Ti ratios result in surface roughening due to more rapid upper-layer nucleation and mound formation. The growth mode of N/Ti-2 films, which have smoother surfaces, is closer to layer-by-layer. (C) 2016 American Vacuum Society.

    Place, publisher, year, edition, pages
    AMER INST PHYSICS, 2016
    National Category
    Condensed Matter Physics
    Identifiers
    urn:nbn:se:liu:diva-130405 (URN)10.1116/1.4953404 (DOI)000379588000027 ()
    Note

    Funding Agencies|Swedish Research Council (VR) Linkoping Linnaeus Initiative LiLi-NFM [2008-6572, 2009-00971, 2013-4018, 2014-5790]; Swedish Government Strategic Research Area Grant in Materials Science on Advanced Functional Materials; Knut and Alice Wallenberg Foundation (Isotope Project)

    Available from: 2016-08-15 Created: 2016-08-05 Last updated: 2019-06-28
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    Growth and Mechanical Properties of Transition Metal Nitrides and Carbides
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  • 277.
    Edström, Daniel
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Sangiovanni, Davide G.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Hultman, Lars
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Chirita, Valeriu
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Effects of atomic ordering on the elastic properties of TiN- and VN-based ternary alloys2014In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 571, no Part 1, p. 145-153Article in journal (Refereed)
    Abstract [en]

    Improved toughness is one of the central goals in the development of wear-resistant coatings. Previous studies of toughness in transition metal nitride alloys have addressed the effects of chemical composition in these compounds. Herein, we use density functional theory to study the effects of various metal sublattice configurations, ranging from fully ordered to fully disordered, on the mechanical properties of VM2N and TiM2N (M2 = W, Mo) ternary alloys. Results show that all alloys display high incompressibility, indicating strong M-N bonds. Disordered atomic arrangements yield lower values of bulk moduli and C11 elastic constants, as well as higher values of C44 elastic constants, compared to ordered structures. We attribute the low C44 values of ordered structures to the formation of fully-bonding states perpendicular to the applied stress. We find that the ductility of these compounds is primarily an effect of the increased valence electron concentration induced upon alloying.

    Download full text (pdf)
    fulltext
  • 278.
    Edström, Daniel
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Sangiovanni, Davide
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Hultman, Lars
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Chirita, Valeriu
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Petrov, Ivan
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology. Department of Materials Science and the Fredrick Seitz Materials Research Laboratory, University of Illinois, Urbana, USA.
    Greene, Joseph
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology. Department of Materials Science and the Fredrick Seitz Materials Research Laboratory, University of Illinois, Urbana, USA.
    Ti and N adatom descent pathways to the terrace from atop two-dimensional TiN/TiN(001) islands2014In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 558, p. 37-46Article in journal (Refereed)
    Abstract [en]

    We use classical molecular dynamics and the modified embedded atom method to determine residence times and descent pathways of Ti and N adatoms on square, single-atom-high, TiN islands on TiN(001). Simulations are carried out at 1000 K, which is within the optimal range for TiN(001) epitaxial growth. Results show that the frequency of descent events, and overall adatom residence times, depend strongly on both the TiN(001) diffusion barrier for each species as well as the adatom island-edge location immediately prior to descent. Ti adatoms, with a low diffusion barrier, rapidly move toward the island periphery, via funneling, where they diffuse along upper island edges. The primary descent mechanism for Ti adatoms is via push-out/exchange with Ti island-edge atoms, a process in which the adatom replaces an island edge atom by moving down while pushing the edge atom out onto the terrace to occupy an epitaxial position along the island edge. Double push-out events are also observed for Ti adatoms descending at N corner positions. N adatoms, with a considerably higher diffusion barrier on TiN(001), require much longer times to reach island edges and, consequently, have significantly longer residence times. N adatoms are found to descend onto the terrace by direct hopping over island edges and corner atoms, as well as by concerted push-out/exchange with N atoms adjacent to Ti corners. For both adspecies, we also observe several complex adatom/island interactions, before and after descent onto the terrace, including two instances of Ti islandatom ascent onto the island surface.

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    Ti and N adatom descent pathways to the terrace from atop two-dimensional TiN/TiN(001) islands
  • 279.
    Edström, Daniel
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Sangiovanni, Davide
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Hultman, Lars
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Petrov, Ivan
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology. Department of Materials Science and the Fredrick Seitz Materials Research Laboratory, University of Illinois, Urbana, USA.
    Greene, Joseph
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology. Department of Materials Science and the Fredrick Seitz Materials Research Laboratory, University of Illinois, Urbana, USA.
    Chirita, Valeriu
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    The dynamics of TiNx (x = 1 – 3) admolecule interlayer and intralayer transport on TiN/TiN(001) islands2015In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 589, p. 133-144Article in journal (Refereed)
    Abstract [en]

    It has been shown both experimentally and by density functional theory calculations that the primary diffusing species during the epitaxial growth of TiN/TiN(001) are Ti and N adatoms together with TiNx complexes (x = 1, 2, 3), in which the dominant N-containing admolecule species depends upon the incident N/Ti flux ratio. Here, we employ classical molecular dynamics (CMD) simulations to probe the dynamics of TiNx (x = 1–3) admolecules on 8 × 8 atom square, single-atom-high TiN islands on TiN(001), as well as pathways for descent over island edges. The simulations are carried out at 1000 K, a reasonable epitaxial growth temperature. We find that despite their lower mobility on infinite TiN(001) terraces, both TiN and TiN2 admolecules funnel toward descending steps and are incorporated into island edges more rapidly than Ti adatoms. On islands, TiN diffuses primarily via concerted translations, but rotation is the preferred diffusion mechanism on infinite terraces. TiN2 migration is initiated primarily by rotation about one of the N admolecule atoms anchored at an epitaxial site. TiN admolecules descend from islands by direct hopping over edges and by edge exchange reactions, while TiN2 trimers descend exclusively by hopping. In contrast, TiN3 admolecules are essentially stationary and serve as initiators for local island growth. Ti adatoms are the fastest diffusing species on infinite TiN(001) terraces, but on small TiN/TiN(001) islands, TiN dimers provide more efficient mass transport. The overall results reveal the effect of the N/Ti precursor flux ratio on TiN(001) surface morphological evolution and growth modes.

  • 280.
    Edström, Daniel
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Sangiovanni, Davide
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Ruhr University of Bochum, Germany.
    Hultman, Lars
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Petrov, Ivan
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering. University of Illinois, IL 61801 USA.
    Greene, Joseph E
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering. University of Illinois, IL 61801 USA.
    Chirita, Valeriu
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Effects of incident N atom kinetic energy on TiN/TiN(001) film growth dynamics: A molecular dynamics investigation2017In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 121, no 2, article id 025302Article in journal (Refereed)
    Abstract [en]

    Large-scale classical molecular dynamics simulations of epitaxial TiN/TiN(001) thin film growth at 1200 K, a temperature within the optimal range for epitaxial TiN growth, with an incident N-to-Ti flux ratio of four, are carried out using incident N energies E-N = 2 and 10 eV and incident Ti energy E-Ti = 2 eV. To further highlight the effect of E-N, we grow a bilayer film with E-N = 2 eV initially and then switch to E-N = 10 eV. As-deposited layers are analyzed as a function of composition, island-size distribution, island-edge orientation, and vacancy formation. Results show that growth with E-N = 2 eV results in films that are globally overstoichiometric with islands bounded by N-terminated polar 110 edges, whereas films grown with E-N = 10 eV are flatter and closer to stoichiometric. However, E-N = 10 eV layers exhibit local N deficiency leading to the formation of isolated 111-oriented islands. Films grown by changing the incident energy from 2 to 10 eV during growth are more compact than those grown entirely with E-N = 2 eV and exhibit greatly reduced concentrations of upper-layer adatoms, admolecules, and small clusters. Islands with 110 edges formed during growth with E-N = 2 eV transform to islands with 100 edges as E-N is switched to 10 eV. Published by AIP Publishing.

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  • 281.
    Edström, Daniel
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Sangiovanni, Davide
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Ruhr Univ Bochum, Germany.
    Hultman, Lars
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Petrov, Ivan
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering. Univ Illinois, IL 61801 USA.
    Greene, Joseph E
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering. Univ Illinois, IL 61801 USA.
    Chirita, Valeriu
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Elastic properties and plastic deformation of TiC- and VC-based alloys2018In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 144, p. 376-385Article in journal (Refereed)
    Abstract [en]

    Transition-metal (TM) carbides are an important class of hard, protective coating materials; however, their brittleness often limits potential applications. We use density functional theory to investigate the possibility of improving ductility by forming pseudobinary cubic (MMC)-M-1-C-2 alloys, for which M-1 = Ti or V and M-2 = W or Mo. The alloying elements are chosen based on previous results showing improved ductility of the corresponding pseudobinary nitride alloys with respect to their parent compounds. While commonly-used empirical criteria do not indicate enhanced ductility in the carbide alloys, calculated stress/strain curves along known slip systems, supported by electronic structure analyses, indicate ductile behavior for VMoC. As VMoC layers are sheared along the 1 (1) over bar0 direction on {111} planes, the stress initially increases linearly up to a yield point where the accumulated stress is partially dissipated. With further increase in strain, the stress increases again until fracture occurs. A similar mechanical behavior is observed for the corresponding TM nitride VMoN, known to be a ductile ceramic material [1]. Thus, our results show that VMoC is a TM carbide alloy which may be both hard and ductile, i.e. tough. (C) 2017 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

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  • 282.
    Edström, Daniel
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Sangiovanni, Davide
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Hultman, Lars
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Petrov, Ivan
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering. University of Illinois, IL 61801 USA; University of Illinois, IL 61801 USA.
    Greene, Joseph E
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering. University of Illinois, USA.
    Chirita, Valeriu
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Large-scale molecular dynamics simulations of TiN/TiN(001) epitaxial film growth2016In: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films, ISSN 0734-2101, E-ISSN 1520-8559, Vol. 34, no 4, p. 041509-1-041509-9Article in journal (Refereed)
    Abstract [en]

    Large-scale classical molecular dynamics simulations of epitaxial TiN/TiN(001) thin film growth at 1200K are carried out using incident flux ratios N/Ti -1, 2, and 4. The films are analyzed as a function of composition, island size distribution, island edge orientation, and vacancy formation. Results show that N/Ti-1 films are globally understoichiometric with dispersed Ti-rich surface regions which serve as traps to nucleate 111-oriented islands, leading to local epitaxial breakdown. Films grown with N/Ti=2 are approximately stoichiometric and the growth mode is closer to layer-by-layer, while N/Ti-4 films are stoichiometric with N-rich surfaces. As N/Ti is increased from 1 to 4, island edges are increasingly polar, i. e., 110-oriented, and N-terminated to accommodate the excess N flux, some of which is lost by reflection of incident N atoms. N vacancies are produced in the surface layer during film deposition with N/Ti-1 due to the formation and subsequent desorption of N-2 molecules composed of a N adatom and a N surface atom, as well as itinerant Ti adatoms pulling up N surface atoms. The N vacancy concentration is significantly reduced as N/Ti is increased to 2; with N/Ti-4, Ti vacancies dominate. Overall, our results show that an insufficient N/Ti ratio leads to surface roughening via nucleation of small dispersed 111 islands, whereas high N/Ti ratios result in surface roughening due to more rapid upper-layer nucleation and mound formation. The growth mode of N/Ti-2 films, which have smoother surfaces, is closer to layer-by-layer. (C) 2016 American Vacuum Society.

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  • 283.
    Edström, Daniel
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering. Orebro Univ, Sweden.
    Sangiovanni, Davide
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Ruhr Univ Bochum, Germany.
    Hultman, Lars
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Petrov, Ivan
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering. Univ Illinois, IL 61801 USA.
    Greene, Joseph E
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering. Univ Illinois, IL 61801 USA; Natl Taiwan Univ Sci and Technol, Taiwan.
    Chirita, Valeriu
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    TiN film growth on misoriented TiN grains with simultaneous low-energy bombardment: Restructuring leading to epitaxy2019In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 688, article id 137380Article in journal (Refereed)
    Abstract [en]

    We perform large-scale molecular dynamics simulations of TiN deposition at 1200 K on TiN substrates consisting of under-stoichiometric (N/Ti = 0.86) misoriented grains. The energy of incoming Ti atoms is 2 eV and that of incoming N atoms is 10 eV. The simulations show that misoriented grains are reoriented during the early stages of growth, after which the film grows 001 epitaxially and is nearly stoichiometric. The grain reorientation coincides with an increase in film N/Ti ratio. As the grains reorient, additional nitrogen can no longer be accommodated, and the film composition becomes stoichiometric as the overlayer grows epitaxially.

    The full text will be freely available from 2021-06-20 11:38
  • 284.
    Edström, Daniel
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering. Orebro Univ, Sweden.
    Sangiovanni, Davide
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Ruhr Univ Bochum, Germany.
    Landälv, Ludvig
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering. Sandvik Coromant AB, Sweden.
    Eklund, Per
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Greene, Joseph E
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering. Univ Illinois, IL 61801 USA; Univ Illinois, IL 61801 USA; Natl Taiwan Univ Sci and Technol, Taiwan.
    Petrov, Ivan
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering. Univ Illinois, IL 61801 USA; Univ Illinois, IL 61801 USA.
    Hultman, Lars
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Chirita, Valeriu
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Mechanical properties of VMoNO as a function of oxygen concentration: Toward development of hard and tough refractory oxynitrides2019In: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films, ISSN 0734-2101, E-ISSN 1520-8559, Vol. 37, no 6, article id 061508Article in journal (Refereed)
    Abstract [en]

    Improved toughness is a central goal in the development of wear-resistant refractory ceramic coatings. Extensive theoretical and experimental research has revealed that NaCl-structure VMoN alloys exhibit surprisingly high ductility combined with high hardness and toughness. However, during operation, protective coatings inevitably oxidize, a problem that may compromise material properties and performance. Here, the authors explore the role of oxidation in altering VMoN properties. Density functional theory and theoretical intrinsic hardness models are used to investigate the mechanical behavior of cubic V0.5Mo0.5N1-xOx solid solutions as a function of the oxygen concentration x. Elastic constant and intrinsic hardness calculations show that oxidation does not degrade the mechanical properties of V0.5Mo0.5N. Electronic structure analyses indicate that the presence of oxygen reduces the covalent bond character, which slightly lowers the alloy strength and intrinsic hardness. Nevertheless, the character of metallic d-d states, which are crucial for allowing plastic deformation and enhancing toughness, remains unaffected. Overall, the authors results suggest that VMoNO oxynitrides, with oxygen concentrations as high as 50%, possess high intrinsic hardness, while still being ductile. Published by the AVS.

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  • 285.
    Ehiasarian, A. P.
    et al.
    Sheffield Hallam University, Sheffield, UK.
    Hovsepian, P. Eh.
    Sheffield Hallam University, Sheffield, UK.
    Hultman, Lars
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Helmersson, Ulf
    Linköping University, Department of Physics, Chemistry and Biology, Plasma and Coating Physics. Linköping University, The Institute of Technology.
    Comparison of microstructure and mechanical properties of chromium nitride-based coatings deposited by high power impulse magnetron sputtering and by the combined steered cathodic arc/unbalanced magnetron technique2004In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 457, no 2, p. 270-277Article in journal (Refereed)
    Abstract [en]

    Sliding, abrasive, and impact wear tests were performed on chromium nitride (CrN)-based coatings deposited on mirror-polished M2 high speed steel substrates by the novel high power impulse magnetron sputtering (HIPIMS) utilising high peak cathode powers densities of 3000 W cm−2. The coatings were compared to single layer CrN and multilayer superlattice CrN/NbN coatings deposited by the arc bond sputtering (ABS) technique designed to improve the coating substrate adhesion by a combined steered cathodic arc/unbalanced magnetron (UBM) sputtering process. The substrates were metal ion etched using non-reactive HIPIMS or steered cathodic arc at a substrate bias voltage of −1200 V. Subsequently a 2- to 3-μm thick CrN or CrN/NbN coating was deposited by reactive HIPIMS or UBM. No bias was used during the HIPIMS deposition, while the bias during UBM growth was in the range 75–100 V. The ion saturation current measured by a flat electrostatic probe reached values of 50 mA cm−2 peak for HIPIMS and 1 mA cm−2 continuous during UBM deposition. The microstructure of the HIPIMS coatings observed by transmission electron microscopy was fully dense in contrast to the voided columnar structure observed in conventional UBM sputtered CrN and CrN/NbN. The sliding wear coefficients of the HIPIMS CrN films of 2.3×10−16 m3 N−1 m−1 were lower by a factor of 4 and the roughness of the wear track was significantly reduced compared to the UBM-deposited CrN. The abrasive wear coefficient of the HIPIMS coating was 2.2×10−13 m3 N−1 m−1 representing an improvement by a factor of 3 over UBM deposited CrN and a wear resistance comparable to that of the superlattice CrN/NbN. The adhesion of the HIPIMS deposited CrN was comparable to state-of-the-art ABS technology.

  • 286.
    Ehiasarian, A.P.
    et al.
    Materials Res. Inst., Sheffield-Hallam Univ., Howard St., Sheffield S1 1WB, United Kingdom.
    Munz, W.-D.
    Münz, W.-D., Materials Res. Inst., Sheffield-Hallam Univ., Howard St., Sheffield S1 1WB, United Kingdom.
    Hultman, Lars
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Helmersson, Ulf
    Linköping University, Department of Physics, Chemistry and Biology, Plasma and Coating Physics . Linköping University, The Institute of Technology.
    Petrov, I.
    Frederick Seitz Mat. Res. Lab., University of Illinois, 104 S. Goodwin Avenue, Urbana, IL 61801, United States.
    High power pulsed magnetron sputtered CrNx films2003In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 163-164, p. 267-272Article in journal (Refereed)
    Abstract [en]

    Microstructure and macroscopic properties of droplet free CrN films deposited by the recently developed high power pulsed magnetron sputtering (HIPIMS) technique are presented. Magnetron glow discharges with peak power densities reaching 3000 W cm-2 were used to sputter Cr targets in both inert and reactive gas atmospheres. The flux arriving at the substrates consisted of neutrals and ions (approx. 70/30) of the sputtered metal and working gas atoms (Ar) with significantly elevated degree of ionization compared to conventional magnetron sputtering. The high-speed steel and stainless steel substrates were metal ion etched using a bias voltage of -1200 V prior to the deposition of CrN films. The film-to-substrate interfaces, observed by scanning transmission electron microscope cross-sections, were clean and contained no phases besides the film and substrate ones or recrystallized regions. CrN films were grown by reactive HIPIMS at floating potential reaching -160 V. Initial nucleation grains were large compared to conventional magnetron sputtered films, indicating a high adatom mobility in the present case. The films exhibited polycrystalline columnar growth morphology with evidence of renucleation. No intercolumnar voids were observed and the corrosion behavior of the film was superior to arc deposited CrNx. A high density of lattice defects was observed throughout the films due to the high floating potential. A residual compressive stress of 3 GPa and a hardness value of HK0.025=2600 were measured. A low friction coefficient of 0.4 and low wear rates against Al2O3 in these films are explained by the absence of droplets and voids known to contribute to extensive debris generation.

  • 287.
    Ehiasarian, A.P.
    et al.
    Materials Research Institute, Sheffield Hallam University, Howard Street, Sheffield S1 1WB, United Kingdom.
    New, R.
    Materials Research Institute, Sheffield Hallam University, Howard Street, Sheffield S1 1WB, United Kingdom.
    Munz, W.-D.
    Münz, W.-D., Materials Research Institute, Sheffield Hallam University, Howard Street, Sheffield S1 1WB, United Kingdom.
    Hultman, Lars
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics.
    Helmersson, Ulf
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Plasma and Coating Physics .
    Kouznetsov, V.
    Chemfilt R and D AB, Kumla Gårdsvägen 28, SE-145 63 Norsborg, Sweden.
    Influence of high power densities on the composition of pulsed magnetron plasmas2002In: Vacuum, ISSN 0042-207X, E-ISSN 1879-2715, Vol. 65, no 2, p. 147-154Article in journal (Refereed)
    Abstract [en]

    The application of high power pulses with peak voltage of -2 kV and peak power density of 3 kWcm-2 to magnetron plasma sources is a new development in sputtering technology. The high power is applied to ordinary magnetron cathodes in pulses with short duration of typically some tens of microseconds in order to avoid a glow-to-arc transition. High plasma densities are obtained which have been predicted to initiate self-sputtering. This study concerns Cr and Ti cathodes and presents evidence of multiply charged metal ions as well as of Ar ions in the dense plasma region of the high power pulsed magnetron discharge and a substantially increased metal ion production compared to continuous magnetron sputtering. The average degree of ionisation of the Cr metal deposition flux generated in the plasma source was 30% at a distance of 50 cm. Deposition rates were maintained comparable to conventional magnetron sputtering due to the low pressure of operation of the pulsed discharge - typically 0.4 Pa (3mTorr) of Ar pressure was used. Observations of the current-voltage characteristics of the discharge confirmed two modes of operation of the plasma source representing conventional pulsed sputtering at low powers (0.2 kWcm-2) and pulsed self-sputtering at higher powers (3 kWcm-2). The optical emission from the various species in the plasma showed an increase in metal ion-to-neutral ratio with increasing power. The time evolution within a pulse of the optical emission from Ar0, Cr0, Cr1+, and Cr2+ showed that at low powers Cr and Ar excitation develops simultaneously. However, at higher powers a distinct transition from Ar to Cr plasma within the duration of the pulse was observed. The time evolution of the discharge at higher powers is discussed. © 2002 Elsevier Science Ltd. All rights reserved.

  • 288. Order onlineBuy this publication >>
    Eklund, Per
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Multifunctional nanostructured Ti-Si-C thin films2007Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    In this Thesis, I have investigated multifunctional nanostructured Ti-Si-C thin films synthesized by magnetron sputtering in the substrate-temperature range from room temperature to 900 °C. The studies cover high-temperature growth of Ti3SiC2 and Ti4SiC3, low-temperature growth of Ti-Si-C nanocomposites, and Ti-Si-C-based multi¬layers, as well as their electrical, mechanical, and thermal-stability properties. Ti3SiC2 and Ti4SiC3 were synthesized homoepitaxially onto bulk Ti3SiC2 from individual sputtering targets and heteroepitaxially onto Al2O3(0001) substrates from a Ti3SiC2 target at substrate temperatures of 700 – 900 °C. In the latter case, the film composition exhibits excess C compared to the nominal target composition due to differences between species in angular and energy distribution and gas-phase scattering processes. Ti buffering is shown to compensate for this excess C. The electrical-resistivity values of Ti3SiC2 and Ti4SiC3 thin films were measured to 21-32 uOhmcm and ~50 uOhmcm, respectively. The good conductivity is because the presence of Si layers enhances the relative strength of the metallic Ti-Ti bonds. The higher density of Si layers in Ti3SiC2 than in Ti4SiC3 explains why Ti3SiC2 is the better conductor of the two. Ti3SiC2 thin films are shown to be thermally stable up to 1000 – 1100 °C. Annealing at higher temperature results in decomposition of Ti3SiC2 by Si out-diffusion to the surface with subsequent evaporation. Above 1200 °C, TiCx layers recrystallized. Nanocomposites comprising nanocrystalline (nc-)TiC in an amorphous (a-)SiC matrix phase were deposited at substrate temperatures in the range 100 – 300 °C. These nc-TiC/a-SiC films exhibit low contact resistance in electrical contacts and a ductile deformation behavior due to rotation and gliding of nc-TiC grains in the matrix. The ductile mechanical properties of nc-TiC/a-SiC are actually more similar to those of Ti3SiC2, which is very ductile due to kinking and delamination, than to those of the brittle TiC. Epitaxial TiC/SiC multilayers deposited at ~550 °C were shown to contain cubic SiC layers up to a thickness of ~2 nm. Thicker SiC layers gives a-SiC due to the corresponding increase in interfacial strain energy leading to loss of coherent-layer growth. Nanoindentation of epitaxial Ti3SiC2/TiC0.67 nanolaminates showed inhibition of kink-band formation in Ti3SiC2, as the lamination with the less ductile TiC effectively hindered this mechanism.

    List of papers
    1. Homoepitaxial growth of Ti-Si-C MAX-phase thin films on bulk Ti3SiC2 substrates
    Open this publication in new window or tab >>Homoepitaxial growth of Ti-Si-C MAX-phase thin films on bulk Ti3SiC2 substrates
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    2007 (English)In: Journal of Crystal Growth, ISSN 0022-0248, E-ISSN 1873-5002, Vol. 304, no 1, p. 264-269Article in journal (Refereed) Published
    Abstract [en]

    Ti3SiC2 films were grown on polycrystalline Ti3SiC2 bulk substrates using DC magnetron sputtering. The crystallographic orientation of the film grains is shown to be determined by the respective substrate-grain orientation through homoepitaxial MAX-phase growth. For a film composition close to Ti:Si:C=3:1:2, the films predominantly consist of MAX phases, both Ti3SiC2 and the metastable Ti4SiC3. Lower Si content resulted in growth of TiC with Ti3SiC2 as a minority phase. Thus, MAX-phase heterostructures with preferred crystallographic relationships can also be realized.

    Keywords
    Scanning electron microscopy, Transmission electron microscopy, X-ray diffraction, Physical vapor deposition processes, Carbides, Nanomaterials
    National Category
    Natural Sciences
    Identifiers
    urn:nbn:se:liu:diva-14471 (URN)10.1016/j.jcrysgro.2007.02.014 (DOI)
    Available from: 2007-05-14 Created: 2007-05-14 Last updated: 2017-12-13
    2. Magnetron sputtering of Ti3SiC2 thin films from a Ti3SiC2 compound target
    Open this publication in new window or tab >>Magnetron sputtering of Ti3SiC2 thin films from a Ti3SiC2 compound target
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    2007 (English)In: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films, ISSN 0734-2101, E-ISSN 1520-8559, Vol. 25, no 5, p. 1381-1388Article in journal (Refereed) Published
    Abstract [en]

    Ti3 Si C2 thin films were synthesized by magnetron sputtering from Ti3 Si C2 and Ti targets. Sputtering from a Ti3 Si C2 target alone resulted in films with a C content of ∼50 at. % or more, due to gas-phase scattering processes and differences in angular and energy distributions between species ejected from the target. Addition of Ti to the deposition flux from a Ti3 Si C2 target is shown to bind the excess C in Ti Cx intergrown with Ti3 Si C2 and Ti4 Si C3. Additionally, a substoichiometric Ti Cx buffer layer is shown to serve as a C sink and enable the growth of Ti3 Si C2.

    National Category
    Natural Sciences
    Identifiers
    urn:nbn:se:liu:diva-14472 (URN)10.1116/1.2757178 (DOI)
    Available from: 2007-05-14 Created: 2007-05-14 Last updated: 2019-01-28
    3. Structural, electrical, and mechanical properties of nc-TiC/a-SiC nanocomposite thin films
    Open this publication in new window or tab >>Structural, electrical, and mechanical properties of nc-TiC/a-SiC nanocomposite thin films
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    2005 (English)In: Journal of Vacuum Science & Technology B, ISSN 1071-1023, E-ISSN 1520-8567, Vol. 23, no 6, p. 2486-2495Article in journal (Refereed) Published
    Abstract [en]

    We have synthesized Ti–Si–C nanocomposite thin films by dc magnetron sputtering from a Ti3SiC2 compound target in an Ar discharge on Si(100), Al2O3(0001), and Al substrates at temperatures from room temperature to 300  °C. Electron microscopy, x-ray diffraction, and x-ray photoelectron spectroscopy showed that the films consisted of nanocrystalline (nc-) TiC and amorphous (a-) SiC, with the possible presence of a small amount of noncarbidic C. The growth mode was columnar, yielding a nodular film-surface morphology. Mechanically, the films exhibited a remarkable ductile behavior. Their nanoindentation hardness and E-modulus values were 20 and 290  GPa, respectively. The electrical resistivity was 330  µ  cm for optimal Ar pressure (4  mTorr) and substrate temperature (300  °C). The resulting nc-TiC/a-SiC films performed well as electrical contact material. These films' electrical-contact resistance against Ag was remarkably low, 6  µ at a contact force of 800  N compared to 3.2  µ for Ag against Ag. The chemical stability of the nc-TiC/a-SiC films was excellent, as shown by a Battelle flowing mixed corrosive-gas test, with no N, Cl, or S contaminants entering the bulk of the films.

    Keywords
    titanium compounds, silicon compounds, wide band gap semiconductors, nanocomposites, amorphous semiconductors, thin films, sputter deposition, electron microscopy, X-ray diffraction, X-ray photoelectron spectra, surface morphology, ductility, indentation, hardness, electrical resistivity, electrical contacts, contact resistance
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-14473 (URN)10.1116/1.2131081 (DOI)
    Available from: 2007-05-14 Created: 2007-05-14 Last updated: 2017-12-13
    4. Microstructure and electrical properties of Ti-Si-C-Ag nanocomposite thin films
    Open this publication in new window or tab >>Microstructure and electrical properties of Ti-Si-C-Ag nanocomposite thin films
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    2007 (English)In: Surface and Coatings Technology, ISSN 0257-8972, Vol. 201, no 14, p. 6465-6469Article in journal (Refereed) Published
    Abstract [en]

    Ti–Si–C–Ag nanocomposite coatings consisting of nanocrystalline TiC in an amorphous Si matrix with segregated Ag were deposited by dual magnetron sputtering from Ti3SiC2 and Ag targets. As evidenced by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy, for Ag contents below 10 at.%, the Ag forms 10 nm large crystallites that are homogeneously distributed in the films. For higher Ag contents, coalescence during growth results in the formation of >  100 nm Ag islands on the film surface. The electrical resistivity of the coatings was measured in a four-point-probe setup, and ranged from 340 μΩcm (for Ti–Si–C coatings without Ag) to 40 μΩcm (for high Ag content).

    Keywords
    Sputtering, Titanium carbide, Silver; Resistivity, X-ray diffraction, Electron microscopy
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-14474 (URN)10.1016/j.surfcoat.2006.12.016 (DOI)
    Available from: 2007-05-14 Created: 2007-05-14 Last updated: 2016-08-31
    5. High-power impulse magnetron sputtering of Ti-Si-C thin films from a Ti3SiC2 compound target
    Open this publication in new window or tab >>High-power impulse magnetron sputtering of Ti-Si-C thin films from a Ti3SiC2 compound target
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    2006 (English)In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 515, no 4, p. 1731-1736Article in journal (Refereed) Published
    Abstract [en]

    We have deposited Ti-Si-C thin films using high-power impulse magnetron sputtering (HIPIMS) from a Ti3SiC2 compound target. The as-deposited films were composite materials with TiC as the main crystalline constituent. X-ray diffraction and photoelectron spectroscopy indicated that they also contained amorphous SiC, and for films deposited on inclined substrates, crystalline Ti5Si3Cx. The film morphology was dense and flat, while films deposited with dc magnetron sputtering under comparable conditions were rough and porous. Due to the high degree of ionization of the sputtered species obtained in HIPIMS, it is possible to control the film composition, in particular the C content, by tuning the substrate inclination angle, the Ar process pressure, and the bias voltage.

    Place, publisher, year, edition, pages
    Institutionen för fysik, kemi och biologi, 2006
    Keywords
    HIPIMS, Titanium silicon carbide
    National Category
    Physical Sciences
    Identifiers
    urn:nbn:se:liu:diva-10437 (URN)10.1016/j.tsf.2006.06.015 (DOI)000242931900079 ()
    Note

    Original publication: J. Alami, P. Eklund, J. Emmerlich, O. Wilhelmsson, U. Jansson, H. Högberg, L. Hultman, & U. Helmersson, High-power impulse magnetron sputtering of Ti-Si-C thin films from a Ti3SiC2 compound target, 2006, Thin Solid Films, (515), 4, 1731-1736. http://dx.doi.org/10.1016/j.tsf.2006.06.015. Copyright: Elsevier B.V., http://www.elsevier.com/.

    Available from: 2007-12-14 Created: 2007-12-14 Last updated: 2017-12-14Bibliographically approved
    6. Electrical resistivity of Tin+1ACn (A = Si, Ge, Sn, n = 1–3) thin films
    Open this publication in new window or tab >>Electrical resistivity of Tin+1ACn (A = Si, Ge, Sn, n = 1–3) thin films
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    2007 (English)In: Journal of Materials Research, ISSN 0884-2914, E-ISSN 2044-5326, Vol. 22, no 8, p. 2279-2287Article in journal (Refereed) Published
    Abstract [en]

    We have investigated the electrical resistivity of (0001)-oriented Tin+1ACn (A = Si, Ge, Sn, n = 1–3) thin films deposited by magnetron sputtering onto Al2O3(0001) substrates at temperatures ranging from 500 to 950 °C. Four-point-probe measurements show that all films are good conductors with resistivity values of ∼21–51 μΩ cm for Ti–Si–C films, ∼15–50 μΩ cm for Ti–Ge–C films, and ∼46 μΩ cm for Ti2SnC. We find a general trend of decreasing resistivity with decreasing n for the Ti–Si–C and Ti–Ge–C systems due to the increased metallicity obtained with increasing density of A-element layers. We also show that crystalline quality and competitive growth of impurity phases affect the measured resistivity values. The effect of a given impurity phase largely depends on its location in the sample. Specifically, a TiCx layer in the center of the film constricts the current flow and results in an increased measured resistivity value. However, TiCx transition or seed layers at the substrate–film interface as well as surface segregation of Ge and Ti5Ge3Cx (for Ti–Ge–C) have only little effect on the measured resistivity values. For the Ti–Sn–C system, the resistivity is mainly influenced by the segregation of metallic Sn, yielding a wide spread in the measured values ranging from 20–46 μΩ cm, in the order of increased film purity.

    National Category
    Natural Sciences
    Identifiers
    urn:nbn:se:liu:diva-14476 (URN)10.1557/jmr.2007.0284 (DOI)
    Available from: 2007-05-14 Created: 2007-05-14 Last updated: 2017-12-13
    7. Photoemission studies of Ti3SiC2 and nanocrystalline-TiC/amorphous-SiC nanocomposite thin films
    Open this publication in new window or tab >>Photoemission studies of Ti3SiC2 and nanocrystalline-TiC/amorphous-SiC nanocomposite thin films
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    2006 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 74, no 4, p. 045417-Article in journal (Refereed) Published
    Abstract [en]

    Photoemissionstudies using synchrotron radiation have been performed on epitaxial Ti3SiC2(0001)and compound nanocrystalline (nc-)TiC/amorphous (a-)SiC thin films deposited by magnetronsputtering. As-introduced samples were found to be covered by surfaceoxides, SiOx and TiOx. These oxides could be removed byin-situ annealing to ~1000  °C. For as-annealed Ti3SiC2(0001), surface Si wasobserved and interpreted as originating from decomposition of Ti3SiC2 throughSi out-diffusion. For nc-TiC/a-SiC annealed in situ to ~1000  °C, thesurface instead exhibited a dominant contribution from graphitic carbon, alsowith the presence of Si, due to C and Siout-diffusion from the a-SiC compound or from grain boundaries.

    Keywords
    titanium compounds, silicon compounds, wide band gap semiconductors, nanocomposites, amorphous state, epitaxial layers, sputtered coatings, photoelectron spectra, surface composition, annealing, decomposition, surface diffusion, grain boundaries
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-14477 (URN)10.1103/PhysRevB.74.045417 (DOI)
    Available from: 2007-05-14 Created: 2007-05-14 Last updated: 2017-12-13
    8. Thermal stability of Ti3SiC2 thin films
    Open this publication in new window or tab >>Thermal stability of Ti3SiC2 thin films
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    2007 (English)In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 55, no 4, p. 1479-1488Article in journal (Refereed) Published
    Abstract [en]

    The thermal stability of Ti3SiC2(0 0 0 1) thin films is studied by in situ X-ray diffraction analysis during vacuum furnace annealing in combination with X-ray photoelectron spectroscopy, transmission electron microscopy and scanning transmission electron microscopy with energy dispersive X-ray analysis. The films are found to be stable during annealing at temperatures up to ∼1000 °C for 25 h. Annealing at 1100–1200 °C results in the rapid decomposition of Ti3SiC2 by Si out-diffusion along the basal planes via domain boundaries to the free surface with subsequent evaporation. As a consequence, the material shrinks by the relaxation of the Ti3C2 slabs and, it is proposed, by an in-diffusion of O into the empty Si-mirror planes. The phase transformation process is followed by the detwinning of the as-relaxed Ti3C2 slabs into (1 1 1)-oriented TiC0.67 layers, which begin recrystallizing at 1300 °C. Ab initio calculations are provided supporting the presented decomposition mechanisms.

    Keywords
    Ti3SiC2 thin films, Phase transformations, X-ray diffraction, Transmission electron microscopy, Ab initio electron theory
    National Category
    Natural Sciences
    Identifiers
    urn:nbn:se:liu:diva-14478 (URN)10.1016/j.actamat.2006.10.010 (DOI)
    Available from: 2007-05-14 Created: 2007-05-14 Last updated: 2017-12-13
    9. Epitaxial TiC/SiC multilayers
    Open this publication in new window or tab >>Epitaxial TiC/SiC multilayers
    2007 (English)In: Physica status solidi (RRL): rapid research letters, ISSN 1862-6254, Vol. 1, no 3, p. 113-115Article in journal (Refereed) Published
    Abstract [en]

    Epitaxial TiC/SiC multilayers were grown by magnetron sputtering at a substrate temperature of 550 °C, where SiC is normally amorphous. The epitaxial TiC template induced growth of cubic SiC up to a thickness of ~2 nm. Thicker SiC layers result in a direct transition to growth of the metastable amorphous SiC followed by renucleation of nanocrystalline TiC layers

    Keywords
    61.10.Nz, 68.37.Lp, 68.55.-a, 81.05.Je, 81.07.Bk, 81.15.Kk
    National Category
    Natural Sciences
    Identifiers
    urn:nbn:se:liu:diva-14479 (URN)10.1002/pssr.200701027 (DOI)
    Available from: 2007-05-14 Created: 2007-05-14 Last updated: 2016-08-31
    10. Intrusion-type deformation in epitaxial Ti3SiC2/TiCx nanolaminates
    Open this publication in new window or tab >>Intrusion-type deformation in epitaxial Ti3SiC2/TiCx nanolaminates
    Show others...
    2007 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 91, no 12, p. 123124-Article in journal (Refereed) Published
    Abstract [en]

    We investigate the deformation of epitaxial Ti3 Si C2 (0001) Ti Cx (111) (x∼0.67) nanolaminates deposited by magnetron sputtering. Nanoindentation and transmission electron microscopy show that the Ti3 Si C2 layers deform via basal plane slip and intrusion into the TiC layers, suppressing kink-band and pile-up deformation behaviors analogous with monolithic Ti3 Si C2. This remarkable response to indentation is due to persistent slip in the TiC layers and prevention of gross slip throughout the nanolaminate by the interleaving Ti3 Si C2 layers. Hardness and Young's modulus were measured as ∼15 and ∼240 GPa, respectively.

    National Category
    Natural Sciences
    Identifiers
    urn:nbn:se:liu:diva-14480 (URN)10.1063/1.2789710 (DOI)
    Available from: 2007-05-14 Created: 2007-05-14 Last updated: 2017-12-13
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