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• 301.
Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics.
Department of Materials Chemistry, The Angström Laboratory, Uppsala University, Uppsala, Swede. Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology. Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics.
Comment on "Pulsed laser deposition and properties of M(n+1)AX(x) phase formulated Ti3SiC2 thin films''2004In: Tribology letters, ISSN 1023-8883, E-ISSN 1573-2711, Vol. 17, no 4, p. 977-978p. 977-978Article in journal (Other academic)

A recent paper by Hu et al. claimed synthesis of the MAX-phase Ti3SiC2 at 100 - 300 degreesC using pulsed laser deposition. In this comment, we find that the evidence presented by Hu et al. is insufficient to show Ti3SiC2 formation. In fact, there is a simpler interpretation of their results from X-ray diffraction and transmission electron microscopy, namely that the material produced is a cubic TiC-based compound.

• 302.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
Layered ternary M(n+1)AX(n) phases and their 2D derivative MXene: an overview from a thin-film perspective2017In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 50, no 11, article id 113001Article, review/survey (Refereed)

Inherently and artificially layered materials are commonly investigated both for fundamental scientific purposes and for technological application. When a layered material is thinned or delaminated to its physical limits, a two-dimensional (2D) material is formed and exhibits novel properties compared to its bulk parent phase. The complex layered phases known as MAX phases (where M = early transition metal, A = A-group element, e.g. Al or Si, and X = C or N) are an exciting model system for materials design and the understanding of process-structure-property relationships. When the A layers are selectively etched from the MAX phases, a new type of 2D material is formed, named MXene to emphasize the relation to the MAX phases and the parallel with graphene. Since their discovery in 2011, MXenes have rapidly become established as a novel class of 2D materials with remarkable possibilities for composition variations and property tuning. This article gives a brief overview of MAX phases and MXene from a thin-film perspective, reviewing theory, characterization by electron microscopy, properties and how these are affected by the change in dimensionality, and outstanding challenges.

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• 303.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
Interdisciplinary Nanoscience Center (iNANO) and Department of Physics and Astronomy, University of Aarhus, DK-800 Aarhus C, Denmark. Interdisciplinary Nanoscience Center (iNANO) and Department of Physics and Astronomy, University of Aarhus, DK-800 Aarhus C, Denmark. Interdisciplinary Nanoscience Center (iNANO) and Department of Physics and Astronomy, University of Aarhus, DK-800 Aarhus C, Denmark.
Thermal Stability and Phase Transformations of γ-/Amorphous-Al2O3 Thin Films2009In: Plasma processes and polymers, ISSN 1612-8850, Vol. 6, no 1, p. 907-911Article in journal (Refereed)

Magnetron-sputtered Al2O3 thin films were annealed in ambient air. The phase compositions of the as-deposited Al2O3 films were (i) fully amorphous, (ii) nanocrystalline γ-Al2O3 in an amorphous Al2O3 matrix, and (iii) fully crystalline γ. For all samples, annealing to 1 100-1 150 °C resulted in a transformation to α-alumina. The transformation paths depend on the phase fraction of γ in the as-deposited films. For amorphous films and films with low initial γ fraction, the intermediate phase θ-Al2O3 appeared in the range of 1 000-1 100 °C. For predominantly crystalline γ-Al2O3 as-deposited films no intermediate Al2O3 phases were observed, indicating a direct γ-to-α phase transformation at ≈1 100 °C.

• 304.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
Photoemission studies of Ti3SiC2 and nanocrystalline-TiC/amorphous-SiC nanocomposite thin films2006In: 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)

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.

• 305. Buy this publication >>
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
Growth and thermoelectric properties of CaMnO3-based thin films2018Licentiate thesis, comprehensive summary (Other academic)

The field of them1oelectrics started in early 19th century. Since the discovery of the Seebeck effect and the Peltier effect, thermoelectric modules have found their way into, mostly, niche applications such as radioisotope thermoelectric generators on space missions. Thermoelectric modules can also be used for cooling, utilizing the Peltier effect.

Thermoelectrics are promising materials due to the operation nature of the modules. That is, they have no moving parts, no exhaust, long lifetime without maintenance, features that make them attractive for many applications. Despite these promising properties, thermoelectric modules are mostly used in niche applications. The main reason for this is conventional modules with the highest efficiency are commonly made of expensive and/or rare elements which prevents mass production.

To tackle this problem, new materials are investigated to find a module that can be made widely available. Oxides are one possibility, where an added benefit is that they are chemically stable even at elevated temperature. The perovskite CaMnO3 is one of the more promising oxides, with elements that are abundant on earth and cheap. The material does suffer from low electrical conductivity which results in a low electrical conductivity and efficiency. A substantial effort has been put in to increase the efficiency of CaMnO3, hut it still needs improvement.

In my thesis, I have investigated the CaMnO3 system. CaMnO3 was synthesized using co-reactive RF-magnetron sputtering and post annealing. The synthesis method is already known hut has not been used for deposition of perovskites. I have also demonstrated that this synthesis method can be used to dope CaMnO3 with niobium at appropriate levels for enhancing the efficiency.

Growth and thermoelectric properties of CaMnO3-based thin films
omslag
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• 306.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
The effects of microstructure, Nb content and secondary Ruddlesden-Popper phase on thermoelectric properties in perovskite CaMn1-xNbxO3 (x=0-0.10) thin films2020In: RSC Advances, ISSN 2046-2069, E-ISSN 2046-2069, RSC ADVANCES, Vol. 10, no 13, p. 7918-7926Article in journal (Refereed)

CaMn1-xNbxO3 (x = 0, 0.5, 0.6, 0.7 and 0.10) thin films have been grown by a two-step sputtering/annealing method. First, rock-salt-structured (Ca,Mn1-x,Nb-x)O thin films were deposited on 11 & x304;00 sapphire using reactive RF magnetron co-sputtering from elemental targets of Ca, Mn and Nb. The CaMn1-xNbxO3 films were then obtained by thermally induced phase transformation from rock-salt-structured (Ca,Mn1-xNbx)O to orthorhombic during post-deposition annealing at 700 degrees C for 3 h in oxygen flow. The X-ray diffraction patterns of pure CaMnO3 showed mixed orientation, while Nb-containing films were epitaxially grown in [101] out of-plane-direction. Scanning transmission electron microscopy showed a Ruddlesden-Popper (R-P) secondary phase in the films, which results in reduction of the electrical and thermal conductivity of CaMn1-xNbxO3. The electrical resistivity and Seebeck coefficient of the pure CaMnO3 film were measured to 2.7 omega cm and -270 mu V K-1 at room temperature, respectively. The electrical resistivity and Seebeck coefficient were reduced by alloying with Nb and was measured to 0.09 omega cm and -145 mu V K-1 for x = 0.05. Yielding a power factor of 21.5 mu W K-2 m(-1) near room temperature, nearly eight times higher than for pure CaMnO3 (2.8 mu W K-2 m(-1)). The power factors for alloyed samples are low compared to other studies on phase-pure material. This is due to high electrical resistivity originating from the secondary R-P phase. The thermal conductivity of the CaMn1-xNbxO3 films is low for all samples and is the lowest for x = 0.07 and 0.10, determined to 1.6 W m(-1) K-1. The low thermal conductivity is attributed to grain boundary scattering and the secondary R-P phase.

fulltext
• 307.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
Formation mechanism and thermoelectric properties of CaMnO3 thin films synthesized by annealing of Ca0.5Mn0.5O films2019In: Journal of Materials Science, ISSN 0022-2461, E-ISSN 1573-4803, Vol. 54, no 11, p. 8482-8491Article in journal (Refereed)

A two-step synthesis approach was utilized to grow CaMnO3 on M-, R- and C-plane sapphire substrates. Radio-frequency reactive magnetron sputtering was used to grow rock-salt-structured (Ca, Mn)O followed by a 3-h annealing step at 800 degrees C in oxygen flow to form the distorted perovskite phase CaMnO3. The effect of temperature in the post-annealing step was investigated using x-ray diffraction. The phase transformation to CaMnO3 started at 450 degrees C and was completed at 550 degrees C. Films grown on R- and C-plane sapphire showed similar structure with a mixed orientation, whereas the film grown on M-plane sapphire was epitaxially grown with an out-of-plane orientation in the [202] direction. The thermoelectric characterization showed that the film grown on M-plane sapphire has about 3.5 times lower resistivity compared to the other films with a resistivity of 0.077cm at 500 degrees C. The difference in resistivity is a result from difference in crystal structure, single orientation for M-plane sapphire compared to mixed for R- and C-plane sapphire. The highest absolute Seebeck coefficient value is -350 mu VK-1 for all films and is decreasing with temperature.

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• 308. Buy this publication >>
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
Disordered Icosahedral Boron-Rich Solids: A Theoretical Study of Thermodynamic Stability and Properties2017Doctoral thesis, comprehensive summary (Other academic)

This thesis is a theoretical study of configurational disorder in icosahedral boron-rich solids, in particular boron carbide, including also the development of a methodological framework for treating configurational disorder in such materials, namely superatom-special quasirandom structure (SA-SQS). In terms of its practical implementations, the SA-SQS method is demonstrated to be capable of efficiently modeling configurational disorder in icosahedral boron-rich solids, whiles the thermodynamic stability as well as the properties of the configurationally disordered icosahedral boron-rich solids, modeled from the SA-SQS method, can be directly investigated, using the density functional theory (DFT).

In case of boron carbide, especially B4C and B13C2 compositions, the SA-SQS method is used for modeling configurational disorder, arising from a high concentration of low-energy B/C substitutional defects. The results, obtained from the DFT-based calculations, demonstrate that configurational disorder of B and C atoms in boron carbide is not only thermodynamically favored at high temperature, but it also plays an important role in altering the properties of boron carbide − for example, restoration of higher rhombohedral symmetry of B4C, a metal-to-nonmetal transition and a drastic increase in the elastic moduli of B13C2. The configurational disorder can also explain large discrepancies, regarding the proper- ties of boron carbide, between experiments and previous theoretical calculations, having been a long standing controversial issue in the field of icosahedral boron- rich solids, as the calculated properties of the disordered boron carbides are found to be in qualitatively good agreement with those, observed in experiments. In order to investigate the configurational evolution of B4C as a function of temperature, beyond the SA-SQS level, a brute-force cluster-expansion method in combination with Monte Carlo simulations is implemented. The results demonstrate that configurational disorder in B4C indeed essentially takes place within the icosahedra in a way that justifies the focus on lowenergy defect patterns of the superatom picture.

The investigation of the thermodynamic stability of icosahedral carbon-rich boron carbides beyond the believed solubility limit of carbon (20 at.% C) demonstrates that, apart from B4C generally addressed in the literature, B2.5C represented by B10Cp2(CC) is predicted to be thermodynamically stable with respect to B4C as well as pure boron and carbon under high pressure, ranging between 40 and 67 GPa, and also at elevated temperature. B2.5C is expected to be metastable at ambient pressure, as indicated by its dynamical and mechanical stabilities at 0 GPa. A possible synthesis route of B2.5C and a fingerprint for its characterization from the simulations of x-ray powder diffraction pattern are suggested.

Besides modeling configurational disorder in boron carbide, the SA-SQS method also opens up for theoretical studies of new alloys between different icosahedral boron-rich solids − for example, (B6O)1−x(B13C2)x and B12(As1−xPx)2. As for the pseudo-binary (B6O)1−x(B13C2)x alloy, it is predicted to display a miscibility gap resulting in B6O-rich and either ordered or disordered B13C2-rich domains for intermediate global compositions at all temperatures up to melting points of the materials. However, some intermixing of B6O and B13C2 to form solid solutions is also predicted at high temperature. A noticeable mutual solubility of icosahedral B12As2 and B12P2 in each other to form B12(As1−xPx)2 disordered alloy is predicted even at room temperature, and a complete closure of a pseudo-binary miscibility gap is achieved at around 900 K.

Apart from B12(As1−xPx)2, the thermodynamic stability of other compounds and alloys in the ternary B-As-P system is also investigated. For the binary B-As system, zincblende BAs is found to be thermodynamically unstable with respect to icosahedral B12As2 and gray arsenic at 0 K and increasingly so at higher temperature, indicating that BAs may merely exist as a metastable phase. This is in contrast to the binary B-P system, in which zinc-blende BP and icosahedral B12P2 are both predicted to be stable. Owing to the instability of BAs with respect to B12As2 and gray arsenic, only a tiny amount of BAs is predicted to be able to dissolve in BP to form BAs1−xPx disordered alloy at elevated temperature. For example, less than 5% BAs can dissolve in BP at 1000 K. As for the binary As-P system, As1−xPx disordered alloys are predicted at elevated temperature − for example, a disordered solid solution of up to ∼75% As in black phosphorus as well as a small solubility of ∼1% P in gray arsenic at 750 K, together with the presence of miscibility gaps.

The thermodynamic stability of three different compositions of α-rhombohedral boron-like boron subnitride, having been proposed so far in the literature, is investigated. Those are, B6N, B13N2, and B38N6, represented respectively by B12(N-N), B12(NBN), and [B12(N-N)]0.33[B12(NBN)]0.67. It is found that, out of these sub- nitrides, only B38N6 is thermodynamically stable from 0 GPa up to ∼7.5 GPa, depending on the temperature, and is thus concluded as a stable composition of α-rhombohedral boron-like boron subnitride.

1. First-principles study of configurational disorder in B4C using a superatom-special quasirandom structure method
Open this publication in new window or tab >>First-principles study of configurational disorder in B4C using a superatom-special quasirandom structure method
2014 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 90, no 2, article id 024204Article in journal (Refereed) Published
##### Abstract [en]

Configurationally disordered crystalline boron carbide, with the composition B4C, is studied using first-principles calculations. We investigate both dilute and high concentrations of carbon-boron substitutional defects. For the latter purpose, we suggest a superatoms picture of the complex structure and combine it with a special quasirandom structure approach for disorder. In this way, we model a random distribution of high concentrations of the identified low-energy defects: (1) bipolar defects and (2) rotation of icosahedral carbon among the three polar-up sites. Additionally, the substitutional disorder of the icosahedral carbon at all six polar sites, as previously discussed in the literature, is also considered. Two configurational phase transitions from the ordered to the disordered configurations are predicted to take place upon an increase in temperature using a mean-field approximation for the entropy. The first transition, at 870 K, induces substitutional disorder of the icosahedral carbon atoms among the three polar-up sites; meanwhile the second transition, at 2325 K, reveals the random substitution of the icosahedral carbon atoms at all six polar sites coexisting with bipolar defects. Already the first transition removes the monoclinic distortion existing in the ordered ground-state configuration and restore the rhombohedral system (R3m). The restoration of inversion symmetry yielding the full rhombohedral symmetry (R (3) over barm) on average, corresponding to what is reported in the literature, is achieved after the second transition. Investigating the effects of high pressure on the configurational stability of the disordered B4C phases reveals a tendency to stabilize the ordered ground-state configuration as the configurationally ordering/disordering transition temperature increases with pressure exerted on B4C. The electronic density of states, obtained from the disordered phases, indicates a sensitivity of the band gap to the degree of configurational disorder in B4C.

##### Place, publisher, year, edition, pages
American Physical Society, 2014
##### National Category
Physical Sciences
##### Identifiers
urn:nbn:se:liu:diva-109591 (URN)10.1103/PhysRevB.90.024204 (DOI)000339481700003 ()
##### Conference
Conference name
Available from: 2014-08-21 Created: 2014-08-21 Last updated: 2018-08-14
2. Configurational order-disorder induced metal-nonmetal transition in B13C2 studied with first-principles superatom-special quasirandom structure method
Open this publication in new window or tab >>Configurational order-disorder induced metal-nonmetal transition in B13C2 studied with first-principles superatom-special quasirandom structure method
2015 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 92, no 1, article id 014202Article in journal (Refereed) Published
##### Abstract [en]

Due to a large discrepancy between theory and experiment, the electronic character of crystalline boron carbide B13C2 has been a controversial topic in the field of icosahedral boron-rich solids. We demonstrate that this discrepancy is removed when configurational disorder is accurately considered in the theoretical calculations. We find that while the ordered ground state B13C2 is metallic, the configurationally disordered B13C2, modeled with a superatom-special quasirandom structure method, goes through a metal to nonmetal transition as the degree of disorder is increased with increasing temperature. Specifically, one of the chain-end carbon atoms in the CBC chains substitutes a neighboring equatorial boron atom in a B-12 icosahedron bonded to it, giving rise to a B11Ce(BBC) unit. The atomic configuration of the substitutionally disordered B13C2 thus tends to be dominated by a mixture between B-12(CBC) and B11Ce(BBC). Due to splitting of valence states in B11Ce(BBC), the electron deficiency in B-12(CBC) is gradually compensated.

##### Place, publisher, year, edition, pages
American Physical Society, 2015
##### National Category
Physical Sciences
##### Identifiers
urn:nbn:se:liu:diva-120344 (URN)10.1103/PhysRevB.92.014202 (DOI)000357484100001 ()
##### Note

Funding Agencies|Swedish Research Council (VR) [621-2011-4417, 330-2014-6336, 2014-4750]; CeNano at Linkoping University; LiLi-NFM; Swedish Government Strategic Research Area Grant in Materials Science

Available from: 2015-07-31 Created: 2015-07-31 Last updated: 2018-08-14
3. Carbon-rich icosahedral boron carbides beyond B4C and their thermodynamic stabilities at high temperature and pressure from first principles
Open this publication in new window or tab >>Carbon-rich icosahedral boron carbides beyond B4C and their thermodynamic stabilities at high temperature and pressure from first principles
2016 (English)In: PHYSICAL REVIEW B, ISSN 2469-9950, Vol. 94, no 5, article id 054104Article in journal (Refereed) Published
##### Abstract [en]

We investigate the thermodynamic stability of carbon-rich icosahedral boron carbide at different compositions, ranging from B4C to B2C, using first-principles calculations. Apart fromB4C, generally addressed in the literature, B2.5C, represented by B10C2p (C-C), where C-p and (C-C) denote a carbon atom occupying the polar site of the icosahedral cluster and a diatomic carbon chain, respectively, is predicted to be thermodynamically stable under high pressures with respect to B4C as well as pure boron and carbon phases. The thermodynamic stability of B2.5C is determined by the Gibbs free energy G as a function of pressure p and temperature T, in which the contributions from the lattice vibrations and the configurational disorder are obtained within the quasiharmonic and the mean-field approximations, respectively. The stability range of B2.5C is then illustrated through the p-T phase diagrams. Depending on the temperatures, the stability range of B2.5C is predicted to be within the range between 40 and 67 GPa. At T greater than or similar to 500 K, the icosahedral C-p atoms in B2.5C configurationally disorder at the polar sites. By investigating the properties of B2.5C, e.g., elastic constants and phonon and electronic density of states, we demonstrate that B2.5C is both mechanically and dynamically stable at zero pressure, and is an electrical semiconductor. Furthermore, based on the sketched phase diagrams, a possible route for experimental synthesis of B2.5C as well as a fingerprint for its characterization from the simulations of x-ray powder diffraction pattern are suggested.

##### Place, publisher, year, edition, pages
AMER PHYSICAL SOC, 2016
##### National Category
Condensed Matter Physics
##### Identifiers
urn:nbn:se:liu:diva-131508 (URN)10.1103/PhysRevB.94.054104 (DOI)000381304300001 ()
##### Note

Funding Agencies|Swedish Research Council (VR) [621-2011-4417, 330-2014-6336, 2014-4750]; Marie Sklodowska Curie Actions [INCA 600398]; CeNano at Linkoping University; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University (Faculty Grant SFO-Mat-LiU) [2009 00971]

Available from: 2016-09-26 Created: 2016-09-23 Last updated: 2018-08-29
4. Effects of configurational disorder on the elastic properties of icosahedral boron-rich alloys based on B6O, B13C2, and B4C, and their mixing thermodynamics
Open this publication in new window or tab >>Effects of configurational disorder on the elastic properties of icosahedral boron-rich alloys based on B6O, B13C2, and B4C, and their mixing thermodynamics
2016 (English)In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 144, no 13, article id 134503Article in journal (Refereed) Published
##### Abstract [en]

The elastic properties of alloys between boron suboxide (B6O) and boron carbide (B13C2), denoted by (B6O)1−x(B13C2)x, as well as boron carbide with variable carbon content, ranging from B13C2 to B4C are calculated from first-principles. Furthermore, the mixing thermodynamics of (B6O)1−x(B13C2)x is studied. A superatom-special quasirandom structure approach is used for modeling different atomic configurations, in which effects of configurational disorder between the carbide and suboxide structural units, as well as between boron and carbon atoms within the units, are taken into account. Elastic properties calculations demonstrate that configurational  disorder in B13C2, where a part of the C atoms in the CBC chains substitute for B atoms in the B12 icosahedra, drastically increase the Young’s and shear modulus, as compared to an atomically ordered state, B12(CBC). These calculated elastic moduli of the disordered state are in excellent agreement with experiments. Configurational disorder between boron and carbon can also explain the experimentally observed almost constant elastic moduli of boron carbide as the carbon content is changed from B4C to B13C2. The elastic moduli of the (B6O)1−x(B13C2)x system are also practically unchanged with composition if boron-carbon disorder is taken into account. By investigating the mixing thermodynamics of the alloys, in which the Gibbs free energy is determined within the mean-field approximation for the configurational entropy, we outline the pseudo-binary phase diagram of (B6O)1−x(B13C2)x. The phase diagram reveals the existence of a miscibility gap at all temperatures up to the melting point. Also, the coexistence of B6O-rich as well as ordered or disordered B13C2-rich domains in the material prepared through equilibrium routes is predicted.

##### Place, publisher, year, edition, pages
American Institute of Physics (AIP), 2016
##### National Category
Physical Sciences
##### Identifiers
urn:nbn:se:liu:diva-122425 (URN)10.1063/1.4944982 (DOI)000374527900023 ()27059576 (PubMedID)
##### Note

Funding agencies:Swedish Research Council (VR) [621-2011-4417, 330-2014-6336, 2011-42-59]; CeNano at Linkoping University; Ministry of Education and Science of the Russian Federation in the framework of Increase Competitiveness Program of NUST "MISiS" [K3-2014-049]; LiLi-

At the time for thesis presentation publication was in status: Manuscript

Available from: 2015-11-02 Created: 2015-11-02 Last updated: 2018-08-14Bibliographically approved
5. Thermodynamic stability and properties of boron subnitrides from first principles
Open this publication in new window or tab >>Thermodynamic stability and properties of boron subnitrides from first principles
2017 (English)In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 95, no 6, article id 064206Article, review/survey (Refereed) Published
##### Abstract [en]

We use the first-principles approach to clarify the thermodynamic stability as a function of pressure and temperature of three different alpha-rhombohedral-boron-like boron subnitrides, with the compositions of B6N, B13N2, and B38N6, proposed in the literature. We find that, out of these subnitrides with the structural units of B-12(N-N), B-12(NBN), and [B-12(N-N)](0.33)[B-12(NBN)](0.67), respectively, only B38N6, represented by [B-12(N-N)](0.33)[B-12(NBN)](0.67), is thermodynamically stable. Beyond a pressure of about 7.5 GPa depending on the temperature, also B38N6 becomes unstable, and decomposes into cubic boron nitride and a-tetragonalboron- like boron subnitride B50N2. The thermodynamic stability of boron subnitrides and relevant competing phases is determined by the Gibbs free energy, in which the contributions from the lattice vibrations and the configurational disorder are obtained within the quasiharmonic and the mean-field approximations, respectively. We calculate lattice parameters, elastic constants, phonon and electronic density of states, and demonstrate that [B-12(N-N)](0.33)[B-12(NBN)](0.67) is bothmechanically and dynamically stable, and is an electrical semiconductor. The simulated x-ray powder-diffraction pattern as well as the calculated lattice parameters of [B-12(N-N)](0.33)[B-12(NBN)](0.67) are found to be in good agreement with those of the experimentally synthesized boron subnitrides reported in the literature, verifying that B38N6 is the stable composition of a-rhombohedral-boron-like boron subnitride.

##### Place, publisher, year, edition, pages
AMER PHYSICAL SOC, 2017
##### National Category
Condensed Matter Physics
##### Identifiers
urn:nbn:se:liu:diva-136168 (URN)10.1103/PhysRevB.95.064206 (DOI)000394658500001 ()
##### Note

Funding Agencies|Swedish Research Council (VR) [621-2011- 4417, 330-2014-6336, 2014-4750]; Marie Sklodowska Curie Actions [INCA 600398]; CeNano at Linkoping University; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University (Faculty Grant SFO-Mat-LiU) [2009 00971]

Available from: 2017-04-03 Created: 2017-04-03 Last updated: 2018-08-29
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Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
First-principles study of configurational disorder in icosahedral boron-rich solids2015Licentiate thesis, comprehensive summary (Other academic)

This thesis is a theoretical study of configurationally disordered icosahedral boronrich solids, in particular boron carbides, using density functional theory and alloy theory. The goal is to resolve discrepancies, regarding the properties of boron carbides, between experiments and previous theoretical calculations which have been a controversial issue in the field of icosahedral boron-rich solids. For instance, B13C2 is observed experimentally to be a semiconductor, meanwhile electronic band structure calculations reveal a metallic character of B13C2 due to its electron deficiency. In B4C, on the other hand, the experimentally observed band gap is unexpectedly smaller, not the usual larger, than that of standard DFT calculations. Another example is given by the existence of a small structural distortion in B4C, as predicted in theoretical calculations, which reduces the crystal symmetry from the experimentally observed rhombohedral (R3m) to the based-centered monoclinic (Cm). Since boron carbide is stable as a single-phase over a broad composition range (~8-20 at.% C), substitution of boron and carbon atoms for one another is conceivable. For this reason, the discrepancies have been speculated in the literature, without a proof, to originate from configurational disorder induced by substitutional defects. However, owing to its complex  atomic structure, represented by 12-atom icosahedra and 3-atom intericosahedral chains, a practical alloy theory method for direct calculations of the properties of the relevant configurations of disordered boron carbides, as well as for a thermodynamic  assessment of their stability has been missing.

In this thesis, a new approach, the superatom-special quasirandom structure (SA-SQS), has been developed. The approach allows one to model configurational disorder in boron carbide, induced by high concentrations of low-energy B/C substitutional defects. B13C2 and B4C are the two stoichiometries, mainly considered in this study, as they are of particular importance and have been in focus in the literature. The results demonstrate that, from thermodynamic considerations, both B13C2 and B4C configurationally disorder at high temperature. In the case of B13C2, the configurational disorder splits off some valence states into the band gap that in turn compensates the electron deficiency in  ordered B13C2, thus resulting in a semiconducting character. As for B4C, the configurational disorder eliminates the monoclinic distortion, thus resulting in the restoration of the higher rhombohedral symmetry. Configurational disorder can also account for an excel lent agreement on elastic moduli of boron carbide between theory and experiment. Thus, several of the previous discrepancies between theory and experiments are resolved.

Inspired by attempts to enhance the mechanical properties of boron suboxide by fabricating boron suboxide-boron carbide composites, as recently suggested in the literature, the SA-SQS approach is used for modeling mixtures of boron suboxide (B6O) and boron carbide (B13C2), denoted by pseudo-binary (B6O)1–x(B13C2)x alloys. The knowledge of configurational disorder, gained from the previous studies of boron carbide, is applied to model the mixing alloys. By investigating the thermodynamics of mixing between B6O and B13C2, the phase diagram of the (B6O)1–x(B13C2)x alloys is outlined and it reveals the existence of a miscibility gap at all temperatures up to the melting point, indicating the coexistence of B6O-rich and either ordered or disordered B13C2-rich domains in (B6O)1–x(B13C2)x alloys under equilibrium condition. However, a limited intermixing of B6O and B13C2 to form solid solutions at high temperature is predicted, e.g. a solid solution of ~5% B13C2 in B6O and ~20% B6O in B13C2 at 2000 K.

1. First-principles study of configurational disorder in B4C using a superatom-special quasirandom structure method
Open this publication in new window or tab >>First-principles study of configurational disorder in B4C using a superatom-special quasirandom structure method
2014 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 90, no 2, article id 024204Article in journal (Refereed) Published
##### Abstract [en]

Configurationally disordered crystalline boron carbide, with the composition B4C, is studied using first-principles calculations. We investigate both dilute and high concentrations of carbon-boron substitutional defects. For the latter purpose, we suggest a superatoms picture of the complex structure and combine it with a special quasirandom structure approach for disorder. In this way, we model a random distribution of high concentrations of the identified low-energy defects: (1) bipolar defects and (2) rotation of icosahedral carbon among the three polar-up sites. Additionally, the substitutional disorder of the icosahedral carbon at all six polar sites, as previously discussed in the literature, is also considered. Two configurational phase transitions from the ordered to the disordered configurations are predicted to take place upon an increase in temperature using a mean-field approximation for the entropy. The first transition, at 870 K, induces substitutional disorder of the icosahedral carbon atoms among the three polar-up sites; meanwhile the second transition, at 2325 K, reveals the random substitution of the icosahedral carbon atoms at all six polar sites coexisting with bipolar defects. Already the first transition removes the monoclinic distortion existing in the ordered ground-state configuration and restore the rhombohedral system (R3m). The restoration of inversion symmetry yielding the full rhombohedral symmetry (R (3) over barm) on average, corresponding to what is reported in the literature, is achieved after the second transition. Investigating the effects of high pressure on the configurational stability of the disordered B4C phases reveals a tendency to stabilize the ordered ground-state configuration as the configurationally ordering/disordering transition temperature increases with pressure exerted on B4C. The electronic density of states, obtained from the disordered phases, indicates a sensitivity of the band gap to the degree of configurational disorder in B4C.

##### Place, publisher, year, edition, pages
American Physical Society, 2014
##### National Category
Physical Sciences
##### Identifiers
urn:nbn:se:liu:diva-109591 (URN)10.1103/PhysRevB.90.024204 (DOI)000339481700003 ()
##### Conference
Conference name
Available from: 2014-08-21 Created: 2014-08-21 Last updated: 2018-08-14
2. Configurational order-disorder induced metal-nonmetal transition in B13C2 studied with first-principles superatom-special quasirandom structure method
Open this publication in new window or tab >>Configurational order-disorder induced metal-nonmetal transition in B13C2 studied with first-principles superatom-special quasirandom structure method
2015 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 92, no 1, article id 014202Article in journal (Refereed) Published
##### Abstract [en]

Due to a large discrepancy between theory and experiment, the electronic character of crystalline boron carbide B13C2 has been a controversial topic in the field of icosahedral boron-rich solids. We demonstrate that this discrepancy is removed when configurational disorder is accurately considered in the theoretical calculations. We find that while the ordered ground state B13C2 is metallic, the configurationally disordered B13C2, modeled with a superatom-special quasirandom structure method, goes through a metal to nonmetal transition as the degree of disorder is increased with increasing temperature. Specifically, one of the chain-end carbon atoms in the CBC chains substitutes a neighboring equatorial boron atom in a B-12 icosahedron bonded to it, giving rise to a B11Ce(BBC) unit. The atomic configuration of the substitutionally disordered B13C2 thus tends to be dominated by a mixture between B-12(CBC) and B11Ce(BBC). Due to splitting of valence states in B11Ce(BBC), the electron deficiency in B-12(CBC) is gradually compensated.

##### Place, publisher, year, edition, pages
American Physical Society, 2015
##### National Category
Physical Sciences
##### Identifiers
urn:nbn:se:liu:diva-120344 (URN)10.1103/PhysRevB.92.014202 (DOI)000357484100001 ()
##### Note

Funding Agencies|Swedish Research Council (VR) [621-2011-4417, 330-2014-6336, 2014-4750]; CeNano at Linkoping University; LiLi-NFM; Swedish Government Strategic Research Area Grant in Materials Science

Available from: 2015-07-31 Created: 2015-07-31 Last updated: 2018-08-14
3. Effects of configurational disorder on the elastic properties of icosahedral boron-rich alloys based on B6O, B13C2, and B4C, and their mixing thermodynamics
Open this publication in new window or tab >>Effects of configurational disorder on the elastic properties of icosahedral boron-rich alloys based on B6O, B13C2, and B4C, and their mixing thermodynamics
2016 (English)In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 144, no 13, article id 134503Article in journal (Refereed) Published
##### Abstract [en]

The elastic properties of alloys between boron suboxide (B6O) and boron carbide (B13C2), denoted by (B6O)1−x(B13C2)x, as well as boron carbide with variable carbon content, ranging from B13C2 to B4C are calculated from first-principles. Furthermore, the mixing thermodynamics of (B6O)1−x(B13C2)x is studied. A superatom-special quasirandom structure approach is used for modeling different atomic configurations, in which effects of configurational disorder between the carbide and suboxide structural units, as well as between boron and carbon atoms within the units, are taken into account. Elastic properties calculations demonstrate that configurational  disorder in B13C2, where a part of the C atoms in the CBC chains substitute for B atoms in the B12 icosahedra, drastically increase the Young’s and shear modulus, as compared to an atomically ordered state, B12(CBC). These calculated elastic moduli of the disordered state are in excellent agreement with experiments. Configurational disorder between boron and carbon can also explain the experimentally observed almost constant elastic moduli of boron carbide as the carbon content is changed from B4C to B13C2. The elastic moduli of the (B6O)1−x(B13C2)x system are also practically unchanged with composition if boron-carbon disorder is taken into account. By investigating the mixing thermodynamics of the alloys, in which the Gibbs free energy is determined within the mean-field approximation for the configurational entropy, we outline the pseudo-binary phase diagram of (B6O)1−x(B13C2)x. The phase diagram reveals the existence of a miscibility gap at all temperatures up to the melting point. Also, the coexistence of B6O-rich as well as ordered or disordered B13C2-rich domains in the material prepared through equilibrium routes is predicted.

##### Place, publisher, year, edition, pages
American Institute of Physics (AIP), 2016
##### National Category
Physical Sciences
##### Identifiers
urn:nbn:se:liu:diva-122425 (URN)10.1063/1.4944982 (DOI)000374527900023 ()27059576 (PubMedID)
##### Note

Funding agencies:Swedish Research Council (VR) [621-2011-4417, 330-2014-6336, 2011-42-59]; CeNano at Linkoping University; Ministry of Education and Science of the Russian Federation in the framework of Increase Competitiveness Program of NUST "MISiS" [K3-2014-049]; LiLi-

At the time for thesis presentation publication was in status: Manuscript

Available from: 2015-11-02 Created: 2015-11-02 Last updated: 2018-08-14Bibliographically approved
fulltext
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presentationsbild
• 310.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering. Max Planck Institute Eisenforsch GmbH, Germany.
Carbon-rich icosahedral boron carbides beyond B4C and their thermodynamic stabilities at high temperature and pressure from first principles2016In: PHYSICAL REVIEW B, ISSN 2469-9950, Vol. 94, no 5, article id 054104Article in journal (Refereed)

We investigate the thermodynamic stability of carbon-rich icosahedral boron carbide at different compositions, ranging from B4C to B2C, using first-principles calculations. Apart fromB4C, generally addressed in the literature, B2.5C, represented by B10C2p (C-C), where C-p and (C-C) denote a carbon atom occupying the polar site of the icosahedral cluster and a diatomic carbon chain, respectively, is predicted to be thermodynamically stable under high pressures with respect to B4C as well as pure boron and carbon phases. The thermodynamic stability of B2.5C is determined by the Gibbs free energy G as a function of pressure p and temperature T, in which the contributions from the lattice vibrations and the configurational disorder are obtained within the quasiharmonic and the mean-field approximations, respectively. The stability range of B2.5C is then illustrated through the p-T phase diagrams. Depending on the temperatures, the stability range of B2.5C is predicted to be within the range between 40 and 67 GPa. At T greater than or similar to 500 K, the icosahedral C-p atoms in B2.5C configurationally disorder at the polar sites. By investigating the properties of B2.5C, e.g., elastic constants and phonon and electronic density of states, we demonstrate that B2.5C is both mechanically and dynamically stable at zero pressure, and is an electrical semiconductor. Furthermore, based on the sketched phase diagrams, a possible route for experimental synthesis of B2.5C as well as a fingerprint for its characterization from the simulations of x-ray powder diffraction pattern are suggested.

• 311.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Max Planck Institute Eisenforsch GmbH, Germany.
First-principles prediction of stabilities and instabilities of compounds and alloys in the ternary B-As-P system2017In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 96, no 2, article id 024202Article in journal (Refereed)

We examine the thermodynamic stability of compounds and alloys in the ternary B-As-P system theoretically using first-principles calculations. We demonstrate that the icosahedral B12As2 is the only stable compound in the binary B-As system, while the zinc-blende BAs is thermodynamically unstable with respect to B12As2 and the pure arsenic phase at 0 K, and increasingly so at higher temperature, suggesting that BAs may merely exist as a metastable phase. On the contrary, in the binary B-P system, both zinc-blende BP and icosahedral B12P2 are predicted to be stable. As for the binary As-P system, As1-xPx disordered alloys are predicted at elevated temperature-for example, a disordered solid solution of up to similar to 75 at.% As in black phosphorus as well as a small solubility of similar to 1 at.% P in gray arsenic at T = 750 K, together with the presence of miscibility gaps. The calculated large solubility of As in black phosphorus explains the experimental syntheses of black-phosphorus-type As1-xPx alloys with tunable compositions, recently reported in the literature. We investigate the phase stabilities in the ternary B-As-P system and demonstrate a high tendency for a formation of alloys in the icosahedral B-12(As1-xPx)(2) structure by intermixing of As and P atoms at the diatomic chain sites. The phase diagram displays noticeable mutual solubility of the icosahedral subpnictides in each other even at room temperature as well as a closure of a pseudobinary miscibility gap around 900 K. As for pseudobinary BAs1-xPx alloys, only a tiny amount of BAs is predicted to be able to dissolve in BP to form the BAs1-xPx disordered alloys at elevated temperature. For example, less than 5% of BAs can dissolve in BP at T = 1000 K. The small solubility limit of BAs in BP is attributed to the thermodynamic instability of BAs with respect to B12As2 and As.

• 312.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering. Max Planck Institute Eisenforsch GmbH, Germany.
Thermodynamic stability and properties of boron subnitrides from first principles2017In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 95, no 6, article id 064206Article, review/survey (Refereed)

We use the first-principles approach to clarify the thermodynamic stability as a function of pressure and temperature of three different alpha-rhombohedral-boron-like boron subnitrides, with the compositions of B6N, B13N2, and B38N6, proposed in the literature. We find that, out of these subnitrides with the structural units of B-12(N-N), B-12(NBN), and [B-12(N-N)](0.33)[B-12(NBN)](0.67), respectively, only B38N6, represented by [B-12(N-N)](0.33)[B-12(NBN)](0.67), is thermodynamically stable. Beyond a pressure of about 7.5 GPa depending on the temperature, also B38N6 becomes unstable, and decomposes into cubic boron nitride and a-tetragonalboron- like boron subnitride B50N2. The thermodynamic stability of boron subnitrides and relevant competing phases is determined by the Gibbs free energy, in which the contributions from the lattice vibrations and the configurational disorder are obtained within the quasiharmonic and the mean-field approximations, respectively. We calculate lattice parameters, elastic constants, phonon and electronic density of states, and demonstrate that [B-12(N-N)](0.33)[B-12(NBN)](0.67) is bothmechanically and dynamically stable, and is an electrical semiconductor. The simulated x-ray powder-diffraction pattern as well as the calculated lattice parameters of [B-12(N-N)](0.33)[B-12(NBN)](0.67) are found to be in good agreement with those of the experimentally synthesized boron subnitrides reported in the literature, verifying that B38N6 is the stable composition of a-rhombohedral-boron-like boron subnitride.

• 313.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering. Max Planck Institute Eisenforsch GmbH, Germany.
Configurational order-disorder induced metal-nonmetal transition in B13C2 studied with first-principles superatom-special quasirandom structure method2015In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 92, no 1, article id 014202Article in journal (Refereed)

Due to a large discrepancy between theory and experiment, the electronic character of crystalline boron carbide B13C2 has been a controversial topic in the field of icosahedral boron-rich solids. We demonstrate that this discrepancy is removed when configurational disorder is accurately considered in the theoretical calculations. We find that while the ordered ground state B13C2 is metallic, the configurationally disordered B13C2, modeled with a superatom-special quasirandom structure method, goes through a metal to nonmetal transition as the degree of disorder is increased with increasing temperature. Specifically, one of the chain-end carbon atoms in the CBC chains substitutes a neighboring equatorial boron atom in a B-12 icosahedron bonded to it, giving rise to a B11Ce(BBC) unit. The atomic configuration of the substitutionally disordered B13C2 thus tends to be dominated by a mixture between B-12(CBC) and B11Ce(BBC). Due to splitting of valence states in B11Ce(BBC), the electron deficiency in B-12(CBC) is gradually compensated.

fulltext
• 314.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
First-principles study of configurational disorder in B4C using a superatom-special quasirandom structure method2014In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 90, no 2, article id 024204Article in journal (Refereed)

Configurationally disordered crystalline boron carbide, with the composition B4C, is studied using first-principles calculations. We investigate both dilute and high concentrations of carbon-boron substitutional defects. For the latter purpose, we suggest a superatoms picture of the complex structure and combine it with a special quasirandom structure approach for disorder. In this way, we model a random distribution of high concentrations of the identified low-energy defects: (1) bipolar defects and (2) rotation of icosahedral carbon among the three polar-up sites. Additionally, the substitutional disorder of the icosahedral carbon at all six polar sites, as previously discussed in the literature, is also considered. Two configurational phase transitions from the ordered to the disordered configurations are predicted to take place upon an increase in temperature using a mean-field approximation for the entropy. The first transition, at 870 K, induces substitutional disorder of the icosahedral carbon atoms among the three polar-up sites; meanwhile the second transition, at 2325 K, reveals the random substitution of the icosahedral carbon atoms at all six polar sites coexisting with bipolar defects. Already the first transition removes the monoclinic distortion existing in the ordered ground-state configuration and restore the rhombohedral system (R3m). The restoration of inversion symmetry yielding the full rhombohedral symmetry (R (3) over barm) on average, corresponding to what is reported in the literature, is achieved after the second transition. Investigating the effects of high pressure on the configurational stability of the disordered B4C phases reveals a tendency to stabilize the ordered ground-state configuration as the configurationally ordering/disordering transition temperature increases with pressure exerted on B4C. The electronic density of states, obtained from the disordered phases, indicates a sensitivity of the band gap to the degree of configurational disorder in B4C.

fulltext
• 315.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
Effects of configurational disorder on the elastic properties of icosahedral boron-rich alloys based on B6O, B13C2, and B4C, and their mixing thermodynamics2016In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 144, no 13, article id 134503Article in journal (Refereed)

The elastic properties of alloys between boron suboxide (B6O) and boron carbide (B13C2), denoted by (B6O)1−x(B13C2)x, as well as boron carbide with variable carbon content, ranging from B13C2 to B4C are calculated from first-principles. Furthermore, the mixing thermodynamics of (B6O)1−x(B13C2)x is studied. A superatom-special quasirandom structure approach is used for modeling different atomic configurations, in which effects of configurational disorder between the carbide and suboxide structural units, as well as between boron and carbon atoms within the units, are taken into account. Elastic properties calculations demonstrate that configurational  disorder in B13C2, where a part of the C atoms in the CBC chains substitute for B atoms in the B12 icosahedra, drastically increase the Young’s and shear modulus, as compared to an atomically ordered state, B12(CBC). These calculated elastic moduli of the disordered state are in excellent agreement with experiments. Configurational disorder between boron and carbon can also explain the experimentally observed almost constant elastic moduli of boron carbide as the carbon content is changed from B4C to B13C2. The elastic moduli of the (B6O)1−x(B13C2)x system are also practically unchanged with composition if boron-carbon disorder is taken into account. By investigating the mixing thermodynamics of the alloys, in which the Gibbs free energy is determined within the mean-field approximation for the configurational entropy, we outline the pseudo-binary phase diagram of (B6O)1−x(B13C2)x. The phase diagram reveals the existence of a miscibility gap at all temperatures up to the melting point. Also, the coexistence of B6O-rich as well as ordered or disordered B13C2-rich domains in the material prepared through equilibrium routes is predicted.

• 316.
Linköping University, Department of Science and Technology, Physics, Electronics and Mathematics. Linköping University, Faculty of Science & Engineering.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry. Linköping University, Faculty of Science & Engineering. Linköping University, Department of Science and Technology, Physics, Electronics and Mathematics. Linköping University, Faculty of Science & Engineering. Linköping University, Department of Science and Technology, Physics, Electronics and Mathematics. Linköping University, Faculty of Science & Engineering.
Synthesis of Mg-doped ZnO NPs via a chemical low-temperature method and investigation of the efficient photocatalytic activity for the degradation of dyes under solar light2020In: Solid State Sciences, ISSN 1293-2558, E-ISSN 1873-3085, Vol. 99, article id 106053Article in journal (Refereed)

Doped semiconductors nanostructures (NSs) have shown great interest as a potential for green and efficient photocatalysis activities. Magnesium (Mg)-doped zinc oxide (ZnO) nanoparticles (NPs) has been synthesized by a one-step chemical low temperature (60 degrees C) co-precipitation method without further calcination and their photocatalytic performance for photodegradation of Methylene blue (MB) dye under the illumination of solar light is investigated. The crystal structure of the synthesized NPs is examined by X-ray diffraction (XRD). XRD data indicates a slight shift towards higher 2 theta angle in Mg-doped samples as compared to the pure ZnO NPs which suggest the incorporation of Mg2+ into ZnO crystal lattice. X-ray photoelectron spectroscopy (XPS), UV-Vis spectrophotometer and cathodoluminescence (CL) spectroscopy, were used to study electronics, and optical properties, respectively. The XPS analysis confirms the substitution of the Zn2+ by the Mg2+ into the ZnO crystal lattice in agreement with the XRD data. The photocatalytic activities showed a significant enhancement of the Mg-doped ZnO NPs in comparison with pure ZnO NPs. Hole/radical scavengers were used to reveal the mechanism of the photodegradation. It was found that the addition of the Mg to the ZnO lattices increases the absorption of the hydroxyl ions at the surface of the NPs and hence acts as a trap site leading to decrease the electron-hole pair and consequently enhancing the photodegradation.

• 317.
Linköping University, Department of Science and Technology. Linköping University, Faculty of Science & Engineering.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering. Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, Faculty of Science & Engineering. Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, Faculty of Science & Engineering.
Synthesis of ZnO nanoparticles by co-precipitation method for solar driven photodegradation of Congo red dye at different pH2018In: PHOTONICS AND NANOSTRUCTURES-FUNDAMENTALS AND APPLICATIONS, ISSN 1569-4410, Vol. 32, p. 11-18Article in journal (Refereed)

• 318.
Linköping University, Department of Science and Technology. Linköping University, Faculty of Science & Engineering.
Low-temperature growth of polyethylene glycol-doped BiZn2VO6 nanocompounds with enhanced photoelectrochemical properties2017In: Journal of Materials Chemistry A, ISSN 2050-7488, Vol. 5, no 3, p. 1112-1119Article in journal (Refereed)

We demonstrate scalable, low-cost and low-temperature (<100 °C) aqueous chemical growth of bismuth–zinc vanadate (BiZn2VO6) nanocompounds by BiVO4 growth on ZnO nanobelts (NBs). The nanocompounds were further doped with polyethylene glycol (PEG) to tune the electronic structure of the materials, as a means to lower the charge carrier recombination rate. The chemical composition, morphology, and detailed nanostructure of the BiZn2VO6 nanocompounds were characterized. They exhibit rice-like morphology, are highly dense on the substrate and possess a good crystalline quality. Photoelectrochemical characterization in 0.1 M lithium perchlorate in carbonate propylene shows that BiZn2VO6 nanocompounds are highly suitable as anodes for solar-driven photoelectrochemical applications, providing significantly better performance than with only ZnO NBs. This performance could be attributed to the heterogeneous catalysis effect at nanocompound and ZnO NB interfaces, which have enhanced the electron transfer process on the electrode surface. Furthermore, the charge collection efficiency could be significantly improved through PEG doping of nanocompounds. The photocurrent density of PEG-doped BiZn2VO6 nanocompounds reached values of 2 mA cm−2 at 1.23 V (vs. Ag/AgCl), over 60% larger than that of undoped BiZn2VO6 nanocompounds. Photoluminescence emission experiments confirmed that PEG plays a crucial role in lowering the charge carrier recombination rate. The presented BiZn2VO6 nanocompounds are shown to provide highly competitive performance compared with other state-of-the art photoelectrodes.

fulltext
• 319. Elisabeth, Abom A.
Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Applied Physics . Center for Microanalysis of Materials, Seitz Materials Research Laboratory, University of Illinois, Urbana, IL 618 01, United States.
Properties of combined TiN and Pt thin films applied to gas sensing2002In: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films, ISSN 0734-2101, E-ISSN 1520-8559, Vol. 20, no 3, p. 667-673Article in journal (Refereed)

The effect of Pt in the proximity of TiN with respect to the oxidation behavior was addressed. TiN was grown at two different temperatures that are known to produce films with varying porosity. Pt was used as the catalytic metal and either deposited on top of the TiN film grown at 400°C or co-sputtered in a reactive atmosphere of Ar and N2 at the two different deposition temperatures. The films were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), x-ray diffraction, Auger electron spectroscopy (AES), and x-ray photoemission spectroscopy (XPS), and the gas response of the sensor to hydrogen, ammonia, propene, and acetaldehyde was measured. Aging studies were also carried out for a period of one month. Overall, significant results were obtained.

• 320.
Linköping University, Department of Physics, Chemistry and Biology, Nanoscale engineering. Linköping University, Faculty of Science & Engineering.
Linköping University, Department of Physics, Chemistry and Biology, Nanoscale engineering. Linköping University, Faculty of Science & Engineering. Linköping University, Department of Physics, Chemistry and Biology, Nanoscale engineering. Linköping University, Faculty of Science & Engineering. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering. Linköping University, Department of Physics, Chemistry and Biology, Plasma and Coating Physics. Linköping University, Faculty of Science & Engineering. Linköping University, Department of Physics, Chemistry and Biology, Nanoscale engineering. Linköping University, Faculty of Science & Engineering.
Structure formation in Ag-X (X = Au, Cu) alloys synthesized far-from-equilibrium2018In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 123, no 16Article in journal (Refereed)

We employ sub-monolayer, pulsed Ag and Au vapor fluxes, along with deterministic growth simulations, and nanoscale probes to study structure formation in miscible Ag-Au films synthesized under far-from-equilibrium conditions. Our results show that nanoscale atomic arrangement is primarily determined by roughness build up at the film growth front, whereby larger roughness leads to increased intermixing between Ag and Au. These findings suggest a different structure formation pathway as compared to the immiscible Ag-Cu system for which the present study, in combination with previously published data, reveals that no significant roughness is developed, and the local atomic structure is predominantly determined by the tendency of Ag and Cu to phase-separate.

fulltext
• 321.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
MAX phase thin films: unique multifunctional ceramics with the elements Ti, Si, Ge, Sn, and C2006Doctoral thesis, comprehensive summary (Other academic)

Mn+1AXn phases are ternary carbides or nitrides (X) consisting of an early transition metal (M), and (A)- group element (group III-V). They combine ceramic and metallic properties with high oxidation and thermal shock resistance as well as low resistivity. Depending on stoichiometry, they can be classified as 211 (n=1), 312 (n=2), and 413 (n=3) phases. The main purpose of this Thesis is to present the synthesis by epitaxial growth of Tin+1ACn (A: Si, Ge, Sn; n=1-3) thin solid films and to report on the material’s intrinsic mechanical and electrical properties. DC magnetron sputtering of MAX-phase carbides from three individual elemental targets is presented as an original and successful deposition method. The emphasis is on the archetypical Ti3SiC2, but I also demonstrate growth of a wide range of other single-crystal Tin+1ACn thin films, including Ti2GeC, Ti3GeC2, Ti2SnC, previously available only in bulk form, as well as completely new phases of Ti4SiC3, Ti4GeC3, and Ti3SnC2, together with some intergrown 523 (211+312) and 725 (312+413) structures.

A combination of x-ray diffraction (XRD), transmission electron micrcoscopy (TEM) analysis, x-ray photoelectron spectroscopy, elastic recoil detection analysis, and Rutherford backscattering spectrometry of the films reveal single-phase and epitaxial growth of Tin+1SiCn(0001) (n = 2, 3) and Ti2GeC MAX phases at substrate temperatures (TS) above 700 to 1000 °C. For TS = 500 – 700 °C, Si is accommodated at twin boundaries between TiC(111) planes. Depositions at TS = RT – 350 °C yield nc-TiC/SiC nanocomposite films or TiC growth with substitutionally incorporated Si due to kinetic constraints. Vacuum-annealing with in situ XRD measurements of the films between 800 – 1400 °C revealed a thermal stability of up to ~1000 °C. A MAX-phase decomposition model is presented within this Thesis. It starts by Si out-diffusion and evaporation from the surface between ~1000 – 1100 °C and is accompanied by any O uptake and SiO evaporation. Subsequently, the free Ti3C2 slabs relax and undergo detwinning. The decomposition process is ended by TiC0.67 formation by C redistribution and recrystallization with void formation.

The mechanical response to deformation was tested on Ti3SiC2(0001) films using nanoindentation. Small applied normal forces yielding a minimum on plastic deformation reveal hardness values of up to 24 GPa, which decrease with larger indentation depths. Young’s moduli between 320 and 343 GPa were measured. Atomic force microscopy (AFM) surface imaging and Focused Ion Beam cross-sectional TEM studies confirm that mechanical deformation in this ductile ceramic takes place by kink formation and delamination along basal planes, due to edge dislocation pile-ups forming the kink boundaries resulting in local deformation-energy dissipation. Friction measurements yield a friction coefficient (μ) of 0.1 for normal loads of FN = 100-200 μN. μ increases to 0.8 with increased FN up to 0.24 N, as delamination and kinking are introduced accompanied by third-body abrasion as shown by scanning electron microscopy. By comparing electrical resistivity values obtained by four-point probe measurements, it is found that all studied MAX-phase thin film systems exhibit good conduction properties.

1. Growth of Ti3SiC2 thin films by elemental target magnetron sputtering
Open this publication in new window or tab >>Growth of Ti3SiC2 thin films by elemental target magnetron sputtering
2004 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 96, no 9, p. 4817-4826Article in journal (Refereed) Published
##### Abstract [en]

Epitaxial Ti3SiC2(0001) thin films have been deposited by dc magnetron sputtering from three elemental targets of Ti, C, and Si onto MgO(111) and Al2O3(0001) substrates at temperatures of 800–900 °C. This process allows composition control to synthesize Mn+1AXn (MAX) phases (M: early transition metal; A: A-group element; X: C and∕or N; n=1–3) including Ti4SiC3. Depositions on MgO(100) substrates yielding the Ti–Si–C MAX phases with (105), as the preferred orientation. Samples grown at different substrate temperatures, studied by means of transmission electron microscopy and x-ray diffraction investigations, revealed the constraints of Ti3SiC2 nucleation due to kinetic limitations at substrate temperatures below 700 °C. Instead, there is a competitive TiCx growth with Si segregation to form twin boundaries or Si substitutional incorporation in TiCx. Physical properties of the as-deposited single-crystal Ti3SiC2 films were determined. A low resistivity of 25 μΩ cm was measured. The Young’s modulus, ascertained by nanoindentation, yielded a value of 343–370 GPa. For the mechanical deformation response of the material, probing with cube corner and Berkovich indenters showed an initial high hardness of almost 30 GPa. With increased maximum indentation loads, the hardness was observed to decrease toward bulk values as the characteristic kink formation sets in with dislocation ordering and delamination at basal planes.

##### National Category
Natural Sciences
##### Identifiers
urn:nbn:se:liu:diva-29682 (URN)10.1063/1.1790571 (DOI)15069 (Local ID)15069 (Archive number)15069 (OAI)
Available from: 2009-10-09 Created: 2009-10-09 Last updated: 2017-12-13
2. Mn+1AXn phases in the Ti-Si-C system studied by thin-film synthesis and ab initio calculations
Open this publication in new window or tab >>Mn+1AXn phases in the Ti-Si-C system studied by thin-film synthesis and ab initio calculations
2004 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 70, no 16, p. 165401-Article in journal (Refereed) Published
##### Abstract [en]

Thin films of Mn+1AXn layered compounds in the Ti-Si-C system were deposited on MgO(111) and Al2O3(0001) substrates held at 900°C using dc magnetron sputtering from elemental targets of Ti, Si, and C. We report on single-crystal and epitaxial deposition of Ti3SiC2 (the previously reported MAX phase in the Ti-Si-C system), a previously unknown MAX phase Ti4SiC3 and another type of structure having the stoichiometry of Ti5Si2C3 and Ti7Si2C5. The latter two structures can be viewed as an intergrowth of 2 and 3 or 3 and 4 M layers between each A layer. In addition, epitaxial films of Ti5Si3Cx were deposited and Ti5Si4 is also observed. First-principles calculations, based on density functional theory (DFT) of Tin+1SiCn for n=1,2,3,4 and the observed intergrown Ti5Si2C3 and Ti7Si2C5 structures show that the calculated difference in cohesive energy between the MAX phases reported here and competing phases (TiC, Ti3SiC2, TiSi2, and Ti5Si3) are very small. This suggests that the observed Ti5Si2C3 and Ti7Si2C5 structures at least should be considered as metastable phases. The calculations show that the energy required for insertion of a Si layer in the TiC matrix is independent of how close the Si layers are stacked. Hardness and electrical properties can be related to the number of Si layers per Ti layer. This opens up for designed thin film structures the possibility to tune properties.

##### National Category
Natural Sciences
##### Identifiers
urn:nbn:se:liu:diva-29680 (URN)10.1103/PhysRevB.70.165401 (DOI)15067 (Local ID)15067 (Archive number)15067 (OAI)
Available from: 2009-10-09 Created: 2009-10-09 Last updated: 2017-12-13
3. Kink formation around indents in laminated Ti3SiC2 thin films studied in the nanoscale
Open this publication in new window or tab >>Kink formation around indents in laminated Ti3SiC2 thin films studied in the nanoscale
2003 (English)In: Scripta Materialia, ISSN 1359-6462, E-ISSN 1872-8456, Vol. 49, no 2, p. 155-160Article in journal (Refereed) Published
##### Abstract [en]

The deformation mechanisms in ductile Ti3SiC2(0 0 0 1) single-crystal films have been analysed by nanoindentation and cross-sectional transmission electron microscopy. Permanent deformation includes formation of kink bands, as the nanolaminated material buckles out at the perimeter of the contact area, and delamination cracks. Evidence is presented for incipient kink-band formation.

##### Keywords
Carbides, Nanoindentation, Nanolaminated MAX phases, Thin films, Transmission electron microscopy
##### National Category
Engineering and Technology
##### Identifiers
urn:nbn:se:liu:diva-46574 (URN)10.1016/S1359-6462(03)00214-8 (DOI)
Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2017-12-13
4. Thermal stability of Ti3SiC2 thin films
Open this publication in new window or tab >>Thermal stability of Ti3SiC2 thin films
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
5. Micro and macroscale tribological behavior of epitaxial Ti3SiC2 thin films
Open this publication in new window or tab >>Micro and macroscale tribological behavior of epitaxial Ti3SiC2 thin films
2008 (English)In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 264, no 11-12, p. 914-919Article in journal (Refereed) Published
##### Abstract [en]

Ti3SiC2(0 0 0 1) thin films prepared by magnetron sputtering were investigated for their response to tribomechanical strain induced during ball-on-disk experiments with 6 mm alumina balls and scratch tests with a 1 μm cono-spherical diamond tip. Normal loads of 100 μN to 0.24 N were applied resulting in a friction coefficient of 0.1 for the low loads. With higher applied normal loads, the friction coefficient increased up to 0.8. Analysis of the wear tracks using atomic force microscopy, scanning electron microscopy, and Raman spectroscopy revealed excessive debris resulting in third-body abrasion and fast wear. The formation of the debris can be explained by the generation of subsurface delamination cracks on basal planes. Subsequent kink formation obstructs the ball movement which results in the removal of the kinked film parts.

##### Place, publisher, year, edition, pages
Amsterdam, Netherlands: Elsevier, 2008
##### National Category
Natural Sciences
##### Identifiers
urn:nbn:se:liu:diva-39728 (URN)10.1016/j.wear.2007.06.013 (DOI)000254766900002 ()50916 (Local ID)50916 (Archive number)50916 (OAI)
Available from: 2009-10-10 Created: 2009-10-10 Last updated: 2017-12-13Bibliographically approved
6. Growth and characterization of MAX-phase thin films
Open this publication in new window or tab >>Growth and characterization of MAX-phase thin films
2005 (English)In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 193, no 1-3, p. 6-10Article in journal (Refereed) Published
##### Abstract [en]

We report that magnetron sputtering can be applied to synthesize MAX-phase films of several systems including Ti–Si–C, Ti–Ge–C, Ti–Al–C, and Ti–Al–N. In particular, epitaxial films of the known phases Ti3SiC2, Ti3GeC2, Ti2GeC, Ti3AlC2, Ti2AlC, and Ti2AlN as well as the newly discovered thin film phases Ti4SiC3, Ti4GeC3 and intergrown structures can be deposited at 900–1000 °C on Al2O3(0001) and MgO(111) pre-seeded with TiC or Ti(Al)N. From XTEM and AFM we suggest a growth and nucleation model where MAX-phase nucleation is initiated at surface steps or facets on the seed layer and followed by lateral growth. Differences between the growth behavior of the systems with respect to phase distribution and phase stabilities are discussed. Characterization of mechanical properties for Tin+1Si–Cn films with nanoindentation show decreased hardness from about 25 to 15 GPa upon penetration of the basal planes with characteristic large plastic deformation with pile up dependent on the choice of MAX material. This is explained by cohesive delamination of the basal planes and kink band formation, in agreement with the observations made for bulk material. Measurements of the electrical resistivity for Ti–Si–C and Ti–Al–N films with four-point probe technique show values of 30 and 39 μΩ cm, respectively, comparable to bulk materials.

##### National Category
Natural Sciences
##### Identifiers
urn:nbn:se:liu:diva-24507 (URN)10.1016/j.surfcoat.2004.08.174 (DOI)6636 (Local ID)6636 (Archive number)6636 (OAI)
Available from: 2009-10-07 Created: 2009-10-07 Last updated: 2017-12-13
7. 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
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
• 322.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
Electrical resistivity of Tin+1ACn (A = Si, Ge, Sn, n = 1–3) thin films2007In: Journal of Materials Research, ISSN 0884-2914, E-ISSN 2044-5326, Vol. 22, no 8, p. 2279-2287Article in journal (Refereed)

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.

• 323.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
Department of Physical Metallurgy and Materials Testing, University of Leoben, Austria. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
Micro and macroscale tribological behavior of epitaxial Ti3SiC2 thin films2008In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 264, no 11-12, p. 914-919Article in journal (Refereed)

Ti3SiC2(0 0 0 1) thin films prepared by magnetron sputtering were investigated for their response to tribomechanical strain induced during ball-on-disk experiments with 6 mm alumina balls and scratch tests with a 1 μm cono-spherical diamond tip. Normal loads of 100 μN to 0.24 N were applied resulting in a friction coefficient of 0.1 for the low loads. With higher applied normal loads, the friction coefficient increased up to 0.8. Analysis of the wear tracks using atomic force microscopy, scanning electron microscopy, and Raman spectroscopy revealed excessive debris resulting in third-body abrasion and fast wear. The formation of the debris can be explained by the generation of subsurface delamination cracks on basal planes. Subsequent kink formation obstructs the ball movement which results in the removal of the kinked film parts.

• 324.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology. Department of Material Chemistry, Uppsala University, The Ångström Laboratory, Uppsala, Sweden . Department of Material Chemistry, Uppsala University, The Ångström Laboratory, Uppsala, Sweden . CEIT (Centro de Estudios e Investigaciones Técnicas e Gipuzkoa), Spain . Research Institute for Technical Physics and Materials Science, Hungary .
Growth of Ti3SiC2 thin films by elemental target magnetron sputtering2004In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 96, no 9, p. 4817-4826Article in journal (Refereed)

Epitaxial Ti3SiC2(0001) thin films have been deposited by dc magnetron sputtering from three elemental targets of Ti, C, and Si onto MgO(111) and Al2O3(0001) substrates at temperatures of 800–900 °C. This process allows composition control to synthesize Mn+1AXn (MAX) phases (M: early transition metal; A: A-group element; X: C and∕or N; n=1–3) including Ti4SiC3. Depositions on MgO(100) substrates yielding the Ti–Si–C MAX phases with (105), as the preferred orientation. Samples grown at different substrate temperatures, studied by means of transmission electron microscopy and x-ray diffraction investigations, revealed the constraints of Ti3SiC2 nucleation due to kinetic limitations at substrate temperatures below 700 °C. Instead, there is a competitive TiCx growth with Si segregation to form twin boundaries or Si substitutional incorporation in TiCx. Physical properties of the as-deposited single-crystal Ti3SiC2 films were determined. A low resistivity of 25 μΩ cm was measured. The Young’s modulus, ascertained by nanoindentation, yielded a value of 343–370 GPa. For the mechanical deformation response of the material, probing with cube corner and Berkovich indenters showed an initial high hardness of almost 30 GPa. With increased maximum indentation loads, the hardness was observed to decrease toward bulk values as the characteristic kink formation sets in with dislocation ordering and delamination at basal planes.

• 325.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
Materials Chemistry, RWTH Aachen University, Germany. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology. Department of Materials Chemistry, Uppsala University, Uppsala, Sweden. Department of Materials Chemistry, Uppsala University, Uppsala, Sweden. Materials Chemistry, RWTH Aachen University, Germany. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
Thermal stability of Ti3SiC2 thin films2007In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 55, no 4, p. 1479-1488Article in journal (Refereed)

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.

• 326. Buy this publication >>
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
Atom Probe Tomography of TiSiN Thin Films2015Licentiate thesis, comprehensive summary (Other academic)

This thesis concerns the wear resistant coating TiSiN and the development of the analysis technique atom probe tomography (APT) applied to this materials system. The technique delivers compositional information through time-of-flight mass spectrometry, with sub-nanometer precision in 3D for a small volume of the sample. It is thus a powerful technique for imaging the local distribution of elements in micro and nanostructures. To gain the full benefits of the technique for the materials system in question, I have developed a method that combines APT with isotopic substitution, here demonstrated by substitution of natN with 15N. This alters the time-of-flight of ions with of one or more N and will thereby enable the differentiation of the otherwise inseparable isotopes 14N and 28Si. Signs of small-scale fluctuations in the data led the development of an algorithm needed to properly visualize these fluctuations. A method to identify the best sampling parameter for visualization of small-scale compositional fluctuations was added to an algorithm originally designed to find the best sampling parameters for measuring and visualizing strong compositional variations. With the identified sampling parameters, the nano-scale compositional fluctuations of Si in the metal/metalloid sub-lattice could be visualized. The existence and size of these fluctuations were corroborated by radial distribution functions, a technique independent of the previously determined sampling parameter. The radial distribution function algorithm was also developed further to ease in the interpretation. The number of curves could thereby be reduced by showing elements, rather than single and molecular ions (of which there were several different kinds). The improvement of the algorithm also allowed interpretation of signs regarding the stoichiometry of SiNy. With a combination of analytical transmission electron microscopy and APT we show Si segregation on the nanometer scale in arc-deposited Ti0.92Si0.0815N and Ti0.81Si0.1915N thin films. APT composition maps and proximity histograms generated from Ti-rich domains show that the TiN contain at least ~2 at. % Si for Ti0.92Si0.08N and ~5 at. % Si for Ti0.81Si0.19N, thus confirming the formation of solid solutions. The formation of relatively pure SiNy domains in the Ti0.81Si0.19N films is tied to pockets between microstructured, columnar features in the film. Finer SiNy enrichments seen in APT possibly correspond to tissue layers around TiN crystallites, thus effectively hindering growth of TiN crystallites, causing TiN renucleation and thus explaining the featherlike nanostructure within the columns of these films.

1. Resolving Mass Spectral Overlaps in Atom Probe Tomography by Isotopic Substitutions: Case of TiSi15N
Open this publication in new window or tab >>Resolving Mass Spectral Overlaps in Atom Probe Tomography by Isotopic Substitutions: Case of TiSi15N
2018 (English)In: Ultramicroscopy, ISSN 0304-3991, E-ISSN 1879-2723, Vol. 184, p. 51-60Article in journal (Refereed) Published
##### Abstract [en]

Mass spectral overlaps in atom probe tomography (APT) analyses of complex compounds typically limit the identification of elements and microstructural analysis of a material. This study concerns the TiSiN system, chosen because of severe mass-to-charge-state ratio overlaps of the 14N+ and 28Si2+ peaks as well as the 14N$\tiny\frac{+}{2}$ and 28Si2+ peaks. By substituting 14N with 15N, mass spectrum peaks generated by ions composed of one or more N atoms will be shifted toward higher mass-to-charge-state ratios, thereby enabling the separation of N from the predominant Si isotope. We thus resolve thermodynamically driven Si segregation on the nanometer scale in cubic phase Ti1-xSix15N thin films for Si contents 0.08 ≤ x ≤ 0.19 by APT, as corroborated by transmission electron microscopy. The APT analysis yields a composition determination that is in good agreement with energy dispersive X-ray spectroscopy and elastic recoil detection analyses. Additionally, a method for determining good voxel sizes for visualizing small-scale fluctuations is presented and demonstrated for the TiSiN system.

##### Place, publisher, year, edition, pages
Elsevier, 2018
##### National Category
Physical Sciences
##### Identifiers
urn:nbn:se:liu:diva-122721 (URN)10.1016/j.ultramic.2017.08.004 (DOI)000415650200007 ()28850866 (PubMedID)
##### Note

Funding Agencies:VINN Excellence Center on Functional Nanoscale Materials (FunMat) [2007-00863]; Swedish Research Council (VR) project [2013-4018]; Swedish Government Strategic Research Area Grant in Materials Science (Grant SFO Mat-LiU) on Advanced Functional Materials [2009-00971]; Knut and Alice Wallenberg Project Isotope

Available from: 2015-11-18 Created: 2015-11-18 Last updated: 2019-08-01Bibliographically approved
2. Solid Solution and Segregation Effects in Arc-Deposited Ti1-xSixN Thin Films Resolved on the nanometer scale by 15N Isotopic Substitution in AtomP robe Tomography
Open this publication in new window or tab >>Solid Solution and Segregation Effects in Arc-Deposited Ti1-xSixN Thin Films Resolved on the nanometer scale by 15N Isotopic Substitution in AtomP robe Tomography
##### Abstract [en]

Nanostructured TiSiN is an important material in wear--‐resistant coatings for extending the lifetime of cutting tools. Yet, the understanding regarding the structure, phase composition, and bonding on the detailed nanometer scale, which determines the properties of TiSiN, is lacking. This limits our understanding of the growth phenomena and eventually a larger exploitation of the material. By substituting natN2 with 15N2 during reactive arc deposition of TiSiN thin films, atom probe tomography (APT) gives elemental sensitivity and sub-nanometer resolution, a finer scale than what can be obtained by commonly employed energy dispersive electron spectroscopy in scanning transmission electron microscopy. Using a combination of analytical transmission electron microscopy and APT we show that arc-deposited Ti0.92Si0.0815N and Ti0.81Si0.1915N exhibit Si segregation on the nanometer scale in the alloy films. APT composition maps and proximity histograms from domains with higher than average Ti content show that the TiN domains contain at least ~2 at. % Si for Ti0.92Si0.08N and ~5 at. % Si for Ti0.81Si0.19N, thus confirming the formation of solid solutions. The formation of relatively pure SiNy domains in the Ti0.81Si0.19N films is tied to pockets between microstructured, columnar features in the film. Finer SiNy enrichments seen in APT possibly correspond to tissue layers around TiN crystallites, thus effectively hindering growth of TiN crystallites, causing TiN renucleation and thus explaining the featherlike nanostructure within the columns of these films. For the stoichiometry of the TiN phase, we establish a global under stoichiometry, in accordance with the tendency for SiNy films to have tetrahedral bonding coordination towards a nominal Si3N4 composition.

##### National Category
Physical Sciences
##### Identifiers
urn:nbn:se:liu:diva-122722 (URN)
Available from: 2015-11-18 Created: 2015-11-18 Last updated: 2018-01-03Bibliographically approved
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• 327.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
Sandvik Coromant, Stockholm, Sweden. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering. Department of Applied Physics, Chalmers University of Technology, Göteborg, Sweden. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
Resolving Mass Spectral Overlaps in Atom Probe Tomography by Isotopic Substitutions: Case of TiSi15N2018In: Ultramicroscopy, ISSN 0304-3991, E-ISSN 1879-2723, Vol. 184, p. 51-60Article in journal (Refereed)

Mass spectral overlaps in atom probe tomography (APT) analyses of complex compounds typically limit the identification of elements and microstructural analysis of a material. This study concerns the TiSiN system, chosen because of severe mass-to-charge-state ratio overlaps of the 14N+ and 28Si2+ peaks as well as the 14N$\tiny\frac{+}{2}$ and 28Si2+ peaks. By substituting 14N with 15N, mass spectrum peaks generated by ions composed of one or more N atoms will be shifted toward higher mass-to-charge-state ratios, thereby enabling the separation of N from the predominant Si isotope. We thus resolve thermodynamically driven Si segregation on the nanometer scale in cubic phase Ti1-xSix15N thin films for Si contents 0.08 ≤ x ≤ 0.19 by APT, as corroborated by transmission electron microscopy. The APT analysis yields a composition determination that is in good agreement with energy dispersive X-ray spectroscopy and elastic recoil detection analyses. Additionally, a method for determining good voxel sizes for visualizing small-scale fluctuations is presented and demonstrated for the TiSiN system.

fulltext
• 328. Buy this publication >>
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
Atom Probe Tomography of Hard Nitride and Boride Thin Films2019Doctoral thesis, comprehensive summary (Other academic)

Hard ceramic thin films, including TiSiN, ZrAlN, ZrB2, and ZrTaB2, with applications for wear-resistant coatings, have been studied using atom probe tomography and correlated with several other analytical techniques, including X-ray diffraction, electron microscopy, and elastic recoil detection analysis. Outstanding obstacles for quantitative atom probe tomography of ceramic thin films have been surmounted.

Mass spectral overlaps in TiSiN, which make 28Si indistinguishable from 14N, was resolved by isotopic substitution with 15N, and the nanostructural distribution of elements was thus revealed in 3-D, which enabled the identification of additional structural elements within the nanostructured Ti0.81Si0.1915N film. Improvements to the growth model of TiSiN by cathodic arc deposition was suggested.

A self-organized nanolabyrinthine structure of ZrAlN, consisting of standing lamellae of fcc-ZrN and hexagonal AlN, was investigated with focus on the onset and limits of the self-organization. The local crystallographic orientational relationships were (001)ZrN || (0001)AlN and <110>ZrN || <2-1-10>AlN. Close to the MgO substrates, a smooth transition region was formed, going from segregated and disordered to the self-organized nanolabyrinthine structure. With increased growth temperature, coarse (111)-oriented ZrN grains occasionally precipitated and locally replaced the nanolabyrinthine structure. Significant local magnification effects rendered the Zr and N signals unusable, thereby inhibiting quantitative compositional analysis of the constituent phases, but the nanostructure was resolved using the Al signal.

Ceramic materials are often affected by correlated evaporation, which can result in losses due to the detector dead-time/space. A compositional correction procedure was suggested, tested against an established procedure, and applied to ZrB2. The correction was found to be less dependent on the isotope abundances and background correction compared to the established procedure. While losses due to dead-time/space occur in atom probe tomography of all materials, the correlative field evaporation behavior of ceramics significantly increases the compositional error. The evaporation behavior of ZrB2 was therefore thoroughly investigated and evidence of preferential retention, correlated evaporation, and inhomogeneous field distributions at a low-index pole was presented. The high mass resolution, relatively low multiple events percentage, and quality of the co-evaporation correlation data was partly attributed to the crystal structure and film orientation, which promoted a layer-by-layer field evaporation.

The evaporation behavior of the related ZrTaB2 films was found to be similar to that of ZrB2. The distribution of Ta in relation to Zr was investigated, showing that the column boundaries were both metal- and Ta-rich, and that there was a significant amount of Ta in solid solution within the columns.

In addition, an instrumental artefact previously not described in atom probe tomography was found in several of the materials investigated in this thesis. The artefact consists of high-density lines along the analysis direction, which cannot be related to pole artefacts. The detection system of the atom probe was identified as the cause, because the artefact patterns on detector histograms coincided with the structure of the microchannel plate. Inconsistencies in the internal boundaries of the microchannel plate multifibers from the manufacturing process can influence the signal to the detector and locally increase the detection efficiency in a pattern characteristic to the microchannel plate in question.

Altogether, this thesis shows that atom probe tomography of nitride and boride thin films is burdened by several artefacts and distortions, but that relevant material outcomes can nevertheless be achieved by informed choices of film isotopic constituents and analytical parameters, exclusion of heavily distorted regions (such as pole artefacts), and the use of compositional correction procedures when applicable.

1. Resolving Mass Spectral Overlaps in Atom Probe Tomography by Isotopic Substitutions: Case of TiSi15N
Open this publication in new window or tab >>Resolving Mass Spectral Overlaps in Atom Probe Tomography by Isotopic Substitutions: Case of TiSi15N
2018 (English)In: Ultramicroscopy, ISSN 0304-3991, E-ISSN 1879-2723, Vol. 184, p. 51-60Article in journal (Refereed) Published
##### Abstract [en]

Mass spectral overlaps in atom probe tomography (APT) analyses of complex compounds typically limit the identification of elements and microstructural analysis of a material. This study concerns the TiSiN system, chosen because of severe mass-to-charge-state ratio overlaps of the 14N+ and 28Si2+ peaks as well as the 14N$\tiny\frac{+}{2}$ and 28Si2+ peaks. By substituting 14N with 15N, mass spectrum peaks generated by ions composed of one or more N atoms will be shifted toward higher mass-to-charge-state ratios, thereby enabling the separation of N from the predominant Si isotope. We thus resolve thermodynamically driven Si segregation on the nanometer scale in cubic phase Ti1-xSix15N thin films for Si contents 0.08 ≤ x ≤ 0.19 by APT, as corroborated by transmission electron microscopy. The APT analysis yields a composition determination that is in good agreement with energy dispersive X-ray spectroscopy and elastic recoil detection analyses. Additionally, a method for determining good voxel sizes for visualizing small-scale fluctuations is presented and demonstrated for the TiSiN system.

##### Place, publisher, year, edition, pages
Elsevier, 2018
##### National Category
Physical Sciences
##### Identifiers
urn:nbn:se:liu:diva-122721 (URN)10.1016/j.ultramic.2017.08.004 (DOI)000415650200007 ()28850866 (PubMedID)
##### Note

Funding Agencies:VINN Excellence Center on Functional Nanoscale Materials (FunMat) [2007-00863]; Swedish Research Council (VR) project [2013-4018]; Swedish Government Strategic Research Area Grant in Materials Science (Grant SFO Mat-LiU) on Advanced Functional Materials [2009-00971]; Knut and Alice Wallenberg Project Isotope

Available from: 2015-11-18 Created: 2015-11-18 Last updated: 2019-08-01Bibliographically approved
2. Self-organized Nanostructuring in Zr0.64Al0.36N Thin Films Studied by Atom Probe Tomography
Open this publication in new window or tab >>Self-organized Nanostructuring in Zr0.64Al0.36N Thin Films Studied by Atom Probe Tomography
2016 (English)In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, p. 233-238Article in journal (Refereed) Published
##### Abstract [en]

We have applied atom probe tomography (apt) to analyze the selforganized structure of wear-resistant Zr0.64Al0.36N thin films grown by magnetron sputtering. Transmission electron microscopy shows that these films grow as a two-dimensional nanocomposite, consisting of interleaved lamellae in a labyrinthine structure, with a size scale of ∼ 5 nm. The structure was recovered in the Al apt signal, while the Zr and N data lacked structural information due to severe local magnification effects. The onset of the self-organized growth was observed to occur locally by nucleation, at 5-8 nm from the MgO substrate, after increasing Zr-Al compositional fluctuations. Finally, it was observed that the self-organized growth mode could be perturbed by renucleation of ZrN.

##### Place, publisher, year, edition, pages
Elsevier, 2016
##### National Category
Natural Sciences
##### Identifiers
urn:nbn:se:liu:diva-84258 (URN)10.1016/j.tsf.2016.07.034 (DOI)000381939700037 ()
##### Note

Funding agencies: VINN Excellence Center on Functional Nanoscale Materials; Swedish Research Council; Swedish Government Strategic Faculty Grant in Materials Science (SFO Mat-LiU) at Linkoping University; Swedish Governmental Agency for Innovation Systems (Vinnova) [2011-0

Vid tiden för disputationen förelåg publikationen som manuskript

Available from: 2012-10-03 Created: 2012-10-03 Last updated: 2020-03-19Bibliographically approved
3. Strategy for simultaneously increasing both hardness and toughness in ZrB2-rich Zr1-xTaxBy thin films
Open this publication in new window or tab >>Strategy for simultaneously increasing both hardness and toughness in ZrB2-rich Zr1-xTaxBy thin films
2019 (English)In: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films, ISSN 0734-2101, E-ISSN 1520-8559, Vol. 37, no 3, article id 031506Article in journal (Refereed) Published
##### Abstract [en]

Refractory transition-metal diborides exhibit inherent hardness. However, this is not always sufficient to prevent failure in applications involving high mechanical and thermal stress, since hardness is typically accompanied by brittleness leading to crack formation and propagation. Toughness, the combination of hardness and ductility, is required to avoid brittle fracture. Here, the authors demonstrate a strategy for simultaneously enhancing both hardness and ductility of ZrB2-rich thin films grown in pure Ar on Al2O3(0001) and Si(001) substrates at 475 degrees C. ZrB2.4 layers are deposited by dc magnetron sputtering (DCMS) from a ZrB2 target, while Zr1-xTaxBy alloy films are grown, thus varying the B/metal ratio as a function of x, by adding pulsed high-power impulse magnetron sputtering (HiPIMS) from a Ta target to deposit Zr1-xTaxBy alloy films using hybrid Ta-HiPIMS/ZrB2-DCMS sputtering with a substrate bias synchronized to the metal-rich portion of each HiPIMS pulse. The average power P-Ta (and pulse frequency) applied to the HiPIMS Ta target is varied from 0 to 1800W (0 to 300 Hz) in increments of 600W (100 Hz). The resulting boron-to-metal ratio, y = B/(Zr+Ta), in as-deposited Zr1-xTaxBy films decreases from 2.4 to 1.5 as P-Ta is increased from 0 to 1800W, while x increases from 0 to 0.3. A combination of x-ray diffraction (XRD), glancing-angle XRD, transmission electron microscopy (TEM), analytical Z-contrast scanning TEM, electron energy-loss spectroscopy, energy-dispersive x-ray spectroscopy, x-ray photoelectron spectroscopy, and atom-probe tomography reveals that all films have the hexagonal AlB2 crystal structure with a columnar nanostructure, in which the column boundaries of layers with 0 amp;lt;= x amp;lt; 0.2 are B-rich, whereas those with x amp;gt;= 0.2 are Ta-rich. The nanostructural transition, combined with changes in average column widths, results in an similar to 20% increase in hardness, from 35 to 42 GPa, with a simultaneous increase of similar to 30% in nanoindentation toughness, from 4.0 to 5.2MPa root m. Published by the AVS.

##### Place, publisher, year, edition, pages
A V S AMER INST PHYSICS, 2019
##### National Category
Inorganic Chemistry
##### Identifiers
urn:nbn:se:liu:diva-159001 (URN)10.1116/1.5093170 (DOI)000472182400035 ()
##### Note

Funding Agencies|Swedish Research Council VR [2014-5790, 2018-03957, 642-2013-8020]; Knut and Alice Wallenbergs foundation [KAW 2015.0043]; VINNOVA [2018-04290]; Aforsk Foundation [16-359]; Carl Tryggers Stiftelse [CTS 15: 219, CTS 17: 166, CTS 14: 431]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University (Faculty Grant SFO Mat LiU) [2009 00971]

Available from: 2019-07-19 Created: 2019-07-19 Last updated: 2020-04-01
4. Atom probe tomography field evaporation characteristics and compositional corrections of ZrB2
Open this publication in new window or tab >>Atom probe tomography field evaporation characteristics and compositional corrections of ZrB2
2019 (English)In: Materials Characterization, ISSN 1044-5803, E-ISSN 1873-4189, Vol. 156, article id 109871Article in journal (Refereed) Published
##### Abstract [en]

The microstructure of stoichiometric ZrB2.0 and B over-stoichiometric ZrB2.5 thin films has been studied using atom probe tomography (APT), X-ray diffraction, and transmission electron microscopy. Both films consist of columnar ZrB2 grains with AlB2-type crystal structure. The narrow stoichiometry range of ZrB2 results in the presence of separate disordered B-rich boundaries even in ZrB2.0. At higher average B content, specifically ZrB2.5, the formation of a continuous network around the sides of the ZrB2 columns is promoted. In addition, the APT field evaporation characteristics of ZrB2 and its influence on the measured local composition has been studied and compared to the average composition from elastic recoil detection analysis (ERDA). Differences in the measured average compositions of the two techniques are explained by the APT detector dead-time/space. A new pile-up pairs correction procedure based on co-evaporation correlation data was thus employed here for the APT data and compared with the 10B-method (the B equivalence of the 13C-method), as well as the combination of both methods. In ZrB2.0, all of the applied compositional correction methods were found to reduce the compositional difference when appropriate isotopic abundances were used. In ZrB2.5, the inhomogeneity of the film likely increased the local APT composition to such an extent that even conservative correction procedures overestimated the B content compared to the ERDA reference. The strengths of the pile-up pairs correction compared the 10B and the combined methods are higher precision, due to it being less dependent on the accuracy of estimated isotopic abundances, and that the correction itself is not dependent on careful background correction of the mass spectrum.

##### Place, publisher, year, edition, pages
Elsevier, 2019
##### Keywords
Atom probe tomography (APT), Zirconium diboride (ZrB), Field evaporation characteristics of borides, Elastic recoil detection analysis (ERDA), Compositional correction procedures, Transition metal diborides
##### National Category
Physical Sciences
##### Identifiers
urn:nbn:se:liu:diva-160356 (URN)10.1016/j.matchar.2019.109871 (DOI)000487565900025 ()
Available from: 2019-09-19 Created: 2019-09-19 Last updated: 2019-11-04Bibliographically approved
fulltext
presentationsbild
• 329.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
Sandvik Coromant, Stockholm, Sweden. Linköping University, Department of Physics, Chemistry and Biology. Linköping University, Faculty of Science & Engineering. SECO Tools AB, Fagersta, Sweden. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering. Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials. Linköping University, Faculty of Science & Engineering. Department of Applied Physics, Chalmers University of Technology, Göteborg, Sweden. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
Solid Solution and Segregation Effects in Arc-Deposited Ti1-xSixN Thin Films Resolved on the nanometer scale by 15N Isotopic Substitution in AtomP robe TomographyManuscript (preprint) (Other academic)

Nanostructured TiSiN is an important material in wear--‐resistant coatings for extending the lifetime of cutting tools. Yet, the understanding regarding the structure, phase composition, and bonding on the detailed nanometer scale, which determines the properties of TiSiN, is lacking. This limits our understanding of the growth phenomena and eventually a larger exploitation of the material. By substituting natN2 with 15N2 during reactive arc deposition of TiSiN thin films, atom probe tomography (APT) gives elemental sensitivity and sub-nanometer resolution, a finer scale than what can be obtained by commonly employed energy dispersive electron spectroscopy in scanning transmission electron microscopy. Using a combination of analytical transmission electron microscopy and APT we show that arc-deposited Ti0.92Si0.0815N and Ti0.81Si0.1915N exhibit Si segregation on the nanometer scale in the alloy films. APT composition maps and proximity histograms from domains with higher than average Ti content show that the TiN domains contain at least ~2 at. % Si for Ti0.92Si0.08N and ~5 at. % Si for Ti0.81Si0.19N, thus confirming the formation of solid solutions. The formation of relatively pure SiNy domains in the Ti0.81Si0.19N films is tied to pockets between microstructured, columnar features in the film. Finer SiNy enrichments seen in APT possibly correspond to tissue layers around TiN crystallites, thus effectively hindering growth of TiN crystallites, causing TiN renucleation and thus explaining the featherlike nanostructure within the columns of these films. For the stoichiometry of the TiN phase, we establish a global under stoichiometry, in accordance with the tendency for SiNy films to have tetrahedral bonding coordination towards a nominal Si3N4 composition.

• 330.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering. Department of Physics, Chalmers University of Technology, Göteborg, Sweden. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
Atom probe tomography field evaporation characteristics and compositional corrections of ZrB22019In: Materials Characterization, ISSN 1044-5803, E-ISSN 1873-4189, Vol. 156, article id 109871Article in journal (Refereed)

The microstructure of stoichiometric ZrB2.0 and B over-stoichiometric ZrB2.5 thin films has been studied using atom probe tomography (APT), X-ray diffraction, and transmission electron microscopy. Both films consist of columnar ZrB2 grains with AlB2-type crystal structure. The narrow stoichiometry range of ZrB2 results in the presence of separate disordered B-rich boundaries even in ZrB2.0. At higher average B content, specifically ZrB2.5, the formation of a continuous network around the sides of the ZrB2 columns is promoted. In addition, the APT field evaporation characteristics of ZrB2 and its influence on the measured local composition has been studied and compared to the average composition from elastic recoil detection analysis (ERDA). Differences in the measured average compositions of the two techniques are explained by the APT detector dead-time/space. A new pile-up pairs correction procedure based on co-evaporation correlation data was thus employed here for the APT data and compared with the 10B-method (the B equivalence of the 13C-method), as well as the combination of both methods. In ZrB2.0, all of the applied compositional correction methods were found to reduce the compositional difference when appropriate isotopic abundances were used. In ZrB2.5, the inhomogeneity of the film likely increased the local APT composition to such an extent that even conservative correction procedures overestimated the B content compared to the ERDA reference. The strengths of the pile-up pairs correction compared the 10B and the combined methods are higher precision, due to it being less dependent on the accuracy of estimated isotopic abundances, and that the correction itself is not dependent on careful background correction of the mass spectrum.

The full text will be freely available from 2021-08-10 08:00
• 331.
Nelson Mandela Metropolitan University, South Africa.
Idaho National Lab, ID 83415 USA. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering. Nelson Mandela Metropolitan University, South Africa.
Notes on the plasma resonance peak employed to determine doping in SiC2015In: Infrared physics & technology, ISSN 1350-4495, E-ISSN 1879-0275, Vol. 72, p. 95-100Article in journal (Refereed)

The doping level of a semiconductor material can be determined using the plasma resonance frequency to obtain the carrier concentration associated with doping. This paper provides an overview of the procedure for the three most common polytypes of SiC. Results for 3C-SiC are presented and discussed. In phosphorus doped samples analysed, it is submitted that the 2nd plasma resonance cannot be detected due to high values of the free carrier damping constant gamma. (C) 2015 Elsevier B.V. All rights reserved.

• 332.
Nelson Mandela Metropolitan University, South Africa .
Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology. Idaho National Lab, ID 83415 USA .
Impact of dielectric parameters on the reflectivity of 3C-SiC wafers with a rough surface morphology in the reststrahlen region2014In: Physica. B, Condensed matter, ISSN 0921-4526, E-ISSN 1873-2135, Vol. 439, p. 115-118Article in journal (Refereed)

A layer-on-substrate model is used to obtain the infrared reflectance for 3C-SiC with a rough surface morphology. The effect of varying dielectric parameters of the "damaged layer" on the observed reflectivity of the 3C-SiC in the reststrahlen region is assessed. Different simulated reflectance spectra are obtained to those if the dielectric parameters of the "substrate" were varied. Most notable changes in the shape of the simulated reststrahlen peak are observed for changes in the high frequency dielectric constant, the phonon damping constant, the phonon frequencies and "thickness" of damaged surface layer.

• 333. Engstrom, C.