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• 1.
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.
X-ray photoelectron spectroscopy: Towards reliable binding energy referencing2020In: Progress in Materials Science, ISSN 0079-6425, E-ISSN 1873-2208, Vol. 107, article id 100591Article, review/survey (Refereed)

With more than 9000 papers published annually, X-ray photoelectron spectroscopy (XPS) is an indispensable technique in modem surface and materials science for the determination of chemical bonding. The accuracy of chemical-state determination relies, however, on a trustworthy calibration of the binding energy (BE) scale, which is a nontrivial task due to the lack of an internal BE reference. One approach, proposed in the early days of XPS, employs the C 1s spectra of an adventitious carbon layer, which is present on all surfaces exposed to air. Despite accumulating criticism, pointing to the unknown origin and composition of the adventitious carbon, this is by far the most commonly used method today for all types of samples, not necessarily electrically insulating. Alarmingly, as revealed by our survey of recent XPS literature, the calibration procedure based on the C 1s peak of adventitious carbon is highly arbitrary, which results in incorrect spectral interpretation, contradictory results, and generates a large spread in reported BE values for elements even present in the same chemical state. The purpose of this review is to critically evaluate the status quo of XPS with a historical perspective, provide the techniques operating principles, resolve myths associated with C 1s referencing, and offer a comprehensive account of recent findings. Owing to the huge volume of XPS literature produced each year, the consequences of improper referencing are dramatic. Our intention is to promote awareness within a growing XPS community as to the problems reported over the last six decades and present a guide with best practice for using the C 1s BE referencing method.

• 2.
Univ Calif Los Angeles, CA 90095 USA.
Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Ruhr Univ Bochum, Germany. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering. Univ Illinois, IL 61801 USA. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering. Univ Illinois, IL 61801 USA; Natl Taiwan Univ Sci and Technol, Taiwan. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
A review of the intrinsic ductility and toughness of hard transition-metal nitride alloy thin films2019In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 688, article id 137479Article, review/survey (Refereed)

Over the past decades, enormous effort has been dedicated to enhancing the hardness of refractory ceramic materials. Typically, however, an increase in hardness is accompanied by an increase in brittleness, which can result in intergranular decohesion when materials are exposed to high stresses. In order to avoid brittle failure, in addition to providing high strength, films should also be ductile, i.e., tough. However, fundamental progress in obtaining hard-yet-ductile ceramics has been slow since most toughening approaches are based on empirical trial-and-error methods focusing on increasing the strength and ductility extrinsically, with a limited focus on understanding thin-film toughness as an inherent physical property of the material. Thus, electronic structure investigations focusing on the origins of ductility vs. brittleness are essential in understanding the physics behind obtaining both high strength and high plastic strain in ceramics films. Here, we review recent progress in experimental validation of density functional theory predictions on toughness enhancement in hard ceramic films, by increasing the valence electron concentration, using examples from the V1-xWxN and V1-xMoxN alloy systems.

• 3.
Drexel Univ, PA 19104 USA; Drexel Univ, PA 19104 USA.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering. Nucl Res Ctr Negev, Israel. 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. Drexel Univ, PA 19104 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, Thin Film Physics. Linköping University, Faculty of Science & Engineering. Drexel Univ, PA 19104 USA. Drexel Univ, PA 19104 USA; Nucl Res Ctr Negev, Israel.
A Tungsten-Based Nanolaminated Ternary Carbide: (W,Ti)(4)C4-x2019In: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 58, no 2, p. 1100-1106Article in journal (Refereed)

Nanolamellar transition metal carbides are gaining increasing interests because of the recent developments of their twodimensional (2D) derivatives and promising performance for a variety of applications from energy storage, catalysis to transparent conductive coatings, and medicine. To develop more novel 2D materials, new nanolaminated structures are needed. Here we report on a tungsten based nanolaminated ternary phase, (W,Ti)(4)C4-x, synthesized by an Al catalyzed reaction of W, Ti, and C powders at 1600 degrees C for 4 h, under flowing argon. X-ray and neutron diffraction, along with Z-contrast scanning transmission electron microscopy, were used to determine the atomic structure, ordering, and occupancies. This phase has a layered hexagonal structure (P6(3)/mmc) with lattice parameters, a = 3.00880(7) angstrom, and c = 19.5633(6) angstrom and a nominal chemistry of (W,Ti)(4)C4-x (actual chemistry, W2.1(1)Ti1.6(1)C2.6(1)). The structure is comprised of layers of pure W that are also twin planes with two adjacent atomic layers of mixed W and Ti, on either side. The use of Al as a catalyst for synthesizing otherwise difficult to make phases, could in turn lead to the discovery of a large family of nonstoichiometric ternary transition metal carbides, synthesized at relatively low temperatures and shorter times.

The full text will be freely available from 2020-01-04 16:13
• 4.
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
• 5.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
Atomically Layered and Ordered Rare-Earth i-MAX Phases: A New Class of Magnetic Quaternary Compounds2019In: Chemistry of Materials, ISSN 0897-4756, E-ISSN 1520-5002, Vol. 31, no 7, p. 2476-2485Article in journal (Refereed)

In 2017, we discovered quaternary i-MAX phases atomically layered solids, where M is an early transition metal, A is an A group element, and X is C-with a ((M2/3M1/32)-M-1)(2)AC chemistry, where the M-1 and M-2 atoms are in-plane ordered. Herein, we report the discovery of a class of magnetic i-MAX phases in which bilayers of a quasi-2D magnetic frustrated triangular lattice overlay a Mo honeycomb arrangement and an Al Kagome lattice. The chemistry of this family is (Mo2/3RE1/3)(2)AlC, and the rare-earth, RE, elements are Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, and Lu. The magnetic properties were characterized and found to display a plethora of ground states, resulting from an interplay of competing magnetic interactions in the presence of magnetocrystalline anisotropy.

• 6.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
Compositional dependence of epitaxial Tin+1SiCn MAX-phase thin films grown from a Ti3SiC2 compound target2019In: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films, ISSN 0734-2101, E-ISSN 1520-8559, Vol. 37, no 2, article id 021506Article in journal (Refereed)

The authors investigate sputtering of a Ti3SiC2 compound target at temperatures ranging from RT (no applied external heating) to 970 °C as well as the influence of the sputtering power at 850 °C for the deposition of Ti3SiC2 films on Al2O3(0001) substrates. Elemental composition obtained from time-of-flight energy elastic recoil detection analysis shows an excess of carbon in all films, which is explained by differences in the angular distribution between C, Si, and Ti, where C scatters the least during sputtering. The oxygen content is 2.6 at. % in the film deposited at RT and decreases with increasing deposition temperature, showing that higher temperatures favor high purity films. Chemical bonding analysis by x-ray photoelectron spectroscopy shows C–Ti and Si–C bonding in the Ti3SiC2 films and Si–Si bonding in the Ti3SiC2 compound target. X-ray diffraction reveals that the phases Ti3SiC2, Ti4SiC3, and Ti7Si2C5 can be deposited from a Ti3SiC2 compound target at substrate temperatures above 850 °C and with the growth of TiC and the Nowotny phase Ti5Si3Cx at lower temperatures. High-resolution scanning transmission electron microscopy shows epitaxial growth of Ti3SiC2, Ti4SiC3, and Ti7Si2C5 on TiC at 970 °C. Four-point probe resistivity measurements give values in the range ∼120 to ∼450 μΩ cm and with the lowest values obtained for films containing Ti3SiC2, Ti4SiC3, and Ti7Si2C5.

• 7.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering. Rhein Westfal TH Aachen, Germany.
Rhein Westfal TH Aachen, Germany. Rhein Westfal TH Aachen, Germany. 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. Rhein Westfal TH Aachen, Germany.
Control over the Phase Formation in Metastable Transition Metal Nitride Thin Films by Tuning the Al+ Subplantation Depth2019In: Coatings, ISSN 2079-6412, Vol. 9, no 1, article id 17Article in journal (Refereed)

The performance of transition metal nitride based coatings deposited by magnetron sputtering, in a broad range of applications including wear-protective coatings on cutting tools and components in automotive engines, is determined by their phase content. The classical example is the precipitation of thermodynamically-favored wurtzite-AlN while alloying TiN with Al to obtain ternary single phase NaCl-structure films with improved high-temperature oxidation resistance. Here, we report on reactive high-power impulse and direct current magnetron co-sputtering (HiPIMS/DCMS) growth of Ti0.31Al0.69N and Zr0.48Al0.52N thin films. The Al concentrations are intentionally chosen to be higher than theoretically predicted solubility limits for the rock salt structure. The goal is to investigate the effect of the incident Al+ energy E-Al(+), controlled by varying the amplitude of the substrate bias applied synchronously with the Al+-rich portion of the ion flux from the Al-HiPIMS source, on the crystalline phase formation. For EAl+ amp;lt;= 60 eV, films contain predominantly the wurtzite phase. With increasing E-Al(+), and thus, the Al subplantation depth, the relative fraction of the NaCl structure increases and eventually for E-Al(+) amp;gt; 250 eV, Ti0.31Al0.69N and Zr0.48Al0.52N layers contain more than 95% of the rock salt phase. Thus, the separation of the film forming species in time and energy domains determines the phase formation of Ti0.31Al0.69N and Zr0.48Al0.52N layers and enables the growth of the cubic phase outside of the predicted Al concentration range. The new film growth concept can be applied to the entire family of multinary transition metal aluminum nitrides, where one of the metallic film constituents is available in the ionized form while the other arrives as neutral.

• 8.
Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
Efficient and Tunable Electroluminescence from In Situ Synthesized Perovskite Quantum Dots2019In: Small, ISSN 1613-6810, E-ISSN 1613-6829, Vol. 15, no 8, article id 1804947Article in journal (Refereed)

Semiconductor quantum dots (QDs) are among the most promising next-generation optoelectronic materials. QDs are generally obtained through either epitaxial or colloidal growth and carry the promise for solution-processed high-performance optoelectronic devices such as light-emitting diodes (LEDs), solar cells, etc. Herein, a straightforward approach to synthesize perovskite QDs and demonstrate their applications in efficient LEDs is reported. The perovskite QDs with controllable crystal sizes and properties are in situ synthesized through one-step spin-coating from perovskite precursor solutions followed by thermal annealing. These perovskite QDs feature size-dependent quantum confinement effect (with readily tunable emissions) and radiative monomolecular recombination. Despite the substantial structural inhomogeneity, the in situ generated perovskite QDs films emit narrow-bandwidth emission and high color stability due to efficient energy transfer between nanostructures that sweeps away the unfavorable disorder effects. Based on these materials, efficient LEDs with external quantum efficiencies up to 11.0% are realized. This makes the technologically appealing in situ approach promising for further development of state-of-the-art LED systems and other optoelectronic devices.

The full text will be freely available from 2020-01-28 13:23
• 9.
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. 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.
Electronic Structure of ß-Ta Films from X-ray Photoelectron Spectroscopy and First-principles Calculations2019In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 470, p. 607-612Article in journal (Refereed)

The electronic structure and chemical bonding of ß-Ta synthesized as a thin 001-oriented film (space group P 21m) is investigated by 4f core level and valence band X-ray photoelectron spectroscopy and compared to α-Ta bulk. For the b-phase, the 4f7/2 peak is located at 21.91 eV and with the 4f5/2 at 23.81 eV which is 0.16 eV higher compared to the corresponding 4f peaks of the a-Ta reference. We suggest that this chemical shift originates from higher resistivity and tensile strain in the ß-Ta film. Furthermore, the 5d-5s states at the bottom of the valence band are shifted by 0.75 eV towards higher binding energy in ß-Ta compared to α-Ta. This is a consequence of the lower number of nearest neighbors with four in ß-Ta compared to eight in the α-Ta phase. The difference in the electronic structures, spectral line shapes of the valence band and the energy positions of the Ta 4f, 5p core-levels of b-Ta versus a-Ta are discussed in relation to calculated states of ß-Ta and α-Ta. In particular, the lower number of states at the Fermi level of ß-Ta (0.557 states/eV/atom) versus α-Ta (1.032 states/eV/atom) that according to Mott’s law should decrease the conductivity in metals and affect the stability by charge redistribution in the valence band. This is experimentally supported from resistivity measurements of the film yielding a value of ~170 µW cm in comparison to α-Ta bulk with a reported value of ~13.1 µW cm.

• 10.
Chinese Acad Sci, Peoples R China.
Element Replacement Approach by Reaction with Lewis Acidic Molten Salts to Synthesize Nanolaminated MAX Phases and MXenes2019In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 141, no 11, p. 4730-4737Article in journal (Refereed)

Nanolaminated materials are important because of their exceptional properties and wide range of applications. Here, we demonstrate a general approach to synthesizing a series of Zn-based MAX phases and Cl-terminated MXenes originating from the replacement reaction between the MAX phase and the late transition-metal halides. The approach is a top-down route that enables the late transitional element atom (Zn in the present case) to occupy the A site in the pre-existing MAX phase structure. Using this replacement reaction between the Zn element from molten ZnCl2 and the Al element in MAX phase precursors (Ti3AlC2, Ti2AlC, Ti2AlN, and V2AlC), novel MAX phases Ti3ZnC2, Ti2ZnC, Ti2ZnN, and V2ZnC were synthesized. When employing excess ZnCl2, Cl-terminated MXenes (such as Ti3C2Cl2 and Ti2CCl2) were derived by a subsequent exfoliation of Ti3ZnC2 and Ti2ZnC due to the strong Lewis acidity of molten ZnCl2. These results indicate that A-site element replacement in traditional MAX phases by late transition-metal halides opens the door to explore MAX phases that are not thermodynamically stable at high temperature and would be difficult to synthesize through the commonly employed powder metallurgy approach. In addition, this is the first time that exclusively Cl-terminated MXenes were obtained, and the etching effect of Lewis acid in molten salts provides a green and viable route to preparing MXenes through an HF-free chemical approach.

The full text will be freely available from 2020-03-01 16:05
• 11.
Chalmers Univ Technol, Sweden.
SweGaN, SE-58330 Linkoping, Sweden. Chalmers Univ Technol, 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, Thin Film Physics. Linköping University, Faculty of Science & Engineering. SweGaN, SE-58330 Linkoping, Sweden. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering. Univ Iceland, Iceland. Chalmers Univ Technol, Sweden. Chalmers Univ Technol, Sweden.
Enhanced Mobility in InAlN/AlN/GaN HEMTs Using a GaN Interlayer2019In: IEEE Transactions on Electron Devices, ISSN 0018-9383, E-ISSN 1557-9646, Vol. 66, no 7, p. 2910-2915Article in journal (Refereed)

An enhancement of the electron mobility (mu) in InAlN/AlN/GaN heterostructures is demonstrated by the incorporation of a thin GaN interlayer (IL) between the InAlN and AlN. The introduction of a GaN IL increases mu at room temperature (RT) from 1600 to 1930 cm(2)/Vs. The effect is further enhanced at cryogenic temperature (5 K), where the GaN IL sample exhibits a mu of 16 000 cm(2)/Vs, compared to 6900cm(2)/Vs without IL. The results indicate the reduction of one or more scattering mechanisms normally present in InAlN/AlN/GaN heterostructures. We propose that the improvement in mu is either due to the suppression of fluctuations in the quantum well subband energies or to reduced Coulomb scattering, both related to compositional variations in the InAlN. HEMTs fabricated on the GaN IL sample demonstrate larger improvement in dc- and high-frequency performance at 5 K; f(max) increases by 25 GHz to 153 GHz, compared to an increase of 6 GHz to 133 GHz without IL. The difference in improvement was associated mainly with the drop in the access resistances.

• 12.
Messiah Coll, PA 17055 USA.
High-power impulse magnetron sputter deposition of TiBx thin films: Effects of pressure and growth temperature2019In: Vacuum, ISSN 0042-207X, E-ISSN 1879-2715, Vol. 169, article id UNSP 108884Article in journal (Refereed)

Titanium boride, TiBx thin films are grown in pure Ar discharges by high-power impulse magnetron sputtering (HiPIMS) from a compound TiB2 target Film compositions are determined by time-of-flight elastic recoil detection analysis and Rutherford backscattering spectrometry as a function of deposition temperature (T-s = 25-900 degrees C) and Ar pressure (p(Ar) = 0.67-2.67 Pa, 5-20 mTorr). For reference, films are also grown by direct current magnetron sputtering (dcMS) under similar conditions. The HiPIMS waveform, average target power P-T, and resulting film compositions are strongly dependent not only on P-Ar, but also on T-s. At high pressures the effect of varying T-s on P-T is minimal, while at lower P-Ar the effect of T-s is more pronounced, due to substrate-temperature-induced gas rarefaction. Films grown by HiPIMS at 0.67 Pa are understoichiometric, with B/Ti = 1.4-1.5, while at 2.67 Pa, B/Ti decreases from 2.4 to 1.4 as T-s increases from 25 to 900 degrees C. dcMS-deposited films are overstoichiometric (B/Ti similar or equal to 3) when grown at low pressures, and near-stoichiometric (B/Ti similar or equal to r 1.9-2.2) for higher P-Ar. All experimental results are explained by differences in the ionization potentials of sputtered Ti and B atoms, together with P-Ar- and T-s-dependent gas-phase scattering.

• 13.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering. Sandvik Coromant AB, Stockholm, Sweden.
Sandvik Coromant AB, Stockholm, Sweden. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering. Applied Nuclear Physics, Department of Physics and Astronomy, Uppsala University, Uppsala, Sweden. SECO Tools AB, Fagersta, Sweden. Sandvik Coromant AB, Stockholm, Sweden. Sandvik Coromant AB, Stockholm, Sweden. 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.
Phase composition and transformations in magnetron-sputtered (Al,V)2O3 coatings2019In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 688, article id 137369Article in journal (Refereed)

Coatings of (Al1-xVx)2O3, with x ranging from 0 to 1, were deposited by pulsed DC reactive sputter deposition on Si(100) at a temperature of 550 °C. XRD showed three different crystal structures depending on V-metal fraction in the coating: α-V2O3 rhombohedral structure for 100 at.% V, a defect spinel structure for the intermediate region, 63–42 at.% V. At lower V-content, 18 and 7 at.%, a gamma-alumina-like solid solution was observed, shifted to larger d-spacing compared to pure γ-Al2O3. The microstructure changes from large columnar faceted grains for α-V2O3 to smaller equiaxed grains when lowering the vanadium content towards pure γ-Al2O3. Annealing in air resulted in formation of V2O5 crystals on the surface of the coating after annealing to 500 °C for 42 at.% V and 700 °C for 18 at.% V metal fraction respectively. The highest thermal stability was shown for pure γ-Al2O3-coating, which transformed to α-Al2O3 after annealing to 1100 °C. Highest hardness was observed for the Al-rich oxides, ~24 GPa. The latter decreased with increasing V-content, larger than 7 at.% V metal fraction. The measured hardness after annealing in air decreased in conjunction with the onset of further oxidation of the coatings.

• 14.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering. Univ Illinois, IL 61820 USA.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering. KIT, Germany. Natl Taiwan Univ, Taiwan. Ecole Polytech Montreal, Canada.
Preface of the special issue "Thin Films Advances" dedicated to the 75th birthday of Professor Joe Greene2019In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 688, article id 137494Article in journal (Other academic)

n/a

• 15.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
Reactive magnetron sputtering of tungsten target in krypton/trimethylboron atmosphere2019In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 688, article id 137384Article in journal (Refereed)

W-B-C films were deposited on Si(100) substrates held at elevated temperature by reactive sputtering from a W target in Kr/trimethylboron (TMB) plasmas. Quantitative analysis by Xray photoelectron spectroscopy (XPS) shows that the films are W-rich between ~ 73 and ~ 93 at.% W. The highest metal content is detected in the film deposited with 1 sccm TMB. The C and B concentrations increase with increasing TMB flow to a maximum of ~18 and ~7 at.%, respectively, while the O content remains nearly constant at 2-3 at.%. Chemical bonding structure analysis performed after samples sputter-cleaning reveals C-W and B-W bonding and no detectable W-O bonds. During film growth with 5 sccm TMB and 500 o C or with 10 sccm TMB and 300-600 o C thin film X-ray diffraction shows the formation of cubic 100-oriented WC1-x with a possible solid solution of B. Lower flows and lower growth temperatures favor growth of W and W2C, respectively. Depositions at 700 and 800 o C result in the formation of WSi2 due to a reaction with the substrate. At 900 o C, XPS analysis shows ~96 at.% Si in the film due to Si interdiffusion. Scanning electron microscopy images reveal a fine-grained microstructure for the deposited WC1-x films. Nanoindentation gives hardness values in the range from ~23 to ~31 GPa and reduced elastic moduli between ~220 and 280 GPa in the films deposited at temperatures lower than 600 o C. At higher growth temperatures the hardness decreases by a factor of 3 to 4 following the formation of WSi2 at 700-800 o C and Si-rich surface at 900 o C.

The full text will be freely available from 2021-06-22 08:00
• 16.
Chinese Acad Sci, Peoples R China; Univ Chinese Acad Sci, Peoples R China.
Single-Atom-Thick Active Layers Realized in Nanolaminated Ti-3(AlxCu1-x)C-2 and Its Artificial Enzyme Behavior2019In: ACS Nano, ISSN 1936-0851, E-ISSN 1936-086X, Vol. 13, no 8, p. 9198-9205Article in journal (Refereed)

A Ti-3(AlxCu1-x)C-2 phase with Cu atoms with a degree of ordering in the A plane is synthesized through the A site replacement reaction in CuCl2 molten salt. The weakly bonded single -atom -thick Cu layers in a Ti-3(AlxCu1-x)C-2 MAX phase provide actives sites for catalysis chemistry. As -synthesized Ti-3(AlxCu1-x)C-2 presents unusual peroxidase-like catalytic activity similar to that of natural enzymes. A fabricated Ti-3(AlxCu1-x)C-2/chitosan/glassy carbon electrode biosensor prototype also exhibits a low detection limit in the electrochemical sensing of H2O2. These results have broad implications for property tailoring in a nanolaminated MAX phase by replacing the A site with late transition elements.

• 17.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
Strategy for simultaneously increasing both hardness and toughness in ZrB2-rich Zr1-xTaxBy thin films2019In: 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)

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.

• 18.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
Synthesis and characterization of (Ti1-xAlx)B2+Delta thin films from combinatorial magnetron sputtering2019In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 669, p. 181-187Article in journal (Refereed)

(Ti1-xAlx)B2+Delta films with a lateral composition gradient of x = [0.30-0.66] and Delta = [0.07-1.22] were deposited on an Al2O3 wafer by dual magnetron sputtering at 400 degrees C from sintered TiB2 and AlB2 targets. Composition analysis indicates that higher Ti:Al ratios favor overstoichiometry in B and a reduced incorporation of O. Transmission electron microscopy reveals distinctly different microstructures of Ti- and Al-rich compositions, with formation of characteristic conical growth features for the latter along with a lower degree of crystallinity and significantly less tissue phase from B segregation at the grain boundaries. For Al-rich films, phase separation into Ti- and Al-rich diboride nanometer-size domains is observed and interpreted as surface-initiated spinodal decomposition. The hardness of the films ranges from 14 to 28 GPa, where the higher values were obtained for the Ti-rich regions of the metal boride.

The full text will be freely available from 2020-10-26 15:00
• 19.
Chinese Acad Sci, Peoples R China.
Synthesis of Novel MAX Phase Ti3ZnC2 via A-site-element-substitution Approach2019In: Journal of Inorganic Materials, ISSN 1000-324X, Vol. 34, no 1, p. 60-64Article in journal (Refereed)

Using Ti3AlC2 as the precursor, a new MAX phase Ti3ZnC2 was synthesized via an A-elemental substitution reaction in a molten salts bath. Composition and crystal structure of Ti3ZnC2 were confirmed by XRD, SEM and TEM analysis. Its structure stability and lattice parameter of Ti3ZnC2 were further proved by a theoretical calculation based on density function theory (DFT). Moreover, thermodynamics of A-elemental substitution reactions based on Fe, Co, Ni, and Cu were investigated. All results indicated that the similar substitution reactions are feasible to form series of MAX phases whose A sites are Fe, Co, Ni, and Cu elements. The substitution reaction was achieved by diffusion of Zn atoms into A-layers of Ti3AlC2, which requires Al-Zn eutectic formation at high temperatures. The molten salts provided a moderate environment for substitution reaction and accelerated reaction dynamics. The major advantage of this substitution reaction is that MAX phase keeps individual metal carbide layers intact, thus the formation of competitive phases, such as MA alloys, was avoided. The proposed A-elemental substitution reactions approach opens a new door to design and synthesize novel MAX phases which could not be synthesized by the traditional methods.

• 20.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
Synthesis of (V2/3Sc1/3)(2)AlC i-MAX phase and V2-xC MXene scrolls2019In: Nanoscale, ISSN 2040-3364, E-ISSN 2040-3372, Vol. 11, no 31, p. 14720-14726Article in journal (Refereed)

We report the synthesis and characterization of a new laminated i-MAX phase, (V2/3Sc1/3)(2)AlC, with in-plane chemical ordering between the M-elements. We also present evidence for the solid solution (V2-xScx)(2)AlC, where x amp;lt;= 0.05. Chemical etching of the Al and Sc results in a two-dimensional (2D) MXene counterpart: V2-xC from the latter phase. Furthermore, etching with HF yields single-sheet MXene of flat morphology, while LiF + HCl gives MXene scrolls. We also show a 4x reduction in etching time for (V2-xScx)(2)AlC compared to V2AlC, suggesting that traces of Sc changes the phase stability, and make the material more susceptible to etching. The results show a path for improved control of MXene synthesis and morphology, which may be applicable also for other MAX/MXene systems.

• 21.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering. Orebro Univ, Sweden.
Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Ruhr Univ Bochum, Germany. 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. Univ Illinois, IL 61801 USA. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering. Univ Illinois, IL 61801 USA; Natl Taiwan Univ Sci and Technol, Taiwan. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
TiN film growth on misoriented TiN grains with simultaneous low-energy bombardment: Restructuring leading to epitaxy2019In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 688, article id 137380Article in journal (Refereed)

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

• 22.
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, Nanostructured Materials. Linköping University, Faculty of Science & Engineering.
X-ray photoelectron spectroscopy studies of Ti1-xAlxN (0 <= x <= 0.83) high-temperature oxidation: The crucial role of Al concentration2019In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 374, p. 923-934Article in journal (Refereed)

The resistance to high-temperature oxidation of Ti1-xAlxN films determines performance in numerous applications including coated cutting tools. Here, we present a comprehensive study covering Ti1-xAlxN films with 0 amp;lt;= x amp;lt;= 0.83 annealed in air for 1 h at temperatures T-a ranging from 500 to 800 degrees C. Layers are grown by the combination of high-power impulse and dc magnetron sputtering (HiPIMS/DCMS) in Ar/N-2 atmospheres. We use X-ray photoelectron spectroscopy to study the evolution of surface chemistry and to reconstruct elemental distribution profiles. No dependence of oxidation process on the phase content, average grain size, or preferred orientation could be confirmed, to the accuracy offered by the employed X-ray diffraction techniques. Instead, our results show that, under the applied test conditions, the Ti1-xAlxN oxidation scenario depends on both x and T-a. The common notion of double-layer Al2O3/TiO2 oxide formation is valid only in a limited region of the x-T-a parameter space (Type-1 oxidation). Outside this range, a mixed and non-conformal Al2O3-TiO2 layer forms, characterized by larger oxide thickness (Type-2 oxidation). The clear distinction between different Ti1-xAlxN oxidation scenarios revealed here is essential for numerous applications that can benefit from optimizing the Al content, while targeting a given operational temperature range.

• 23.
SweGaN AB, Teknikringen 8D, Linköping, Sweden.
Department of Microtechnology and Nanoscience, Chalmers University of Technology, Gothenburg, Sweden. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering. SweGaN AB, Teknikringen 8D, Linköping, Sweden. Department of Microtechnology and Nanoscience, Chalmers University of Technology, Gothenburg, Sweden. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering. Department of Microtechnology and Nanoscience, Chalmers University of Technology, Gothenburg, Sweden. SweGaN AB, Teknikringen 8D, Linköping, Sweden.
A GaN-SiC hybrid material for high-frequency and power electronics2018In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 113, no 4, article id 041605Article in journal (Refereed)

We demonstrate that 3.5% in-plane lattice mismatch between GaN (0001) epitaxial layers and SiC (0001) substrates can be accommodated without triggering extended defects over large areas using a grain-boundary-free AIN nucleation layer (NL). Defect formation in the initial epitaxial growth phase is thus significantly alleviated, confirmed by various characterization techniques. As a result, a high-quality 0.2-mu m thin GaN layer can be grown on the AIN NL and directly serve as a channel layer in power devices, like high electron mobility transistors (HEMTs). The channel electrons exhibit a state-of-the-art mobility of amp;gt;2000 cm(2)/V-s, in the AlGaN/GaN heterostructures without a conventional thick C- or Fe-doped buffer layer. The highly scaled transistor processed on the heterostructure with a nearly perfect GaN-SiC interface shows excellent DC and microwave performances. A peak RF power density of 5.8 W/mm was obtained at V-DSQ = 40 V and a fundamental frequency of 30 GHz. Moreover, an unpassivated 0.2-mu m GaN/AIN/SiC stack shows lateral and vertical breakdowns at 1.5 kV. Perfecting the GaN-SiC interface enables a GaN-SiC hybrid material that combines the high-electron-velocity thin GaN with the high-breakdown bulk SiC, which promises further advances in a wide spectrum of high-frequency and power electronics.

• 24.
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. 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.
­Chemical Bonding in Epitaxial ZrB2 Studied by X-ray Spectroscopy2018In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 649, p. 89-96Article in journal (Refereed)

The chemical bonding in an epitaxial ZrB2 film is investigated by Zr K-edge (1s) X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectroscopies and compared to the ZrB2 compound target from which the film was synthesized as well as a bulk α-Zr reference. Quantitative analysis of X-ray Photoelectron Spectroscopy spectra reveals at the surface: ~5% O in the epitaxial ZrB2 film, ~19% O in the ZrB2 compound target and ~22% O in the bulk α-Zr reference after completed sputter cleaning. For the ZrB2 compound target, X-ray diffraction (XRD) shows weak but visible   11, 111, and 220 peaks from monoclinic ZrO2 together with peaks from ZrB2 and where the intensity distribution for the ZrB2 peaks show a randomly oriented target material.  For the bulk α-Zr reference no peaks from any crystalline oxide were visible in the diffractogram recorded from the 0001-oriented metal. The Zr K-edge absorption from the two ZrB2 samples demonstrate more pronounced oscillations for the epitaxial ZrB2 film than in the bulk ZrB2 attributed to the high atomic ordering within the columns of the film. The XANES exhibits no pre-peak due to lack of p-d hybridization in ZrB2, but with a chemical shift towards higher energy of 4 eV in the film and 6 eV for the bulk compared to α-Zr (17.993 keV) from the charge-transfer from Zr to B. The 2 eV larger shift in bulk ZrB2 material suggests higher oxygen content than in the epitaxial film, which is supported by XPS. In EXAFS, the modelled cell-edge in ZrB2 is slightly smaller in the thin film (a=3.165 Å, c=3.520 Å) in comparison to the bulk target material (a=3.175 Å, c=3.540 Å) while in hexagonal closest-packed metal (α-phase, a=3.254 Å, c=5.147 Å). The modelled coordination numbers show that the EXAFS spectra of the epitaxial ZrB2 film is highly anisotropic with strong in-plane contribution, while the bulk target material is more isotropic. The Zr-B distance in the film of 2.539 Å is in agreement with the calculated value from XRD data of 2.542 Å. This is slightly shorter compared to that in the ZrB2 compound target 2.599 Å, supporting the XANES results of a higher atomic order within the columns of the film compared to bulk ZrB2.

• 25.
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. Univ Illinois, IL 61801 USA; Univ Illinois, IL 61801 USA. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering. Univ Illinois, IL 61801 USA; Univ Illinois, IL 61801 USA. 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.
Controlling the B/Ti ratio of TiBx thin films grown by high-power impulse magnetron sputtering2018In: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films, ISSN 0734-2101, E-ISSN 1520-8559, Vol. 36, no 3, article id 030604Article in journal (Refereed)

TiBx thin films grown from compound TiB2 targets by magnetron sputter deposition are typically highly over-stoichiometric, with x ranging from 3.5 to 2.4, due to differences in Ti and B preferential-ejection angles and gas-phase scattering during transport from the target to the substrate. Here, the authors demonstrate that stoichiometric TiB2 films can be obtained using highpower impulse magnetron sputtering (HiPIMS) operated in power-controlled mode. The B/Ti ratio x of films sputter-deposited in Ar is controllably varied from 2.08 to 1.83 by adjusting the length of HiPIMS pulses t(on) between 100 and 30 mu s, while maintaining average power and pulse frequency constant. This results in peak current densities J(T), peak ranging from 0.27 to 0.88 A/cm(2). Energy- and time-resolved mass spectrometry analyses of the ion fluxes incident at the substrate position show that the density of metal ions increases with decreasing t(on) due to a dramatic increase in J(T, peak) resulting in the strong gas rarefaction. With t(on)amp;lt;60 mu s (J(T),(peak)amp;gt; 0.4 A/cm(2)), film growth is increasingly controlled by ions incident at the substrate, rather than neutrals, as a result of the higher plasma dencity and, hence, electron-impact ionization probablity. Thus, since sputter- ejected Ti atoms have a higher probability of being ionized than B atoms, due to their lower first-ionization potential and larger ionization cross-section, the Ti concentration in as-deposited films increases with decreasing ton (increasing J(T,peak)) as ionized sputtered species are steered to the substrate by the plasma in order to maintain charge neutrality. Published by the AVS.

• 26.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
Effects of N2 Partial Pressure on Growth, Structure, and Optical Properties of GaN Nanorods Deposited by Liquid-Target Reactive Magnetron Sputter Epitaxy2018In: Nanomaterials, ISSN 2079-4991, Vol. 8, no 4, article id 223Article in journal (Refereed)

GaN nanorods, essentially free from crystal defects and exhibiting very sharp band-edge luminescence, have been grown by reactive direct-current magnetron sputter epitaxy onto Si (111) substrates at a low working pressure of 5 mTorr. Upon diluting the reactive N2 working gas with a small amount of Ar (0.5 mTorr), we observed an increase in the nanorod aspect ratio from 8 to ~35, a decrease in the average diameter from 74 to 35 nm, and a two-fold increase in nanorod density. With further dilution (Ar = 2.5 mTorr), the aspect ratio decreased to 14, while the diameter increased to 60 nm and the nanorod density increased to a maximum of 2.4 × 109 cm−2. Yet, lower N2 partial pressures eventually led to the growth of continuous GaN films. The observed morphological dependence on N2 partial pressure is explained by a change from N-rich to Ga-rich growth conditions, combined with reduced GaN-poisoning of the Ga-target as the N2 gas pressure is reduced. Nanorods grown at 2.5 mTorr N2 partial pressure exhibited a high intensity 4 K photoluminescence neutral donor bound exciton transitions (D0XA) peak at ~3.479 eV with a full-width-at-half-maximum of 1.7 meV. High-resolution transmission electron microscopy corroborated the excellent crystalline quality of the nanorods.

• 27.
Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Ruhr University of Bochum, Germany.
University of Illinois, IL 61801 USA; Cornell University, NY 14853 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, 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. University of Illinois, USA. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering. University of Illinois, USA.
Effects of surface vibrations on interlayer mass transport: Ab initio molecular dynamics investigation of Ti adatom descent pathways and rates from TiN/TiN(001) islands2018In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 97, no 3, article id 035406Article in journal (Refereed)

We carried out density-functional ab initio molecular dynamics (AIMD) simulations of Ti adatom (Ti-ad ) migration on, and descent from, square TiN(100) epitaxial islands on TiN(001) at temperatures (T) ranging from 1200 to 2400 K. Adatom-descent energy barriers determined via ab initio nudged-elastic-band calculations at 0 Kelvin suggest that Ti interlayer transport on TiN(001) occurs essentially exclusively via direct hopping onto a lower layer. However, AIMD simulations reveal comparable rates for Ti-ad descent via direct hopping vs push-out/exchange with a Ti island-edge atom for T amp;gt;= 1500 K. We demonstrate that this effect is due to surface vibrations, which yield considerably lower activation energies at finite temperatures by significantly modifying the adatom push-out/exchange reaction pathway.

• 28.
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. Ruhr Univ Bochum, Germany. 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. Univ Illinois, IL 61801 USA. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering. Univ Illinois, IL 61801 USA. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
Elastic properties and plastic deformation of TiC- and VC-based alloys2018In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 144, p. 376-385Article in journal (Refereed)

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

• 29.
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. Mat Ctr Leoben Forsch GmbH, Austria. Univ Leoben, Austria. 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. Univ Illinois, IL 61801 USA; Univ Illinois, IL 61801 USA. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering. Univ Illinois, IL 61801 USA; Univ Illinois, IL 61801 USA. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering. Univ Leoben, Austria.
Enhanced Ti0.84Ta0.16N diffusion barriers, grown by a hybrid sputtering technique with no substrate heating, between Si(001) wafers and Cu overlayers2018In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 8, article id 5360Article in journal (Refereed)

We compare the performance of conventional DC magnetron sputter-deposited (DCMS) TiN diffusion barriers between Cu overlayers and Si(001) substrates with Ti0.84Ta0.16N barriers grown by hybrid DCMS/high-power impulse magnetron sputtering (HiPIMS) with substrate bias synchronized to the metal-rich portion of each pulse. DCMS power is applied to a Ti target, and HiPIMS applied to Ta. No external substrate heating is used in either the DCMS or hybrid DCMS/HiPIMS process in order to meet future industrial thermal-budget requirements. Barrier efficiency in inhibiting Cu diffusion into Si(001) while annealing for 1 hour at temperatures between 700 and 900 degrees C is investigated using scanning electron microscopy, X-ray diffraction, four-point-probe sheet resistance measurements, transmission electron microscopy, and energy-dispersive X-ray spectroscopy profiling. Ti0.84Ta0.16N barriers are shown to prevent large-scale Cu diffusion at temperatures up to 900 degrees C, while conventional TiN barriers fail at amp;lt;= 700 degrees C. The improved performance of the Ti0.84Ta0.16N barrier is due to film densification resulting from HiPIMS pulsed irradiation of the growing film with synchronized Ta ions. The heavy ion bombardment dynamically enhances near-surface atomic mixing during barrier-layer deposition.

• 30.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
Growth and mechanical properties of 111-oriented V0.5Mo0.5Nx/Al2O3(0001) thin films2018In: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films, ISSN 0734-2101, E-ISSN 1520-8559, Vol. 36, no 5, article id 051512Article in journal (Refereed)

Pseudobinary V0.5Mo0.5Nx(111) alloys with the Bl-NaCl crystal structure are grown on Al2O3(0001) substrates in an ultra-high-vacuum system by reactive magnetron sputter deposition in mixed Ar/N-2 atmospheres at temperatures T-s between 100 and 900 degrees C. Nitrogen-to-metal, N/(V + Mo), fractions x vary monotonically from 0.9 +/- 0.1 with T-s = 100 degrees C to 0.4 +/- 0.1 at T-s = 900 degrees C. Nitrogen loss at higher growth temperatures leads to a corresponding decrease in the relaxed lattice parameter a(o) from 4.21 +/- 0.01 angstrom at T-s = 300 degrees C to 4.125 +/- 0.005 angstrom with T-s = 900 degrees C. Scanning electron micrographs of cube-corner nanoindents extending into the substrate show that the films are relatively ductile, exhibiting material pile-up (plastic flow) around the indent edges. Nanoindentation hardnesses H and elastic moduli E, obtained using a calibrated Berkovich tip, of V0.5Mo0.5Nx(111) layers increase with increasing T-s(decreasing x) from 15 +/- 1 and 198 +/- 5 GPa at 100 degrees C to 23 +/- 2 and 381 +/- 11 GPa at 900 degrees C. These values are lower than the corresponding results obtained for the 001-oriented V0.5Mo0.5Nx films In addition, film wear resistance increases with increasing T-s, while the coefficient of friction, under 1000 mu N loads, is 0.09 +/- 0.01 for all layers. Published by the AVS.

• 31.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
Influence of InAiN Nanospiral Structures on the Behavior of Reflected Light Polarization2018In: NANOMATERIALS, ISSN 2079-4991, Vol. 8, no 3, article id 157Article in journal (Refereed)

The influence of structural configurations of indium aluminum nitride (InA1N) nanospirals, grown by reactive magnetron sputter epitaxy, on the transformation of light polarization are investigated in terms of varying structural chirality, growth temperatures, titanium nitride (TiN) seed (buffer) layer thickness, nanospiral thickness, and pitch. The handedness of reflected circularly polarized light in the ultraviolet-visible region corresponding to the chirality of nanospirals is demonstrated. A high degree of circular polarization (P-c) value of 0.75 is obtained from a sample consisting of 1.2 mu m InA1N nanospirals grown at 650 degrees C. A film-like structure is formed at temperatures lower than 450 degrees C. At growth temperatures higher than 750 degrees C, less than 0.1 In-content is incorporated into the InA1N nanospirals. Both cases reveal very low P-c-A red shift of wavelength at P-c peak is found with increasing nanospiral pitch in the range of 200-300 nm. The P-c decreases to 0.37 for two-turn nanospirals with total length of 0.7 mu m, attributed to insufficient constructive interference. A branch-like structure appears on the surface when the nanospirals are grown longer than 1.2 mu m, which yields a low P-c around 0.5, caused by the excessive scattering of incident light.

• 32.
Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering. Nanjing Tech Univ, Peoples R China.
Long Electron-Hole Diffusion Length in High-Quality Lead-Free Double Perovskite Films2018In: Advanced Materials, ISSN 0935-9648, E-ISSN 1521-4095, Vol. 30, no 20, article id 1706246Article in journal (Refereed)

Developing environmentally friendly perovskites has become important in solving the toxicity issue of lead-based perovskite solar cells. Here, the first double perovskite (Cs2AgBiBr6) solar cells using the planar structure are demonstrated. The prepared Cs2AgBiBr6 films are composed of high-crystal-quality grains with diameters equal to the film thickness, thus minimizing the grain boundary length and the carrier recombination. These high-quality double perovskite films show long electron-hole diffusion lengths greater than 100 nm, enabling the fabrication of planar structure double perovskite solar cells. The resulting solar cells based on planar TiO2 exhibit an average power conversion efficiency over 1%. This work represents an important step forward toward the realization of environmentally friendly solar cells and also has important implications for the applications of double perovskites in other optoelectronic devices.

• 33.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
Magnetic properties and structural characterization of layered (Cr0.5Mn0.5)(2)AuC synthesized by thermally induced substitutional reaction in (Cr0.5Mn0.5)(2)GaC2018In: APL MATERIALS, ISSN 2166-532X, Vol. 6, no 2, article id 026104Article in journal (Refereed)

The magnetic properties of the new phase (Cr0.5Mn0.5)(2)AuC are compared to the known MAX-phase (Cr0.5Mn0.5)(2)GaC, where the former was synthesized by thermally induced substitution reaction of Au for Ga in (Cr0.5Mn0.5)(2)GaC. The reaction introduced a lattice expansion of similar to 3% along the c-axis, an enhancement of the coercive field from 30 mT to 140 mT, and a reduction of the Curie temperature and the saturation magnetization. Still, (Cr0.5Mn0.5)(2)AuC displays similar features in the magnetic field-and temperature-dependent magnetization curves as previously reported magnetic MAX phases, e.g., (Cr0.5Mn0.5)(2)GaC and (Mo0.5Mn0.5)(2)GaC. Thework suggests a pathway for tuning the magnetic properties of MAX phases. (c) 2018 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license.

• 34.
Drexel Univ, PA 19104 USA.
Drexel Univ, PA 19104 USA. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering. Drexel Univ, PA 19104 USA. Univ Grenoble Alpes, France. Drexel Univ, PA 19104 USA. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering. Drexel Univ, PA 19104 USA. Drexel Univ, PA 19104 USA.
Magnetic properties of Cr2AlB2, Cr3AlB4, and CrB powders2018In: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 767, p. 474-482Article in journal (Refereed)

The MAB phases are ternary, atomically laminated compounds that crystallize with orthorhombic structures and consist of transition metal (M) boride sublattices interleaved with single or double layers of Al. To date, the magnetic properties of ferromagnetic Fe(2)AIB(2) have been well-studied experimentally, but those of most end member MAB phases with other transition metals remain poorly understood. Herein, predominantly single-phase Cr(3)AIB(4) and Cr(2)AIB(2) powders, with minor amounts of CrB impurities, were synthesized by heating mixtures of chromium monoboride (CrB), aluminum (Al), and boron or CrB and Al under flowing Ar. These reactants were found to substantially suppress the formation of undesired phases in the Cr-Al-B system. The magnetic properties of Cr(3)AIB(4), Cr(2)AIB(2) and CrB powders were characterized. All compounds exhibit paramagnetic behavior down to 4 K, with susceptibilities that are quite weakly temperature dependent at higher temperatures and a Curie-Weiss-like component prominent at low temperatures. Magnetization isotherms of the three compounds, showed approximately linear behavior above 5 kOe and no saturation of the magnetic moment up to 40 kOe, which is consistent with paramagnetism. The magnitude of the magnetic moments showed little variation with composition, on a per Cr atom basis. While the exact nature of the Curie-Weiss component is not entirely clear, we tentatively attribute it to dilute extrinsic impurities. (C) 2018 Elsevier B.V. All rights reserved.

• 35.
CONACYT-Instituto de Física, Benemérita Universidad Autónoma de Puebla, Apdo. Post. J-48, Puebla, Pue, Mexico.
Micro-tribological performance of fullerene-like carbon and carbon-nitride surfaces2018In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 128, p. 104-112Article in journal (Refereed)

We studied the microtribological behavior of amorphous and fullerene-like (FL) carbon and carbon-nitride coatings deposited by filtered-cathodic-arc. All films show similar friction coefficients but different wear mechanisms. The FL films exhibit a surface swelling with the formation of a layer that thickens during the test, limiting wear and maintaining a low friction. X-ray photoelectron spectroscopy on worn FL film surfaces show an increase in the sp(2)-content, indicating that the lubricious layer generated by the wear process is probably the result of re-hybridization due to plasticity induced by localized shear. In contrast, the wear results of the amorphous films, involving tribomechanical and tribochemical surface phenomena, show that the surface layer formed during sliding is a precursor to the onset of wear.

• 36.
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. 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.
Origin of Chemically Ordered Atomic Laminates (i-MAX): Expanding the Elemental Space by a Theoretical/Experimental Approach2018In: ACS Nano, ISSN 1936-0851, E-ISSN 1936-086X, Vol. 12, no 8, p. 7761-7770Article in journal (Refereed)

With increased chemical diversity and structural complexity comes the opportunities for innovative materials possessing advantageous properties. Herein, we combine predictive first-principles calculations with experimental synthesis, to explore the origin of formation of the atomically laminated i-MAX phases. By probing (Mo2/3M1/32)(2)AC (where M-2 = Sc, Y and A = Al, Ga, In, Si, Ge, In), we predict seven stable i-MAX phases, five of which should have a retained stability at high temperatures. (Mo2/3Sc1/3)(2)GaC and (Mo2/3Y1/3)(2)GaC were experimentally verified, displaying the characteristic in-plane chemical order of Mo and Sc/Y and Kagome-like ordering of the A-element. We suggest that the formation of i-MAX phases requires a significantly different size of the two metals, and a preferable smaller size of the A-element. Furthermore, the population of antibonding orbitals should be minimized, which for the metals herein (Mo and Sc/Y) means that A elements from Group 13 (Al, Ga, In) are favored over Group 14 (Si, Ge, Sn). Using these guidelines, we foresee a widening of elemental space for the family of i-MAX phases and expect more phases to be synthesized, which will realize useful properties. Furthermore, based on i-MAX phases as parent materials for 2D MXenes, we also expect that the range of MXene compositions will be expanded.

• 37.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
Univ Grenoble Alpes, France. Univ Grenoble Alpes, France. Univ Grenoble Alpes, France. ESRF, France. ESRF, France. Univ Grenoble Alpes, France. Inst Chim Clermont Ferrand, France. UCLouvain, Belgium. UCLouvain, Belgium. 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. Drexel Univ, PA 19104 USA. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
Rare-earth (RE) nanolaminates Mo4RE4Al7C3 featuring ferromagnetism and mixed-valence states2018In: PHYSICAL REVIEW MATERIALS, ISSN 2475-9953, Vol. 2, no 11, article id 114401Article in journal (Refereed)

Rare-earth-based (RE) nanolaminates have attracted attention recently because of their complicated magnetism and their potential as precursors for strongly correlated two-dimensional materials. In this work, we synthesized a class of nanolaminates with a Mo4RE4Al7C3 chemistry, where RE = Ce or Pr. Powder samples of both phases were characterized with respect to structure and composition. Single crystals of Mo4Ce4Al7C3 were used for magnetization measurements. The crystal structure was investigated by means of x-ray diffraction and scanning transmission electron microscopy. Magnetization analysis reveals a ferromagnetic ground state with a Curie temperature of similar to 10.5 K. X-ray absorption near-edge structure provides experimental evidence that Ce is in a mixed-valence state. X-ray magnetic circular dichroism shows that only the Ce atoms with 4f(1) configuration occupying one of the two possible sites are ferromagnetically coupled, with a saturation moment of similar to 1.2 mu(B) per atom. We thus classify Mo4Ce4Al7C3 as a ferromagnetic, mixed-valence compound.

• 38.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
Uppsala Univ, Sweden. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
Reference binding energies of transition metal carbides by core-level x-ray photoelectron spectroscopy free from Ar+ etching artefacts2018In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 436, p. 102-110Article in journal (Refereed)

We report x-ray photoelectron spectroscopy (XPS) core level binding energies (BEs) for the widely-applicable groups IVb-VIb transition metal carbides (TMCs) TiC, VC, CrC, ZrC, NbC, MoC, HfC, TaC, and WC. Thin film samples are grown in the same deposition system, by dc magnetron co-sputtering from graphite and respective elemental metal targets in Ar atmosphere. To remove surface contaminations resulting from exposure to air during sample transfer from the growth chamber into the XPS system, layers are either (i) Ar+ ion-etched or (ii) UHV-annealed in situ prior to XPS analyses. High resolution XPS spectra reveal that even gentle etching affects the shape of core level signals, as well as BE values, which are systematically offset by 0.2-0.5 eV towards lower BE. These destructive effects of Ar+ ion etch become more pronounced with increasing the metal atom mass due to an increasing carbon-to-metal sputter yield ratio. Systematic analysis reveals that for each row in the periodic table (3d, 4d, and 5d) C 1s BE increases from left to right indicative of a decreased charge transfer from TM to C atoms, hence bond weakening. Moreover, C 1s BE decreases linearly with increasing carbide/metal melting point ratio. Spectra reported here, acquired from a consistent set of samples in the same instrument, should serve as a reference for true deconvolution of complex XPS cases, including multinary carbides, nitrides, and carbonitrides. (C) 2017 Elsevier B.V. All rights reserved.

• 39.
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.
Reliable determination of chemical state in x-ray photoelectron spectroscopy based on sample-work-function referencing to adventitious carbon: Resolving the myth of apparent constant binding energy of the C 1s peak2018In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 451, p. 99-103Article in journal (Refereed)

The full text will be freely available from 2020-04-27 17:09
• 40.
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.

• 41.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Department of Science and Technology. Linköping University, Faculty of Science & Engineering.
Resolving the debated atomic structure of the metastable cubic SiNx tissue phase in nanocomposites with TiN2018In: Physical Review Materials, ISSN 2475-9953, Vol. 2, no 9, article id 093608Article in journal (Refereed)

The TiN/SiNx nanocomposite and nanolaminate systems are the archetype for super if not ultrahard materials. Yet, the nature of the SiNx tissue phase is debated. Here, we show by atomically resolved electron microscopy methods that SiNx is epitaxially stabilized in a NaCl structure on the adjacent TiN(001) surfaces. Additionally, electron energy loss spectroscopy, supported by first-principles density functional theory calculations infer that SiNx hosts Si vacancies.

• 42.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering. Univ Manchester, England.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering. Univ Fed Bahia, Brazil. Univ Fed Bahia, Brazil. 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.
Self-Healing in Carbon Nitride Evidenced As Material Inflation and Superlubric Behavior2018In: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 10, no 19, p. 16238-16243Article in journal (Refereed)

All known materials wear under extended mechanical contacting. Superlubricity may present solutions, but is an expressed mystery in C-based materials. We report negative wear of carbon nitride films; a wear-less condition with mechanically induced material inflation at the nanoscale and friction coefficient approaching ultralow values (0.06). Superlubricity in carbon nitride is expressed as C-N bond breaking for reduced coupling between graphitic-like sheets and eventual N-2 desorption. The transforming surface layer acts as a solid lubricant, whereas the film bulk retains its high elasticity. The present findings offer new means for materials design at the atomic level, and for property optimization in wear-critical applications like magnetic reading devices or nanomachines.

• 43.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
Self-structuring in Zr1-xAlxN films as a function of composition and growth temperature2018In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 8, article id 16327Article in journal (Refereed)

Nanostructure formation via surface-diffusion-mediated segregation of ZrN and AIN in Zr1-xAlxN films during high mobility growth conditions is investigated for 0 amp;lt;= x amp;lt;= 1. The large immiscibility combined with interfacial surface and strain energy balance resulted in a hard nanolabyrinthine lamellar structure with well-defined (semi) coherent c-ZrN and w-AlN domains of sub-nm to similar to 4 nm in 0.2 amp;lt;= x amp;lt;= 0.4 films, as controlled by atom mobility. For high AlN contents (x amp;gt; 0.49) Al-rich ZrN domains attain wurtzite structure within fine equiaxed nanocomposite wurtzite lattice. Slow diffusion in wurtzite films points towards crystal structure dependent driving force for decomposition. The findings of unlikelihood of isostructural decomposition in c-Zr1-xAlxN, and stability of w-Zr1-xAlxN (in large x films) is complemented with first principles calculations.

• 44.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
IHI Ionbond AG, Industriestraße 211, Olten CH-4600, Switzerland. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. 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.
Silicon carbonitride thin films deposited by reactive high power impulse magnetron sputtering2018In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 335, p. 248-256Article in journal (Refereed)

Amorphous silicon carbonitride thin films for biomedical applications were deposited in an industrial coating unit from a silicon target in different argon/nitrogen/acetylene mixtures by reactive high power impulse magnetron sputtering (rHiPIMS). The effects of acetylene (C2H2) flow rate, substrate temperature, substrate bias voltage, and HiPIMS pulse frequency on the film properties were investigated. Low C2H2 flow rates (<10 sccm) resulted in silicon nitride-like film properties, seen from a dense morphology when viewed in cross-sectional scanning electron microscopy, a hardness up to ∼22 GPa as measured by nanoindentation, and Si-N bonds dominating over Si-C bonds in X-ray photoelectron spectroscopy core-level spectra. Higher C2H2 flows resulted in increasingly amorphous carbon-like film properties, with a granular appearance of the film morphology, mass densities below 2 g/cm3 as measured by X-ray reflectivity, and a hardness down to 4.5 GPa. Increasing substrate temperatures and bias voltages resulted in slightly higher film hardnesses and higher compressive residual stresses. The film H/E ratio showed a maximum at film carbon contents ranging between 15 and 30 at.% and at elevated substrate temperatures from 340 °C to 520 °C.

• 45.
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. 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.
Site-controlled growth of GaN nanorod arrays by magnetron sputter epitaxy2018In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 660, p. 950-955Article in journal (Refereed)

Catalyst-free GaN nanorod regular arrays have been realized by reactive magnetron sputter epitaxy. Two nanolithographic methods, nanosphere lithography (NSL) and focused ion beam lithography (FIBL), were applied to pattern Si substrates with TiNx masks. The growth temperature was optimized for achieving selectivity and well-faceted nanorods grown onto the NSL-patterned substrates. With increasing temperature from 875 to 985 °C, we observe different growth behaviors and associate them with selective insensitive, diffusion-dominated, and desorption-dominated zones. To further achieve site-specific and diameter control, these growth parameters were transferred onto FIBL-patterned substrates. Further investigation into the FIBL process through tailoring of milling current and time in combination with varying nanorod growth temperature, suggests that minimization of mask and substrate damage is the key to attain uniform, well-defined, single, and straight nanorods. Destruction of the mask results in selective area growth failure, while damage of the substrate surface promotes inclined nanorods grown into the openings, owning to random oriented nucleation.

• 46.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering. Rhein Westfal TH Aachen, Germany.
Rhein Westfal TH Aachen, Germany. Rhein Westfal TH Aachen, Germany. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
Substantial difference in target surface chemistry between reactive dc and high power impulse magnetron sputtering2018In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 51, no 5, article id 05LT01Article in journal (Refereed)

The nitride layer formed in the target race track during the deposition of stoichiometric TiN thin films is a factor 2.5 thicker for high power impulse magnetron sputtering (HIPIMS), compared to conventional dc processing (DCMS). The phenomenon is explained using x-ray photoelectron spectroscopy analysis of the as-operated Ti target surface chemistry supported by sputter depth profiles, dynamic Monte Carlo simulations employing the TRIDYN code, and plasma chemical investigations by ion mass spectrometry. The target chemistry and the thickness of the nitride layer are found to be determined by the implantation of nitrogen ions, predominantly N+ and N-2(+) for HIPIMS and DCMS, respectively. Knowledge of this method-inherent difference enables robust processing of high quality functional coatings.

• 47.
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. KIT, Germany; TUD, Germany. Virginia Tech, VA 24061 USA; Virginia Tech, VA 24061 USA. University of Calif Berkeley, CA 94720 USA.
Tailoring of surface plasmon resonances in TiN/(Al0.72Sc0.28)N multilayers by dielectric layer thickness variation2018In: Journal of Materials Science, ISSN 0022-2461, E-ISSN 1573-4803, Vol. 53, no 6, p. 4001-4009Article in journal (Refereed)

Alternative designs of plasmonic metamaterials for applications in solar energy-harvesting devices are necessary due to pure noble metal-based nanostructures incompatibility with CMOS technology, limited thermal and chemical stability, and high losses in the visible spectrum. In the present study, we demonstrate the design of a material based on a multilayer architecture with systematically varying dielectric interlayer thicknesses that result in a continuous shift of surface plasmon energy. Plasmon resonance characteristics of metal/semiconductor TiN/(Al,Sc)N multilayer thin films with constant TiN and increasing (Al,Sc)N interlayer thicknesses were analyzed using aberration-corrected and monochromated scanning transmission electron microscopy-based electron energy loss spectroscopy (EELS). EEL spectrum images and line scans were systematically taken across layer interfaces and compared to spectra from the centers of the respective adjacent TiN layer. While a constant value for the TiN bulk plasmon resonance of about 2.50 eV was found, the surface plasmon resonance energy was detected to continuously decrease with increasing (Al,Sc)N interlayer thickness until 2.16 eV is reached. This effect can be understood to be the result of resonant coupling between the TiN bulk and surface plasmons across the dielectric interlayers at very low (Al,Sc)N thicknesses. That energy interval between bulk and decreasing surface plasmon resonances corresponds to wavelengths in the visible spectrum. This shows the potential of tailoring the materials plasmonic response by controlling the (Al,Sc)N interlayer thickness, making TiN-based multilayers good prospects for plasmonic metamaterials in energy devices.

• 48.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
W-Based Atomic Laminates and Their 2D Derivative W1.33C MXene with Vacancy Ordering2018In: Advanced Materials, ISSN 0935-9648, E-ISSN 1521-4095, Vol. 30, no 21, article id 1706409Article in journal (Refereed)

Structural design on the atomic level can provide novel chemistries of hybrid MAX phases and their MXenes. Herein, density functional theory is used to predict phase stability of quaternary i-MAX phases with in-plane chemical order and a general chemistry (W2/3M1/32)(2)AC, where M-2 = Sc, Y (W), and A = Al, Si, Ga, Ge, In, and Sn. Of over 18 compositions probed, only twowith a monoclinic C2/c structureare predicted to be stable: (W2/3Sc1/3)(2)AlC and (W2/3Y1/3)(2)AlC and indeed found to exist. Selectively etching the Al and Sc/Y atoms from these 3D laminates results in W1.33C-based MXene sheets with ordered metal divacancies. Using electrochemical experiments, this MXene is shown to be a new, promising catalyst for the hydrogen evolution reaction. The addition of yet one more element, W, to the stable of M elements known to form MAX phases, and the synthesis of a pure W-based MXene establishes that the etching of i-MAX phases is a fruitful path for creating new MXene chemistries that has hitherto been not possible, a fact that perforce increases the potential of tuning MXene properties for myriad applications.

• 49.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
Age hardening in (Ti1-xAlx)B2+Delta thin films2017In: Scripta Materialia, ISSN 1359-6462, E-ISSN 1872-8456, Vol. 127, p. 122-126Article in journal (Refereed)

Thin films of (Ti0.71Al0.29)B2+1.08 have been deposited by magnetron sputtering. Post-deposition annealing at 1000 degrees C for 1 h results in increased hardness and elastic modulus, from 32 to 37 GPa and from 436 to 461 GPa, respectively. In both as-deposited and annealed states the films adhere well to the substrate, indicating no considerable internal stress. The initial high hardness is attributed to a columnar microstructure consisting of crystalline (Ti,Al)B-2 columns separated by an amorphous B matrix. The observed age hardening corresponds to phase separation within the (Ti,Al)B-2 columns including the formation of Ti-deficient crystallites within the grain interior upon annealing. (C) 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

• 50.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
Drexel University, PA 19104 USA. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering. Drexel University, PA 19104 USA. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
Atomic structure and lattice defects in nanolaminated ternary transition metal borides2017In: MATERIALS RESEARCH LETTERS, ISSN 2166-3831, Vol. 5, no 4, p. 235-241Article in journal (Refereed)

We use analytical aberration-corrected high-resolution scanning transmission electron microscopy to image the atomic structure of the layered ternary transition metal (M) borides, Cr2AlB2, Fe2AlB2, and MoAlB. In these ternaries, MB layers and Al single or double atomic layers are interleaved. The atomic positions of the M elements and Al are clearly resolved by Z-contrast images. The following structural defects are also found and described herein: a 90 degrees twist boundary along [010] in Cr2AlB2, a tilt boundary in Fe2AlB2, and Mo2AlB2-like stacking faults in MoAlB, where some of the MB-based structures are intercalated by one (instead of two) Al layer(s).

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