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| 2. |
- Hultman, Lars, et al.
(författare)
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Interface structure in superhard TiN-SiN nanolaminates and nanocomposites : film growth experiments and ab initio calculations
- 2007
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 75
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Tidskriftsartikel (refereegranskat)abstract
- Nanostructured materials-the subject of much of contemporary materials research-are defined by internal interfaces, the nature of which is largely unknown. Yet, the interfaces determine the properties of nanocomposites and nanolaminates. An example is nanocomposites with extreme hardness70-90 GPa, which is of the order of, or higher than, diamond. The Ti-Si-N system, in particular, is attracting attention for the synthesis of such superhard materials. In this case, the nanocomposite structure consists of TiN nanocrystallites encapsulated in a fully percolated SiNx "tissue phase" (1 to 2 monolayers thick) that is assumed to be amorphous. Here, we show that the interfacial tissue phase can be crystalline, and even epitaxial with complex surface reconstructions. Using in situ structural analyses combined with ab initio calculations, we find that SiNx layers grow epitaxially, giving rise to strong interfacial bonding, on both TiN(001) and TiN(111) surfaces. In addition, TiN overlayers grow epitaxially on SiNx/TiN(001) bilayers in nanolaminate structures. These results provide insight into the development of design rules for new nanostructured materials.
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| 3. |
- Höglund, Carina, et al.
(författare)
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Cubic Sc1-xAlxN solid solution thin films deposited by reactive magnetron sputter epitaxy onto ScN(111)
- 2009
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Ingår i: JOURNAL OF APPLIED PHYSICS. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 105:11, s. 132862-
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Tidskriftsartikel (refereegranskat)abstract
- Reactive magnetron sputter epitaxy was used to deposit thin solid films of Sc1-xAlxN (0 andlt;= x andlt;= 1) onto MgO(111) substrates with ScN(111) seed layers. Stoichiometric films were deposited from elemental Sc and Al targets at substrate temperatures of 600 S C. The films were analyzed by Rutherford backscattering spectroscopy, elastic recoil detection analysis, x-ray diffraction, and transmission electron microscopy. Results show that rocksalt structure (c)-Sc1-xAlxN solid solutions with AlN molar fractions up to similar to 60% can be synthesized. For higher AlN contents, the system phase separates into c- and wurtzite structure (w)-Sc1-xAlxN domains. The w-domains are present in three different orientations relative to the seed layer, namely, Sc1-xAlxN(0001)parallel to ScN(111) with Sc1-xAlxN[(1) over bar2 (1) over bar0]parallel to ScN[1 (1) over bar0], Sc1-xAlxN(10 (1) over bar1)parallel to ScN(111) with Sc1-xAlxN[(1) over bar2 (1) over bar0]parallel to ScN[1 (1) over bar0], and Sc1-xAlxN(10 (1) over bar1)parallel to ScN(113). The results are compared to first-principles density functional theory calculations for the mixing enthalpies of c-, w-, and zinc blende Sc0.50Al0.50N solid solutions, yielding metastability with respect to phase separation for all temperatures below the melting points of AlN and ScN.
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| 4. |
- Höglund, Carina, et al.
(författare)
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Wurtzite-structure Sc1-xAlxN solid solution films grown by reactive magnetron sputter epitaxy : structural characterization and first-principles calculations
- 2010
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Ingår i: Journal of Applied Physics. - : American Institute of Physics. - 0021-8979 .- 1089-7550. ; 107:12, s. 123515-
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Tidskriftsartikel (refereegranskat)abstract
- AlN(0001) was alloyed with ScN with molar fractions up to ~22%, while retaining a singlecrystal wurtzite (w-) structure and with lattice parameters matching calculated values. Material synthesis was realized by magnetron sputter epitaxy of thin films starting from optimal conditions for the formation of w-AlN onto lattice-matched w-AlN seed layers on Al2O3(0001) and MgO(111) substrates. Films with ScN contents between 23% and ~50% exhibit phase separation into nanocrystalline ScN and AlN, while ScN-rich growth conditions yield a transformation to rocksalt-structure Sc1-xAlxN(111) films. The experimental results are analyzed with ion beam analysis, X-ray diffraction, and transmission electron microscopy, together with ab-initio calculations of mixing enthalpies and lattice parameters of solid solutions in wurtzite, rocksalt, and layered hexagonal phases.
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| 5. |
- Karlsson, Linda, 1984-
(författare)
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Transmission Electron Microscopy of 2D Materials : Structure and Surface Properties
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- During recent years, new types of materials have been discovered with unique properties. One family of such materials are two-dimensional materials, which include graphene and MXene. These materials are stronger, more flexible, and have higher conductivity than other materials. As such they are highly interesting for new applications, e.g. specialized in vivo drug delivery systems, hydrogen storage, or as replacements of common materials in e.g. batteries, bulletproof clothing, and sensors. The list of potential applications is long for these new materials.As these materials are almost entirely made up of surfaces, their properties are strongly influenced by interaction between their surfaces, as well as with molecules or adatoms attached to the surfaces (surface groups). This interaction can change the materials and their properties, and it is therefore imperative to understand the underlying mechanisms. Surface groups on two-dimensional materials can be studied by Transmission Electron Microscopy (TEM), where high energy electrons are transmitted through a sample and the resulting image is recorded. However, the high energy needed to get enough resolution to observe single atoms damages the sample and limits the type of materials which can be analyzed. Lowering the electron energy decreases the damage, but the image resolution at such conditions is severely limited by inherent imperfections (aberrations) in the TEM. During the last years, new TEM models have been developed which employ a low acceleration voltage together with aberration correction, enabling imaging at the atomic scale without damaging the samples. These aberration-corrected TEMs are important tools in understanding the structure and chemistry of two-dimensional materials.In this thesis the two-dimensional materials graphene and Ti3C2Tx MXene have been investigated by low-voltage, aberration-corrected (scanning) TEM. High temperature annealing of graphene covered by residues from the synthesis is studied, as well as the structure and surface groups on single and double Ti3C2Tx MXene. These results are important contributions to the understanding of this class of materials and how their properties can be controlled.
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