| 1. |
- Dahlqvist, Martin, et al.
(författare)
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Complex magnetism in nanolaminated Mn2GaC
- 2014
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- We have used first-principles calculations and Heisenberg Monte Carlo simulations to search for the magnetic ground state of Mn2GaC, a recently synthesized magnetic nanolaminate. We have, independent on method, identified a range of low energy collinear as well as non-collinear magnetic configurations, indicating a highly frustrated magnetic material with several nearly degenerate magnetic states. An experimentally obtained magnetization of only 0.29 per Mn atom in Mn2GaC may be explained by canted spins in an antiferromagnetic configuration of ferromagnetically ordered sub-layers with alternating spin orientation, denoted AFM[0001]. Furthermore, low temperature X-ray diffraction show a new basal plane peak appearing upon a magnetic transition, which is consistent with the here predicted change in inter-layer spacing for the AFM[0001] configuration.
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| 2. |
- Xie, Mengyao, et al.
(författare)
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Structural, free-charge carrier and phonon properties of zinc-blende and wurtizte polymorphs in InN epitaxial layers
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- We present a comprehensive study of the structural, phonon and free electron properties of zincblende InN films containing inclusion of wurtzite InN. Appropriate methods based on X-ray diffraction and Infrared spectroscopic ellipsometry to identify wurtizte and zinc-blende InN and quantify their phase ratio are developed and discussed. Thorough analysis on the formation of the cubic and wurtzite phases is presented and their evolution with film thickness is discussed in detail. The freecharge carrier and phonon properties of the two phases are discussed together with the determination of electron accumulation at the zinc-blende InN (001) and wurtzite (10̅11) surfaces.
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| 3. |
- Fallqvist, Amie, et al.
(författare)
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Evidence for B1-cubic SiNx by Aberration-Corrected Analytical STEM
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- The crystal structure of epitaxially stabilized SiNx layers on TiN(001) was investigated by analytical aberration corrected electron microscopy. Atomically resolved images of the structure, which were acquired by scanning transmission electron microscopy using high angle annular dark field and annular bright field detectors, are used to identify the B1-cubic structure of SiNx. To corroborate the acquired images, image simulations were performed using candidate structures. Complementary to imaging, spatially resolved electron energy loss spectroscopy of the epitaxial SiNx layers was performed to acquire the symmetry specific nitrogen near edge fine-structure. Finally, full potential calculations performed to determine the near edge structure from candidate crystal structures confirms the existence of B1-cubic SiNx.
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| 4. |
- Hsu, Chih-Wei, et al.
(författare)
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Homogeneous high In content InxGa1-x N films by supercycle atomic layer deposition
- 2022
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Ingår i: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films. - : American Institute of Physics (AIP). - 0734-2101 .- 1520-8559. ; 40:6
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- InxGa1-x N is a strategically important material for electronic devices given its tunable bandgap, modulated by the In/Ga ratio. However, current applications are hindered by defects caused by strain relaxation and phase separation in the material. Here, we demonstrate growth of homogeneous InxGa1-x N films with 0.3 < x < 0.8 up to similar to 30 nm using atomic layer deposition (ALD) with a supercycle approach, switching between InN and GaN deposition. The composition is uniform along and across the films, without signs of In segregation. The InxGa1-x N films show higher In-content than the value predicted by the supercycle model. A more pronounced reduction of GPC(InN) than GPC(GaN) during the growth processes of InN and GaN bilayers is concluded based on our analysis. The intermixing between InN and GaN bilayers is suggested to explain the enhanced overall In-content. Our results show the advantage of ALD to prepare high-quality InxGa1-x N films, particularly with high In-content, which is difficult to achieve with other growth methods.
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| 5. |
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| 6. |
- Mockute, Aurelija, et al.
(författare)
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Nanolaminated (Cr,Mn)2AlC alloys by magnetron sputtering and ab initio calculations
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- We present an ab initio theoretical analysis of the temperature-dependent stability of hexagonal inherently nanolaminated (Cr1-xMnx)2AlC. The results indicate energetic stability over the composition range x = 0.0 to 0.5 for temperatures 600 to 900 K. Corresponding alloy thin films were grown by magnetron sputtering from four elemental targets. X-ray diffraction in combination with analytical transmission electron microscopy including electron energy-loss spectroscopy and energy dispersive X-ray spectroscopy analysis revealed that the films were epitaxial (0001)-oriented single crystals with x up to 0.16.
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| 7. |
- Persson, Per O A, et al.
(författare)
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Exploring the thermal behavior and diffusive functionality of structural defects and phase boundaries in near-stoichiometric chromium diborides by in situ scanning transmission electron microscopy
- 2024
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Ingår i: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films. - : A V S AMER INST PHYSICS. - 0734-2101 .- 1520-8559. ; 42:2
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Near-stoichiometric chromium diboride films were subject to in situ annealing inside a scanning transmission electron microscope to access the thermal behavior of the film and embedded structural planar defects. Independent of films' stoichiometry, the planar defects were unaffected by the applied heat treatments. On the contrary, the interfaces between the boron-rich tissue phase and the CrB2 phase were reshaped in the overstoichometric CrB2 film. At high temperatures, diffusion of contact metal species (platinum) from the focused ion beam sample preparation was triggered, with subsequent migration onto the sample. This resulted in the formation of metal-rich regions as directly observed and characterized at the atomic level. We determined that platinum did not react with the diboride structure but is accommodated by various defects present in the film.
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| 8. |
- Petruhins, Andrejs
(författare)
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Synthesis and characterization of Ga-containing MAX phase thin films
- 2014
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The study of magnetic Mn+1AXn (MAX) phases (n = 1 − 3, M – a transition metal, A – an A group element, X – C or N) is a recently established research area, fuelled by theoretical predictions and first confirmed experimentally through alloying of Mn into the well-known Cr2AlC and Cr2GeC. Theoretical phase stability investigations suggested a new magnetic MAX phase, Mn2GaC, containing Ga which is liquid close to room temperature. Hence, alternative routes for MAX phase synthesis were needed, motivating a further development of magnetron sputtering from liquid targets.In this thesis, (Cr1-xMnx)2GaC 0 ≤ x ≤ 1 MAX phase thin films have been synthesized from elemental and/or compound targets, using ultra high vacuum magnetron sputtering. Initial thin film synthesis of Cr2GaC was performed using elemental targets, including liquid Ga. Process optimization ensured optimal target size and crucible geometry for containing the Ga. Films were deposited at 650 °C on MgO(111) substrates. X-ray diffraction and transmission electron microscopy confirms the growth of epitaxial Cr2GaC MAX phase with minor inclusions of Cr3Ga.To explore the magnetic characteristics upon Mn alloying, synthesis of (Cr0.5Mn0.5)2GaC thin films was performed from elemental Ga and C and a composite Cr/Mn target of 1:1 composition. Films were deposited on MgO(111), Al2O3(0001) (with or without NbN seed layer), and 4° off-cut 4H-SiC(0001) substrates. The films are smooth and of high structural quality as confirmed by X-ray diffraction and transmission electron microscopy. The film composition measured by high resolution energy dispersive X-ray spectroscopy confirms a composition corresponding to (Cr0.5Mn0.5)2GaC. The magnetic response, as measured with vibrating sample magnetometry, displays a ferromagnetic component, however, the temperature dependence of the magnetic moments and saturation fields suggests competing magnetic interaction and possible non-collinear magnetic ordering.Finally, inspired by theoretical predictions, a new member of the MAX phase family, Mn2GaC, was synthesized. This is the first MAX phase containing Mn as a sole M element. X-ray diffraction and transmission electron microscopy confirms the characteristic MAX phase structure with a 2:1:1 composition. Theoretical work suggests that the magnetic ground state is almost degenerate between ferromagnetic and anti-ferromagnetic. Vibrating sample magnetometry shows ferromagnetic response with a transition temperature Tc of 230 K. However, also for this phase, complex magnetism is suggested. Altogether, the results indicate a new family of magnetic nanolaminates with a rich variation of magnetic ground states.
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| 9. |
- Rantzer, Annika, et al.
(författare)
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Sputter-deposited a-Si:H for p-i-n photodiodes
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- DC magnetron sputter deposition is explored as an alternative for fabricating vertically integrated sensor systems in the form of p-i-n diodes of hydrogenated amorphous silican deposited on CMOS integrated circuit substrates in a post-processing step. We focus here on dopant oncorporation and surface morphological evolution during synthesis of the p-i-n diode sensor structures. The Doping was accomplished using doped targets in a mixed H2/Ar environment. Incorporated P concetrations range from 2.62 to 4.8 x 1019 cm-3 with corresponding conductivities, σ, up to 1.4 x10-5 ohm-1cm-1. B contentrations are between 2.79 and 6.7 X 1020 cm-3 with σ = 4 x 10-5 to 4 x 10-2 ohm-1cm-1. The results of the dopant incorporation are in agreement with reported molecular dynamics simulations. The best intrinsic films have a light to dark conductivity ratio of 102 for white light at an intensity of 10 W/m2. The dark conductivity is a 8 x 10-9 ohm-1cm-1. We conclude that dc magnetron sputter deposition is a good candidate for future device fabrication.
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| 10. |
- Tao, Quanzheng, 1989-
(författare)
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Synthesis and characterization of two- and three-dimensional nanolaminated carbides
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis is focused towards the synthesis and characterization of novel nanolaminated materials in primarily bulk (powder) form. Of particular interest is magnetic materials, or laminates that can be used as precursor for two-dimensional (2D) materials. 2D materials typically display a large surface-to-volume ratio, and as such they are very promising for applications within energy storage and catalysis. A more recently discovered family of 2D transition metal carbides/nitrides, called MXenes, are currently attracting a lot of attention. MXenes are produced by selective etching of parent 3D nanolaminates, so called MAX phases, facilitating removal of selected atomic layers, and formation of 2D sheets.In my work on new nanolaminates as precursors for 2D materials, I have synthesized (Mo2/3Sc1/3)2AlC and have studied its crystal structure. It was found that Mo and Sc are chemically ordered in the metal layers, with the in-plane ordering motivating the notation i-MAX for this new type of MAX phase alloy. By selective etching of Sc and Al, we thereafter produced a 2D materials with ordered vacancies, Mo1.33C, and studied the electrochemical properties. It was found that the material displayed a high capacitance, ~1200 F cm-3, which is 65% higher that the counterpart without vacancies, Mo2C.I also synthesized a previously not known out-of-plane ordered Mo2ScAlC2 MAX phase. By selective etching of Al, we produced a 2D material, Mo2ScC2, which is correspondingly ordered in the out-of-plane direction. Another related laminated material was also discovered and synthesized, Sc2Al2C3, and its crystal structure was determined. The material is potentially useful for conversion into a 2D material. I have also shown that Sc2Al2C3 is an example of a series of materials with the same crystal structure, with Sc replaced by other metals.Magnetic materials are used in many applications, such as for data storage devices. In particular, layered magnetic materials are of interest due to their anisotropic structure and potential formation of interesting magnetic characteristics. I have been synthesizing and characterizing magnetic nanolaminates, starting with the (V,Mn)3GaC2 MAX phase in the form of an epitaxial thin film. Analysis of the magnetic behavior showed a ferromagnetic response above room temperature I thereafter showed that our previously discovered family of i-MAX phases could be expanded with a subclass of ordered nanolaminates based on rare earth (RE) elements, of the general formula (Mo2/3RE1/3)2AlC , where RE=Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, and Lu. I studied their crystal structure by scanning transmission microscopy (STEM), X-ray diffraction (XRD), and neutron diffraction. We found that these phases can crystalize in three different structures, of space group C2/m, C2/c, and Cmcm, respectively. The magnetic behavior was studied and the magnetic structure of two materials could be determined. We suggest that the complex behavior identified is due to competing magnetic interaction and frustration.I also synthesized another rare earth-based nanolaminate, Mo4Ce4Al7C3. The crystal structure was investigated by single crystal X-ray diffraction and STEM. Magnetization analysis reveal a ferromagnetic ground state below 10.5 K. X-ray absorption near-edge structure provide evidence that Ce is in a mixed-valence state. X-ray magnetic circular dichroism shows that only one of the two Ce sites are magnetic.
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