| 1. |
- Halim, Joseph, 1985-, et al.
(författare)
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Synthesis of Two-Dimensional Nb1.33C (MXene) with Randomly Distributed Vacancies by Etching of the Quaternary Solid Solution (Nb2/3Sc1/3)2AlC MAX Phase
- 2018
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Ingår i: ACS Applied Nano Materials. - : American Chemical Society (ACS). - 2574-0970. ; 1:6, s. 2455-2460
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Tidskriftsartikel (refereegranskat)abstract
- Introducing point defects in two-dimensional (2D) materials can alter or enhance their properties. Here, we demonstrate how etching a laminated (Nb2/3Sc1/3)2AlC MAX phase (solid solution) of both the Sc and Al atoms results in a 2D Nb1.33C material (MXene) with a large number of vacancies and vacancy clusters. This method is applicable to any quaternary, or higher, MAX phase, wherein one of the transition metals is more reactive than the other and could be of vital importance in applications such as catalysis and energy storage. We also report, for the first time, on the existence of solid solution (Nb2/3Sc1/3)3AlC2 and (Nb2/3Sc1/3)4AlC3 phases.
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| 2. |
- Junaid, Muhammad, et al.
(författare)
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Epitaxial Growth of GaN (0001)/Al2O3 (0001) by Reactive High Power Impulse Magnetron Sputter Deposition
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Epitaxial GaN (0001) thin films were grown on Al2O3 (0001) substrates by reactive high power impulse magnetron sputtering of liquid Ga targets in a mixed N2/Ar discharge. A combination of x-ray diffraction, electron microscopy, atomic force microscopy, μ-Raman mapping and spectroscopy, μ-photoluminescence, time of flight elastic recoil detection, and cathodoluminescence showed the formation of relaxed and strained domains in the same films. While the strained domains form due to ion bombardment during growth, the relaxed domains exhibit
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| 3. |
- Mockuté, Aurelija, et al.
(författare)
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Age hardening in (Ti1-xAlx)B2+Delta thin films
- 2017
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Ingår i: Scripta Materialia. - : Elsevier BV. - 1359-6462 .- 1872-8456. ; 127, s. 122-126
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 4. |
- Mockuté, Aurelija, et al.
(författare)
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Synthesis and characterization of (Ti1-xAlx)B2+Delta thin films from combinatorial magnetron sputtering
- 2019
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Ingår i: Thin Solid Films. - : ELSEVIER SCIENCE SA. - 0040-6090 .- 1879-2731. ; 669, s. 181-187
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Tidskriftsartikel (refereegranskat)abstract
- (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.
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| 5. |
- Muhammad, Junaid, et al.
(författare)
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Two-domain formation during the epitaxial growth of GaN (0001) on c-plane Al2O3 (0001) by high power impulse magnetron sputtering
- 2011
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Ingår i: Journal of Applied Physics. - : American Institute of Physics (AIP). - 0021-8979 .- 1089-7550. ; 110:12, s. 123519-
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Tidskriftsartikel (refereegranskat)abstract
- We study the effect of high power pulses in reactive magnetron sputter epitaxy on the structural properties of GaN (0001) thin films grown directly on Al2O3 (0001) substrates. The epilayers are grown by sputtering from a liquid Ga target, using a high power impulse magnetron sputtering power supply in a mixed N2/Ar discharge. X-ray diffraction, micro-Raman, micro-photoluminescence, and transmission electron microscopy investigations show the formation of two distinct types of domains. One almost fully relaxed domain exhibits superior structural and optical properties as evidenced by rocking curves with a full width at half maximum of 885 arc sec and a low temperature band edge luminescence at 3.47 eV with the full width at half maximum of 10 meV. The other domain exhibits a 14 times higher isotropic strain component, which is due to the higher densities of the point and extended defects, resulting from the ion bombardment during growth. Voids form at the domain boundaries. Mechanisms for the formation of differently strained domains, along with voids during the epitaxial growth of GaN are discussed.
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| 6. |
- Palisaitis, Justinas, et al.
(författare)
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Where is the unpaired transition metal in substoichiometric diboride line compounds?
- 2021
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Ingår i: Acta Materialia. - : PERGAMON-ELSEVIER SCIENCE LTD. - 1359-6454 .- 1873-2453. ; 204
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Tidskriftsartikel (refereegranskat)abstract
- The atomic structure and local composition of high quality epitaxial substoichiometric titanium diboride (TiB1.9) thin film, deposited by unbalanced magnetron sputtering, were studied using analytical high-resolution scanning transmission electron microscopy, density functional theory, and image simulations. The unpaired Ti is pinpointed to inclusion of Ti-based stacking faults within a few atomic layers, which terminates the {1 (1) over bar 00} prismatic planes of the crystal structure and attributed to the absence of B between Ti planes that locally relaxes the structure. This mechanism allows the line compound to accommodate off-stoichiometry and remain a line compound between defects. The planar defects are embedded in otherwise stoichiometric TiB2 and are delineated by insertion of dislocations. An accompanied decrease in Ti-Ti bond lengths along and across the faults is observed. (c) 2020ActaMaterialiaInc. PublishedbyElsevierLtd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/)
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| 7. |
- ul-Hassan, Jawad, et al.
(författare)
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Growth and properties of SiC on-axis homoepitaxial layers
- 2010
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Ingår i: ICSCRM 2009. - : Trans Tech Publications. ; , s. 83-88
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Konferensbidrag (refereegranskat)abstract
- Homoepitaxial growth has been performed on 3 Si-face on-axis 4H-SiC substrates using standard gas system in a horizontal Hot-wall chemical vapor deposition system. Substrate surface damages are found to act as preferential nucleation sites for 3C inclusions also, the surface morphology after in-situ etching is found to largely influence the polytype stability in the epilayer. Different in-situ etching conditions were studied where Si-rich conditions are found to be better. Growth parameters and starting growth conditions are refined to obtain stable polytype in the epilayer. High quality homoepitaxial layers with 100% 4H-SiC are obtained on 3 substrates. Different optical and structural techniques are used to characterize the layers and to understand the growth mechanisms. The layers are found to be of high quality and no epitaxial defects typically found on off-axis epitaxial layers are observed. A high surface roughness is observed in these layers, however higher growth rate significantly lowers the surface roughness without affecting the polytype stability in the epilayer.
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