| 1. |
- Sidnov, K. P., et al.
(författare)
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Effect of alloying on elastic properties of ternary Ni-Al-Ti system: Experimental validation
- 2016
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Ingår i: Journal of Alloys and Compounds. - : ELSEVIER SCIENCE SA. - 0925-8388 .- 1873-4669. ; 688, s. 534-541
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Tidskriftsartikel (refereegranskat)abstract
- Using combustion synthesis approach we fabricated B2 NiAl intermetallic compound as well as quasibinary Ni(Al50Ti50) alloy, where half Al atoms are randomly substituted by transitional metal Ti. Youngs modulus for synthesized materials was measured and appeared to be 222 +/- 10 GPa for NiAl and 175 +/- 15 GPa for Ni(Al50Ti50) phases. Using first-principles simulations in the framework of the Density Functional Theory, we investigate the elastic properties of Ni(Al1-xTix) system, including single-crystal, as well as polycrystalline elastic moduli. Direct comparison of the experimental and theoretical values of the Youngs modulus demonstrates that the employed theoretical approach allows carefully predict elastic properties of NiAl-based intermetallics. In particular, we predict that alloying NiAl with Ti should increase the ductility of the intermetallic phase. (C) 2016 Elsevier B.V. All rights reserved.
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| 2. |
- Evropeytsev, E. A., et al.
(författare)
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Coexistence of type-I and type-II band line-ups in 1-2 monolayer thick GaN/AlN single quantum wells
- 2017
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Ingår i: 4TH INTERNATIONAL SCHOOL AND CONFERENCE ON OPTOELECTRONICS, PHOTONICS, ENGINEERING AND NANOSTRUCTURES (SAINT PETERSBURG OPEN 2017). - : IOP PUBLISHING LTD.
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Konferensbidrag (refereegranskat)abstract
- GaN/AlN quantum wells (QWs) with varied nominal thickness of 0.5-4 monolayers have been studied by time-resolved photoluminescence (PL) spectroscopy. The structures demonstrate an emission peak with the thickness-dependent wavelength in the range 225-320 nm. The observed temporal behavior of PL between 225 and 280 nm can be described as a superposition of fast and slow decaying components with characteristic decay time constants of the order of 0.1-0.7 ns and 7-30 ns, respectively. The fast PL component with the decay time smaller than 1 ns dominates in the thicker GaN insertions and tends to vanish in the thinnest ones, where the slow PL component becomes progressively longer. These observations imply formation in the GaN/AlN monolayer-thick layers of an inhomogeneous excitonic system involving both direct and indirect in space excitons.
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| 3. |
- Toropov, A. A., et al.
(författare)
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AlGaN Nanostructures with Extremely High Room-Temperature Internal Quantum Efficiency of Emission Below 300 nm
- 2017
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Ingår i: Journal of Electronic Materials. - : SPRINGER. - 0361-5235 .- 1543-186X. ; 46:7, s. 3888-3893
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Tidskriftsartikel (refereegranskat)abstract
- We present theoretical optimization of the design of a quantum well (QW) heterostructure based on AlGaN alloys, aimed at achievement of the maximum possible internal quantum efficiency of emission in the mid-ultraviolet spectral range below 300 nm at room temperature. A sample with optimized parameters was fabricated by plasma-assisted molecular beam epitaxy using the submonolayer digital alloying technique for QW formation. High-angle annular dark-field scanning transmission electron microscopy confirmed strong compositional disordering of the thus-fabricated QW, which presumably facilitates lateral localization of charge carriers in the QW plane. Stress evolution in the heterostructure was monitored in real time during growth using a multibeam optical stress sensor intended for measurements of substrate curvature. Time-resolved photoluminescence spectroscopy confirmed that radiative recombination in the fabricated sample dominated in the whole temperature range up to 300 K. This leads to record weak temperature-induced quenching of the QW emission intensity, which at 300 K does not exceed 20% of the low-temperature value.
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| 4. |
- Toropov, A. A., et al.
(författare)
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Exciton recombination in spontaneously formed and artificial quantum wells AlxGa1-xN/AlyGa1-yN (x < y similar to 0.8)
- 2016
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Ingår i: PHYSICA STATUS SOLIDI C: CURRENT TOPICS IN SOLID STATE PHYSICS, VOL 13 NO 5-6. - : WILEY-V C H VERLAG GMBH. ; , s. 232-238
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Konferensbidrag (refereegranskat)abstract
- We report on photoluminescence (PL) spectroscopy and electron microscopy studies of an AlGaN quantum well (QW) structure grown by molecular beam epitaxy under metal-rich conditions with substrate rotation. Both techniques reveal unintentional formation within the AlGaN barriers of a quasiperiodic structure of thin Ga-rich layers, whose period is controlled by both the substrate rotation rate and the AlGaN growth rate. These compositional modulations act as 1-3 monolayer thick QWs emitting below 250 nm with an internal quantum efficiency (IQE) as high as similar to 30% at room temperature under weak excitation. Variational calculations of the QW exciton properties indicate that the observed high IQE can result from strong three-dimensional localization of the excitons confined in the narrow QWs. (C) 2016 WILEY-VCH Verlag GmbH amp; Co. KGaA, Weinheim
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