Degradation Mechanism of Crystalline Quality and Luminescence in In0.42Ga0.58N/GaN Double Heterostructures with Porous InGaN Layer

ABSTRACTThe apparent thermal stability of hydrogen passivated Mg acceptors in GaN is a function of the annealing ambient employed, with H2 leading to a reactivation temperature approximately 150°C higher than N2. The dissociation of Mg-H complexes and the loss of hydrogen from GaN are sequential processes, with reactivation occurring at ≤700°C for annealing under N2, while significant concentrations of hydrogen remain in the crystal even at 900°C in implanted samples. The hydrogen is gettered to regions of highest defect density such as the InGaN layer in a GaN/InGaN double heterostructure. The addition of an accelerating potential for 2H+ ions in the plasma did not greatly affect the deuterium profiles.

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Structure and Orientation of As Precipitates in LT-MBE Grown GaAs

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100088816 ◽

1991 ◽

Vol 49 ◽

pp. 900-901 ◽

Cited By ~ 1

Author(s):

Alain Claverie ◽

Zuzanna Liliental-Weber

Keyword(s):

Transport Properties ◽

Layer Thickness ◽

Growth Temperature ◽

Low Temperatures ◽

Lattice Parameter ◽

Crystalline Quality ◽

Insulating Properties ◽

Lt Gaas

GaAs layers grown by MBE at low temperatures (in the 200°C range, LT-GaAs) have been reported to have very interesting electronic and transport properties. Previous studies have shown that, before annealing, the crystalline quality of the layers is related to the growth temperature. Lowering the temperature or increasing the layer thickness generally results in some columnar polycrystalline growth. For the best “temperature-thickness” combinations, the layers may be very As rich (up to 1.25%) resulting in an up to 0.15% increase of the lattice parameter, consistent with the excess As. Only after annealing are the technologically important semi-insulating properties of these layers observed. When annealed in As atmosphere at about 600°C a decrease of the lattice parameter to the substrate value is observed. TEM studies show formation of precipitates which are supposed to be As related since the average As concentration remains almost unchanged upon annealing.

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TEM study of very thin InGaAsP layers grown by liquid-phase epitaxy

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100176496 ◽

1990 ◽

Vol 48 (4) ◽

pp. 672-673

Author(s):

N.A. Bert ◽

A.O. Kosogov

Keyword(s):

Liquid Phase ◽

Liquid Phase Epitaxy ◽

Chemical Vapor ◽

Growth Conditions ◽

Dark Field ◽

Organic Chemical ◽

Simple Liquid ◽

Cross Sectional ◽

Conventional Procedure ◽

Double Heterostructures

The very thin (<100 Å) InGaAsP layers were grown not only by molecular beam epitaxy and metal-organic chemical vapor deposition but recently also by simple liquid phase epitaxy (LPE) technique. Characterization of their thickness, interfase abruptness and lattice defects is important and requires TEM methods to be used.The samples were InGaAsP/InGaP double heterostructures grown on (111)A GaAs substrate. The exact growth conditions are described in Ref.1. The salient points are that the quarternary layers were being grown at 750°C during a fast movement of substrate and a convection caused in the melt by that movement was eliminated. TEM cross-section specimens were prepared by means of conventional procedure. The studies were conducted in EM 420T and JEM 4000EX instruments.The (200) dark-field cross-sectional imaging is the most appropriate TEM technique to distinguish between individual layers in 111-v semiconductor heterostructures.

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Structures of c-di-GMP/cGAMP degrading phosphodiesterase VcEAL: identification of a novel conformational switch and its implication

Biochemical Journal ◽

10.1042/bcj20190399 ◽

2019 ◽

Vol 476 (21) ◽

pp. 3333-3353 ◽

Cited By ~ 3

Author(s):

Malti Yadav ◽

Kamalendu Pal ◽

Udayaditya Sen

Keyword(s):

Active Site ◽

Metal Binding ◽

Metal Ion ◽

Triosephosphate Isomerase ◽

Catalytic Mechanism ◽

Degradation Mechanism ◽

Structural Basis ◽

Conserved Residues ◽

Phosphodiester Bond ◽

Cyclic Dinucleotides

Cyclic dinucleotides (CDNs) have emerged as the central molecules that aid bacteria to adapt and thrive in changing environmental conditions. Therefore, tight regulation of intracellular CDN concentration by counteracting the action of dinucleotide cyclases and phosphodiesterases (PDEs) is critical. Here, we demonstrate that a putative stand-alone EAL domain PDE from Vibrio cholerae (VcEAL) is capable to degrade both the second messenger c-di-GMP and hybrid 3′3′-cyclic GMP–AMP (cGAMP). To unveil their degradation mechanism, we have determined high-resolution crystal structures of VcEAL with Ca2+, c-di-GMP-Ca2+, 5′-pGpG-Ca2+ and cGAMP-Ca2+, the latter provides the first structural basis of cGAMP hydrolysis. Structural studies reveal a typical triosephosphate isomerase barrel-fold with substrate c-di-GMP/cGAMP bound in an extended conformation. Highly conserved residues specifically bind the guanine base of c-di-GMP/cGAMP in the G2 site while the semi-conserved nature of residues at the G1 site could act as a specificity determinant. Two metal ions, co-ordinated with six stubbornly conserved residues and two non-bridging scissile phosphate oxygens of c-di-GMP/cGAMP, activate a water molecule for an in-line attack on the phosphodiester bond, supporting two-metal ion-based catalytic mechanism. PDE activity and biofilm assays of several prudently designed mutants collectively demonstrate that VcEAL active site is charge and size optimized. Intriguingly, in VcEAL-5′-pGpG-Ca2+ structure, β5–α5 loop adopts a novel conformation that along with conserved E131 creates a new metal-binding site. This novel conformation along with several subtle changes in the active site designate VcEAL-5′-pGpG-Ca2+ structure quite different from other 5′-pGpG bound structures reported earlier.

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Stochastic Models of Particle Trajectories in Turbulent Atmosphere Flows by Using the LANGEVIN Equations

Proceedings ◽

10.3390/proceedings2020063032 ◽

2020 ◽

Vol 1 (1) ◽

Author(s):

Youssra El Qasemy ◽

Abdelfatah Achahbar ◽

Abdellatif Khamlichi

Keyword(s):

Wind Speed ◽

Wind Turbine ◽

Classical Method ◽

Degradation Mechanism ◽

Transformation Process ◽

Langevin Equations ◽

Turbulence Data ◽

Power Curves ◽

And Diffusion ◽

Fluctuating Wind

The stochastic behavior of wind speed is a particular characteristic of wind energy production, which affects the degradation mechanism of the turbine, resulting in stochastic charging on the wind turbine. A model stochastic is used in this study to evaluate the efficiency of wind turbine power of whatever degree given fluctuating wind turbulence data. This model is based on the Langevin equations, which characterize, by two coefficients, drift and diffusion functions. These coefficients describe the behavior of the transformation process from the input wind speed to the output data that need to be determined. For this present work, the computation of drift and diffusion functions has been carried out by using the stochastic model to assess the output variables in terms of the torque and power curves as a function of time, and it is compared by the classical method. The results show that the model stochastic can define the efficiency of wind turbine generation more precisely.

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Synthesis, Characterization and Thermal Degradation of Some New 3,5-dimethyl Pyrazole Derivatives

Revista de Chimie ◽

10.37358/rc.17.2.5444 ◽

2017 ◽

Vol 68 (2) ◽

pp. 317-322

Author(s):

Anca Mihaela Mocanu ◽

Constantin Luca ◽

Alina Costina Luca

Keyword(s):

Thermal Degradation ◽

Degradation Mechanism ◽

New Products ◽

Analysis Data ◽

Biological Properties ◽

Elemental Analysis Data ◽

Ftir Analysis ◽

Spectral Measurements ◽

Chemical Structures ◽

And Storage

The purpose of this research is to synthetize, characterize and thermal degradation of new heterolytic derivates with potential biological properties. The derivates synthesis was done by obtaining new molecules with pyralozone structure which combine two pharmacophore entities: the amidosulfonyl-R1,R2 phenoxyacetil with the 3,5-dimethyl pyrazole which can have potential biological properties. The synthesis stages of the new products are presented as well as the elemental analysis data and IR, 1H-NMR spectral measurements made for elucidating the chemical structures and thermostability study which makes evident the temperature range proper for their use and storage. The obtained results were indicative of a good correlation of the structure with the thermal stability as estimated by means of the initial degradation temperatures as well as with the degradation mechanism by means of the TG-FTIR analysis.

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Comparison of phase modulation of GaAs/AlGaAs double heterostructures

Electronics Letters ◽

10.1049/el:19870960 ◽

1987 ◽

Vol 23 (25) ◽

pp. 1391 ◽

Cited By ~ 10

Author(s):

J. Faist ◽

F.K. Reinhart ◽

D. Martin

Keyword(s):

Phase Modulation ◽

Double Heterostructures

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Recent Achievements in Development of TiO2-Based Composite Photocatalytic Materials for Solar Driven Water Purification and Water Splitting

Materials ◽

10.3390/ma13061338 ◽

2020 ◽

Vol 13 (6) ◽

pp. 1338 ◽

Cited By ~ 7

Author(s):

Klara Perović ◽

Francis M. dela Rosa ◽

Marin Kovačić ◽

Hrvoje Kušić ◽

Urška Lavrenčič Štangar ◽

...

Keyword(s):

Water Treatment ◽

Transition Metal ◽

Photocatalytic Degradation ◽

Water Splitting ◽

Water Purification ◽

Degradation Mechanism ◽

Living Environment ◽

Solar Irradiation ◽

Metal Chalcogenides ◽

Photocatalytic Water Splitting

Clean water and the increased use of renewable energy are considered to be two of the main goals in the effort to achieve a sustainable living environment. The fulfillment of these goals may include the use of solar-driven photocatalytic processes that are found to be quite effective in water purification, as well as hydrogen generation. H2 production by water splitting and photocatalytic degradation of organic pollutants in water both rely on the formation of electron/hole (e−/h+) pairs at a semiconducting material upon its excitation by light with sufficient photon energy. Most of the photocatalytic studies involve the use of TiO2 and well-suited model compounds, either as sacrificial agents or pollutants. However, the wider application of this technology requires the harvesting of a broader spectrum of solar irradiation and the suppression of the recombination of photogenerated charge carriers. These limitations can be overcome by the use of different strategies, among which the focus is put on the creation of heterojunctions with another narrow bandgap semiconductor, which can provide high response in the visible light region. In this review paper, we report the most recent advances in the application of TiO2 based heterojunction (semiconductor-semiconductor) composites for photocatalytic water treatment and water splitting. This review article is subdivided into two major parts, namely Photocatalytic water treatment and Photocatalytic water splitting, to give a thorough examination of all achieved progress. The first part provides an overview on photocatalytic degradation mechanism principles, followed by the most recent applications for photocatalytic degradation and mineralization of contaminants of emerging concern (CEC), such as pharmaceuticals and pesticides with a critical insight into removal mechanism, while the second part focuses on fabrication of TiO2-based heterojunctions with carbon-based materials, transition metal oxides, transition metal chalcogenides, and multiple composites that were made of three or more semiconductor materials for photocatalytic water splitting.

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Epitaxial lift-off CdTe/MgCdTe double heterostructures for thin-film and flexible solar cells applications

Applied Physics Letters ◽

10.1063/5.0049377 ◽

2021 ◽

Vol 118 (18) ◽

pp. 181101

Author(s):

Jia Ding ◽

Cheng-Ying Tsai ◽

Zheng Ju ◽

Yong-Hang Zhang

Keyword(s):

Thin Film ◽

Solar Cells ◽

Double Heterostructures ◽

Lift Off

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