SLS Structures Research Articles

Electronic Properties of CrB/Co2CO2 Superlattices by Multiple Descriptor-Based Machine Learning Combined with First-Principles.

In recent times, newly unveiled 2D materials exhibiting exceptional characteristics, such as MBenes and MXenes,have gained widespread application across diverse domains, encompassing electronic devices, catalysis, energy storage, sensors, and various others. Nonetheless, numerous technical bottlenecks persist in the development of high-performance, structurally flexible, and adjustable electronic device materials. Research investigations have demonstrated that 2D van der Waals superlattices (vdW SLs) structures comprising materials exhibit exceptional electrical, mechanical, and optical properties. In this work, the advantages of both materials are combined and compose the vdW SLs structure of MBenes and MXenes, thus obtaining materials with excellent electronic properties. Furthermore, it integrates machine learning (ML) with first-principles methods to forecast the electrical properties of MBene/MXene superlattice materials. Initially, various configurations of MBene/MXene superlattice materials are explored, revealing that distinct stacking methods exert significant influence on the electronic structure of MBene/MXene materials. Specifically, the BABA-type stacking of CrB (layer A) and Co2CO2 MXene (layer B) is most stable configureation. Subsequently, multipledescriptors of the structure are constructed to predict the density of states of vdW SLs through the employment of MLtechniques. The best model achieves a mean absolute error (MAE) as low as 0.147 eV.

Enhance the efficiency of green-yellow LED by optimizing the growth condition of preparation layer

Abstract The effects of the preparation layer grown under different conditions, which is an InGaN/GaN SLs structure inserted between the n-GaN layer and the MQWs, on the performance of green-yellow LED have been investigated. In this paper, the quality of InGaN/GaN multiple quantum wells (MQWs) and the optoelectronic properties of LED have been focused on. According to the experimental results, when the growth temperature of GaN barriers in SLs was increased, the interface between InGaN layers and GaN layers became more abrupt, and the indium distribution in the quantum wells became more uniform. In consequence, the forward voltage was reduced, the external quantum efficiency (EQE) was improved. By decreasing the growth rate of the high temperature barriers, the indium uniformity became even better, forward voltage was reduced again and EQE was further improved.

Worst crosstalk analysis in heterogeneous and trench assisted heterogeneous multicore fiber for different core counts and layouts

In order to obtain appreciably low worst crosstalk level in high core count multicore fiber, heterogeneous MCF with different core configurations and layouts have been investigated analytically using coupled mode equation. The variations in worst crosstalk behavior with respect to the bending radius, core configurations, core layouts, and outer cladding thickness have been analyzed. Further, the core count dependent variations in worst crosstalk level, core pitch, and peak bending radius in different core layouts have been presented. It has been observed that the selection of core configuration, core layout, and outer cladding thickness have significant impact on the reduction in worst crosstalk level. For example, in 12-core normal-index heterogeneous MCF with SLS structure, the core Configuration 1 can provide the worst crosstalk level reduced by 7.09 dB and 16.92 dB in comparison to the other two core configurations, i.e., Configuration 2, and Configuration 3, respectively. Further, for the same core count with TA Configuration 1, SLS core layout can achieve the reduced worst crosstalk level in comparison with circular ORS and DRS, hexagonal ORS and DRS respectively by 24.62 dB, 25.86 dB, 28.87 dB and 30.64 dB.

The effect of AlGaN bulk and AlGaN/GaN superlattice cladding layers on performance characteristics of deep violet InGaN DQW lasers

This paper reports performance characteristics of InGaN-based DQW laser diodes with different SLS cladding layer (CL) structures using the ISE TCAD software. LDs with SLSs as CLs were shown to have superior optical and electrical properties compared to LDs with bulk AlGaN CLs.The simulation results show the variation of output power, threshold current, slope efficiency, and differential quantum efficiency (DQE) from 13.51 to 10.88 mA, 20.92 to 41.27 mW, 1.83 to 1.87 W/A and 57.88 to 59.10%, for bulk to SLS CLs. Results show the increased operating current, electron and hole carrier densities and radiative recombination which enhanced output power and reduced threshold current for the structure with the SLS down CL. Using SLS in upper CL doesn't have significant effect on operating current, it increase the slope efficiency and DQE. Using SLS structure simultaneously in up and down CLs enhances the output power, DQE and slop efficiency, and decreases the threshold current.

InGaAs/InAsSb strained layer superlattices for mid-wave infrared detectors

Investigation of growth and properties of InGaAs/InAsSb strained layer superlattices, identified as ternary strained layer superlattices (ternary SLSs), is reported. The material space for the antimony-based SLS detector development is expanded beyond InAs/InAsSb and InAs/(In)GaSb by incorporating Ga into InAs. It was found that this not only provides support for strain compensation but also enhances the infrared (IR) absorption properties. A unique InGaAs/InAsSb SLS exists when the conduction band of InGaAs aligns with that of InAsSb. The bandgap of this specific InGaAs/InAsSb SLS can then be tuned by adjusting the thickness of both constituents. Due to the enhanced electron-hole wavefunction overlap, a significant increase in the absorption coefficient was theoretically predicted for ternary SLS as compared to current state-of-the-art InAs/InAsSb SLS structures, and an approximately 30%–35% increase in the absorption coefficient was experimentally observed. All the samples examined in this work were designed to have the same bandgap of approximately 0.240 eV (5.6 μm) at 150 K.

Crystal structure analysis of icosahedral lumazine synthase fromSalmonella typhimurium, an antibacterial drug target

Riboflavin biosynthesis is an essential pathway in bacteria, in contrast to animals, which obtain riboflavin from their diet. Therefore, the enzymes involved in the riboflavin-biosynthesis pathway are potential targets for the development of antibacterial drugs. Lumazine synthase, an enzyme that is involved in the penultimate step of riboflavin biosynthesis, catalyzes the formation of 6,7-dimethyl-8-ribityllumazine from 3,4-dihydroxy-2-butanone 4-phosphate and 5-amino-6-ribitylamino-2,4-(1H,3H)-pyrimidinedione. Lumazine synthase from Salmonella typhimurium (sLS) has been cloned, overexpressed, purified and was crystallized in three forms, each with different crystal packing. The crystal structure of sLS in the monoclinic space group P2(1) has been determined with 60 subunits per asymmetric unit, packed as an icosahedron, at 3.57 Å resolution. Interestingly, sLS contains an N-terminal proline residue (Pro11) which had previously been suggested to disrupt the formation of the icosohedral assembly. In addition, comparison of the structure of sLS with known orthologous lumazine synthase structures allowed identification of the amino-acid residues involved in substrate binding and catalysis. The sLS structure reported here could serve as a starting point for the development of species-specific antibacterial drugs.

In silico study on the effect of F19T mutation on amyloid-b peptide (10-35)

The wild type (WT) amyloid-beta (10-35) peptide, Abeta (10-35), and its F19T mutant have been studied by molecular dynamics simulations at 340 K in explicit water solvent each for over 3.4 ms. The WT peptide has a strong preference to form an E22-K28 loop (44% of total conformations) and a reasonable stability for a strand-loop-strand (SLS, L17-M35) (9%). The F19T mutant has a significantly lower population of E22-K28 loop (14%) and SLS structure (1.7%), but has a high population of Q15-D23 loop (48%). A specific interaction pattern among D23, V24, E22 and K28 was found to stabilize the E22-K28 loop in WT. Our results are in agreement with several experimental observations including: (1) the NOE constraints for the Abeta are reproduced; (2) the regions (15-23) and (22-28) can form loops; (3) the WT peptide is more structured than the F19T mutant. The current results also support our early proposal that the SLS structure might be important intermediate for monomer deposition to fibril, which explains the experimental fact that F19T mutant resists deposition to fibril.

Mass exchange in an experimental new-generation life support system model based on biological regeneration of environment

An experimental model of a biological life support system was used to evaluate qualitative and quantitative parameters of the internal mass exchange. The photosynthesizing unit included the higher plant component (wheat and radish), and the heterotrophic unit consisted of a soil-like substrate, California warms, mushrooms and microbial microflora. The gas mass exchange involved evolution of oxygen by the photosynthesizing component and its uptake by the heterotroph component along with the formation and maintaining of the SLS structure, growth of mushrooms and California worms, human respiration, and some other processes. Human presence in the system in the form of “virtual human” that at regular intervals took part in the respirative gas exchange during the experiment. Experimental data demonstrated good oxygen/carbon dioxide balance, and the closure of the cycles of these gases was almost complete. The water cycle was nearly 100% closed. The main components in the water mass exchange were transpiration water and the watering solution with mineral elements. Human consumption of the edible plant biomass (grains and roots) was simulated by processing these products by a unique physicochemical method of oxidizing them to inorganic mineral compounds, which were then returned into the system and fully assimilated by the plants. The oxidation was achieved by “wet combustion” of organic biomass, using hydrogen peroxide following a special procedure, which does not require high temperature and pressure. Hydrogen peroxide is produced from the water inside the system. The closure of the cycle was estimated for individual elements and compounds. Stoichiometric proportions are given for the main components included in the experimental model of the system. Approaches to the mathematical modeling of the cycling processes are discussed, using the data of the experimental model. Nitrogen, as a representative of biogmic elements, shows an almost 100% closure of the cycle inside the system. The proposed experimental model of a biological system is discussed as a candidate for potential application in the investigations aimed at creating ecosystems with largely closed cycles of the internal mass exchange. The formation and maintenance of sustainable cycling of vitally important chemical elements and compounds in biological life support systems (BLSS) is an extremely pressing problem. To attain the stable functioning of biological life support systems (BLSS) and to maintain a high degree of closure of material cycles in than, it is essential to understand the character of mass exchange processes and stoichiometnc proportions of the initial and synthesized components of the system.

Atomic incorporation efficiencies for strained [formula omitted] superlattice structures grown by metalorganic vapour phase epitaxy

Symmetrically strained (GaIn)As Ga(PAs) superlattice (symm. SLS) structures have been grown by metalorganic vapour phase epitaxy on (100) GaAs substrate and analyzed by high-resolution X-ray diffraction (XRD) investigations. These studies reveal the high crystalline perfection with respect to small fluctuations in strain and individual layer thicknesses of the 50 period symm. SLS structures, having a total thickness of 1 |Gmm. Dynamical XRD theory has been applied to evaluate the precise values of thicknesses and incorporated concentrations in the respective strained ternary layers. The strain-induced reduction in In-incorporation is determined quantitatively for the compressive strained (GaIn)As layer. The P-incorporation rate and the growth efficiency of the tensile strained Ga(PAs) layer is experimentally evaluated and discussed in conjunction with theoretical incorporation models.

Optical properties of [formula omitted] and [formula omitted] strained-layer superlattices and heterostructures

The optical properties of InAsP InP and InAs InAsP strained-layer heterostructures were studied. Photoluminescence emission from InAs xP 1−x single quantum wells with thicknesses 2–16 nm was observed in the energy range 0.9–1.4 eV. Full width at half maximum of the PL peaks was 12–25 meV for the thinnest walls. The observed energy shifts were in excellent agreement with theoretical predictions using a finite-well model and taking strain effects into account. InAs xP 1−x InP SLS structures with periods of 2–19 nm exhibited emission in the energy range 0.8–1.3 eV. Higher energy transitions were studied by photoconductivity. Infrared transmission measurements on InAs InAs 0.84P 0.16 strained layer superlattices showed an absorption edge about 30meV higher in energy than the InAs bandgap.

Controversy of critical layer thickness for InGaAs/GaAs strained-layer epitaxy

The critical layer thickness for InxGa1−xAs layers in InxGa1−xAs/GaAs single strained quantum wells (SSQW’s) and strained-layer superlattices (SLS’s) are investigated. Photoluminescence microscopy (PLM) images and x-ray rocking curves for two series of SSQW and SLS structures corresponding to many different layer thicknesses were obtained. We find that the PLM technique, which directly images dislocations and is sensitive to low dislocation densities, is much more suitable for determining the onset of dislocation creation. The x-ray technique can detect lattice relaxation by dislocations but only at relatively high densities of dislocations. Using the former technique, we determine critical thicknesses of 190 Å for SSQW’s and 250 Å for SLS’s with x≊0.2. These results are near the theoretical predictions of J. W. Matthews, S. Mader, and T. B. Light [J. Appl. Phys. 41, 3800 (1970)] (150 and 300 Å, respectively) and are much lower than results obtained by x-ray or other techniques which sense lattice relaxation.

Ion Implantation Disorder in Strained-Layer Superlattices

AbstractCantilever-beam bending and RBS channeling measurements have been used to examine implantation-induced disorder and stress buildup in In0.2Ga0.8As/GaAs SLS structures. Implantation fluences from 1011 to 1015/cm2 were used for 150 keV Si, 320 keV Kr, and 250 keV Zn in SLS and GaAs bulk materials. The critical fluence for saturation of compressive stress occurs prior to amorphous layer formation and is followed by stress relief. For all the ions the maximum ion induced stress scales with energy density into atomic processes and stress relief occurs above ∼1 × 1020: keV/cm3. Stress relief is more pronounced for the SLSs than for bulk GaAs. We suggest that stress-relief may lead to slip or other forms of inelastic material flow in SLSs, which would be undesirable for active regions in device applications. Such material flow may be avoided by limiting maximum fluences or by multiplestep implantation and annealing cycles (or hot implants) at high fluences.

An Evaluation of Implantation-Disordering of (Inga)As/Gaas Strained-Layer Superlattices

AbstractWe have examined the optical and transport properties of In.2Ga.8As/GaAs straled-kayer superlZotices (SLS's), which have been implanted either with 5 × 1015/cm2, 250keV Zn+ or with 5 × 1014/cm2, 70keV Be+ and annealed under an arsenic overpressure at 600 °C. For both cases, electrical activation in the implantation-doped regions equalled that of similar implants and anneals in bulk GaAs, even though the Be implant retained the SLS structure, while the Zn implant intermixed the SLS layers to produce an alloy semiconductor of the average SLS composition. Photoluminescence intensities in the annealed implanted regions were significantly reduced from that of virgin material, apparently due to residual implant damage. Diodes formed from both the Be- and the Zn-implanted SLS's produced electroluminescence intensity comparable to that of grown-junction SLS diodes in the same chemical system, despite the implantation processing and the potential for vertical lattice mismatch in the Zn-disordered SLS device. These results indicate that Zn-disordering can be as useful in strained-layer superlattices as in lattice-matched systems.