Altering the Optical Properties of GaAsSb-Capped InAs Quantum Dots by Means of InAlAs Interlayers

Abstract In this work, we investigate the optical properties of InAs quantum dots (QDs) capped with composite In0.15Al0.85As/GaAs0.85Sb0.15 strain-reducing layers (SRLs) by means of high-resolution X-ray diffraction (HRXRD) and photoluminescence (PL) spectroscopy at 77 K. Thin In0.15Al0.85As layers with thickness t = 20 Å, 40 Å, and 60 Å were inserted between the QDs and a 60-Å-thick GaAs0.85Sb0.15 layer. The type II emissions observed for GaAs0.85Sb0.15-capped InAs QDs were suppressed by the insertion of the In0.15Al0.85As interlayer. Moreover, the emission wavelength was blueshifted for t = 20 Å and redshifted for t ≥ 40 Å resulting from the increased confinement potential and increased strain, respectively. The ground state and excited state energy separation is increased reaching 106 meV for t = 60 Å compared to 64 meV for the QDs capped with only GaAsSb SRL. In addition, the use of the In0.15Al0.85As layers narrows significantly the QD spectral linewidth from 52 to 35 meV for the samples with 40- and 60-Å-thick In0.15Al0.85As interlayers

RC beam strengthening using hinge and anchorage approach

Retrofitting of existing structures using adhesively bonded plates has been a major growth area in civil engineering and has gained well-deserved popularity over the past few years. This strengthening technique is in line with sustainable practices in construction and can be used to preserve eminent structures of historical or cultural values. This study aims to present an ideal design model for strengthening reinforced concrete elements using the hinge and anchorage design philosophies for retrofitting and plating existing structures. This includes a check on the intermediate crack (IC), critical diagonal crack (CDC), and plate end (PE) debonding mechanisms. The results of a theoretical model for an FRP plated reinforced concrete beam element were presented, and the findings showed that plating increased the shear at the datum point to cause a diagonal crack by 46.7%. The increase in moment capacity due to plating the hogging region was 64.3% while allowing for 30% moment redistribution from the sagging region to the hogging region. The accompanying increase in uniformly distributed load due to 30% moment redistribution was 42.8%. The results of the theoretical model were compared with previous design models for IC debonding to which it has been shown that following the anchorage approach, a higher strain in the plate may be allowed as compared to the hinge approach. In addition to the theoretical model presented, analysis on an FRP plated RC beam and slab were also presented to show the effect of different plate widths on the moment capacity and PE moment capacity

Evolving sequence mutations in the Middle East Respiratory Syndrome Coronavirus (MERS-CoV)

Background: Middle East respiratory syndrome coronavirus (MERS-CoV) has continued to cause sporadic outbreaks of severe respiratory tract infection over the last 8 years. Methods: Complete genome sequencing using next-generation sequencing was performed for MERS-CoV isolates from cases that occurred in Riyadh between 2015 and 2019. Phylogenetic analysis and molecular mutational analysis were carried out to investigate disease severity. Results: A total of eight MERS-CoV isolates were subjected to complete genome sequencing. Phylogenetic analysis resulted in the assembly of 7/8 sequences within lineage 3 and one sequence within lineage 4 showing complex genomic recombination. The isolates contained a variety of unique amino acid substitutions in ORF1ab (41), the N protein (10), the S protein (9) and ORF4b (5). Conclusion: Our study shows that MERS-CoV is evolving. The emergence of new variants carries the potential for increased virulence and could impose a challenge to the global health system. We recommend the sequencing every new MERS-CoV isolate to observe the changes in the virus and relate them to clinical outcomes

Optical properties of self-assembled InAs quantum dots based P–I–N structures grown on GaAs and Si substrates by Molecular Beam Epitaxy

Extensive work on InAs quantum dots grown on GaAs substrates has been reported in the literature. However, research in the use of different substrate materials such as silicon to achieve an ideal and full integration of photonic and electronic systems is still a challenge. In this work we have investigated the effect of the substrate material (Si and GaAs) and strain reducing layer on the optical properties of InAs quantum dots for possible applications in laser devices grown by Molecular Beam Epitaxy. Two InAs quantum dots structures with similar active regions grown on GaAs and Si substrates using strain reducing layer consisting of InAs QDs/6 nm In0.15Ga0.85As have been investigated. Atomic Force Microscopy, Transmission Electron Microscopy, and photoluminescence have been used for the characterization of the samples. We have observed a red shift of the InAs QD photoluminescence peak energy for the sample grown on Si substrate as compared to the sample grown on GaAs substrate, which was associated with residual biaxial strain from the Si/GaAs heterointerface. This red-shift of the photoluminescence peak energy is accompanied by a broadening of the photoluminescence spectrum from ∼31 meV to a value of ∼46 meV. This broadening is attributed to the quantum dots size inhomogeneity increase for samples grown on Si substrate. This result open new insights for the controlling the emission of InAs quantum dots for photonic devices integration using Si substrates