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The indirect nature of silicon (Si) emission currently limits the monolithic integration of photonic circuitry with Si electronics. Approaches to circumvent the optical shortcomings of Si include band structure engineering via alloying (e.g., Si

The structural and optical properties of buffer mediated epitaxial germanium (Ge) layer were investigated and compared with bulk n-type and p-type Ge substrates. An interconnected dual-chamber molecular beam epitaxy (MBE) system was used to grow a 280 nm thin Ge epilayer on (100)GaAs substrate with an intermediate AlAs buffer layer. The lattice-matched, abrupt Ge/AlAs heterointerface was analyzed using cross-sectional transmission electron microscopic analysis, and no elemental interdiffusion was detected via secondary ion mass spectrometry. A strong direct gap transition, compared to the indirect gap transition, and a series of phonon-assisted transitions was observed by photoluminescence (PL) spectroscopy. In addition, the intensity of the direct gap recombination decreases with decreasing PL measurement temperatures, which was ascribed to the reduced density of Γ-valley electrons available for recombination at lower temperature. Furthermore, the intensity ratio between the direct and indirect optical transition drastically decreases with decreasing temperature in both n-type epitaxial and p-type bulk Ge. An empirical relation in both direct and indirect peak position with temperature was established. The observed strong luminescence in 280 nm thick epitaxial Ge at room temperature is vital for Ge-based photonic devices. In addition, the quality of the epitaxial Ge layer grown via MBE is on par with bulk Ge substrates. Submitted version

Lead halide perovskite nanocrystals, whether formed by their own nucleation and growth or by ion diffusion into the lattice of others, are still under investigation. Moreover, beyond isotropic nanocrystals, fabricating anisotropic perovskite nanocrystals by design has remained difficult. Exploring the lattice of orthorhombic-phase Cs

A joint experimental and theoretical framework for the decoupling of boron (B) doping and stoichiometric-induced modifications to the structural properties and electronic band structure of germanium (Ge)/AlAs(001) heterostructures is presented. The effect of B-induced stress on nearest-neighbor Ge bonds is quantified via X-ray diffractometry and Raman spectroscopic analysis and subsequently interpreted through the lens of density functional perturbation theory. Similarly, experimental determination of the energy band alignment at the p-type Ge:B/AlAs heterointerface is understood using a density functional theory approach to model the influence of heterointerface stoichiometry and interatomic bonding between group IV and III–V interfacial atoms on the valence and conduction band discontinuities. The modeled two monolayer interatomic diffusion at the Ge/AlAs heterointerface is confirmed via atom probe tomography analysis, demonstrating a ∼6 A interfacial width. These results present a unified picture of th...

Significance How small can a water cluster be and still stabilize ice I, the macroscopic crystal polymorph? What is the nature of coexistence between ice and liquid in small clusters? In this work, we show that the smallest water clusters that can sustain ice contain only around 90 water molecules. Our experimental and theoretical analysis suggests that the melting transition in these small droplets is very different from macroscopic water and our everyday experience. When cooled slightly below their freezing temperature, water clusters with less than ∼ 150 molecules can oscillate in time between the liquid and crystalline state. These results can be significant to understand the state of water confined in proteins and other materials.

Postsynthesis halide treatment can brighten perovskite nanocrystals. While this has been recently explored for undoped nanocrystals having only the exciton emission, herein, the impact of halide-enriched and -deficient environments was studied for dual-emitting Mn(II)-doped CsPbBr3 nanorods. This was performed by adopting a self-regulated approach where the nanorod solution reversibly switched the color brightness from blue to orange and vice versa by dilution and evaporation, respectively. With control experiments, it was established that the color switching was not due to a change in the rate of the exciton energy transfer from host to dopant energy states; rather, it was related to self-regulated fulfilling and again creating halide vacancies observed with variation of nanorod concentration. Being that the halide vacancy was established as one of the key factors for controlling the brightness of these nanocrystals, this reversible switching in doped CsPbBr3 adds new fundamental insight into controlling...

Organisms that thrive at cold temperatures produce ice-binding proteins to manage the nucleation and growth of ice. Bacterial ice-nucleating proteins (INP) are typically large and form aggregates in the cell membrane, while insect hyperactive antifreeze proteins (AFP) are soluble and generally small. Experiments indicate that larger ice-binding proteins and their aggregates nucleate ice at warmer temperatures. Nevertheless, a quantitative understanding of how size and aggregation of ice-binding proteins determine the temperature Thet at which proteins nucleate ice is still lacking. Here, we address this question using molecular simulations and nucleation theory. The simulations indicate that the 2.5 nm long antifreeze protein TmAFP nucleates ice at 2 ± 1 °C above the homogeneous nucleation temperature, in good agreement with recent experiments. We predict that the addition of ice-binding loops to TmAFP increases Thet, but not enough to compete in efficiency with the bacterial INP. We implement an accurate procedure to determine Thet of surfaces of finite size using classical nucleation theory, and, after validating the theory against Thet of the proteins in molecular simulations, we use it to predict Thet of the INP of Ps. syringae as a function of the length and number of proteins in the aggregates. We conclude that assemblies with at most 34 INP already reach the Thet = -2 °C characteristic of this bacterium. Interestingly, we find that Thet is a strongly varying nonmonotonic function of the distance between proteins in the aggregates. This indicates that, to achieve maximum freezing efficiency, bacteria must exert exquisite, subangstrom control of the distance between INP in their membrane.

A compact and portable 99Mo-99 mTc generator based on solvent-extraction, mimic to the conventional 99Mo-99 mTc alumina column generator is much-needed commodity for use in hospital radiopharmacy setup. The present study includes the development of a portable, simple and low cost 99Mo/99 mTc-generator based on MEK solvent extraction technique to obtain a very high concentration of no-carrier added (nca) 99 mTc solution, where low specific activity 99Mo source is obtained through 98Mo(n, γ)99Mo reaction in a research reactor. The unit is intended for operation under the conditions of medical radiological laboratories. Technical trials showed that the mean time of preparation of sodium [99mTc] pertechnetate radiopharmaceutical did not exceed 15 min. The quality and yield of 99 mTc-pertechnetate is upto the mark for formulation of radiopharmaceuticals.

The lack of reports on the high-temperature performance of tri-gate GaN power HEMTs has raised serious concern on their competitiveness. This work demonstrates the first normally-off tri-gate GaN HEMT that can block kilovolts at 150 °C and zero gate bias. The key enabling device design is a new type of tri-gate, the junction tri-gate, which comprises p-n junction wrapping around AlGaN/GaN fins in the gate region. At 150 °C, the GaN tri-gate junction HEMT (Tri-JHEMT) retains strong gate control and stable threshold voltage, while the traditional tri-gate metal-insulator-semiconductor (MIS) HEMTs fabricated on the same wafer shows a large threshold voltage shift and inferior capabilities of voltage blocking. These results show the excellent thermal stability of GaN Tri-JHEMTs and their great potentials for power electronics applications.

Herein, we report a complexation reaction between Zn2+ ions present on the surface of an orange-red-emitting environmentally sustainable Mn2+-doped ZnS QD and a non-emitting copper quinolate (CuQ2) complex, which leads to the formation of a greenish blue-emitting surface zinc quinolate (ZnQ2) complex. The synchronous contribution of the surface ZnQ2 complex and Mn2+-doped ZnS QD is directed towards the generation of photostable bright white light (at λex – 355 nm) with chromaticity coordinates of (0.34, 0.42), color rendering index (CRI) of 71 and color-correlated temperature (CCT) of 5046 K. The ZnQ2 complexed Mn2+-doped ZnS QD is herein called as quantum dot complex (QDC). The excitation- and time-dependent tunability in emission, chromaticity, CRI and CCT of QDC revealed their futuristic applications in light-emitting devices with an anticipated color output. The current work also shows the catalytic behavior of Mn2+-doped ZnS QDs towards facilitating the formation of surface ZnQ2 from CuQ2, which is not feasible with regard to the reactivity of CuQ2 under normal conditions according to the Irving–William series. The rate of the reaction was observed to be first order with respect to CuQ2 at 20 °C, and the complexation constant for the formation of ZnQ2 was estimated to be 8.3 × 105 M−1. This is important for understanding the surface chemistry of metal chalcogenide QDs towards complexation reactions.

Department of Chemistry, West Bengal State University, Barasat, Kolkata-700 126, India E-mail: jhimli.sengupta@gmail.com Manuscript received online 29 November 2020, revised and accepted 27 December 2020 An impasse in the realm of public health has been undergoing since December due to outbreak of COVID-19. As a consequence of this impasse, different countries are tumbling into an even deeper recession. The life of economically backward people came to a grinding halt on account of the recurrent lockdown. To bear the cost for the treatment of COVID-19 is nearly to impossible for them. It is well known fact that the best preventive measure against COVID-19 should be vitamin-D supplementation for those who are vitamin-D insufficient or deficient. Nearly 1 billion people worldwide have low level of vitamin-D. We know vitamin-D plays a vital role to the function of immune system and vitamin-D supplements have previously been proven safe and effective to reduce the risk of viral respiratory tract infection. Recently, some study have shown a strong relation between severe vitamin-D deficiency and death rate in COVID-19. It has been recorded that patients with lower level of vitamin- D had higher risk of death than patients having no deficiency in vitamin-D. Mortality rate is quite high in 20 European countries and in USA because the people of this countries are vitamin-D deficient. Thus, vitamin-D supplementation can be a very good preventive treatment against COVID-19.

Department of Chemistry, West Bengal State University, Barasat, Kolkata-700 126, India E-mail: jhimli.sengupta@gmail.com Manuscript received online 12 October 2020, revised and accepted 30 November 2020 Carbohydrate-based organic Schiff bases having biological, catalytic and pharmaceutical activities have great demand. A se­ries of new organic Schiff bases were synthesized starting from diacetone-D-glucose following the general protocol of con­densation between amine and aldehyde, either both having sugar moiety (condensation of amino sugar with aldehyde sugar), and/or at least one component having sugar moiety. All the compounds that we synthesised were characterised by NMR, FT­IR, and mass spectral studies. One of the organic Schiff base SSB-4 which was synthesized by condensation of amino sugar with aldehyde sugar, expected to be a good precursor for the synthesis of macrocycle and might also show some biological activity.

To develop low-moment, low-damping metallic ferromagnets for power-efficient spintronic devices, it is crucial to understand how magnetic relaxation is impacted by the addition of nonmagnetic elements. Here, we compare magnetic relaxation in epitaxial Fe films alloyed with light nonmagnetic elements of V and Al. FeV alloys exhibit lower intrinsic damping compared to pure Fe, reduced by nearly a factor of 2, whereas damping in FeAl alloys increases with Al content. Our experimental and computational results indicate that reducing the density of states at the Fermi level, rather than the average atomic number, has a more significant impact in lowering damping in Fe alloyed with light elements. Moreover, FeV is confirmed to exhibit an intrinsic Gilbert damping parameter of $\simeq$0.001, among the lowest ever reported for ferromagnetic metals., 28 pages, 9 figures

The ESCRT complexes drive membrane scission in HIV-1 release, autophagosome closure, MVB biogenesis, cytokinesis, and other cell processes. ESCRT-I is the most upstream complex and bridges the system to HIV-1 Gag in virus release. The crystal structure of the headpiece of human ESCRT-I comprising TSG101–VPS28–VPS37B–MVB12A was determined, revealing an ESCRT-I helical assembly with a 12 molecule repeat. Electron microscopy confirmed that ESCRT-I subcomplexes form helical filaments in solution. Mutation of VPS28 helical interface residues blocks filament formation in vitro and autophagosome closure and HIV-1 release in human cells. Coarse grained simulations of ESCRT assembly at HIV-1 budding sites suggest that formation of a 12-membered ring of ESCRT-I molecules is a geometry-dependent checkpoint during late stages of Gag assembly and HIV-1 budding, and templates ESCRT-III assembly for membrane scission. These data show that ESCRT-I is not merely a bridging adaptor, but has an essential scaffolding and mechanical role in its own right., Reporting Summary Further information on experimental design is available in the Nature Research Reporting Summary linked to this article.

In this work, an in situ SiO2 passivation technique using atomic layer deposition (ALD) during the growth of gate dielectric TaSiOx on solid-source molecular beam epitaxy grown (100)InxGa1–xAs and (110)InxGa1–xAs on InP substrates is reported. X-ray reciprocal space mapping demonstrated quasi-lattice matched InxGa1–xAs epitaxy on crystallographically oriented InP substrates. Cross-sectional transmission electron microscopy revealed sharp heterointerfaces between ALD TaSiOx and (100) and (110)InxGa1–xAs epilayers, wherein the presence of a consistent growth of an ∼0.8 nm intentionally formed SiO2 interfacial passivating layer (IPL) is also observed on each of (100) and (110)InxGa1–xAs. X-ray photoelectron spectroscopy (XPS) revealed the incorporation of SiO2 in the composite TaSiOx, and valence band offset (ΔEV) values for TaSiOx relative to (100) and (110)InxGa1–xAs orientations of 2.52 ± 0.05 and 2.65 ± 0.05 eV, respectively, were extracted. The conduction band offset (ΔEC) was calculated to be 1.3 ± 0.1 eV for (100)InxGa1–xAs and 1.43 ± 0.1 eV for (110)InxGa1–xAs, using TaSiOx band gap values of 4.60 and 4.82 eV, respectively, determined from the fitted O 1s XPS loss spectra, and the literature-reported composition-dependent InxGa1–xAs band gap. The in situ passivation of InxGa1–xAs using SiO2 IPL during ALD of TaSiOx and the relatively large ΔEV and ΔEC values reported in this work are expected to aid in the future development of thermodynamically stable high-κ gate dielectrics on InxGa1–xAs with reduced gate leakage, particularly under low-power device operation.

Capacitance-voltage characterization of epitaxial n-type (100)Ge and (110)Ge metal-oxide-semiconductor capacitors (MOS Cs) was performed using two work function Al and Pt gate metals to evaluate the orientation effect on flat-band voltage (VFB) shift, Fermi level pinning factor (S), and interface induced defects (Dit). These epitaxial (100)Ge/AlAs/GaAs and (110)Ge/AlAs/GaAs heterostructures were grown in-situ using two separate molecular beam epitaxy (MBE) chambers. A VFB shift of >700 mV, S > 0.5, and Dit value of ~ 6 × 1011 cm−2 eV−1 in the energy range of 0.05 eV to 0.3 eV below the conduction band, have been demonstrated from epitaxial n-type (100)Ge and (110)Ge surfaces, which are comparable to the reported bulk Ge MOS-C values, suggesting a robust MOS-C developed process as well as device quality epitaxial (100)Ge and (110)Ge layers on GaAs substrates using an AlAs intermediate buffer. Thus, the metal work function engineering on device-quality MBE grown crystallographically oriented Ge materials, can offer a promising path for extending the performance and application of Ge-based field-effect transistors for low-power devices.

Heteroepitaxial magnetoelectric (ME) composites are promising for the development of a new generation of multifunctional devices, such as sensors, tunable electronics, and energy harvesters. However, challenge remains in realizing practical epitaxial composite materials, mainly due to the interfacial lattice misfit strain between magnetostrictive and piezoelectric phases and strong substrate clamping that reduces the strain-mediated ME coupling. Here, we demonstrate a nonstrain-mediated ME coupling in PbZr0.52Ti0.48O3 (PZT)/La0.67Sr0.33MnO3 (LSMO) heteroepitaxial composites that resolves these challenges, thereby, providing a giant magnetodielectric (MD) response of ∼27% at 310 K. The factors driving the magnitude of the MD response were found to be the magnetoresistance-coupled dielectric dispersion and piezoelectric strain-mediated modulation of magnetic moment. Building upon this giant MD response, we demonstrate a magnetic field sensor architecture exhibiting a high sensitivity of 54.7 pF/T and desira...

Cold-adapted organisms produce antifreeze and ice-nucleating proteins to prevent and promote ice formation. The crystal structure of hyperactive bacterial antifreeze protein (AFP) MpAFP suggests that this protein binds ice through an anchored clathrate motif. It is not known whether other hyperactive AFPs and ice-nucleating proteins (INPs) use the same motif to recognize or nucleate ice. Here we use molecular simulations to elucidate the ice-binding motifs of hyperactive insect AFPs and a model INP of Pseudomonas syringae. We find that insect AFPs recognize ice through anchored clathrate motifs distinct from that of MpAFP. By performing simulations of ice nucleation by PsINP, we identify two distinct ice-binding sites on opposite sides of the β-helix. The ice-nucleating sequences identified in the simulations agree with those previously proposed for the closely related INP of Pseudomonas borealis based on the structure of the protein. The simulations indicate that these sites have comparable ice-nucleating efficiency, but distinct binding motifs, controlled by the amino acid sequence: one is an anchored clathrate and the other ice-like. We conclude that anchored clathrate and ice-like motifs can be equally effective for binding proteins to ice and promoting ice nucleation.

Crystallization of ice from deeply supercooled water and amorphous ices - a process of fundamental importance in the atmosphere, interstellar space, and cryobiology - results in stacking disordered ices with a wide range of metastabilities with respect to hexagonal ice. The structural origin of this high variability, however, has not yet been elucidated. Here we use molecular dynamics simulations with the mW water model to characterize the structure of ice freshly grown from supercooled water at temperatures from 210 to 270 K, the thermodynamics of stacking faults, line defects, and interfaces, and to elucidate the interplay between kinetics and thermodynamics in determining the structure of ice. In agreement with experiments, the ice grown in the simulations is stacking disordered with a random distribution of cubic and hexagonal layers, and a cubicity that decreases with growth temperature. The former implies that the cubicity of ice is determined by processes at the ice/liquid interface, without memory of the structure of buried ice layers. The latter indicates that the probability of building a cubic layer at the interface decreases upon approaching the melting point of ice, which we attribute to a more efficient structural equilibration of ice at the liquid interface as the driving force for growth wanes. The free energy cost for creating a pair of cubic layers in ice is 8.0 J mol(-1) in experiments, and 9.7 ± 1.9 J mol(-1) for the mW water model. This not only validates the simulations, but also indicates that dispersion in cubicity is not sufficient to explain the large energetic variability of stacking disordered ices. We compute the free energy cost of stacking disorder, line defects, and interfaces in ice and conclude that a characterization of the density of these defects is required to predict the degree of metastability and vapor pressure of atmospheric ices.