Breaking the absorption limit of Si toward SWIR wavelength range via strain engineering

Silicon has been widely used in the microelectronics industry. However, its photonic applications are restricted to visible and partial near-infrared spectral range owing to its fundamental optical bandgap (1.12 eV). With recent advances in strain engineering, material properties, including optical bandgap, can be tailored considerably. This paper reports the strain-induced shrinkage in the Si bandgap, providing photosensing well beyond its fundamental absorption limit in Si nanomembrane (NM) photodetectors (PDs). The Si-NM PD pixels were mechanically stretched (biaxially) by a maximum strain of similar to 3.5% through pneumatic pressure-induced bulging, enhancing photoresponsivity and extending the Si absorption limit up to 1550 nm, which is the essential wavelength range of the lidar sensors for obstacle detection in self-driving vehicles. The development of deformable three-dimensional optoelectronics via gas pressure-induced bulging also facilitated the realization of unique device designs with concave and convex hemispherical architectures, which mimics the electronic prototypes of biological eyes.1

Antibacterial efficacy of Jackfruit rag extract against clinically important pathogens and validation of its antimicrobial activity in Shigella dysenteriae infected Drosophila melanogaster infection model

513-522Exploration of alternative sources of antibacterial compounds is an important and possibly an effective solution to the current challenges in antimicrobial therapy. Plant derived wastes may offer one such alternative. Here, we investigated the antibacterial property of extract derived from a part of the Jackfruit (Artocarpus heterophyllus Lam.) called ‘rag’, generally considered as fruit waste. Morpho-physical characterization of the Jackfruit rag extract (JFRE) was performed using Gas-chromatography, where peaks indicative of furfural; pentanoic acid; and hexadecanoic acid were observed. In vitro biocompatibility of JFRE was performed using the MTT assay, which showed comparable cellular viability between extract-treated and untreated mouse fibroblast cells. Agar well disc diffusion assay exhibited JFRE induced zones of inhibition for a wide variety of laboratory and clinical strains of Gram-positive and Gram-negative bacteria. Analysis of electron microscope images of bacterial cells suggests that JFRE induces cell death by disintegration of the bacterial cell wall and precipitating intracytoplasmic clumping. The antibacterial activity of the JFREs was further validated in vivo using Shigella dysenteriae infected fly model, where JFRE pre-fed flies infected with S. dysenteriae had significantly reduced mortality compared to controls. JFRE demonstrates broad antibacterial property, both in vitro and in vivo, possibly by its activity on bacterial cell wall

Excitation power-independent photoluminescence of inverted quantum hut structures embedded in SiGe superlattice

Optical properties of semiconductor nanostructures can be quite different from the bulk semiconductors. We present here results of a photoluminescence study of MBE-grown SiGe superlattice structures having inverted quantum huts of Ge formed below Ge-on-Si interfaces. As these structures form by continuous alloying with the lower Si layers, the interfacial strain is greatly reduced, leading to a band-alignment, which is different from that obtained for conventional quantum dots formed above Ge-on-Si interfaces. Thus, unlike conventional Ge quantum dots, the presented quantum structures exhibit excitation power-independent photoluminescence emission. Temperature dependence of photoluminescence energy follows typical relation expected in a semiconductor, but at higher temperature when dominating contribution comes from the tip of the quantum hut, change in the photoluminescence energy becomes weakly dependent on temperature. These results may be influential in the development of silicon-based optical materials

Fabrication of Si/ZnS Radial Nanowire Heterojunction Arrays for White Light Emitting Devices on Si Substrates

Well-separated Si/ZnS radial nanowire heterojunction-based light-emitting devices have been fabricated on large-area substrates by depositing n-ZnS film on p-type nanoporous Si nanowire templates. Vertically oriented porous Si nanowires on p-Si substrates have been grown by metal-assisted chemical etching catalyzed using Au nanoparticles. Isolated Si nanowires with needle-shaped arrays have been made by KOH treatment before ZnS deposition. Electrically driven efficient white light emission from radial heterojunction arrays has been achieved under a low forward bias condition. The observed white light emission is attributed to blue and green emission from the defect-related radiative transition of ZnS and Si/ZnS interface, respectively, while the red arises from the porous surface of the Si nanowire core. The observed white light emission from the Si/ZnS nanowire heterojunction could open up the new possibility to integrate Si-based optical sources on a large scale

Multifunctional White-Light-Emitting Metal–Organic Gels with a Sensing Ability of Nitrobenzene

In this study, three novel luminescent nanofibrous metal–organic gels (MOGs) have been synthesized by the reaction of 1,3,5-tris­(3-pyridylmethoxyl)­benzene (<b>L</b>) with chloride salts of Cd­(II), Hg­(II), and Cu­(II). The metal–ligand coordination, intermolecular π–π stacking and several other weak interactions found to play an important role in the formation of nanofibrous materials. The gel materials are characterized by rheology, diffuse reflectance spectra and various microscopic techniques such as TEM, FESEM, and AFM. The gels MOG-1 and MOG-2 were found to exhibit significant white photoluminescence, whereas the MOG-3 exhbits green emission upon excitation at 325 nm. Furthermore, the MOG-1 has shown its application as a chemosensor for the remarkable detection of nitroaromatics such as nitrobenzene (NB), 2,4-dinitrophenol (DNP). The significant quenching response for NB and DNP is attributed to the strong charge-transfer interactions between the electron-deficient aromatic ring of NB and the electron rich aromatic group of <b>L</b> in MOG-1. The crystal structure of Cd­(II) complex of <b>L</b> reveals the formation one-dimensional network which contains strong π–π interactions within and between the networks and these strong π–π interactions generate the free charge carrier in all these nanofibrous gels

Orientation-dependent optical characterization of atomically thin transition metal ditellurides

Molybdenum ditellurides (MoTe2) have recently attracted attention owing to their excellent structurally tunable nature between 1T???(metallic)- and 2H(semiconducting)-phases; thus, the controllable fabrication and critical identification of MoTe2 are highly desired. Here, we semi-controllably synthesized 1T???- and 2H-MoTe2 crystals using the atmospheric pressure chemical vapor deposition (APCVD) technique and studied their grain-orientation dependency using polarization-sensitive optical microscopy, Raman scattering, and second-harmonic generation (SHG) microspectroscopy. The polycrystalline 1T???-MoTe2 phase with quasi-1D ???Mo-Mo??? zigzag chains showed anisotropic optical absorption, leading to a clear visualization of the lattice domains. On the other hand, 2H-MoTe2 lattice grains did not exhibit any discernible difference under polarized light illumination. The combined aforementioned microscopy techniques could be used as an easy-to-access and non-destructive tool for a quick and solid identification of intended lattice orientation development in industry-scale MoTe2 crystal manufacturing