Optoelectronic Properties of Atomically Thin MoxW(1-x)S2 Nanoflakes Probed by Spatially-Resolved Monochromated EELS

Band gap engineering of atomically thin two-dimensional (2D) materials has attracted a huge amount of interest as a key aspect to the application of these materials in nanooptoelectronics and nanophotonics. Low-loss electron energy loss spectroscopy has been employed to perform a direct measurement of the band gap in atomically thin MoxW(1−x)S2 nanoflakes. The results show a bowing effect with the alloying degree, which fits previous studies focused on excitonic transitions. Additional properties regarding the Van Hove singularities in the density of states of these materials, as well as high energy excitonic transition, have been analysed as well.

Preparation and Characterizations of NiS/ZnS Bilayer Thinfilm by Chemical Bath Deposition Method

NiS/ZnS thin films were grown by Chemical Bath Deposition (CBD) technique using eqimolar aqueous solutions of zinc chloride, nickel chloride and thiourea as precursor. Silicon glass substrates were placed in glass bottles with polypropylene autoclave screw caps containing the precursors described above, and the bath temperature is maintained at 95°C. X-ray diffraction 28/8 scans showed that the only crystallographic phase present was the hexagonal wurtzite structure. Scanning electron microscopy showed the formation of nanostructures, consisting of hexagonal structures of a few hundred nanometers. The photoluminescence spectra of NiS/ZnS bilayer were recorded at 18-295 K using a cw He-Cd laser (325 nm) and pulsed laser (266 nm). The NiS/ZnS nanostructure exhibit an ultraviolet emission band centered at ;:::; 3.87eV in the vicinity of the band edge, which is attributed to the well-known excitonic transition in ZnS. The optical properties such as refractive index, electrical and optical conductivities were determined by using UV- VIS absorption spectrometry. The band gap energy was determined as 1.45 eV.

Temperature Dependent Excitonic Transition Energy and Enhanced Electron-Phonon Coupling in Layered Ternary SnS2-xSex Semiconductors with Fully Tunable Stoichiometry

In this study, a series of SnS2-xSex (0 ≤ x ≤ 2) layered semiconductors were grown by the chemical–vapor transport method. The crystal structural and material phase of SnS2-xSex layered van der Waals crystals was characterized by X-ray diffraction measurements and Raman spectroscopy. The temperature dependence of the spectral features in the vicinity of the direct band edge excitonic transitions of the layered SnS2-xSex compounds was measured in the temperature range of 20–300 K using the piezoreflectance (PzR) technique. The near band-edge excitonic transition energies of SnS2-xSex were determined from a detailed line-shape fit of the PzR spectra. The PzR characterization has shown that the excitonic transitions were continuously tunable with the ratio of S and Se. The parameters that describe the temperature variation of the energies of the excitonic transitions are evaluated and discussed.

Impact of annealing temperature on structural, optical and morphological properties of ZnO Nanoparticles Synthesized by a simple precipitation method

Objective: Herein, we report zinc oxide (ZnO) nanoparticles (NPs) synthesized by a simple precipitation method using zinc acetate dihydrate (Zn(CH3CO2)2. 2H2O) and sodium hydroxide (NaOH) precursors in aqueous media. Method: As synthesized material was annealed at different temperatures to check phase formation and its purity. Result: At room temperature sample shows the formation of zinc hydroxide and at high temperature (100, 200 & 300 oC) shows the formation of ZnO. Synthesized materials were analyzed by different techniques. X-ray diffraction analysis shows the formation of hexagonal crystal structure. Morphological features were analyzed by the SEM technique which shows agglomerated nanoparticles. Conclusion: The optical properties of ZnO were studied by using UV analysis and showed intrinsic excitonic transition property of the ZnO semiconductor. Further, with an increase in annealing temperature crystalline size, agglomeration of nanoparticles found to be increased whereas band gap decreases.

PbI2 Single Crystal Growth and Its Optical Property Study

In this work, we used the chemical vapor transport (CVT) method to grow PbI2 crystals using iodine as a self-transporting agent. The crystals’ structure, composition, and uniformity were confirmed by X-ray diffraction (XRD) and electron probe microanalysis (EPMA) measurements. We investigated the band gap energy using absorption spectroscopy measurements. Furthermore, we explored the temperature dependence of the band gap energy, which shifts from 2.346 eV at 300 K to 2.487 eV at 20 K, and extracted the temperature coefficients. A prototype photodetector with a lateral metal–semiconductor–metal (MSM) configuration was fabricated to evaluate its photoelectric properties using a photoconductivity spectrum (PC) and persistent photoconductivity (PPC) experiments. The resonance-like PC peak indicates the excitonic transition in absorption. The photoresponse ILight/IDark-1 is up to 200%.