Three-dimensional Quantum-size Effect In Chemically Deposited Cadmium Selenide Films

Optical band gaps, Eg, up to 0.5 eV higher than in single-crystal samples, are observed for chemically deposited films of CdSe and explained in terms of a quantum-size effect, whereby the electrons are localized in individual crystallites. The increase in Eg depends strongly on deposition temperature, with the greatest increase obtained at the lowest temperature. Annealing at temperatures above the deposition temperature causes a decrease in Eg; this decrease is stronger at higher annealing temperature. Structural studies of the as-deposited layers showed them to be composed of microcrystalline, cubic CdSe, and electron microscopy resolved them into individual crystallites of typically 4080-A diameter, depending on deposition temperature. This is the first example reported of a three-dimensional quantum-size effect in a film. © 1987 The American Physical Society.3684215422

A Study on MoS 2 Thin Films Electrochemically Deposited in Ethylene Glycol at 165°C

The electrosynthesis of nanoparticle thin films of MoS 2 from solutions of (NH 4 ) 2 MoS 4 in ethylene glycol at 165°C, is described. The as-deposited MoS 2 thin films (~150 nm thick) were X-ray amorphous and exhibited featureless optical absorption spectra over the 1-3.5 eV spectral range. High resolution transmission electron microscopy (HRTEM) revealed the presence of single or double (0002) plane-sized 2H-MoS 2 thin nanoplatelets (~2-3 nm) embedded in an amorphous matrix. Annealing the as-deposited samples under Ar for 1 h at 550°C, resolved a broad and weak-intensity peak in the respective X-ray spectra, identified as th

Line Defects in Molybdenum Disulfide Layers

Layered molecular materials and especially MoS2 are already accepted as promising candidates for nanoelectronics. In contrast to the bulk material, the observed electron mobility in single-layer MoS2 is unexpectedly low. Here we reveal the occurrence of intrinsic defects in MoS2 layers, known as inversion domains, where the layer changes its direction through a line defect. The line defects are observed experimentally by atomic resolution TEM. The structures were modeled and the stability and electronic properties of the defects were calculated using quantum-mechanical calculations based on the Density-Functional Tight-Binding method. The results of these calculations indicate the occurrence of new states within the band gap of the semiconducting MoS2. The most stable non-stoichiometric defect structures are observed experimentally, one of which contains metallic Mo-Mo bonds and another one bridging S atoms

Nanoparticles Produced by Laser Ablation of HfS in Liquid Medium: Inorganic Fullerene-Like Structures of Hf2S

Inorganic fullerene-like structures (IF) of the layered hafnium sulfide, Hf2S, have been synthesized by the laser ablation of HfS3 in tert-butyl disulfide medium. Apart from the Hf2S IFs exhibiting quasi-spherical as well as faceted nested-shell geometries, quasi-spherical nanoparticles of HfS were observed by this means. Whereas Hf2S has anti-NbS2 structure with S layers sandwiched between two Hf layers, HfS has the nonlayered WC-type structure. The nanoparticles of HfS show excess sulfur in the core, and they do not possess closed-shell geometry. The mechanism of formation of these nanoparticles has also been discussed

Nanostructural and nanochemical investigation of luminescent photoelectrochemically etched porous n-type silicon

Porous silicon obtained on n-type silicon by photoelectrochemical etching in HF, is formed of a macroporous silicon layer beneath a nanoporous silicon layer. Microstructural investigations and chemical analysis at the atomic level of the nanoporous silicon film (obtained from a highly doped (111) oriented Si substrate) have been done by high resolution transmission electron microscopy (HRTEM) and electron energy loss spectroscopy (EELS) using a scanning transmission electron microscope (STEM). We have found chat the nanoporous Si consists of a regular Si macroarray with triangular geometry. Nanometer-size tangled wires are contained within and attached to the macroarray. HRTEM images clearly demonstrate the existence of quantum-sized Si wires made of a crystalline core covered with an amorphous layer. Electron energy loss spectra (EELS) have been recorded for different positions of the incident probe across the quantum-sized Si wires. The results obtained in the low-loss region and at the Si L$_{23}$ edge have been compared with those recorded on reference specimens (Si/SiO$_2$ interface and hydrogenated Si sample). Although they do not exclude the presence of one or a few monolayers of foreign species, of hydrogen in particular, on the outer surface, our results generally support the quantumconfinement model to interpret the observed photoluminescence in nanoporous Si