Potential well

About: Potential well is a research topic. Over the lifetime, 1430 publications have been published within this topic receiving 30812 citations.

CdSe quantum dots using selenourea as selenium source in polymer matrix

Abstract: In this paper we have synthesized cadmium selenide quantum dots in aqueous medium at low temperature of 80 °C through chemical route. Three different concentrations of polyvinyl alcohol (PVA) 6, 8 and 10 wt% was used as a capping agent to prevent coagulation in quantum dots. An alternative precursor selenourea was used in place of selenium powder as a selenium source. Thin film of CdSe/PVA nanocomposite was made by spin coating and characterized by UV–Vis spectroscopy; Scanning electron microscopy (SEM), Transmission electron microscopy (TEM) and Fourier transform infra red spectroscopy. For electrical measurements temperature dependent DC conductivity has been performed. From UV–Visible absorption measurement it has been observed that on increasing PVA concentration the absorption edge shifts and bandgap calculated comes out to be more than the bulk CdSe material due to quantum confinement effect. This indicates blue shift and reduction in crystallite size with increase in PVA concentration. This tunability of bandgap with size is very effective in solar cell application. SEM/TEM micrograph confirms the zero dimensional shape of the prepared quantum dot with average size in the range of 6 nm. The DC conductivity measurement shows increase in conductivity with increase in temperature which confirms semiconducting behaviour of CdSe quantum dot.

Enhanced H 2 sensing properties of a-plane ZnO prepared on c-cut sapphire substrate by sputtering

Abstract: Zinc oxide (ZnO) thin films have been prepared on c-plane sapphire substrate by magnetron sputtering technique. The influence of deposition time on the structural, optical and photoluminescence properties of the films have been investigated. XRD patterns reveal the growth of preferentially oriented (101) non-polar a-plane ZnO film with hexagonal wurtzite structure. The PL peak shifts towards lower wavelength for deposition time up to 20 min, which is in consistent with the results obtained from UV absorption studies. The blue shift in the PL peak confirms the possibility for quantum confinement effect. The band gap energy of the film increases from 3.33 to 3.38 eV, indicating enhanced quantum confinement effects. FESEM micrographs showed that the films have a smooth and dense morphology with uniform grain growth. Hydrogen sensing measurements indicated that a-plane ZnO film on c-sapphire showed higher response than c-plane ZnO film reported earlier. The sensor response of 44 nm thick ZnO film exhibit highest response of 145 towards 500 ppm H2 gas at the operating temperature of 200 °C.

Quantum Size Effect in Superconducting Aluminum Films

Abstract: High-quality aluminum films on GaAs substrates are studied experimentally. The critical temperature of superconductivity is found to increase markedly with decreasing the film thickness. The observed phenomenon is considered as a manifestation of the quantum confinement effect, which affects both the density of states and the electron–phonon interaction.

OD-XAS and EXAFS: Structure and Luminescence in Ge Quantum Dots

Abstract: The source of visible luminescence from Ge nanocrystalline materials has been attributed to various phenomena such as the quantum confinement effect, surface contributions, and so on. In order to understand the origin of this light emission we have performed extended x-ray absorption fine structure (EXAFS) and optically-detected x-ray absorption spectroscopy (OD-XAS) using x-ray excited optical luminescence (XEOL) measurements on a range of Ge quantum dots prepared by various routes including stain etching, sol-gel method, and laser ablation. Such XEOL and OD-XAS studies on Ge and Ge-O rich regions allowed us to determine specificlocal sites responsible for PL.