Optical properties and electrical bistability of CdS nanoparticles synthesized in dodecanethiol

We reported the synthesis of CdS semiconductor nanoparticles using a simple one-pot reaction by thermolysis of cadmium acetylacetonate in dodecanethiol. Optical measurements of the as-obtained CdS nanoparticles revealed that their optical properties were closely related to surface effects. Based upon the cocktail of poly (N-vinylcarbazole) (PVK) and CdS nanoparticles, a bistable device was fabricated by a simple solution processing technique. Such a device exhibited a remarkable electrical bistability, which was attributed to the electric field-assisted charge transfer between PVK and the CdS nanoparticles capped by dodecaethiol. The conduction mechanism changed from an injection-controlled current to a bulk-controlled one during switching from OFF-state to ON-state.

Effects of Hydrogen Plasma Treatment on the Electrical and Optical Properties of ZnO Films: Identification of Hydrogen Donors in ZnO

Wurtzite ZnO has many potential applications in optoelectronic devices, and the hydrogenated ZnO exhibits excellent photoelectronic properties compared to undoped ZnO; however, the structure of H-related defects is still unclear. In this article, the effects of hydrogen-plasma treatment and subsequent annealing on the electrical and optical properties of ZnO films were investigated by a combination of Hall measurement, Raman scattering, and photoluminescence. It is found that two types of hydrogen-related defects, namely, the interstitial hydrogen located at the bond-centered (H-BC) and the hydrogen trapped at a O vacancy (H-O), are responsible for the n-type background conductivity of ZnO films. Besides introducing two hydrogen-related donor states, the incorporated hydrogen passivates defects at grain boundaries. With increasing annealing temperatures, the unstable H-BC atoms gradually diffuse out of the ZnO films and part of them are converted into H-O, which gives rise to two anomalous Raman peaks at 275 and 510 cm(-1). These results help to clarify the relationship between the hydrogen-related defects in ZnO described in various studies and the free carriers that are produced by the introduction of hydrogen.

Optical properties of Mn+ doped GaAs

The above work was supported by the national Basic Research Program of China (2006cb604904, 2006cb604908), the hi-tech R & D program of China (2006aa03z0408, 2006aa03z0404), the scientific research Fund of Central South University of Forstry and Technology.

Tunable optical properties of nano-Au on vanadium dioxide

The optical properties of Au nanoparticles deposited on thermochromic thin films of VO2 are investigated using spectroscopy. A localized modification on the transmittance spectrum of VO2 film is formed due to the presence of Au nanoparticles which exhibit localized surface plasmon resonance (LSPR) in the visible-near IR region. The position of the modification wavelength region shows a strong dependence on the Au mass thickness and shifts toward the red as it increases. On the other hand, it was found that the LSPR of Au nanoparticles can be thermally tunable because of the thermochromism of the supporting material of VO2. The LSPR wavelength, lambda(SPR), shifts to the blue with increasing temperature, and shifts back to the red as temperature decreases. A fine tuning is achieved when the temperature is increased in a stepwise manner.

Optical properties of a novel neodymium pentafluoropropionate binuclear complex

A novel neodymium pentafluoropropionate binuclear complex, Nd(C(2)F(5)COO)(3)Dipy (Dipy: 2,2'-dipyridyl), was synthesized and characterized by single-crystal X-ray diffraction. At a concentration of 0.2 M in DMSO-d(6), the Judd-Ofelt parameters (Omega(2), Omega(4), Omega(6)) were calculated from the UV-Vis spectrum. According to the small value of Omega(2) and the zero splitting energy of (4)F/(3/2) level, a symmetric ligand field of the complex was confirmed in DMSO-d(6). Strong emission of the complex in DMSO-d(6) at 1057 nm with a decay time about 1.3 mu s were detected when excited at 800 nm pumped by a laser diode. The stimulated emission cross-section of (4)F(3/2) -> (4)I(11/2) fluorescence transition was 2.36 x 10 (20) cm(2) and comparable with some laser glasses, which indicated good radiative properties of this neodymium pentafluoropropionate binuclear complex in liquid matrix. (c) 2008 Elsevier B.V. All rights reserved.

Investigation on the strain relaxation of InGaN layer and its effects on the InGaN structural and optical properties

The evolution of strain and structural properties of thick epitaxial InGaN layers grown on GaN with different thicknesses are investigated. It is found that, with increase in InGaN thickness, plastic relaxation via misfit dislocation generation becomes a more important strain relaxation mechanism. Accompanied with the relaxation of compressive strain, the In composition of InGaN layer increases and induces an apparent red-shift of the cathodoluminescence peak of the InGaN layer. On the other hand, the plastic relaxation process results in a high defect density, which degrades the structural and optical properties of InGaN layers. A transition layer region with both strain and In composition gradients is found to exist in the 450-nm-thick InGaN layer.

Correlation of electrical and optical properties in dually Cd+ and N+ ion-implanted GaAs

Cd in GaAs is an acceptor atom and has the largest atomic diameter among the four commonly-used group-II shallow acceptor impurities (Be, Mg, Zn and Cd). The activation energy of Cd (34.7 meV) is also the largest one in the above four impurities, When Cd is doped by ion implantation, the effects of lattice distortion are expected to be apparently different from those samples ion-implanted by acceptor impurities with smaller atomic diameter. In order to compensate the lattice expansion and simultaneously to adjust the crystal stoichiometry, dual incorporation of Cd and nitrogen (N) was carried out into GaAs, Ion implantation of Cd was made at room temperature, using three energies (400 keV, 210 keV, 110 keV) to establish a flat distribution, The spatial profile of N atoms was adjusted so as to match that of Cd ones, The concentration of Cd and N atoms, [Cd] and [N] varied between 1 x 10(16) cm(-3) and 1 x 10(20) cm(-3). Two type of samples, i.e., solely Cd+ ion-implanted and dually (Cd+ + N+) ion-implanted with [Cd] = [N] were prepared, For characterization, Hall effects and photoluminescence (PL) measurements were performed at room temperature and 2 K, respectively. Hall effects measurements revealed that for dually ion-implanted samples, the highest activation efficiency was similar to 40% for [Cd] (= [N])= 1 x 10(18) cm(-3). PL measurements indicated that [g-g] and [g-g](i) (i = 2, 3, alpha, beta,...), the emissions due to the multiple energy levels of acceptor-acceptor pairs are significantly suppressed by the incorporation of N atoms, For [Cd] = [N] greater than or equal to 1 x 10(19) cm(-3), a moderately deep emission denoted by (Cd, N) is formed at around 1.45-1.41 eV. PL measurements using a Ge detector indicated that (Cd, N) is increasingly red-shifted in energy and its intensity is enhanced with increasing [Cd] = [N], (Cd, N) becomes a dominant emission for [Cd] = [N] = 1 x 10(20) cm(-3). The steep reduction of net hole carrier concentration observed for [Cd]/[N] less than or equal to 1 was ascribed to the formation of (Cd, N) which is presumed to be a novel radiative complex center between acceptor and isoelectronic atoms in GaAs.