New observation on the formation of PbS clusters in zeolite-Y

PbS clusters in zeolite-Y have been prepared with the reaction of Pb2+-ion-exchanged zeolite-Y with Na2S in solution at room temperature. Their absorption spectra show dramatic blue shifts from that of the bulk PbS. Obvious change of both the absorption edges and peak positions upon PbS concentrations have been observed. These phenomena provide evidences that PbS clusters have been formed within the zeolite. The absorption spectra show featureless structure and have no tails near the absorption edges. As the PbS loading density becomes higher, the absorption bands become stronger and sharpen. Order PbS clusters lattice with high quality might be formed in the supercages of zeolite-Y. (C) 1996 American Institute of Physics.

DIRECT OBSERVATION FOR THE REDUCTION OF EXCITON BINDING-ENERGY INDUCED BY PERPENDICULAR ELECTRIC-FIELD

We experimentally study the effect of perpendicular electric field on the exciton binding energy using a specially designed step quantum well. From photoluminescence spectra at the temperature of 77 K, we have directly observed remarkable blueshift of the exciton peak due to the transition from spatially direct to spatially indirect excitons induced by electric field. (C) 1995 American Institute of Physics.

Observation of deep electron states in n-type Al-doped ZnS1-xTex grown by molecular beam epitaxy

Deep level transient spectroscopy (DLTS) technique was used to investigate deep electron states in n-type Al-doped ZnS1-xTex epilayers grown by molecular fiction epitaxy (MBE), Deep level transient Fourier spectroscopy (DLTFS) spectra of the Al-doped ZnS1-xTex (x = 0. 0.017, 0.04 and 0.046. respectively) epilayers reveal that At doping leads to the formation of two electron traps at 0.21 and 0.39 eV below the conduction hand. 1)DLTFS results suggest that in addition to the rules of Te as a component of [lie alloy as well as isoelectronic centers, Te is also involved in the formation of all electron trip, whose energy level relative to the conduction hand decreases a, Te composition increases.

Observation of the resonant Raman behavior of individual single-walled carbon nanotubes

The different resonant Raman scattering process of single-walled carbon nanotubes (SWNTs) has been found between the Stokes and anti-Stokes sides of the radial breathing modes (RBMs), and this provides strong evidence that Raman spectra of some special diametric SWNTs are in resonance with their electronic transitions between the singularities in the one-dimensional electronic density of states in the valence and conduction bands, and other SWNTs axe beyond the resonant condition. Because of the coexistence of resonant and non-resonant Raman scattering processes for different diametric SWNTs, the relative intensity of each RBM does not reflect the proportion of a particular SWNT.

Observation of defects in GaN epilayers

GaN epilayers grown on sapphire substrates nitridated for various lengthy periods were investigated by light scattering tomography (LST) and Raman scattering. In the LST images of the plane-view epilayers, the light scattering defects distribute in [<11(2)over bar 0>] directions. The defect density is lower in epilayer grown on substrate nitridated for a longer period. The defects are believed to be straight threading edge dislocations on {<1(1)over bar 00>} planes. The Raman shift of E-2 mode is larger in the sample grown on substrate nitridated for a longer period. Our results show that the stress is higher in the sample with fewer dislocations.

Observation of N-Shaped Negative Differential Resistance in GaAs-Based Modulation-Doped Field Effect Transistor with InAs Quantum Dots

N-shaped negative differential resistance (NDR) with a high peak-to-valley ratio (PVR) is observed in a GaAs-based modulation-doped field effect transistor (MODFET) with InAs quantum dots (QDs) in the barrier layer (QDFET) compared with a GaAs MODFET. The NDR is explained as the real-space transfer (RST) of high-mobility electrons in a channel into nearby barrier layers with low mobility, and the PVR is enhanced dramatically upon inserting the QD layer. It is also revealed that the QD layer traps holes and acts as a positively charged nano-floating gate after a brief optical illumination, while it acts as a negatively charged nano-floating gate and depletes the adjacent channel when charged by the electrons. The NDR suggests a promising application in memory or high-speed logic devices for the QDFET structure.