Xuexuan Qu

A new approach for synthesizing Ge quantum crystallites embedded in a‐SiNx films

In this letter, we present a new approach for synthesizing Ge quantum crystallites embedded in a‐SiNx films. On the basis of preferential chemical bonding formation of Si‐N and Ge‐Ge, thin films with Ge clusters embedded in a‐SiNx matrix have been prepared by the plasma enhanced chemical vapor deposition method with reactant gases of SiH4, GeH4 and NH3 mixed in hydrogen plasma at substrate temperature of 250 °C. Then the as‐deposited films were annealed at 800 °C for 30 min in the vacuum for the crystallization of Ge clusters and the growth of nanometer‐sized Ge quantum crystallites. These samples were characterized by infrared absorption spectra, transmission electron microscopy, x‐ray diffraction, and Raman scattering spectra. The average size of Ge crystallites was found to be about 200 A. By choosing conditions of the deposition and thermal‐annealing treatment, the size of Ge quantum crystallites can be prepared in a controlled manner.

Thermal analysis of the ferroelastic phase transitions of LaxPr1−xP5O14

The specific heat capacities of LaxPr1-xP5O14 crystals with x=0.9 and 0.7 were measured with a differential scanning calorimeter over the temperature range 350-450 K. A jump in the specific heat capacity at the phase transition temperature of 402 K and one thermal anomaly at about 385 K were found within experimental error. Factors contributing to the specific heat capacities were considered.

Preparation of Ge quantum crystallites embedded in a-SiNx matrix by the PECVD method

Abstract Preparation of Ge quantum crystallites embedded in a-SiN x matrix was successfully achieved by the PECVD technique and followed thermal annealing treatment at 800°C. The microscopic heterogeneity of the as-deposited and thermal-annealed films were analyzed by the TEM and X-ray diffraction. We have found that substrate temperature is a critical parameter for the formation of Ge clusters. The temperature and time duration of annealing determine the size of Ge quantum crystallites. We are temporarily using the diffusion-limited growth model to explain the crystallization mechanism of this quantum material.

Radiative transition with visible light in crystallized aGe:H/aSiNX:H multiquantum-well structures

Abstract Crystallized aGe:H/aSiNX:H multiquantum-well (MQW) structures were prepared by a computer controlled plasma enhanced chemical vapor deposition method and then crystallized by Ar+ laser annealing technique. The layered structures and the crystallinity of the samples were determined by means of X-ray diffraction (XRD) spectroscopy. The crystallized samples showed a radiative transition with visible light as the Ge well layer thickness was less than 4 nm. This may preliminary be explained by the quantum confinement of electrons and holes.

Visible photoluminescent Ge nanocrystals embedded in a-SiNx films

Ge nanocrystals embedded in a-SiNx matrix were prepared by the PECVD method with SiH4, GeH4 and NH3 mixed in H2 plasma and followed the thermal-annealing treatment, which was based on the preferential chemical bonding formation of Si-N and Ge-Ge. The samples were characterized by infrared absorption, X-ray diffraction, Raman scattering spectra and TEM micrograph. Visible photoluminescence was observed at room temperature with the PL peak at about 560 nm and the linewidth about 0.45 eV. We are temporarily using the quantum confinement model to explain the PL mechanism.

Phonon Spectra of a-SiNx: H/Si Heterostructures Observed by Brillouin Light Scattering

Low-frequency phonon spectra in a-SiNx: H/Si heterostructures have been observed by means of Brillouin light scattering. Measurement of the frequency shift on longitudinal and transverse acoustic phonons as well as on surface phonons enabled us to extract accurately two independent elastic moduli: c11 and c44 deduced from phase velocities of bulk acoustic modes and scattering wavevector, within effective medium approximation.