Wenxiu Cheng

Improvement of Ge self-organized quantum dots by use of Sb surfactant

A Sb-mediated growth technique is developed to deposit Ge quantum dots (QDs) of small size, high density, and foe of dislocations. These QDs were grown at low growth temperature by molecular beam epitaxy. The photoluminescence and absorption properties of these Ge QDs suggest an indirect-to-direct conversion, which is in good agreement with a theoretical calculation

Optical transition in SiGe self-organized dots

It is found that the SiGe alloy self-organizers into uniform quantum dots embedded in the Si layer during the growth of a strained Si/Ge short period superlattice on a Si(001) substrate at a temperature of 800 °C by molecular beam epitaxy. The peak of photoluminescence from the quantum dots is at an energy higher than the band gap of Si. The intensity is two orders of magnitude higher than that of SiGe/Si quantum well.

Influence of growth conditions on Al-Ga interdiffusion in low-temperature grown AlGaAs/GaAs multiple quantum wells

Low-temperature growth and subsequent rapid thermal anneal were used to intermix Al and Ga atoms in AlGaAs/GaAs multiple quantum wells (QWs). The intermixed samples were characterized by photoluminescence (PL) spectroscopy, and the observed blue shifts in PL energies are interpreted as the result of modification of the QW shape due to the enhanced Al-Ga interdiffusion in the samples. The enhancement of interdiffusion was found to be strongly dependent on the growth and annealing conditions. In addition, the saturation behavior of Al-Ga interdiffusion was also observed.

Martensitelike spontaneous relaxor-normal ferroelectric transformation in Pb(Zn1∕3Nb2∕3)O3–PbLa(ZrTi)O3 system

The spontaneous relaxor-normal ferroelectric transformation was found in the tetragonal composition of Pb(Zn1∕3Nb2∕3)O3–PbLa(ZrTi)O3 (0.3PZN–0.7PLZT) complex ABO3 system. The corresponding dielectric permittivities and losses of different compositions located near the morphotrophic phase boundary were analyzed. By reviewing all of the results about this type of transformation in previous references, the electric, compositional, structural, and thermodynamic characteristics of the spontaneous relaxor-normal transformation were proposed. Additionally, the adaptive phase model for martensite transformation proposed by Khachaturyan et al. [Phys. Rev. B 43, 10832 (1991)] was introduced into this ferroelectric transformation to explain the unique transformation pathway and associated features such as the tweedlike domain patterns and the dielectric dispersion under the critical transition temperature. Due to the critical compositions near the MPB, the ferroelectric materials just fulfill the condition, in which...

Effect of anisotropy on the ferroelectric, optical, and electro-optic properties of PLZT transparent ceramics prepared by uniaxial hot-press sintering techniques

PLZT (X/70/30) ceramics with different La contents (X = 7.45, 7.51,7.57, 7.63) were fabricated to study the effect of anisotropy on ferroelectric, optical, and electro-optic properties in parallel and normal to the uniaxial hot-press sintering direction (abbreviated as parallel and normal), respectively. All samples show the square hysteresis loops but the tetragonality with ferroelectricity is more evident in a parallel direction than that in normal direction. The high transmittances (≥60%, 0.35mm, visible to near infrared light) are obtained. However, the transmittances and the light scattering contrast ratios are higher in the normal direction. The PLZT (7.63/70/30) ceramic exhibits the more stable electrically controlled light scattering behavior in parallel direction and its contrast ratio reaches to the maximum 1.37 in a normal direction in this system.

Phase diagram for the 0.3Pb(Zn1/3Nb2/3)O3–0.7Pb0.96La0.04 (ZrTi)0.99O3 solid solution in the vicinity of morphotropic phase boundary

The dielectric behaviours of numerous specimens near the morphotropic phase boundary (MPB) of the 0.3Pb(Zn1/3Nb2/3)O3–0.7Pb0.96La0.04 (ZrxTi1 − x)0.99O3 (x = 0.50–0.53) relaxor ferroelectric system were measured. The results revealed that the poled specimens on the rhombohedral side underwent a rhombohedral–tetragonal transition on heating, and the depoled specimens on the tetragonal side experienced a spontaneous relaxor–normal transition on cooling. A phase diagram based on the dielectric permittivity measurements was proposed for this solid solution. The diagram showed that the polarization made the MPB bend sharply towards the rhombohedral-rich region. On the basis of these results in this and previous similar investigations, some common characteristics of complex relaxor ABO3 perovskite systems near the MPB were proposed.

Room-temperature luminescence from SiGe self-organized dots

Abstract It is found that the SiGe alloy self-organizes into uniform quantum dots embedded in the Si layer during the growth of strained SiGe Si multilayers on a Si(001) substrate by molecular beam epitaxy. The energy of photoluminescence from the quantum dots is higher than that of the indirect band gap of Si, and the luminescence of the quantum dots exceed quantum well by three orders of magnitude, room-temperature photoluminescence from SiGe quantum dots is first observed.

Fabrication, Microstructure and Magnetic Properties of LiZn Ferrites by Hot Pressing Method

The effects of sintering temperature on microstructure, phase, electrical and magnetic properties of LiZn ferrites prepared by hot pressing methods were examined systematically. All the ferrites were spinel strustures sintered at the temperature above 1050°C. At higher than 1100°C, pores within the grains appeared due to the volatilization of lithium. The DC electrical resistivity ρ increased firstly and decreased dramatically because of the Fe2+ formation. The magnetic properties showed that the saturation magnetization (Ms) increased and coercive field (Hc) decreased with the increasing temperature. The hot pressing method is proven an effective way to obtain the densified LiZn ferrites.

Fabrication and characteristics of relaxor ferroelectric PZN-PZT (53/47) thin films by a MOD process

Relaxor ferroelectric (1-x)Pb(Zn1/3Nb2/3)O3 - xPb(Zr0.53Ti0.47)O3 (abbreviated as PZN-PZT (53/47)) (x=0.4-1.0) thin films were prepared by a metallic-organic decomposition (MOD) process on Pt/Ti/SiO2/Si substrates. The influence of PZT (53/47) content on the film phase component has been investigated and analyzed. The ferroelectric and piezoelectric properties of the PZN-PZT(53/47) thin films have been examined and discussed. The lattice spacing d111 of the thin film was found to have a maximum value when the PZT (53/47) content x is about 0.7~0.8; which was attributed to the film lattice distortion. Compared with the pure PZT (53/47) thin film, the 0.2PZN-0.8PZT (53/47) thin film was found to have a much lower coercive electric field (Ec) while the spontaneous and remanent polarization was not decreased obviously. Also a more intensive piezoresponse in micro-area of the 0.2PZN-0.8PZT (53/47)) thin film has been observed by a modified AFM.

Effects of Annealing on Properties of PLZT (8/68/32) Electrically Controlled Light Scattering Ceramics

PLZT (8/68/32) electrically controlled light scattering ceramics with fully dense microstructure and high transmittance were prepared by a hot-press sintering method. The effects of annealing on dielectric, ferroelectric, optical and electrically controlled light scattering properties were examined and analysed. The XRD patterns indicated that all sintered specimens were well crystallized and the peak of 2θ∼30.8° gradually shifted to high degree. The temperature dielectric spectrum manifested the obvious relax or phase transition. And the double-look-like ferroelectric hysteresis loops revealed the tendency to transform a slim loop with the significant reduction in remnant polarization and coercive field via annealing treatment. Then the transmittance (from 58 to 62%, E = 0, λ = 632.8 nm) and contrast ratio (from 545:1 to 699:1) clearly increased after annealing treatment. The light scattering behavior of the PLZT samples was improved obviously.