Huanming Lu

Preparation and properties of TiB2 nanoparticle reinforced copper matrix composites by in situ processing

Abstract A copper matrix composite reinforced by in situ TiB 2 nanoparticle was prepared by reactions of B 2 O 3 , carbon and titanium in copper–titanium melt. The microstructure and mechanical and electrical properties of the as-drawn in situ composite were investigated. The results showed that the in situ-formed TiB 2 particles, which had a size of about 50 nm, exhibited a homogenous dispersion in the copper matrix. Due to their reinforcement, the tensile strength and hardness of the in situ Cu–TiB 2 composite significantly improved. Moreover, the as-drawn in situ composite had a high electrical conductivity.

Calculation of critical layer thickness considering thermal strain in Si1−xGex/Si strained-layer heterostructures

In this article, interactions of thermal strain in growth of Si1−xGex strained-layers on Si are analyzed. A formula of critical layer thickness (hc) is obtained based on energy balance considering thermal strain under the assumption that the screw dislocation energy density equals to the sum of the areal strain energy density and thermal strain energy density. The relationship between the thermal expansion coefficient associated with thermal strain and Ge content x is linear. Our calculated values for hc of Si1−xGex strained layers on Si substrates versus mismatch, considering thermal strain, are better agreement with measurements of hc by People and Bean.

Quasi-aligned ZnO nanotubes grown on Si substrates

Quasi-aligned ZnO nanotubes have been grown on silicon substrates by metalorganic chemical vapor deposition without using any catalyst. Two kinds of ZnO nanotubular structures were found: Nanotubes with single walls and nanotubes with double walls. The nanotubes were grown along the [001] direction. Room-temperature photoluminescence measurements of the ZnO nanotubes indicate strong ultraviolet emission and weak green emission. A new growth mode for these ZnO nanotubes is proposed, which can be used to prepare other nanotubular structures.

Microstructure study of ZnO thin films on Si substrate grown by MOCVD

The microstructure of zinc oxide thin films on silicon substrates grown by metalorganic chemical vapour deposition (MOCVD) was characterized. The cross-sectional bright-field transmission electron microscopy (TEM) image showed that small ZnO columnar grains were embedded into large columnar grains, and the selected-area electron diffraction pattern showed that the ZnO/Si thin films were nearly c-axis oriented. The deviation angle along the ZnO (0?0?0?1) direction with respect to the growth direction of Si (1?0?0) was no more than 5?. The [0?0?0?1]-tilt grain boundaries in ZnO/Si thin films were investigated symmetrically by plan-view high resolution TEM. The boundaries can be classified into three types: low-angle boundaries described as an irregular array of edge dislocations, boundaries of near 30? angle with facet structures and large-angle boundaries with symmetric structure which could be explained by a low ? coincident site lattice structure mode. The research was useful to us for finding optimized growth conditions to improve ZnO/Si thin film quality.

Highly c-axis oriented LiNbO3 thin film grown on SiO2/Si substrates by pulsed laser deposition

Abstract Highly c -axis oriented LiNbO 3 thin film has been deposited on the SiO 2 /Si substrate by KrF excimer pulsed laser deposition (PLD) technique under optimized conditions of 30-Pa oxygen pressure and 600 °C substrate temperature. The amorphous SiO 2 buffer layer was coated on the Si (001) wafer by thermal oxidation in situ. X-ray diffraction (XRD) and transmission electron microscopy (TEM) measurements confirm that the film shows superior crystalline quality and highly c -axis oriented texture. Neither the Li-enriched LiNbO 3 target nor a biased electric field was applied during the deposition.

Microstructure and defect investigations of the as-grown and annealed ZnO/Si thin films

The microstructure and defects of as-grown and annealed ZnO/Si thin films were investigated by high-resolution transmission electron microscopy (HRTEM). The cross-sectional bright-field TEM images showed that the ZnO thin films consisted of columnar grains. The selected-area electron diffraction pattern showed that the ZnO/Si thin film were c-axis oriented and the deviation angle along the ZnO (0001) direction with respect to the growth direction was no more than 5°. The grain boundaries can be classified into three types: low-angle boundaries, boundaries near a 30 deg angle with (101¯0) facet structures and large-angle boundaries. In addition to grain boundary, the as-grown and annealing processing defects were also investigated by HRTEM. The crystal quality of the ZnO/Si thin films can be improved by annealing at 600 °C. However, at too high an annealing temperature of 800 °C, the newly produced processing defects such as three layer stacking fault and double stacking fault were formed. The research was...

Thermal warpage of Czochralski silicon wafers grown under a nitrogen ambience

The thermal warpage of nitrogen-doped Czochralski (NCZ) silicon wafers affected by preannealing was investigated. After preannealing at 1000 °C for 6 h, the warpage of the NCZ silicon wafers was suppressed during subsequently thermal warping tests, while the silicon wafers grown under an argon ambient (ACZ) showed an increase in warpage. Nitrogen was considered to be very effective to increase the mechanical strength of silicon wafers because of the formation of nitrogen-oxygen clusters with smaller sizes. After preannealing at 1000 °C for 16 h, both ACZ and NCZ silicon wafers showed a large increase of warpage due to the large amount of oxygen precipitation.

The growth and investigation of SiGe films on buried Ge islands

SiGe/Si films on buried Ge islands on Si substrates were deposited using an ultrahigh vacuum chemical vapor deposition system at a temperature of 620°C in comparison with a single-step SiGe film with the same Ge content and growth temperature. X-ray diffraction measurements show that the crystalline quality of the SiGe films on the buried Ge islands was better than that without buffers, and the top SiGe films were relaxed. The high-resolution cross-sectional transmission electron microscopy images show that the size of the three dimension Ge islands is about 60 nm and the top SiGe film on buried Ge islands is better crystallographically than that grown without buffers.

SiGe Epitaxy with Graded Buffer by Ultrahigh Vacuum Chemical Vapor Deposition

A SiGe/Si epilayer with a linear-step-graded buffer was grown by ultrahigh vacuum chemical vapor deposition technique at a relatively high growth temperature (780° C) and a relatively high growth rate. Almost linear Ge content variation was realized in the buffer layer due to the Ge segregation to the growing surface during epitaxial growth. Double crystal x-ray diffraction and Raman spectroscopy show that the upper layer is fully relaxed. However, the measured results show that the density of dislocation in the composition graded structure is much lower than that in single-step epilayer structures.

Preparation and characterization of ZnO nanotubes

ZnO nanotubes were grown by metalorganic chemical vapor deposition (MOCVD) on silicon substrates without using any catalyst. Scanning electron microscopy measurement revealed that the ZnO nanotubes have hexagonal outer shape and round inner shape, the outer diameter is of 60/spl sim/110 nm and the wall thickness is 10/spl sim/15 nm. Transmission electron microscopy measurement showed that the nanotubes are single crystals with c-axis growth orientation. Low-temperature photoluminescence measurements revealed intense ultraviolet light emission near the band gap of ZnO at 3.37 eV, and show almost no broad green photoluminescence emission band related to native defects.