Biaxial stress of ZnO film deposited on quartz was measured by side-inclination x-ray diffraction technique, indicating that the film is subjected to a tensile stress. One part of the stress is induced by thermal mismatch between the ZnO and the quartz and increases with annealing temperature, while another part results from lattice mismatch and is about 1.03GPa. The optical band gap of the ZnO film shows a blueshift with increasing biaxial tensile stress, opposed to the change of the band gap with biaxial tensile stress for GaN. The mechanism of the stress-dependent band gap is suggested in the present work.
Undoped MgxZn1−xO thin films with Mg content of 0⩽x⩽0.20 were grown on c-sapphire substrate by plasma-assisted molecular beam epitaxy. The MgxZn1−xO shows n-type conduction in Mg content of x⩽0.05, and the carrier concentration decreases slowly from 1018to1017cm−3 with increasing Mg content. However, as x⩾0.10, the MgxZn1−xO begins to show p-type conduction, and the carrier concentration goes down sharply to 1015cm−3 firstly and then increases slowly with increasing Mg content from 1015to1016cm−3. The mechanism of transformation from n to p type and change of the carrier concentrations with Mg content were investigated by photoluminescence and absorption measurements as well as first-principle calculation.
The interfacial charge phenomenon of MgO/low-density polyethylene (LDPE) and SiO2/LDPE nanocomposites was measured by synchrotron radiation small-angle X-ray scattering. Based on the Porod theory, the Porod curve of SiO2/LDPE nanocomposite shows negative divergence but the LDPE and MgO/LDPE do not, which reveals that interfacial charge may exist in the SiO2/LDPE nanocomposite. The DC dielectric properties of the nanocomposites are closely related to the interfacial charge. Experimental results show that the SiO2/LDPE nanocomposite has lower DC conductivity, less space charge, and higher DC breakdown strength than the MgO/LDPE nanocomposite. It is thought that the interfacial charge has a positive effect on the DC dielectric performance of nanocomposites, and the mechanism could be attributed to the scattering effects of the interfacial charge on the carrier migration. There is no obvious interfacial charge in the MgO/LDPE nanocomposite, but it still has excellent DC dielectric properties compared with LDPE, which indicates that the interfacial charge is not the only factor affecting the dielectric properties; the dipole interface layer and the reduction of free volume can also inhibit the migration of carriers and decrease electrons free path, improving the dielectric performance.
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