ZnO particles embedded in SiO2 thin films were prepared by a radio-frequency magnetron sputtering technique. X-ray diffraction (XRD) and optical-absorption spectra showed that ZnO particles with hexagonal wurtzite structure had been embedded in the SiO2 matrix, and the size of ZnO particles increased with increasing annealing temperature from 773to973K. Raman-scattering and Fourier transform infrared (FTIR) spectrum measurements also confirmed the presence of ZnO particles. When the annealing temperature was lower than 973K, room-temperature photoluminescence (PL) spectra showed dominative deep-level emissions in the visible region and very weak ultraviolet emissions. As the annealing temperature increased to 973K, an emission band in the ultraviolet region besides the emissions from free and bound excitons recombination was observed in the low-temperature PL spectra. The origin of the ultraviolet emission bands was discussed with the help of temperature-dependent PL spectra. When the annealing temperature was higher than 973K, Zn2SiO4 particles were formed, as shown by XRD and FTIR results.
(Mn, N)-codoped ZnO films were grown on fused silica substrates by reactive magnetron cosputtering. X-ray diffraction measurements reveal that the films have the single-phase wurtzite structure with c-axis preferred orientation. X-ray photoelectron spectroscopy studies indicate the incorporation of both divalent Mn2+ and trivalent N3− ions into ZnO lattice. Acceptor doping with nitrogen partly compensates the “native donors,” which results in a low electron concentration of 3.16×1016cm−3 though p-type conductivity is not achieved. (Mn, N)-codoped ZnO films show significant ferromagnetism with Curie temperature above 300K. The mechanism of ferromagnetic coupling in codoped ZnO is discussed based on a bound magnetic polaron model.
The Zn(1-x)Mn(x)O (x = 0, 0.16, and 0.25) thin films were grown on fused quartz substrates by reactive magnetron cosputtering. X-ray-diffraction measurement revealed that all the films were single phase and had wurtzite structure with c-axis orientation. As Mn concentration increased in the Zn(1-x)Mn(x)O films, the c-axis lattice constant and band-gap energy increased gradually. In Raman-scattering studies, an additional Mn-related vibration mode appeared at 520 cm(-1). E(2H) phonon line of Zn(1-x)Mn(x)O alloy was broadened asymmetrically and redshifted as a result of microscopic structural disorder induced by Mn(2+) random substitution. The Zn(0.84)Mn(0.16)O film exhibited a ferromagnetic characteristic with a Curie temperature of approximately 62 K. However, with increasing Mn concentration to 25 at. %, ferromagnetism disappeared due to the enhanced antiferromagnetic superexchange interactions between neighboring Mn(2+) ions.
Semitransparent flexible resistive-switching memory devices, using amorphous InGaZnO as the switching layer, are fabricated on plastic substrates at room temperature. The device shows high performance, excellent flexibility, and mechanical endurance in bending tests. No performance degradation occurs, and the stored information is not lost after bending the device to different angles and up to 10 5 times. Studies on the temperature-dependent electrical properties reveal that the conducting channels of the low-resistance state are composed of oxygen-deficient defects, and partial oxidation of these defects switches the device to the high-resistance state. The unique electronic structure and flexible mechanical properties of amorphous InGaZnO ensure stable device performance in flexible applications.
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