In the past several decades, dilute magnetic semiconductors, particularly the dilute magnetic oxides have evolved into an important branch of materials science due to their potential application in spintronic devices combining of properties of semiconductors and ferromagnets. In spite of a major effort devoted to the mechanism of ferromagnetism with a high Curie temperature in these materials, it still remains the most controversial research topic, especially given the unexpected do ferromagnetism in a series of undoped wide-band-gap oxides films or nanostructures. Recently, an abundance of research has shown the critical role of various defects in the origin and control of spontaneous magnetic ordering, but contradicting views from intertwined theoretical calculations and experiments require more in-depth systematic research. In our previous work, considerable efforts have been focused on two major oxides, i.e. ZnO and Zr02. This review will present a summary of current experimental status of this defect-driven ferromag- netism in dilute magnetic oxides （DMOs）.
Isomers and homologues of organic pollutants are hard to distinguish-especially in trace amounts-due to the similarities in their physical and chemical properties. We report here that by identifying the Raman characteristics of isomers of monochlorobiphenyls, these compounds can be recognized, even at trace levels, by using the surface-enhance Raman scattering method with silver nanorods as a substrate. When dissolved in acetone, 2-, 3-, and 4-chlorobiphenyls were detected at a concentration of 10^(-8) mol/L, at which their characteristic Raman peaks were visible. This study may provide a fast, simple, and sensitive method for the detection and recognition of organic pollutants such as polychlorinated biphenyls.
Slanted Fe nanorods prepared by glancing angle deposition on silicon substrates exhibited easy magnetization along their growth axis. By using a thin gold film on a silicon substrate as a buffer layer, slanted Fe nanorods can be realigned towards the substrate surface normal by a strong magnetic field. After realignment, the Fe nanorods retained the easy magnetization axis along their growth axis. The effects of the realignment by the strong magnetic field on the properties of the slanted Fe nanorods were also investigated. This study provides a possible way to fabricate magnetic nanostructures for perpendicular recording applications.
An effective surface enhanced Raman scattering（SERS） substrate is designed and fabricated by synthesis of Si O2 nanorods array via glancing angle deposition, followed by coating Au nanoparticles onto Si O2 surface in order to create numerous ＂hot spots＂. The detecting sensitivity of such substrate could be optimized by simply adjusting the deposition time of Au. Thus, it can be used for detection of Rhodamine 6G at concentration as low as 10^-9M. Furthermore, our SERS substrate is applied to detect 5 μg/g polychlorinated biphenyls in soil sample, which proves its potential for trace environmental pollutants detection.
Tantalum （Ta） oxide flhns with tunable structural color were fabricated easily using anodic oxidation. The structure, components, and surface valence states of the oxide films were investigated by using gazing incidence X-ray diffractometry, X-ray photoelectron microscopy, and surface analytical techniques. Their thickness and optical properties were studied by using spectroscopic ellipsometry and total reflectance spectrum. Color was accurately defined using L＊a＊b＊ scale. The thickness of compact Ta2O5 films was linearly dependent on anodizing voltage. The film color was tunable by adjusting the anodic voltage. The difference in color appearance resulted from the interference behavior between the interfaces of air-oxide and oxide metal.
Diluted magnetic oxides have evolved into a popular branch of materials science during the last decade. In the first few years, people attributed the ferromagnetism to the magnetic dopants. However, the observation of ferromagnetism in undoped HfO2 thin films made it more controversial and promoted extensive research on the ferromagnetism in various undoped oxides. Both of the experimental w-orks and theoretical studies have shown that intrinsic defects in oxide nanomaterials play a crucial role in the origin of such an unexpected ferromagnetism, in spite of some contradicting views which kind of defects is predominant. In the past several years, we have conducted systematic and thorough research on the room temperature ferromagnetism in undoped ZrO2 thin films, and clarif some physics behind it. We firstly prepared undoped ZrO2 thin films by different w-ays, such as Pulsed electron bean deposition, magnetron sputtering, and electron beam evaporation, and successfully obtained ZiO2 thin films wdth different crystalline structure, in particular a pure high-temperature stabilized one, by adjusting some preparation parameters during the deposition process or post-annealing treatment. A phase-dependent ferromagnetism w-as then confinmed to exist in such ZiO2 thin films. Further, w-e conducted exhaustive defect analysis and characterization by X-ray photoelectron spectroscopy, photoluminescence spectra, and electron paramagnetic resonance, respectively, and found the oxygen vacancy, specifically the single ionized oxygen vacancy （Vo＋） , has a remarkable influence on the enhancement of ferromagnetism. Herein, we will review the work in detail on the phase-dependent and oxygen vacancy-enhanced room temperature ferromagnetism in undoped ZrO2 thin films.Keywords Zi thin film ferromagnetism phase-dependent oxygen vacancy
