The longitudinal generalized magneto-optical ellipsometry （GME） method is extended to the measurement of three- layer ultrathin magnetic films. In this work, the theory of the reflection matrix is introduced into the GME measurement to obtain the reflective matrix parameters of ultrathin multilayer magnetic films with different thicknesses. After that, a spectroscopic ellipsometry is used to determine the optical parameter and the thickness of every layer of these samples, then the magneto-optical coupling constant of the multilayer magnetic ultrathin film can be obtained. After measurements of a series of ultrathin Fe films, the results show that the magneto-optical coupling constant Q is independent of the thickness of the magnetic film. The magneto-optical Kerr rotations and ellipticity are measured to confirm the validity of this experiment. Combined with the optical constants and the Q constant, the Kerr rotations and ellipticity are calculated in theory. The results show that the theoretical curve fits very well with the experimental data.
In this article we review recent transport property studies on topological insulator thin films grown by molecular beam epitaxy.In pure Bi2Se3 ultrathin films we find an insulating ground state in the presence of weak antilocalization,which indicates the relevance of electron interaction effect.In magnetically doped Bi2Se3 film we observe a systematic crossover between weak localization and weak antilocalization with varied magnetic doping,temperature,and magnetic field.These results demonstrate the intricate interplay between topological delocalization,electron interaction,and broken time reversal symmetry in topological insulator thin films.
Quantum Hall effect （QHE）, as a class of quantum phenomena that occur in macroscopic scale, is one of the most important topics in condensed matter physics. It has long been expected that QHE may occur without Landau levels so that neither external magnetic field nor high sample mobility is required for its study and application, Such a QHE free of Landau levels, can appear in topological insulators （TIs） with ferromagnetism as the quantized version of the anomalous Hall effect, i.e., quantum anomalous Hall （QAH） effect. Here we review our recent work on experimental realization of the QAH effect in magnetically doped TIs. With molecular beam epitaxy, we prepare thin films of Cr-doped （Bi,Sb）2Te3 TIs with well- controlled chemical potential and long-range ferromagnetic order that can survive the insulating phase. In such thin films, we eventually observed the quantization of the Hall resistance at h/e2 at zero field, accompanied by a considerable drop in the longitudinal resistance. Under a strong magnetic field, the longitudinal resistance vanishes, whereas the Hall resistance remains at the quantized value. The realization of the QAH effect provides a foundation for many other novel quantum phenomena predicted in TIs, and opens a route to practical applications of quantum Hall physics in low-power-consumption electronics.
In the present work, post-annealing is adopted to investigate the formation and the correlation of Sb complexes and Zn interstitials in Sb-ion implanted ZnO films, by using Raman scattering technique and electrical characterizations. The damage of Zn sublattice, produced by ion bombardment process is discerned from the unrecovered E2 （L） peak in annealed high Sb＋ dose implanted samples. It is suggested that the Zn sublattice may be strongly affected by the introduction of Sb dopant because of the formation of Sbzn-2Vz,, complex acceptor. The appearance of a new peak at 510 cm-1 in the annealed high dose Sb＋ implanted samples is speculated to result from （Zn interstitials-O interstitials） Zni-Oi complex, which is in a good accordance with the electrical measurement. The p-type ZnO is difficult to obtain from the Sb＋ implantation, however, which can be realized by in-situ Sb doping with proper growth conditions instead.
The role of temperature on the oxidation dynamics of Cu20 on ZnO （0001） was investigated during the oxidation of Cu （111）/ZnO （0001） by using oxygen plasma as the oxidant. A transition from single crystalline Cu20 （111） orientation to micro-zone phase separation with multiple orientations was revealed when the oxidation temperature increased above 300 ~ C. The experimental results clearly show the effect of the oxidation temperature with the assistance of oxygen plasma on changing the morphology of Cu （111） film and enhancing the lateral nucleation and migration abilities of cuprous oxides. A vertical top-down oxidation mode and a lateral migration model were proposed to explain the different nucleation and growth dynamics of the temperature-dependent oxidation process in the oxidation of Cu （lll）/ZnO （0001）.
Photodynamic therapy (PDT) is a very effective treatment for port wine stains (PWS). To guide and assess PDT treatment, a handheld optical coherence tomography (OCT) probe was designed for real-time imaging of the PWS patient. The system uses a light source with a center wavelength of 1310 nm, -3 dB bandwidth of 90 nm and an optical power of 9 mW. The system also has a spatial resolution of 8 μm (lateral) × 7 μm (axial), an imaging rate of 4 frames per second, and a 102 dB sensitivity. We then demonstrate that the OCT imaging system can clearly distinguish between normal and PWS tissues. Therefore, the system can provide valuable guidance for PDT treatment.
WANG TianShiWANG ChengMingHUANG NaiYanZHANG JianGU YingXUE Ping
