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Co-doped ZnO films were synthesized by ion beam sputtering using multilayer (ZnO/Co) growth. Both the distribution and the chemical states of Co in ZnO can be well controlled by varying the ratio of the nominal layer thickness of ZnO to Co. Transmission electron microscopy indicated that all of the as-deposited Zn1-x(Co)xO films were polycrystalline with a (0002) preferred orientation. The local microstructures and chemical states were identified by Z-contrast imaging and electron energy loss spectroscopy. In ZnO (1.5 nm)/Co (0.1 nm), homogeneous Co-doped ZnO was observed to have been formed through interdiffusion. However, decreasing or increasing the thickness of ZnO leads to the formation of Co clusters in the ZnO matrix or Zn1-x(Co)xO multilayers, respectively. For ZnO thickness≧1.5 nm, Co is substituted for Zn, and its valence state is 2+. All Co-doped ZnO films show room-temperature ferromagnetic behavior, which appears to depend strongly on the Co distribution. [ABSTRACT FROM AUTHOR]

The type-IV diluted magnetic semiconductor (DMS) [Si(20 Å)/Mn(x)]30 multilayers (MLs) with nominal thickness x=1, 1.5, and 2.0 Å have been prepared by molecular beam epitaxy. The structure, magnetism, and electrical property of these MLs were investigated. Above room temperature ferromagnetism has been observed and structure probed by x-ray absorption spectroscopy. The Mn local structure is similar to Si simulation and the Mn chemical valences of the MLs are in the range from zero (Mn foil) to Mn+2. The relative carrier concentration is sensitive to the formation of room temperature ferromagnetism, suggesting that hole mediated mechanism play an important role in Si:Mn DMSs. [ABSTRACT FROM AUTHOR]

We investigated the room temperature ferromagnetism and their local coordination environment of Co and Mn doped in ZnO single crystal films. Both films show room temperature ferromagnetism and the saturated magnetization of the Mn-doped ZnO film is stronger than that of the Co-doped films. From the analysis on the local structures of Zn, Co, and Mn, we verify that the lattice distortions mainly surround the Co and Mn dopants. Due likely to the relatively large cation size, the Mn dopant would induce a greater local lattice distortion. We suggest that the local environment disorder between the Co and Mn dopants may play a role to the origin of ZnO based diluted magnetic semiconductor films. [ABSTRACT FROM AUTHOR]

The frequency and temperature variation of magnetoimpedance in Ni-Zn ferrite thin films fabricated by spray plating method were studied. It is observed that the frequency induces a metal -- insulator crossover behavior in impedance spectra. The frequency behavior of the electrical properties of the film can be modeled by an equivalent circuit composed of resistance and capacitance. The relaxation time and activation energy of the conductivity were calculated. The result suggests that the high-frequency conductivity of the spin-spray plating of a Ni-Zn ferrite film is predominantly associated with the dielectric, rather than by magnetization, dynamics. Mechanisms underlying high-frequency transport are discussed. [ABSTRACT FROM AUTHOR]

The impedance of chemical vapor deposited CrO[sub 2] and Cr[sub 2]O[sub 3] bilayered thin films, composed of polycrystalline and amorphous structure, have been systematically studied in function of frequency and temperature. In the polycrystalline-CrO[sub 2]/amorphous-Cr[sub 2]O[sub 3] bilayer, the real part of impedance at low frequency (f<300 kHz) demonstrates a sharp transition at temperature around 330 K, with a specific feature of positive temperature coefficient, similar to the variation of dc resistance occurs at ferroelectric-paraelectric transition in the BaTiO[sub 3] ceramics. In contrast, the imaginary part of impedance, at frequency f>300 kHz, shows a characteristic of negative temperature coefficient. Further analysis of the frequency dependence of the impedance shows the contribution from the dynamics of both the dielectric and magnetic dipoles in the layers. Comparison of polycrystallineCrO[sub 2] and amorphous-Cr[sub 2]O[sub 3] single layer with the CrO[sub 2]/Cr[sub 2]O[sub 3] bilayer is discussed. [ABSTRACT FROM AUTHOR]

The declining number of physician scientists is an alarming issue. A systematic review of all existing programs described in the literature was performed, so as to highlight which programs may serve as the best models for the training of successful physician scientists. Multiple databases were searched, and 1,294 articles related to physician scientist training were identified. Preference was given to studies that looked at number of confirmed publications and/or research grants as primary outcomes. Thirteen programs were identified in nine studies. Eighty-three percent of Medical Scientist Training Program (MSTP) graduates, 77% of Clinician Investigator Training Program (CI) graduates, and only 16% of Medical Fellows Program graduates entered a career in academics. Seventy-eight percent of MSTP graduates succeeded in obtaining National Institute of Health (NIH) grants, while only 15% of Mayo Clinic National Research Service Award-T32 graduates obtained NIH grants. MSTP physician scientists who graduated in 1990 had 13.5 ± 12.5 publications, while MSTP physician scientists who graduated in 1975 had 51.2 ± 38.3 publications. Additionally, graduates from the Mayo Clinic's MD-PhD Program, the CI Program, and the NSRA Program had 18.2 ± 20.1, 26.5 ± 24.5, and 17.9 ± 26.3 publications, respectively. MSTP is a successful model for the training of physician scientists in the United States, but training at the postgraduate level also shows promising outcomes. An increase in the number of positions available for training at the postgraduate level should be considered. [ABSTRACT FROM AUTHOR]