arXiv subjects

J. S. Yang

Publications and source records attributed to J. S. Yang.

4 recordsLinked to original sources

arXiv2011

Scientific Productivity, Research Funding, Race and Ethnicity

In a recent study by Ginther et al., the probability of receiving a U.S. National Institutes of Health (NIH) RO1 award was related to the applicant's race/ethnicity. The results indicate black/African-American applicants were 10% less likely than white peers to receive an award, after controlling for background and qualifications. It has generated a widespread debate regarding the unfairness of the NIH grant review process and its correction. In this paper, the work by Ginther et al. was augmented by pairing analysis, axiomatically-individualized productivity and normalized funding success measurement. Although there are racial differences in R01 grant success rates, normalized figures of merit for funding success explain the discrepancy. The suggested "leverage points for policy intervention" are in question and require deeper and more thorough investigations. Further adjustments in policies to remove racial disparity should be made more systematically for equal opportunity, rather than being limited to the NIH review process.

stat.AP↗

arXiv2007

Surface versus bulk characterization of the electronic inhomogeneity in a VO_{2} film

We investigated the inhomogeneous electronic properties at the surface and interior of VO_{2} thin films that exhibit a strong first-order metal-insulator transition (MIT). Using the crystal structural change that accompanies a VO_{2} MIT, we used bulk-sensitive X-ray diffraction (XRD) measurements to estimate the fraction of metallic volume p^{XRD} in our VO_{2} film. The temperature dependence of the p$^{XRD}$ was very closely correlated with the dc conductivity near the MIT temperature, and fit the percolation theory predictions quite well: $σ$ $\sim$ (p - p_{c})^{t} with t = 2.0$\pm$0.1 and p_{c} = 0.16$\pm$0.01. This agreement demonstrates that in our VO$_{2}$ thin film, the MIT should occur during the percolation process. We also used surface-sensitive scanning tunneling spectroscopy (STS) to investigate the microscopic evolution of the MIT near the surface. Similar to the XRD results, STS maps revealed a systematic decrease in the metallic phase as temperature decreased. However, this rate of change was much slower than the rate observed with XRD, indicating that the electronic inhomogeneity near the surface differs greatly from that inside the film. We investigated several possible origins of this discrepancy, and postulated that the variety in the strain states near the surface plays an important role in the broad MIT observed using STS. We also explored the possible involvement of such strain effects in other correlated electron oxide systems with strong electron-lattice interactions.

cond-mat.str-el↗

arXiv2003

Kinetic Roughening of Ion-Sputtered Pd(001) Surface: Beyond the Kuramoto-Sivashinsky Model

We investigate the kinetic roughening of Ar$^+$ ion-sputtered Pd(001) surface both experimentally and theoretically. \textit{In situ} real-time x-ray reflectivity and \textit{in situ} scanning tunneling microscopy show that nanoscale adatom islands form and grow with increasing sputter time $t$. Surface roughness, $W(t)$, and lateral correlation length, $ξ(t)$, follows the scaling laws, $W(t)\sim t^β$ and $ξ(t)\sim t^{1/z}$ with the exponents $β\simeq 0.20$ and $1/z\simeq 0.20$, for ion beam energy $ε=0.5$ keV, which is inconsistent with the prediction of the Kuramoto-Sivashinsky (KS) model. We thereby extend the KS model by applying the Sigmund theory of sputter erosion to the higher order, ${\cal O}(\nabla^4, h^2)$, where $h$ is surface height, and derive a new term of the form $\nabla^2(\nabla h)^2$ which plays an indispensable role in describing the observed morphological evolution of the sputtered surface.

cond-mat.stat-mech↗

arXiv2002

Formation of Co nanoclusters in epitaxial Ti_{0.96} Co_{0.04} O_2 thin films and their ferromagnetism

Anatase Ti0.96Co0.04O2 films were grown epitaxially on SrTiO3 (001) substrates by using plused laser deposition with in-situ reflection high-energy electron diffraction. The oxygen partial pressure, PO2, during the growth was systematically varied. As PO2 decreased, the growth behavior was changed from a 2-dimensional layer-by-layer-like growth to a 3-dimensional island-like one, which resulted in an increase in the saturation magnetization. These structural and magnetic changes were explained in terms of the formation of cobalt clusters whose existence was proved by transmission-electron-microscopie studies. Our work clearly indicates that the cobalt clustering will cause room-temperature ferromagnetism in the Co-doped TiO2 films.

cond-mat.mtrl-sci↗