Yingge Du

Intrinsic Diffusion of Hydrogen on Rutile TiO2(110)

The combined experimental and theoretical study of intrinsic hydrogen diffusion on bridge-bonded oxygen (BBO) rows of TiO 2(110) is presented. Sequences of isothermal scanning tunneling microscopy images demonstrate a complex behavior of hydrogen formed by water dissociation on BBO vacancies. Different diffusion rates are observed for the two hydrogens in the original geminate OH pair suggesting the presence of a long-lived polaronic state. For the case of separated hydroxyls, both theory and experiment yield comparable temperature-dependent diffusion rates. Density functional theory calculations show that there are two comparable low energy diffusion pathways for hydrogen motion along the BBO from one BBO to its neighbor, one by a direct hop and the other by an intermediate minimum at a terrace O. The values of kinetic parameters (prefactors and diffusion barriers) determined experimentally and theoretically are significantly different and indicate the presence of a more complex diffusion mechanism. We speculate that the hydrogen diffusion proceeds via a two-step mechanism: the initial diffusion of localized charge, followed by the diffusion of hydrogen. Both experiment and theory show the presence of repulsive OH-OH interactions.

Formation of O adatom pairs and charge transfer upon O2 dissociation on reduced TiO2(110)

Scanning tunneling microscopy and density functional theory have been used to investigate the details of O(2) dissociation leading to the formation of oxygen adatom (O(a)) pairs at terminal Ti sites. An intermediate, metastable O(a)-O(a) configuration with two nearest-neighbor O atoms is observed after O(2) dissociation at 300 K. The nearest-neighbor O(a) pairs are destabilized by Coulomb repulsion of charged O(a)s and separate further along the Ti row into energetically more favorable second-nearest neighbor configuration. The potential energy profile calculated for O(2) dissociation on Ti rows and following O(a)s separation strongly supports the experimental observations. Furthermore, our results suggest that the itinerant electrons associated with the O vacancies (V(O)) are being utilized in the O(2) dissociation process at the Ti row. Experimentally this is supported by the observation that not all V(O)s can be healed by O(2) exposure at 300 K, as some V(O)s becoming less reactive due to supplying certain charge to O(a)s. Further, theoretical results show that at least two oxygen vacancies per O(2) molecule are required in order for the O(2) dissociation at the Ti row to become viable.

Perovskite Sr‐Doped LaCrO3 as a New p‐Type Transparent Conducting Oxide

Epitaxial La1-x Srx CrO3 deposited on SrTiO3 (001) is shown to be a p-type transparent conducting oxide with competitive figures of merit and a cubic perovskite structure, facilitating integration into oxide electronics. Holes in the Cr 3d t2g bands play a critical role in enhancing p-type conductivity, while transparency to visible light is maintained because low-lying d-d transitions arising from hole doping are dipole forbidden.

Reproducible tip fabrication and cleaning for UHV STM

Several technical modifications related to the fabrication and ultra-high vacuum (UHV) treatments of the scanning tunneling microscope (STM) tips have been implemented to improve a reliability of the tip preparation for high-resolution STM. Widely used electrochemical etching drop-off technique has been further refined to enable a reproducible fabrication of the tips with a radius <or= 3 nm. For tip cleaning by a controllable UHV annealing, simple and flexible setup has been developed. Proper W tip preparation has been demonstrated via an imaging of the TiO2 (110) surface atomic structure.

Hole-induced insulator-to-metal transition in L a 1 − x S r x Cr O 3 epitaxial films

We have investigated the evolution of the electronic properties of

Adsorption states and mobility of trimethylacetic acid molecules on reduced TiO2(110) surface

\mathrm{L}{\mathrm{a}}_{1\ensuremath{-}x}\mathrm{S}{\mathrm{r}}_{x}\mathrm{Cr}{\mathrm{O}}_{3}\phantom{\rule{0.16em}{0ex}}(0\ensuremath{\le}x\ensuremath{\le}1)

Strain Accommodation by Facile WO6 Octahedral Distortion and Tilting during WO3 Heteroepitaxy on SrTiO3(001)

epitaxial films deposited by molecular beam epitaxy (MBE) using x-ray diffraction, x-ray photoemission spectroscopy, Rutherford backscattering spectrometry, x-ray absorption spectroscopy, electrical transport, and ab initio modeling.

Anticorrelation between surface and subsurface point defects and the impact on the redox chemistry of TiO2(110)

\mathrm{LaCr}{\mathrm{O}}_{3}

Formation of Cu2O quantum dots on SrTiO3 (100): Self-assembly and directed self-assembly

is an antiferromagnetic insulator, whereas

The effects of core-level broadening in determining band alignment at the epitaxial SrTiO3(001)/p-Ge(001) heterojunction

\mathrm{SrCr}{\mathrm{O}}_{3}