Syed Mohammad Fakruddin Shahed

Epitaxial growth of CeO2(111) film on Ru(0001): scanning tunneling microscopy (STM) and x-ray photoemission spectroscopy (XPS) study.

We formed an epitaxial film of CeO2(111) by sublimating Ce atoms on Ru(0001) surface kept at elevated temperature in an oxygen ambient. X-ray photoemission spectroscopy measurement revealed a decrease of Ce(4+)/Ce(3+) ratio in a small temperature window of the growth temperature between 1070 and 1096 K, which corresponds to the reduction of the CeO2(111). Scanning tunneling microscope image showed that a film with a wide terrace and a sharp step edge was obtained when the film was grown at the temperatures close to the reduction temperature, and the terrace width observed on the sample grown at 1060 K was more than twice of that grown at 1040 K. On the surface grown above the reduction temperature, the surface with a wide terrace and a sharp step was confirmed, but small dots were also seen in the terrace part, which are considerably Ce atoms adsorbed at the oxygen vacancies on the reduced surface. This experiment demonstrated that it is required to use the substrate temperature close to the reduction temperature to obtain CeO2(111) with wide terrace width and sharp step edges.

Atomically resolved Larmor frequency detection on Si(111)-7×7 oxide surface

We demonstrate that the electron spin resonance–scanning tunneling microscope can detect the Larmor frequency of a single spin with the atomic scale resolution on the oxygen-adsorbed Si(111)-7×7 surface. The spin signal from the Si dangling bond was detected on the oxygen-induced bright Si adatom with the Larmor frequency corresponding to g∼2.00. However, no peak was detected on the dark adatom that is tied with an oxygen atom and the dangling bond is disappeared.

Scanning Tunneling Microscope Study of Surface Morphology Variation of CeO2(111) with Changing Annealing Condition

The surface morphology variation of CeO2(111) with changing annealing condition was examined by scanning tunneling microscopy (STM). Hexagonal islands and pits containing two types of step edge have been found as characteristic features in a short-time-annealed surface. We observed that the triangular pits having only one type of step edge increase in number with annealing time, while the hexagonal pits and islands decrease and the deviated hexagonal pits increase. Step edges of the hexagonal pits that have higher coordinative saturation get preferential thermodynamic stability to form triangular pits, the most stable surface structures on the CeO2(111) surface in the equilibrium stage of annealing. These results have important implications for controlling catalytic activity on ceria.

Deposition of an Ultraflat Graphene Oxide Nanosheet on Atomically Flat Substrates

In this study, graphene oxide (GO) sheets produced in the form of stable aqueous dispersions were deposited on Au (111), freshly cleaved mica, and highly oriented pyrolytic graphite (HOPG) substrates. Atomic force microscopy (AFM) and scanning electron microscopy (SEM) were used to study the presence and distinct contact of GO sheets on the substrates. It was revealed from the topography images that high-quality ultraflat GO monolayer sheets formed on the substrates without distinct cracking/wrinkling or folding. GO sheets with apparent height variation observed by microscopy also indicate ultraflat deposition with clear underlying steps. It was observed that ultrasonication and centrifuge steps prior to deposition were very effective for getting oxidation debris (OD)-free ultraflat single monolayer GO nanosheets onto substrates and that the process depends on the concentration of supplied GO solutions.

Metal Electrode Formation on Organic Film Using Xe-Buffer-Layer-Assisted Deposition for Efficient Measurement of Inelastic Tunneling Spectroscopy

We demonstrate that, by using a Xe-buffer-layer-assisted deposition, a metal electrode can be formed on an organic film without altering the chemical properties of the molecules. A new efficient measurement of inelastic tunneling spectroscopy (IETS) was demonstrated by attaching the scanning tunneling microscopy (STM) tip to the Au cluster. Au electrode was formed on a Xe buffer layer condensed on an alkanethiol self-assembled monolayer (SAM), in which the Xe layer prevents direct interaction between hot metal atoms and molecules in the film. An IETS measurement executed with the new method revealed the robustness of the molecules at the metal-film interface.