Size dependence of nanostructures: Impact of bond order deficiency

Auger parameter and Wagner plot in the characterization of chemical states by X-ray photoelectron spectroscopy: a review

Two-dimensional layered MoS2 shows great potential for nanoelectronic and optoelectronic devices due to its high photosensitivity, which is the result of its indirect to direct band gap transition when the bulk dimension is reduced to a single monolayer. Here, we present an exhaustive study of the band alignment and relativistic properties of a van der Waals heterostructure formed between single layers of MoS2 and graphene. A sharp, high-quality MoS2-graphene interface was obtained and characterized by micro-Raman spectroscopy, high-resolution X-ray photoemission spectroscopy (HRXPS), and scanning high-resolution transmission electron microscopy (STEM/HRTEM). Moreover, direct band structure determination of the MoS2/graphene van der Waals heterostructure monolayer was carried out using angle-resolved photoemission spectroscopy (ARPES), shedding light on essential features such as doping, Fermi velocity, hybridization, and band-offset of the low energy electronic dynamics found at the interface. We show th...

Band Alignment and Minigaps in Monolayer MoS2-Graphene van der Waals Heterostructures

The purpose of this article is to provide an overview of the surface structures of the clean surfaces of tetrahedrally coordinated semiconductors within the context of identifying the main features of their structural chemistry. We develop the point of view that the surface regions of these materials form twodimensional (2D) compounds whose bonding is constrained by the requirement of epitaxy with the substrate1 and that the coordination chemistry of these compounds differs from that of molecules or (three-dimensional) bulk solids in specific ways.2 Our coverage is confined to low-index faces. Specifically, our interest lies in the atomic geometries of ideal single-crystal regions of surfaces rather than in the morphology of surfaces with multiple domains, steps, or defects. Finally, although similar considerations have been applied to interpret oxide surface structures more generally,3 our attention herein is confined to tetrahedrally coordinated elemental and binary compound semiconductors. The traditional approach to constructing a review of this type is to consider each surface separately and to describe the structural studies4-11 or theoretical predictions of surface structure4-7,12,13 for each individual surface. This procedure offers an abundance of case histories, but little by way of guidance concerning how to make sense out of the wealth of Dr. Charles B. Duke is Senior Research Fellow at Xerox Corporation. Prior to holding this position, he was Deputy Director and Chief Scientist of the Pacific Northwest Division of the Battelle Memorial Institute and Affiliate Professor of Physics at the University of Washington. From 1972 to 1988 he held various technical and management positions at the Xerox Research Laboratories in Webster, NY and was an Adjunct Professor of Physics at the University of Rochester. During 1969−72, he was a Professor of Physics and member of the Materials Research Laboratory and Coordinated Science Laboratory at the University of Illinois in Urbana, IL, following six years as a staff member of the General Electric Corporate Research and Development Center in Schenectady, NY. He received his Ph.D. in physics from Princeton in 1963 following a B.S. Summa Cum Laude with distinction in mathematics from Duke University in 1959. He is a Fellow and an Honorary Member of the American Vacuum Society, a Fellow of the American Physical Society, a Fellow of the IEEE, and a life member of Sigma Xi. In 1977, Dr. Duke received the Medard W. Welch Award in Vacuum Science and Technology. In 1979 he served as President of the American Vacuum Society, and since 1979, as Treasurer of its Electronic Materials and Processing Division. He served on the Board of Directors of the American Vacuum Society for seven years. He was chairman of the 1977 Gordon Research Conference on the Chemistry and Physics of Solids and of the 1983 Gordon Research Conference on Organic Thin Films and Solid Surfaces. In 1981 he was named one of the ISI 1000 internationally most cited scientists. During 1985−86 he served as founding editor-in-chief of the Journal of Materials Research, the official journal of the Materials Research Society. From 1988 to 1992 and 1995 to 1997, he served (will be serving) on the council of the Materials Research Society, serving as Treasurer during 1991−2. In 1992 he was named editor of Surface Science. In 1993 he was elected to the National Academy of Engineering. He is serving on the Council of the American Physical Society during 1995−8. He was chairman of the Board of Editors of the Journal of Vacuum Science and Technology during 1976−82 and is currently a member of the editorial boards of Journal of Materials Research, Critical Reviews of Solid-State and Materials Sciences, Surface Science Reports, the Chemistry and Physics of Surfaces and Interfaces, and the Encyclopedia of Applied Physics. He served on the Governing Board of the American Institute of Physics from 1976 to 1987, being a member of the Board’s Executive Committee, Corporate Associates Committee, Educational Policy Committee, Journals Committee, and Committee on Public Education and Information. He has written over 350 papers on surface science, materials research, semiconductor physics, and the electronic structure of molecular solids, as well as a monograph on electron tunneling in solids. He is the editor of Surface Science: The First Thirty Years. 1237 Chem. Rev. 1996, 96, 1237−1259

Semiconductor Surface Reconstruction: The Structural Chemistry of Two-Dimensional Surface Compounds.

The methodology of ab initio molecular dynamics, wherein finite-temperature dynamical trajectories are generated by using forces computed "on the fly" from electronic structure calculations, has had a profound influence in modern theoretical research. Ab initio molecular dynamics allows chemical processes in condensed phases to be studied in an accurate and unbiased manner, leading to new paradigms in the elucidation of microscopic mechanisms, rationalization of experimental data, and testable predictions of new phenomena. The purpose of this work is to give a brief introduction to the technique and to review several important recent developments in the field. Several illustrative examples showing the power of the technique have been chosen. Perspectives on future directions in the field also will be given.

https://www.pnas.org/content/pnas/102/19/6654.full.pdf

Ab initio molecular dynamics: Concepts, recent developments, and future trends

Extremely well-resolved Si 2p core-level spectra have been obtained from the clean Si(001) surface. Spectra from the cold c(4×2) and the RT 2×1 surfaces are very similar, implying that the local structure of the two reconstructions is the same. Shifted components originating from both up and down atoms of asymmetric dimers, as well as second-layer atoms, are identified. The split of ∼0.55 eV between the two dimer-atom components points to a substantial charge transfer within the dimers. We find no support for the recently proposed crystal-field splitting of the surface components

Core-level spectroscopy of the clean Si(001) surface: Charge transfer within asymmetric dimers of the 2 x 1 and c(4 x 2) reconstructions.

Atomic origins of the surface components in the Si 2p core-level spectra of the Si(111)7 x 7 surface.

The electronic structure of the $\mathrm{Si}(111)7\ifmmode\times\else\texttimes\fi{}7$ surface has been studied in detail at a sample temperature of 55 K with high-energy-resolution angle-resolved photoemission. The photoemission spectra show a previously undetected surface-state structure at \ensuremath{\approx}0.5 eV below the Fermi level that we assign to dangling-bond states located mainly to the adatoms near the corner holes of the $7\ifmmode\times\else\texttimes\fi{}7$ reconstruction. Detailed dispersion curves obtained at 55 K are presented for the three uppermost, dangling-bond derived, surface states. Surface sensitive Si $2p$ spectra obtained in this low-temperature study still show a comparatively broad line shape. Possible reasons for this are discussed.

Low-temperature photoemission study of the surface electronic structure of Si ( 111 ) 7 × 7

Very sharp photoemission spectra have been obtained from the Si(111)-(1 \ifmmode\times\else\texttimes\fi{} 1):H and Si(111)-(1 \ifmmode\times\else\texttimes\fi{} 1):D surfaces prepared by a simple well-defined in situ method. Both the Si $2p$ core-level spectra and the valence band spectra are essentially identical to spectra reported for the chemically prepared (1 \ifmmode\times\else\texttimes\fi{} 1):H surface. We can conclusively exclude contributions from Si-H(D) stretching vibrational losses to the Si $2p$ core-level spectra, contrary to a recent suggestion. The line shape of the component originating from the surface Si atoms is found to be asymmetric, which we assign to asymmetric phonon broadening.

Y.-C. Chao

Papers

Core-level spectroscopy of the clean Si(001) surface: Charge transfer within asymmetric dimers of the 2 x 1 and c(4 x 2) reconstructions.

Atomic origins of the surface components in the Si 2p core-level spectra of the Si(111)7 x 7 surface.

Low-temperature photoemission study of the surface electronic structure of Si ( 111 ) 7 × 7

Si 2p core-level spectroscopy of the Si(111)-(1 x 1):H and Si(111)-(1 x 1):D surfaces: Vibrational effects and phonon broadening.

High-resolution core-level studies of silicon surfaces