Fundamental processes in Si/Si and Ge/Si epitaxy studied by scanning tunneling microscopy during growth

Reactions at surfaces studied by ab initio dynamics calculations

Due to the development of efficient algorithms and the improvement of computer power it is now possible to map out potential energy surfaces (PES) of reactions at surfaces in great detail. This achievement has been accompanied by an increased effort in the dynamical simulation of processes on surfaces. The paradigm for simple reactions at surfaces -- the dissociation of hydrogen on metal surfaces -- can now be treated fully quantum dynamically in the molecular degrees of freedom from first principles, i.e., without invoking any adjustable parameters. This relatively new field of ab initio dynamics simulations of reactions at surfaces will be reviewed. Mainly the dissociation of hydrogen on clean and adsorbate covered metal surfaces and on semiconductor surfaces will be discussed. In addition, the ab initio molecular dynamics treatment of reactions of hydrogen atoms with hydrogen-passivated semiconductor surfaces and recent achievements in the ab initio description of laser-induced desorption and further developments will be addressed.

The development of manipulation tools that are not too ‘fat’ or too ‘sticky’ for atomic scale assembly is an important challenge facing nanotechnology1. Impressive nanofabrication capabilities have been demonstrated with scanning probe manipulation of atoms2,3,4,5 and molecules4,6 on clean surfaces. However, as fabrication tools, both scanning tunnelling and atomic force microscopes suffer from a loading deficiency: although they can manipulate atoms already present, they cannot efficiently deliver atoms to the work area. Carbon nanotubes, with their hollow cores and large aspect ratios, have been suggested7,8 as possible conduits for nanoscale amounts of material. Already much effort has been devoted to the filling of nanotubes8,9,10,11 and the application of such techniques12,13. Furthermore, carbon nanotubes have been used as probes in scanning probe microscopy14,15,16. If the atomic placement and manipulation capability already demonstrated by scanning probe microscopy could be combined with a nanotube delivery system, a formidable nanoassembly tool would result. Here we report the achievement of controllable, reversible atomic scale mass transport along carbon nanotubes, using indium metal as the prototype transport species. This transport process has similarities to conventional electromigration, a phenomenon of critical importance to the semiconductor industry17,18.

Carbon nanotubes as nanoscale mass conveyors

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.

X-ray photoelectron diffraction patterns of K $2p$ core levels have been measured for the Si(001) 2 \ifmmode\times\else\texttimes\fi{} 1-K surface. From a kinematical analysis of the diffraction patterns, it is concluded that a sawtooth-type arrangement of the potassium double array is present over the substrate. This is in disagreement with an existing assumption of the one dimensionality of the alkalimetal-Si(001) systems.

Photoelectron diffraction study of Si(001) 2 × 1-K surface: Existence of a potassium double layer

Surface electronic structure of a single-domain Si(111)4 × 1-In surface: a synchrotron radiation photoemission study

Surface Core-Level Photoelectron Diffraction from Si Dimers at the Si(001)-(2×1) Surface

The submonolayer growth of Ge on single domain Si(001)-(2 X 1) has been studied using high resolution photoemission by monitoring the Ge 3d and Si 2p core levels as functions of coverage, electron ...

Mixed Ge-Si Dimer Growth at the Ge/Si(001)-( 2×1) Surface

Surface reconstructions of a submonolayer Sb/Si(111) system were investigated by low-energy electron diffraction and X-ray photoelectron spectroscopy. It has been found that the surface superstructures of diffuse 2×2 (or three-domain 2×1), √3×√3, 5√3×5√3 and 7√3×7√3 are formed for the Sb coverages around one monolayer.

Tadashi Abukawa

Papers

Photoelectron diffraction study of Si(001) 2 × 1-K surface: Existence of a potassium double layer

Surface electronic structure of a single-domain Si(111)4 × 1-In surface: a synchrotron radiation photoemission study

Surface Core-Level Photoelectron Diffraction from Si Dimers at the Si(001)-(2×1) Surface

Mixed Ge-Si Dimer Growth at the Ge/Si(001)-( 2×1) Surface

Low Energy Electron Diffraction and X-Ray Photoelectron Spectroscopy Studies of the Formation of Submonolayer Interfaces of Sb/Si(111)