A.A. Saranin

Hydrogen interaction with clean and modified silicon surfaces

The present report deals with the main aspects of the interaction of hydrogen with the atomically clean crystalline silicon surfaces and submonolayer metal/silicon interfaces. After a brief presentation of the experimental techniques applied nowadays in the hydrogen/silicon interaction studies, the main recent results obtained in this field are reviewed. For the case of clean silicon surfaces, hydrogen interaction is shown to change greatly their structure and properties. The main regularities of the hydrogenation of silicon and the features of the processes on the hydrogen-adsorbed silicon surfaces (chemical reactions, metal film growth, silicon and germanium epitaxy) are discussed. The atomic hydrogen interaction with the metal/silicon submonolayer interfaces results in most cases in the agglomeration of the two-dimensional metal layers into the three-dimensional metal islands. The application of this process for the structural investigations is demonstrated. The feasibility of the selective deposition and extraction of H atoms by a tip of scanning tunneling microscope is shown to open wide opportunities for nanostructure fabrication.

Family of the metal-induced Si(111)3×1 reconstructions with a top Si atom density of 4/3 monolayer

Abstract Using scanning tunneling microscopy (STM), the common features and peculiarities of the Si(111)3×1 reconstructions induced by Na, Ag, Ca, and Mg have been studied. From the quantitative consideration of the Si mass transport occurring at the 7×7→3×1 transformation, the top Si atom density has been found, and it appears to be the same, 4/3 monolayer, for all surface structures under consideration. A thorough examination of the numerous high-resolution STM images of Si(111)3×1–Na surfaces reveals that all 3×1 domains have a unique orientation with respect to the Si(111) substrate. The recently proposed double-π-bonded chain and honeycomb chain-channel models appear to be the only models that fit these experimental findings properly.

Restructuring process of the Si(111) surface upon Ca deposition

Abstract Using scanning tunneling microscopy and high-resolution spot profile analysis low-energy electron diffraction (SPA-LEED), the process of Si(111)3×1-Ca phase formation induced by Ca adsorption on Si(111)7×7 samples has been studied. Our observation revealed that what has been considered to be 3×1 reconstruction is actually a mixture of 3×2 and c(6×2) reconstructions. The redistribution of Si atoms in a top Si(111) layer has been found to play a critical role in the Si(111)3×2-Ca growth. From the quantitative consideration of Si mass transport balance, top Si atom density of Si(111)3×2-Ca phase has been determined to be a 4/3 monolayer.

Two-Dimensional Superconductor with a Giant Rashba Effect: One-Atom-Layer Tl-Pb Compound on Si(111).

A one-atom-layer compound made of one monolayer of Tl and one-third monolayer of Pb on a Si(111) surface having √3×√3 periodicity was found to exhibit a giant Rashba-type spin splitting of metallic surface-state bands together with two-dimensional superconducting transport properties. Temperature-dependent angle-resolved photoelectron spectroscopy revealed an enhanced electron-phonon coupling for one of the spin-split bands. In situ micro-four-point-probe conductivity measurements with and without magnetic field demonstrated that the (Tl, Pb)/Si(111) system transformed into the superconducting state at 2.25 K, followed by the Berezinskii-Kosterlitz-Thouless mechanism. The 2D Tl-Pb compound on Si(111) is believed to be the prototypical object for prospective studies of intriguing properties of the superconducting 2D system with lifted spin degeneracy, bearing in mind that its composition, atomic and electron band structures, and spin texture are already well established.

A Strategy to Create Spin-Split Metallic Bands on Silicon Using a Dense Alloy Layer

To exploit Rashba effect in a 2D electron gas on silicon surface for spin transport, it is necessary to have surface reconstruction with spin-split metallic surface-state bands. However, metals with strong spin-orbit coupling (e.g., Bi, Tl, Sb, Pt) induce reconstructions on silicon with almost exclusively spin-split insulating bands. We propose a strategy to create spin-split metallic bands using a dense 2D alloy layer containing a metal with strong spin-orbit coupling and another metal to modify the surface reconstruction. Here we report two examples, i.e., alloying reconstruction with Na and Tl/Si(111)1 × 1 reconstruction with Pb. The strategy provides a new paradigm for creating metallic surface state bands with various spin textures on silicon and therefore enhances the possibility to integrate fascinating and promising capabilities of spintronics with current semiconductor technology.

Large spin splitting of metallic surface-state bands at adsorbate-modified gold/silicon surfaces

Finding appropriate systems with a large spin splitting of metallic surface-state band which can be fabricated on silicon using routine technique is an essential step in combining Rashba-effect based spintronics with silicon technology. We have found that originally poor structural and electronic properties of the surface can be substantially improved by adsorbing small amounts of suitable species (e.g., Tl, In, Na, Cs). The resultant surfaces exhibit a highly-ordered atomic structure and spin-split metallic surface-state band with a momentum splitting of up to 0.052 Å−1 and an energy splitting of up to 190 meV at the Fermi level. The family of adsorbate-modified surfaces, on the one hand, is thought to be a fascinating playground for exploring spin-splitting effects in the metal monolayers on a semiconductor and, on the other hand, expands greatly the list of material systems prospective for spintronics applications.

Interaction of the atomic hydrogen with Si(111)3 × 3-Al surface: LEED and AES results

Using LEED and AES the RT structural transformations from Si(111)3 × 3-Al to Si(111)1 × 1-(A1, H) induced by atomic hydrogen has been studied. It has been found that transformation kinetics is determined by the exposure time and does not depend on the pressure during exposure. Upon heating at temperatures above 700°C the 3 × 3-Al structure reappears, but the Al coverage is always less than the original coverage. Isothermal desorption of Al from the Si(111)3 × 3-Al structure has been studied. It has been shown that Al desorption does not produce noticeable effect on the Al coverage in the reappeared 3 × 3 structure. It has been concluded that a fall in Al coverage is determined not by the formation of the volatile Al-hydride but rather by the interaction of uncontrollable contaminants (oxygen-containing molecules) with aluminum.

Random and ordered arrays of surface magic clusters

Surface magic clusters (SMCs) are clusters exhibiting enhanced stability at certain sizes on a particular surface. Through the formation of SMCs, it is possible to grow an ensemble of nanostructures on a surface with extremely small or essentially zero size dispersion. Such an ensemble of nanostructures with identical size and atomic structure is highly desirable for certain nanotechnologies that rely on the homogeneity in the physical and chemical properties of the constituent nanostructures. This review summarizes current experimental observations and understanding of SMCs and discusses the most recent progress in the formation of a two-dimensional lattice of SMCs, whose constituent clusters have not only identical size and structure but also the same local environment due to the translational symmetry of the system.

Stepwise self-assembly of C60 mediated by atomic scale moiré magnifiers

Self-assembly of atoms or molecules on a crystal surface is considered one of the most promising methods to create molecular devices. Here we report a stepwise self-assembly of C₆₀ molecules into islands with unusual shapes and preferred sizes on a gold-indium-covered Si(111) surface. Specifically, 19-mer islands prefer a non-compact boomerang shape, whereas hexagonal 37-mer islands exhibit extraordinarily enhanced stability and abundance. The stepwise self-assembly is mediated by the moiré interference between an island with its underlying lattice, which essentially maps out the adsorption-energy landscape of a C₆₀ on different positions of the surface with a lateral magnification factor and dictates the probability for the subsequent attachment of C₆₀ to an islands periphery. Our discovery suggests a new method for exploiting the moiré interference to dynamically assist the self-assembly of particles and provides an unexplored tactic of engineering atomic scale moiré magnifiers to facilitate the growth of monodispersed mesoscopic structures.

Si(100)4 × 3-In surface phase: identification of silicon substrate atom reconstruction

Abstract The arrangement of Si substrate atoms in Si(100)4 × 3-In surface phase was studied using removal of In atoms at exposure of the surfaces to atomic hydrogen and monitoring the surface transformations by low energy electron diffraction and Auger electron spectroscopy. The Si(100)4 × 3-In surface was found to transform at H exposure to Si(100)4 × 1-H(In) surface showing definitely that Si substrate atoms are reconstructed. The persistence of 4 × 1 structure at high hydrogen exposures (when no Si dimerization can be preserved) unambiguously reduces the choice of possible structural models of Si substrate reconstruction to only three candidates. In turn, STM data [A.A. Baski et al., Phys. Rev. B 43 (1991) 9316] of ∼0.5 ML Si atom density in Si(100)4 × 3-In phase leaves a single realistic structure, namely Si(100) surface having every second Si atom double row missing.