V.G. Lifshits

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.

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.

Coadsorption of Au and Ag atoms on the Si(111) surface

Abstract A three-component surface phase formed by codeposition of Au and Ag on Si(111) has been studied with Auger electron spectroscopy (AES) and low-energy electron diffraction (LEED). It has been shown that if the amount of silver atoms on the surface exceeds a certain value (which is dependent on the Au amount on the Si surface), two types of three-component surface structures may form. In case θ Au 1 3 ML a solid solution of Au atoms in the Si(111)√3-Ag superlattice is formed; when θ Au > 1 3 ML the Si(111)√21-(Au, Ag) structure is observed.

The formation of MnSi(111) interface at room and high temperatures

Abstract The formation of a Mn Si (111) interface is studied by depositing submonolayer to several monolayer coverages θ of Mn at controlled rates and at different substrate and annealing temperatures. The observation of various surface phase formations, their transitions, and their dependence on deposition parameters are probed by Auger electron spectroscopy (AES), low energy electron diffraction (LEED) and electron energy loss spectroscopy (ELS). Deposition of Mn at very low rates (0.15 ML min −1 ) resulted in the formation of epitaxial structures even at room temperature (RT). It is observed for the first time that up to 1 ML, the low rate of arrival (deposition rate −1 ) of Mn atoms at the Si(111) surface facilitates the growth of a Mn Si (111)-7 × 7 surface phase. Mn atoms arriving thereafter accumulate in the layer-by-layer (Frank-van der Merwe) mode resulting in the 1 × 1 epitaxial growth of Mn at least up to 2–3 ML at RT. Annealing at 350°C of the RT deposited Mn (1 θ 3 ML) Mn Si (111) system results in a sharp √3 × √3 phase, which corresponds to the formation of manganese silicide as observed by ELS. It is found that using the 1 × 1 surface phase as a template results in high quality epitaxial √3 × √3 silicide formation. Deposition at low rates onto heated (350°C) Si(111) leads to Si(111)Mn 7 × 7 surface phase with the excess adatoms forming islands on the surface (Stranski-Krastanov mode).

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.

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.

Structural transformations at room temperature adsorption of In on Si(111)√3 × √3-In surface: LEED-AES-STM study

Abstract Low energy electron diffraction (LEED), Auger electron spectroscopy (AES) and scanning tunnelling microscopy (STM) have been used to study the evolution of the surface structure upon room temperature deposition of In onto In-predeposited Si(111)√3 × √3-In surface. The sequential formation of the Si(111)2 × 2 and Si(111)√7 × √3 surface phases has been detected and coverage ranges of their existence have been determined. STM observations have revealed that the Si(111)2 × 2-In phase has a honeycomb-like atomic structure with depressions in T 4 positions. The structural model built of In trimers has been proposed. The “low-temperature” Si(111)√7 × √3-In phase shows up in STM images as parallel rows of protrusions and its structure has been found to differ from the structure of the known “high-temperature” Si(111)√7 × √3-In phases. The inheritance of the defects at the structural transition from √3 × √3 structure to 2 × 2 structure has been discussed.

Agglomeration of submonolayer Ag films on Si(111) induced by the interaction with atomic hydrogen

Abstract We have used Auger electron spectroscopy to characterize the agglomeration of Ag layers with coverages of 0.2 to 1.2 ML induced by the interaction with atomic hydrogen. Originally uniform Ag films agglomerate during the interaction with atomic hydrogen to form Ag islands. The model calculations of Ag and Si Auger peak intensities after complete Ag agglomeration have been performed for the case of island growth. Our results have shown that the height of Ag islands increases with the increase of the original Ag coverage, while the total area covered by Ag islands is constant and independent of the original Ag coverage.

Growth of extra-thin ordered aluminum films on Si(111) surface

Abstract The conditions of surface phase formation have been studied by means of Auger electron spectroscopy and low-energy electron diffraction for a specified amount of Al deposited on clean Si(111)7 × 7 surface kept at constant temperature, from room temperature up to 700°C. The formation phase diagram for the Al/Si(111) system is presented. The regularities of epitaxial Al(111) growth on top Si(111)—Al surface phases are discussed.

Ordered surface phases in Sb/Si(110) systems

Abstract Sb desorption from a Sb submonolayer interface with a Si(110) substrate was studied with LEED and AES. The decrease of Sb coverage was found to result in the formation of sequences of the ordered surface phases, β(2 × 3), (2 × 1), α(2 × 3) and 0 14 1 −2 The process of the formation of different phases influences the Sb desorption kinetics. The trimer-type structural model was proposed for the atomic structure of the ordered Sb/Si(110) interfaces.