E.A. Khramtsova

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.

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.

Thermal nitridation of the Si(110) by NH3: LEED and AES study

Abstract The Si(110) surface was thermally nitrided by NH3 gas. The investigation was performed in the temperature range of 560–1050°C by exposure to a low pressure of ammonia (10−5−10−6 Torr). Auger electron spectroscopy (AES) and low energy electron diffraction were used to study the nitridation process. It was found that nitridation occurs by two different stages, namely, the initial fast step arbitrary limited at 500 L and the much slower and saturating step at higher exposures. AES data indicated that the growth mode is controlled by the growth temperature. At high substrate temperature, the Sinitride layer grows in the initial stage as a set of epitaxial islands. When the entire surface is covered by islands, the growth mode converts to a layer-by-layer one. At lower temperature the nitridation process is essentially layer-by-layer in the whole exposure range. During thermal nitridation the original Si(110) surface structure gradually converts to the Si-nitride structure with hexagonal symmetry and the surface-lattice unite cell vectors of 2.85 A.

LEED-AES reexamination of the Ai/Si(111) “γ-phase”

Abstract The saturating Al adlayer grown on Si(111 ) at 500–700°C (so-called Al/Si(111) “γ-phase”) was characterized by means of low-energy electron diffraction (LEED) and Auger electron spectroscopy (AES). The formation of the “γ-phase” was found to complete upon adsorption of 0.6 monolayers of Al after which the sticking coefficient of Al drops abruptly and no additional Al can be adsorbed at temperatures above ~ 500°C. The precise examination of the LEED data revealed that the Al/Si(111) “γ-phase” has an 8 × 8 periodicity.

Formation of the Si(111)8 × 8-N structure by reaction of NH3 with a Si(111) surface

Abstract The Si(111) surface was thermally nitrided at 850–1020°C by exposure to low pressures (5 × 10 −6 Torr) of ammonia. Auger electron spectroscopy (AES) and low energy electron diffraction (LEED) have been used to study the nitridation processes. It was found that, at initial stage the nitride layer grows as flat 5 ± 1 A thick islands, which have an 8 × 8 structure. When the entire surface is covered by islands, the formation of the 8 × 8-N surface phase is completed and growth of bulk silicon nitride starts. In the latter case the growth mode changes to a layer-by-layer one.

4 × 1-Si substrate atoms reconstruction in the Si(111)4 × 1-In structure

Abstract The room temperature interaction of atomic hydrogen with the Si(111)4 × 1-In surface phase was studied using low energy electron diffraction and Auger electron spectroscopy. It was found that the underlying atomic layer of a substrate of the Si(111)4 × 1-In surface phase has a reconstruction with the same periodicity as the In layer. Our experimental data evidently show that atomic hydrogen is a powerful tool for the investigation of the atomic structure of surface phases forming on the silicon surface.

Comparative study of the atomic hydrogen interaction with Si(110)“4 × 6”-Al and Si(111)√3 × √3-Al surfaces

Abstract The effect of room temperature atomic hydrogen exposure and subsequent thermal annealing of the Si (110)“4 × 6”- Al surface has been investigated by using low energy electron diffraction (LEED) and Auger electron spectroscopy (AES). The behaviour of the Si (110)“4 × 6”- Al and Si(111)√3 × √3-Al surfaces were compared. It was found that on the Si(110) surface H atoms cause the agglomeration of the uniform aluminium layer into very small Al islands as on the Si(111) surface. In both cases the atomic hydrogen interaction induced the structural transformation of the original structure into the 1 × 1. The subsequent thermal annealing of both Si(111)1 × 1-H(Al) and Si(110)1 × 1-H(Al) surfaces leads to the restoring of the initial surface structures. Analysis of the isochronal annealing curves has shown a one-stage reappearing process of the √3 × √3 structure and a two-stage one of the “4 × 6”. This difference has been ascribed to the anisotropy of the surface diffusion of Al atoms on the Si(110) surface

Chemical and structural transformations in the Al/Si(111)8×8-N system

Abstract Chemical and structural transformations in the Al/Si(111)8 × 8-N system were studied by Auger electron spectroscopy (AES) and low energy electron diffraction (LEED). After deposition of aluminum on the Si(111)8 × 8-N surface and subsequent heating, the chemical composition and the structure of the surface change. It has been demonstrated by AES that aluminum reduces the silicon nitride, forming AlN at annealing temperatures ranging from 650 to 850°C. Annealing at 650°C results in the formation of a disordered AlN film and accumulation of Al on the surface. Annealing at 750°C results in the formation of the Si(111)7 × 7-AlN structure and the desorption of excess Al from the surface. The structure of Si(111)7 × 7-AlN corresponds to the (0001) plane of bulk AlN, compressed by 4%. Annealing at 850°C results in the formation and subsequent desorption of AlN and the recovery of the clean Si(111)7 × 7 surface.

Effect of NH3 adsorption on the atomic structure of Si(111) √3 × √3 - Al and Si(111) √3 × √3 - Ag surfaces

The room temperature (RT) adsorption of ammonia (NH3) on Si(111)√3 × √3-Al and Si(111)√3 × √3-Ag surfaces has been studied using LEED and AES. The transformation from Si(111)√3 × √3-Al surface structure to Si(111)1 × 1-(Al, H) upon NH3 exposure has been found to be similar to the previously observed structural transformation induced by exposure in the atomic hydrogen. It has been demonstrated that the transformation is caused by hydrogen atoms which are generated by NH3 dissociation on the Si(111)√3 × √3-Al surface. It has been estimated that about 0.1 ML of ammonia molecules is needed to complete the structural transformation. No interaction of NH3 with the Si(111)√3 × √3-Ag surface has been found. The dissociation of NH3 molecules is believed to be impossible on this surface