Teruo Hanawa

Initial growth process and surface structure of Ag on Si(111) studied by low-energy Ion-Scattering Spectroscopy (ISS) and LEED-AES

Abstract The growth process of silver on a Si(111) substrate has been studied in detail by low-energy ion-scattering spectroscopy (ISS) combined with LEED-AES. Neon ions of 500 eV were used as probe ions of ISS. The ISS experiments have revealed that the growth at room temperature and at high temperature are quite different from each other even in the submonolayer coverage range. The following growth models have been proposed for the respective temperatures. At room temperature, the deposited Ag forms a two-dimensional (2D) island at around 2/3 monolayer (ML) coverage, where the Ag atoms are packed commensurately with the Si(111)1 substrate. One third of the substrate Si surface remains uncovered there. Then it starts to develop into Ag crystal, and at a few ML coverage a 3D island of bulk Ag crystal grows directly on the substrate. An intermediate layer, which covers uniformly the whole surface before the growth of Ag crystal, does not exist. At high temperatures (>~200°C), the well-known Si (111)√3- Ag layer is formed as an intermediate layer, which consists of 2/3 ML of Ag atoms and covers the whole surface uniformly. These Ag atoms are embedded in the first double layer of the Si substrate. It is concluded that the formation of the √3 structure needs relatively high activation energy which may originate from the large displacement of Si atoms owing to the embedment of the Ag atoms, and does not proceed below about 200°C. The most stable state of the Ag atoms on the outermost Si layer is in the shape of an island, both for the Si(111) surface and for the Si (111)√3- Ag surface.

LEED-AES study of the AuSi(100) system

Abstract The system Au/Si(100) has been studied using LEED and AES. Au films grow as Au(111) | Si(100) having six azimuthally rotated orientations at low deposition temperatures below 50°C after the formation of intermediate gold suicide layers. Crystalline gold silicide thin layers are formed on the Au(111) film after heat treatment at 100–400°C. Two types of suicide LEED pattern observed seem to have no correlation with crystallographic data reported on quenched alloy films. Heat treatment over 450°C leads to agglomeration of the film, producing a series of Au-induced superstructures. Heat treatment of the Au film over 1000°C regenerates the clean Si surface accompanied with many etch pits.

A TOF-ISS/ERDA apparatus for solid surface analysis

Abstract A time-of-flight (TOF) system has been constructed to perform surface-structure analysis by impact collision ion scattering spectroscopy with primary noble-gas ions and scattered-neutral detection. The structure of thin Ag films (1–5 ML thickness) deposited onto a clean Si(111) substrate has been studied.

Low energy ion scattering study of adsorption and desorption processes of Pb on Si(111) surfaces

Abstract The initial growth process and the thermal desorption process of Pb on the Si(111) substrate have been studied in detail by LEED and ISS (low-energy ion-scattering spectroscopy), where neon ions of 500 eV were used as probe ions. The growth of Pb on a Si(111)7 substrate follows the Stranski-Krastanov growth mechanism, which is common to a room temperature substrate and a 340°C one. However, the intermediate layer at room temperature and at 340°C are different from each other in its structure and formation process. The intermediate layer at room temperature is a Pb(111) layer whose orientation is identical to the substrate, while that at 340°C is a Si(111)1-Pb layer consisting of 1 ML of Pb. The ISS data suggest that extremely small 2D (two-dimensional) islands of the Pb(111) formed in the mid-course coalesce into the Pb(111) layer, and that the 1-Pb layer starts to form when the density of the 2D gas phase initially formed comes up to a critical value (which is 0.27 ML at 340°C). When a heat treatment is made in the course of the deposition, the Si (111) 3 - Pb (α) intermediate layer which probably consists of 4 3 ML of Pb is formed before the formation of 3D islands. The thermal desorption process of the Si(111)1-Pb layer can be divided into the two steps, namely, (1) the desorption of the 1-Pb layer leaving the Si (111) 3 - Pb (β) structure consisting of 1 3 ML of Pb behind and (2) that of the 3 - Pb (β) structure. The kinetics of the first step is zero-order, while the second step has a high order kinetics. It is proposed that the Pb atoms of the √3-Pb(β) structure are bonded to three Si atoms, and such a bonding configuration is responsible for the high order desorption kinetics observed.

Atomic Arrangement of the Si(111)-√3×√3-Ag Structure Derived from Low-Energy Ion-Scattering Spectroscopy

Si(111)-√3×√3-Ag surface structure has been studied by low-energy ion-scattering spectroscopy using neon ions with an energy of 500 eV, combined with LEED-AES. It has been proposed that Ag atoms giving rise to the √3 structure are slightly embedded below the outermost Si layer, including consequent displacements of the substrate Si atoms.

A leed-aes study of thin Pd films on Si(111) and (100) substrates

Abstract A system Pd (deposit)-Si (substrate) has been studied by LEED and AES. Pd 2 Si formed on Si(111) became epitaxial after a short time of annealing at a temperature between 300 and 700°C, while the Pd 2 Si formed on Si(100) did not, in both cases the surfaces of the Pd 2 Si being covered with a very thin Si layer. A sequence of superstructures (3√3 × 3√3), (1 × 1), and (2√3 × 2√3) was observed successively in Pd/Si(111) as the annealing temperature was increased. A (√3 × √3) structure was obtained by sputtering the 3√3 surface slightly. It was found that the √3 structure corresponds to Pd 2 Si(0001)-(1 × 1) grown epitaxially on Si(111), and that the 3√3 structure comes from the thin Si layer accumulated over the silicide surface, while the 2√3 and 1 structures arise from a submonolayer of Pd adsorbed on Si(111). Superstructures observed on a Pd/Si(100) system are also studied.

Elastic recoil detection analysis of hydrogen adsorbed on solid surfaces

Abstract An experimental apparatus for quantitative analysis of hydrogen adsorbed on solid surfaces is described. Elastic recoil detection analysis (ERDA) by a 6 MeV F3+ ion beam determines the hydrogen coverage and a LEED-Auger system is used to monitor the order and cleanliness of the specimen surface. The method has been applied to a H/Si(111)-7 × 7 system.

Thermally induced accumulation of silicon on palladium silicide surfaces as studied by Auger electron spectroscopy

A clean surface of a palladium silicide grown on a Si(111) plane has been studied by Auger electron spectroscopy. Heat treatment of the silicide in the temperature range 250–600 °C causes the accumulation of a thin layer of elementary Si over its surface. The accumulated thickness has been estimated to be about 3 A and does not depend on heating temperatures and periods examined.

Electronic properties and atomic arrangement of the Ag/Si(111) interface

Abstract Variations of the work function and photoelectric yield spectra of a Ag/Si(111) system were investigated as a function of Ag film thickness and substrate temperatures. It was clarified that monolayer deposition of Ag onto Si at room temperature cause a decrease in the work function, while the deposition at 500°C did an increase. The results could be closely correlated with the atomic arrangement derived from low-energy ion scattering spectroscopy and low-energy electron diffraction.

Inelastic effect in low-energy He+ ion scattering from solid surfaces

Abstract Values of the inelastic loss energy Q are investigated for the systems (He+−Ag, Au, Ta, and W) by the scattered-particle method at a fixed scattering angle of 90° and incident ion energies ranging from 300 to 1000 eV. The experiments are performed by an ISS unit with high energy resolution. It is found that the observed loss Q gradually increases and reaches about 5–6 eV even for Ag and Au surfaces at the incident energy of 1000 eV. In addition, the data for the oxygen contaminated Ta, and W surfaces suggest that two inelastic loss processes are involved and one of these is enhanced by the existence of oxygen.