J. Yuhara

Effects of foreign metals on the thermal stability of noble metal adsorbates at the Si(111) surface

Abstract Effects of monolayer foreign metals on the thermal stability of noble metal adsorbates (Au, Ag, and Cu) at the Si(111) surface have been studied by means of LEED-AES-RBS techniques. It is found that the thermal stability of Au atoms at the Si(111) surface does not change due to deposition of both Ag and Cu atoms and subsequent annealing. On the other hand, it is found that the thermal stability of Ag at the Si(111) surface decreases due to coexistence of Au atoms on the post annealing but is not influenced by coexistence of Cu atoms. Moreover, it is shown that Cu atoms deposited on the Si(111)-√3 × √3-Ag and √3 × √3-Au surfaces become very unstable on the post annealing.

Thermal stability of two-dimensional atomic structures of Au-Ag adsorbates on Si(111) surfaces

Isochronal annealing of Au–Ag binary adsorbates at the Si(111) surface at temperatures from 200 to 430 °C has been studied by means of low energy electron diffraction, Auger electron spectroscopy, and Rutherford backscattering spectroscopy techniques. It was found that a √3×√3−(Au,Ag) structure was formed by annealing for 15 min at 200 °C Ag atoms on the Si(111)–5×1‐Au surface at Au coverages less than 0.60 ML, and that the √3×√3 structure was kept until Ag decreases from 0.70 ML down to 0.18 ML due to the annealing, while the initial Au coverage was kept. Furthermore, when the Ag atoms, which are more than 0.60 ML, on the Si(111)–√3×√3‐Au surface were annealed at 200 °C, a new structure of 2√3×2√3‐(Au,Ag) was observed. Then, the √21 ×√21R(±10.89 °)‐(Au,Ag) structure was formed by prolonged isochronal annealing and was kept until Ag decreases down to 0.12 ML, while the initial Au coverage was kept. From analysis of the decay curves of Ag coverage, it was determined that the activation energies for Ag atom...

Studies on 2D Au-Cu binary adsorbates on Si(111) surfaces by means of combined LEED/AES/RBS techniques

Isothermal annealing at 170°C and subsequent isochronal annealing for 5 min of Au-Cu binary adsorbates on the Si(111) surface have been studied by means of combined LEED/AES/RBS techniques. In cases of deposition of Cu onto the 5 × 1-Au/Si(111) surface as well as of Au onto the quasi-5 × 5-Cu/Si(111) surface it is found that a √3 × √3 structure is formed by the initial isothermal annealing for 3 min at Au coverages between 0.35 and 0.60 ML and that for prolonged isothermal annealing the 3×3 structure persists keeping the initial Au coverage, while the Cu content decreases to a certain equilibrium coverage corresponding to a the equilibrium Cu-to-Au ratio of 14−13. The stabilization of the 3×3 structure, which at the Au/Si(111) surface below 0.60 ML of Au, is ascribed to coexistence of Cu. Achievement of the equilibrium Cu coverage is concluded to certify formation of a 2D ordered alloy of Au-Cu on the Si(111) surface. The dynamic behavior of Au and Cu binary adsorbates at the Si(111) surface and the atomic arrangement of Au and Cu at the 3×3 surface are also discussed.

Ion impact desorption of metal atoms from Si(111)-3 × 3-metal surfaces

Abstract The cross-sections for desorption and recoil-implantation of Ag and Au at the Si(111)-√3 × √3 -metal surfaces by keV Ar+ ions have been measured by means of LEED, AES and RBS techniques to determine their surface binding energy. The concentration decay of metal atoms at the Si (111)- 3 × 3 -metal surfaces has been measured by means of AES and RBS techniques as a function of Ar+ fluence. From the concentration decay profiles, the cross-sections for desorption and recoil-implantation are determined as functions of Ar+ energy. It is determined that the surface binding energies of Ag and Au are 0.6 eV and 2.7 eV, respectively, by fitting the calculated recoil-production cross-sections to the experimental recoil-implantation cross-sections. Both cross-sections are discussed in comparison with the sputtering cross-section of the substrate.

Commensurate–incommensurate phase transition between 6×6 and √3×√3 + satellite structures of the Au/Si(111) surface

Alternate annealing in the low‐ (≤250 °C) and high‐ (≥400 °C) temperature regimes of the Au/Si(111) surface at different Au coverages prepared by room‐temperature deposition and isothermal annealing in the high‐temperature regime at over‐(ML) coverages have been studied by means of low energy electron diffraction (LEED), Auger electron spectroscopy (AES), and Rutherford backscattering spectroscopy (RBS). It is found that the 6×6 pattern and the √3×√3+satellite pattern are formed at 0.9–2.2 ML coverages by annealing for several minutes at 250 and 500 °C, respectively, when there exist an Au surface peak and a diffusion tail extended towards the lower energy behind the Au peak and that the phase transition between both patterns is reversible by alternate annealing in two temperature regimes as long as the diffusion tail is not diminished. From this result, the 6×6 structure is ascribed to excess embedded Au atoms situated at the ordered sites and Au atoms constituting the √3×√3 structure at the top surface....

Phase transition of the Si(111)–Au surface from √3 ×√3 to 5×1 structure studied by means of the low‐energy electron diffraction, Auger electron spectroscopy, and Rutherford backscattering spectroscopy techniques

The changes of the Au coverage and the structure of the Si(111)–√3×√3‐Au surface induced by isothermal annealing in the temperature range of 500–575 °C have been studied by means of low‐energy electron diffraction (LEED), Auger electron spectroscopy, and Rutherford backscattering spectroscopy techniques. It is found that the Au coverages by RBS and AES at each temperature decay exponentially down to 0.75 ML, above which only the LEED pattern of √3×√3 spots is observed, and decay biexponentially from 0.75 ML and a mix of √3×√3 + 5×1 spots is observed down to 0.54 ML at 575 °C, 0.52 ML at 550 °C, and 0.61 ML at 530 °C, below which only the LEED pattern of 5×1 spots is observed. From analysis of the decay curves of Au coverages, it is determined that the activation energies for Au atoms to be dissolved from the √3×√3 structure and the 5×1 structure into the bulk and for phase transition of the Au/Si(111) surface from the √3×√3 to the 5×1 structure are 2.5±0.5, 2.8±1.0, and 1.6±0.4 eV, respectively. The proce...

The change of atomic structures and compositions of (Pb, Sn)/Si(111) surfaces by thermal annealing

Abstract Changes of atomic structures and compositions of (Pb,Sn)/Si(111) surfaces by isochronal annealing have been studied by means of low energy electron diffraction–Rutherford backscattering spectroscopy (LEED–RBS) techniques. It is found that on isochronal annealing the (Pb,Sn)/Si(111) surfaces show a new superstructure of 7 × 3 at Pb and Sn coverage of around 0.3 and 0.6 ML, respectively. Moreover, the Pb coverage on the Sn Si(111) 7 × 3 -(Pb,Sn) surface decays at a temperature a little bit higher due to coexistence of 7 × 3 Pb atoms than that on the Si(111) 3 × 3 -Pb surface, while the Sn coverage shows a little decrease. These results suggest that the binary atoms of Pb and Sn form a 2-dimensional (2D) alloy on the Si(111) surface, in contrast to those of Ag and Cu which have a very similar bulk phase.

The interaction of Ni adsorbate with the AgSi(111) surface

Abstract The change of atomic structures and compositional ratios by isochronal annealing of Ag–Ni binary adsorbates at the Si(111) surface has been studied by means of LEED-AES-RBS techniques at temperatures from 200°C to 700°C. It is found that the surface coverage of Ni deposited on the Si(111)−√3 × √3−Ag surface decreases to 0 ML on annealing at 250°C for 15 min, while the Ag surface coverage is not changed by Ni deposition and subsequent annealing up to 350°C. It is also found on annealing at 350°C that Ag on the Si(111)−√19 × √19−Ni surface produces the √3 × √3 LEED pattern and the Ni coverage by AES decreases to 0 ML. These results indicate that Ag and Ni atoms are not bound to each other on the Si(111) surface, and that Ag atoms preferentially occupy the surface with forming the √3 × √3−Ag structure and Ni atoms dissolve into the Si bulk. Moreover, it is found that the room temperature deposition of Ni onto the Si(111)−3 × 1−Ag surface produces a mixed structure of √3 × √3 and 3 × 1, which is changed into the single √3 × √3 structure by subsequent annealing at 200°C. It indicates that Ag atoms move from the 3 × 1−Ag site into the √3 × √3−Ag site due to the co-existence of Ni adsorbates.

Thermal behavior of deuterium implanted into SrCe0.95Yb0.05O3-δ

Abstract The concentration change of D and H retained in SrCe0.95Yb0.05O3−δ by 5 keV D2+ and H2+ irradiation and subsequent thermal annealing has been studied by means of the elastic recoil detection (ERD) and Rutherford backscattering (RBS) techniques. It has been found that the saturation concentration of D implants is D/SrCe0.95Yb0.05O3−δ=1.1. Decay curves of D concentration on isothermal annealing show that the retained numbers of D decrease rapidly and hereafter gradually, and finally reach a constant level at each temperature. The decay curves have been analyzed using the mass balance equations for free and trapped species of D, which include the rate constants of the thermal detrapping, retrapping and local molecular recombination between free species leading to the release of D. The analysis indicates that the activation energy for thermal detrapping is 0.56 eV and that for effective molecular recombination is 1.7 eV. These data are compared with some data obtained from the other measurement.

Local atomic arrangement of Pb and Sn on the Si(111)√3×√3-(Pb,Sn) surface

A 3/3-(Pb,Sn) surface was studied by means of scanning tunneling microscopy (STM) and core-level photoelectron spectroscopy (PES) to identify its local atomic arrangement. Observed spots in STM were classified into three types, which were white and gray (a), gray and white (b), and black and gray (g) spots in the filled- and empty-state images, respectively. The STM images also showed a local 3/3-(Pb,Sn) arrangement in the 3/3-(Pb,Sn) surface. Both Pb 5d and Sn 4d core-levels spectra indicated that there were two components on the 3/3-(Pb,Sn) surface, and the peak positions and shapes of Pb 5d and Sn 4d core-levels of the 3/3-(Pb,Sn) surface were almost the same as those of the 3/3-Pb and 3/3-Sn surfaces. Comparison between the heights of the STM spots on the single and binary adsorbate surfaces and their core-levels spectra suggested that Sn and Pb were located at a and b positions, respectively. The nominal coverage of the local 3/3-(Pb,Sn) arrangement was determined to be 1/9 and 2/9 ml for Sn and Pb, respectively. # 2002 Elsevier Science B.V. All rights reserved.