Kazuyuki Ueda

Initial oxidation studies on Fe(100) by means of photoelectric work function measurements combined with auger electron spectroscopy

Abstract An initial oxidation process of Fe (100) is studied by means of photoelectric work function measurements combined with Auger electron spectroscopy in the oxygen pressure of 10 −9 −10 −5 Torr at room temperature. The crystal surface was initially observed as to its work function and Auger spectrum, and it was step wise exposed to each oxygen atmosphere. The work function and Auger signals (Fe 46 eV, S 148 eV and O 508 eV) were observed in each step, where an intensity of the 46 eV iron Auger peak showed a slow decrease with increasing oxygen exposure, and finally the 46 eV peak split into two peaks (41 eV and 49 eV) as a result of formation of oxides. Each experimental run in the oxidation process showed different results for different initial conditions of the sample surface. That is, a chemically clean surface was oxidized in the early stage of the oxidation. On the other hand, a cathode protection effect was observed on the surface which was increased in work function due to sulfur coverage.

Desorption study of a proton from H/Si(100) by electron stimulated desorption spectroscopy

Abstract Adsorption and desorption of hydrogen on a Si(100) surface have been investigated by time-of-flight type electron stimulated desorption spectroscopy (TOF-ESD). The ESD proton yield increases initially and decreases after taking a maximum at 500 L (langmuir) against the atomic hydrogen exposure at room temperature, while it increases linearly with the molecular hydrogen exposure. Threshold energies of an incident electron for proton desorption are measured for several surface conditions. Threshold energies are 20 eV for 360 L atomic hydrogen and 26 eV for 1760 L atomic hydrogen which induces a structure change to (1 × 1). The threshold energy for 2560 L molecular hydrogen is 20 eV. From the characteristics of 2 eV peak component in the kinetic energy distribution of desorbed protons, it is suggested that the threshold energies only depend on the life time of localized surface excitonic states.

Oxygen Adsorption Study on Rh(100) Surface by Electron-Stimulated Desorption Spectroscopy

Adsorption states of oxygen on a Rh (100) surface have been studied by electron-stimulated desorption (ESD) spectroscopy. The ESD measurement was performed time sequentially during exposure of the surface to oxygen and heating of the surface. At least three adsorption states were distinguished for oxygen by ESD. One state gave no ESD ions at low temperature. The other two states gave ESD oxygen ions of different kinetic energies. The yield of ESD oxygen ions changed drastically at 350 and 500 K. Decrease of oxygen on the surface was clearly observed above 600 K in hydrogen gas.

Detection of Hydrogen on Nickel (110) Surface by Electron-Stimulated Desorption

Hydrogen on a nickel (110) surface was investigated by means of an electron-stimulated desorption (ESD) technique in ultrahigh vacuum. The ESD-H+ yield increased with exposure time to a residual gas pressure of 8×10-11 Torr at surface temperatures below 400 K. The yield was decreased by electron beam irradiation for a certain period and increased again after irradiation ended. The rate of increase was slower at lower specimen temperatures. The Arrhenius plot of the rate of increase indicates that there is an activation barrier of 0.046 eV required for increasing the amount of hydrogen on the surface. This result is explained by the segregation of hydrogen from a subsurface region.

A study of hydrogen adsorption on the silicon single crystal surfaces by electron stimulated desorption (TOF-ESD)

Abstract The adsorption of hydrogen on a silicon surface plays an important role in the reconstruction of the surface structure and terminations of the dangling bonds of the surface atoms. Hydrogen adsorption experiments on Si(100) and Si(111) surfaces were perfomed using the electron stimulated desorption spectroscopy (TOF-ESD) combined with the thermal desorption spectroscopy (TDS). The H + signal intensity of TOF-ESD was observed on Si(100) but not Si(111) after hydrogen exposure in spite of observing hydrogen desorptions from both surfaces in TDS.

A study of the oxygen adsorption process on a titanium single crystal surface by electron stimulated desorption

Abstract An initial adsorption stage of oxygen on a Ti single crystal surface has been investigated by means of an electron stimulated desorption (ESD) using a time-of-flight (TOF) technique. We have reported previously that oxygen has two adsorption states on a clean Ti surface at room temperature. In addition to the previous report we have measured the work-function changes depending on oxygen exposure and threshold energies for the ESD of oxygen ions. As a result, we concluded that the two adsorption states are a dissociative adsorption state and a molecular adsorption state on the surface, respectively.

A study of surface defect of Si(511) by RHEED and LEED

Surface step structures on Si(511) originating from an oxidation-induced stacking fault have been investigated by RHEED and LEED for the first time. Si(511) with oxidation-induced stacking faults showed only a streaky diffraction pattern in the [255] direction. Upon in-situ heat treatment at about 1000°C, an ordered (2×1) structure appeared on the surface instead of the Si(511)-3×1 structure normally observed for Si(511). This structural change with temperature is considered as being due to a partial recovery of disordered surface step structure formed on the recovered (100) terrace region of Si(511).

Surface wave excitation Auger electron spectroscopy of Si(001) reconstructed surfaces

Abstract We have developed a new angle-resolved Auger electron spectroscopy method which allows the characterization of the valence electron states of crystalline surfaces. The method, surface wave excitation Auger electron spectroscopy (SWEAES), utilizes an electron beam for RHEED as a primary excitation of AES under the grazing incidence condition. In this method, the incident angle of the electron beam for RHEED is first adjusted to excite the specific diffraction rods (spots). Especially, the surface wave resonance (SWR) condition is realized to excite surface electron waves which propagate parallel to the surface. Then, the Auger spectrum is measured simultaneously with RHEED observation. The surface electron waves are effectively used for the selective excitation of the core holes of surface atoms. Therefore, the Auger spectrum well reflects the electronic states of the surface atoms. We demonstrate for the first time the SWEAES results on the surface electronic states of the reconstructed Si(001) surface. The Si[2s, 3p, 3s] and Si[2s, 2p, 3p] Auger transition components were clearly resolved in the Si[2s, 2p, V] (V = 3s, 3p) Auger valence electron spectra of the Si(001) reconstructed surface. It is also revealed that the [2s, 2p, 3s] Auger transition intensity is enhanced at the SWR beam-incidence condition. The results suggest that the enhancement is due to local charge transfer caused by the formation of surface Si-Si dimers. The conclusion is also confirmed by the Ar + -ion irradiation experiments and also by a simple theoretical calculation of Auger valence electron spectra based on the Si tetrahedral cluster model.

Auger valence electron spectroscopy of a structural phase transformation in metastable alpha-Sn grown on InSb (001)

Abstract A type of surface structural transformation of metastable alpha-Sn epitaxially grown on InSb (001) has been investigated in situ with RHEED and Auger valence electron spectroscopy. Concerned with structural transformation of bulk Sn from the alpha (diamond cubic structure) to beta (tetragonal structure) phase, a type of surface structural transformation has been observed in RHEED. The eoitaxial layer of alpha-Sn showed a 2 × 1 two-domain superstructure. Upon heating, the superstructure disappeared at the critical temperature. Three-dimensional islands were found by transformation in the thick specimens. The transformation temperature depended on the layer thickness of metastable alpha-Sn. Related to the structural transformation, the spectral change in Sn[4 p, V, V ] Auger transition has been found also at the critical temperature. The Auger and RHEED data suggest the crucial role of the lattice matching condition between the epitaxial layer and the substrate on the critical temperature.

Studies of hydrogen adsorption on silicon (100) surfaces by means of time-of-flight type electron stimulated desorption spectroscopy (TOF-ESD)

Abstract The termination with hydrogen of a silicon surface for the epitaxial growth becomes an important technique. The adsorption processes of atomic hydrogen on Si(100) surfaces have been studied by means of a time-of-flight type electron stimulated desorption spectroscopy (TOF-ESD). The ESD has a fairly high sensitivity for the yield of H + against atomic hydrogen exposure. A characteristic of hydrogen adsorption reveals different modes for different surface orientations. An energy distribution curve of desorbed ion was also obtained from the TOF spectrum. Over 1000 Langmuir exposures of atomic hydrogen gave the structural change from the (2×1) to (1×1).