Tetsuji Gotoh

Photon Stimulated Desorption of Positive Ions from LiF

Photon stimulated desorption (PSD) of positive ions from LiF is observed in the photon energy region between 30 and 70 eV. The creation of the Li+(1s→2s) core exciton leads to the rapid rise of both Li+ and F+ desorption yields. It is found that PSD of positive ions from LiF is due to the interatomic Auger transition. The yield spectrum of F+ ions is different from that of Li+ ions above 60 eV. The F+ yield spectrum has a deep valley at around 63 eV, while the Li+ spectrum shows a plateau in the same region. However the difference in the yield spectra of Li+ and F+ ions can not be explained at present.

Observation of ion desorption from MgO(001) by electron bombardment

Electron ( E + , H 2 + and O + ) from a MgO(001) surface are observed by means of a quadrupole mass analyser (QMA) and by Time-of-Flight (TOF) methods. The desorbed oxygen ions have two different kinetic energies, 7.8 and 4.6 eV. The origin of the ions with the lower energy is identified as adsorbed species which are ionized by electron bombardment (from examining experimental results). The total yield of oxygen ions rises above energies of 80 eV for the primary electron beam. This threshold energy of 80 eV corresponds to the core-hole creation energy in the 2p state of Mg 2+ . The desorption of the faster oxygen ion is explained by the Knotek-Feibelman mechanism of the electronic transitions following core-hole creation in the Mg 2+ ion.

Photoionization efficiency curves in the threshold region for Bin (n ⩽ 4) molecules

Photoionization efficiency curves for Bin (n ≤ 4) in their threshold region (7.05 to 8.40 eV) have been measured by using synchrotron radiation, which crosses a molecular beam coupled with a time-of-flight mass spectrometer. Resonance lines due to autoionization are observed only for the monomer. The photoionization spectrum of Bi2 shows a depletion of intensity, which indicates a predissociation of Bi2 to Bi+ + Bi. Bi3 and Bi4 show only slowly varying profiles.

Water vapor desorption from molybdenite

Abstract The desorption of gases, especially water vapor, from molybdenite has been studied by cleavage or heating the sample. It was found that the major desorbed gases were H,H 2 and H 2 O at cleavage MoS 2 samples. The result shows that there was water as well as hydrogen in van der Waals gaps of MoS 2 crystals. Results of temperature-programmed desorption also suggest water desorption from the bulk.

Observation of a titanium surface by desorbed ion images with a scanning electron microscope

Abstract When metallic titanium is annealed above 900°C, grain growth and segregation of sulfur to the surface occur. Using an electron scanning microscope, we have observed the secondary electron image, the sulfur Auger image and the electron stimulated desorbed ion image for a titanium specimen annealed above 900°C and exposed to hydrogen. It is found that the intrinsic titanium surface adsorbs hydrogen which diffuses from the surface into the bulk, and that segregated sulfur blocks such a hydrogen transfer. We also found that sulfur does not segregate at the grain boundaries but over the whole surface. However, the sulfur Auger image suggests that the segregation occurs easily in some crystalline surfaces but not in others.

Observation of angle-, mass- and energy-resolved ESD ions from the MgO(001) surface

Observation of ion desorption from MgO(001) by electron stimulated desorption (ESD) was carried out. The desorbed oxygen ions had peak values in two different emitting directions. From the terrace site ions were emitted in the surface normal direction and from the step site in a tilted direction from the surface normal. Ion emission from a step-rich surface such as the (011)-plane was also observed and its peak intensity was found to be in the [011]-direction.

Threshold behavior of synchrotron radiation photoionization for Bin (n≤4)

Ionization profiles in the threshold region (7.05 to 8.40 eV) have been measured for Bi n ( n ≤4) by using synchrotron radiation, which crosses a molecular beam coupled with a time-of-flight mass spectrometer. Resonance lines due to autoionization are observed only for monomer. The photoionization spectrum of Bi 2 shows a depletion of intensity, which indicates a predissociation of Bi 2 to Bi + + Bi. Bi 3 and Bi 4 show only slowly varying profiles.

Water desorption from van der Waals gaps of molybdenite crystal

Abstract Water desorption from van der Waals gaps in MoS 2 single crystal was observed by cleavage experiments and temperature programmed desorption (TPD) experiments. At cleavage hydrogen atoms or molecules as well as water vapor are identified as the major desorbed species. Emission of these gases decreases significantly after preheating of samples at about 700 °C for 24 h. TPD experiments were carried out with two types of specimen, flake (~5mm) and powder (~0.3mm), using different heating rates of 1 and 0.2 °C/s. Thermal desorption spectra of these specimens, with or without preheating, show several desorption peaks. The spectrum from the flake sample, preheated at 180 °C 17 h 0.2 °C/s, shows a peak from the bulk. Value of the activation energy of desorption was obtained using observed shift of the peak temperature in two different heating rates and was of about 1 eV. This activation energy corresponds to the diffusion energy of water molecules in the van der Waals gap.

Positive Ion Desorption from MgO by Low Energy Electron Irradiation

Observations of low energy (up to 1.5 keV) electron stimulated desorption and light emission have been performed on the Mg0 (001) surface. Enitted species have been detected by means of a quadrupole mass spectrometer (QMS) and by time-of-flight (T0F) methods for the desorbed ions, and a photomultiplier tube through a monochromator for light emission (wavelength about 400 nm). Onset energies of the light emission and the desorption of 0+ ions with respect to primary electron beam energy have been observed at 80 eV and these onset energies correspond to the binding energy of 2p electrons in Mg2+. The energy distribution of the desorbed H+ ions has also been observed as a function of the primary electron energy.