Akemi Takano

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.

Time Sequential Measurement of the Precursor State of Oxygen on the Titanium Surface by Means of Time-of-Flight Spectroscopy for Electron Stimulated Desorption

An adsorption process of oxygen on the titanium single-crystal surface of (100) has been investigated by means of a time-of-flight spectrometer for the electron stimulated desorption (ESD). An oxidation experiment has been performed at the oxygen pressure ranging from 1 to 8×10-8 Torr. TOF spectra of ESD signals were obtained sequentially by a digital acquisition system. In an initial adsorption stage, the O+ ESD signal intensity grew depending on the oxygen exposure. The O+ signal peaks have the most probable kinetic energies of 3.5±0.4 eV and 1.8±0.2 eV. The higher-energy peak is identified as the ESD signal from molecularly adsorbed oxygen on the surface, and the lower one as that from the chemically adsorbed oxygen.

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 Electron-Stimulated Desorption of Adsorbed CO on (001) Plane of Molybdenum Surface by Means of Time-of-Flight Spectroscopy

Adsorption and desorption processes of carbon monoxide have been investigated on the (001) plane of molybdenum by using electron-stimulated desorption (ESD) accompanied by time-of-flight (T-O-F) spectroscopy. Thermal desorption spectroscopy has also been performed complementarily on the CO adsorbed surface. A desorption spectrum of excited oxygen ions from CO adsorbed on the Mo(001) surface during heating is very different in shape at higher temperatures from the thermal desorption spectrum. A proposal for a temperature dependence of reneutralization for desorbed ions is given.

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).

A Study on Energy Distributions of Oxygen Ions Desorbed from CO-Adsorbed Ni(110) by Time-of-Flight Electron-Stimulated Desorption (TOF-ESD)

Ion energy distributions (IEDs) of oxygen ions desorbed from a CO-adsorbed Ni(110) surface by electron stimulation of various primary energies between 200 and 900 eV have been studied using a time-of-flight electron-stimulated desorption (TOF-ESD) apparatus. The IEDs represent different profiles for different desorption mechanisms. The IED of O+ ions stimulated by a shake-off mechanism was Gaussian distribution with a peak at 3.6 eV and a half width at a half maximum (HWHM) of 2 eV, while the IED by direct ionization of the valence electron is asymmetric and distributed from 3 to 10 eV with a peak at about 5 eV which seems to be decomposed into two Gaussian distributions.

Hydrogen termination study of silicon dangling bonds by electron stimulated desorption spectroscopy (TOF-ESD)

Abstract An electron stimulated desorption spectrometer (ESD) for hydrogen study has been newly developed using a combination of a micro-channel plate (MCP) and a time-of-flight technique. It allows in situ measurements of LEED, Auger analysis, ESD and ESD ion angular distribution (ESDIAD) at the same probing point. Threshold energies of incident electrons for ESD protons were newly observed between 12 and 18 eV, ranging from 400 langmuir (L) to 1200 L atomic hydrogen, which accompanied a reconstruction from (2×1) to (1×1) on the Si(100) surface.

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

Abstract Hydrogen adsorption on silicon surfaces has been studied by time-of-flight type electron-stimulated desorption spectroscopy (TOF-ESD). Adsorption characteristics of atomic hydrogen reveals different modes for different surface treatments. The ESD yield of H + versus exposure of atomic hydrogen increased initially, and decreased gradually giving a definite peak at 500 langmuir (L) for flat surfaces, accompanying a structure change from 2 × 1 to 1 × 1 after 1000 L exposure. While for a vicinal surface of Si(100) H + increased rapidly and saturated at a certain value.