Hazime Shimizu

Effect of target temperature on surface composition changes of Cu−Ni alloys during Ar ion bombardment

The effect of target temperature on surface composition changes of Cu−Ni alloys during Ar ion bombardment was studied by means of quantitative Auger electron spectroscopy. After sputtering at various temperatures the surface composition changes were analyzed at room temperature. At room temperature, the surface was enriched with Ni. It was found that the sputtering yield ratio of Cu/Ni was 1.9 over a whole range of the composition and that the value was almost coincident with that estimated from pure metals. As the temperature increased, the inclination toward Ni enrichment was enhanced. Though the sputtering yields of pure metals were independent of the temperature, in the alloys the yield ratio increased to 3.5 at 250 °C. However, above 400 °C the yield ratios decreased. The surface composition was mainly determined by the fast diffusion of Cu on the sputter−damaged layers.

High resolution electron microscopy of graphite defect structures after KeV hydrogen ion bombardment

Abstract Structure changes of graphite due to keV-energy hydrogen ion bombardment are studied by means of high resolution electron microscopy (HREM). Highly graphitized vapor grown graphite fibers of diameters around 700 nm are irradiated side on with 1 keV H + ion beam to various fluences ranging from 1 × 10 14 to 1 × 10 18 H + /cm 2 . The (002) lattice fringe images from the fiber side edges give “edge-on” projections of several tens of nanometers deep layers of the H + implanted graphite basal face, thus enabling direct observation of defect profiles in the surface layer. In a 1 keV H + ion bombardment at ambient temperature, interlayer spacing, d 002 , within 12 nm from the graphite surface increases from the initial value of 0.336 nm to larger values ranging from 0.40 to 0.53 nm at an ion fluence of 1 × 10 17 H + /cm 2 . The d 002 value ranges from 0.45 to 0.58 nm at an ion fluence of 1 × 10 18 H + /cm 2 . Mean crystallite size, L a , on the other hand, decreases with fluence from the initial value above 100 nm to an equilibrium at 0.5 nm after a 1 keV H + irradiation to a fluence of1 × 10 17 H + /cm 2 . The increase in the interlayer spacing is attributed at least to an increased van der Waals radius of the hexagonal carbon networks due to chemical bonding between lattice carbon atoms and hydrogen atoms at interlayer positions.

Effect of surface segregation on angular distributions of atoms sputtered from binary alloys

Abstract The angular distribution of atoms sputtered from binary alloys (Cu/Ni, Co/Ni, and Fe/Ni) were investigated in relation to the surface segregation phenomenon of one component of the alloys. For the Cu/Ni alloy which has a tendency of strong Cu segregation at the alloy surface, the preferred Ni ejection was observed in the direction of target normal under the sputtering at both RT and 300°C. The preferred Co ejection in target normal directions was clearly discerned only at 300°C for the sputtering of the Co/Ni alloy, while no distinct preferred ejection of one component was observed for the Fe/Ni alloy.

Gold Substrates for Scanning Tunneling Microscopy of Adsorbed Species

Atomically flat substrates of gold were prepared by evaporation onto cleaved mica for scanning tunneling microscopic and spectroscopic studies of adsorbates. The surface morphology was investigated with a scanning tunneling microscope (STM) and a scanning electron microscope. The STM data were analyzed through a fractallike statistical procedure. Bulk crystallography was also investigated by means of X-ray diffraction. On the gold substrate showing hydrophilic characteristics, monolayer Langmuir-Blodgett film of cadmium arachidate was deposited, and successfully imaged by STM.

Dose Rate Effect of the Preferential Sputtering of Copper-Nickel Alloys by Argon Ion at Elevated Temperatures

Compositional changes of the surface during argon ion bombardment were studied in copper-nickel alloys at temperatures up to 873 K by means of Auger electron spectroscopy (AES). Since at elevated temperatures the effect of impinging beam density was large, nickel enrichment was observed at high ion beam densities. At low ion beam densities copper enrichment occurred instead. The results are explained by the balance between the preferential sputtering of copper from the surface and enhanced diffusion of copper to the surface through the sputter-damaged layer.

Excimer laser ablation of cryogenic NO2 films

Cryogenic NO2 films were ablated by a XeCl excimer laser. Only NO2 molecules were detected by a time-of-flight method. Velocity distribution of ablated NO2 molecules was found to be almost thermal. The derived temperature of the fitted Maxwell-Boltzmann distributions depended on the thickness of cryogenic NO2 film in the range from 300 K to 1100 K. The fastest NO2 observed in the present experiment had a translational energy of 0.5 eV.

Resolution of time‐of‐flight mass spectrometers evaluated for secondary neutral mass spectrometry

Mass resolution of a time‐of‐flight mass spectrometer with a two‐stage electrostatic reflector is calculated for secondary neutral mass spectrometry. The instrument parameters are optimized for energy and space focusing: correcting the flight time difference due to the energy width ΔE of sputtered particles and the spatial width Δs of an ionizing laser beam. The effect of Δs can be compensated by applying an acceleration field to the ionizing region, and the maximum resolution becomes about 1000 for ΔE=10 eV and Δs=1.0 mm.

Possibility and current status of absolute XHV measurement by laser ionization

Abstract The current status and possibility of XHV measurement by laser ionization using second harmonics of a picosecond YAG laser are discussed. Under the condition that incident laser energy was 30 mJ/pulse and the laser beam was focused with a spherical lens (focal length f = 250 mm) to a power density sufficient for the saturation of H 2 ionization at the focal point, the minimum pressure in an XHV chamber was measured. From the minimum pressure estimated by extrapolation (5 × 10 −11 Pa) and the ion counting rate at that pressure (one count during 500 laser shots), the volume of the ionization region was expected to be 1.7 × 10 −4 mm 3 . The ionization region was then measured experimentally under the same laser beam conditions. It was found that the ionization region has a spindle shape with maximum diameter of 45 μm and the length of 1.2 mm. The estimated volume is larger than the expected volume by a factor between 4 and 12. The ion detection efficiency of the electron multiplier is one of the major factors affecting the difference, and it can be reduced to within a factor of 3. On the basis of the results, the possibility of absolute measurement of XHV pressure by laser ionization is discussed.

Pressure measurement method using laser ionization for xhv

Abstract A pressure measurement method for xhv using laser ionization has been developed. By means of nonresonant multiphonon ionization, the proportional relation between the amount of laser-generated ions and the gas pressure is experimentally verified in the range 1 × 10−3−2 × 10−8 Pa. Also, a nonresonant 4-photon ionization of the He atom, which has the highest ionization potential of all atoms and molecules, and saturations of ionization for Xe, Kr, O2 and especially for H2, which is a main residual molecule in uhv and xhv, are successfully observed. In addition, a high-sensitivity ion-detection system for the exact measurement of several atoms and molecules in xhv is prepared. Noise due to scattered laser light is discussed.

New counting system for detection of charged particles: application to ions generated by a pulsed laser beam

A new counting system for charged particles, which is suitable for the counting of pulse trains arriving in a short time, was constructed. The system is composed of a microchannel‐plate intensifier, a CCD camera, a frame buffer, a particle counter, and a personal computer. Ion (or electron) pulses incident on the microchannel plate are amplified and then converted to photoradiating spots on a fluorescent screen. The image of the bright spots on the screen is taken by the camera and stored in the frame buffer. The computer processes the stored data and counts the number of bright spots. The performance of the system was examined by applying it to the detection of ions generated by a pulse laser. More than 300 photoions generated by one laser pulse (pulse width: 30 ns) were successfully counted, indicating that the peak counting rate of the system exceeds 1010 cps.