Hirofumi Miki

Crystallization Process of Polycrystalline Silicon by KrF Excimer Laser Annealing

We have investigated the crystallization of a-Si films by means of pulsed KrF excimer laser annealing as a function of irradiation energy density (E L), using transmission electron microscopy (TEM), Raman scattering spectroscopy and secondary ion mass spectrometry (SIMS). The grain size increased gradually at 0.2–0.4 J/cm2, while a drastic enlargement of grains occurred with lateral growth at 0.6–0.8 J/cm2. The stress in the films decreased with a decrease in the thickness of the fine grain (FG) layer until the FG layer finally disappeared. We proposed a model in which a drastic enlargement of grains at high E L is controlled by the nucleation rate, the solidification velocity, and the nucleus density of initial growth. It was found that poly-Si films with large grains ( 0.5–0.9 µm), high purity of C ( ~3×1016 cm-3) and low stress were obtained in the high E L regime ( 0.6–0.8 J/cm2).

Adsorption and dissociation of NO on Pt(100) and (310) studied by AES, UPS and XPS

Abstract Adsorption states of nitric oxide on Pt(100) and Pt(310) surfaces were studied by Auger electron spectroscopy (AES), ultraviolet and X-ray photoelectron spectroscopy (UPS and XPS). The molecular NO and the dissociated N and O atoms coexist on both the platinum surfaces at room temperature. As the temperature rises, a part of the molecules desorbs quickly and another part decomposes into N and O up to 420 K for Pt(100) and 400 K for Pt(310). The N atoms desorb as N2 up to 420 K. A part of the dissociated O atoms penetrates into a few atomic layers of the platinum crystals up to about 600 K, and they diffuse back to the surface with the thermal desorption of O2 at higher temperatures. The Pt(310) surface is slightly more active for the N-O bond breaking than Pt(100), and less than Pt(410).

Coadsorption of carbon monoxide and hydrogen on polycrystalline rhodium

Abstract The coadsorption of carbon monoxide and hydrogen on polycrystalline rhodium filament has been studied by thermal desorption mass spectrometry. From a series of thermal desorption spectra of CO and H 2 from rhodium as a function of the exposure time to the gas mixture of CO and H 2 , it is indicated that there are a single broad peak for CO and three peaks designated as β 1 , β 2 , β 3 for hydrogen. Thermal desorption of hydrogen is complex. CO and β 1 -hydrogen coadsorb on the rhodium surface with their partial pressures in the initial stage of the exposure to the gas mixture and then the β 1 -hydrogen adsorbed on the surface is replaced by CO with the further exposure time. The kinetics for the replacement of β 1 -hydrogen by CO may be discussed from the standpoint of the L-H reaction process. The β 2 -and β 3 -hydrogen are observed with a longer exposure time after the elimination of β 1 -hydrogen. It may be suggested that the β 3 -hydrogen peak is attributed to the desorption of hydrogen absorbed in the bulk. The nature of β 2 -hydrogen is also briefly mentioned in possible implications.

Chemisorption of NO on a Pt surface: II. An FEM study

Abstract The adsorption of nitric oxide on a Pt surface has been studied by field emission microscopy (FEM) and work function measurements. The singularity of the Pt(014) plane for the NO adsorption is observed in FEM patterns. The work functions of (012) and (113) increase by 1.0 and 0.4 eV by the NO adsorption at room temperature, respectively. The surface diffusion of the oxygen atom is observed in the range of 375–450 K on the O 2 -adsorbed surface at room temperature. The Pt oxide is formed on the surface in the range of 600–1000 K for the NO adsorption. NO is considered to adsorb nondissociatively on the (113) plane, desorb as a molecule, dissociate partially around 400 K, desorb as NO, N 2 and O 2 on the (012) plane, and adsorb dissociatively on the (014) plane.

Chemisorption of NO on Pd single crystals studied by UPS, AES and XPS

The chemisorption of NO on Pd(100) was studied by uv photoelectron spectroscopy (UPS), Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS), and was compared with that on Pd(111). The UPS results showed that the peaks derived from atomic N and O were found for NO-saturated. Pd(100) at room temperature. The NO-derived peaks disappeared at about 350 K and the N- and/or O-derived peak increased in intensity with increasing temperature. Signals from adsorbed N and NO were also found at 397.0 and 400.4 eV in the N(1s) XP spectra, respectively, at room temperature. The N(KLL) intensity increased for sample temperature increasing up to 360 K, began to decrease at 540 K and disappeared at 800 K. For the O(KLL) intensity, the corresponding temperatures above were 360, 730 and 920 K, respectively. The results obtained here suggest that a considerable amount of NO on Pd(100) dissociates into N and O contrary to the case of Pd(111), and that the N and O partially diffuse into the bulk, the oxygen forming a palladium oxide layer at room temperature. The nitrogen in the bulk diffuses back to the surface at higher temperatures.

Measurements of outgassing rate from copper and copper alloy chambers

Abstract Using a newly-developed sealing system of copper alloy (CrCu) Conflat-flange with an oxygen-free copper gasket, the outgassing rate from an all chromium-copper (Cr 0.5%, Cu 99.5%) alloy chamber has been measured using the throughput method. After 10 h evacuation at 20 °C, the outgassing rate became 1.02 × 10 −7 Pa m 3 s −1 m −2 nitrogen equivalency. After a low temperature bakeout at 100 °C for 24 h the outgassing rate reached the ultralow level of 3.75 × 10 −12 Pa m 3 s −1 m −2 nitrogen equivalency. This value is about the same as that from oxygen-free high-conductivity (OFHC) copper after bakeout at 250 °C. Increasing the chromium copper bakeout temperature to 250 °C does not change the result.

Chemisorption of NO on Pt(210) studied by UPS, XPS and AES

Abstract The chemisorption of NO on the Pt(210) surface has been studied by photoelectron spectroscopy (UPS and XPS) and Auger electron spectroscopy (AES). The UPS results show that NO molecular orbitals appear at 2.8, 9.6, 11.3 and 14.8 eV below the Fermi level after full coverage of NO on the Pt(210) surface at room temperature. These molecular orbitals originate from 2 π , 1 π , 5 σ and 4 σ , respectively. The peak from the 1 π orbital shifts to the lower binding energy side by 0.6 eV with increasing temperature. The molecular levels disappear at around 450 K. The energy shift of the 1π orbital is caused by the increase of the N−O bond length, which correlates with the change of adsorption state of NO; that is, from the terminal sites to the bridge sites. The disappearance temperature of the NO molecular orbitals, T D , and the decreasing temperature of the N(KLL) Auger electron intensity, T A , correlate with the surface activity for NO decomposition. From the UPS and AES results for the Pt surfaces, the order of activity for the NO decomposition is as follows: (410) > (310) > (100) > (210) > (110)

Coadsorption of no and other small gases (H2 and CO) on polycrystalline rhodium surface

The coadsorption of NO and other small gases (H2 and CO) on a polycrystalline Rh filament has been studied by thermal desorption mass spectroscopy, using 15NO. The sample was exposed to a mixture of nitric oxide and other gases with various concentrations of 15NO at room temperature. It is indicated that NO, CO and H2 coadsorbs on the rhodium surface, and NO desorbs as N2 and O2. NO is adsorbed mainly in the dissociation at lower coverage and molecular adsorption becomes dominant at higher coverage. But the amount of desorbed O2 was very small. The chemisorption of CO is affected by the chemisorbed NO. Thermal desorption of hydrogen is detected when the value of P15NO/PCO is very small. The hydrogen adsorbed on the rhodium surface is replaced by NO with a longer exposure time.

Anisotropy in the spatial distribution of reactive carbon dioxide desorption from narrow terraces on a reconstructed iridium (110)(1 × 2) surface

Abstract The spatial distribution of reactive CO 2 desorption on a reconstructed Ir(110)( l × 2) surface was measured by means of angle-resolved thermal desorption. Two-directional desorption collimated along the terrace-surface normal was analyzed in detail. The desorption component shows a sharp angular distribution parallel to the surface trough and a much sharper distribution perpendicular to it. This anisotropy is correlated with the structure around the reaction sites.

Chemisorption of NO on W(100) and W(110) surfaces studied by AES and UPS

Abstract The chemisorption of nitric oxide on W(100) and W(110) surfaces at room temperature has been studied by Auger electron spectroscopy (AES) and ultraviolet photoelectron spectroscopy (UPS). The AES results indicate that the O(KLL) peak shifts to lower energy on W(100), but the N(KLL) peak shifts to lower energy on W(110) with increasing coverage of NO. The UPS results indicate that the overlapping peaks of the O(2p) and N(2p) levels appear at −6.5 eV on W(100) and at −6.0 eV on W(110). It may be considered that these peaks indicate dissociative adsorption on W(100) and W(110) at room temperature. There are two states, at −6.5 and −7.4 eV below the Fermi level, in oxygen atoms on W(100) at higher coverage of NO; and from the chemical shifts of the O(KLL) Auger peak and O(2p) UPS peak, the change of the extra-atomic relaxation energy for oxygen atoms on W(100) is estimated to be −2.4 eV. On the other hand there are two states, at −6.0 and −7.6 eV, in nitrogen atoms on W(110) at higher coverage of NO. The change of the extra-atomic relaxation energy for nitrogen atoms on W(110) is estimated to be −6.2 eV. The peak at −4.3 eV on W(100) is considered to be derived from the hybrid orbital energy owing to W oxides formed on the W surface. At higher coverage of NO on W(110) at room temperature, the (1π + 5σ) levels of molecular NO appear at −9.4 eV below the Fermi level.