Shigeru Sugai

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).

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.

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)

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.

Structure of Pt(100) for NO adsorption studied by FEM and LEED

Abstract The Pt(100) surface structure was observed by field emission microscopy (FEM) and low energy electron diffraction (LEED) in the process of adsorption and desorption of NO. The clean Pt(100) surface has a reconstructed structure, such as a Pt(100)(5 × 20) or Pt(100)(5 × 20)R0.7° structure, at room temperature. The LEED results show that the reconstructed structure changes to a fuzzy c(4 × 2) + (1×1) structure at full coverage of NO. With increasing temperature, the c(4 × 2) structure disorders around 350 K, a (1 × 1) structure appears around 400 K, streak and superstructure spots appear above 420 K. The FEM results indicate that the (100) area, that is the darkest part on the clean FEM pattern, becomes bright with fine structures such as a circle, a disk and an X-shape; with increasing NO exposure, it becomes dark above 0.6 L and the X-shape changes to a cross shape above 0.9 L. The cross shape is disarranged around 450 K, and the (100) area returns to the darkest part above 500 K; however, the size of the area differs from that of the clean pattern. We consider the appearance of the characteristic shapes at lower coverage and the disappearance of the cross shape around 450 K to be correlated with the transformation from the (5 × 20) to the (1 × 1) structure and vice versa, respectively. The cross shape is created by the domain boundary.

Chemisorption of N2 and NO on polycrystalline molybdenum

Abstract The adsorption of nitric oxide and nitrogen on a polycrystalline Mo filament at room temperature has been studied by thermal desorption spectroscopy (TDS), field-emission microscopy (FEM) and work function measurements, using 15 NO and 15 N 2 . The chemisorption behavior of N 2 on molybdenum resembles that of tungsten. At low coverage, 15 NO and 15 N 2 adsorb dissociatively on the Mo surface and molecular adsorption becomes dominant at higher coverage. At higher coverage in the NOMo system, the peak temperature of the desorption of 15 N 2 from the 15 NO layer on Mo shifts to higher value. The retrograding behavior of the desorption peak temperature is attributed to the lateral molecule interactions on the molybdenum surface. The attractive interaction energy, e , is about 8.4 kcal/mol. The variations in the FEM pattern and in the work function of the 15 NO chemisorbed Mo tip with heating to about 1400 K are similar to the results of the O 2 chemisorbed Mo tip which appeared above 1400 K. In the temperature range of 300–1350 K, the regions around the (112) of the NO- and N 2 -covered Mo tip become brighter and show similar changes in the FEM pattern. It is also found that the oxygen resulting from the dissociation of 15 NO chemisorbed on the Mo surface plays a similar role as the oxygen in the O 2 Mo system.

Chemisorption of NO on polycrystalline Pd surface studied by TDS, AES, UPS and XPS

Abstract The adsorbed state of NO on polycrystalline Pd surfaces has been studied by thermal desorption spectroscopy (TDS), Auger electron spectroscopy (AES), ultra-violet photoelectron spectroscopy (UPS) and X-ray photoelectron spectroscopy (XPS). UPS results showed that molecular adsorption was characterized by additional maxima at -3.5, -8.8 and -14.2 eV at room temperature below the Fermi level which were derived from the highest occupied molecular orbitals of NO. These peaks almost disappeared by heating to about 500 K, and another additional maximum appeared at -6 eV above 400 K which was derived from atomic orbitals of N and O, and persisted up to 700 K. XPS and TDS results indicated the presence of two states in NO adsorption on the Pd surface at room temperature which were characterized by adsorption in bridge sites and linear single on-top sites, and the NO adsorption states depended on the amount of CO in the residual gases. Small amounts of N2O and CO2 were observed to desorb during heating of adsorbed NO.

States of no adsorbed on W(100), (110) and (111) studied by electron stimulated desorption

Abstract The adsorption states of 15 NO on W(100), (110) and (111) surfaces at room temperature have been studied by electron stimulated desorption (ESD). The only ion ejected by electron bombardment (5 μA/cm 2 , 100 eV) is O + for all the surfaces exposed to 15 NO. On (110) and (111) surfaces, the incident electron energy effect on the ion intensity, measured with a quadrupole mass spectrometer (QMS), is characterized by a broad peak with a maximum in the region of 120–150 eV and a gradual increase above 300 eV. The ion energy distribution, measured with the retarding field method, forms a single peak, and its shape does not depend on the electron energy. Various neutral ESD species such as NO, N, O, N 2 and O 2 are detected only for the (110) surface. The NO, N 2 and O 2 ESD intensities fall in the same manner by heating the sample and disappear at about 420 K. It is considered that a part of the surface species forms molecular NO and complexes such as N 2 O and NO 2 . The results for (100) and (111) surfaces give evidence that NO dissociates completely into N and O.