A. Namiki

Laser‐induced vapor deposition of silicon

Silicon films were deposited when silane was irradiated with a pulsed CO2 laser. This laser‐induced vapor deposition occurs effectively when the laser is tuned to an absorption frequency of SiH4. Efficiency was so high that an unfocused beam of 1.3 MW/cm2 sufficed. Any thermal effects are ruled out. Deposition is induced efficiently at gas pressures above 100 Torr, indicating that a collision‐aided process is involved.

Orientation dependence of rotational excitation in no scattering from Ag(111)

Abstract Scattering experiments with oriented NO beams on Ag(111) have been performed. The scattered molecules are detected by a resonantly enhanced multiphoton ionization. A dependence of the rotational rainbow upon the scattering angle has been observed. The first results of the steric effect measured for single rotational ( J ) levels of scattered molecules are presented. The J =18.5 state is produced preferentially when the O-end collides first with the surface. For the J =8.5 state we find that the N-down geometry is preferable. These results are in qualitative agreement with theory.

O2− formation at Si(001)

A 450 eV−3 keV O2+ beam incident at 5° to a carefully flattened Si(001) surface was used to probe the adiabatic potential energy surface for the O2Si(001) adsorption/reaction system in the limit of low coverage. Over the full incident energy range, O2- an are formed as scattering products. We argue that the O2− product correlates with an O2−-like region on the potential energy surface and therefore propose that an O2−-like species is an intermediate or precursor in the dissociative adsorption of O2 on Si(001). Classical trajectory calculations indicate that a large amount of collision induced dissociation occurs at all energies.

Dynamics of laser sputtering at GaN, GaP, and GaAs surfaces

Laser sputtering of GaAs, GaP, and GaN has been studied by measuring angle‐resolved time‐of‐flight (TOF) distributions of emitted neutral particles. The observed mean translational energy and sputtering yield were found to show strong forward peaking depending on the laser power densities, thence on the desorption yield. This fact can be explained in terms of postdesorption collisions among desorbed particles as predicted theoretically [I. NoorBatcha, R. R. Lucchese, and Y. Zeiri, J. Chem. Phys. 86, 5816 (1987); 898, 5251 (1988), and Kelly and R. W. Dreyfus, Surf Sci. 198, 263 (1988); Nucl. Instr. Methods B 32, 341 (1988); J. Chem. Phys. 92, 5048 (1990)]. However, the observed velocity distributions of sputtered particles were found to be in contradiction with the so‐called shifted Maxwellian, because the best‐fitted center of mass velocities for Ga were always found to be negative. In addition, Kelly’s Mach number M, estimated from the energy spectra, was found to be significantly larger than those estim...

A molecular beam study of alkali promotion of NO sticking on Si(100): Local promotion in a single collision regime

Alkali–metal (K and Cs) promotion for sticking of nitrogen oxide molecule (NO) on Si(100) has been studied using a molecular beam method combined with an Auger electron spectroscopy (AES) and a laser ionization spectroscopy [resonance enhanced multiphoton ionization (REMPI)]. The observed sticking probability S shows a good correlation with alkali coverage, indicating that the alkali promotion is local in nature. The decay of S as a function of NO dose as observed with AES shows an anticorrelation with the evolution of the direct‐inelastic scattering intensity as obtained with REMPI. This fact is understood as follows: since the direct‐inelastic scattering occurs mostly in a single collision process with the surface, local alkali promotion is realized in a single collision of the incident NO molecule with the alkali–metal adsorbates. The decay of S as a function of NO dose is then analyzed with a reaction cross section. The evaluated reaction cross sections are close to the area of the 2×1 unit cell, and ...

Molecular beam study on scattering and sticking of molecular oxygen at Si(100)

Abstract Molecular beam techniques have been used to probe the dynamics of oxidation of a Si(100) surface as a function of incident energy E i , incident angle θ i and surface temperature T s . The angular distributions of scattered O 2 from Si(100) are clearly bimodal, exhibiting both trapping desorption and direct inelastic scattering. The initial sticking probability, S 0 , is measured with AES as a function of E i . At E i = 0.09 eV , where the trapping-desorption process is dominant. S 0 decreases with T s . On the other hand, at E i = 0.9 eV , S 0 increases with T s . Since the direct inelastic scattering is dominant at this energy, this fact indicates that sticking of O 2 for high E i occurs without physisorption.

Behavior of positive ions ejected from laser-irradiated CdS

The dynamic behavior of ions ejected by pulsed nitrogen laser irradiation of the single‐crystal CdS have been ivestigated with a dynamic mass spectroscopic method. The energetic ions are generated through a process different from that of slow neutrals. The ion produced below 80 mJ/cm2 laser power is created at the surface and accelerated by a Madelung potential, reaching the kinetic energy of 100 eV. At a higher power region, relatively slow cadmium ions showed a Maxwellian velocity distribution suggesting the laser‐generated gaseous plasma. Three possible mechanisms for ion formation are presented.

Supersonic molecular beam scattering of Cl2 from clean and alkali-covered Si(100)2×1

The sticking probability s0 of Cl2 at Si(100)2 × 1 is determined as a function of translational energy Ei. At low Ei the process is precursor-mediated. At high Ei a direct process is observed. The former is not influenced by alkali adsorption, while the latter is clearly promoted, resulting in si ≈ 1 at the fully alkali-covered surface. From electron-stimulated desorption, both induced and observed by Auger electron spectroscopy, we conclude that for θK,Cs < 0.3 ML the Cl adsorbates are covalently bound like on the clean surface. For high θK,Cs an ionic bond seems more likely.

Investigation of the dynamics of the O2/Si(001) adsorption system by small-angle ion-surface scattering

Abstract The small non-adiabaticity associated with the slow collision of a 450 eV to 3 keV O 2 + beam incident at 5° to a carefully flattened Si(001) surface was used to probe the adiabatic potential energy surface for the O 2 /Si(001) adsorption/reaction system in the limit of low coverage. The scattering products include O 2 − and O − . From the observation of efficient O 2 − formation and th dependence of the negative-ion yields on beam energy, we infer that O 23 − is an intermediate or precursor in the dissociative chemisorption of O 2 on Si(001). The total yield of negative ions (O 2 − and O − ) is high in comparison with similar experiments on th O 2 /Ag(111) system. This may be explained by a reduced reneutralisation probability on the exit trajectory due to the band gap of Si.

Temperature Dependence of Desorption in Highly Photo-Excited CdS

Dependence of laser-induced desorption on both substrate temperature and emission angle have been studied in CdS by using the pulse mass counting method. The effective translational temperature ( T trans ) of particles ejected toward the angle of 0° from the surface normal is much higher than that toward 45°. The T trans of each particle, S, S 2 and Cd, is different among them. T trans does not exhibit the surface temperature even when the time-of-flight spectra can be fitted with a Maxwellian velocity distribution. Arrhenius plots of desorption yields for the substrate temperature before laser irradiation show rather complicated features. Estimation of the temperature rise at surface by calculating the thermal diffusion equation gives the linear relationship in the Arrhenius plot. The enthalpy for desorption is estimated to be 0.44±0.1 eV. This value is considerably smaller than that (2.2 eV) obtained in the free vacuum vaporization (ref. 13), suggesting the contribution of the electronic excitation effect.