We have examined the reactions on Si(100) induced by collision of hyperthermal chlorine or Xe atoms. It is demonstrated that etching reactions are enhanced by kinetic energy of incident atomic and molecular chlorine for the temperature range between 200 and 400°C. The dominant etch products are SiCl2 for both beams irradiation. The etching rate is dependent on the translational energy of chlorine atoms and molecules. All etching reactions are slightly dependent on the sample temperature, and their activation energies are about 0.2 eV. No etching products was observed from chlorine adsorbed Si(100) surfaces with irradiation of hyperthermal Xe beams (∼5 eV). These results suggest that the enhanced etching reaction follows an Eley-Rideal reaction mechanism where the reaction is mainly driven by the kinetic energy of incident chlorine. However, when the Xe atom beams were impinged on the fluorinated surfaces which were prepared by the exposure of XeF2, desorption of fluoride (SiF3 or SiF4) from the fluorinated layers was observed. After the Xe irradiation, SiF4 perk disappeared in the temperature-programmed desorption spectra. As a result of collision of Xe atoms, precursor of the thermal desorption of SiF4 desorbs from the fluorinated surfaces. It is clearly demonstrated that a collision-induced reaction of the fluorinated layer by hyperthermal Xe atoms.
Sputtering with gas cluster ions, which are aggregates of a few thousands of atoms, has been investigated experimentally and theoretically. Cluster ion beam etching is equivalent to low-energy high-current ion etchings with very low damage. Interesting new phenomena resulting from multiple collisions of incoming atoms in a very localized area were found. A surface smoothing effect is one of the typical phenomena, which is caused by lateral sputtering in which many atoms are ejected from the substrate in a lateral direction. Molecular dynamics simulation clearly shows that these sputtered atoms are ejected from the edge of craters formed by cluster ion impact.
Interaction of highly charged ions with metalic and insulator surfaces were briefly reviewed with particular attention on hollow atoms (ions) extracted in vacuum. The paper firstly discusses some properties of highly charged ions, which is followed by the interaction of them with metallic surfaces including the classical over barrier model, hollow atoms in the first and the second generations, and several experimental findings which support the idea of the classical over barrier model. Then the major part of the present paper summarizes new findings, and future prospects relating to the extraction of hollow atoms (ions) into vacuum, which are realized employing microcapillary targets. The final part is devoted to briefly discuss recent findings on the interaction of highly charged ions with insulater targets, which include some interesting behavior of the potential sputtering of protons.
Plasma assisted deposition methods have been widely used so far to synthesize varieties of thin films. However, charged particles such as electrons and ions, which are inevitably included in plasma, hit surfaces of thin film while the films are being deposited and deteriorate the characteristics of the films. In this article we first describe our results concerning titanium oxides deposition by a “pulsed beam deposition method” and show that active oxygen species are necessary to synthesize completely oxidized titanium oxide thin films. Subsequently, we introduce a high intensity radical beam source which does not emit charged particles and its performance with a review of radical beam sources and methods to determine the intensity of radical beam. Finally, we conclude with some examples of the application of the radical beam source to the synthesis of ceramic films.
Fabrication of an ozone jet generator system and its application to the formation of ultra-thin silicon dioxide film was discussed. Superior features of using ozone and/or atomic oxygen in an oxidation process is highlighted through the comparison of reactivity among various oxidizing reagent, and also through the survey of their applications to SiO2 formation. Then the characteristics of the new ozone jet generator, which can supply high purity ozone flux and was specially designed to overcome the current problems in handling high purity ozone, was described in detail. Finally, the oxidation mechanism of Si with ozone, which was investigated by XPS and SHG methods, was discussed focusing on the role of atomic oxygen generated by the dissociation of ozone on silicon surface.
A dual ion beam deposition apparatus was newly developed, which consists of a positive ion beam line, a negative ion beam line and an ultra-high vacuum deposition chamber. The machine can generate mass-analyzed very low energy ion beams with positive and negative charges at the same time with the ion energy range from 10 eV to 20 keV. It is possible to deposit both ions not only simultaneously but also alternatively. The machine has a wide possibility to fabricate ultra-pure materials or non-traditional materials, and is also useful to study fundamental processes of ion beam deposition and/or ion solid surface interactions. Using this new equipment, carbon nitride films were fabricated by simultaneous deposition of C- and N+ ions with the ion energy varying from 50 to 400 eV. The films were analyzed by Rutherford backscattering (RBS), Fourier Transform Infrared Spectroscopy (FTIR) and Raman scattering. It was found that the maximum composition ratio (N/C)c was about 0.9, the film structure was like amorphous carbon and the amount of C-N triple bonds tended to decrease with decreasing nitrogen ion energy.
Dynamics of the defect, phase defect 'type-P' formed on Si(100) surface dimer rows, was studied at 6 K by scanning tunneling microscopy. Pair creation and annihilation of the type-P defects were observed clearly. It was observed that step edges and dimer vacancy defects work as sources and absorbers of the type-p defects. Interaction between the phase defects existing on the adjacent dimer rows was very weak at 6 K compared to that observed at ∼100 K. This resulted in the comparable structural change between c(4×2) and p(2×2) arrangements; dynamics of the type-P defects looked almost equivalent in c(4×2) and p(2×2) arrangements at 6 K. With consideration of the interaction between dimers, the observed characteristic properties were considered to be related to the temperature dependence of the dimer interactions, in addition to the phenomena of the ordinary order-disorder phase transition between c(4×2)+p(2×2) and unique c(4×2) structures.
We evaluate the bonding force subjecting on the water molecule sorbed on the surface of 2:1 type clay mineral by using semi-empirical molecular orbital calculation, and compare it with the binding forces of soild and liquid phases of water. We can consider that molecular orbital calculation is a useful and helpful tool for characterizing the properties of water molecules present in the clay minerals.
Recently it has been revealed that alkali-metal adsorption on metal surfaces does not always imply overlayer formation. Unusual structures including substitution between alkali-metal atoms and substrate atoms are observed with development of structural determination techniques. We introduce these structures and discuss about the origin of the formation. Main part of this article is Li adsorption on Cu(001) surface. With increasing Li coverage, the surface structure of Cu(001) evolves as (2×1), (3×3) and (4×4) at room temperature. The (2×1) structure consists of missing-rows in the top layer of the Cu(001) surface, in which Li atoms are located. The (3×3) and (4×4) structures are complex structure including substituting Li atoms and Li adatoms.
The surface reaction of trimethylgallium (TMG) is discussed as a function of relaxed or reconstructed GaAs surface structure on the basis of pulsed molecular beam scatterings from stoichiometry controlled GaAs(100), (110) and (111)B surfaces. The results are interpreted within the framework of the precursor-mediated adsorption mechanism, where TMG surface reaction is determined by the depth of the precursor state and the stability of the surface structure. It is believed that the precursor state is deepened by the electrostatic behavior in the GaAs surface structure. The topmost As atoms which have only bonds to As atoms hinder TMG trapping in the precursor state; implying the mechanism of the growth suppression on the (2×2)-reconstructed (111)B surface and the As-passivation technique.
Ion-beam-induced epitaxial crystallization (IBIEC) is an appropriate method for the crystalline growth of semiconducting materials with non-thermal-equilibrium composition. In this review, I focus on the synthesis of the Si-based group IV semiconductors, such as Si1-xGex, Si1-x-yGexCy, Si1-yCy and Si1-zSnz formed by ion implantation. As far as Si1-x-yGexCy grown by IBIEC is concerned, Si atoms are substitutionally replaced with C atoms, and hence the lattice matching between Si1-x-yGexCy and Si is better for IBIEC than for solid phase epitaxial growth (SPEG), because of the formation of SiC in the latter. However, small vacancy clusters are produced in the samples grown by IBIEC. Efforts should be made to annihilate these defects. I also demonstrate the feasibility of synthesizing Si1-yCy and Si1-zSnz with non-thermal-equilibrium composition by IBIEC.