Transient processing of titanium silicides on single-crystal Si in a non-isothermal reactor provides high quality films. Heat from quartz-hal?gen tungsten lamps and a small temperature gradient act as driving forces for the reaction. The temperature gradient, small compared to the concentration gradient, shows negligible influence on the formation process. The influence of sample reflectivity on the other hand is appreciable. From Xe+ marker experiments, Si atoms are found to be the moving species either up or down the temperature gradient. Small amount of TiSi as an intermediate phase is found to be coexistent with TiSi2. The silicide formation of the implanted wafers is somewhat slower than that of the unimplanted wafers.

We have studied the native oxide of silicon (110) and the changes roduced by MeV ion bombardment using transmission ion channeling of 5.9 MeV 9Be, and Elastic Recoil Detection Analysis (ERDA). Transmission channeling was used to measure interfacial nonregistered Si and adsorbed C and 0. ERDA was used to measure the surface concentration of H. MeV ions were found to cause an increase in the interfacial nonregistered silicon which saturates at approximately one monolayer. Rapid desorption of hydrogen was observed. The effect of 2 keV electrons on the silicon native oxide was also studied by Auger Electron Spectroscopy.

A velocity spectrum of neutral sputtered particles as well as a low resolution mass spectrum of sputtered molecular ions i" has been measured for 4.74 MeV 19F+2 incident on UF4 . The r velocity spectrum is dramatically different from spectra taken with low energy (keV) bombarding ions, and is shown to be consistent with a hot plasma of atoms in thermal equilibrium inside the target. We propose a "thermalized ion explosion" model for high energy sputtering which is also expected to describe track formation in dielectric materials. The model is shown to be consistent with the observed total sputtering yield and the dependence of the yield on the primary ionization rate of the incident ion. t Supported in part by the National Aeronautics and Space Administration [NGR 05-002-3331, the National Science Foundation [PHY79-23638) and the Department of Energy [EX-76G-03-1305]. 1 ONE OF THE BAND AIb PREPRINT SERIFS IN ATOMIC & APPLIED PHYSICS April 1980

Utilizing the transmission ion channeling technique and a Monte Carlo simulation of the channeling of He ions in Si, we have been able to determine surface structure by comparing experimental to simulated scattered ion energy distributions. In analyzing data for {110} beam incidence, we have found that planar oscillations persist well past 2000 A in our Monte Carlo simulations. These oscillations yield no benefit to this method of data analysis but can make analysis more difficult by the requirement for more accurate Si thickness determination.

We present scanning tunneling microscopy (STM) results that show the superstructure on the highly oriented pryrolytic graphite (HOPG) surface. The superlattice appears to be the result of an apparent twist boundary dislocation. The crucial point of the observation is that the superlattice changes simultaneously its constant from 18 to 72 nm when we go around the screw dislocation in the plane perpendicular to the dislocation vector. Based on available models of the graphite surface top layers, we are able to simulate observed STM images. Our STM observation of the superstructure lattice, whose lattice constant varies continuously, gives strong evidence that the superlattice is of Moiré pattern nature, but a correct model can be built only if the graphite electronic structure is taken into consideration.

We report on experiments in which picosecond ultrasonic techniques are used to investigate the modification of interfacial bonding that results from ion implantation. The bonding is studied through measurements of the acoustic reflection coefficient at the interface. This method is nondestructive and can be used to create a map of the variation of the bonding over the area of the interface.

We have used picosecond ultrasonics to study the effects of ion irradiation on the interfacial bonding between gold films and a silicon substrate. Acoustic vibrations are excited in the metal film when a picosecond light pulse is absorbed. The rate at which these vibrations damp out via sound transmission across the interface into the substrate gives a measure of the adhesion of the film to the substrate. The films were irradiated with 2.5 MeV helium ions with doses between 7×10 14 and 8×10 16 ions cm −2 . The adhesion, as measured by the rate of acoustic damping, was found to be significantly improved by the ion irradiation.

We have tested the single adatom exchange model for surfactant-mediated growth. Using two samples with different coverages of Ge on Sb-terminated Si(100), we generated energy distributions of scattered MeV ions from transmission ion channeling experiments. We studied the system both after room temperature deposition of Ge and after annealing at 350°C. We then compared simulated energy distributions for the single adatom exchange model to the experimental energy distributions. No combination of temperature and coverage produced a good fit between data and simulations of this model. Before annealing, however, a model having Ge in dimer-like sites on top of undisturbed Sb dimers describes the data well for both Ge coverages.

Using transmission ion channeling, we have made the first measurement of the Ge dimer geometry for the monohydride-covered Ge/Si(100)-2×1 surface. Comparison of calculated angular scans with experimental angular scans near the 〈100〉 and 〈110〉 directions has resulted in a measured Ge dimer bond length of 2.8 Å, which is 8% longer than the corresponding dimer bond length reported for Ge on Si(100) in the absence of H. This elongation is similar to that reported for Si dimers on the Si(100) surface. Also, relative to the (100) surface plane, the dimers change from tilted without H to untilted with H.

This paper describes the observation of {110} planar oscillations of 3 MeV protons transmitted through a 0.5 mu m thick [001] silicon crystal using ion channeling patterns produced on a fluorescent viewing screen. Gradual variations in the crystal thickness allowed the exit angular distribution of the protons to be sampled al different depths into the crystal, revealing effects due to the coherent planar oscillations. This work necessitated the use of a focused MeV proton beam from a nuclear microprobe to generate channeling patterns from selected, micron-size regions and the necessary ion optics are developed here. The recorded channeling patterns are interpreted with the help of Monte Carlo computer simulations.

Scattered ion energy distribution for the system Sb/Ge/Si(100) are studied using transmission ion channeling. One monolayer (ML) of Sb was deposited on the clean Si(100) surface prior to deposition of one ML of Ge at 350 degrees C. Experimental energy distributions for the [100], {110}, and "random" directions are compared with simulated energy distributions obtained by overlapping trial adsorbate positions (relative to bulk positions) with ion positions in the channel at the beam-exit surface. Ion positions and energies are calculated via a Monte Carlo simulation of channeling that incorporates a model for channeled ion energy loss. We find that the energy distributions clearly show that the surfactant, Sb, moves to the surface upon Ge deposition at 350 degrees C. Further, our results are consistent with the sites recently reported by Grant et al. [Surf. Sci. 316 (1994) L1088], for Sb deposited on Ge/Si(100), namely, tilted Sb dimers on Ge asymmetrically displaced from bulk sites.

The preferred bonding site of Sb on Si(100) is investigated using transmission ion channeling. A Monte Carlo simulation that includes a model for channeled ion energy loss has been used to calculate scattering yields and energy distributions for trial adatom sites. A method of data collection and analysis was developed to use the calculated scattering yields and energy distributions for quantitative site determination. The Sb site thus found agrees well with previous experiments on this system, namely, the Sb is in a modified bridge site with a bond length of 2.80±0.10 Å and a distance above the bulk-extrapolated silicon surface of 1.63±0.10 Å. However, the vibrational amplitude necessary for the simulated energy distributions to match experiment is anisotropic, apparently in contradiction with other results. A possible resolution is proposed.

This letter demonstrates that ion channeling patterns, produced by the passage of 3 MeV protons through a 0.5 μm thick [001] silicon crystal, can be transported and manipulated to produce enlarged or reduced area patterns using magnetic quadrupole lenses. The different effects on the ion channeling patterns obtained by using single quadrupole lenses and quadrupole multiplets are shown. The maximum attainable magnification under present conditions is investigated and a fundamental limitation to this process is identified as being the energy spread gained by the proton beam as it passes through the crystal.

The energy distributions for 2.5-MeV ${\mathrm{He}}^{+}$ ions incident on thin Si single crystals are studied. Detailed angular scans are taken through the 〈110〉 and 〈100〉 axial directions along the {111} and {110} planar directions as well as perpendicular to the planar directions for Si(110) (0.74- and 1.4-\ensuremath{\mu}m-thick) and Si(100) (0.75-\ensuremath{\mu}m-thick) samples, respectively. Complex structures in the distributions are observed throughout the angular scans. The experimental distributions are reasonably well reproduced by a Monte Carlo simulation using the semiclassical approximation [N. M. Kabachnik, V. N. Kondratev, and O. V. Chumanova, Phys. Status Solidi B 145, 103 (1988)] for energy loss to core electrons and the two-component free-electron-gas model for energy loss to valence electrons. Systematic deviations between theory and experiment are observed and discussed in terms of an increased penetration depth necessary for ${\mathrm{He}}^{+}$ ions to become fully ionized when channeled.

MeV transmission ion channeling has been used to investigate the structure of 0.95 ML of Sb deposited on 0.81 ML of Ge grown pseudomorphically on the Si(100) surface. It is shown that the sb overlayer is composed of asymmetric dimers, in contrast to the symmetric dimers reported in the literature on the Sb-terminated clean Si(100) surface. It is further shown that the Ge reconstruction is lifted upon Sb deposition and Ge then occupies a near-bulk site. The characterization of the underlying Ge layer provides additional and convincing evidence for Sb dimer asymmetry.

An angular dependence of the energy distributions for 625 keV H+ ions transmitted through a 0.57 μm thick Si(100) single crystal is studied. The angular scans have been taken through the 〈100〉 axis along the {110} plane and through the {110} plane at an angle of 6° with respect to the 〈100〉 axis. The experimental distributions have been reproduced by a Monte Carlo simulation assuming individual contributions to the energy loss due to close and distant collisions of the H ion with inner-shell as well as valence electrons. The relative contributions of core and valence electrons to the stopping have been investigated.

The energy distributions for 625-keV ${\mathrm{H}}^{+}$ ions transmitted through thin Si single crystals are studied for detailed angular scans through the 〈110〉 and 〈100〉 axial as well as the {111} and {110} planar channels. Well-resolved structures in the distributions taken near the 〈110〉 axial direction are observed. The experimental energy-loss distributions are very well reproduced by a Monte Carlo simulation using the semiclassical approximation model for core electrons and the two-component free-electron-gas model for valence electrons. The best fit to the data is obtained if the model energy losses are scaled up for core electrons and down for valence electrons by several percent. The experimental distributions can also be reproduced by assuming the mean excitation energy for distant collisions of the ion with core electrons equal to 1.4 times the binding energy for a given shell. No significant differences between the distributions obtained using the solid-state and free-atom valence electron densities have been found. The evolution of the distributions for the 〈110〉 axial scan is discussed in terms of ion trajectories and the flux distribution. Also, the azimuthally averaged mean energy loss is studied as a function of tilt angle with respect to the 〈110〉 axis.

Transmission ion channeling has been used to investigate the bonding geometry of Ge on the Si(100)-2X1 surface at a coverage of 0.6 ML. It is shown that this surface is terminated by asymmetric Ge-Ge dimers with a bond length of 2.6 angstrom and a tilt of 12-degrees, in agreement with previous results. The structure of the surface is shown to vary with Ge coverage, which is possibly attributable to the strain induced during growth by the 4% lattice mismatch between Ge and Si.

Transmission ion channeling is a powerful analytical tool for determining surface structure, but involves special equipment and sample preparation considerations. We describe an ultrahigh vacuum structural analysis and sample preparation facility for transmission ion channeling studies of monolayer films on clean semiconductor surfaces. After samples are cleaned and films deposited, they can be moved under vacuum and investigated using low energy electron diffraction, Auger electron spectroscopy, atomic resolution scanning tunneling microscopy, or, using an ion scattering chamber attached to a beamline of a 3.5 MeV Van de Graaff accelerator, transmission ion channeling. Transmission channeling can determine the bonding position of adatoms to typically 0.1 Å resolution, and is one of the few techniques able to measure reconstruction at a buried interface or to detect the presence of order in the midst of disorder. These aspects of the technique are illustrated by a site determination of a monolayer of Sb deposited on Si(100) and by a determination of the pseudomorphic fraction of thin Ge films deposited on Si(100) at low growth temperatures.

Thin Ge single crystals (≤1 μm) up to 4 mm in diameter have been fabricated from epitaxial Ge films grown by atmospheric pressure chemical vapor deposition on Si(100) wafers. The thin Ge windows are formed by chemically etching away both the Si substrate and the region of the Ge film near the interface that contains misfit dislocations associated with heteroepitaxial growth and relaxation of the Ge films. The resulting Ge films are comparable in crystalline quality to bulk Ge wafers, as indicated by ion channeling studies.