T.S. Noggle

Ion-solid interactions during ion beam deposition of 74Ge and 30Si on Si at very low ion energies (0–200 eV range)☆

Atomic collisions in solids in the 40–200 eV energy range have been studied both theoretically and experimentally to determine the feasibility of the ion beam deposition (IBD) of amorphous and/or epitaxial layers. IBD was first modeled by a rate equation including the target sputtering yield and the ion self-sputtering, range and range straggling. To obtain preliminary values of those parameters, Monte Carlo simulations with TRIMSPUT were used. The surface binding energy (SBE) appeared to be an important parameter of the simulation for sputtering yields under 200 eV. By fitting the SBE with available sputtering data for AR on Si below 1 keV, a very good agreement was obtained between simulations and sputtering data of other ion-target combinations. Experimentally, 30Si and 74Ge ions were deposited on Si 〈100〉 at 300 K and 700 K. Cross-section TEM combined with ion scattering and ion channeling showed that IBD can provide very thin (3 nm) though perfectly continuous films with sharp interfaces (<1 nm). IBD damage to the substrate saturates as a function of dose, is negligible below 40 eV, and presents an interesting annihilation/long range diffusion behavior as a function of the temperature during irradiation.

Characterization of reordered (001) Au surfaces by positive-ion-channeling spectroscopy, LEED, and AES

An extensive investigation of the atomic arrangement on the (001) Au surface has been performed using the techniques of positive−ion−channeling spectroscopy (PICS), LEED, and AES. Both the normal surface in which the Au atoms are ordered in a square array and the reordered surface where it is proposed that the topmost layer of Au atoms are ordered in a hexagonal array have been examined. LEED and AES have been used in determining that the normal atomic arrangement producing the (1×1) LEED pattern is observed only when contamination is present, while the reordered surface producing the complex (5×20) LEED pattern is observed on surfaces which are atomically clean. The yield and energy distributions of 1 MeV 4He+ ions scattered from the oriented Au crystals have been used to determine the number of effective monolayers constituting the normal and reordered surfaces. Single alignment surface peaks and minimum yields have been determined, and experimental data are compared with predictions made by computer si...

Low‐temperature epitaxy of Si and Ge by direct ion beam deposition

Amorphous, polycrystalline, and epitaxial thin films of Si and Ge have been grown by ion beam deposition (IBD) under ultrahigh‐vacuum conditions. IBD involves the direct deposition of ions onto single‐crystal substrates from mass‐ and energy‐analyzed beams with energies of 10 to 200 eV. The IBD films were characterized by Rutherford backscattering, ion channeling, cross‐section transmission electron microscopy, and x‐ray diffraction. The effects of substrate temperature, ion energy, and substrate cleaning were studied. Differences in the formation of epitaxial thin films on p‐ and n‐type Si substrates were observed with n− Si showing better epitaxy at low temperatures. Epitaxial overlayers which showed good minimum yields by ion channeling (3%–4%) have been produced at temperatures as low as 375u2009°C for Ge on Ge(100) and Si on Si(100).

Low-temperature epitaxial growth of Si and Ge and fabrication of isotopic heterostructures by direct ion beam deposition*

Direct ion beam deposition (IBD) is utilized to deposit isotopic thin films and heterostructures and to achieve high-quality epitaxial growth of 74Ge on Ge(100) and 30Si on Si(100) at temperatures as low as 400°C. Anomalous damage is observed during IBD at 400° and 600°C that results in a band of buried loops at depths 50 times normal and a defect-free region near the original surface. An unexplained doping effect is reported for epitaxial growth of Si on Si at 20-40 eV, 400°C where high-quality epitaxy occurs on n-type Si but amorphous films form on p-type.

Ion radiation damage in copper

Transmission electron microscopy techniques have been used to study dislocation loop type damage as a function of depth in copper single crystals irradiated with MeV Cu, Ni and He ions at room temperature. By comparing the location of the peak in the experimental depth profiles with calculated damage energy curves, the electronic stopping powers of Cu and Ni ions in copper were deduced. The deduced electronic stopping powers have been compared with those predicted by Lindhard et al., Bricc, and the Northcliffe and Schilling tables. It was found that the deduced stopping powers agreed well with the Northcliffe and Schilling values corrected for Z2 oscillations by the method proposed by Ward et al. In the case of 1 MeV He ions, good agreement was obtained between the observed damage peak position and that calculated using the experimental electronic stopping of Ziegler and Chu and that of White and Mueller.

Ion beam deposition in materials research

Abstract Ion beam deposition (IBD) is the direct formation of thin films using a low-energy (tens of eV) mass-analyzed ion beam. The process allows depositions in which the energy, isotopic species, deposition rate, defect production, and many other beam and sample parameters can be accurately controlled. This paper will review recent research at ORNL on the IBD process and the effects of deposition parameters on the materials properties of deposited thin films, epitaxial layers, and isotopic heterostructures. A variety of techniques including ion scattering/channeling, cross-sectional transmission electron microscopy, scanning electron microscopy, and Auger spectroscopy has been used for analysis. The fabrication of isotopic heterostructures of 74 Ge and 30 Si will be discussed, as well as the fabrication of metal and semiconductor overlayers on Si and Ge. The use of IBD for low-temperature epitaxy of 30 Si on Si and 76 Ge on Ge will be presented. The use of self-ion sputter cleaning and in situ reactive ion cleaning as methods for preparing single-crystal substrates for epitaxial deposition will be discussed. Examples of IBD formation of oxides and suicides on Si at low temperatures will also be presented.

Ion Radiation Damage

The depth distribution of damage energy deposited in solids by energetic ions has been calculated and results are compared with the experimental damage found in copper which has been irradiated with 1016 1-MeV protons at ambient temperature. The general form of the experimental damage profile from the transmission electron microscope measurements agrees well with that calculated.

ORIENTATION DEPENDENCE OF INTENSITY AND ENERGY LOSS OF HYPERCHANNELED IONS.

Abstract Energy loss measurements are reported for 21.6–60 MeV 127I and 3 MeV 4He ions transmitted through thin single crystals of Au and Ag along directions parallel or nearly parallel to 〈110〉 directions in the crystals. A systematic investigation of 21.6 MeV 127I ions in Ag indicates that for incidence angles within 0.12° of [O11] up to 10 percent of the transmitted ions have energy losses significantly lower than that for ions transmitted parallel to (111). The behavior of these ions is consistent with that expected for ions which are confined within one particular axial channel throughout the crystal. This specific type of axial channeling we call hyperchanneling. The data for hyperchanneled 21.6 MeV 127I in Ag are analyzed in detail and discussed in terms of a theory developed on the basis of potential energy contours obtained from the continuum potentials of the surrounding rows of atoms. Comparison of theory and experiment suggests that these ions undergo more multiple scattering than can be accou...

Depth distribution of self-ion damage and comparison of ion damage rates to neutron damage rates for aluminum

Abstract Resistivity damage rates as a function of ion penetration depth were measured for 2.7 to 5.4 MeV Al ions in aluminium. These damage rates accurately scale with damage energy calculations for a large fraction of the range of the ions, but are ~14% low in the region of the maxima in the damage curves. This difference in the peak region was related to changes in the damage efficiency expected from differences in the recoil spectra in the peak region compared to the incident beam. Deviation from the LSS velocity proportional electronic stopping was indicated by these experiments and an improved agreement between experiment and calculations was obtained by adjustment of the parameters in the Brice formula for the electronic stopping cross section. The fission spectrum neutron damage production rate in aluminum was measured and compared with the ion damage rates. The damage efficiency of the neutron damage is in agreement with the ion damage efficiencies within ~8%.

Time-Resolved Study of Silicon During Pulsed-Laser Annealing *

Near-surface temperatures and temperature gradients have been studied in silicon during pulsed laser annealing. The investigation was carried out using nanosecond resolution x-ray diffraction measurements made at the Cornell High Energy Synchrotron Source. Thermal-induced-strain analyses of these real-time, extended Bragg scattering measurements have shown that the lattice temperature reached the melting point during 15 ns, 1.1 to 1.5 J/cm/sup 2/ ruby laser pulses and that the temperature of the liquid-solid interface remained at that temperature of the liquid-solid interface remained at that temperature throughout the high reflectivity phase, after which time the surface temperature subsided rapidly. The temperature gradients below the liquid-solid interface were found to be in the range of 10/sup 70/C/cm.