[en] We have performed computer simulations of epitaxial growth and low-energy ion bombardment for comparison with reflection high-energy electron diffraction (RHEED) measurements. The simulations are based on a hybrid Monte Carlo/rate equation approach which includes the processes of defect creation (adatom and surface vacancy), surface diffusion, and attachment and detachment from steps and islands. In this work, we focus on simulating the experimental observations of ion-induced RHEED oscillations and cancellation of RHEED oscillations during simultaneous ion bombardment and growth. For the interaction of the low-energy ion with the surface, we consider two mechanisms: preferential sputtering (where the sputtering cross section depends on the atomic coordination) and mobile vacancies. Our results indicate that the primary interaction of the ion beam with the surface is probably through the creation of mobile vacancies, and that the degree of preferential sputtering is not large

[en] Surface displacements due to low energy (100-300 eV) Xe ion bombardment of the Ge(001) 2x1 reconstructed surface are investigated by in situ RHEED measurements of surface roughening. The near-exponential decay in RHEED intensity due to displacements of Ge atoms at the surface is shown to depend sensitively on the Xe energy and flux. Iso-damage rate curves at 100 degree C are used to establish a fixed amount of defect annealing and to determine the number of surface displacements per Xe as a function of Xe energy. The calculated number of near-surface displacements per Xe exhibits a similar energy dependence. Comparison of experiment and calculation indicates an efficiency for the production of stable surface defects of about 50% at a temperature of 100 degree C and damage rate of 2x10¹² displacements/cm²-sec. Results indicate this approach will allow the threshold energies for surface atom displacements to be measured. 7 refs., 4 figs

[en] Surface roughening and smoothing of SiO₂ by low energy ion bombardment were investigated using in situ energy dispersive x-ray reflectivity. Bombardment of nominally smooth surfaces (initial roughness approx. 0.4 nm) by 1 keV Xe increases the surface roughness linearly with fluence. Bombardment of initially rough surfaces (roughness approx. 1 nm) by 0.2--1 keV H results in an exponential decrease in roughness with fluence at a rate that increases with energy. The smoothing rate has a different energy dependence than the etching rate, ruling out a simple relation between material removal and surface morphology. A H ion induced relaxation mechanism is suggested for the smoothing behavior

[en] This paper describes a new technique for measuring X-ray reflectivity using energy dispersive X-ray detection. The benefits of the method are the use of a fixed scattering angle and parallel detection of all energies simultaneously. These advantages make the technique more compatible with growth chambers and useable with laboratory X-ray sources. The authors find excellent agreement between the calculated Fresnel reflectivity and the reflectivity obtained from a smooth Ge (001) surface. Reflectivities obtained during 500 eV Xe ion bombardment of Ge surfaces demonstrate the sensitivity of the technique to be better than 1 Angstrom

[en] Using in situ, real-time reflection high energy electron diffraction (RHEED), the authors have measured the evolution of Ge(001) surface morphology during simultaneous molecular beam epitaxy and Ar ion beam bombardment. Surprisingly, low-energy Ar ions during growth tend to smoothen the surface. Bombardment by the ion beam without growth roughens the surface, but the surface can be reversibly smoothened by restoring the growth beam. The authors have measured the effect of such ion beam growth smoothening above and below the critical temperature for intrinsic growth roughening. At all measured growth temperatures the surface initially smoothens, but below the critical roughening temperature the final surface morphology is rough whereas above this temperature the final morphology is smooth

[en] The kinetics of surface roughening of Ge(001) during 200 eV Xe ion bombardment and during Ge molecular beam epitaxy (MBE) are studied by real-time reflection high-energy electron diffraction. In both cases, initially smooth surfaces reach a steady state roughness which depends on temperature and incident ion or adatom flux. The data are analyzed in terms of a phenomenological model in which beam-induced roughening competes with beam-induced smoothening, and in which the defect creation rate and surface diffusivity are fitting parameters. For comparable fluxes, the temperature dependences for the net roughening induced by ions and adatoms are strikingly similar, implying a similarity in the surface diffusivities of vacancies and adatoms. For the case of ion-induced roughening, approximately one surface defect (in units of displaced surface atoms) is created per ion which is consistent with calculations assuming that a large fraction of atomic displacements recombine without producing surface defects at these ion energies

[en] Low-energy hydrogen ion beams are shown to clean and rapidly smoothen Ge(001) surfaces that have been subjected to severe oxygen roughening. Characteristic smoothening times of 1000 s are found at 500 degree C for 200 to 600 eV hydrogen ion beams at fluxes of 200 nA/cm². By comparing hydrogen and noble gas ion bombardment at various temperatures, we show that the hydrogen ion smoothening effect consists of both physical and chemical mechanisms which act to free pinned surface sites of contaminants and enable subsequent thermal smoothening of the germanium surface. Such oxygen roughened surfaces can be recovered to a state suitable for epitaxial growth without resorting to high-temperature annealing, keV ion sputtering or additional growth

[en] We characterize the development of nanometer scale topography (roughness) on SiO₂ surfaces as a result of low energy, off-normal ion bombardment, using in situ energy dispersive x-ray reflectivity and atomic force microscopy. Surfaces roughen during sputtering by heavy ions (Xe), with roughness increasing approximately linearly with ion fluence up to 10¹⁷ cm^-2. A highly coherent ripple structure with wavelength of 30 nm and oriented with the wave vector parallel to the direction of incidence is observed after Xe sputtering at 1 keV. Lower frequency, random texture is also observed. Subsequent light ion (H, He) bombardment smoothens preroughened surfaces. The smoothing kinetics are first order with ion fluence and strongly dependent on ion energy in the range 0.2--1 eV. We present a linear model to account for the experimental observations which includes roughening both by random stochastic processes and by development of a periodic surface instability due to sputter yield variations with surface curvature which leads to ripple development. Smoothing occurs via ion bombardment induced viscous flow and surface diffusion. From the smoothing kinetics with H and He irradiation we measure the radiation enhanced viscosity of SiO₂ and find values on the order of 1--20x10¹² N s m^-2. The viscous relaxation per ion scales as the square root of the ion induced displacements in the film over the range of the ion penetration, suggesting short-lived defects with a bimolecular annihilation mechanism. The surface instability mechanism accounts for the ripple formation, while inclusion of stochastic roughening produces the random texture and reproduces the observed linear roughening kinetics and the magnitude of the overall roughness

[en] We report oscillations in diffracted electron intensities during ion bombardment of Si(100) by 200- and 250-eV Xe, both alone and with sequential and simultaneous epitaxy. Analysis of the phase and frequency of the oscillations shows that, to first order, ion bombardment ''undoes'' previous epitaxy and cancels or partially cancels simultaneous deposition. Surprisingly, the phase relationship of growth and sputtering is both antisymmetric and linear, indicating that the ion-induced oscillations are dominated by simple, vacancy-mediated, layer-by-layer sputtering

[en] The authors performed computer simulations of epitaxial growth and ow-energy ion bombardment for comparison with reflection high-energy electron diffraction (RHEED) measurements. The simulations are based on a hybrid Monte Carlo/rate equation approach which includes the processes of defect creation (adatom and surface vacancy), surface diffusion, and attachment and detachment from steps and islands. In this paper, the authors focus on simulating the experimental observations of ion-induced RHEED oscillations and cancellation of RHEED oscillations during simulations ion bombardment and growth. For the interaction of the low-energy ion with the surface, we consider two mechanisms: preferential sputtering (where the sputtering cross section depends on the atomic coordination) and mobile vacancies. Our results indicate that the primary interaction of the ion beam with the surface is probably through the creation of mobile vacancies, and that the degree of preferential sputtering is not large