[en] Sputtering by collimated low energy ion beams can spontaneously create periodic structures on many surfaces. The pattern results from the balance between roughening by atom removal and smoothing, typically by surface diffusion. Experiments on a number of surfaces are considered in terms of linear and non-linear models of surface evolution

[en] Sputtering of surfaces by collimated, low-energy ion beams results in spontaneous pattern formation in many systems. In order to explore the mechanisms that control the pattern formation, we have used in situ light scattering to measure the evolution of sputtered Si(0 0 1) surfaces. The results are interpreted within a linear instability model originally proposed by R.M. Bradley and J.M.E. Harper [J. Vac. Sci. Technol. A 6 (1988) 2390] that includes the dependence of the sputter yield on the local surface morphology

[en] The time evolution of the amplitude of periodic nanoscale ripple patterns formed on Ar+ sputtered Si(OOl ) surfaces was examined using a recently developed in situ spectroscopic technique. At sufficiently long times, we find that the amplitude does not continue to grow exponentially as predicted by the standard Bradley-Harper sputter rippling model. In accounting for this discrepancy, we rule out effects related to the concentration of mobile species, high surface curvature, surface energy anisotropy, and ion-surface interactions. We observe that for all wavelengths the amplitude ceases to grow when the width of the topmost terrace of the ripples is reduced to approximately 25 nm. This observation suggests that a short circuit relaxation mechanism limits amplitude . growth. A strategy for influencing the ultimate ripple amplitude is discussed

[en] We report the first experimental observation of non-classical morphological equilibration of a corrugated crystalline surface. Periodic rippled structures with wavelengths of 290-550 nm were made on Si(OO1) by sputter rippling and then annealed at 650 - 750 ampersand deg;C. In contrast to the classical exponential decay with time, the ripple amplitude, A_λ(t), followed an inverse linear decay, A_λ(t)= A_λ(0)/(1 +k_λt), agreeing with a prediction of Ozdemir and Zangwill. We measure the activation energy for surface relaxation to be 1.6 ampersand plusmn;0.2 eV, consistent with an interpretation that dimers mediate transport

[en] We report the first experimental observation of nonclassical morphological equilibration of a corrugated crystalline surface. Periodic rippled structures with wavelengths of 290-550 nm were made on Si(001) by sputter rippling and then annealed at 650-750 degree sign C . In contrast to the classical exponential decay with time, the ripple amplitude A_λ(t) followed an inverse linear decay, A_λ(t)=A_λ( 0)/(1+k_λt) , agreeing with a prediction of Ozdemir and Zangwill. We measure the activation energy for surface relaxation to be 1.6±0.2 eV , consistent with the fundamental energies of creation and migration on Si(001). (c) 2000 The American Physical Society

[en] When collimated beams of low energy ions are used to bombard materials, the surface often develops a periodic pattern or ''ripple'' structure. Different types of patterns are observed to develop under different conditions, with characteristic features that depend on the substrate material, the ion beam parameters, and the processing conditions. Because the patterns develop spontaneously, without applying any external mask or template, their formation is the expression of a dynamic balance among fundamental surface kinetic processes, e.g., erosion of material from the surface, ion-induced defect creation, and defect-mediated evolution of the surface morphology. In recent years, a comprehensive picture of the different kinetic mechanisms that control the different types of patterns that form has begun to emerge. In this article, we provide a review of different mechanisms that have been proposed and how they fit together in terms of the kinetic regimes in which they dominate. These are grouped into regions of behavior dominated by the directionality of the ion beam, the crystallinity of the surface, the barriers to surface roughening, and nonlinear effects. In sections devoted to each type of behavior, we relate experimental observations of patterning in these regimes to predictions of continuum models and to computer simulations. A comparison between theory and experiment is used to highlight strengths and weaknesses in our understanding. We also discuss the patterning behavior that falls outside the scope of the current understanding and opportunities for advancement

[en] Measurements of stress generation in Cu during low energy ion irradiation show that the induced stress depends on temperature and ion flux. A steady-state compressive stress is observed during irradiation, which turns into tensile stress after the irradiation is stopped. The results cannot be explained by the incorporation of gas ions alone, and point defects generated by the ions must be considered. In this work, the authors develop a continuum model that includes ion implantation, sputtering, and defect diffusion to explain the experimental data. The authors show that the experimental results can be reproduced primarily by considering a difference in diffusivity between interstitials and vacancies

[en] Recent experiments and atomic scale computations indicate that the standard continuum models of diffusion in stressed solids do not accurately describe transport, deformation and stress in Li–Si alloys. We suggest that this is because classical models do not account for the irreversible changes in atomic structure of Si that are known to occur during a charge–discharge cycle. A more general model of diffusion in an amorphous solid is described, which permits unoccupied Si lattice sites to be created or destroyed. This may occur as a thermally activated process; or as a result of irreversible plastic deformation under stress. The model predicts a range of phenomena observed in experiment that cannot be captured using classical models, including irreversible changes in volume resulting from a charge–discharge cycle, asymmetry between the tensile and compressive yield stress, and a slow evolution in mechanical and electrochemical response over many charge–discharge cycles

[en] We have measured the temperature and flux dependence of the wavelength of surface ripples spontaneously formed by low-energy sputtering of a Cu(001) surface. We find that the temperature dependence of the ripple wavelength is non-Arrhenius, with a greater apparent activation at high temperature than at low temperature. Furthermore, the dependence of the wavelength on flux changes significantly with temperature. In the high-temperature regime, the wavelength decreases as the ion flux increases, while at low temperature, the wavelength is essentially independent of flux. We explain these results by a quantitative model that includes the mechanisms controlling the concentration of mobile defects on the surface in the two temperature regimes. At low temperature, mobile defects are induced by the ion beam while at higher temperature, the defects are thermally generated

[en] We have used low energy ion beams to spontaneously create patterns (sputter ripples) on Cu(001) surfaces. The evolution of the ripple amplitude and wavelength was measured in situ by using light scattering. At the temperatures (415-455 K) and ion fluxes (10¹⁴-10¹⁵ ions cm^-2 s^-1) studied, the ripple formation process is found to be similar to that described by the Bradley-Harper instability theory, i.e., the wavelength does not change appreciably with time, the orientation is determined by the ion beam direction and the amplitude increases exponentially during the early stages of growth. The flux dependence of the growth rate and wavelength is measured to determine the kinetics of defect production and annihilation on the surface