Grazing incidence ion bombardment results in the formation of nanoripples that induce an anisotropic optical reflection The evolution of the reflectance anisotropy has been monitored in situ with reflectance anisotropy spectroscopy. The Rayleigh-Rice theory ͑RRT͒ has been used to analyze the optical spectra quantitatively and provides the evolution of the average ripple period and root-mean-squared surface roughness. After an incipient phase, both the increase in the periodicity and the roughness vary roughly with the square root of the sputter time. Additional high-resolution low-energy electron diffraction ͑HR-LEED͒ measurements have been performed to characterize details of the average structure created by ion bombardment.

The initial stages of homoepitaxial growth of Cu͑001͒ have been studied by combining experiments and simulations. The investigated temperature window ranges from 200 to 300 K, the deposition rates vary from about 0.5 to 5 monolayer ͑ML͒/min, and the coverage ranges up to about 10 ML. The simulated data have been extracted from a kinematic Monte Carlo approach using a bulk-continued fcc lattice and energetic activation barriers taken from recent literature. The experimental data are thermal energy helium-uptake curves measured in situ during growth. The Ehrlich-Schwoebel barriers for descent from ͗110͘-oriented and ͗100͘-oriented steps have been used as fitting parameters for the heights of the first and second maxima of the temporal oscillations in the He-uptake curves. Remarkable agreement has been achieved in the entire parameter space except for temperatures below about 230 K. The deviations in the latter range are attributed to failure of the bulkcontinued fcc lattice due to, e.g., contraction, etc., becoming of importance for small adatom islands. This result allows an unequivocal determination of the Ehrlich-Schwoebel barrier associated with interlayer mass transport via a kink site ͑i.e., a ͗100͘ segment͒ in otherwise straight ͗110͘ steps, amounting to E ES ͗100͘ = −5 Ϯ 3 meV. The Ehrlich-Schwoebel barrier associated with ͗110͘ is determined at E ES ͗110͘ = 120 meV or higher. The perfect agreement between simulated and the experimental data in the wide range of parameter space also permits a quantitative evaluation of both coarsening, i.e., the increase in the lateral length scale of the structures and the kinetic roughening during growth. The lateral length scale varies with time to the power n = 0.22Ϯ 0.01 in perfect agreement with experimental literature data. Roughening exponents ␤ = 0.5 and 0.25 have been obtained for 250 and 290 K, respectively, also in very good agreement with previous experimental findings.

The growth of yeast cells to high densities at low, but constant, oxygen concentrations is difficult because the cells themselves respire oxygen; hence, as cell mass increases, so does oxygen consumption. To circumvent this problem, we have designed a system consisting of a computer-controlled gas flow train that adjusts oxygen concentration in the gas flow to match cellular demand. It does this by using a proportional-integral-differential algorithm in conjunction with a three-way valve to mix two gases, adjusting their proportions to maintain the desired oxygen concentration. By modeling yeast cell yields at intermediate to low oxygen concentrations, we have found that cellular respiration declines with oxygen concentration, most likely because of a decrease in the expression of genes for respiratory proteins. These lowered rates of oxygen consumption, together with the gas flow system described here, allow the growth of yeast cells to high densities at low oxygen concentrations. This system can also be used to grow cells at any desired oxygen concentration and for regulated shifts between oxygen concentrations.

Ion bombardment induced surface structures on Cu͑001͒ have been studied under conditions obeying the previously "coined athermal Bradley-Harper ͑BH͒ region." Off-normal ion impact along the ͗110͘ and the ͗100͘ azimuth at 200 K gives rise to different high-resolution low-energy electron-diffraction patterns. Unanticipated and marked deviations from the inherent fourfold symmetry are obtained already at a polar angle of incidence as low as 10°. Experiments with 800 eV Ar + ions ͑flux 6 ϫ 10 12 ions cm −2 s −1 and fluence 4.3 ϫ 10 16 ions cm −2 ͒ clearly show BH behavior for bombardment along ͓100͔ in contract to bombardment along ͓110͔. This observation is attributed to the higher probability for surface penetration of ions when incident along ͗100͘. This remarkable finding is further corroborated by measurement at various energies between 0.2 and 2 keV along ͓100͔.

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