Dot and ripple nanopatterns on Si surfaces with defined symmetry and characteristic dot spacings of 50-70 nm were created by 1 keV Ar ion irradiation at normal incidence and simultaneous co-deposition of Fe atoms at grazing incidence. Fe was continuously supplied from different sputter targets surrounding the Si substrate, leading to a steady-state Fe content in the near-surface region of the substrates. The pattern formation is self-organized, most probably caused by ion-induced phase separation. Patterns were analyzed with atomic force microscopy and the Fe content in the irradiated layer was measured with Rutherford backscattering. The symmetries of the produced patterns are isotropic, four-fold symmetric, three-fold symmetric and various types of two-fold symmetric patterns, depending on the geometrical arrangement of the sputter targets. Pattern formation was studied for a steady-state coverage of Fe between 0.5 and 3.3 × 10 15 Fe cm −2 . The threshold coverage for the onset of pattern formation is about 0.5-1 × 10 15 Fe cm −2 . The coherence length of the patterns is comparable to the average dot spacing. Nevertheless, the autocorrelation analysis reveals a residual long-range periodicity of some patterns. The dot spacing can be adjusted between about 20 nm and several hundred nm depending on the ion species and ion energy.
Polycrystalline nickel layers, deposited on Si(1 1 0) wafers via electron beam evaporation to a thickness of 29 or 68–70 nm, were thermally annealed in vacuo at 493 or 530 K. The elemental interdiffusion across the Ni/Si interface was measured by means of Rutherford backscattering spectroscopy, and the relaxation of stress and grain growth by means of x-ray diffraction. At 530 K, a slight logarithmic increase in the interface variance with the annealing time, but no crystalline silicide formation was observed. The in-plane magneto-optical Kerr effect and magnetic force microscopy were used to investigate the changes in the magnetic properties. With increasing annealing time, the decrease in coercivity and gain in magnetic remanence were correlated with the relaxation of stress. Similarities with ion-irradiated Ni/Si couples will be discussed.
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