We report that silicon surfaces develop an array of sharp conical spikes when irradiated with 500 laser pulses of 100-fs duration, 10-kJ/m2 fluence in 500-Torr SF6 or Cl2. The spikes are up to 40-μm tall, and taper to about 1-μm diam at the tip. Irradiation of silicon surfaces in N2, Ne, or vacuum creates structured surfaces, but does not create sharp conical spikes.

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We report visible luminescence from SiOx formed by microstructuring silicon surfaces with femtosecond laser pulses in air. Incorporation of oxygen into the silicon lattice occurs only where the laser beam strikes the surface. Laser microstructuring therefore offers the possibility of writing submicrometer luminescent features without lithographic masks. The amount of oxygen incorporated into the silicon surface depends on the laser fluence; the peak wavelength of the primary luminescence band varies between 540 and 630 nm and depends on the number of laser shots. Upon annealing, the intensity of the primary luminescence band increases significantly without any change in the luminescence peak wavelength, suggesting that the luminescence comes from defects rather than quantum confinement.

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We studied the surface femtochemistry of CO/O 2 /Pt(111) induced with 0.3 ps laser pulses over a wide range of wavelength and fluence. Below 10 J/mm 2 , the yields depend linearly on fluence. Above 10 J/mm 2 , the yields scale nonlinearly in the fluence. From the dependence of the yields on wavelength, we determine that the nonlinear surface femtochemistry is influenced by nonthermal substrate electrons.

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We have studied chemically adsorbed glycine on the hydrophilic surface of the oxidized surface of silicon. A stable adsorbate layer is formed, which consists of zwitterionic glycine molecules. Most importantly, these zwitterionic molecules have a tendency for orientation in a direction perpendicular to the substrate surface, with COO- groups away from the surface and the NH3+ groups toward the surface.