Intensity distribution in the sample plane (a, f) (contrast enhanced for clarity) and corresponding patterns in 150-nm-thick SiO x films obtained with single pulses of varying fluences at 248 nm, mask period 40 μm (b to e), and mask period 20 μm (g to k). By heating the sample to >1,000 K, the material is oxidized to SiO2 leading to a chemically even more stable silica wire grid (Figure 4). Figure 4 Pattern before and after annealing. Grid pattern generated in a 90-nm-thick

SiO x film at 248-nm laser wavelength: (a) 185 mJ/cm2, before annealing; (b) 210 mJ/cm2, after selleck inhibitor oxidation to SiO2 by high-temperature annealing (1,273 K, 16 h). Grids with periods from the sub-micron check details range to more than 10 μm have been fabricated by this method. The particular final shape depends on the irradiation pattern, the fluence, and the film thickness. Figure 5 displays grids with wire diameters of about 50 nm. In Figure 5a, the nanowires bridge a distance of 5 μm, so that the length/diameter ratio amounts to 100:1. Figure 5b demonstrates that nanogrids with a sub-micron mesh width (800 nm) can be made. In this case, the self-supporting wires have a diameter of 50 nm, too. Figure 5 Grids with wire diameters at the nanoscale. (a) Grid pattern generated in a 144-nm-thick SiO x film using a laser wavelength of 248 nm and a fluence of 300 mJ/cm2. (b)

Grid pattern generated in a 28-nm-thick SiO x film using a laser wavelength of 193 nm and a fluence of 130 mJ/cm2. Discussion Ricolinostat order The method utilizes the combination of pulsed laser heating and softening of a thin film, expansion, fracture and shaping due to pressure generation and surface tension, and resolidification in the final shape. It shows that a pulsed laser forming process is possible that delivers reproducible patterns, which depend on the irradiation pattern, but do not directly reproduce the mask or irradiation pattern. The forming of films in the described way is possible for film thickness below about 200 nm. For thicker films, a transfer process of intact film pads is observed instead [10]. It is assumed that for the grid-forming process complete melting of the film

is necessary, but vaporization must be limited to an extent, that the remaining molten material can be formed by the shock wave generated by this vaporization in combination with surface tension. Regarding the optical absorption depth Cisplatin supplier and the thermal diffusion length for the given laser and material parameters, 200 nm corresponds to a maximum depth to which the melting temperature can be reached without excessive boiling [11]. Assuming that the final topographies for low or medium fluence represent intermediate states of the process at high fluence, the formation of a nanogrid array can be understood as follows: The blister formation starts at the points of maximum intensity. Some time later, the heated film is elevated in the whole irradiated area and is connected to the substrate only at the border of the remaining non-irradiated spots in between.