Single pulse excimer laser nanostructuring of thin silicon films: Nanosharp cones formation and a heat transfer problem

Abstract

We present analytical and computer modeling along with an experiment on the formation of sharp conical tips on monocrystalline silicon thin films, silicon-on-insulator, subjected to irradiation by single 25 ns pulses from a KrF excimer laser focused into a spot several micrometers in diameter. These fabricated structures have heights of about 1 m and apical radii of curvature of several tens of nanometers. We offer a simplified analytical model for the formation of these structures. The computer simulation includes two-dimensional time-dependant heat transfer and phase transformations in Si films on SiO 2 substrates that result from the laser irradiation ͑the Stefan problem͒. It is shown that upon irradiation and initial melting, the liquid/solid interface remains mainly parallel to the surface of the film. After the laser pulse, the molten material self-cools and resolidifies. The solid/liquid interface moves predominately laterally toward the center of the irradiated spot, forming an almost vertical front. We discuss the relation between the dynamics of the melting/freezing front movement and the displacement of material in the irradiated spot.

Insight into electronic mechanisms of nanosecond-laser ablation of silicon

“…They demonstrate, however, a variety of physical effects that have not been fully understood. There are still debates about ultrafast melting, 1-5 resolidification dynamics, [6][7][8] surface structure modification, 9,10 thermal and nonthermal mechanisms of ablation, 6,[11][12][13][14][15][16][17][18] and direct cluster emission. 16,[19][20][21] This stimulates extensive studies, both experimental and theoretical, of the dynamics of laser heating, melting, resolidification, and ablation of silicon under laser irradiation with different pulse durations and laser wavelengths.…”

Holographic Fabrication of Periodic Microstructures by Interfered Femtosecond Laser Pulses

“…The induced periodic microstructure depicted by an AFM: (d) Energy is 75 J per pulse, (g) Energy is 30 J per pulse, (f) (i) Three-dimensional image of the microstructure of (d) and (g) respectively, (e) (h) The cross section of the microstructure in the direction of black line showed in (d) and (g) respectively subsequent posterior part of the pulse also removed the central plasma very swiftly by means of light pressure, so there is a tiny hole formed in the center of the enhanced spot. However, in the region of the molten liquid, there were two distinct interaction components because of Marangoni effect, thermocapillary and chemicapillary, which resulted from the thermal potential of a temperature gradient and the chemical potential of a compositional gradient, respectively [17,[36][37]. The thermocapillary force moved the molten material outward from the center, while the chemicapillary force moved the molten material toward the center [38][39] as depicted in Fig.…”

Surface Treatments to Modulate Bioadhesion: A Critical Review

“…By increasing the temperature whilst decreasing the liquid's surface tension, the liquid is pulled from the hotter to the cooler regions [47]. Convective and thermocapillary forces can then cause significant deformations that are frozen in during solidification [48,49]. Vast improvements in both laser technology and processing techniques have resulted in the possibility of micro-processing to produce surface patterning using direct beam scanning [2].…”