Ultrafast pulsed laser irradiation is demonstrated to be able to produce surface nano-structuring and simultaneous crystallization of amorphous silicon thin film in one step laser processing. After fs laser irradiation on 80 nm-thick a-Si deposited on Corning 1737 glass substrate, the color change from light yellow to dark brown was observed on the sample surface. AFM images show that the surface nano-spike pattern was produced on amorphous-Si:H film by fs laser irradiation. Furthermore, micro-Raman results indicate that the a-Si has been crystallized into nanocrystalline Si. Also, the absorptance of the fs laser treated Si thin film was found to increase in the spectrum range of below bandgap compared to original untreated a-Si. The developed process has a potential application in fabrication of high efficiency Si thin film solar cells.
Laser drilling of single crystalline silicon carbide (SiC) wafer in air, under water, and under methanol with a 355 nm wavelength laser is investigated and compared. Among these different media, laser drilling of SiC under a solvent, methanol, is found to produce holes with a relatively cleaner and smoother surface. Ablated particle redeposition at the entrance and exit of the holes is minimized. Minimum oxide (i.e., silicon dioxide) or heat-affected zones are observed and the surface finish inside the holes is much smoother and more uniform as compared with those drilled in air and under water. The improvement of drilling quality can be attributed to the relatively lower boiling temperature and better wettability of the solvents, which enhance the effects of cooling (thermal damage free) and ablated particle cleaning during laser drilling. It is found that the quality of laser drilling of SiC varied with the thickness of solvent layer, that is, water and methanol. A solvent layer of 500 mm is suggested to be used for the enhancement of laser ablation rate and quality.
A simple approach to fabricate two-dimensional nanobump arrays on silicon (Si) substrate is reported. In the process, a single 248 nm excimer laser pulse was applied on a self-assembled monolayer of 1.5-μm-diameter silica microspheres on a n-doped (100) Si wafer. After laser irradiation at a fluence of 300 mJ/cm2, a regular array of conical Si nanobumps surrounded by a ring shaped trench were fabricated. The structure of the nanobump arrays was characterized by scanning electron microscope, and atomic force microscope. The formed nanobumps were determined to be Si-based bumps with energy disperse spectroscopy. The mechanisms involved in the formation of nanobumps were discussed.
For different applications of the pulsed-laser deposition (PLD) technique and for particular PLD chambers, different multi-target carousels are required. Here we describe three designs of a multi-target carousel for PLD which present separately the advantages of sufficient target cooling, reduced probability of jamming in operation and an adjustable target-to-flange distance. These carousels can be applied in various simple and small PLD systems where commercial products are not suitable, as well as in laser-molecular-beam-epitaxy (L-MBE) systems. They are of simple structure, low cost and may be constructed in a normal workshop.
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