ABSTRACT
Experimental results are presented on the formation of self-organized nanostructures (NSs) on a bulk Al target under its ablation in liquids--water and ethanol--with short laser pulses from 180 femtoseconds (fs) through 350 picoseconds (ps). NSs are characterized by atomic force microscopy, field emission scanning electron microscopy, optical absorption spectroscopy and x-ray diffraction. The period of NSs does not depend on the laser wavelength used from 248 through 800 nm and is approximately 200 nm. NSs on Al show the characteristic absorption peak in the near UV which has been attributed to plasmon oscillation of electrons. The wings of this peak, extending to the visible, lead to a distinct yellow coloration of the processed Al surface. Ultrafast laser structuring of bulk aluminum in liquids may be potentially a promising technique for efficient production of nanosized aluminum.
Subject(s)
Aluminum/chemistry , Aluminum/radiation effects , Crystallization/methods , Lasers , Nanostructures/chemistry , Nanostructures/ultrastructure , Nanotechnology/methods , Macromolecular Substances/chemistry , Materials Testing , Molecular Conformation , Particle Size , Solutions , Surface PropertiesABSTRACT
The effect of laser pulse duration on the morphology, composition, crystallinity and optical properties of self-organized Si microcones fabricated using 248 nm laser pulses (500 fs, 5 ps and 15 ns) in an SF(6) atmosphere, is presented in this paper. Despite distinct differences in the morphology, the Si cones show similar structure and composition independently of the laser pulse duration used: a core of single-crystalline Si, covered by a few hundred nanometer thick, sulfur-doped nanocrystalline Si layer, where no amorphous Si is present. The obtained features exhibit strong below-bandgap absorptance, making them excellent candidates for Si based photodetectors with improved spectral response.
ABSTRACT
We report on the wettability properties of silicon surfaces, simultaneously structured on the micrometre-scale and the nanometre-scale by femtosecond (fs) laser irradiation to render silicon hydrophobic. By varying the laser fluence, it was possible to control the wetting properties of a silicon surface through a systematic and reproducible variation of the surface roughness. In particular, the silicon-water contact angle could be increased from 66° to more than 130°. Such behaviour is described by incomplete liquid penetration within the silicon features, still leaving partially trapped air inside. We also show how controllable design and tailoring of the surface microstructures by wettability gradients can drive the motion of the drop's centre of mass towards a desired direction (even upwards).
