The surface morphology of single crystal (100) Si wafers irradiated by 266 nm and 1064 nm laser pulses emitted by a solid state Nd:YAG laser has been investigated. The morphology of the bottom of craters remained flat and almost featureless after 266 nm single or multipulse laser irradiation up to the maximum fluence of 18 J/cm<SUP>2</SUP> used in this study. The rims of the craters showed signs of radial liquid flow but it was apparent that the vaporization process was confined to the surface region. A different morphology was observed on the bottom of the craters formed by the 1064 nm wavelength laser pulses. Because this wavelength is absorbed in volume, (alpha) <10<SUP>4</SUP>cm<SUP>-1</SUP>, a rather thick liquid Si pool formed at the surface. For laser fluences higher than 3-5 J/cm<SUP>2</SUP> evidence of boiling sites were observed on the bottom of the crater, especially for multipulse irradiation. An evolution of surface morphology, from waves towards deep cavity was observed with the increase of pulse number. By analyzing the cavity formation mechanisms, their density and shape, we suggest that they were induced by heterogeneous boiling and not homogeneous boiling.
Thin Y<SUB>2</SUB>O<SUB>3</SUB> films were directly grown on (100) Si substrates by the pulsed laser deposition technique. It has been found by high resolution cross-section transmission electron microscopy, x-ray reflectometry and x-ray photoelectron spectroscopy (XPS) that at the interface between Si and the grown layer, an interfacial layer always formed. Depth-profiling and angle-resolved XPS investigations showed that this layer consists of a mixture of substoichiometric SiO<SUB>x</SUB>(x<2) and the deposited Y<SUB>2</SUB>O<SUB>3</SUB> layer, without forming an yttrium silicate. The thickness of this interfacial layer depended on the oxygen pressure and temperature used during the deposition. The main oxygen source for its formation is the physiosorbed oxygen which is trapped inside the grown layer during the laser ablation process. When the thickness of this low-k SiO<SUB>x</SUB> was reduced by decreasing the oxygen pressure during laser ablation below the optimum value, a marked degradation of the electrical properties of the structure was noticed.
The crystallinity, stoichiometry and optical and electrical properties of thin Y<SUB>2</SUB>O<SUB>3</SUB>, ZnO and Ba<SUB>0.5</SUB>Sr<SUB>0.5</SUB>TiO<SUB>3</SUB> films grown using an in situ ultraviolet (UV)- assisted pulsed laser deposition (UVPLD) technique have been studied. With respect to films grown by conventional PLD under similar conditions but without UV illumination, the UVPLD grown films exhibited better quality, especially for lower substrate temperatures. They also contained less physisorbed oxygen than the conventional PLD grown layers. These improvements can be explained by the action of several factors. Firstly, deep UV photons and ozone ensure a better in situ cleaning of the substrate. Secondly, the presence during the ablation-growth process of more reactive gaseous species like ozone and atomic oxygen formed by photodissociation of molecular O<SUB>2</SUB> promotes the oxygenation of the films. Thirdly, absorption of UV photons by adatoms could result in an increased surface mobility. All these factors have a beneficial effect upon crystalline growth, especially for moderate substrate temperatures, where the thermal energy available for the process is rather limited.