Applied Surface Science, Vol.252, No.22, 7904-7910, 2006
Pulsed laser ablation of borax target in vacuum and hydrogen DC glow discharges
The aim of our experiment was to produce a material with B-H bonds for applications in hydrogen storage and generation. By using KrF excimer laser (lambda = 248 nm) ablation of borax (Na2B4O7) target, thin films were deposited on KBr and silicon substrates. Ablation was performed both in vacuum and in hydrogen atmosphere. DC glow discharge technique was utilized to enhance hydrogen gas ionization. Experiments were performed using laser fluence from 5 to 20 J/cm(2), Films were deposited under gas pressure of 1 x 10(-5) to 5 x 10(-2) mbar and substrate temperatures of 130-450 degrees C. Scanning electron microscopy analysis of films showed presence of circular particulates. Film thickness, roughness and particulates number increased with increase in laser fluence. Energy dispersive X-ray spectroscopy analysis shows that sodium content in the particulates is higher than in the target. This effect is discussed in terms of atomic arrangements (both at surface and bulk) in systems where ionic and covalent bonds are present and by looking at the increased surface/bulk ratio of the particulates with respect to the deposited films. The Fourier transform infrared spectroscopy measurements showed presence of B-O stretching and B-O-B bending bonds. Possible reasons for absence of B-H bonds are attributed to binding enthalpy of the competing molecules. (c) 2005 Elsevier B.V. All rights reserved.