Deposition of nitrides and oxides of aluminum and titanium by pulse laser irradiation
- PDF / 2,031,893 Bytes
- 9 Pages / 576 x 792 pts Page_size
- 90 Downloads / 249 Views
Deposits of nitrides and oxides of Al and Ti have been produced by laser irradiation of Al and Ti targets in air, N 2 , and NH 3 + N 2 gases. Microstructure and constituent phases in these deposits have been examined by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and x-ray diffractometry (XRD). The distribution of metalloid elements has been investigated by Rutherford backscattering spectrometry (RBS). On the basis of the results of these examinations, the nitride and oxide deposits have been shown to be formed by reactions between ambient gas and metal-melt or metal-vapor which take place during pulse laser irradiation.
I. INTRODUCTION
II. EXPERIMENTAL PROCEDURES
Metal nitride or metal oxide thin film has enormous potential for advancing the expanding optoelectronic processing capabilities as well as localized surface hardening and protection for micromechanical applications. Especially A1N and TiN have a large bandgap, high melting point, and high thermal conductivity, and they are chemically inert. These thin films are commonly formed by chemical vapor deposition (CVD) techniques. However, the high temperatures required for these processes limit their use to refractory substrates. In contrast to the CVD techniques, pulsed laser deposition is one of the techniques that allows us to use lower substrate temperatures. Formations of TiN films by laser ablation of bulk nitrides1'2 as well as laser-induced nitridation of various metal surfaces in reactive ambient gases3"5 or liquid media6'7 have been reported. Laserinduced formation of ultrafine powders of oxides and nitrides8 has also been examined by many researchers. However, questions such as why some metals form nitrides but others do not when they are irradiated in N2 gas, and why some metals form nitrides but others form oxides by laser irradiation in air have not been answered yet. Furthermore, multi-irradiation effects such as that the content of metalloid elements on the irradiated metal surface increases with increasing irradiation shot number 9-10 have not been explained yet. To answer such questions, we need a reliable model of laser-induced nitridation or oxidation of metals. In this paper, we first report detailed microscopic observations of the deposits produced by laser irradiation of Al and Ti in air, N 2 , and NH 3 + N 2 gases, and then crystalline structures of constituent phases and the distribution of metalloid elements in the deposits are revealed. Second, we propose mechanisms for the formation of oxides and nitrides during laser irradiation of metals, which explain the present results well.
Figure l(a) shows the schematic diagram of the laser deposition apparatus, which is composed of a laser radiation system and an ambient gas control chamber where target metal and substrate are set. A laser beam from a pulsed Nd+ doped glass laser (wavelength: 1.06 /zm; pulse duration: 1 X 10""8 s; 4 J per pulse) was focused on the target metal surface. The angle between the laser beam and the target surface normal was 45°.
Data Loading...
