Structural study of TiB 2 film by grazing incidence X-ray diffraction

Abstract

X-ray refractive indices of materials are slightly less than unity. Thus, total external reflection occurs at small incidence angles and the component of the electro-magnetic wave entering into the material becomes strongly attenuated 1. Marra e t al. 2 who took notice of this total external reflection phenomenon proposed a new method for structural studies of interface and surface. In this method, intensities are recorded at scattering angles of 20 in directions inclined to the plane formed by the incident beam and the surface normal. Thus, it is sometimes called the surface diffraction method. This surface diffraction has a different geometry from the parallel beam method with a small incidence angle ct on a sample surface and a 20 scan of a detector which is a typical X-ray diffraction technique for structural studies of a thin film supported on a substrate. This conventional method is successfully applicable to a film of, at least, a few hundred nanometers thickness 3. However, Lim e t al. 4 devised a new technique for an investigation of a thinner film by utilizing the total external reflection for the conventional method. A distinctive feature of this method is that the depth profile of atomic structures can be obtained because the X-ray penetration depth changes from several hundred nanometres to a few nanometres by varying the incidence angle ct to the sample surface from below to above the critical angle ~c. In the present study, we used Lim e t al. 's method in order to obtain structural data of a film of titanium diboride (TiB2). Titanium diboride has recently received much attention as a possible new ceramic material by indicating several attractive properties such as higher melting point (about 3000 K), good thermal conductivity, excellent chemical stability and good corrosion resistance 5'6. A TiB2 film grown on a silicon single crystal was prepared by a co-sputter deposition technique with a multiple sputtering apparatus explained in ref. 7. Titanium and boron of 99.9% purity were used as sputtering targets of 76.2 mm in diameter and 3 mm in thickness which were attached to water-cooled backingplates for magnetron sputtering. Sputter deposition was carried out in an argon atmosphere at a pressure of 0.67 Pa after evacuation to 5 x 10 -4 Pa. Titanium and