Selective Area Laser Induced Deposition of Metal Boride Thin Films
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Selective area deposition of metal films from solution was reported for the deposition of copper [15] and other materials including complex compounds [16-17]. In one of these laser induced solution deposition studies from solution, copper chloride and nido-decaborane was used [15]. Similarly, we have used a chloride and a nido-borane to deposit rare earth borides from solution as in the copper deposition. In this paper we present the development of deposition techniques for gadolinium boride and lanthanum boride on glass substrates from solution. EXPERIMENTAL All deposition experiments were performed on substrates immersed in solutions containing various mixtures of methanol, cyclohexane, tretrahydrofuran (THF), diethylether and benzene. Different ratios of the solutes, rare earth chlorides and nido-decaborane, were used. Depositions were undertaken on glass substrates, and the exposure time of samples was varied from 0.5 to 20 hours. Laser flux was 20 to 30 Watts/cm2 in the visible and 2 to 5 Watts/cm 2 in the UV for all samples. The laser-induced solution deposition system (LISD system) utilized an argon ion laser (1-90 Coherent) as detail as elsewhere [18]. The structure of the deposited films was characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The compositions were identified by energy dissipative X-ray analysis (EDX). The deposition was explored with both ultraviolet (333 nm to 363 nm) and visible (514 nrm) radiation. 91 Mat. Res. Soc. Symp. Proc. Vol. 558 02000 Materials Research Society
RESULTS AND DISCUSSION Laser induced reactions of gadolinium chloride and decaborane in the visible (hv= 2.4 eV) using a mixture of 10 - 120 mmol THE (36 - 48%), 10 - 100 mmol cyclohexane (36 - 48%), 2 - 25 mmol diethylether (3 - 28%) and 3 - 15 mmol (< 1%) methanol as the solvent resulted in depositions of a relatively uniform thin film as seen in Figure 1. EDX measurements show no
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Figure 1: Scanning electron micrographs (SEM) of LISD deposits on glass substrates from a solution of methanol, TEF, cyclohexane, and diethylether. (a) gadolinium sub-borides (b) gadolinium hexaboride. 92
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Figure 2: X-ray diffraction pattern of gadolinium hexaboride on glass substrate, imaged in Figure 1(b). trace of a chlorine inclusion in these films and X-ray diffraction clearly shows the diffraction lines associated with GdB6. These films resemble those through the corresponding gas phase reaction [11 12] but the prominence of the diffraction line, as seen in Figure 2, clearly indicates that these films grown from solution are considerably more textured than those grown in the vacuum reactor. Thus, while the film is polycrystalline, the crystallites are oriented. The deposition is largely restricted to the area of the substrate illuminated by the laser indicative of some selective area deposition. We have tried to deposit gadolinium hexaborides on parts used in D.C. plasma display device cathodes. The results suggest that, to some extent, the deposition of
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