Preparation of Metal Nitrides Via Laser Induced Photolytic Decomposition of Metal-Amides
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ABSTRACI" Irradiation of {[(CH 3)3 Si] 2 N} 3Y, Zr[N(C 2H 5 )2]4 , and Nb[N(C 2 Hs) 2]4 by the 1.064 pm line of a pulsed Nd:YAG laser results in the decomposition of Zr[N(C 2H 5 )2] 4 and Nb[N(C 2 H5 )2]4 while {[(CH 3)3 Si] 2N} 3Y remains unaffected. The decomposition is photolytic and is accompanied by a visible emission tracing the path of the incident beam. The decomposition products form corresponding carbide/nitrides on pyrolysis in vacuum and nitrides on pyrolysis in an ammonia atmosphere. The spectroscopic investigation of the visible emission, and the pyrolysis of the decomposition products to metal nitrides is described. INTRODUCTION The importance of lasers in the preparation of materials is well-established for the deposition of metals and metal-oxides [1]. However, there are relatively few examples of the preparation of non-oxide materials. For example, Si, Si3 N4 , SiC, Si/C/N, and TiB 2 have been prepared by taking advantage of a strong infra-red absorption band of precursors coincident with a wavelength of the CO 2 laser [2-6]. Other examples of laser prepared materials are FeSiC [7], SiB [8], B4 C [9], B and TiB 2 [10]. We have recently shown that tetrakis-(dimethylamino)titanium, Ti[N(CH 3)2] 4 , decomposes upon irradiation by 1.064 ptm light from a pulsed Nd:YAG laser [11]. There is no vibration nor electronic transition coincident with this frequency of laser light. Broad band visible emission from the vapor phase above the Ti[N(CH 3)2]4 sample accompanies the laser irradiation. As the laser intensity is increased, the emission develops structure indicating the formation of Ti and Ti+. Both the visible emission and the formation of atomic titanium indicate multiphoton dissociation of Ti[N(CH 3)214 and/or its decomposition products. We also noted the formation of an amorphous grey-black residue upon prolonged irradiation of Ti[N(CH 3 )2]4 at 1.064 pm which could be pyrolyzed to TiN or TiN/TiC materials depending on firing conditions [11,12]. We employed this photodecomposition method to prepare TiN-A12 0 3, TiN-TiO 2 , and TiN-Si 3N 4 composites [12]. In contrast, TiCI4 , Ti(OR) 4 , Si(NMe 2)4 , and B(NMe 2)3 do not decompose under 1.064 pm irradiation. The present report describes the effects of 1.064pm radiation on Y{N[(CH 3 )3 Si] 2} 3 , Zr[N(C 2H5 )2] 4 , and Nb[N(C 2 H5 )2]4 . The yttrium amide remains unaffected after prolonged irradiation but the zirconium and niobium amides decompose. After removal of the undecomposed amides, the residues are fired in vaccum or in a flowing NH 3 /N2 atmosphere to obtain metal carbide/nitrides or nitrides, respectively. These results show that the laser induced photolytic decomposition is not unique to molecules containing Ti-N bonds among metal amides. EXPERIMENTAL PROCEDURE All materials used in these experiments were handled in either a dry-box [argon atmosphere] or a high-vacuum system with nitrogen atmosphere using Schlenk techniques to 135 Mat. Res. Soc. Symp. Proc. Vol. 410 01996 Materials Research Society
exclude air and moisture [13]. Hexanes we
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