Interactions of trimethyl gallium and trimethyl aluminum with Ni(111): a TPD, SIMS and AES study

Abstract

The interaction of trimethyl gallium (TMG) and trimethyl aluminum (TMA) with Ni(111) was studied using TPD, SSIMS and AES. At 100 K and low exposures, TMG adsorbs dissociatively; below 0.3 L, some atomic Ga forms, but up to 2.4 L, CH 3 and dimethyl gallium (DMG) are the main products. For higher exposures, including multilayers, molecular adsorption dominates. While multilayers desorb intact at 155 K, there is no parent desorption from the first layer. During TPD, the first dissociation occurs below 200 K and is dominated by CH 3 and DMG formation. Over a broad temperature range, 100 to 500 K, DMG decomposes to leave atomic Ga and C. Above 250 K, there is evidence for nucleation of Ga into islands and rearrangement of Ni-Ga bonds. Some CH 3's undergo dehydrogenation above 150 K; others are hydrogenated at 250 K, yielding gaseous CH 4. The TPD of H 2 has peaks at 372 and 422 K; the former rate is limited by recombination of H atoms bound to Ni; the latter rate is controlled by C-H bond cleavage. The dissociative uptake of TMG increases when the dosing is done at higher Ni temperatures. Complete dissociation of C-Ga bonds, i.e. atomic Ga, H and C, is preferred at low exposures; DMG accumulates at high exposures. The surface Ga and C formed at low exposures modify the subsequent surface reactivity and increase the thermal stability of DMG. A new pathway opens for doses at elevated temperatures (200–400 K) and involves intra- and/or inter-molecular decomposition and reaction of DMG to produce CH 4, H 2 and GaCH. GaCH decomposes between 500 and 700 K, with simultaneous release of H 2. The chemistry of TMA on Ni(111) is analogous to that of TMG. Multilayer TMA, which is dimerized, desorbs in monomer form at 185 K. Surface Al nucleates at a higher temperature (300 K) than does surface Ga.