Adsorption and Thermal Decomposition of Hydrazoic Acid on Al(111)

The surface chemistry of hydrazoic acid (HN3) on Al(111) was investigated from 100 to 800 K with temperature-programmed desorption, infrared reflection−absorption spectroscopy (IRRAS), Auger electron spectroscopy, and low-energy electron diffraction (LEED). IRRAS suggests that the first monolayer dissociatively chemisorbs as N2(ads) and NH(ads) at 120 K. Subsequently, HN3 adsorbs molecularly in two phases, a physisorbed second layer and a condensed multilayer. In the former, the N3 chain of the HN3 is aligned normal to the substrate surface, while in the latter HN3 exhibits a random orientation. Molecular HN3 desorbs at 125 K, and two decomposition products, N2 and H2, desorb at 295 and 615 K, respectively. Mixed-isotope desorption experiments show that N2 is derived from an intact NN species, rather than from recombinative desorption of N(ads), and is consistent with the IRRAS observation of chemisorbed N2. IRRAS indicates that the NH species dissociates into N(ads) and H(ads) above 320 K, with H2 thermal desorption resulting from dissociation of the AlHx (1 ≤ x ≤ 3) moiety. After the sample was annealed at 800 K, N was observed with Auger spectroscopy. The partially nitrided Al(111) surface exhibits a concentric, double hexagonal LEED pattern indicating AlN(0001) islands. IRRAS indicates that the islands are Al-terminated and capped with H at temperatures as high as 700 K.