Surface chemistry of the N-containing precursor dimethylhydrazine on Cu

This article focuses on the surface chemistry of an N-containing precursor, dimethylhydrazine (DMH), on Cu. DMH both adsorbs and decomposes on clean Cu at room temperature. N–N, C–N, and N–H bonds are cleaved, resulting in the immediate desorption of $N2$ and $CH4$ and leaving DMH species that, during subsequent heating, lead to $N2$ and $CH4$ desorption. There is evidence that $CH3$ groups dehydrogenate to form methylene, $CH2$⁠, that inserts into Cu–C and Cu–N bonds, and leads to $C2H4$⁠, $C2H5N$⁠; $C3H7NH2$⁠, and $C3H6NH2$⁠. The activation energy of DMH decomposition on the clean surface is about 10.8 kJ/mol. The 300 K reactivity of a clean Cu surface is reduced by repeated DMH doses and temperature programmed desorption. Passivation is attributed to the alteration of active surface sites by small amounts of retained reaction products, presumably containing C, the concentration of which lie below x-ray photoelectron spectroscopy detection limits. DMH decomposition and surface synthesis pathways are discussed.