Surface Chemistry of Azomethane Adsorbed on Si(111)-7 × 7 Surface Studied by SR-Photoemission, HREELS, and STM

• Published in: The journal of physical chemistry. B 2003-02, Vol.107 (6), p.1387-1394
• Main Authors: Klauser, Ruth, Tai, Y, Chan, Y. L, Chuang, T. J
• Format: Article
• Language: English
• ISSN: 1520-6106; 1520-5207
• DOI: 10.1021/jp022283i

The adsorption and thermal decomposition behavior of azomethane on the Si(111)-7 × 7 surface has been studied by high-resolution electron energy loss spectroscopy (HREELS), synchrotron radiation photoelectron spectroscopy (SR-PES) in the soft X-ray and UV photon energy ranges, and scanning tunneling microscopy (STM). It is found that at 90 K substrate temperature, azomethane is adsorbed largely intact in both trans and cis forms. The decomposition of the molecules starts at an annealing temperature around 200 K with NN bond breaking, and at 300 K, a mixture of remaining intact azomethane, NCH x , and Si−NH x species is present on the surface with three distinct N 1s photoemission peaks. At this temperature, the Si−N species begins to appear as nitride, but no Si−C bonding is detected. Carbon dissociates from nitrogen and reacts directly with the Si surface above 400 K with CH3 adsorption as an intermediate adspecies. The CH3 adsorption is strongly enhanced if azomethane is thermally precracked prior to the exposure. At 700 K, all surface carbon and nitrogen are bonded to Si. The remaining hydrogen is desorbed at 1000 K, and Si−C and Si−N phases are formed. After it is annealed to 1500 K, photoemission features typical for the clean Si(111)-7 × 7 surface are immediately recovered. Si−C and Si−N species are desorbed, leaving a homogeneous but disordered surface with an underlying 1 × 1 structure, which transforms back into the 7 × 7 structure by forming characteristic triangular-shaped patterns as intermediate steps in the surface reconstruction process.