Different Adsorbed States of 1,4-Cyclohexadiene on Si(001) Controlled by Substrate Temperature

• Published in: Journal of physical chemistry. C 2007-02, Vol.111 (6), p.2557-2564
• Main Authors: Kato, Hiroyuki S, Wakatsuchi, Masayuki, Kawai, Maki, Yoshinobu, Jun
• Format: Article
• Language: English
• ISSN: 1932-7447; 1932-7455
• DOI: 10.1021/jp066525g

To elucidate the thermal chemical processes of 1,4-cyclohexadiene (C6H8) on Si(001), the adsorption states were characterized by temperature-programmed desorption (TPD), low-energy electron diffraction (LEED), and high-resolution electron energy-loss spectroscopy (HREELS), in comparison with those for benzene (C6H6) and cyclohexene (C6H10). Consequently, three types of adsorption states, i.e., π-complex, single di-σ bonding, and double di-σ bonding species, were identified. At 85 K, all 1,4-cyclohexadiene molecules are adsorbed as π-complex species in the first layer. With increasing substrate temperature, above 150 K, these π-complex species chemically convert to single di-σ bonding species by [2 + 2] cycloaddition with a Si dimer. Upon further heating above 300 K, most single di-σ bonding species are dehydrogenated into benzene and then the benzene molecules desorb from the surface. In contrast, double di-σ bonding species are formed preferentially in low exposure at 300 K, and are dehydrogenated into benzene above 600 K.