To elucidate the thermal chemical processes of 1,4-cyclohexadiene (C 6 H 8 ) 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 (C 6 H 6 ) and cyclohexene (C 6 H 10 ). 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.

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Pentacene films were fabricated by molecular beam deposition on two silicon (Si) substrates. One of the substrates was Si(001) with a chemisorbed 1,4-cyclohexadiene surfactant buffer and the other was Si(001) with a SiO2 oxide layer. The 1,4-cyclohexadiene buffered surface was characterized by high-resolution electron energy loss spectroscopy (HREELS). 1,4-cyclohexadiene molecules were adsorbed on the clean Si(001) (2×1) substrate forming Si-C covalent bonds at 300 K and a well-ordered (2×1) structure was preserved even after adsorption of the molecules. The chemisorbed 1,4-cyclohexadiene layer is thermally stable at approximately room temperature. The morphology and crystallinity of the pentacene films were investigated by atomic force microscopy (AFM) and X-ray diffraction (XRD) analysis, respectively. The AFM images showed larger grains exceeding 1 µm for the pentacene film deposited on the Si(001) substrate with 1,4-cyclohexadiene buffer, whereas the small grains of 200 nm on average were observed for the film on Si(001) with SiO2 under the same deposition rate and substrate temperature.