Internal energy distributions in the CO and CO2 molecules formed by molecular-beam surface reactions on a polycrystalline Pt foil have been studied by using FT-IR emission spectroscopy. The CO molecules produced by partial oxidation of n-butane or iso-butane at a surface temperature of 1500 K are substantially vibrationally excited (vibrational temperature : Tv=2300 K), but rotationally very cool (rotational temperature : TR=360 K). The low TR value is not due to the rotational relaxation by the gas phase collision. In contrast, the CO molecules produced by CH3OH decomposition are not vibrationally excited at all. This impliee that the mechanism is different between the partial oxidation of butane and the decomposition of CH3OH. On the other hand, the CO2 molecules produced and desorbed by oxidation of CH3OH is both vibrationally and rotationally excited, but the internal energy distributions of the CO2 molecules are different from those formed by the, CO+O2 reaction or the CO+O reaction. These differences in internal energy distributions can provide us with some information on the dynamics (including the structure of the activated complex and the energy transfer processes) of surface catalyzed reactions.
SiO2 films (thickness : 500 nm) deposited on Si(100) by plasma- and thermal-assisted chemical vapor deposition (CVD) using tetraethylorthosilicate (TEOS) were studied by Fourier transform infrared spectroscopy (FTIR), etch rate, and variable-energy positron annihilation spectroscopy. As the substrate temperature at deposition was raised, the density of the SiO2 films increased and the Si-OH impurity content decreased. On the other hand, Si-OH impurities in the SiO2 films could not be removed even at a substrate temperature of 440°C The Si-OH content in plasma-assisted CVD SiO2 films was much lower than that in thermal-assisted CVD SiO2 films at the same substrate temperature. It was found from FTIR and the positron study that the water tended to exist as Si-OH clusters, whose surroundings had more open space than those of normally bonded O3≡Si-O-Si≡O3.
Nitrogen, one of the most chemically inactive molecules, does not adsorb on A12O3 and Pt/Al2O3 catalysts at room temperature. However, once it was excited by plasma discharge using radio-frequency (13.56 MHZ), activated adsorption of nitrogen occurred on Pt/Al2O3 and Al2O3 at room temperature. The characterization of chemisorbed N2 and its chemical reactivity with hydrogen have been studied by temperature programmed desorption (TPD) and infrared spectroscopy (IR). The adsorbed nitrogen on Pt/Al2O3 or Al2O3 was desorbed below 300°C by TPD, and IR spectra of the adsorbed nitrogen on Pt/Al2O3 were observed at ca . 2260 and 2230 cm-1, which were assigned to N-N stretching vibration. Since almost the same absorption bands were observed with N2 on Al2O3, it was considered that N2(a) was chemisorbed mainly on the Al2O3 support . The H2 exposure experiment at room temperature showed that the infrared bands of N2(a) on the Al2O3 support (without Pt) did not change, but the intensity of the spectrum of N2 on the Pt/Al2O3 catalyst decreased significantly with time. Moreover, NH3 was detected in the liquid N2 trap by GC after the TPD run. It was proposed that the N2(a) reacted with the hydrogen spilt-over from the Pt surface to form other species like NHx(a) (X=1∼3) even at room temperature.
Hydrophobic properties have been investigated on chemically adsorbed monolayers which were formed on glass surfaces from perfluoroalkyl trichlorosilane solutions. The hydrophobic properties of the monolayers on the glass were estimated by measuring static and dynamic contact angles. The monolayers were hydrophobic as highly as polytetrafluoroethylene. The glass surfaces were found to be modified into hydrophobicity with only a monolayer of Perfluoroalkyl compounds without lowering the transparency of the glasses.