Department of Chemistry and WATLab, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada.
J Chem Phys. 2010 May 7;132(17):174702. doi: 10.1063/1.3400647.
Vibrational electron energy loss spectroscopy (EELS) has been used to characterize the adsorption of acetic acid on Si(111)7 x 7 at room temperature and as a function of annealing temperature. At room temperature, acetic acid is found to undergo O-H dissociative adsorption to form predominantly unidentate adstructure. The equilibrium geometry and the corresponding characteristic vibrational wavenumbers of the adstructures were obtained by density functional theory calculations and are found to be in good accord with the vibrational EELS data. Annealing the sample near 473 K marked the onset of C-O dissociation of the acetate adstructure with the emergence of Si-O-Si vibrational modes at 720 and 1020 cm(-1). Further annealing to 673 K caused a marked intensity reduction in the C-C stretch at 930 cm(-1) and in the CH(3) vibrational features at 1360 and 2990 cm(-1), suggesting further dissociation of the adstructures. The complete removal of the blueshifted Si-H stretching mode at 2275 cm(-1) upon further annealing to 773 K is consistent with the recombinative desorption of H(2) from Si monohydrides expected in this temperature range. The emergence of the Si-C stretching mode at 830 cm(-1) at 873 K is in good accord with the formation of SiC. Similar thermal evolution of the vibrational features have also been observed for acetic acid adsorption on a sputtered Si(111) surface.
振动电子能量损失谱（EELS）已被用于在室温下和随退火温度变化来表征乙酸在 Si(111)7 x 7 上的吸附。在室温下，发现乙酸经历 O-H 离解吸附，形成主要的单齿吸附结构。通过密度泛函理论计算得到了吸附结构的平衡几何形状和相应的特征振动波数，发现与振动 EELS 数据吻合良好。将样品在接近 473 K 的温度下退火，标志着醋酸吸附结构的 C-O 离解开始，在 720 和 1020 cm(-1) 处出现 Si-O-Si 振动模式。进一步退火至 673 K 导致在 930 cm(-1) 处的 C-C 伸缩振动和在 1360 和 2990 cm(-1) 处的 CH(3)振动特征的强度显著降低，表明吸附结构进一步离解。进一步退火至 773 K 时，在 2275 cm(-1) 处的 Si-H 伸缩模式的完全消失与 Si 单氢化物在该温度范围内预期的 H(2)的复合解吸一致。在 873 K 时，在 830 cm(-1) 处出现 Si-C 伸缩模式，这与 SiC 的形成一致。在溅射的 Si(111)表面上吸附乙酸时，也观察到类似的振动特征的热演化。
