In situ SFG spectroscopy of film growth. II. Deposition of formic acid on Ni(110) surface

摘要

Infrared-visible sum-frequency generation (SFG) spectroscopy was used to monitor in situ the growth of multiple layers of formic acid on a Ni(110) surface. The signal by the CH stretching band displayed a characteristic interference pattern as the deposition proceeded and the feature was analyzed by the formula presented in the preceding article. The effect of substrate structure was examined to reveal that the deposition of a SFG active layer on alien surfaces requires the substrate temperature higher than 138 K with the optimum at 158 K, but the same growth as under the optimum condition was sustained at 143 K once the active layer had been formed beforehand. No SFG-wise change was observed when the sample temperature was changed in vacuum either from the SFG undetectable 143-153 K or to the opposite direction to indicate that the layers formed at the two temperatures are not related with phase transition. However, the deposition of the SFG-active layer took place at 143 K, when the sample was precovered by the active layer or the SFG-inactive layer was heated to 153 K. Covering by a DCOOD layer, which has no SFG signal at the examined frequency, gave a significant suppression of the interference feature. An interpretation is given on the crystal structure and molecular orientation of the SFG-active and SFG-inactive layers. (C) 1998 American Institute of Physics. [References: 28]