The structures of physisorbed and chemisorbed formic acid on Si(1 1 1)-7 × 7

The reaction of formic acid on Si(1 1 1)-7 × 7 was investigated using X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS) and high-resolution electron energy loss spectroscopy (HREELS). The hydroxyl and carbonyl O 1s core levels of chemisorbed formic acid display chemical shifts of 2.4 and 0.2 eV respectively, compared with those of physisorbed molecules. The HREELS spectra of chemisorbed formic acid show the absence of stretching and bending modes of the O–H bond, the appearance of Si–H (2089 cm−1) and the Si–O (680 cm−1) stretching modes and the retained stretching mode of CO at 1703 cm−1. Our results clearly suggest that formic acid dissociates to form monodentate formate species and H-atom on the adatom–rest atom pair of Si(1 1 1)-7 × 7.