Self-assembled monolayers (SAMs) of ω-(4‘-methylbiphenyl-4-yl) alkanethiols CH3(C6H4)2(CH2) n SH (BPn, n = 3 and 4) on Au(111) substrates were studied using scanning tunneling microscopy (STM) and low-energy electron diffraction (LEED). Preparation at elevated temperature results in highly ordered layers with large domains. Whereas the (2√3 × √3) structure of the BP3 SAMs is similar to that reported previously for other aromatic thiols, SAMs made from BP4 exhibit a very different structure. A (5√3 × 3)rect unit cell containing 8 molecules is found which corresponds to a packing density reduced by 25% compared to that of BP3. The odd−even effect observed in the molecularly resolved STM images of BP3 and BP4, therefore, confirms the pronounced influence of the spacer chain on the structure of these biphenyl-based SAMs.

COOH-terminated organic surfaces were prepared by self-assembly of different organothiols, mercaptohexadecanoic acid (MHDA) and mercaptomethylterphenylcarboxylic acid (MMTA), on Au substrates. The SAMs were explored by infrared reflection-absorption spectroscopy and X-ray photoelectron spectroscopy. A rather strong dependence on preparation conditions is observed which explains inconsistencies between previous studies reported for these systems. Using optimized preparation conditions, films with a high degree of molecular orientation could be prepared. A significant amount of disorder, however, is induced by hydrogen bonds between the terminating -COOH groups. An organothiol with a more rigid backbone, MMTA, is demonstrated to yield carboxy-terminated SAMs which are more straightforward to prepare and which show a significantly higher degree of order.