We investigated the frictional properties and the durability of self-assembled double layers using pin-on-plate methods and X-ray photoclectron spectroscopy (XPS). We found that double layers made from octadecanethiol, (ODT) and mercaptohexadecanoic acid (MHA) connected via Cu ions exhibited lower frictional coefficients (approximately 0.1-0.15) than that of ODT monolayer (similar to 0.2). XPS measurements revealed that ratios of C(1s)/Au(4f) after friction tests were lower than that before friction but was higher than that measured on ODT monolayer, suggesting that some of ODT molecules were desorbed from the surface, i.e. formation of loosely packing molecular layers after friction. These findings suggest that the loosely packed molecular layer contributed to decrease the friction. (c) 2004 Elsevier B.V. All rights reserved.