Young’s Modulus of Fatty Acid Adsorption Films on Si Surface Measured Using Ar Gas Cluster Ion Beams

Abstract

Boundary lubrication films adsorbed on solid surfaces reduce friction and wear by reducing solid contact and have a significant contribution to the friction coefficient. To probe the contact mechanism at the surface, it is necessary to understand the elastic properties of both the solid surface and the boundary lubricant film. However, it is difficult to determine the elastic properties because the boundary lubricant film is a monolayer adsorbed on a solid surface. In this study, samples deposited on silicon substrates using the Langmuir–Blodgett (LB) method were prepared to determine the elastic modulus of the boundary lubricant film. The Young’s moduli of fatty acid films adsorbed on Si substrates deposited by the LB method and rinsed with acetone were measured using time-of-flight secondary ion mass spectroscopy (TOF-SIMS) with Ar gas cluster ion beams (Ar-GCIBs). The coverage of the fatty acid films after rinsing decreased with the carbon number of the fatty acids. The final Young’s moduli can be obtained by correcting the Young’s moduli measured using Ar-GCIB with the coverage of fatty acid films. Those were independent of the carbon number (C14‒C20) of the fatty acids and were estimated to be approximately 45 GPa.

Keywords

• adsorption
• fatty acid
• boundary lubrication
• elastic modulus
• gas cluster ion beam