Microtribological studies of unlubricated and lubricated surfaces using atomic force friction force microscopy

Microtribological studies were performed on unlubricated and lubricated (Z-15 and Z-DOL with hydroxyl end groups) silicon, double grafted C-18 layer, Langmuir-Blodgett (LB) film, gold film and mica samples in ambient, dry nitrogen and dry air environments using atomic force/friction force microscopy (AFM/FFM). A sharp tip of AFM/FFM sliding on a surface simulates a single asperity contact. The silicon samples lubricated with Z-15 and Z-DOL lubricant films exhibit lower coefficient of microfriction than that of the unlubricated silicon sample. Microfriction values are lower than that of the macrofriction. ploughing contribution is responsible for the higher macrofriction values. The microfriction experiments on bare silicon and lubricated with Z-15 and Z-DOL carried out in dry nitrogen and dry air exhibit lower coefficient of microfriction values than those in ambient atmosphere measurements. Dewetting of the liquid film in a humid environment is believed to be responsible for higher microfriction. The dependence of scanning velocity on microfriction was studied and it was found that the friction force decreases with an increase in the scanning velocity for the liquid-lubricated samples in the humid environment and it is relatively insensitive to scanning velocity in dry environments. Alignment of Liquid molecules (shear thinning) is believed to be responsible for the drop in microfriction at high scanning velocities. Micro- and nanowear tests reveal that the chemically bonded Z-DOL lubricant is more durable than the Z-15, double grafted C-18, LB and gold films. (C) 1996 American Vacuum Society.