Effect of Medium on Interaction Forces between Atomic Force Microscopy (AFM) Tip and Gold Nanoparticle

Abstract

Atomic Force Microscopy (AFM) has become powerful tool not only to study the surface topography but also the interaction forces between the tip and the sample. In this works, the measurement of the forces was determined by using AFM imaging in air and in liquid environment. Then, the force-distance (FD) curve was analysed to determine the interaction forces between the tip and the samples. The forces was computed from the pull-off forces of FD curve. When the FD curve are required in air, a thin layer of water (liquid contaminant layer) adsorbed on the sample surface exerts a meniscus or capillary force. Instead, when working in a liquid, the capillary force is eliminated and other forces becomes relevant. The force present is the van der Waals force and electric double layer force. The net force between the tip and the samples is the vector sum of several forces. In air, the dominant component of the adhesion force between the tip and the sample is believed to be the capillary force while in liquid, the dominant components present is the van der Waals force. The adhesion force ranging from 10 to 100 nN have been reported for imaging in air and the adhesion force of 5 to 104 nN observed in our studies lies well within this range. Meanwhile, in liquid, the adhesion force obtained from this work is in the range of 0.1-40 nN and it is lies within the range reported previously which is as low as 100 pN. Detecting forces is an important step toward developing new analytical and biomedical devices such as biosensors.