Imaging Electrochemical Controlled Chemical Gradients Using Pulsed Force Mode Atomic Force Microscopy

Extract

The electrochemical formation of gradients in self assembled monolayers has been demonstrated recently [1]. The capacity to image these gradients provides useful information on the physical chemistry of electrochemical striping.

Imaging chemical gradients requires the ability to sense the chemical moiety on the top of the self-assembled monolayer. This has been accomplished by derivatizing an atomic force microscope (AFM) tip with molecules selected to have specific interactions with the sample in a technique known as chemical force microscopy [2]. Typical tapping mode AFM is then used to image the sample; the tip is oscillated vertically above the sample and the tip-sample interaction modulates the amplitude of the tip.

The sample adhesion, sample stiffness, and sample topography all influence the oscillation amplitude of the tip. Pulsed Force Mode (PFM) [3] is an extension for atomic force microscopes. The PFM electronics introduces a sinusoidal modulation to the z-piezo of the AFM with an amplitude between 10 to 500 nm at a user selectable frequency between 100 Hz and 2 kHz.