What is Charge Gradient Microscopy (CGM)?

Charge Gradient Microscopy (CGM) is a new application of Conductive AFM (CAFM) that enables the measurement of screening and polarization charges on polar surfaces. Unlike conventional CAFM, no external bias is applied to the sample. Rather, the AFM tip is scanned at high velocity over the sample to “scrape” screening ions from the surface while the CAFM amplifier simultaneously quantifies the charges. Its high speed enables the measurement of not only the bound charge but also the dynamics of the screening process under non-equilibrium conditions. For instance, the collected charge can be measured as a function of the relative humidity of the air around the sample. This application note presents an example of these measurements on ferroelectric single-crystal periodically-poled lithium niobate (PPLN) as a representative polar surface.

The application note describes:

• What is the CGM technique?
• How are unpaired ionic bonds on the surface of PPLN screened?
• What conditions maximize the collected charge?
• How does the ambient relative humidity affect screening?

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