Gallery of various surface potential AFM images illustrating the charge patterns on polymer films generated by rubbing polymer covered cotton swabs across the surface (top row: PAAm rubbed by COC). The rubbing direction is from top to bottom. The lower right shows a complete trace of PVAc rubbed by PAAm (110 µm x 162 µm composed of two separate scans). The color scale varies slightly from image to image but in all images, the potential signal covers a range of a few volts. Imaged with the MFP-3D AFM, 90 µm scan size.