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(Color online) Schematic representation of the four-step ZAM protocol: First, a weakly biased AFM tip is brought towards the surface of the film (whose thickness was in the range of ). Second, the tip is held at reference point . Third, the AFM cantilever, oscillating at , is slowly retracted from point to point while simultaneously applying a bias voltage of : this step forms the nanostructures, high and wide, on the surface. Bottom: Three dots formed using an exposure time of ; the AFM tip was lifted from and the tip bias was .
(Color online) Block diagram of the electric force microscopy (EFM) technique. To reduce unwanted noise, an ac modulation signal (, rms) is applied to the tip and the vertical deflection response signal (which contains information of surface electric potential) is recovered using a lock-in amplifier. The image is collected after the ZAM protocol is completed.
(Color online) Examples of geometric functionalization of the surface. (a) ( high dots), (b) ( high dots), (c) ( high dots), (d) ( high dots), and (e) ( high dots) films. The tip is retracted from the surface to a distance in the range of ; the tip bias is varied between and . The height of the features increases from , which appears to correlate with film thickness. EFM data suggest that positive electric charge is deposited on the surface (in the darker colored regions as shown) and dissipates later. However, all the physically patterned features remain intact for . (e) Example of silicon surface oxidation using the ZAM protocol (the tip is retracted from and a negative bias of was applied): the height of the features was less than .
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