DFM-AFM

Fig. 20. Comparison among CM-AFM, NC-AFM and DFM-AFM lithographies (a) the topographic image and (b) the surface potential one after CM-AFM lithography (c) the topographic image and (d) the surface potential one after NC-AFM lithography and (e) the topographic image and (f) the surface potential one after DFM-AFM lithography.

Fig. 21. Dependence of DFM-AFM lithography on the pulse bias voltage and the application time of pulse bias (a) illustration of the pulse bias voltage and application time of pulse bias used, (b) topographic image and (c) surface potential image.

On the other hand, the different result was obtained for DFM-AFM lithography. The anodic oxidation does not occur in this lithography because the sufficient current is not injected, which is proved in the lithography using the hydrogen-terminated silicon substrate. That is, SAM is not removed from the substrate surface and a different chemical reaction occurs on the SAM surface. 

Fig. 24. Surface potential images for the ODS-SAM surfaces after DFM-AFM lithography (a) in vacuum (3.5 x 10 4Pa, 24 °C) and (b) in dry nitrogen (relative humidity <1%,24°C).

To minimize effects of friction and other lateral forces in the topography measurements in contact-modes AFMs and to measure topography of the soft surface, AFMs can be operated in so-called tapping mode [53,54]. It is also referred to as intermittent-contact or the more general term Dynamic Force Mode" (DFM). A stiff cantilever is oscillated closer to the sample than in the noncontact mode. Part of the oscillation extends into the repulsive regime, so the tip intermittently touches or taps" the surface. Very stiff cantilevers are typically used, as tips can get stuck" in the water contamination layer. The advantage of tapping the surface is improved lateral resolution on soft samples. Lateral forces... 

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