Large-range high-speed dynamic-mode atomic force microscope imaging: adaptive tapping towards minimal force

In this paper, a software-hardware integrated approach is proposed for high-speed, large-range tapping mode imaging of atomic force microscope (AFM). High speed AFM imaging is needed in various applications, particularly in interrogating dynamic processes at nanoscale such as polymer crystallization process. Achieving high speed in tapping-mode AFM imaging is challenging as the probe-sample interaction during the imaging process is highly nonlinear, making the tapping motion highly sensitive to the probe sample spacing, and thereby, difficult to maintain at high speed. Increasing the speed via hardware bandwidth enlargement, however, leads to a substantially reduction of the imaging area. Contrarily, the imaging speed can be increased without loss of the scan size through control (algorithm)-based approach. For example, the recently-developed adaptive multiloop mode (AMLM) technique has demonstrated its efficacy in increasing the tapping-mode imaging speed without loss of scan size. Further improvement, however, has been limited by the hardware bandwidth and the online signal processing speed and computation complexity involved. Thus, in this paper, the AMLM technique is further enhanced to optimize the probe tapping regulation, and integrated with a field programmable gate array platform to further increase the imaging speed without loss of quality and scan range. Experimental implementation of the proposed approach demonstrates that high-quality imaging can be achieved at a high-speed scanning rate of 100 Hz and higher, and over a large imaging area of over 20μm.