Enhancement and recovery in atomic force microscopy images

Abstract

Summary. Atomic force microscopy (AFM) images have become increasingly useful in the study of biological, chemical and physical processes at the atomic level. The acquisition of AFM images takes more time than the acquisition of most optical images, so that the avoidance of unnecessary scanning becomes important. Details that are unclear from a scan may be enhanced using various image processing techniques. This chapter reviews various interpolation and inpainting methods and considers them in the specific application of AFM images. Lower-resolution AFM data is simulated by subsampling the number of scan lines in an image, and reconstruction methods are used to recreate an image on the original domain.The methods considered are classified in the categories of linear interpolation, nonlinear interpolation, and inpainting. These techniques are evaluated based on qualitative and quantitative measures, showing the extent to which scans times can be reduced while preserving the essence of the original features. A further application is in the removal of streaks, which can occur due to scanning errors and post-processing corrections. Identified streaks are removed, and the resulting unknown region is filled using inpainting. IntroductionThe atomic force microscope (AFM) is an extremely high magnification microscope [5]. It achieves its high resolution by moving an atomically sharp probe over surfaces and recording the highly localized interaction force. Isolating specific interaction forces such as electrostatic, magnetic, specific chemical interactions, van der Waals attraction, and Pauli repulsion enable the AFM to measure many surface properties in addition to topography [20,12,22,2,29,17]. The AFM is also able to measure surfaces in any environment from liquids, to corrosive gases and vacuum. The high resolution, versatility, and broad information content make AFM a frequent choice for nanoscience imaging.The current standard method of AFM data collection is the raster scan. The probe starts by traveling along the "fast scan direction," or in the +x direction. As it reaches the end of the scan region, it takes a small step in the "slow can direction," or +y direction, and scans in the −x direction until it retraces the x displacement. Another small step in the +y direction is taken and the scanner moves in the +x direction to initiate another scan line. Continuing in this manner, an image is formed. The backward (retrace) scans are often displayed independently from the forward (trace) scans due to errors in position from scanner nonlinearities and hysteresis. A feedback mechanism maintains the probe-sample interaction at constant force to ensure that the probe is not damaged by contact with the sample.Because the AFM is a local probe it must collect data serially to construct an image over time which can be a significant disadvantage. The sample and probe are massive objects that are difficult to accelerate requiring relatively slow scan velocities otherwise the feedback mechanism that holds the interaction force...

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