Improvement in the imaging performance of atomic force microscopy: A survey

Nanotechnology is the branch of science which deals with the manipulation of matters at an extremely high resolution down to the atomic level. In recent years, atomic force microscopy (AFM) has proven to be extremely versatile as an investigative tool in this field. The imaging performance of AFMs is hindered by: 1) the complex behavior of piezo materials, such as vibrations due to the lightly damped low-frequency resonant modes, inherent hysteresis, and creep nonlinearities; 2) the cross-coupling effect caused by the piezoelectric tube scanner (PTS); 3) the limited bandwidth of the probe; 4) the limitations of the conventional raster scanning method using a triangular reference signal; 5) the limited bandwidth of the proportional-integral controllers used in AFMs; 6) the offset, noise, and limited sensitivity of position sensors and photodetectors; and 7) the limited sampling rate of the AFM's measurement unit. Due to these limitations, an AFM has a high spatial but low temporal resolution, i.e., its imaging is slow, e.g., an image frame of a living cell takes up to 120 s, which means that rapid biological processes that occur in seconds cannot be studied using commercially available AFMs. There is a need to perform fast scans using an AFM with nanoscale accuracy. This paper presents a survey of the literature, presents an overview of a few emerging innovative solutions in AFM imaging, and proposes future research directions. Note to Practitioners-An atomic force microscope (AFM) is a scientific instrument capable of investigating, controlling, and manipulating matter on a nanoscale. It is a fundamental part of research in the field of nanotechnology because of its capability to obtain three-dimensional images of specimens in the areas of life sciences and materials science. However, the imaging performances of currently available AFMs are restricted by limitations which, during the last two decades, several works have attempted to overcome in order to meet present demands. This article presents an overview of developments in AFM imaging, emphasizing the key roles of: the modeling, control techniques, and mechanical structural designs of an AFM's piezoelectric tube scanner and probe; different scanning methods; and sensor noise compensation techniques.