Design and control of multi-actuated atomic force microscope for large-range and high-speed imaging

Characteristics and Functionality of Cantilevers and Scanners in Atomic Force Microscopy

In this paper, we provide a systematic review of atomic force microscopy (AFM), a fast-developing technique that embraces scanners, controllers, and cantilevers. The main objectives of this review are to analyze the available technical solutions of AFM, including the limitations and problems. The main questions the review addresses are the problems of working in contact, noncontact, and tapping AFM modes. We do not include applications of AFM but rather the design of different parts and operation modes. Since the main part of AFM is the cantilever, we focused on its operation and design. Information from scientific articles published over the last 5 years is provided. Many articles in this period disclose minor amendments in the mechanical system but suggest innovative AFM control and imaging algorithms. Some of them are based on artificial intelligence. During operation, control of cantilever dynamic characteristics can be achieved by magnetic field, electrostatic, or aerodynamic forces.

Review: Advanced Atomic Force Microscopy Modes for Biomedical Research

Visualization of biomedical samples in their native environments at the microscopic scale is crucial for studying fundamental principles and discovering biomedical systems with complex interaction. The study of dynamic biological processes requires a microscope system with multiple modalities, high spatial/temporal resolution, large imaging ranges, versatile imaging environments and ideally in-situ manipulation capabilities. Recent development of new Atomic Force Microscopy (AFM) capabilities has made it such a powerful tool for biological and biomedical research. This review introduces novel AFM functionalities including high-speed imaging for dynamic process visualization, mechanobiology with force spectroscopy, molecular species characterization, and AFM nano-manipulation. These capabilities enable many new possibilities for novel scientific research and allow scientists to observe and explore processes at the nanoscale like never before. Selected application examples from recent studies are provided to demonstrate the effectiveness of these AFM techniques.

An ultrafast piezoelectric Z-scanner with a resonance frequency above 1.1 MHz for high-speed atomic force microscopy

The Z-scanner is the major component limiting the speed performance of all current high-speed atomic force microscopy systems. Here, we present an ultrafast piezoelectric Z-scanner with a resonance frequency above 1.1 MHz, achieving a record response time of ∼0.14 µs, approximately twice as fast as conventional piezoelectric-based Z-scanners. In the mechanical design, a small piezo-stack is supported at its bottom four vertices on a cone-like hollow, allowing the resonance frequency of the Z-scanner to remain as high as that of the piezo in free vibration. Its maximum displacement, ∼190 nm at 50 V, is large enough for imaging bio-molecules. For imaging bio-molecules in a buffer solution, the upper half of the Z-scanner is wrapped in a thin film resistant to water and chemicals, providing an excellent waterproof and mechanical durability without lowering the resonance frequency. We demonstrate that this Z-scanner can observe actin filaments, fragile biological polymers, for more than five times longer than the conventional Z-scanner at a tip velocity of 800 µm/s.

High-Speed Atomic Force Microscopy of the Structure and Dynamics of Calcite Nanoscale Etch Pits

Calcite dissolution is initiated by the formation of a nanoscale etch pit followed by step edge propagation and hence strongly influenced by the interactions between surface diffusing ions and step edges. However, such atomic-scale dynamics are mostly inaccessible with current imaging tools. Here, we overcome this limitation by using our recent development of high-speed frequency modulation atomic force microscopy. By visualizing atomic-scale structural changes of the etch pits at the calcite surface in water, we found the existence of mobile and less-mobile surface adsorption layers (SALs) in the etch pits. We also found that some etch pits maintain their size for a long time without expansion, and their step edges are often associated with less-mobile SALs, suggesting their step stabilization effect.

A high-speed atomic force microscopy with super resolution based on path planning scanning

An atomic force microscopy generally adopts a raster scanning method to obtain the image of the sample morphology. However, the raster method takes too much time on the base part without focusing enough on the object, thereby restricting the scanning speed of an AFM. To solve this problem, this paper proposes a novel path planning based scanning method to achieve high-speed scanning with super resolution for AFMs. Specifically speaking, a fast scanning process is first carried out to generate a low-resolution image with less time, then a convolutional neural network is designed to construct a super-resolution image based on the fast scanning image. Afterwards, an advanced detection algorithm is proposed to achieve the accurate object detection and localization. Furthermore, an improved ant colony optimization algorithm is proposed to realize the path planning for scanning the objects with high quality, whose imaging result is then matched with the previous super-resolution image to construct the entire sample image, thus achieving fast scanning with super resolution. Experimental and application results demonstrate the good performance of the proposed scanning method.

Active control of acoustics-caused nano-vibration in atomic force microscope imaging

In this paper, we propose a finite-impulse-response (FIR)-based feedforward control approach to mitigate the acoustic-caused probe vibration during atomic force microscope (AFM) imaging. Compensation for the acoustic-caused probe vibration is important, as environmental disturbances including acoustic noise induce nano-scale probe vibration, directly affecting the AFM performance in applications such as imaging, nanomechanical characterization, and nanomanipulation. Although conventional passive noise cancellation apparatus has been employed, limitation exists, and residual noise still persists. Thus, a FIR-based active feedforward control approach is developed, by exploring a data-driven approach to account for the vibrational dynamics of the probe caused by the environmental acoustic noise in the controller design. An experimental implementation in AFM imaging application is presented and discussed to illustrate the proposed technique. Experimental results show that the FIR-based feedforward control is promising to not only complement, but also alleviate the limitations of passive noise control in AFM operations.

Rotational scanning atomic force microscopy

A non-raster scanning technique for atomic force microscopy (AFM) imaging which combines rotational and translational motion is presented. The use of rotational motion for the fast scan axis allows us to significantly increase the scanning speed while imaging a large area (diameter > 30 μm). An image reconstruction algorithm and the factors influencing the resolution of the technique are discussed. The experimental results show the potential of the rotational scanning technique for high-throughput large area AFM investigation.