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Nanoscale Characterization
Published in Ram K. Gupta, Sanjay R. Mishra, Tuan Anh Nguyen, Fundamentals of Low Dimensional Magnets, 2023
Arvind Kumar, Swati, Manish Kumar, Neelabh Srivastava, Anadi Krishna Atul
AFM is one of the non-destructive techniques used for measuring quantitatively the surface roughness and nano-textures. It consists of a probe at the end of the cantilever with a sharp tip (nominal tip radius of the order of 10 nm) which raster scans the specimen surfaces with the help of piezoelectric sensors. In AFM scanning, a cantilever tip senses the force between surface and tip. Herein, the tip is attached to the cantilever across the free end and is brought towards the surface. Interaction between surface and cantilever shows positive and negative deflections, i.e. indication of attractive and repulsive forces. This laser detection system is bulky and costly. Another easy and convenient method for the detection of deflection of laser and cantilever is performed by using piezoresistive AFM probes, which are made up of piezoresistive elements that act as a strain gauge. This strain gauge is fabricated by Wheatstone Bridge, although it is not like a laser detection system. A constant force is maintained between the probe and sample while raster scanning is done across the surface in AFM. The separation distance between the tip and the sample relies on the interaction forces. If the separation between the tip and the sample is closer, there will be repulsive interaction, whereas a larger separation shows an attractive one. 3D images of the surface can be scanned by monitoring the motion of the probe. This technique is also useful for size measurements or manipulations of nano-objects. AFM imaging could be performed in three different modes: namely, contact mode, tapping mode, and non-contact mode.
Atomic Force Microscopy
Published in Arthur T. Hubbard, The Handbook of Surface Imaging and Visualization, 2022
Andrew A. Gewirth, John R. LaGraff
The AFM works by sensing the force applied between a tip and a sample surface held in close proximity to each other. This force is usually manifested as a displacement of a spring, the proportionality between force and displacement being given by Hooke’s law: F = −kx where F is the force, k is the force constant, and x is the displacement. However, more recent designs measure the force directly by using strain gauges.5 A schematic of an AFM is shown in Figure 2.1. The tip is held at the end of a spring (in this case a cantilever made from Si), which provides a restoring force to counter that arising from the interaction between the sample and tip. Changes in the deflection of the spring or cantilever are thus equivalent to changes in the tip-sample force. The cantilever deflection is monitored, and a feedback mechanism actuates a piezoceramic, which moves to maintain constant cantilever deflection and hence constant force between sample and tip. The piezoceramic deflection is then plotted, giving lines of constant force. The tip-sample interaction can also be mediated by magnetic, electric, or other interactions. The AFM is clearly one of a large family of proximal probe microscopes. Some of these are described elsewhere in this volume.
Borate Phosphor
Published in S. K. Omanwar, R. P. Sonekar, N. S. Bajaj, Borate Phosphors, 2022
The AFM is a kind of scanning probe microscope in which a topographical image of the sample surface can be achieved based on the interactions between a tip and a sample surface. The AFM was invented by Gerd Binning et al. in 1986 at IBM Zurich based on the STM (scanning tunneling microscope) already presented in 1981. While the latter depends on the conductive samples, the AFM allows also the use of non-conductive samples. In 1987, the inventors were awarded the Nobel Prize in Physics for the achievements.
Polymer-modified asphalt binders’ properties deterioration under the action of chloride salt
Published in Road Materials and Pavement Design, 2023
Wassiou Aboudou Ogbon, Huining Xu, Wei Jiang, Chengwei Xing
Atomic Force Microscopy (AFM) is a type of scanning probe microscopy. AFM has been widely used to provide insight into the micro-structures that can be observed on the surface of binders. The asphalt is soft and sticky, so the tapping mode was used for testing. Special attention is needed in sample preparation as surface topography can be highly influenced by the preparation process itself. In this paper, AFM was utilised to investigate the surface microscopic morphology of asphalt binders and quantitatively evaluate them via roughness theory. Based on the AFM results, the roughness parameters were automatically obtained using the Nanoscope software. For each kind of asphalt, three samples were prepared for parallel testing, and the scan was undertaken on one point for each sample. Therefore, their scanning results can be obtained for each asphalt, and take the average as the final result.
Applications of atomic force microscopy-based imaging and force spectroscopy in assessing environmental interfacial processes
Published in Critical Reviews in Environmental Science and Technology, 2022
Yuyao Zhang, Xiaoying Zhu, Chiheng Chu, Xin Xiao, Baoliang Chen
As shown in Figure S1a (Supplementary material), an atomic force microscope is mainly comprised of a piezoelectric ceramic tube, a feedback control, and force sensor systems that contain a laser, a tip and a photo-detector. In a typical AFM imaging operation, the piezoelectric ceramic tube controls the tip and moves it onto the substrate. The deflection of the tip, caused by the force interactions from the substrate, can be captured by sensors, and then the feedback control gives back the signal to the piezoelectric tube, to keep a stable signal of the tip at the interface. Notably, the principle of AFM imaging is similar to that of blind reading by touching. According to different types of feedback signals, AFM imaging modes could roughly be divided into contact mode (based on deflections) and oscillating mode (based on frequency, phase or amplitude) (Friedbacher & Fuchs, 1999). Oscillating mode could be further divided into intermittent-contact mode and non-contact mode according to the regimes for oscillating (Friedbacher & Fuchs, 1999). Non-contact mode was the most commonly used mode that could achieve high-resolution and high-speed imaging of AFM in liquid environments because of its high sensitivity and fast scan rate. Thus, non-contact mode is suitable to detect micro-molecules for pollutants and dynamic environmental processes.
Advanced abrasive-based nano-finishing processes: challenges, principles and recent applications
Published in Materials and Manufacturing Processes, 2022
Manjesh Kumar, Anupam Alok, Vikash Kumar, Manas Das
From Fig. 7, it is conceived that various types of complex free-from components have been finely polished by the AFM method throughout the years. The maximum improvement in the surface finish is also achieved by more than 95%. The minimum achieved Ra is 30 nm for Hip joint made of Co-Cr alloy. From Fig. 7, it can also be concluded that the final surface finish also depends upon the initial surface roughness of workpiece. Components from mild copper to robust Co-Cr alloys and ceramics could be effectively polished by the AFM method (Fig. 7).[109] AFM provides accuracy, quality and versatility for a variety of uses in aerospace, automobile, engineering, die polishing, medical implants and pumping systems. Initially, the AFM methodology was proposed to systematically deburr the inner surfaces of aircraft valve heads and spools.[100] Currently, even in the most restricted locations, AFM may process lots of holes, gaps or sides in one activity. Abrasive flow finishing method not just eliminates burrs (induced while machining) in and around the spring collet and even enhances spring collet surface roughness, roundness and geometrical accuracy.[120] AFM method can also polish complex surfaces like diesel engine fuel spraying nozzle uniformly.[121] Properly AFM-processed injectors improve the nozzle’s discharge coefficient and, therefore, can increase combustion efficiency and emissions.