Atomic Force Microscopy: Understanding Basic Modes and Advanced Applications

Since the invention of atomic force microscopy (AFM) by Binning and colleagues in 1986, there has been tremendous growth in the use of AFM and related spin-off techniques. As the author has rightly pointed out, the development has been driven by two groups of researchers; one that has dedicated AFM instrumentation and second being users with a variety of different samples. The beauty of AFM is that it is far less expensive than transmission electron microscopy and surface science techniques and can be used to provide excellent images of a whole host of organic and inorganic materials in air and in different environments. The dedicated researchers are often pushing the limits of AFM capabilities thereby opening up new applications. The second group of users often either those that are sure of what they are ‘‘seeking’’ or ‘‘curious’’ and ‘‘unsure’’ of what to expect! The latter group is therefore dependent on AFM operators in central research facilities in academia or research laboratories be they government ones or corporate ones. Given these situations, it is nevertheless worth noting the lack of formal AFM education and training. Training by AFM manufacturers tend to be with a narrow range of customer samples without in-depth fundamental understanding of the physics and engineering involved in AFM. There are two other concerns raised by the author. One is the lack of rigorous discussion amongst users at central facilities on data interpretation and AFM data is used as part of other materials characterization techniques and reviewers of journals pay only cursory attention to AFM results. This appears to be the primary motivation for the author to produce a comprehensive monograph that includes the use of mathematics which is not too complicated. The material covered in this book is based on the author’s vast experience with AFM that includes training users at a central facility, a university laboratory course at the undergraduate level, a graduate course taken primarily by PhD students and short courses intended for industrial users. The author and publisher need to be commended for making this effort to produce a very useful monograph on AFM. The book begins with a very good overview of AFM where the heart of the instrument is the measurement of surface height of the sample surface using a sharp solid tip. The tip can be moved over the sample surface or it can remain stationary while the sample is moved under the probe. Thus, surface topography is imaged often by a color scheme to show variations in height. The author mentions that it is important to keep in mind that the range of measurements is several micrometers vertically with subnanometer height resolution while laterally the range is several tens of micrometers with the best lateral resolution of 1 nm. It is remarkable that from height numbers one derive huge amount of physical as well as statistical data that are important for technological performance or biological functionality. Some of these are in microelectronics, tribology, polymer-drug coatings, intrabody medical devices, cellular membranes, and various surface components amongst others. Since height measurements are obtained along with X and Y scan ranges, one can obtain a 3D perspective that can be extremely useful. The author mentions that the vertical scale is often exaggerated to bring out features for viewing and that this methodology is acceptable as long as the viewer is made aware of this beforehand. In very simple language, the author explains the principle of the operation of an AFM in that the local height is measured by the concept of touching the surface with the sharp tip that is attached to a flexible microcantilever which behaves like a spring. The local height is actually measured indirectly since the bending of the microcantilever changes the reflection position of a laser beam, incident on the cantilever, which is a captured by a photodiode. The cantilever is roughly 100 mm long while the tip height is 10mm giving rise to measurable force range from pico-Newtons to micro-Newtons depending on the spring constants of cantilevers. Therefore the calibration of the shift in laser beam spot on the photodiode is a very critical need for successful and useful AFM imaging. Excellent explanation is given to the different modes of AFM operation like the quasistatic contact mode, the dynamic tapping mode, and phase imaging. The author has developed the chapters in an interesting manner that should be of benefit to the reader. After the introductory chapter, the concept of distance dependent forces is explained. In reality, proper understanding of the physical phenomena initially separated from instrumentation and later on to explain the working of AFM to carry out these accurate measurements is essential. The following chapter covers the methodology of topographic imaging mentioned earlier, including possibilities of artifacts, choice of tips, and imaging mode as well as post-processing of data. Emphasis is placed on making sure that the images are truly representative of Materials and Manufacturing Processes, 29: 765–766, 2014 Copyright # Taylor & Francis Group, LLC ISSN: 1042-6914 print=1532-2475 online DOI: 10.1080/10426914.2013. 864415