Scanned Probe Microscopy introduction

Since the introduction of scanning tunnelling microscopy, a family of scanning probe microscopies (SPMs) have been developed (Table 3.1), with three main branches resulting from three different types of probe. All of the methods have in common the ability to image surfaces in real space at nanometre or better resolution, are straightforward to implement and are relatively low in cost. 

C. J. Chen, Introduction to Scanning Tunneling Microscopy, Oxford University Press, New York, 1993 R. Wiesendanger, Scanning Probe Microscopy and Spectroscopy Methods and Applications, Cambridge University Press (1994). 

Experimental approaches to bioelectrochemical systems include other techniques which introduce new environments for interfacial bioelectrochemical function. Introduction of single-crystal, atomically planar electrode surfaces has opened a basis for the use of the scanning probe microscopies, STM and AFM, also for biological macromolecules. Importantly this extends to the electrochemical STM mode where electrochemical surfaces, adsorbate molecules, and now also biological macromolecules can be mapped directly in their natural aqueous environment, with full electrochemical potential control in situ STM and... 

As described in the introduction, submicrometer disk electrodes are extremely useful to probe local chemical events at the surface of a variety of substrates. However, when an electrode is placed close to a surface, the diffusion layer may extend from the microelectrode to the surface. Under these conditions, the equations developed for semi-infinite linear diffusion are no longer appropriate because the boundary conditions are no longer correct [97]. If the substrate is an insulator, the measured current will be lower than under conditions of semi-infinite linear diffusion, because the microelectrode and substrate both block free diffusion to the electrode. This phenomena is referred to as shielding. On the other hand, if the substrate is a conductor, the current will be enhanced if the couple examined is chemically stable. For example, a species that is reduced at the microelectrode can be oxidized at the conductor and then return to the microelectrode, a process referred to as feedback. This will occur even if the conductor is not electrically connected to a potentiostat, because the potential of the conductor will be the same as that of the solution. Both shielding and feedback are sensitive to the diameter of the insulating material surrounding the microelectrode surface, because this will affect the size and shape of the diffusion layer. When these concepts are taken into account, the use of scanning electrochemical microscopy can provide quantitative results. For example, with the use of a 30-nm conical electrode, diffusion coefficients have been measured inside a polymer film that is itself only 200 nm thick [98]. 

Scanning electrochemical microscopy (SECM the same abbreviation is also used for the device, i.e., the microscope) is often compared (and sometimes confused) with scanning tunneling microscopy (STM), which was pioneered by Binning and Rohrer in the early 1980s [1]. While both techniques make use of a mobile conductive microprobe, their principles and capabilities are totally different. The most widely used SECM probes are micrometer-sized ampero-metric ultramicroelectrodes (UMEs), which were introduced by Wightman and co-workers 1980 [2]. They are suitable for quantitative electrochemical experiments, and the well-developed theory is available for data analysis. Several groups employed small and mobile electrochemical probes to make measurements within the diffusion layer [3], to examine and modify electrode surfaces [4, 5], However, the SECM technique, as we know it, only became possible after the introduction of the feedback concept [6, 7],... 

The imaging of biologically relevant polymers must be performed in most cases under liquids in order to reduce the forces between the scanned probe tip and the sample surface or, more importantly, to ensure that the polymers of interest retain their integrity, shape, and biological function when studied by AFM approaches. This Chapter will provide an introduction to AFM operation under liquid and will elucidate the peculiarities of force microscopy operation in conjunction with a liquid cell. Finally, ex situ and in situ studies of biopolymeric specimens will be highlighted. 

The introduction and development of Micro-Thermal Analysis are described and discussed by Duncan Price in Chapter 3. The atomic force microscope (AFM) forms the basis of both scanning thermal microscopy (SThM) and instruments for performing localised thermal analysis. The principles and operation of these techniques, which exploit the abilities of a thermal probe to act both as a very small heater and as a thermometer, in the surface characterisation of materials are described in detail. The... 

Due to such advantages as high resolution that can approach the real atomic and molecular scale, and the ability to perform real-time measurement that cannot be matched by traditional microscopy, scanning tunneling microscopy (STM) and atomic force microscopy (AFM) have attracted considerable attention since their introduction from researchers in various fields. The operational procedure of these microscopes is to position an atomically sharp detector needle to less than several nanometers from the surface of a sample, probe the interaction between the detector needle and the sample, scan the sample surface two-dimensionally, and obtain the surface image (an unprecedented method). If the interaction that is probed is the tunneling of the electron that is well known in quantum mechanics, the technique is called STM (T indicates tunneling). If, on the other hand, atomic force (van der Waals force) is used, it is called AFM. 

Because of its simplicity of use and quantitative results, Scanning Electrochemical Microscopy (SECM) has become an indispensable tool for the study of surface reactivity. The fast expansion of the SECM field during the last several years has been fueled by the introduction of new probes, commercially available instrumentation, and new practical applications. Scanning Electrochemical Microscopy, Second Edition offers essential background and in-depth overviews of specific applications in self-contained chapters. 

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