Scanning probe microscopy techniques

Principles and Characteristics The term scanning probe microscopy (SPM) encompasses a family of techniques that provides images of surface topography and, in some cases, surface properties, on the atomic scale. SPM is an imaging tool with a vast dynamic range, spanning the realms of optical and electron microscopes. The principle of SPM is very similar to profilometry, where a hard sharp tip is scanned across a surface and its vertical movements are monitored. The main SPM techniques are given in Table 5.30. 

The general scheme of any SPM apparatus includes several major components which allow line-by-line scanning with an atomically sharp tip while monitoring nm scale cantilever deflections in vertical and horizontal directions. Precise 3D movements of either a sample or a cantilever (within a fraction of a nm) are provided by a tube piezoelement. The SPM 

Nature of probe Electronic surface states Local Van der Waals forces Electromagnetic Held near surface 

Method Local conductivity Local surface hardness Surface topography of insulators Surface properties Optical microscopy (not diffraction-limited) 

Local spectroscopy Most developed Limited capabilities Excellent capabihties 

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Other more advanced microscopic techniques have been developed, including near-held scanning optical microscopy [166] and scanning probe microscopy techniques, such as atomic force microscopy and scanning tunnelling microscopy [166, 167],... 

The usual objective of scanning probe microscopy techniques [41] is to provide images of a solid surface—normally topographic information— with up to atomic resolution. However, they can also be used to probe local solution composition and electrode reactions, as will be described. 

Scanning Probe microscopy techniques are extremely useful for analysing surfaces, but cannot lead to bulk information. They will be used each time surface properties are important, i.e. when surfaces are used for themselves (tribological applications, adhesion, etc.). However, in some cases, the study of transport phenomena (such as thermal or electrical conductivity) by modified AFM may lead to bulk characterisation such as the formation of a percolating nanotube network for instance. 

It should be noted that most of the microstructural data to be presented rely on different characterization techniques using electron microscopy in combination with other scanning probe microscopy techniques, e.g. scanning tunneling microscopy (STM) and atomic force microscopy (AFM). The details of specimen preparation and the analysis techniques of electron microscopy are described in other chapters of this book and are therefore not further covered in this chapter. The references provided in the chapter are merely a selection, since the field of research is vivid and the number of publications is large. The goal is to show the salient features which can be further explored by use of the referenced literature. 

Characterizing these many aspects of microstructure is necessary to establish relationships between primary chemical structure, processing, and performance. Currently, the most commonly used methods are scanning probe microscopy techniques such as atomic force microscopy (AFM) or kelvin probe force microscopy... 

Employing TERS in UHV systems There are a number of surface science tools available for samples in UHV which allow us to characterize the state of a surface. Surface and adlayer structures can be determined by LEED (low electron energy diffraction) as weU as by SPM (scanning probe microscopy) techniques. While the kind of chemical interactions can be studied, for example, with AES (Auger electron spectroscopy), EELS (energy electron loss spectroscopy) permits the identification of the chemical nature of the adsorbed species. TERS, on the other hand, may provide similar but also complementary information on the chemical identity under UHV conditions. As an additional advantage, TERS and SPM permit the identification and characterization of the spatial region from which this information is accumulated. 

In summary, the invention and development of scanning-probe microscopy techniques opened new ways... 

Overview of scanning probe microscopy techniques produced by Nanoscience Instruments Inc... 

Bhushan, Bharat, Harald Fuchs, and Masahiko Tomi-tori, eds. Applied Scanning Probe Methods VIII Scanning Probe Microscopy Techniques (NanoScience and Technology). Berlin Springer, 2008. Provides the most up-to-date information on this rapidly evolving technology and its applications. 

Tools are required to characterize these structures, and the most widely used methods rely on various scanning probe microscopy techniques. All of these techniques rely on the use of a specialized "tip" that is brought into proximity to the surface to be visualized. As schematically shown below, the tip moves around the surface and maps out macroscopic features or electronic properties of the surface using a variety of techniques. In the scheme shown, the tip encounters a raised rectangle and moves over it. Rastoring the tip back and forth over the surface maps out the full length of the rectangle. Several techniques of this type have been developed, but we only describe four here. 

Figure 2. The Skal-Shklovskii-DeGennes model for the carbon-black-polymer composite, and the scanning probe microscopy technique used to image the conductive network at the surface.

Scanning probe microscopy techniques commonly used for electrochemical measurements include SICM, SECM, and SECM-SICM. Each technique has distinct advantages and disadvantages. Important considerations are type(s) of signal detected, feedback mechanism, imaging conditions, relative ease of probe fabrication and resolution, many of which are interrelated. In the following section, SICM, SECM, and SECM-SICM will be considered relative to one another. 

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