Scanning probe techniques basic principle

Within the numerous proximal probe techniques developed in the years following the breakthrough inventions of the STM (1) and AFM (5), scanning force microscopy (8) represents a family of scanning probe techniques that rely in their contrast mechanism on various forces between probe tip and sample (9-12) (see Atomic Force Microscopy). In order to provide a basis for an understanding and appreciation of the SFM work on polymers (13-18), as presented in this review, the basic principles of SFM, as well as selected imaging modes, are briefly discussed. 

This chapter is concerned with the study of interfacial processes and reactions that occur essentially at electrically insulating interfaces, where the role of the SECM tip is often to induce and monitor the reaction of interest. The work herein is an update of Chapter 12 Probing reactions at solid/liquid interfaces of the first edition of Scanning Electrochemical Microscopy [4] and highlights how the basic principles of the SECM-induced transfer (SECMIT) mode (or equilibrium perturbation mode) and related techniques— notably (multi-) potential step transient methods—can be applied to a wide variety of interfaces where flux measurements have traditionally been difficult. 

We first experimented with the Quartz Crystal Microbalance (QCM) in order to measure the ablation rate in 1987 (12). The only technique used before was the stylus profilometer which revealed enough accuracy for etch rate of the order of 0.1 pm, but was unable to probe the region of the ablation threshold where the etch rate is expressed in a few A/pulse. Polymer surfaces are easily damaged by the probe tip and the meaning of these measurements are often questionable. Scanning electron microscopy (21) and more recently interferometry (22) were also used. The principle of the QCM was demonstrated in 1957 by Sauerbrey (22) and the technique was developed in thin film chemistiy. analytical and physical chemistry (24). The equipment used in this work is described in previous publications (25). When connected to an appropriate oscillating circuit, the basic vibration frequency (FQ) of the crystal is 5 MHz. When a film covers one of the electrodes, a negative shift <5F, proportional to its mass, is induced ... 

Most scanning electrochemical microscopy (SECM) experiments are conducted in the amperometric mode, yet microelectrodes have for many years been used as potentiometric devices. Not surprisingly, several SECM articles have described how the tip operated in the potentiometric mode. In this chapter we aim to present the background necessary to understand the differences between amperometric and potentiometric SECM applications. Since many aspects of SECM are covered elsewhere in this monograph, we have focused on the progress made in the held of potentiometric microelectrodes and presented it in the context of SECM experiments. Starting with an historical perspective, the key discoveries that facilitated the development and applications of micro potentiometric probes are highlighted. Fabrication techniques and recipes are reviewed. Basic theoretical principles are covered as well as properties and technical operational details. In the second half of the chapter, SECM potentiometric applications are discussed. There the differences between the conventional amperometric mode are developed and emphasized. 

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