Key principles of scanning probe microscopy

Point (b) is the more significant since many macromolecnlar assemblies do not have the fantastic symmetry of a virus particle or of GroEL or GroES. Therefore, the production of high resolution images becomes much more difficult where there is lower molecular symmetry, although far from impossible. 

Scanning probe microscopy will increasingly become another class of imaging technique able to provide equivalent and even complementary structural information to cryo-electron 

The underlying principles of STM are essentially very simple indeed. If a sharp metal tip is placed within a distance, dT of a few A from a conducting sample surface and a bias voltage, Uz, is applied between tip and surface, a tunnelling current. It, will be established between tip and surface due to a quantum mechanical tunnelling effect that is generated under conditions 

In a classical sense, if an electron with total energy Er meets a potential barrier, Vq, of higher energy, then the electron is unable to pass through. However, in a quantum mechanical 

The squared modulus of Dj is the equivalent of a squared wavefunction, otherwise familiar as the probability density function characteristic of atomic and molecular orbitals. Another 

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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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