Scanning tunneling microscopy principles

Scanning tunneling spectroscopy (STS) can, in principle, probe the electronic density of states of a singlewall nanotube, or the outermost cylinder of a multi-wall tubule, or of a bundle of tubules. With this technique, it is further possible to carry out both STS and scanning tunneling microscopy (STM) measurements at the same location on the same tubule and, therefore, to measure the tubule diameter concurrently with the STS spectrum. No reports have yet been made of a determination of the chiral angle of a tubule with the STM technique. Several groups have, thus far, attempted STS studies of individual tubules. 

The very new techniques of scanning tunnelling microscopy (STM) and atomic force microscopy (AFM) have yet to establish themselves in the field of corrosion science. These techniques are capable of revealing surface structure to atomic resolution, and are totally undamaging to the surface. They can be used in principle in any environment in situ, even under polarization within an electrolyte. Their application to date has been chiefly to clean metal surfaces and surfaces carrying single monolayers of adsorbed material, rendering examination of the adsorption of inhibitors possible. They will indubitably find use in passive film analysis. 

Fig. 1. Principle of scanning tunneling microscopy. A sharp needlelike tip probes the surface atomic structure ofaspecimenby closely scanningthe surface, utilizing extreme sensitivity of the vacuum tunneling current to the tunneling gap. From Sakurai et al. (10) with permission.

H.-J. Guntherodt and R. Wiesendanger (eds) Scanning Tunneling Microscopy I General Principles and Applications to Clean and Adsorbate-Covered Surfaces, Springer, Berlin, 1992. 

Tsukada, M., Kobayashi, K., and Ohnishi, S. (1990). First-principle theory of the scanning tunneling microscopy simulation. J. Vac. Sci. Technol. A 8, 160-165. 

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 basic principle of scanning tunneling microscopy (STM) is based on the tunneling current between a metallic tip, which is sharpened to a single atom point, and a conducting material (Fig. 1). A small bias voltage (mV to Y) is applied between an atomically sharp tip and the sample. 

Fig. 1. Basic principle of the scanning tunneling microscopy technique.

This chapter has been reorganized to place greater emphasis on the physical structure of the atom, as determined from the classic experiments of Thomson, Millikan, and Rutherford. The chapter ends with direct scanning tunneling microscopy images of individual atoms in chemical reactions. Section 1.6 in Principles of Modern Chemistry, fifth edition (mole, density, molecular volume), has been moved to Chapter 2, which now gives a comprehensive treatment of formulas, stoichiometry, and chemical equations. 

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