Scanning probe techniques measurement

Additional suggested resources for the reader include introductory articles on scanning probe techniques for materials properties measurement [82,83J. A comprehensive manual describing various surface preparation techniques, experimental procedures and instrumentation is also a good resource [84J, although the more recent modulation based techniques are not covered. Key textbooks include Johnson s on contact mechanics [51J and Israelachvili s on surface forces [18J, as well as a treatment of JKR/DMT issues by Maugis [85J. 

The concept of resolution in AFM is different from radiation-based microscopies because AFM imaging is a three-dimensional imaging technique. There is an important distinction between images resolved by wave optics and those resolved by scanning probe techniques. The former is limited by diffraction, whereas the latter is limited primarily by apical probe geometry and sample geometry. Usually the width of a DNA molecule is loosely used as a measure of resolution, because it has a known diameter of 2.0 nm in its B form. 

S. Prokhorova, for skillful measurements with scanning probe techniques. This work was financially supported by the Deutsche Forschungsgemeinschaft (SH 46/2-1), Graduiertenkol-leg-328 Molecular organization and dynamics on surfaces and interfaces . 

The techniques involved are single-molecule spectroscopy including optical (fluorescence) methods and single-molecule mechanical manipulation including scanning probe techniques (e.g., force measurements). 

Near-field scanning optical microscopy is a scanning probe technique that enables optical measurements to be conducted with very high spatial resolution [7-9]. NSOM overcomes the diffraction barrier that restricts the spatial resolution in conventional optical measurements and provides both optical and topographical information on samples with nanometric spatial resolution. 

While the experimental details involved in implementing NSOM can be found elsewhere [7,8], it is instructive to briefly discuss the two main obstacles that must be overcome in order to conduct NSOM measurements. These revolve around aperture formation and implementing a feedback system for tip-sample distance control. For the former, as in all scanning probe techniques, the quality of the measurements is in large part dictated by the quality of the probe. For the latter, as the schematic in Fig. 1 suggests, high resolution requires that the NSOM probe be maintained within nanometers of the sample surface. 

SECM is an electrochemical scanning probe technique where the measured current is caused by an electrochemical reaction at the tip (15). The overall apparatus for SECM is similar to that used for ESTM, that is, a bipotentiostat is used to control the tip potential... 

Other scanned probe techniques such as atomic force microscopy may provide a type of spectroscopy by measuring the force on the tip as a function of distance, but are little used. The scanning near-field optical microscopy (SNOM) method can also provide standard far-field optical spectroscopy techniques but at an almost atomic resolution. 

Scanning electrochemical microscopy (SECM) is a scanning probe technique in which the probe is a disk ultramicroelectrode (typical radius in the 5 to 25 pm range) that scans the surface of the investigated sample facing it [157]. SECM measurements are carried out in... 

Scanning tunneling microscopy (STM) and atomic force microscopy (AFM) are scanning probe techniques, in which sharp solid probe scans over the specimen surface and provides topographic information. STM provides information at the atomic level and can identify the arrangement of atoms on sample surface, hi this technique, a sharp tungsten tip is scanned very close to the sample surfece and tunneling current is measured. The current is inversely proportional to the tip-sample separation. AFM makes nse of a sihcon nitride probe mounted on a flexible cantilever. The movement of the cantilever is monitored by a laser beam focused on the surface as the probe scans the sample surface, attractive and repulsive forces between the probe and the surface are measured. 

Force measurements have been performed with scanning probe techniques to study protein properties and protein-surface interactions. Apart from specific recognition and specific interactions,"" single-molecule force spectroscopy,adhesion forces between ligand-receptor pairs, " and protein adsorption... 

The experimental challenge generated a considerable progress in experimental tools for investigating flow boundary conditions using the most recent developments in optics and scanning probe techniques. A large variability still exists in the results of slip experiments, so it is important first to consider the different experimental methods used to measure a slip. Two broad classes of experimental approaches have been used so far, indirect and direct (local) methods. 

Variously designed weight-loss coupon, electrochemical and surface analytical techniques have been utilized in REM-based corrosion inhibitors and conversion coatings research. In particular, electrochemical techniques including EIS and polarization measurements have been widely used to evaluate corrosion inhibition by REM compounds under various environmental conditions. Relatively less attention has been paid to the evaluation of localized corrosion inhibition by REM-based compounds, probably because of methodological difficulties and complexities in making accurate localized corrosion rate measurements. Recently developed techniques such as the scanning probe techniques, electrochemical noise analysis and the wire beam electrode are expected to be useful tools in further REM inhibitor research. 

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