Near distance control

Karrai, K., and R. D. Grober. 1995. Piezoelectric tip-sample distance control for near-field optical microscopes. Appl. Phys. Lett. 66 1842-1844. 

A video microscope is not required for an SECM instrument, but it is very useful and is a highly recommended addition. A video microscope is preferred over a normal optical microscope because it allows the probe to be continuously observed while operating the instrument. A video record of the experiment is also available. The video microscope aids in positioning the probe in generation/collection experiments, where the lack of a feedback response makes accurate distance control difficult. In addition, video microscopy helps in positioning the probe near features of interest on the substrate. 

J Barenz, O Hollricher, O Marti. An easy-to-use non-optical shear-force distance control for near-field optical microscopes. Rev Sci Instrum 67 1912-1916, 1996. 

Eo o, and e lzr are the oxidation potential of D, Ae reduction potential of A, the 0-0 excitation energy of the excited molecule, and the Coulombic interaction energy between and A " in a solvent of dielectric constant e of distance r apart, respectively. When AG is negative, the radical ions are produced in an exothermic process at near diffusion-controlled rates. 

R Brunner, A Bietsch, O Hollricher, O Marti. Distance control in near-field optical microscopy with piezoelectrical shear-force detection suitable for imaging in liquids. Rev Sci Instrum 68 1769-1772, 1997. 

Kramer, A., T. Hartmann, S. M. Stadler and R. Guckenberger (1995). "An optical tip-sample distance control for a scanning near-field optical microscope." Ultramicroscopy 61(1 -4, Select Papers from the 3rd International Conference on Near-Field Optics and Related Techniques, 1995) 191-195. 

Different methods have been worked out and used for distance checking, adjustment, and control. Shear force based distance control is getting broadscale applied in SECM. Actually, the nature of the shear force is still not clearly understood. It is a short range interaction between a thin vibrating probe and the surface. It is most likely contributed by the viscosity of the surface confined water, the van der Waals forces, or some kinds of near field atomic forces [63]. 

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