Scanning probe techniques tunneling microscopy

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. 

Finally, scanning tunneling microscopy and spectroscopy (STM/STS) are scanned probe techniques based on the tunneling of electrons across an Angstrom-scale gap between a sample surface and a sharp metal tip electrically connected in a biased circuit. It can provide both geometric and electronic structure information. In contrast to LEED, it locally probes direct space for this information with atomic resolution. It is extremely surface sensitive compared to the other mentioned techniques, which sample information... 

The ability to control the position of a fine tip in order to scan surfaces with subatomic resolution has brought scanning probe microscopies to the forefront in surface imaging techniques. We discuss the two primary techniques, scanning tunneling microscopy (STM) and atomic force microscopy (AFM) the interested reader is referred to comprehensive reviews [9, 17, 18]. 

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. 

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