Thermal microscopy heating

M. Chirtoc. and J.F. Hemy, 3co hot wire method for micro-heat transfer measurements From anemometry to scaiming thermal microscopy (SThM), Europ. Phys. J., Special Topics, 153, 343-348 (2008). 

The diermal conductivity contrast image obtained by scanning thermal microscopy represents a convolution of the true thermal transport properties of the specimen with artefacts arising from changing tip-sample thermal contact area caused by any surface roughness of the specimen [48]. When the probe encounters a depression on the surface, the area of contact between the tip and sample increases, resulting in increased heat flux from the tip to the sample. More power is required to maintain the tip temperature at the set-point value and... 

Scanning thermal microscopy (SThM) is a contact AFM technique that allows spatial mapping of temperature or thermal conductivity across a sample surface in addition to topography. Most thermal probes utilize a temperature-sensitive resistor placed on the end of the tip. These resistor probes can be fabricated from a V-shaped Wollaston wire made of a platinum inner core and outer sheath of silver, in which the silver sheath is etched away at the V-shaped tip. Eigure 19 shows a Wollaston wire probe. In passive mode, the tip is scanned across a heated sample under constant-force feedback (contact mode) and a small current is passed through the probe to sense the tip resistance. The resistance value at any point is a measure of the local temperature, and thus a temperature map and topographic image may be produced simultaneously. 

The thermal properties of a surface can be determined with a lateral resolution of 2000 A using scanning thermal microscopy (SThM). The scanning tip is in the form of a thermocouple which is heated by a laser. The thermal loss to the surface of a bulk or thin film is then measured. 

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