Imaging probes sample roughness

Similar to all scanning microscopies, the resolution in SFM depends on the effective size of the probe and its modifications which arise from sample-probe interactions. Theoretically, the effective size is determined by the probe geometry and the force-distance dependence between the tip and sample. In addition, the aperture increases because of the tip-sample deformation, surface roughness, capillary forces, and various sources of noise. Experimentally, the resolution is limited by the sensitivity of the force detection system, the image noise, and the scanner precision. 

In this example (Section 7.5.18) ATM rather than STM was used. Whereas STM depends on electron transfer between the specimen and the tip of the probe, AFM depends only on mechanical forces and is independent of the conductance of the specimen, and this may be an advantage for alloys of A1 with oxides that show poor conductance. In other experiments AFM images of an Al-Cu alloy immersed in 1M HC1 were recorded. After 24 hr new pits were formed and the ones formed earlier have grown. After 6 hr the sample was severely damaged and the surface is very rough. 

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... 

Figure 3.1 A high aspect ratio probe is capable of imaging rough samples, as it is able to image between the surface features (shaded spheres). A low aspect ratio probe is not able to do this as well and is thus more suited to flatter surfaces...

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