Scanning thermal imaging

Other SFM methods, including scanning thermal imaging (68), electrochemical (69), and noncontact mode SFM (19) have been recently reviewed. 

A pyroelectric vidicon or pyrovidicon is a video camera tube that operates in the IR (2-20 pm) region instead of the visible spectrum. Electronically scanned thermal imaging systems based on pyrovidicons and filtered to operate in the 8-14 pm atmospheric window provide qualitative thermal images and are classified as thermal viewers. Figure 2.21 is a cross-sectional schematic of a pyrovidicon camera tube used in pyrovidicon imagers. The output of the pyrovidicon tube is compatible with standard video processing electronics. 

Flammiche A, Flourston D J, Pollock FI M, Reading M and Song M 1996 Scanning thermal microscopy sub-surface imaging, thermal mapping of polymer blends, localised calorimetry J. Vac. Sol. Technol. B 14 1486... 

There are many excellent differential scanning calorimeter systems available which can be used to measure the specific heat which, when combined with the sample density can be used to give c . The thermal diffusivity (which can be important for thermal imaging systems if the target is not reticulated) can be measured directly on a pyroelectric substrate using the laser intensity modulation method described by Lang [23],... 

Figure 4-21. (a) Configuration of phase-locked scanning pyrometer and (b) resulting thermal image of wafer. 

Microthcrmal analysis combines thermal analysis with atomic force microscopy. It is actually a family of scanning thermal microscopy techniques in which ihcrmal properties of a surface arc measured as a function of temperature and used to produce a thermal image. In microthcrmal analysis the tip of an atomic force microscope is replaced by a thermally sensitive probe such as a thermistor or thermocouple. The surface temperature can be changed externally or by the probe acting both as a heater and as a temperature-measuring device. 

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 9.10 Thermal images of a PVC/PB immiscible blend. (Reprinted with permission from Journal Of Vacuum Science and Technology B., Scanning thermal microscopy Subsurface imaging, thermal mapping of polymer blends, and localized calorimetry by A. Hammiche, D.J. Hourston, H. M. Pollock et al., 14, 2, 1486-1491. Copyright (1996) American Institute of Physics)...

Series/Parallel Scan with time delay and integration remains the principal approach to advanced thermal imaging systems. However, for applications where only a small number of resolution elements are needed, two-dimensional staring detector arrays with CCD or CID readout are being considered [8.106]. This does away with the scanner and a focal optics used with conventional systems. However, to compensate for nonuniformities, both dc offset and gain correction must be made on a pixel by pixel basis. Detector responsivity and readout nonlinearities will increase the number of computations needed for sufficient correction and only experience with the stability of different types of arrays will determine how often the correction algorithms must be calibrated [8.107,108]. 

Sij = +1 for total reflection and s,y = — 1 for total absorption of (plane) thermal waves incident on an interface. Subsurface reflection or absorption may result in measurable surface temperature change. Surface temperature changes obtained by scanning an excitation beam across the sample surface may contain subsurface information limited to the depth of the thermal diffusion length. The subsurface thermal image may thus be obtained by analysis of the surface temperature change. 

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