Scanning thermal probe microscopy

The effect of film thickness on Tg can also be determined by measuring the surface softening temperature of corresponding polymer films using a heated AFM-like tip in scanning thermal probe microscopy. Scanning thermal probe microscopy probes the change in film modulus via the cantilever deflection induced by the thermal probe. As shown in Fig. 4.31, the cantilever deflects markedly when the PS film softens and hence, the onset of the Tg can be assessed. Systematic studies showed that PS on SiC>2 exhibits an altered Tg for film thicknesses below 50 nm. 

It is noteworthy that prior to the advent of scanning probe microscopy electrochemically driven reconstruction phenomena had been identified and studied using traditional macroscopic electrochemical measurements [210,211], However, STM studies have provided insight as to the various atomistic processes involved in the phase transition between the reconstructed and unreconstructed state and promise to provide an understanding of the macroscopically observed kinetics. An excellent example is provided by the structural evolution of the Au(lOO) surface as a function of potential and sample history [210,211,216-223], Flame annealing of a freshly elec-tropolished surface results in the thermally induced formation of a dense hexagonal close-packed reconstructed phase referred to as Au(100)-(hex). For carefully annealed crystals a single domain of the reconstructed phase... 

In the author s opinion, the better approach to experimentally study the morphology of the silica surface is with the help of physical adsorption (see Chapter 6). Then, with the obtained, adsorption data, some well-defined parameters can be calculated, such as surface area, pore volume, and pore size distribution. This line of attack (see Chapter 4) should be complemented with a study of the morphology of these materials by scanning electron microscopy (SEM), transmission electron microscopy (TEM), scanning probe microscopy (SPM), or atomic force microscopy (AFM), and the characterization of their molecular and supramolecular structure by Fourier transform infrared (FTIR) spectrometry, nuclear magnetic resonance (NMR) spectrometry, thermal methods, and possibly with other methodologies. 

Scanning Probe microscopy techniques are extremely useful for analysing surfaces, but cannot lead to bulk information. They will be used each time surface properties are important, i.e. when surfaces are used for themselves (tribological applications, adhesion, etc.). However, in some cases, the study of transport phenomena (such as thermal or electrical conductivity) by modified AFM may lead to bulk characterisation such as the formation of a percolating nanotube network for instance. 

Microthermal analysis is a recently introduced thermoanalytical technique that combines the principles of scanning probe microscopy with thermal analysis via replacement of the probe tip with a thermistor. This allows samples to be spatially scanned in terms of both topography and thermal conductivity, whereby placing the probe on a specific region of a sample and heating, it is possible to perform localized thermal analysis experiments on those regions. 

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 introduction and development of Micro-Thermal Analysis are described and discussed by Duncan Price in Chapter 3. The atomic force microscope (AFM) forms the basis of both scanning thermal microscopy (SThM) and instruments for performing localised thermal analysis. The principles and operation of these techniques, which exploit the abilities of a thermal probe to act both as a very small heater and as a thermometer, in the surface characterisation of materials are described in detail. The... 

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... 

V.V. Gorhunov, N. Fuchigami, J.L. Hazel, and V.V. Tsukruk, Probing surface microthermal properties hy scanning thermal microscopy, Langmuir, 15, 8340-8343 (1999). 

Scanning Thermal Microscopy The scanning probe-based thermal microscope (SThM) gives information about the temperature distributions and allows for quantitative determination of the local thermal conductivity in a sample. A resistive probe is employed which both captures the topographic information as well as the temperature/thermal conductivity profile with a resolution of a few milliKelvin. Table 2 provides a list of the more established members of the scanning probe microscope family. 

Scanning thermal microscopy is discussed in the article on Scanning probe microscopy... 

Optical microscopy Phase contrast microscopy Polarized light microscopy Scanning electron microscopy Scanning ion conductance microscope Scanning probe microscopy Scanning thermal profiler... 

Scanning thermal microscopy (SThM) was used to estimate the surface distribution of the microthermal properties (for details see Ref 21). As can be seen from the images obtained in this mode (Figure 8, substantial thermal contrast for PB and PS phases can be detected at the probe temperature above 50 C. A geometrical contribution is also clearly visible However, taking into account that the effective thermal contact area for polymeric materials is about 1 pm [21], we can refer the major contribution in different thermal re onse for the polymer film to different thermal conductivities of glassy and rubber phases. 

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