Thermal diffusion length

Degree of thermal diffusion is an important factor in treating rapid annealing, since it will govern in-depth crystallinity of poly-Si films formed and thermal damage to glass substrates. One-dimensional thermal diffusion coefficient can 

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If a laser pulse of sub-picosecond duration is used, deposition of the laser energy to the sample is so rapid that the thermal diffusion length is determined by the diffusion of hot electrons before they transfer the energy to the lattice of the solid sample. 

Porous materials, such as silica and alumina, have thermal diffusion lengths of approximately 10 m, which is much less than the typical thickness of pressed discs. The small thermal diffusion length gives photoacoustic spectroscopy a larger dynamic range than transmission methods when applied to powdered samples. An additional advantage is the ease of sample preparation, since photoacoustic spectroscopy uses powdered samples with no special preparation required. 

Dt the thermal diffusion length is the distance the thermal wave can travel through the sample (cm)... 

The typical polymer or rubber sample would be classified as optically transparent or opaque and thermally thick except possibly for the strongest bands. In this case the signal intensity would be proportional to the product of the optical absorption coefficient (P) and the thermal diffusion length and show a - 3/2 dependence on the modulation frequency (to). The angular modulation frequency is a product of the interferometer mirror velocity and the wavenumber ... 

The applicability of the continuum model is determined by the local value of the non-dimensional Knudsen number (Kn) which is defined as the ratio of the mean free path (lufp) of the heat-carrier medium to the system reference length scale (say thermal diffusion length). Microscale... 

Fig. 11.6. Schematic diagrams of thermal diffusion in cases of thick and thin a-Si films [27], The total generated heat in thick a-Si films is larger than that in thin a-Si films, whereas the total thermal diffusion length from the surface is relatively small in case of thick a-Si, resulting in crystallization at lower lamp irradiance...

The deterioration of the grating (shown in Fig. 91) with successive pulses cannot be attributed to thermal effects, since in an experiment using a mask and projection technique (1 pm slit pattern and multiple pulses with 200 mj cm-2) sharp contours remained. Additionally, the thermal diffusion length for the laser pulse corresponds only to 30-40 nm for commercial polymers such as poly(ethylene terephthalate). 

Shape Factor, Thermal Resistance, and Diffusion Length. The shape factor S, the thermal resistance R, and the thermal diffusion length A are three useful and related thermal parameters. They are defined by the following relationships ... 

As according to Eq. (25) the thermal diffusion length Ps is inversely proportional to the square root of the chopping frequency 00, nondestructive depth profiling is possible. 

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