Thermal Nanosystems and Nanomaterials
Heat transfer laws for conduction, radiation and convection change when the dimensions of the systems in question shrink. The altered behaviours can be used efficiently in energy conversion, respectively bio- and high-performance mater
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Nanostructures Patrice Chantrenne, Karl Joulain, and David Lacroix
2.1 Introduction As stated in Chap. 1, when the size of a solid object becomes of the same order of magnitude as the mean free path of the energy carriers, heat transfer is no longer diffusive. The notion of thermal conductivity, defined by Fourier’s law for the diffusive regime, can then no longer be used. However, the thermal conductivity is such a common thermophysical parameter that this definition is still used when energy transport is non-diffusive. An equivalent thermal conductivity is then used which depends on the shape and size of the solid, the temperature, and the temperature gradient. The latter parameter is often not taken into account and this may be a source of error. Nanostructures such as nanoparticles are of great interest in many applications. They are candidates for biomedical applications such as drug delivery and thermal treatment of cancer. They are used in nanofluids to improve convective heat transfer, with or without phase change (boiling, condensation). Nanotubes, nanowires, and nanofilms are widely considered in microelectronic applications as components, connecting wires [1], and sensors. Nanostructures are also of great help in physics for various experiments [2, 3]. Finally, all kinds of nanoparticles are used in nanocomposite materials. Most nanostructures are made of dielectric materials (mainly due to the importance of microelectronic applications), although some are made of electrically conducting materials. In each application, the nanostructure interacts with its surroundings, and of course heat transfer in nanostructured materials or systems depends on these interactions, but also on their intrinsic thermal properties. When the thermal control of the system of interest is important, some knowledge of the thermal properties of each nanostructure is required. This knowledge may come from either experimental determination or theoretical prediction. But it is no easy matter to handle this aspect of nanostructures, and in many cases they have not been thermally
S. Volz (ed.), Thermal Nanosystems and Nanomaterials, Topics in Applied Physics, 118 c Springer-Verlag Berlin Heidelberg 2009 DOI 10.1007/978-3-642-04258-4 2,
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Patrice Chantrenne, Karl Joulain, and David Lacroix
characterised. Each nanostructure requires a specific experimental setup, which is often itself nanostructured. A brief review of this experimental work is proposed in the appendix on p. 58. Compared with experimental investigation, many more publications are devoted to modelling heat transfer in nanostructures and to predicting their thermal conductivity. In these papers, previous experimental results are used to validate the theoretical approach. Section 2.2.1 reviews the physics of the vibrational properties of a semiconductor that underlie heat transport in such materials. This basis is essential for understanding the numerical models discussed in Sects. 2.2.2–2.3.2. Section 2.3.3 describes a technique that stands on its own, namely
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