Boundary scattering

Lin J., and Pence T.J., 1996, Wave attenuation by Mnetically active phase boundary scattering during displacivephase transformations. Preprint... 

Fig. 19. (a) Measured temperature dependence of resistance for bismuth nanowire arrays of various wire diameters dw (Heremans et al, 2000). (b) R(T)/R(290 K) for bismuth wires of larger dw measured by Hong et al. (1999). (c) Calculated R(T)/R(300 K) of 36-nm and 70-nm bismuth nanowires (Lin et al, 2000b). The dashed curve refers to a 70-nm poly crystalline wire with increased boundary scattering. 

R(T) is predicted to display a monotonic temperature dependence at a high defect level. This is illustrated by the dashed curve in Fig. 19(c) for polycrystalline 70-nm bismuth wires. Because the nanowires prepared by electrochemical deposition were found to be polycrystalline, their carriers would experience more boundary scattering, resulting in the monotonic R(T) behavior noted experimentally in Fig. 19(b). 

AP-CVD ZnO Hu and Gordon [10,28] observed an increase of electron mobility p with increasing film thickness d, both for boron-doped and for gallium-doped AP-CVD ZnO films, with a more pronounced slope for small thickness. They attributed this behavior to the influence of the grain boundary scattering effect, which is dominant for thinner films that are composed of smaller crystallites. 

The reduction in <5 corresponds to the reduction in p and in the haze factor as observed in Figs. 6.28b and 6.29b, respectively. As the carrier density N does not vary with H2O/DEZ, we can safely assume that the density of ionized impurities within the ZnO films also remains constant when the H2O/DEZ ratio is increased. The observed decrease in p would therefore be induced here solely by an increase in grain boundary scattering, i.e., by an increase in the density of grain boundaries. This increase of grain boundary density evidently occurs when the grains become smaller (i.e., when <5 is reduced). 

In addition to mechanical properties, other physical properties of polycrystaUine materials, such as electrical and thermal conduction, are also affected by microstmcture. Although polycrystals are mechanicaUy superior to single crystals, they have inferior transport properties. Point defects (vacancies, impurities) and extended defects (grain boundaries) scatter electrons and phonons, shortening their mean free paths. Owing to... 

Asheghi, M., Y.K. Leung, S.S. Wong, and K.E. Goodson, Phonon-Boundary Scattering in Thin Silicon Layers. Applied Physics Letters, 1997. 71(13) p. 1798-1800. 

Liu, W. and M. Asheghi, Phonon-Boundary Scattering in Ultrathin Single-Crystal Silicon Layers. Applied Physics Letters, 2004. 84(19) p. 3819-3821. 

Figure 2. Shear localization in Ti four times compressed and additionally strained by 15% at 400°C deformation relief (a) and TEM image of dislocation boundary scattering (b).

CNT junctions and agglomerates, or via the matrix. In all these cases, the transition occurs via an interface, and, thus, the coupling losses can be attributed to an intense phonon boundary scattering. At the same time the thermal conductivity decreases with the increase in temperature (if the temperature is near the melting point of the matrix). This indicates that the thermal conductivity of the composites is dominated by the interface thermal transport between the nanotube/matrix or nanotube/nanotube interface. Thus, it is believed that the decreased effective thermal conductivity of the studied composites could be due to the high interface thermal resistance across the nanotube/matrix or nanotube/nanotube interfaces. 

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