The enormous amount of basic research into carbon nanotubes has sparked interest in the potential applications of these novel materials. One promising use of carbon nanotubes is as fillers in a composite material to improve mechanical behaviour, electrical transport and thermal transport. For composite materials with high thermal conductivity, the thermal conductance across the nanotube-matrix interface is of particular interest. Here we use picosecond transient absorption to measure the interface thermal conductance (G) of carbon nanotubes suspended in surfactant micelles in water. Classical molecular dynamics simulations of heat transfer from a carbon nanotube to a model hydrocarbon liquid are in agreement with experiment. Our findings indicate that heat transport in a nanotube composite material will be limited by the exceptionally small interface thermal conductance (G approximately 12 MW m(-2) K(-1)) and that the thermal conductivity of the composite will be much lower than the value estimated from the intrinsic thermal conductivity of the nanotubes and their volume fraction.

The cross-plane thermal conductivity of four Si/Si 0.7 Ge 0.3 superlattices and three Si 0.84 Ge 0.16 /Si 0.76 Ge 0.24 superlattices, with periods ranging from 45 to 300 and from 100 to 200 Å, respectively, were measured over a temperature range of 50 to 320 K. For the Si/Si 0.7 Ge 0.3 superlattices, the thermal conductivity was found to decrease with a decrease in period thickness and, at a period thickness of 45 Å, it approached the alloy limit. For the Si 0.84 Ge 0.16 /Si 0.76 Ge 0.24 samples, no dependence on period thickness was found and all the data collapsed to the alloy value, indicating the dominance of alloy scattering. This difference in thermal conductivity behavior between the two superlattices was attributed to interfacial acoustic impedance mismatch, which is much larger for Si/Si 0.7 Ge 0.3 than for Si 0.84 Ge 0.16 /Si 0.76 Ge 0.24. The thermal conductivity increased slightly up to about 200 K, but was relatively independent of temperature from 200 to 320 K.

We use time-domain thermoreflectance to show that interface thermal conductance, G, is proportional to the thermodynamic work of adhesion between gold and water, WSL, for a series of five alkane-thiol monolayers at the gold-water interface. WSL is a measure of the bond strength across the solid-liquid interface. Differences in bond strength, and thus differences in WSL, are achieved by varying the terminal group (ω-group) of the alkane-thiol monolayers on the gold. The interface thermal conductance values were in the range 60–190 MW m−2 K−1, and the solid-liquid contact angles span from 25° to 118°.

Monolithically integrated active cooling is an attractive way for thermal management and temperature stabilization of microelectronic and optoelectronic devices. SiGeC can be lattice matched to Si and is a promising material for integrated coolers. SiGeC/Si superlattice structures were grown on Si substrates by molecular beam epitaxy. Thermal conductivity was measured by the 3 method. SiGeC/Si superlattice microcoolers with dimensions as small as 40ϫ40 m 2 were fabricated and characterized. Cooling by as much as 2.8 and 6.9 K was measured at 25°C and 100°C, respectively, corresponding to maximum spot cooling power densities on the order of 1000 W/cm 2 . © 2001 American Institute of Physics. ͓DOI: 10.1063/1.1356455͔Thermoelectric ͑TE͒ refrigeration in a solid-state active cooling method with high reliability. Bi 2 Te 3 -based TE coolers are widely used for cooling and temperature stabilization of microelectronic and optoelectronic devices, but their processing is a bulk technology and is incompatible with integrated circuit fabrication process. Solid-state coolers monolithically integrated with microelectronic and optoelectronic devices are an attractive way to achieve compact and efficient cooling. It can lower the cost of fabrication and packaging, and can selectively cool individual key devices instead of the whole chip. However, the thermoelectric figure of merit ͑ZT͒ is quite low for most of the semiconductors used in microelectronics and optoelectronics. This makes it difficult to get high cooling performance. Recently heterostructure thermionic and superlattice coolers have been proposed, and theoretical calculations show that large improvements in ZT can be achieved and efficient refrigeration becomes possible with coolers made of conventional semiconductor materials.

Combinatorial methods offer an efficient approach for the development of new materials. Methods for generating combinatorial samples of materials, and methods for characterizing local composition and structure by electron microprobe analysis and electron-backscatter diffraction are relatively well developed. But a key component for combinatorial studies of materials is high-spatial-resolution measurements of the property of interest, for example, the magnetic, optical, electrical, mechanical or thermal properties of each phase, composition or processing condition. Advances in the experimental methods used for mapping these properties will have a significant impact on materials science and engineering. Here we show how time-domain thermoreflectance can be used to image the thermal conductivity of the cross-section of a Nb-Ti-Cr-Si diffusion multiple, and thereby demonstrate rapid and quantitative measurements of thermal transport properties for combinatorial studies of materials. The lateral spatial resolution of the technique is 3.4 microm, and the time required to measure a 100 x 100 pixel image is approximately 1 h. The thermal conductivity of TiCr(2) decreases by a factor of two in crossing from the near-stoichiometric side of the phase to the Ti-rich side; and the conductivity of (Ti,Nb)(3)Si shows a strong dependence on crystalline orientation.

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The filling fraction limitation (FFL) in n-type CoSb3 skutterudites is far below that of p-type (Fe,Co)­Sb3-based skutterudites, and it is critical to increase FFL for accomplishing high thermoelectric figure of merit (ZT max). Here, a series of Yb x Co4–y Fe y Sb12 alloys with x = 0.25–0.5 and y = 0.1–0.5 were synthesized, which demonstrate a clear increase of the FFL of Yb from ∼0.3 in CoSb3 to 0.5. Ultralow thermal conductivities of 2.0–2.5 W/m·K at 300 K and 1.75 W/m·K at ∼600 K have been achieved, which are the lowest values reported among skutterudite materials and comparable with p-type skutterudites. These ultralow thermal conductivities result from the combination of secondary phase scattering and phonon scattering from dynamic electron exchange between Fe2+ and Co3+. High ZT max values of 1.28 at 740 K and 1.34 at 780 K are obtained, which are among the best values reported in the temperature range of 740–800 K. The temperature at which maximum ZT max appears is shifted below 850 K. These results are highly exciting toward the development of multistage segmented and cascade thermoelectric power generators for in-air operations.

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