For the first time, the latent heat of fusion DH m for Sn particles formed by evaporation on inert substrate with radii ranging from 5 to 50 nm has been measured directly using a novel scanning nanocalorimeter. A particle-size-dependent reduction of DH m has been observed. An "excluded volume" is introduced to describe the latent heat of fusion from the enhanced surface melting of small particles. Melting point depression has also been found by our nanocalorimetric technique. [S0031-9007(96)00495-4]

Obtaining thermoelectric materials with high figure of merit ZT is an exacting challenge because it requires the independent control of electrical conductivity, thermal conductivity and Seebeck coefficient, which are often unfavourably coupled. Recent works have devised strategies based on nanostructuring and alloying to address this challenge in thin films, and to obtain bulk p-type alloys with ZT>1. Here, we demonstrate a new class of both p- and n-type bulk nanomaterials with room-temperature ZT as high as 1.1 using a combination of sub-atomic-per-cent doping and nanostructuring. Our nanomaterials were fabricated by bottom-up assembly of sulphur-doped pnictogen chalcogenide nanoplates sculpted by a scalable microwave-stimulated wet-chemical method. Bulk nanomaterials from single-component assemblies or nanoplate mixtures of different materials exhibit 25-250% higher ZT than their non-nanostructured bulk counterparts and state-of-the-art alloys. Adapting our synthesis and assembly approach should enable nanobulk thermoelectrics with further increases in ZT for transforming thermoelectric refrigeration and power harvesting technologies.

ZnO is a promising high figure-of-merit (ZT) thermoelectric material for power harvesting from heat due to its high melting point, high electrical conductivity σ, and Seebeck coefficient α, but its practical use is limited by a high lattice thermal conductivity κ(L). Here, we report Al-containing ZnO nanocomposites with up to a factor of 20 lower κ(L) than non-nanostructured ZnO, while retaining bulklike α and σ. We show that enhanced phonon scattering promoted by Al-induced grain refinement and ZnAl(2)O(4) nanoprecipitates presages ultralow κ ∼ 2 Wm( -1) K(-1) at 1000 K. The high α∼ -300 μV K(-1) and high σ ∼ 1-10(4) Ω(-1 )m(-1) result from an offsetting of the nanostructuring-induced mobility decrease by high, and nondegenerate, carrier concentrations obtained via excitation from shallow Al donor states. The resultant ZT ∼ 0.44 at 1000 K is 50% higher than that for the best non-nanostructured counterpart material at the same temperature and holds promise for engineering advanced oxide-based high-ZT thermoelectrics for applications.

Manipulating interfacial thermal transport is important for many technologies including nanoelectronics, solid-state lighting, energy generation and nanocomposites. Here, we demonstrate the use of a strongly bonding organic nanomolecular monolayer (NML) at model metal/dielectric interfaces to obtain up to a fourfold increase in the interfacial thermal conductance, to values as high as 430 MW m(-2) K(-1) in the copper-silica system. We also show that the approach of using an NML can be implemented to tune the interfacial thermal conductance in other materials systems. Molecular dynamics simulations indicate that the remarkable enhancement we observe is due to strong NML-dielectric and NML-metal bonds that facilitate efficient heat transfer through the NML. Our results underscore the importance of interfacial bond strength as a means to describe and control interfacial thermal transport in a variety of materials systems.

Single-walled carbon nanotubes (SWNTs) exhibit a range of unusual mechanical and electronic properties because of their unique structure and dimensions. Here we report another unusual property. We accidentally discovered that SWNTs ignite when exposed to a conventional photographic flash. This photoeffect occurs for SWNTs prepared by the carbon arc, laser ablation, or chemical vapor deposition upon exposure to a camera flash at close range (several cm away from the sample). Ignition did not occur for multiwalled nanotubes, graphite powder, fluffy carbon soot, or C6o.Frames taken from a real-time video recording of burning SWNTs after the application of the photoflash (Fig. 1, A and B) show red hot spots immediately after the flash (Fig. 1B). The sample bums down in air, generating CO and CO2 and leaving behind oxidized catalyst particles (such as Ni-Y or Fe, used for SWNT synthesis) and traces of disordered carbonaceous materials. The effect we describe occurs only on dry, "fluffy," as-prepared nanotube samples (see below). After flashing SWNTs, we observed an associated large photoacoustic effect caused by the absorption of incident light on the SWNT samples, in which acoustic waves are caused by the expansion and contraction of trapped gases (1).Ignition and burning occur when local increases in temperature are sufficient to initiate the oxidation of the carbon and propagate as more heat is released by this exothermic reaction. Flashlight consists of a combination of various wavelengths, which intend to emulate sunlight (without the ultraviolet light). In air, the average light power needed to ignite SWNTs was found to be 100 mW cm-2 (?20 mW) for a sample density of about 0.2 g cm-3 (pulse rise time: 50 pxs; decay time: 1.2 ms). When the sample is compacted to higher densities, larger power is needed to ignite SWNTs; for densities >1 g cm-3, ignition occurs at about 300 mW cm-2. At higher densities, the tubes are less prone to catching fire because of the lack of oxygen access and loss of heat into the bulk of the sample.Thermal conductivity of nanotubes along the tube axes is expected to be very high (2-4). Bulk SWNTs form bundles that crisscross each other in the pristine samples (Fig. 1C). The heat pulse generated by the absorption of flashlight will initially be confined to the tubes within a bundle, especially along their axes. The high trapped thermal energy densities, necessary for ignition, are most easily attained when the bundles are separated and surrounded by oxygen, and the heat wave is locally confined in the nanotube structures. As the material is compacted, Fig. 1. (A and B) Sequence of burning of SWN sample (about 2 cm outer diameter) showing the fl sample soon after flashing exhibiting the ignited ' with burning red and yellow spots. (C) High-resoli sion electron microscopy (HRTEM) image of pris which a cross section of an individual bundle is cl (D) Typical HRTEM image of remaining carbona obtained after flashing SWNTs in air; the presence ed single-walled structures such as nanohorns is n ...