The making of composites has served as a working principle of achieving material properties beyond those of their homogeneous counterparts. The classical effective-medium theory models the constituent phases with local properties drawn from the corresponding bulk values, whose applicability becomes questionable when the characteristic size of individual domains in a composite shrinks to nanometer scale, and the interactions between domains induced by interfacial and size effects become important or even dominant. These unique features of nanocomposites have enabled engineering of extraordinary thermoelectric materials with synergistic effects among their constituents in recent years. For other applications requiring high thermal conductivity, however, interfacial and size effects on thermal transport in nanocomposites are not favorable, although certain practical applications often call for the composite approach. Therefore, understanding nanoscale transport in nanocomposites can help determine appropriate strategies for enhancing the thermal performance for different applications. We review the emerging principles of heat and charge transport in nanocomposites and provide working examples from both thermoelectrics and general thermal engineering.

We have used low-energy electron diffraction and microscopy to compare the growth of graphene on hydrogen-free Ge(111) and Ge(110) from an atomic carbon flux. Growth on Ge(110) leads to significantly better rotational alignment of graphene domains with the substrate. To explain the poor rotational alignment on Ge(111), we have investigated experimentally and theoretically how the adatom reconstructions of Ge interact with graphene. We find that the ordering transition of the Ge(111) adatom reconstruction is not significantly perturbed by graphene. Density functional theory calculations show that graphene on reconstructed Ge(110) has large-amplitude corrugations, whereas it is remarkably flat on reconstructed Ge(111). We argue that the absence of corrugations prevents graphene islands from locking into a preferred orientation.

Gd2TixZr2−xO7 (x = 0 to 2) pyrochlore was irradiated by 30 MeV C60 clusters, which provide an extremely high ionizing energy density. High-resolution transmission electron microscopy revealed a complex ion-track structure in Gd2Ti2O7 and Gd2TiZrO7, consisting of an amorphous core and a shell of a disordered, defect-fluorite structure. As compared with the irradiation by 1.5 GeV U ions with the highest energy loss, the track structure is consistent with tracks created by monoatomic swift heavy ions, but the diameters (with the entire diameter of 17 nm for Gd2Ti2O7 and 15 nm for Gd2TiZrO7) are significantly larger due to the much smaller velocity and higher energy density of the C60 ions. Ion tracks created by monoatomic ions are challenging to describe by HRTEM, as the boundary between disordered fluorite and pyrochlore matrix is less distinct. However, the C60 irradiation shows a clearly resolved ion track with completely crystalline, disordered, defect-fluorite structure around an amorphous core. Based on the distinct boundaries of the track morphology, inelastic thermal-spike calculations were used to describe the track size and extract critical energy densities for the interpretation of the complex core–shell morphologies for the different pyrochlore compositions.

In this study, the mechanism of ferrite grain refinement during warm compression deformation in the (γ + α) region of Cu–P–Cr–Ni–Mo weathering steel was analyzed by optical microscopy and electron backscatter diffraction. Results showed that fine equiaxed ferrite grains surrounded by high-angle boundaries (HABs) formed along the initial boundaries as the strain is increased. As the deformation temperature decreased, some low-angle boundaries shifted to HABs in intragranular ferrite, and ferrite grain refinement was promoted by continuous dynamic recrystallization. Microstructural observations also indicated that the fine ferrite grains of approximately 1.4–3 μm in size can be obtained by deformation at 750 °C with a strain over 0.69 because of ferrite dynamic recrystallization. Moreover, both strain and deformation temperature influenced the ferrite grain size and volume fraction. Thus, the predominant mechanism for ferrite grain refinement in the (γ + α) region was continuous dynamic recrystallization.

Experimental evidences for a recently proposed mechanism of tin-induced crystallization of amorphous silicon are presented. The mechanism discusses a crystalline phase growth through cyclic processes of formation and decay of a super-saturated solution of silicon in molten tin at the interface with the amorphous silicon. The suggested mechanism is validated using a nonlinear dynamical model that takes into account the mass diffusion of the components of the system, heat transfer caused by latent (crystallization) heat release and amorphous silicon dissolution events, and concentration nonuniformities created by silicon crystallization. The analysis of a stationary-state solution of the model confirms the existence of periodic solutions for the partial volume of the crystalline phase and other system's variables. Possible applications of the proposed mechanism in manufacturing of cost-effective nanocrystalline silicon films for the third-generation solar cell technology are discussed.

Titanium (Ti) thin films were deposited by DC magnetron sputtering at conventional conditions with different substrate temperature, deposition rate, and inert gas pressure. The compositional, structural, morphological, and optical properties of the Ti films were investigated. It is shown that the films were crystalline with α-Ti phase and hcp structure only. The crystallinity increased with increase in substrate and deposition rate. Analysis of the atomic force microscopy images shows that the films were uniform, crack free, and adhered well to the substrate. It is found that, a strong relation existed between the structural and optical properties of the films. The optical properties of the Ti films were most influenced under the deposition conditions. From this dependence, the optimum deposition conditions are obtained to prepare metallic, crystalline, and dense Ti films with smooth surface under conventional conditions.

In this study, BaCu(B2O5) (BCB) is utilized as the sintering aids to decrease the sintering temperature of Ba3(Co0.4Zn0.6)2Fe24O41 [(Co0.4Zn0.6)2Z]. The influence of BCB addition on the microstructures as well as the dielectric and magnetic properties of the (Co0.4Zn0.6)2Z ceramic samples is investigated. It is found that the 5 wt% BCB added (Co0.4Zn0.6)2Z sintered at 925 °C exhibits both a high relative density of about 95% and a homogeneous microstructure with few pores existing. Both the relative permittivity and permeability of the sample keep stable from 10 to 800 MHz. Also, the dielectric and magnetic loss are low and effectively suppressed within a wide frequency range. For the specimen with 5 wt% BCB, the dielectric and magnetic loss tangent are 0.003 and 0.039 at 200 MHz, respectively. In addition, a compatibility test with Ag powders has been carried out. The optimized properties indicate that this kind of low temperature sintered Z-type hexaferrite is a good candidate for the applications of multilayer chip inductors.