Xuezhao Shi

Enhanced thermoelectric figure of merit of CoSb3 via large-defect scattering

We have measured the structural, chemical, and transport properties of a series of CoSb3 skutterudite samples modified by fullerene additions of 0, 0.52, 3.28, 3.90, 4.77, and 6.54 mass%. Fullerene is a 60-atom carbon molecule that forms microsize clusters between the grain boundaries of CoSb3. We observed that the dominant scattering mechanism in the electrical transport changes from impurity scattering to grain-boundary scattering near a C60 content of ∼5–6 mass%, and that thermal conductivity decreases with increasing C60 content. A significant increase in the thermoelectric figure of merit is achieved for 6.54 mass% C60 compared to the pure CoSb3.

Effects of partial substitution of transition metals for cobalt on the high-temperature thermoelectric properties of Ca3Co4O9+δ

Polycrystalline samples of Ca3Co4−xMxO9+δ (M=Ni, Fe, Mn, Cu; x=0–0.6) have been prepared using sol-gel procedure followed by spark plasma sintering. Their thermoelectric properties have been carefully examined from room temperature to 1000 K. Substitution of Ni and Fe for Co caused the significant increase of electrical resistivity, but the thermopower changed only slightly. The magnitude of the increases in electrical resistivity and thermopower for the Mn-substituted samples was the most pronounced as compared with Ni- and Fe-substituted samples in the same substitution content, which could be explained by the strong localization of charge caused by Mn substitution. Temperature dependence of electrical conductivity showed that the hole hopping conduction mechanism was dominant for all samples. The activation energy increased with increasing substitution content. On the other hand, the Cu substitution resulted in decreases of both electrical resistivity and thermopower, and the activation energy remained...

One-Pot Synthesis of Graphene-Supported Monodisperse Pd Nanoparticles as Catalyst for Formic Acid Electro-oxidation

To synthesize monodisperse palladium nanoparticles dispersed on reduced graphene oxide (RGO) sheets, we have developed an easy and scalable solvothermal reduction method from an organic solution system. The RGO-supported palladium nanoparticles with a diameter of 3.8 nm are synthesized in N-methyl-2-pyrrolidone (NMP) and in the presence of oleylamine and trioctylphosphine, which facilitates simultaneous reduction of graphene oxide and formation of Pd nanocrystals. So-produced Pd/RGO was tested for potential use as electrocatalyst for the electro-oxidation of formic acid. Pd/RGO catalyzes formic acid oxidation very well compared to Pd/Vulcan XC-72 catalyst. This synthesis method is a new way to prepare excellent electrocatalysts, which is of great significance in energy-related catalysis.

Organic phase synthesis of monodisperse iron oxide nanocrystals using iron chloride as precursor

Monodisperse iron oxide nanocrystals were synthesized by a simplified method using iron chloride as precursor. In the presence of Cl ions, the as-produced iron oxide nanocrystals preferred a cubic shape with {100} facets exposed. The function of halogens including Cl and Br ions on stabilizing {100} facets of spinel structured iron oxides, rather than the regulation of thermolysis kinetics and surfactants, was found influential on the shape control of nanocubes in this organic phase approach. The synthesis can be also extended for cobalt ferrite nanocubes and cobalt oxide polyhedrons.

Surface-enhanced Raman scattering properties of highly ordered self-assemblies of gold nanorods with different aspect ratios

Gold nanorods with aspect ratios of from 1 (particles) to 31.6 were synthesized by the seed-mediated method and packed in a highly ordered structure on a large scale on silicon substrates through capillary force induced self-assembly behaviour during solvent evaporation. The gold nanorod surface exhibits a strong enhancing effect on Raman scattering spectroscopy. The enhancement of Raman scattering for two model molecules (2-naphthalenethiol and rhodamine 6G) is about 5-6 orders of magnitude. By changing the aspect ratio of the Au nanorods, we found that the enhancement factors decreased with the increase of aspect ratios. The observed Raman scattering enhancement is strong and should be ascribed to the surface plasmon coupling between closely packed nanorods, which may result in huge local electromagnetic field enhancements in those confined junctions.

Influence of Si Co-doping on electrical transport properties of magnesium-doped boron nanoswords

Magnesium-doped boron nanoswords were synthesized via a thermoreduction method. The as-prepared nanoswords are single crystalline and β-rhombohedral (β-rh) phase. Electrical transport measurements show that variable range hopping conductivity increases with temperature, and carrier mobility has a greater influence than carrier concentration. These results are consistent with the three dimensional Mott’s model (M. Cutler and N. F. Mott, Phys. Rev. 181, 1336 (1969)) besides a high density of localized states at the Fermi level compared with bulk β-rh boron. Conductivity of Mg-doped boron nanoswords is significantly lower than that of “pure” (free of magnesium) boron nanoswords. Electron energy loss spectroscopy studies confirm that the poorer conductivity arises from silicon against magnesium doping.

Magnetospectroscopy of high-purity InP grown by gas source molecular beam epitaxy

Magneto-photoconductivity spectra related to the bound phonons and resonant polaron effect on Si donors in high-purity InP have been investigated. Not only the transition from the 1s ground state to bound phonon state (1s+LO) of Si donors, but also the antilevel crossings of the (3, 1, 0) metastable state with the bound phonon states (1s+LO) and (2p−1+LO) are clearly observed in high magnetic fields. The results demonstrate the bound phonon in Si-doped InP consists of both electron and phonon via multiphonon processes and there is a resonant interaction between LO phonons and impurity-bound electrons in InP.

Study of the ground state splitting of N–O complexes in Cz–Si grown under nitrogen atmosphere

Far‐infrared absorption spectra of Cz–Si grown under a reduced pressure of high pure nitrogen atmosphere have been investigated at different temperatures. Seven new series of lines resulting from the ground state splitting of N–O complexes [D(N–O)s] have been observed. The results indicate that the D(N–O)s have different structures. In addition, according to effective mass approximation, the binding energies of the split ground states have been obtained.