One of the keywords in recent space law literature is “new space activities.” Do you agree with the use of this term, and what is your understanding of it? Are we really talking about “new” activities or about a “new” space?

Thermoelectric CuIn1-xAlxTe2 compounds (x=0, 0.05, 0.1, 0.15, 0.50) have been synthesized by solid state reaction followed by spark plasma sintering. The influence of Al substitution on electrical and thermal transport properties has been investigated in the CuInTe2 compounds. It was found that the Seebeck coefficient and electrical conductivity is reduced by isovalent replacement of In with Al. Our first principle calculation indicates Al substitution leads to the widen band gap, the reduction in the number of degeneracy of valence band and the effective mass. Furthermore, a large reduction in thermal conductivity is achieved through the enhanced phonon scattering via point defect as well as the nano-sized particles observed between grain boundaries and on the grain surface. In spite of the reduced charge transport properties, an improved figure-of- merit ZT is achieved, reaching 0.8 at 800 K, 33% higher in comparison to the pure CuInTe2 compound.

We have modified Sb2Te3 thin film thermoelectric materials by scanning a femtosecond laser across the film surface to create track-like nanostructures. These nanotracks have widths of 50-80 nm and a periodicity of ∼ 130 nm. We show that the nanotrack morphology is highly dependent on laser fluence and scan speed. Moreover, we performed transient thermoreflectance measurements on a laser-irradiated film and found a thermal conductivity reduction of 4.5% in the nanostructured regions compared to that of the unmodified regions. These results suggest the potential use of femtosecond pulsed lasers to create nanostructured thermoelectric materials with improved performance.

PbTe-based materials are promising for efficient heat energy to electricity conversion. We present studies of the thermoelectric properties of the PbTe-SrTe system. X-ray diffraction patterns reveal that all the samples crystallize in the rock salt structure without noticeable secondary phase. Na2Te doping of the PbTe-SrTe materials resulting in a positive sign Hall coefficient indicating p-type conduction. Lattice thermal conductivity is significantly decreased with the insertion of SrTe in PbTe lattice. The ZT ∼ 1.3 of these materials is derived from their very low thermal conductivities and reasonably high power factor at 800 K.

We explored the effect of K and K-Na substitution for Pb atoms in the lattice of PbTe, in an effort to test a hypothesis for the development of a resonant state that may enhance the thermoelectric power. At 300K the data can adequately be explained by a combination of a single and two-band model for the valence band of PbTe depending on hole density that varies in the range 1-15 × 1019 cm-3. A change in scattering mechanism was observed in the temperature dependence of the electrical conductivity, σ, for samples concurrently doped with K and Na which results in significantly enhanced σ at elevated temperatures and hence power factors. Thermal conductivity data provide evidence of a strong interaction between the light- and the heavy-hole valence bands at least up to 500K. Figure of merits as high as 1.3 at 700K were measured as a result of the enhanced power factors.

We made photonic crystals composed of artificial opals infiltrated with ZnS semiconductor nanocrystals by using self-assembly and solvothermal methods. Scanning electron microscopy images show that the silica spheres exhibit a well-ordered arrangement and the ZnS nanocrystals grow homogenously inside the opal matrix and the as-synthesized ZnS nanocrystals reveal a cubic phase from X-ray diffraction pattern. Furthermore, the optical properties of the infiltrated opals with different ZnS filling ratio are also studied by transmission spectroscopy respectively. It is proposed that the position of the stop band can be easily designed by controlling the infiltration ratio of ZnS. These results demonstrate an effective and practical route to obtain high-performance photonic crystal structures.

Bramble-like mesostructured nickel oxide/surfactant fibers were synthesized by using anionic surfactants (sodium dodecylsulfonate or sodium dodecylsulfate: SDS) as templates, and nickel salts as inorganic precursors, via the “S-I+” route in alkaline condition. The as-prepared samples were characterized by X-ray diffraction (XRD), Scanning electron microscopy (SEM), Fourier transform infrared (FT-IR) spectroscopy and thermogravimetry-differential thermal analysis (TG/DTA) techniques. Such form of mesostructure nickel oxide is found for the first time and is believed to have potential applications in catalysis, host-guest chemistry, and electrochemical devices.