The band edge optical characterization of solution-synthesized CdS nanowires (NWs) is described. Investigated wires are made through a solution−liquid–solid approach that entails the use of low-melting bimetallic catalyst particles to seed NW growth. Resulting diameters are approximately 14 nm, and lengths exceed 1 µm. Ensemble diameter distributions are ∼13%, with corresponding intrawire diameter variations of ∼5%. High-resolution transmission electron micrographs show that the wires are highly crystalline and have the wurtzite structure with growth along at least two directions: [0001] and [101̅0]. Band edge emission is observed with estimated quantum yields between ∼0.05% and 1%. Complementary photoluminescence excitation spectra show structure consistent with the linear absorption. Carrier cooling dynamics are subsequently examined through ensemble lifetime and transient differential absorption measurements. The former reveals unexpectedly long band edge decays that extend beyond tens of nanoseconds. The latter indicates rapid intraband carrier cooling on time scales of 300–400 fs. Subsequent recovery at the band edge contains significant Auger contributions at high intensities which are usurped by other, possibly surface-related, carrier relaxation pathways at lower intensities. Furthermore, an unusual intensity-dependent transient broadening is seen, connected with these long decays. The effect likely stems from band-filling on the basis of an analysis of observed spectral shifts and line widths.

Excitation/emission polarization anisotropies (ρexc∕emm) of single CdSe nanowires (NWs) were studied for their size, frequency, and dielectric environment dependencies. Single NW optical experiments show strong ρexc dielectric environment dependencies for both thick and thin NWs in agreement with classical dielectric contrast models. Furthermore, no excitation frequency sensitivities were seen for both thick and thin wires, in air and under poly(methyl methacrylate) (PMMA). Moderate radial dependencies were also found for NWs embedded in PMMA. Complementary emission anisotropy measurements yielded significant radial and dielectric environment sensitivities with statistically smaller ρemm values than ρexc. A moderate ρemm frequency dependence was observed for thin NWs in PMMA.

As an effort to further explore the possible complex oxide catalysts for methanol electrooxidation, a library of perovskites (ABO3; A = Ba, Ca, Sr, La; B = Fe, Ru) were synthesized and tested. A novel screening strategy, featuring energy-efficient and rapid solution combustion (SC) synthesis techniques in combination with a throughput catalyst activity testing method, was employed. It was demonstrated that most of these mixed-conductor complex perovskites with ruthenium on the B-site are promising candidates for the development of effective catalysts. A possible reaction pathway on the perovskite (e.g., ARuO3) surface is proposed in analogy to the well-established reaction mechanism of methanol oxidation on a Pt surface. Additional experiments by using ethanol and formic acid as fuels were conducted to give further insights on the proposed reaction pathway. Furthermore, composite perovskite−Pt compositions were also synthesized directly by the SC method for the design of multifunctional catalysts, where the optimum amount of noble metal was found to be ∼10 wt %. These novel catalysts, containing 4 times less platinum, display comparable apparent catalytic activity to standard Pt−Ru alloy. Structure and surface properties of these novel catalysts were also studied by using X-ray photoelectron spectroscopy and X-ray diffraction techniques. The above findings strongly suggest that the proposed approach for design of multifunctional catalysts is practical and effective.

An accurate gravimetric apparatus based on a contactless magnetic suspension microbalance was developed. This unit was used to measure the hydrogen storage capacity for a variety of carbon nanotubes (CNTs) at room temperature and hydrogen pressures up to 11.5 MPa. The results show that regardless of their synthesis methods, purities, and nanostructures all investigated CNT products possess relatively low hydrogen storage capacities (<0.2 wt %). For comparison, the adsorption characteristics of theses samples were also measured at a pressure of 0.1 MPa and liquid nitrogen temperature (approximately 77 K) by a conventional volumetric approach. The methodological aspects related to the accuracy of the hydrogen uptake measurements are also discussed.

Enhancements of third-order nonlinear optical response in the triplet excited state of finite open single-walled carbon nanotubes