ABSTRACT
Octahedral PbSe colloidal nanocrystals (NCs) are used to assemble a solid. Because of the special feature of the apexes of the octahedrons, the cross-sectional area of the inter-dot tunneling junctions is much smaller than that formed between spherical NCs. The inter-dot separation between NCs is easily adjusted by mild thermal treatment. Like a spherical NC-solid, the resistance of the octahedral NC-solid is exponentially dependent on the inter-dot separation. On the contrary, due to the difference in the cross-sectional area between the NCs, electron transport in the octahedral NC-solid does not follow the same model used for the explanation of electron transport in a spherical NC-solid. Through analyses of current-voltage and resistance-temperature behaviors, we have confirmed that the model of fluctuation-induced tunneling conduction fits very well with all of the data and explains the variation in the electrical properties of octahedral PbSe colloidal NC-solids after thermal annealing.
ABSTRACT
Bulk nanostructured materials are made from the assembly of octahedral PbSe nanocrystals. After thermal annealing, the artificial bulk demonstrates a large difference in behavior depending on the temperature, and a large variation of room-temperature resistivity of up to seven orders of magnitude. This variation originates from the high-indexed sharp edges of the octahedral nanocrystals. As the nanocrystals are arranged in the edge-to-edge configuration, which was observed in scanning electron microscopy images, the inter-nanocrystal capacitance is small due to the small parallel area between the nanocrystals. The small capacitance results in a high thermal fluctuation voltage and drives electron transport. The temperature-dependent resistivity and the electric field-dependent current are highly in agreement with the model of fluctuation-induced tunneling conduction. Thermal annealing reduces the inter-nanocrystal separation distance, creating a large variation in the electrical properties. Specifically, octahedral-shaped PbSe nanocrystals are employed in tailoring the electron transport in bulk nanostructured materials.
ABSTRACT
A novel hybrid surface-enhanced Raman scattering (SERS) substrate based on Au nanoparticles decorated inverse opal (IO) photonic crystal (PhC) is presented. In addition to the enhancement contributed from Au nanoparticles, a desired Raman signal can be selectively further enhanced by appropriately overlapping the center of photonic bandgap of the IO PhC with the wavelength of the Raman signal. Furthermore, the lattice structure of the IO PhC provides excellent control of the distribution of Au nanoparticles to produce SERS spectra with high uniformity. The new design of SERS substrate provides extra maneuverability for ultra-high sensitivity sensor applications.
