An aqueous suspension of 5 vol% silicon (Si) nanoparticles was directionally solidified at substrate temperatures between −10 and −25 °C, resulting in colonies of aligned pure ice dendrites separated by interdendritic Si particles packed walls. Channels are created by sublimation of the dendrites, and the surrounding Si walls are densified by sintering. The resulting Si foams exhibit a 76 ± 2% macroporosity, with the width of the ice-templated channels and the Si walls decreasing with solidification temperature, from 106 to 60 µm and from 34 to 17 µm, respectively. Si walls show high surface roughness from inverse templating of short secondary ice dendrite arms.

Graphene oxide sheets have recently gained immense interest as a building block for graphene based materials and devices. Rapid developments have been made in the chemistry and applications of GO. However, assembly, too, plays a critical role in the final properties of bulk graphene based materials as it determines the microstructures of the 2D sheets. There is thus a pressing need for controllable assembly strategies. Based on the recent identification of the pH dependent surfactant-like behavior of GO sheets, we are now able to control the tiling morphologies of such sheets to produce thin films with either wrinkled or overlapped types of microstructures. This allows for the deconvolution of the effects of these two basic morphological features in the electrical and optical properties of the resulting thin films, providing a well-defined example of the processing-microstructure-properties relationship for this unique soft material building block.

Graphene oxide (GO) is a nonstoichiometric two-dimensional material obtained from the chemical oxidation and exfoliation of graphite, which has recently attracted intense research interest as a precursor for bulk production of graphene. GO has long been believed to be hydrophilic due to its dispersibility in water. Recent work in our group, however, has found that GO is actually a two-dimensional amphiphile; the edge of the sheet-like material is hydrophilic, while the basal plane of the material contains more hydrophobic graphitic nanodomains. To prove the concept, we demonstrate GO’s surface activity at an air-water interface, as well as its utility in dispersing insoluble aromatic materials such as toluene, graphite, and carbon nanotubes in water. As a colloidal surfactant which can be converted to a conducting material, GO presents unique possibilities for aqueous solution processing of organic electronic materials.

Graphitic nanomaterials such as graphene, carbon nanotubes (CNT), and C60 fullerenes are promising materials for energy applications because of their extraordinary electrical and optical properties. However, graphitic materials are not readily dispersible in water. Strategies to fabricate all-carbon nanocomposites typically involve covalent linking or surface functionalization, which breaks the conjugated electronic networks or contaminates functional carbon surfaces. Here, we demonstrate a facile surfactant-free strategy to create such all-carbon composites. Fullerenes, unfunctionalized single walled carbon nanotubes, and graphene oxide sheets can be conveniently co-assembled in water, resulting in a stable colloidal dispersion amenable to thin film processing. The thin film composite can be made conductive by mild thermal heating. Photovoltaic devices fabricated using the all-carbon composite as the active layer demonstrated an on-off ratio of nearly 106, an open circuit voltage of 0.59V, and a power conversion efficiency of 0.21%. This photoconductive and photovoltaic response is unprecedented among all-carbon based materials. Therefore, this surfactant-free, aqueous based approach to making all-carbon composites is promising for applications in optoelectronic devices.

Localized surface plasmon resonances (LSPR), collective electron oscillations in nanoparticles, are being heavily scrutinized for applications in chemical and biological sensing, as well as in prototype nanophotonic devices. This phenomenon exhibits an acute dependence on the particle’s size, shape, composition, and environment. The detailed characterization of the structure-function relationship of nanoparticles is obscured by ensemble averaging. Consequently, single-particle data must be obtained to extract useful information from polydisperse reaction mixtures. Recently, a correlated high resolution transmission electron microscopy (HRTEM) LSPR technique has been developed and applied to silver nanocubes. We report here a second generation of experiments using this correlation technique, in which statistical analysis is performed on a large number of single particles. The LSPR dependence on size, shape, material, and environment was probed using silver right bipyramids, silver cubes, and gold cubes. It was found that the slope of the dependence of LSPR peak on size for silver bipyramids increases as the edges become sharper. Also, a plasmon shift of 96 nm was observed between similar silver and gold cubes, while a shift of 26 nm was observed, for gold cubes, between substrates of refractive index (RI) of 1.5 and 2.05.