We report the synthesis of ultra-low-density three-dimensional macroassemblies of graphene sheets that exhibit high electrical conductivities and large internal surface areas. These materials are prepared as monolithic solids from suspensions of single-layer graphene oxide in which organic sol-gel chemistry is used to cross-link the individual sheets. The resulting gels are supercritically dried and then thermally reduced to yield graphene aerogels with densities approaching 10 mg/cm(3). In contrast to methods that utilize physical cross-links between GO, this approach provides covalent carbon bonding between the graphene sheets. These graphene aerogels exhibit an improvement in bulk electrical conductivity of more than 2 orders of magnitude (∼1 × 10(2) S/m) compared to graphene assemblies with physical cross-links alone (∼5 × 10(-1) S/m). The graphene aerogels also possess large surface areas (584 m(2)/g) and pore volumes (2.96 cm(3)/g), making these materials viable candidates for use in energy storage, catalysis, and sensing applications.

Nearly monodisperse hollow gold nanospheres (HGNs) with tunable interior and exterior diameters have been synthesized by sacrificial galvanic replacement of cobalt nanoparticles. It is possible to tune the peak of the surface plasmon band absorption between 550 and 820 nm by carefully controlling particle size and wall thickness. Cobalt particle size is tunable by simultaneously changing the concentration of sodium borohydride and sodium citrate, the reducing and capping agent, respectively. The thickness of the gold shell can be varied by carefully controlling the addition of gold salt. With successful demonstration of ensemble as well as single HGN surface-enhanced Raman scattering, these HGNs have shown great potential for chemical and biological sensing applications, especially those requiring nanostructures with near-IR absorption.

Laser-induced phototherapy is a new therapeutic use of electromagnetic radiation for cancer treatment. The use of targeted plasmonic gold nanoparticles can reduce the laser energy necessary for selective tumor cell destruction.

Developing three-dimensional (3D) graphene assemblies with properties similar to those individual graphene sheets is a promising strategy for graphene-based electrodes. Typically, the synthesis of 3D graphene assemblies relies on van der Waals forces for holding the graphene sheets together, resulting in bulk properties that do not reflect those reported for individual graphene sheets. Here, we report the use of sol-gel chemistry to introduce chemical bonding between the graphene sheets and control the bulk properties of graphene-based aerogels. Adjusting synthetic parameters allows a wide range of control over surface area, pore volume, and pore size, as well as the nature of the chemical cross-links (sp(2) vs sp(3)). The bulk properties of the graphene-based aerogels represent a significant step toward realizing the properties of individual graphene sheets in a 3D assembly with surface areas approaching the theoretical value of an individual sheet.

Hollow gold−silver double-shell nanospheres (AuAgHNSs) have been synthesized and their structural, optical, and single-particle surface-enhanced Raman scattering (SERS) properties characterized. The structure of these AuAgHNSs have been determined by transmission electron microscopy (TEM), revealing a uniform silver outer shell of approximately 3 nm deposited by seed-mediated growth on 28 ± 6.2 nm hollow gold nanospheres (AuHNSs). Their plasmon resonance combines the energies of both the silver and the gold shells, broadening the absorption profile, while their overall structure maintains a spherical shape. This property is useful for SERS and other applications that require small, spherical nanostructures and broad, tunable absorption. The mechanism of silver growth on AuHNSs and gold NPs is proposed as silver island formation before complete encapsulation. SERS studies of mercaptobenzoic acid (MBA) before and after silver deposition show a 4−5-fold enhancement over AuHNSs with little change in signal consistency, while solid NPs exhibit little or no signal improvement. A change in the relative peak intensity in the MBA Raman spectrum before and after silver coating is attributed to the effect of orientation and binding of thiols to gold and silver surfaces.

Low-density metal foams have many potential applications in electronics, energy storage, catalytic supports, fuel cells, sensors, and medical devices. Here, we report a new method for fabricating ultralight, conductive silver aerogel monoliths with predictable densities using silver nanowires. Silver nanowire building blocks were prepared by polyol synthesis and purified by selective precipitation. Silver aerogels were produced by freeze-casting nanowire aqueous suspensions followed by thermal sintering to weld the nanowire junctions. As-prepared silver aerogels have unique anisotropic microporous structures, with density precisely controlled by the nanowire concentration, down to 4.8 mg/cm and an electrical conductivity up to 51 000 S/m. Mechanical studies show that silver nanowire aerogels exhibit "elastic stiffening" behavior with a Young's modulus up to 16 800 Pa.

We report an aqueous solution-phase synthesis of continuous gold nanotubes with controllable shape, size, and length, tens of nm in diameter, a few nm in wall thickness, and up to 5 μm in length. Alignment is induced by magnetic field manipulation and synthetic parameters using cobalt nanoparticles as sacrificial templates. Because of the ease with which magnetic fields may be manipulated, precise placement should be not only possible, but also relatively simple as compared to other methods. This approach represents an important alternative for producing one-dimensional metal nanotube structures.

We present results of Monte Carlo simulations of random bond Potts models in two dimensions, for different numbers of Potts states, q. We introduce a simple scheme which yields continuous selfdual distributions of the interactions. As expected, we find multifractal behavior of the correlation functions at the critical point and obtain estimates of the exponent ηn for several moments, n, of the correlation functions, including typical (n → 0), average (n = 1) and others. In addition, for q = 8, we find that there is only a single correlation length exponent ν describing the correlation length away from criticality. This is numerically very close to the pure Ising value, ν = 1.