ABSTRACT

Writing Conductive Lines with Hot Tips The interface within devices between conductors, semiconductors, and insulators is usually created by stacking patterned layers of different materials. For flexible electronics, it can be advantageous to avoid this architectural constraint. Graphene oxide, formed by chemical exfoliation of graphite, can be reduced to a more conductive form using chemical reductants. Wei et al. (p. 1373 ) now show that layers of graphene oxide can also be reduced using a hot atomic force microscope tip to create materials comparable to those of organic conductors. This process can create patterned regions (down to 12 nanometers in width) that differ in conductivity by up to four orders of magnitude.

We report a process to form large-area, few-monolayer graphene oxide films and then recover the outstanding mechanical properties found in graphene to fabricate high Young's modulus ( =185 GPa), low-density nanomechanical resonators. Wafer-scale films as thin as 4 nm are sufficiently robust that they can be delaminated intact and resuspended on a bed of pillars or field of holes. From these films, we demonstrate radio frequency resonators with quality factors (up to 4000) and figures of merit ( f x Q>10(11)) well exceeding those of pure graphene resonators reported to date. These films' ability to withstand high in-plane tension (up to 5 N/m) as well as their high Q-values reveals that film integrity is enhanced by platelet-platelet bonding unavailable in pure graphite.

Charged molecular templates were created to direct the placement of single-layer graphite oxide (GO) sheets. The distribution of the GO sheets depended on the surface functionalization, background passivation, pH, and deposition time. Electrostatic attraction guides the templating of the GO sheets and, consequently, templating could be modulated by adjusting the pH of the deposition solution. In contrast to CNT immobilization, we find that the GO sheets do not adhere to the bare Au surface.

Here we describe the synthesis of Au nanorods directly on glass surfaces using seed-mediated deposition of Au from AuCl4- onto surface-attached 3-5 nm diameter Au nanoparticles (AuNPs) in the presence of cetyltrimethylammonium bromide (CTAB). The average length (200 nm to 1.2 microm) and aspect ratio (6-22) of the nanorods increases with increasing AuCl4- concentration. Short, low aspect ratio Au nanorods are manipulated with an atomic force microscopy (AFM) tip, while longer, high aspect ratio nanorods are bent and broken with the AFM tip.

This paper describes the use of atomic force microscopy to directly image surface-attached 3-5 nm diameter gold nanoparticle seeds before and after seed-mediated growth into gold nanorods (Au NRs) and other shapes (spheres, triangles, and hexagons). Results show that Au NRs form from seeds growing in either one or two directions. A direct correlation exists between seed diameter and NR diameter; small diameter seeds form small diameter NRs. However, correlation between seed diameter and nanostructure shape or NR length is less evident. We describe our results in terms of growth mechanisms proposed in the literature and discuss possible reasons for the large size dispersity observed for surface-grown Au NRs. A better understanding of Au NR and other metal and semiconductor one-dimensional (1D) growth processes is necessary to improve synthesis, tailor their properties, and utilize 1D nanostructures for useful technological applications.

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