Chemical doping of large-area stacked graphene films for use as transparent, conducting electrodes

Graphene is considered a leading candidate to replace conventional transparent conducting electrodes because of its high transparency and exceptional transport properties. The effect of chemical p-type doping on graphene stacks was studied in order to reduce the sheet resistance of graphene films to values approaching those of conventional transparent conducting oxides. In this report, we show that large-area, stacked graphene films are effectively p-doped with nitric acid. The doping decreases the sheet resistance by a factor of 3, yielding films comprising eight stacked layers with a sheet resistance of 90 O/ at a transmittance of 80%. The films were doped either after all of the layers were stacked (last-layer-doped) or after each layer was added (interlayer-doped). A theoretical model that accurately describes the stacked graphene film system as a resistor network was developed. The model defines a characteristic transfer length where all the channels in the graphene films actively contribute to electrical transport. The experimental data shows a linear increase in conductivity with the number of graphene layers, indicating that each layer provides an additional transport channel, in good agreement with the theoretical model

Encoding molecular-wire formation within nanoscale sockets

(Figure Presented) Wire straits: Three-component molecular wires were constructed in situ by first assembling a monolayer of a bifunctional arene on the electrode surfaces, such that only one end of the molecule (thiol) reacts with the electrode. Then, a second molecule was used to chemically bridge the gap between the termini of the films. Coordination chemistry in this context provides a versatile method to reversibly form molecular-scale wires (see picture). EDTA = ethylenediaminetetraacetate. © 2007 Wiley-VCH Verlag GmbH & Co. KGaA.link_to_subscribed_fulltex

DNA-Directed Self-Assembly of Highly Ordered and Dense Single-Walled Carbon Nanotube Arrays

Single-walled carbon nanotubes (SWNT or CNT) have unique and well-known high-performance material properties that can enable revolutionary increases in the performance of electronic devices and architectures. However, fabrication of large-scale SWNT-based ICs is an enormously challenging, unsolved problem, and self-assembly is likely needed for critical steps. Over the past several years, methods have been introduced to created ordered carbon nanotube structures using DNA guided self-assembly. In this chapter, we briefly review the challenges involved in using DNA to assemble SWNT nanostructures, and then give detailed methods to assemble dense, aligned SWNT arrays. In particular, we discuss the preparation of DNA wrapped single-walled nanotubes (DNA-CNTs) using commercial carbon nanotube products that are suitable for electronics applications. Then, we discuss methods to characterize DNA-CNTs using fluid mode atomic force microscopy (AFM). Finally, we give detailed procedures for assembly of DNA-CNTs into dense parallel arrays via linker induced surface assembly (LISA)

Monolayer coverage and channel length set the mobility in self-assembled monolayer field-effect transistors

The mobility of self-assembled monolayer field-effect transistors (SAMFETs) traditionally decreases dramatically with increasing channel length. Recently, however, SAMFETs using liquid-crystalline molecules have been shown to have bulk-like mobilities that are virtually independent of channel length. Here, we reconcile these scaling relations by showing that the mobility in liquid crystalline SAMFETs depends exponentially on the channel length only when the monolayer is incomplete. We explain this dependence both numerically and analytically, and show that charge transport is not affected by carrier injection, grain boundaries or conducting island size. At partial coverage, that is when the monolayer is incomplete, liquid-crystalline SAMFETs thus form a unique model system to study size-dependent conductance originating from charge percolation in two dimensions.

Bottom-up organic integrated circuits

Self-assembly—the autonomous organization of components into patterns and structures—is a promising technology for the mass production of organic electronics. Making integrated circuits using a bottom-up approach involving self-assembling molecules was proposed in the 1970s. The basic building block of such an integrated circuit is the self-assembled-monolayer field-effect transistor (SAMFET), where the semiconductor is a monolayer spontaneously formed on the gate dielectric. In the SAMFETs fabricated so far, current modulation has only been observed in submicrometre channels, the lack of efficient charge transport in longer channels being due to defects and the limited intermolecular π–π coupling between the molecules in the self-assembled monolayers. Low field-effect carrier mobility, low yield and poor reproducibility have prohibited the realization of bottom-up integrated circuits. Here we demonstrate SAMFETs with long-range intermolecular π–π coupling in the monolayer. We achieve dense packing by using liquid-crystalline molecules consisting of a π-conjugated mesogenic core separated by a long aliphatic chain from a monofunctionalized anchor group. The resulting SAMFETs exhibit a bulk-like carrier mobility, large current modulation and high reproducibility. As a first step towards functional circuits, we combine the SAMFETs into logic gates as inverters; the small parameter spread then allows us to combine the inverters into ring oscillators. We demonstrate real logic functionality by constructing a 15-bit code generator in which hundreds of SAMFETs are addressed simultaneously. Bridging the gap between discrete monolayer transistors and functional self-assembled integrated circuits puts bottom-up electronics in a new perspective.