We report the first observation of anomalous diffusion in nanometer scale direct deposition processes utilizing dip-pen nanolithography (DPN). DPN permits quite general nanostructure patterns to be drawn on flat surfaces. Here we demonstrate experimentally, and discuss theoretically, the situation in which the molecular ink in DPN binds weakly to the surface. We observe, for the weak-binding case of 1-dodecylamine on mica, that anomalous diffusion occurs, leading to nearly fractal deposition patterns.

High-performance single-wall carbon nanotube field-effect transistors (SWNT-FETs) are fabricated using directed assembly and mass-produced carbon nanotubes (CNTs). These FETs exhibit operating characteristics comparable to state-of-the-art devices, and the process provides a route to large-scale functional CNT circuit assembly that circumvents problems inherent in processes relying on chemical vapor deposition (CVD). Furthermore, the integration of hydrophobic self-assembled monolayers (SAMs) in the device structure eliminates the primary source of gating hysteresis in SWNT-FETs, which leads to hysteresis-free FET operation while exposing unmodified nanotube surfaces to ambient air.Carbon nanotubes have remarkable physical and electrical properties that distinguish them as ideal components for nano-and molecular electronics 1 . Efforts devoted to incorporating them in device fabrication are probably best highlighted by progress in FETs 2-7 , which are fundamental to many nanotube-based applications from computing to sensing. So far, however, most high-performance 1 CNT-FETs have been fabricated using SWNTs grown on-substrate via CVD, while devices produced through 'directed assembly' and/or utilizing mass-produced have tried to keep pace. Nevertheless, CVD tends to produce large-diameter, small bandgap nanotubes, and the high-temperatures involved in the growth process often preclude integration with pre-existing circuit structures. For such reasons, high-performance FETs made by procedures more compatible with conventional semiconductor fabrication techniques are desirable and may represent a precursor to large-scale CNT circuit assembly for future industrial applications. Here, we demonstrate the directed-assembly 8,9 of SWNT-FETs using nanotubes grown by high-pressure decomposition of carbon monoxide (HiPCO), which produces large quantities of small-diameter, semiconducting SWNTs. These devices exhibit operating characteristics comparable with state-of-the-art FETs based on SWNTs from various sources, including CVD 10-12 .Notably, our devices can be operated free of gating hysteresis while exposing clean SWNT surfaces to ambient air. Previously, this hysteresis-free operation was possible only by encasing the FET in a polymer 13 , rendering it difficult for further circuit integration and inoperable for certain applications, such as sensing. Furthermore, since our method does not require any high-temperature processing steps, it is compatible with conventional semiconductor device fabrication processes.The SWNT-FETs are prepared by adapting a directed assembly technique 8 involving the controlled deposition of methyl-terminated (-CH 3 ) SAMs. These monolayers are placed either by microcontact printing or immersion to functionalize the metal electrodes and gate insulator, thereby creating a template for the subsequent placement and alignment of nanotubes. The schematic diagram depicting this procedure is shown in Figs. 1a-d. Five sets of source-drain electrodes each having a ~1-2 μm wide x 100 μm long gap ar...

We report the fabrication of arrays of single and multiple out-of-plane nanowire devices on a single substrate, an important step for the fabrication of novel three-dimensional devices and the integration of individually addressable nanowires onto current Si planar technology platforms. Vertical nanowire device fabrication can greatly increase device densities; however integrating such devices into arrays with registry to the substrate requires precise control over the number and position of the nanowires. Here we report the directed assembly of gold nanoparticle seeds into patterned arrays for the growth of nanowires using chemical recognition and electrophoretic methods. Chemical recognition provides highly reproducible control of the position and number of nanoparticles per pattern element and is shown to be in good agreement with a simple electrostatic model. Individually addressed out-of-plane, vapor-liquid-solid grown Ge nanowires with single and multiple nanowires per element are fabricated and electrically characterized.

Detection of reagent-free specific biomolecular interactions through sensing of nanoscopic magnetic labels provides one of the promising routes to biosensing with solid-state devices. In particular, Hall sensors based on semiconductor heterostructures have shown exceptional magnetic moment sensitivity over a large dynamic field range suitable for magnetic biosensing using superparamagnetic labels. Here we demonstrate the capability of such micro-Hall sensors to detect specific molecular binding using biotin-streptavidin as a model system. We apply dip-pen nanolithography to selectively biotinylate the active areas of InAs micro-Hall devices with nanoscale precision. Specific binding of complementarily functionalized streptavidin-coated superparamagnetic beads to the Hall crosses occur via molecular recognition, and magnetic detection of the assembled beads is achieved at room temperature using phase-sensitive micro-Hall magnetometry. The experiment constitutes the first unambiguous demonstration of magnetic detection of specific biomolecular interactions with semiconductor micro-Hall sensors, and the selective molecular functionalization and resulting localized bead assembly demonstrate the possibility of multiplexed sensing of multiple target molecules using a single device with an array of micro-Hall sensors.