Field-directed Assembly Research Articles

Field-directed assembly of patchy anisotropic microparticles with defined shape

Electromagnetic fields can generate orientation-dependent, long range interactions between colloidal components that direct their into highly ordered structures, such as small ordered clusters, chains, and large crystalline lattices. While much effort has been devoted to exploring the assembly of spherical colloids, few reports have investigated the directed assembly of non-spherical particles with Janus or patchy morphologies. Here, we use photolithographic techniques to fabricate a wide range of anisotropically shaped patchy particles and follow their in liquid suspensions under the influence of electric and magnetic fields. We analyze the assembly of several types of patchy particles across a range of field parameters and fluid compositions, and report a number of distinct, well-ordered, architectures including cylindrical, prismatic, and staggered chains. The structures assembled from anisotropic patchy components provide a glimpse into the range of architectures that can be created by combining field directed with rationally designed particles. By using numerical simulations to model the electric and magnetic field interactions between these particles, we interpret the results of the assembly process and explain how they can be controlled by the position of the metal facet, the frequency (for AC fields), or magnetic susceptibility of the medium. The resulting structures, and similar ones produced through the field-directed assembly of patchy anisotropic particles, can possess unique electrical and optical properties and may have potential applications in a number of future technology applications such as microactuators, metamaterials and multiferroic materials.

ChemInform Abstract: Recent Advances in Large‐Scale Assembly of Semiconducting Inorganic Nanowires and Nanofibers for Electronics, Sensors and Photovoltaics

AbstractReview: 200 refs.

Recent advances in large-scale assembly of semiconducting inorganic nanowires and nanofibers for electronics, sensors and photovoltaics

Semiconducting inorganic nanowires (NWs), nanotubes and nanofibers have been extensively explored in recent years as potential building blocks for nanoscale electronics, optoelectronics, chemical/biological/optical sensing, and energy harvesting, storage and conversion, etc. Besides the top-down approaches such as conventional lithography technologies, nanowires are commonly grown by the bottom-up approaches such as solution growth, template-guided synthesis, and vapor-liquid-solid process at a relatively low cost. Superior performance has been demonstrated using nanowires devices. However, most of the nanowire devices are limited to the demonstration of single devices, an initial step toward nanoelectronic circuits, not adequate for production on a large scale at low cost. Controlled and uniform assembly of nanowires with high scalability is still one of the major bottleneck challenges towards the materials and device integration for electronics. In this review, we aim to present recent progress toward nanowire device assembly technologies, including flow-assisted alignment, Langmuir-Blodgett assembly, bubble-blown technique, electric/magnetic- field-directed assembly, contact/roll printing, planar growth, bridging method, and electrospinning, etc. And their applications in high-performance, flexible electronics, sensors, photovoltaics, bioelectronic interfaces and nano-resonators are also presented.

Crossbar heterojunction field effect transistors of CdSe:In nanowires and Si nanoribbons

Crossbar heterojunction arrays of n-CdSe:In nanowires (NWs) and p-Si nanoribbons (NRs) were built by ac electrical field-directed assembly. The junctions showed significant rectifying characteristics. With the p-Si NRs as gates, the junctions function as junction field effect transistors (JFETs) with high stability and reproducibility in performance. A small variation in gate voltage from −2 to −1 V was demonstrated to manipulate the current in n-CdSe:In NW channels by a factor near 103. The JFETs also showed a subthreshold swing value (67 mV/dec) approaching the theoretical limit (60 mV/dec), suggesting the great application potentials of the junctions in integrated nanoelectronics.

Electric field-directed assembly of gold and platinum nanowires from an electrolysis process

Gold and platinum nanowires have been grown on a silicon dioxide surface between two microfabricated electrodes from an electrolysis process under an AC signal with a DC offset. In the process, the anode electrode acted as a sacrificing layer and oxidized to metal ions. The metal ions were reduced to particles and aligned along the electric field forming nanowires connected with the cathode. Greater than 10 V and 12 V DC offset were required for growing gold and platinum nanowires, respectively. Other factors affecting the growth of the nanowires include frequency of applied bias and gap between the electrodes.

Integrating nanowires with substrates using directed assembly and nanoscale soldering

This paper describes a new methodology for integrating nanowires with micropatterned substrates using directed assembly and nanoscale soldering. Nanowires containing ferromagnetic nickel segments were fabricated by electrodeposition in nanoporous membranes. The nanowires were released by dissolution of the membrane and subsequently aligned relative to micropatterned substrates using magnetic field-directed assembly. After assembly, the wires were permanently bonded to the substrates using solder reflow to form low-resistance electrical contacts. This is the first demonstration of the use of nanoscale solder reflow to form low-resistance electrical interconnects between nanowires and substrates, and we demonstrated the utility of the strategy by fabricating a nanowire-based functional analog integrator.