Selected Publications
Bottom-up fabrication using DNA is a promising approach for the creation of nanoarchitectures. Accordingly, nanomaterials with specific electronic, photonic, or other functions are precisely and programmably positioned on DNA nanostructures from a disordered collection of smaller parts. These self-assembled structures offer significant potential in many domains such as sensing, drug delivery, and electronic device manufacturing. This review describes recent progress in organizing nanoscale morphologies of metals, semiconductors, and carbon nanotubes using DNA templates. We describe common substrates, DNA templates, seeding, plating, nanomaterial placement, and methods for structural and electrical characterization. Finally, our outlook for DNA-enabled bottom-up nanofabrication of materials is presented.
Self-assembly nanofabrication is increasingly appealing in complex nanostructures, as it requires fewer materials and has potential to reduce feature sizes. The use of DNA to control nanoscale and microscale features is promising but not fully developed. In this work, we study self-assembled DNA nanotubes to fabricate gold nanowires for use as interconnects in future nanoelectronic devices. We evaluate two approaches for seeding, gold and palladium, both using gold electroless plating to connect the seeds. These gold nanowires are characterized electrically utilizing electron beam induced deposition of tungsten and four-point probe techniques. Measured resistivity values for 15 successfully studied wires are between 9.3 × 10−6 and 1.2 × 10−3 Ωm. Our work yields new insights into reproducible formation and characterization of metal nanowires on DNA nanotubes, making them promising templates for future nanowires in complex electronic circuitry.
We report on a large-area, high-aspect-ratio, carbon nanotube (CNT) forest structure produced at BYU acting as a window/separator for a hollow cathode EUV lamp. The structure has large-surface-area, high light trans-mission, and differential pumping. CNT fabrication allows for variable dimensions, which allows various EUV distributions and pressure gradients to be possible. Theory is presented for predicting such distributions and gradients. Several structures have been fabricated; their dimensions, properties, and predicted distributions and gradients are given.
DNA origami templated fabrication enables bottom-up fabrication of nanoscale structures from a variety of functional materials, including metal nanowires. We studied the impact of low temperature annealing on the morphology and conductance of DNA templated nanowires. Nanowires were formed by selective seeding of gold nanorods on DNA origami and gold electroless plating of the seeded structures. At low annealing temperatures (160° C for seeded-only and 180° C for plated) the wires broke up and separated into multiple, isolated islands. Through the use of polymer-constrained annealing, the island formation in plated wires was suppressed up to annealing temperatures of 210° C. Four-point electrical measurements showed that wires remained conductive after a polymer-constrained anneal at 200° C.
The fabrication and examination of a porous silica thin film, potentially for use as an insulating thin film, were investigated. A vertically aligned carbon nanotube (CNT) forest, created by chemical vapor deposition (CVD), was used as scaffolding to construct the porous film. Silicon was deposited on the CNT forest using low-pressure CVD (LPCVD) and then oxidized to remove the CNTs and convert the silicon to silica for electrical or thermal passivation (e.g., thermal barrier). Thermal conductivity was determined using a 1D heat-transfer analysis that equated radiative heat loss in a vacuum with conduction through the substrate and thin film stack. A comparison of the surface temperature differences between a sample film and a reference of comparable thermal resistance enabled determination of the increase in the thermal resistance and of the thermal conductivity of the films. For film thicknesses of approximately 55 μm, the cross-plane thermal conductivity was found to be 0.054–0.071 W m–1 K–1 over 378–422 K. This thermal conductivity value is in the range of other silica aerogels and consistent with the low gravimetric density of 0.15 g cm–3 for the samples. The film is also relatively smooth and flat, with an average arithmetic mean roughness of 1.04 μm.
DNA-based nanofabrication of inorganic nanostructures has potential application in electronics, catalysis, and plasmonics. Previous DNA metallization has generated conductive DNA-assembled nanostructures; however, the use of semiconductors and the development of well-connected nanoscale metal—semiconductor junctions on DNA nanostructures are still at an early stage. Herein, we report the first fabrication of multiple electrically connected metal—semiconductor junctions on individual DNA origami by location-specific binding of gold and tellurium nanorods. Nanorod attachment to DNA origami was via DNA hybridization for Au and by electrostatic interaction for Te. Electroless gold plating was used to create nanoscale metal—semiconductor interfaces by filling the gaps between Au and Te nanorods. Two-point electrical characterization indicated that the Au—Te—Au junctions were electrically connected, with current—voltage properties consistent with a Schottky junction. DNA-based nanofabrication of metal—semiconductor junctions opens up potential opportunities in nanoelectronics, demonstrating the power of this bottom-up approach.