David W. Price

Molecular random access memory cell

Electronically programmable memory devices utilizing molecular self-assembled monolayers are reported. The devices exhibit electronically programmable and erasable memory bits compatible with conventional threshold levels and a memory cell applicable to a random access memory is demonstrated. Bit retention times >15 min have been observed.

Room-temperature negative differential resistance in nanoscale molecular junctions

Molecular devices are reported utilizing active self-assembled monolayers containing the nitroamine [2′-amino-4,4′-di(ethynylphenyl)-5′-nitro-1-benzenethiolate] or the nitro compound [4,4′-di(ethynylphenyl)-2′-nitro-1-benzenethiolate] as the active components. Both of these compounds have active redox centers. Current–voltage measurements of the devices exhibited negative differential resistance at room temperature and an on–off peak-to-valley ratio in excess of 1000:1 at low temperature.

Synthesis and preliminary testing of molecular wires and devices.

Presented here are several convergent synthetic routes to conjugated oligo(phenylene ethynylene)s. Some of these oligomers are free of functional groups, while others possess donor groups, acceptor groups, porphyrin interiors, and other heterocyclic interiors for various potential transmission and digital device applications. The syntheses of oligo(phenylene ethynylene)s with a variety of end groups for attachment to numerous metal probes and surfaces are presented. Some of the functionalized molecular systems showed linear, wire-like, current versus voltage (I(V)) responses, while others exhibited nonlinear I(V) curves for negative differential resistance (NDR) and molecular random access memory effects. Finally, the syntheses of functionalized oligomers are described that can form self-assembled monolayers on metallic electrodes that reduce the Schottky barriers. Information from the Schottky barrier studies can provide useful insight into molecular alligator clip optimizations for molecular electronics.

Fabrication approach for molecular memory arrays

We present an approach to tackle long-standing problems in contacts, thermal damage, pinhole induced short circuits and interconnects in molecular electronic device fabrication and integration. Our approach uses metallic nanowires as top electrodes to connect and interconnect molecular wires assembled on electrode arrays in crossbar architectures. Using this simple and reliable approach, we have revealed intriguing memory effects for several different molecular wires, and demonstrated their applications in molecular memory arrays. Our approach has great potential to be used for fast screening of molecular wire candidates and construction of molecular devices.

Electromagnetic wave properties of polymer blends of single wall carbon nanotubes using a resonant microwave cavity as a probe

A resonant microwave cavity operating in the TM010 mode was used to determine the microwave susceptibility of single walled carbon nanotubes (SWNT) that are blended in polymer matricies. The frequencies of the probe signal were 9.8, 11.4, and 35.93 GHz. Samples of 3%–19% blends of SWNT in polycarbonate were tested to determine the best blends for shielding of devices from microwaves at these frequencies. It appears that blends of 9%–11% are very effective in shielding the electric vector of electromagnetic waves. Both the electric vector and the magnetic vectors were probed by the process to determine the nature of coupling between the SWNTs and the applied fields. Some details are given about the apparatus design that enables computer collection and processing of the data to be achieved. An electronic differentiation technique was used to allow the second derivative of the cavity absorption profile to be displayed for precise measurement. Data are presented to show the relative microwave absorption for d...

Hack-a-vote: Security issues with electronic voting systems

In a quest for election legitimacy, officials are increasingly deploying direct recording electronic (DRE) voting systems. A project to assess their trustworthiness revealed both the ease of introducing bugs into such systems and the difficulty of detecting them during audits.

Molecular wires, switches, and memories.

Abstract: Design and measurements of molecular wires, switches, and memories offer an increased device capability with reduced elements. We report: Measurements on through‐bond electronic transport properties of nanoscale metal‐1,4‐phenylene diisocyanide‐metal junctions are reported, where nonohmic thermionic emission is the dominant process, with isocyanide‐Pd showing the lowest thermionic barrier of 0.22 eV; robust and large reversible switching behavior in an electronic device that utilizes molecules containing redox centers as the active component, exhibiting negative differential resistance (NDR) and large on‐off peak‐to‐valley ratio (PVR) are realized; erasable storage of higher conductivity states in these redox‐center‐containing molecular devices are observed; and a two‐terminal electronically programmable and erasable molecular memory cell with long bit retention time is demonstrated.

Improved and new syntheses of potential molecular electronics devices

New syntheses of ethyl and nitro substituted oligo(phenylene ethynylene)s (OPEs) have been developed. To further explore whether the presence of nitro functionality in OPEs leads to switching and memory capabilities, new nitro substituted OPEs have been designed and synthesized. An isatogen-based system, a structure that is isomeric to the nitro OPE, has been synthesized. Additionally, pyridine-based and chromium-based compounds have been synthesized. We surmise that redox reactions of these candidates may impart switching capabilities and electrochemical studies are shown. U-shaped OPEs were synthesized to inhibit leakage of metals deposited during formation of top contacts on self-assembled monolayers (SAMs). The OPEs contain either thiol-based moieties or isonitrile groups to enable formation of SAMs on metal substrates.

Biphenyl- and fluorenyl-based potential molecular electronic devices

Abstract New potential molecular electronics devices have been synthesized based on our knowledge of systems that we previously studied. Research has shown that simple molecular systems demonstrate negative differential resistance (NDR) and memory characteristics. The new molecules rely primarily on the redox properties of the compounds to improve upon the solid-state characteristics already observed. Electrochemical tests have been performed in order to evaluate the redox properties with the hope that the electrochemical results can be used as a predictive tool to evaluate the usefulness of those compounds in device configurations.

Accoutrements of a molecular computer: switches, memory components and alligator clips

Abstract Several second generation memory components consisting of oligo(phenylene ethynylene)s containing easily reducible functionalities consisting of either nitro or quinone cores have been synthesized for incorporation into molecular electronic devices. Additionally, two new types of contacts between organic compounds and a metal surface based on diazonium salts or pyridine have been synthesized and integrated into molecules for use in molecular electronic devices.