RESUMEN
As-synthesized single-walled carbon nanotubes (SWCNTs) are a mixture of metallic and semiconducting tubes, and separation is essential to improve the performances of SWCNT-based electric devices. Our chemical sensor monitors the conductivity of an SWCNT network, wherein each tube is wrapped by an insulating metallosupramolecular polymer (MSP). Vapors of strong electrophiles such as diethyl chlorophosphate (DECP), a nerve agent simulant, can trigger the disassembly of MSPs, resulting in conductive SWCNT pathways. Herein, we report that separated SWCNTs have a large impact on the sensitivity and selectivity of chemical sensors. Semiconducting SWCNT (S-SWCNT) sensors are the most sensitive to DECP (up to 10000% increase in conductivity). By contrast, the responses of metallic SWCNT (M-SWCNT) sensors were smaller but less susceptible to interfering signals. For saturated water vapor, increasing and decreasing conductivities were observed for S- and M-SWCNT sensors, respectively. Mixtures of M- and S-SWCNTs revealed reduced responses to saturated water vapor as a result of canceling effects. Our results reveal that S- and M-SWCNTs compensate sensitivity and selectivity, and the combined use of separated SWCNTs, either in arrays or in single sensors, offers advantages in sensing systems.
RESUMEN
Nanoscale devices that are sensitive to measurement history enable memory applications, and memristors are currently under intense investigation for robustness and functionality. Here we describe the fabrication and performance of a memristor-like device that comprises a single TiO2 nanowire in contact with Au electrodes, demonstrating both high sensitivity to electrical stimuli and high levels of control. Through an electroforming process, a population of charged dopants is created at the interface between the wire and electrode that can be manipulated to demonstrate a range of device and memristor characteristics. In contrast to conventional two-terminal memristors, our device is essentially a diode that exhibits memristance in the forward bias direction. The device is easily reset to the off state by a single voltage pulse and can be incremented to provide a range of controllable conductance states in the forward direction. Electrochemical modification of the Schottky barrier at the electrodes is proposed as an underlying mechanism, and six-level memory operations are demonstrated on a single nanowire.
RESUMEN
Single crystal iron nanocubes are produced by simply heating a bilayer film. This surface energy driven growth (SEDG) method exploits the difference in surface energies of the components (γ(Fe) ~ 2.2 J m(-2) versus γ(Nd) ~ 0.7 J m(-2)) in the binary alloy Fe-Nd system to produce nanocubes of the higher energy Fe component. The dimensions of the cubes range from tens to hundreds of nanometers in size and can be controlled by changing the initial thickness of iron in the deposited Fe-Nd bilayer prior to annealing at 700 °C. The composition and structure of the nanocubes was confirmed by transmission electron microscopy analysis as single crystal bcc iron in the α-phase. The cubes were found to exist as core-shell structures with the α-phase encased by an intermetallic Fe-Nd phase, characteristic of the SEDG growth mechanism.
RESUMEN
Connectivity in metallic nanowire networks with resistive junctions is manipulated by applying an electric field to create materials with tunable electrical conductivity. In situ electron microscope and electrical measurements visualize the activation and evolution of connectivity within these networks. Modeling nanowire networks, having a distribution of junction breakdown voltages, reveals universal scaling behavior applicable to all network materials. We demonstrate how local connectivity within these networks can be programmed and discuss material and device applications.
