UW Nanodevice Physics Lab   Current grant abstracts

 

Correlated-electron devices on the surface of vanadium dioxide

Army Research Office grant 56073-PH (April 09 -) PI: Cobden

We propose to study the electronic properties of the reduced surface of VO2 crystals and its potential as a substrate for direct patterning of nanoscale electronic devices.  During our recent work on VO2 nanobeams we found that a thin and stable conducting layer forms on their surface after storage or brief heating in an oxygen-free environment.  The layer probably constitutes a strongly correlated quasi-two-dimensional electron system, which can conveniently be modified and patterned with high accuracy by local oxidation or reduction of the surface.  In some cases it appears to exhibit a phase transition below 200 K, reminiscent of the behavior of lower oxides such as V2O3.  Our objectives will be to optimize the growth, tuning, quality and stabilization of this layer; to determine its structure, using e.g. transmission electron microscopy; to pattern it using scanning-probe, electron-beam or optical direct writing; to fabricate nanoscale conducting elements, wires and dots within it; to attempt to gate it; and to characterize the resulting devices by magnetotransport, scanning probe and optical measurements, from room down to liquid helium temperatures.  We think this system offers many possibilities for exploring and exploiting the combination of strong correlation effects and nanoscale phenomena.

 

Matter Adsorbed on Nanoscale Devices

NSF DMR grant 0907690 (June 09 -) PI: Vilches, co-PI: Cobden

This project will measure the properties and phases of matter in the form of a single layer of atoms or simple molecules deposited on one, two, or bundled single-walled carbon nanotubes. With already designed, constructed and tested very sensitive one- and two-suspended nanotube mechanical oscillators vibrating in the upper megahertz range to act as extremely sensitive mass balances (at the level of a few atoms), this project will measure mass adsorption isotherms using atoms from the He isotopes to Xe, and the interesting molecules of hydrogen, nitrogen and oxygen. Due to the pristine surface and very low mass of the suspended nanotubes, this project will map accurately phase boundaries, measure critical and tri-critical parameters of two-dimensional (2d) matter, study 2d to one-dimensional (1d) crossover behavior as a function of temperature and adsorbed mass, obtain excellent values of heats of adsorption for both classical and quantum mechanical monolayers, and study the effect of surface adsorbates on the electronic properties of the substrate, which may lead to the fabrication of new ultra sensitive matter specific detectors. For those systems of interest, this project will measure the crystalline structure and the phonon spectrum of the adsorbates through an international collaboration using the facilities in Grenoble, France. Graduate and undergraduate students participating are being trained in contemporary electronic, thermodynamic, scanning and scattering measurement techniques, all applicable to nanotechnology.

 

Intrinsic properties of correlated materials derived from combined nanoscale transport and ultrafast spatiotemporal imaging experiments

DoE BES grant DE-SC0002197 (July 09 -) PI: Cobden, co-PI: Raschke

The goal of this program is to study strongly correlated materials on the nanoscale by applying a combination of electrical measurements and new scanning near-field optical techniques to homogeneous single-domain nanoscale samples and microcrystalline films. One part of the project will be to construct a unique combined system for doing scattering-scanning near-field optical microscopy (s-SNOM) measurements and dc transport on sub-domain-size nanocrystals in a controlled environment, in magnetic and electric fields, and at a variable temperature. The main focus will be on materials which have domain structure in the bulk arising from long-range forces, either elastic, electric or magnetic, that compete with short-range electronic order. We have recently demonstrated the power of the approach in two systems: vanadium dioxide, which is famous for its metal-insulator transition; and manganites, which are a representative class of multiferroics. These materials serve as examples of binary and ternary correlated oxides, respectively, exhibiting phase transitions, submicron domains due to various kinds of interactions, and sensitivities to stoichiometry, doping and strain. We will continue and expand our investigations of these materials in nanoscale form, to uncover more of the properties of the homogeneous phases and the fundamental physics of the phase transitions occurring within them using dc transport and nano-IR, -Raman and -ultrafast s-SNOM. This will allow us to understand the way bulk properties emerge as domain structure and strain appear in larger samples. We will investigate ways to control the materialsí properties, for instance by tuning the synthesis in a feedback loop with the nano-analysis, modifying the oxidation state or doping at the surface after growth, or applying large electric fields and strain by building them into appropriate nanodevice structures. We will investigate new kinds of electronic and optoelectronic device action based on gate-switching of electronic phases or optically accessed magnetic memory. We will also transfer the techniques to other correlated materials having different kinds of electronic properties and applications, including newly available crystalline organic conductors, and other oxides such as cuprates, titanates, tungstates, and vanadates which are available in stable nanoscale crystal form from collaborators.