Bulletin of the American Physical Society
80th Annual Meeting of the APS Southeastern Section
Volume 58, Number 17
Wednesday–Saturday, November 20–23, 2013; Bowling Green, Kentucky
Session GE: Nanoscience and Condensed Matter III |
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Chair: Richard Haglund, Vanderbilt University Room: 5 |
Friday, November 22, 2013 1:30PM - 2:06PM |
GE.00001: Metal oxide/porous silicon nanocomposites for variable resistance devices Invited Speaker: Jeremy Mares Variable resistance electronic components have recently experienced growing interest owing to applications such as ReRAM technologies, memristor-based neuromorphic architectures and artificial neural networks. Such devices are typically nanometer-scale in size and require either high-resolution lithography or very refined thin-film growth techniques to realize devices with observably variable conductivity. Here, we present an elegant and economical method for achieving macroscopic (i.e., mm- or cm-scale) continuous-state variable conductivity devices using a metal oxide/porous silicon nanocomposite. We present the first observation of variable resistance in such nanocomposites (described colloquially as ``memristance''), and a mathematical model for the observed behavior is proposed which explains the time-varying, field-dependent conductivity modulation based on ionic defect migration in the metal oxide nanocrystallites. The variable conductivity phenomena observed are also shown to depend on the composition of the films. The model shows excellent agreement with experimental data and allows for estimation of ionic defect mobilities. Multicycle nonvolatility in the devices is shown to be on the order of 1000 s. [Preview Abstract] |
Friday, November 22, 2013 2:06PM - 2:42PM |
GE.00002: Effects of exciton-plasmon coupling in zinc oxide thin films and nanowires Invited Speaker: Richard Mu Zinc oxide with a direct bandgap of 3.35 eV has been studied extensively in the forms of thin films and nanostructures because of its potential applications in optoelectronics, sensing and nanolasers. Its optical emission spectrum is characterized by two principal emission bands: a sharp band-edge exciton emission line in the ultraviolet, and a broad emission band centered around 2.33 eV generally believed to come from a variety of donor-acceptor defects. In this talk, I will discuss recent experiments that show how to use plasmonic nanostructures in the form of rough metallic surfaces and metal nanoparticles to control the optical emission characteristics of ZnO thin films and nanowires. The principal results include: (1) The enhancement of the band-edge emission over the defect emission by a factor of nearly 100 even in highly defective thin films by coupling to surface plasmon polaritons; (2) femtosecond laser studies of emission from ZnO/MgO interfaces that show that the donor-acceptor pairs are found principally at surfaces and interfaces; and (3) recent results from ZnO/MgO core/shell nanowires that show how Fabry-Perot cavity modes in the nanowires experience differential band-edge emission rates depending on their coupling to the localized surface-plasmon resonance of Ag nanoparticles. In conclusion, the implications of this last finding for ultraviolet nanolasers will be discussed. [Preview Abstract] |
Friday, November 22, 2013 2:42PM - 3:18PM |
GE.00003: Tuning Electrical and Optical Properties of 2D Atomic Crystals Invited Speaker: A.K.M. Newaz Two-dimensional (2D) atomic crystals are recently discovered materials that are only atoms thick, and yet can span laterally over millimeters. The diverse family of such materials includes graphene, a semimetal with massless relativistic charge carriers, and monolayer molybdenum disulfide (MoS$_2$), a direct band gap semiconductor with strong spin-orbit interaction. Since every atom in these materials belongs to the surface, their physical properties are greatly affected by the immediate microenvironment. In my talk, I will demonstrate the wide tunability of the electrical and optical properties of both graphene and MoS2 and discuss some novel device applications. In the first part of the talk, I will demonstrate the use of graphene field effect transistors (FETs) in sensing different physical parameters of {\it{nanometer-thick}} interfacial liquid volumes. I will show that charge carrier scattering in graphene can be efficiently suppressed, i.e., the electronic quality can be improved, by placing graphene into a higher dielectric liquid environment. In the second part of my talk, I will focus on mononalyer MoS$_2$ and demonstrate that its optical properties, fluorescence quantum yield and transparency, can be tuned via electrical gating. In particular, we have observed a hundredfold modulation of excitonic photoluminescence from MoS$_2$ at room temperature by varying the electric fields within $\pm 1.7$ MV/cm. Our findings demonstrate that MoS$_2$ is the thinnest possible electroactive material. [Preview Abstract] |
Friday, November 22, 2013 3:18PM - 3:54PM |
GE.00004: Enhanced single molecule mass spectrometry via gold nanoclusters Invited Speaker: Joseph Reiner Single molecule nanopore sensing is a powerful tool that has been used to characterize the size, charge and structure of various analyte molecules. The technique employs an electrophysiology apparatus that measures the current through a single isolated nanopore. Typical amplifier bandwidths for this system are limited to ca. 100 kHz. This means the analyte molecules must remain in the nanopore for extended periods (relative to nanometer diffusion times) in order to be detectable. Methods for increasing the analyte/nanopore interaction times have generally relied on modifications to the nanopore and/or analyte systems. I will describe a new, passive, method that employs single gold clusters protected with glutathione ligands (Au$_{25}$SG$_{18})$ that diffuse into and are trapped within the nanopore volume. These negatively charged clusters are both characterized by the nanopore and used to increase the interaction time of a test analyte molecule (polyethylene glycol (PEG)) within the nanopore/cluster region. Initial results indicate greater than an order of magnitude increase in PEG residence times within an alpha hemolysin nanopore. I will describe these results and discuss the implications for improving the nanopore SMMS methodology. [Preview Abstract] |
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