Bulletin of the American Physical Society
2015 Annual Meeting of the APS Mid-Atlantic Section
Volume 60, Number 14
Friday–Sunday, October 23–25, 2015; Morgantown, West Virginia
Session A6: Nanostructures and Materials |
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Chair: Edward Flagg, West Virginia University Room: Waterfront Hotel Salon F |
Saturday, October 24, 2015 10:30AM - 10:42AM |
A6.00001: Understanding the intrinsic water wettability of graphite and MoS$_{\mathrm{2}}$ Andrew Kozbial, Zhiting Li, Haitao Liu, Lei Li Wetting behaviour of 2D materials is important for understanding fundamental surface properties along with practical use in application. Changes in wetting can negatively impact device performance because surface properties of 2D materials are strongly dependent on adhesive forces between the constituent materials and its interaction with water. Graphene and 2D transition metal dichalcogenides (TMDCs) are interesting candidates for ultrasensitive electronic and optoelectronic devices. The atomic thinness of 2D materials makes them particularly sensitive to slight changes in the surround environment. We have reported on the wetting of HOPG and graphene, showing that water contact angle (WCA) is strongly dependent on hydrocarbon contamination. Experimental evidence indicates that the clean, mildly-hydrophilic surface adsorbs airborne hydrocarbons resulting in the traditionally observed hydrophobicity. This effect has been extended to MoS$_{\mathrm{2}}$ (a TMDC) and can potentially be responsible for apparent hydrophobicity of many other materials. This talk will provide background on our results, their applicability in practical application, and our recent research results towards understanding the true, intrinsic WCA of 2D materials. [Preview Abstract] |
Saturday, October 24, 2015 10:42AM - 10:54AM |
A6.00002: Characterization of Diamond Surface Termination and Electrical Properties Mariela Georgieva, James Weil, A. Glen Birdwell, Pankaj Shah, Frank Crowne, Tony Ivanov To develop diamond surfaces that exhibit better electrical properties for high-power devices, we have studied the effects of the surface termination on starting materials from two different single crystal diamond substrate suppliers. In particular, effects of the initial steps in the diamond Field Effect Transistor (FET) fabrication process on the diamond surface properties were investigated. This was accomplished by using Atomic Force Microscopy (AFM), Raman spectroscopy, and Kelvin probe microscopy, which measure the topological, chemical and structural, and electrical properties, respectively. Topography is studied through sample roughness, chemical and structural information is made available by analysis of Raman spectral features, and the electrical properties are quantified through work function values. The different diamond terminations that are compared are post-polish (as received from substrate suppliers), post-oxygenation, and post-hydrogenation. [Preview Abstract] |
Saturday, October 24, 2015 10:54AM - 11:06AM |
A6.00003: Design of Scattering Scanning Near-field Optical Microscope Dustin Schrecongost The objective of this work is to construct a functional scattering type Scanning Near-Field Optical Microscope (s-SNOM), and to understand the working mechanisms. An s-SNOM is an instrument made of two separate instruments working in unison. One instrument is a scanning optical microscope focusing light onto a raster scanning sample surface. The second is an Atomic Force Microscope (AFM) operating in noncontact mode. The AFM uses a small probe that interacts with the sample surface to map out the topography of the surface. An s-SNOM uses both instruments simultaneously by focusing the light onto the probe of the AFM. This probe acts as a nano-antenna and confines the light allowing for light-matter interaction to be inferred below the resolution of the diffraction limit of light. This s-SNOM system is ultra-high vacuum compatible and variable temperature. It is efficient at collecting scattered light due to the focusing objective being an elliptical mirror which collects 360$^{\mathrm{o}}$ of light around the major axis. This s-SNOM system will be used for direct imaging of surface plasmons. Intended works are inducing surface plasmons on graphene and InSe thin films. Also dielectric properties of materials will be interpreted such as metal-insulator phase transitions in NbO$_{\mathrm{2}}$ and VO$_{\mathrm{2}}$. [Preview Abstract] |
Saturday, October 24, 2015 11:06AM - 11:42AM |
A6.00004: Screening of charge impurities and defects: alternative mechanisms for the detection of gases on graphene and nanotubes Invited Speaker: Jorge Sofo In gas detection with carbon nanotubes or graphene, the change in conductivity due to molecular adsorption has been attributed to changes in carrier density due to charge transfer. However, these explanation does not take into account several physical effects. 1) The counter-ions left after the charge transfer process lower the mobility and might compensate the effect of extra carriers. 2) The experimental results are not consistent with variations in the ionization potential or electron affinities of the adsorbates. We explore alternative explanations to this observations. One is based on the screening produced by the molecules on the charge impurities of the substrate. Given that the scattering with these impurities is the main limiting factor of the conductivity, the change in screening produced by the molecules has a substantial effect on the conductivity. Using the dielectric function of graphene at the RPA level and the impurity scattering in the first Born approximation. We explain the increase in conductivity. Another mechanism is the effect of lattice imperfections and their interaction with the detected molecules. Changes in the conductivity produced by vacancies, and chemisorbed molecules are calculated and correlated with the experimental measurement. [Preview Abstract] |
Saturday, October 24, 2015 11:42AM - 11:54AM |
A6.00005: Graphene/Oxide Heterostructure devices Weitao Dai, Cheng Cen Engineering graphene's properties in nanoscale with minimum material degradation and maximum flexibility is an outstanding challenge in graphene based technologies. Here we present a method targeting at on-demand tuning of graphene based on the integration of graphene and a novel complex oxide heterostructure. The recent development of complex oxides has raised the prospect for new classes of electronic devices. In particular, researchers have discovered a high-mobility two-dimensional electron gas forming at the interface between LaAlO3 (LAO) and SrTiO3 (STO). More interestingly, in samples with 3-unit-cell LAO film grown on STO substrate, a biased conducting atomic force microscope probe can locally and reversibly controls the interfacial metal-insulator transition. The close coupling of graphene with these programmable interfacial nanostructures in graphene/LAO/STO heterostructures presents numerous device opportunities. Samples with contacts addressing graphene and oxide interface separately were fabricated. CVD graphene was transferred using PMMA and then patterned. Si/LAO/STO substrates was designed and fabricated to solve graphene visibility problem. Transport experiments were performed on the hybrid bilayer conducting system and strong mutual gating effect was observed. In summary good quality graphene/LAO/STO transport samples were fabricated and characterized, which paved the way to the various graphene/LAO/STO based optical and electrical devices such as plasmon waveguide, photo emitting diode, etc. [Preview Abstract] |
Saturday, October 24, 2015 11:54AM - 12:06PM |
A6.00006: Detection and Modeling of Saturation Behavior of Eu Ion Emission in Eu-doped GaN under UV Excitation Natalie Hernandez, Ciara Kerckhove, Volkmar Dierolf Europium doped Gallium Nitride (GaN:Eu) has been recognized as a candidate for the red-emitting active layer in nitride-based light emitting diodes. To better comprehend and improve the excitation energy transfer from the excited GaN host to the Eu ion, we performed an extensive study of GaN:Eu and GaN co-doped with Eu and silicon (GaN:Eu,Si) which were grown under varied growth and temperature conditions. In these experiments, we investigated the optical accessibility of Eu ions within the GaN host by using above band gap excitation in which the Eu centers were excited indirectly after the creation of charge carriers and/or electron-hole pairs. By employing confocal spectroscopy, we were able to measure the saturation behavior of the Eu emission. From this data, the percentage of the Eu population that was optically accessible and the excitation efficiency of the energy transfer between the host material and the Eu ions were determined. We determined that only a few percent of the total Eu ion concentration were emitting. Our results suggest that most of the Eu ions within the GaN do not participate in photoluminescence. Further studies were undertaken to compare these results to the emission from InGaN, the current material used in commercialized blue and green LEDs. [Preview Abstract] |
Saturday, October 24, 2015 12:06PM - 12:18PM |
A6.00007: Switching field distributions in nanoisland arrays with perpendicular magnetic anisotropy Susan Kempinger, Robert Fraleigh, Paul Lammert, Vincent Crespi, Peter Schiffer, Nitin Samarth Experimental measurements of the magnetization switching process in dipole coupled arrays of single domain magnetic islands can provide important insights into the dynamical properties of interacting spin systems. Lithographically patterned arrays of interacting nanoscale islands of Co/Pt multilayers provide a useful model system in this context because the perpendicular magnetic anisotropy allows the use of diffraction-limited Kerr imaging to track the magnetization states of individual islands as a function of an external magnetic field. We are able to optically resolve, spatially isolate, and extract the switching field of each island in an array. The interaction strength is tuned by changing the geometry and the spacing between islands. Comparisons of data from strongly and weakly interacting arrays demonstrate the effect of the dipolar interactions. To further demonstrate the effectiveness of our local approach to measuring switching field distributions, we compare to the $\Delta $ H(M, $\Delta $ M) method, commonly used for bit-patterned media to separate the intrinsic and magnetic dipolar contributions to a switching field distribution. We show that our local measurements are in good agreement with these global measurements, and that interactions cause broadening of the distributions. This project was funded by the US Department of Energy, Office of Basic Energy Sciences, Materials Sciences and Engineering Division under Grant No. DE-SC0010778 [Preview Abstract] |
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