Bulletin of the American Physical Society
2009 APS March Meeting
Volume 54, Number 1
Monday–Friday, March 16–20, 2009; Pittsburgh, Pennsylvania
Session L27: Focus Session: Graphene Device and Applications II |
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Sponsoring Units: FIAP Chair: Marcus Freitag, IBM Room: 329 |
Tuesday, March 17, 2009 2:30PM - 3:06PM |
L27.00001: Graphene and chemically modified graphene sensors Invited Speaker: Molecular sensing via sp$^{2}$-bonded carbon nanomaterials is a promising research area in both nanoscience and nanotechnology. In general these materials are thermally and chemically stable, come in a variety of different geometries (spheres, tubes, and sheets), and are process compatible with conventional micro-lithographic techniques. In this talk we focus on atomically thin sheets of sp$^{2}$-bonded carbon, known as graphene, and discuss their sensing properties when exposed to chemical vapors. The remarkable physical properties of graphene-- from near ballistic electron conduction to ultra high stiffness ($>$ 5 times that of steel)-- make it a unique system to study both electronic and mechanical transduction modes. Finally, we demonstrate the utility of graphene-based films is greatly expanded after chemical functionalization. In this regard, chemically modified graphene (CMG) is emerging as a material system whose properties are complementary to nominally pure graphene for sensing applications. [Preview Abstract] |
Tuesday, March 17, 2009 3:06PM - 3:18PM |
L27.00002: Intrinsic Response of Graphene Vapor Sensors Ye Lu, Yaping Dan, Nicholas Kybert, Charlie Johnson Ye Lu$^{1}$, Yaping Dan$^{1}$, Nicholas J. Kybert$^{2}$, A. T. Charlie Johnson$^{1}$, $^{1}$\textit{University of Pennsylvania, USA }$^{2 }$\textit{University of Warwick, UK.}Graphene is a purely two-dimensional material that has extremely favorable chemical sensor properties. It is known, however, that conventional nanolithographic processing typically leaves a resist residue on the graphene surface, whose impact on the sensor characteristics of the system has not yet been determined. Here we show that the contamination layer both degrades the electronic properties of the graphene and masks graphene's intrinsic sensor responses. The contamination layer chemically dopes the graphene, enhances carrier scattering, and acts as an absorbent layer that concentrates analyte molecules at the graphene surface, thereby enhancing the sensor response. We demonstrate a cleaning process that verifiably removes the contamination on the device structure and allows the intrinsic chemical responses of graphene to be measured. Additionally, methods of functionalizing clean graphene device as high quality chemical vapor sensor are explored. Funding: JSTO DTRA and the Army Research Office Grant {\#}W911NF-06-1-0462, NSF-NSEC/NBIC DMR-0425780, REU program of the Laboratory for Research on the Structure of Matter (N.J.K.). [Preview Abstract] |
Tuesday, March 17, 2009 3:18PM - 3:30PM |
L27.00003: Single-layer Graphene Motion and Mass Sensors with Electrical Readout. Changyao Chen, Sami Rosenblatt, Kirill Bolotin, Horst Stormer, Philip Kim, Tony Heinz, James Hone We report for the first time the implementation of graphene electromechanical resonators that can detect their own motion. Suspended single-layer graphene field-effect transistors allow for electrical detection of the resonances while functioning as heterodyne mixers in a manner analogous to the operation of a radio receiver. Mechanical resonances occur in the 10-100 MHz range, can be lithographically-tailored, are tunable by tens of MHz, and have quality factors up to 200 while operated in vacuum at room temperature. Furthermore, by analyzing the frequency response of the resonators, we succeed in weighing both the pristine single-layer graphene and with a layer of organic material deposited on. [Preview Abstract] |
Tuesday, March 17, 2009 3:30PM - 4:06PM |
L27.00004: Electronic and magnetic functions of nanographene-based host-guest system Invited Speaker: The electronic structure of nanographene having open edges crucially depends on its edge shape. According to theoretical predictions, nanographene has nonbonding $\pi $-electron state (edge state) localized in zigzag edges. We investigated the electronic structure of graphene edges, the magnetism of the edge-state spins in nanographene and the effect of host-guest interaction on the magnetism. For magnetic investigations, we employed nanoporous activated carbon fiber (ACF) having a 3D disordered network of nanographite domains, each of which is a stack of 3-4 nanographene sheets. STM/STS investigations of hydrogen-terminated graphene edges confirm the presence of edge states around zigzag edges, in good agreement with theoretical works. The feature of the edge state depends on the detailed geometry of the edge structures. The magnetism of nanographene in ACF has a ferrimagnetism feature with a net magnetic moment, for which the cooperation of ferromagnetic intra-zigzag-edge and ferromagntic/antiferromagnetic inter-zigzag-edge interactions is responsible. Heat-treatment, which induces an insulator-metal transition, brings about spin glass state of the edge-state spins in the vicinity of the transition. Physisorption of guest species such as water, organic molecules, rare gas in the ACF nanopores generates a high-spin/low-spin magnetic switching phenomenon, in which a discontinuous reduction of the magnetic moment takes place. This is explained in terms of the strengthening of the inter-graphene-sheet antiferromagnetic interaction, which is induced by the mechanical compression of nanographite domains by the condensed guest molecules. The magnetic oxygen molecules physisorbed in the nanopores work seriously to decrease the magnetoresistance in ACF as a consequence of the interaction between the oxygen molecule spins and edge-state spins. [Preview Abstract] |
Tuesday, March 17, 2009 4:06PM - 4:18PM |
L27.00005: Investigation of Molecular Functionalizing Agents for Graphene Device Optimization. Damon Farmer, Yu-Ming Lin, Ali Afzali-Ardakani, Phaedon Avouris Due to its linear dispersion relation and the predicted chiral nature of its quasiparticles, graphene has become a material of intense experimental and theoretical investigation. There has been rapid progress in the fabrication and understanding of graphene devices. However, many key issues still need to be addressed in order to fully exploit graphene for technological applications. Here, we identify stable molecular compounds that can be used as dopants and functionalizing agents on graphene. As dopants, these compounds are used to both modify the potential profile in the channel region of graphene devices, and reduce parasitic resistances in these devices. As functionalizing agents, these compounds serve as nucleation sites for the uniform growth of thin high-$\kappa $ gate dielectrics, allowing for enhanced capacitive coupling with the graphene channel. The characteristics of graphene devices employing these molecular compounds will be presented, and problems associated with the implementation of these molecules in graphene devices will be discussed. [Preview Abstract] |
Tuesday, March 17, 2009 4:18PM - 4:30PM |
L27.00006: Fabrication and Chemical Doping of Carbon-based Transparent Electrodes George Tulevski, Ali Afzali The use of carbon-based materials (carbon nanotubes and graphene) as transparent electrodes has attracted enormous interest due to their high conductivities, transparency and potential as a lower cost alternative to traditional transparent electrode materials (i.e. Indium Tin Oxide). This talk will focus on using solution processes to suspend both carbon nanotubes and graphene flakes in solution and the fabrication of transparent electrodes from these solutions. Solutions were prepared using both surfactants and organic solvents, followed by purification to remove large aggregates and impurities. A variety of chemical dopants were then employed including metal salts and small organic molecules. The sheet resistance of the resultant films can be significantly reduced with chemical doping. [Preview Abstract] |
Tuesday, March 17, 2009 4:30PM - 4:42PM |
L27.00007: Atomic Layer Deposition (ALD) methods for fabricating graphene devices - theory and experiments Yvette Hancock, Samiul Haque, Maarit Karppinen, Asta K\"arkk\"ainen, Leo K\"arkk\"ainen, Reijo Lehteneimi, Pirjo Pasanen, Juho Per\"al\"a, Elina Sahramo, Karri Saloriutta ALD has the potential to be a well controlled method for coating and patterning graphene structures and making new generation devices. We have investigated the ALD of 5 nm thin coatings of high-k dielectric Al2O3 onto graphene, and have determined the selectivity of the chemical specific deposition, for example, to the edges or starting from defect sites. Experimentally, we see an affinity for Al2O3 to coat the edges of graphene, which is also supported by our ab initio calculations. The affinity of the Al2O3 coating with the edges of graphene allows us to make a mask, which could then be used to fabricate graphene nanoribbons of widths less than 50nm that are also gated. [Preview Abstract] |
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