Johnson, A T
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Publication Fabrication of Photonic Crystals with high refractive index(2007-03-09) Xu, Yongan; Yang, Shu; Moon, Jun Hyuk; Johnson, Alan T; Dan, Yaping; Perry, Joseph W; Adibi, Ali; Hotchkiss, Peter; Marder, Seth• Complete photonic bandgap • High contrast of refractive index (RI) • Polymer material with a low RI • Inorganic material with a higher RI, such as silicon, titania. • Fabrication of diamond-like PCs by MBIL, • Fabrication of high RI inorganic PCs via double templating, • Core-shell morphology of replica • Pinch-off problem • Development of combined level-surface to address pinch-off problem • Electrodeposition of titania 3D structure • Electrophoretic deposition of surface charged nanoparticlesPublication Gate Coupling to Nanoscale Electronics(2009-05-07) Datta, Sujit S.; Strachan, Douglas R.; Johnson, A.T. CharlieThe realization of single-molecule electronic devices, in which a nanometer-scale molecule is connected to macroscopic leads, requires the reproducible production of highly ordered nanoscale gaps in which a molecule of interest is electrostatically coupled to nearby gate electrodes. Understanding how the molecule-gate coupling depends on key parameters is crucial for the development of high-performance devices. Here we directly address this, presenting two- and three-dimensional finite-element electrostatic simulations of the electrode geometries formed using emerging fabrication techniques. We quantify the gate coupling intrinsic to these devices, exploring the roles of parameters believed to be relevant to such devices. These include the thickness and nature of the dielectric used, and the gate screening due to different device geometries. On the singlemolecule ( ~ 1 nm) scale, we find that device geometry plays a greater role in the gate coupling than the dielectric constant or the thickness of the insulator. Compared to the typical uniform nanogap electrode geometry envisioned, we find that nonuniform tapered electrodes yield a significant 3 orders of magnitude improvement in gate coupling. We also find that in the tapered geometry the polarizability of a molecular channel works to enhance the gate coupling.Publication Optimized Photolithographic Fabrication Process for Carbon Nanotube Devices(2011-04-14) Khamis, Samuel M.; Johnson, A. T. Charlie; Jones, R. A.We have developed a photolithographic process for the fabrication of large arrays of single walled carbon nanotube transistors with high quality electronic properties that rival those of transistors fabricated by electron beam lithography.Abuffer layer is used to prevent direct contact between the nanotube and the novolac-based photoresist, and a cleaning bake at 300C effectively removes residues that bind to the nanotube sidewall during processing. In situ electrical measurement of a nanotube transistor during a temperature ramp reveals sharp decreases in the ON-state resistance that we associate with the vaporization of components of the photoresist. Data from nearly 2000 measured nanotube transistors show an average ON-state resistance of 250 ± 100 kΩ. This new process represents significant progress towards the goal of highyield production of large arrays of nanotube transistors for applications including chemical sensors and transducers, as well as integrated circuit components.Publication Probing Spin-charge Relation by Magnetoconductance in One-dimensional Polymer Nanofibers(2012-10-12) Choi, A.; Kim, K. H; Hong, S. J; Goh, M.; Akagi, K.; Kaner, R. B; Johnson, A.T. Charlie; Kirova, N. N; Bonnell, Dawn A; Brazovskii, S. A; Mele, Eugene J.; Park, Y. WPolymer nanofibers are one-dimensional organic hydrocarbon systems containing conducting polymers where the nonlinear local excitations such as solitons, polarons, and bipolarons formed by the electron-phonon interaction were predicted. Magnetoconductance (MC) can simultaneously probe both the spin and charge of these mobile species and identify the effects of electron-electron interactions on these nonlinear excitations. Here, we report our observations of a qualitatively differentMC in polyacetylene (PA) and in polyaniline (PANI) and polythiophene (PT) nanofibers. In PA, the MC is essentially zero, but it is present in PANI and PT. The universal scaling behavior and the zero (finite)MC in PA (PANI and PT) nanofibers provide evidence of Coulomb interactions between spinless charged solitons (interacting polarons which carry both spin and charge).Publication Nanoenabled microelectromechanical sensor for volatile organic chemical detection(2009-06-05) Zuniga, Chiara; Rinaldi, Matteo; Khamis, Samuel M.; Johnson, A. T.; Piazza, GianlucaA nanoenabled gravimetric chemical sensor prototype based on the large scale integration of single-stranded DNA (ss-DNA) decorated single-walled carbon nanotubes (SWNTs) as nanofunctionalization layer for aluminum nitride contour-mode resonant microelectromechanical (MEM) gravimetric sensors has been demonstrated. The capability of two distinct single strands of DNA bound to SWNTs to enhance differently the adsorption of volatile organic compounds such as dinitroluene (simulant for explosive vapor) and dymethyl-methylphosphonate (simulant for nerve agent sarin) has been verified experimentally. Different levels of sensitivity (17.3 and 28 KHz µm^2/fg) due to separate frequencies of operation (287 and 450 MHz) on the same die have also been shown to prove the large dynamic range of sensitivity attainable with the sensor. The adsorption process in the ss-DNA decorated SWNTs does not occur in the bulk of the material, but solely involves the surface, which permits to achieve 50% recovery in less than 29 s.Publication DNA-decorated carbon nanotube-based FETs as ultrasensitive chemical sensors: Discrimination of homologues, structural isomers, and optical isomers(2012-04-17) Khamis, S. M.; Jones, R. A.; Johnson, A.T. Charlie; Preti, G.; Kwak, J.; Gelperin, A.We have explored the abilities of all-electronic DNA-carbon nanotube (DNA-NT) vapor sensors to discriminate very similar classes ofmolecules.We screened hundreds ofDNA-NT devices against a panel of compounds chosen because of their similarities. We demonstrated that DNA-NT vapor sensors readily discriminate between series of chemical homologues that differ by single methyl groups. DNA-NT devices also discriminate among structural isomers and optical isomers, a trait common in biological olfactory systems, but only recently demonstrated for electronic FET based chemical sensors.Publication DNA-decorated Graphene Chemical Sensors(2010-01-01) Lu, Ye; Goldsmith, Brett R; Kybert, Nicholas; Johnson, CharlieGraphene is a two-dimensional material with exceptional electronic properties and enormous potential for applications. Graphene’s promise as a chemical sensor material has been noted but there has been little work on practical chemical sensing using graphene, and in particular, how chemical functionalization may be used to sensitize graphene to chemical vapors. Here we show one route towards improving the ability of graphene to work as a chemical sensor by using single stranded DNA as a sensitizing agent. The resulting devices show fast response times, complete and rapid recovery to baseline at room temperature, and discrimination between several similar vapor analytes.Publication Graphene-Protein Bioelectronic Devices with Wavelength-Dependent Photoresponse(2012-01-18) Lu, Ye; Lerner, Mitchell B.; Qi, Zhengqing John; Mitala, Joseph J.; Discher, Bohdana M.; Lim, Jong Hsien; Johnson, A.T. CharlieWe implemented a nanoelectronic interface between graphene field effect transistors (FETs) and soluble proteins. This enables production of bioelectronic devices that combine functionalities of the biomolecular and inorganic components. The method serves to link polyhistidine-tagged proteins to graphene FETs using the tag itself. Atomic force microscopy and Raman spectroscopy provide structural understanding of the bio/nano hybrid; current-gate voltage measurements are used to elucidate the electronic properties. As an example application, we functionalize graphene FETs with fluorescent proteins to yield hybrids that respond to light at wavelengths defined by the optical absorption spectrum of the protein.Publication Response to “Comment on ‘Electrospun hybrid organic/inorganic semiconductor Schottky nanodiode’ ” [Appl. Phys. Lett. 89, 176101 (2006)](2006-10-25) Pinto, Nicolas J.; González, Rosana; Johnson, A.T. Charlie; MacDiarmid, Alan G.Publication Photoluminescence and Band Gap Modulation in Graphene Oxide(2009-03-19) Luo, Zhengtang; Vora, Patrick; Mele, Eugene J; Johnson, A.T. Charlie; Kikkawa, James MWe report broadband visible photoluminescence from solid graphene oxide, and modifications of the emission spectrum by progressive chemical reduction. The data suggest a gapping of the two-dimensional electronic system by removal of π-electrons. We discuss possible gapping mechanisms, and propose that a Kekule pattern of bond distortions may account for the observed behavior.