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Search Results: 1 - 10 of 95221 matches for " George W. Flynn "
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Atmospheric Oxygen Binding and Hole Doping in Deformed Graphene on a SiO2 Substrate
Sunmin Ryu,Li Liu,Stephane Berciaud,Young-Jun Yu,Haitao Liu,Philip Kim,George W. Flynn,Louis E. Brus
Physics , 2010, DOI: 10.1021/nl1029607
Abstract: Using micro-Raman spectroscopy and scanning tunneling microscopy, we study the relationship between structural distortion and electrical hole doping of graphene on a silicon dioxide substrate. The observed upshift of the Raman G band represents charge doping and not compressive strain. Two independent factors control the doping: (1) the degree of graphene coupling to the substrate, and (2) exposure to oxygen and moisture. Thermal annealing induces a pronounced structural distortion due to close coupling to SiO2 and activates the ability of diatomic oxygen to accept charge from graphene. Gas flow experiments show that dry oxygen reversibly dopes graphene; doping becomes stronger and more irreversible in the presence of moisture and over long periods of time. We propose that oxygen molecular anions are stabilized by water solvation and electrostatic binding to the silicon dioxide surface.
High-Resolution Scanning Tunneling Microscopy Imaging of Mesoscopic Graphene Sheets on an Insulating Surface
Elena Stolyarova,Kwang Taeg Rim,Sunmin Ryu,Janina Maultzsch,Philip Kim,Louis E. Brus,Tony F. Heinz,Mark S. Hybertsen,George W. Flynn
Physics , 2007, DOI: 10.1073/pnas.0703337104
Abstract: We present scanning tunneling microscopy (STM) images of single-layer graphene crystals examined under ultrahigh vacuum conditions. The samples, with lateral dimensions on the micron scale, were prepared on a silicon dioxide surface by direct exfoliation of single crystal graphite. The single-layer films were identified using Raman spectroscopy. Topographic images of single-layer samples display the honeycomb structure expected for the full hexagonal symmetry of an isolated graphene monolayer. The absence of observable defects in the STM images is indicative of the high quality of these films. Crystals comprised of a few layers of graphene were also examined. They exhibited dramatically different STM topography, displaying the reduced three-fold symmetry characteristic of the surface of bulk graphite.
Graphene Oxidation: Thickness Dependent Etching and Strong Chemical Doping
Li Liu,Sunmin Ryu,Michelle R. Tomasik,Elena Stolyarova,Naeyoung Jung,Mark S. Hybertsen,Michael L. Steigerwald,Louis E. Brus,George W. Flynn
Physics , 2008, DOI: 10.1021/nl0808684
Abstract: Patterned graphene shows substantial potential for applications in future molecular-scale integrated electronics. Environmental effects are a critical issue in a single layer material where every atom is on the surface. Especially intriguing is the variety of rich chemical interactions shown by molecular oxygen with aromatic molecules. We find that O2 etching kinetics vary strongly with the number of graphene layers in the sample. Three-layer-thick samples show etching similar to bulk natural graphite. Single-layer graphene reacts faster and shows random etch pits in contrast to natural graphite where nucleation occurs at point defects. In addition, basal plane oxygen species strongly hole dope graphene, with a Fermi level shift of ~0.5 eV. These oxygen species partially desorb in an Ar gas flow, or under irradiation by far UV light, and readsorb again in an O2 atmosphere at room temperature. This strongly doped graphene is very different than graphene oxide made by mineral acid attack.
Evolution of Diabetic Maculopathy from Marked Exudation to Subretinal Fibrosis: Clinical and Spectral Domain Optical Coherence Tomography Features  [PDF]
Daniel S. Churgin, Jonathan H. Tzu, Harry W. Flynn
Open Journal of Ophthalmology (OJOph) , 2015, DOI: 10.4236/ojoph.2015.54025
Abstract: Diabetic maculopathy with marked exudation may lead to subretinal fibrosis. Two patients observed over multiple years evolved from macular exudation into subretinal fibrosis with severe visual loss. Spectral domain optical coherence tomography and color photographs document the clinical changes.
A Retrospective Renal Study from a Lupus Vasculitis Clinic  [PDF]
Gaurav Singh, Lauren White, Patrick Flynn, Sajan Thomas, Lakshmanan Jeyaseelan, Mani Thenmozhi, George John, Paul Kubler, D. Ranganathan
Open Journal of Nephrology (OJNeph) , 2015, DOI: 10.4236/ojneph.2015.53012
Abstract: Aim: In July 2009, a combined Renal Rheumatology Lupus Vasculitis (RRLV) clinic, the first of its kind for adult patients in Australia, was started at Royal Brisbane & Women’s Hospital. This is an audit of progression of renal disease to assess if patients attending this clinic had comparable results to published studies of similar cohorts with lupus Nephritis (LN) and vasculitis. Methods: We conducted a retrospective audit of all the patients who attended this clinic from July 2009 to October 2013. There were 33 patients followed up in the vasculitis group and 36 in the LN group. Patients with other connective tissue disorders were excluded from the analysis as the numbers were insignificant. Results: The mean estimated glomerular filtration rate of vasculitis and LN patients improved from 32.06 to 45.82 ml/min/1.73m2 and 62.42 to 65.53 ml/min/1.73m2 respectively. The mean urine protein/creatinine ratio of vasculitis and LN patients improved from 420 to 85 and 406 to 70 respectively. No patients died in either group. One vasculitis and two LN patients required maintenance dialysis. Three LN patients underwent renal transplantation. Conclusion: The results show excellent patient and renal survival and support the concept of a combined renal rheumatology clinic in managing renal disease from systemic connective tissue disorders.
Pharmacotherapies for Diabetic Retinopathy: Present and Future
Stephen G. Schwartz,Harry W. Flynn Jr.
Experimental Diabetes Research , 2007, DOI: 10.1155/2007/52487
Abstract: Diabetic retinopathy remains a major cause of worldwide preventable blindness. Measures to avoid blindness include medical management (control of blood sugar, blood pressure, and serum lipids) and ocular management (laser photocoagulation and pars plana vitrectomy). Adjunctive pharmacologic therapies (intravitreal triamcinolone acetonide and anti-vascular endothelial growth factor agents) have shown early promise in the treatment of both diabetic macular edema and proliferative diabetic retinopathy. Other medications under investigation include the fluocinolone acetonide implantable device, extended-release dexamethasone implant, oral ruboxistaurin, and intravitreal hyaluronidase.
Pars plana vitrectomy for primary rhegmatogenous retinal detachment
Stephen G Schwartz,Harry W Flynn Jr
Clinical Ophthalmology , 2008,
Abstract: Stephen G Schwartz, Harry W Flynn JrDepartment of Ophthalmology, Bascom Palmer Eye Institute, University of Miami Miller School of Medicine, Miami, FL, USAAbstract: Pars plana vitrectomy (PPV) is growing in popularity for the treatment of primary rhegmatogenous retinal detachment (RD). PPV achieves favorable anatomic and visual outcomes in a wide variety of patients, especially in pseudophakic RD. A growing number of clinical series, both retrospective and prospective, have demonstrated generally comparable outcomes comparing PPV and scleral buckling (SB) under a variety of circumstances. The Scleral Buckling Versus Primary Vitrectomy in Rhegmatogenous Retinal Detachment (SPR) study is a multicenter, randomized, prospective, controlled clinical trial comparing SB versus PPV. This study should provide useful guidelines in the future. At this time, the choice of SB versus PPV should be based on the characteristics of the RD, the patient as a whole, and the experience and preference of the individual retinal surgeon.Keywords: pars plana vitrectomy, rhegmatogneous retinal detachment, scleral buckling
Entanglement in Massive Coupled Oscillators
N. L. Harshman,W. F. Flynn
Physics , 2009,
Abstract: This article investigates entanglement of the motional states of massive coupled oscillators. The specific realization of an idealized diatomic molecule in one-dimension is considered, but the techniques developed apply to any massive particles with two degrees of freedom and a quadratic Hamiltonian. We present two methods, one analytic and one approximate, to calculate the interatomic entanglement for Gaussian and non-Gaussian pure states as measured by the purity of the reduced density matrix. The cases of free and trapped molecules and hetero- and homonuclear molecules are treated. In general, when the trap frequency and the molecular frequency are very different, and when the atomic masses are equal, the atoms are highly-entangled for molecular coherent states and number states. Surprisingly, while the interatomic entanglement can be quite large even for molecular coherent states, the covariance of atomic position and momentum observables can be entirely explained by a classical model with appropriately chosen statistical uncertainty.
The origin of the 3.4 micron feature in Wild 2 cometary particles and in ultracarbonaceous interplanetary dust particles
Graciela Matrajt,George Flynn,Don Brownlee,Dave Joswiak,Sasa Bajt
Physics , 2013, DOI: 10.1088/0004-637X/765/2/145
Abstract: We analyzed 2 ultra-carbonaceous interplanetary dust particles and 2 cometary Wild 2 particles with infrared spectroscopy. We characterized the carrier of the 3.4 micron band in these samples and compared its profile and the CH2/CH3 ratios to the 3.4 micron band in the diffuse interstellar medium (DISM), in the insoluble organic matter (IOM) from 3 primitive meteorites, in asteroid 24 Themis and in the coma of comet 103P/Hartley 2. We found that the 3.4 micron band in both Wild 2 and IDPs is similar, but different from all the other astrophysical environments that we compared to. The 3.4 micron band in IDPs and Wild 2 particles is dominated by CH2 groups, the peaks are narrower and stronger than in the meteorites, asteroid Themis, and the DISM. Also, the presence of the carbonyl group C=O at 1700 cm-1 (5.8 micron) in most of the spectra of our samples, indicates that these aliphatic chains have O bonded to them, which is quite different from astronomical spectra of the DISM. Based on all these observations we conclude that the origin of the carrier of the 3.4 micron band in IDPs and Wild 2 samples is not interstellar, instead, we suggest that the origin lies in the outermost parts of the solar nebula.
Visualizing Individual Nitrogen Dopants in Monolayer Graphene
Liuyan Zhao,Rui He,Kwang Taeg Rim,Theanne Schiros,Keun Soo Kim,Hui Zhou,Christopher Gutiérrez,S. P. Chockalingam,Carlos J. Arguello,Lucia Pálová,Dennis Nordlund,Mark S. Hybertsen,David R. Reichman,Tony F. Heinz,Philip Kim,Aron Pinczuk,George W. Flynn,Abhay N. Pasupathy
Physics , 2011, DOI: 10.1126/science.1208759
Abstract: In monolayer graphene, substitutional doping during growth can be used to alter its electronic properties. We used scanning tunneling microscopy (STM), Raman spectroscopy, x-ray spectroscopy, and first principles calculations to characterize individual nitrogen dopants in monolayer graphene grown on a copper substrate. Individual nitrogen atoms were incorporated as graphitic dopants, and a fraction of the extra electron on each nitrogen atom was delocalized into the graphene lattice. The electronic structure of nitrogen-doped graphene was strongly modified only within a few lattice spacings of the site of the nitrogen dopant. These findings show that chemical doping is a promising route to achieving high-quality graphene films with a large carrier concentration.
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