517 research outputs found
Plasmas and Controlled Nuclear Fusion
Contains reports on three research projects.U. S. Atomic Energy Commission (Contract AT(30-1)-3980
Graphene Oxidation: Thickness Dependent Etching and Strong Chemical Doping
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.Comment: 15 pages, 5 figure
Atmospheric Oxygen Binding and Hole Doping in Deformed Graphene on a SiO2 Substrate
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.Comment: 17 pages, 5 figure
Vibrational States of the Hydrogen Isotopes on Pd(111)
The ground and excited vibrational states for the three hydrogen isotopes on
the Pd(111) surface have been calculated. Notable features of these states are
the high degree of anharmonicity, which is most prominently seen in the weak
isotopic dependence of the parallel vibrational transition, and the narrow
bandwidths of these states, which imply that atomic hydrogen is localized on a
particular surface site on time scales of 100 picoseconds or more. Experiments
to resolve ambiguities concerning the present system are suggested.Comment: Surface Science Letters, 302, L305 (1994
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First results for a superconducting imaging-surface sensor array for magnetoencephalography
Magnetoencephalography (MEG) follows from the initial fundamental work of Cohen in 1968 and development by several groups, most notably at MIT and at NYU, based on the development of the Superconducting QUantum Interference Device (SQUID) using the Josephson effect. The SQUID`s incredible sensitivity to magnetic fields permits the measurement of the very weak magnetic fields emitted from the human brain due to intracellular neuronal currents. Current growth in MEG is dominated by multiple sensor arrays covering much of the head. These new large devices have primarily been developed and made commercially available by several companies including BTI in the US, CTF in Canada, and Neuromag in Finland. Large projects are also in place in Japan. These systems contain more than 100 sensors spaced at various intervals over the head using various configurations of magnetometers and gradiometers. The different designs available on the market are driven by factors such as detection efficiency, cost, and application. They now present a completely novel whole-head SQUID array system using a superconducting imaging-surface gradiometer concept derived at Los Alamos. Preliminary tests have demonstrated higher performance, lower noise, and additional shielding of background fields while using simpler fabrication techniques than existing whole-head MEG systems, which should reduce production costs
Plasmas and Controlled Nuclear Fusion
Contains research objectives and reports on three research projects.National Science Foundation (Grant GK-1165
Therapeutic androgen receptor ligands
In the past several years, the concept of tissue-selective nuclear receptor ligands has emerged. This concept has come to fruition with estrogens, with the successful marketing of drugs such as raloxifene. The discovery of raloxifene and other selective estrogen receptor modulators (SERMs) has raised the possibility of generating selective compounds for other pathways, including androgens (that is, selective androgen receptor modulators, or SARMs)
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