3,983 research outputs found
High mobility two-dimensional electron system on hydrogen-passivated silicon(111) surfaces
We have fabricated and characterized a field-effect transistor in which an
electric field is applied through an encapsulated vacuum cavity and induces a
two-dimensional electron system on a hydrogen-passivated Si(111) surface. This
vacuum cavity preserves the ambient sensitive surface and is created via room
temperature contact bonding of two Si substrates. Hall measurements are made on
the H-Si(111) surface prepared in aqueous ammonium fluoride solution. We obtain
electron densities up to cm and peak mobilities of
cm/V s at 4.2 K.Comment: to appear in Applied Physics Letter
Neutrino Scattering in a Magnetic Field
Motivated by the evidence for a finite neutrino mass we examine anew the
interaction of neutrinos in a magnetic field. We present the rate for radiative
scattering for both massless and massive neutrinos in the standard model and
give the corresponding numerical estimates. We also consider the effects
arising from a possible neutrino magnetic moment.Comment: 10 pages, 3 figures; Acknowledgements added 05.07.200
Integer quantum Hall effect on a six valley hydrogen-passivated silicon (111) surface
We report magneto-transport studies of a two-dimensional electron system
formed in an inversion layer at the interface between a hydrogen-passivated
Si(111) surface and vacuum. Measurements in the integer quantum Hall regime
demonstrate the expected sixfold valley degeneracy for these surfaces is
broken, resulting in an unequal occupation of the six valleys and anisotropy in
the resistance. We hypothesize the misorientation of Si surface breaks the
valley states into three unequally spaced pairs, but the observation of odd
filling factors, is difficult to reconcile with non-interacting electron
theory.Comment: 4 pages, 4 figures, to appear in Physical Review Letter
Temperature-dependent transport in a sixfold degenerate two-dimensional electron system on a H-Si(111) surface
Low-field magnetotransport measurements on a high mobility (mu=110,000
cm^2/Vs) two-dimensional (2D) electron system on a H-terminated Si(111) surface
reveal a sixfold valley degeneracy with a valley splitting <= 0.1 K. The
zero-field resistivity rho_{xx} displays strong temperature dependence for 0.07
< T < 25 K as predicted for a system with high degeneracy and large mass. We
present a method for using the low-field Hall coefficient to probe intervalley
momentum transfer (valley drag). The relaxation rate is consistent with Fermi
liquid theory, but a small residual drag as T->0 remains unexplained.Comment: 5 pages, 4 figures; revised and slightly shortened for publication
Global Health and Economic Impacts of Future Ozone Pollution
Abstract and PDF report are also available on the MIT Joint Program on the Science and Policy of Global Change website (http://globalchange.mit.edu/).We assess the human health and economic impacts of projected 2000-2050 changes in ozone pollution using the MIT Emissions Prediction and Policy Analysis-Health Effects (EPPA-HE) model, in combination with results from the GEOS-Chem global tropospheric chemistry model that simulated climate and chemistry effects of IPCC SRES emissions. We use EPPA to assess the human health damages (including acute mortality and morbidity outcomes) caused by ozone pollution and quantify their economic impacts in sixteen world regions. We compare the costs of ozone pollution under scenarios with 2000 and 2050 ozone precursor and greenhouse gas emissions (SRES A1B scenario). We estimate that health costs due to global ozone pollution above pre-industrial levels by 2050 will be ) and that acute mortalities will exceed 2 million. We find that previous methodologies underestimate costs of air pollution by more than a third because they do not take into account the long-term, compounding effects of health costs. The economic effects of emissions changes far exceed the influence of climate alone.United States Department of Energy, Office of
Science (BER) grants DE-FG02-94ER61937 and DE-FG02-93ER61677, the United States
Environmental Protection Agency grant EPA-XA-83344601-0, and the industrial and foundation
sponsors of the MIT Joint Program on the Science and Policy of Global Change
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