Surface Polar Phonon Dominated Electron Transport in Graphene

The effects of surface polar phonons on electronic transport properties of monolayer graphene are studied by using a Monte Carlo simulation. Specifically, the low-field electron mobility and saturation velocity are examined for different substrates (SiC, SiO2, and HfO2) in comparison to the intrinsic case. While the results show that the low-field mobility can be substantially reduced by the introduction of surface polar phonon scattering, corresponding degradation of the saturation velocity is not observed for all three substrates at room temperature. It is also found that surface polar phonons can influence graphene electrical resistivity even at low temperature, leading potentially to inaccurate estimation of the acoustic phonon deformation potential constant

Unexpected Structures for Intercalation of Sodium in Epitaxial Graphene-SiC Interfaces

We show using scanning tunneling microscopy, spectroscopy, and ab initio calculations that several intercalation structures exist for Na in epitaxial graphene on SiC(0001). Intercalation takes place at room temperature and Na electron-dopes the graphene. It intercalates in-between single-layer graphene and the carbon-rich interfacial layer. It also penetrates beneath the interfacial layer and decouples it to form a second graphene layer. This decoupling is accelerated by annealing and is verified by direct Na deposition onto the interface layer. Our observations show that intercalation in graphene is fundamentally different than in graphite and is a versatile means of electronic control.Comment: 10 pages text, 2 pages, references, and 4 figure page

First principle theory of correlated transport through nano-junctions

We report the inclusion of electron-electron correlation in the calculation of transport properties within an ab initio scheme. A key step is the reformulation of Landauer's approach in terms of an effective transmittance for the interacting electron system. We apply this framework to analyze the effect of short range interactions on Pt atomic wires and discuss the coherent and incoherent correction to the mean-field approach.Comment: 5 pages, 3 figure

Macroscopic polarization and band offsets at nitride heterojunctions

Ab initio electronic structure studies of prototypical polar interfaces of wurtzite III-V nitrides show that large uniform electric fields exist in epitaxial nitride overlayers, due to the discontinuity across the interface of the macroscopic polarization of the constituent materials. Polarization fields forbid a standard evaluation of band offsets and formation energies: using new techniques, we find a large forward-backward asymmetry of the offset (0.2 eV for AlN/GaN (0001), 0.85 eV for GaN/AlN (0001)), and tiny interface formation energies.Comment: RevTeX 4 pages, 2 figure

First Principles Analysis of Electron-Phonon Interaction in Graphene

The electron-phonon interaction in monolayer graphene is investigated by using density functional perturbation theory. The results indicate that the electron-phonon interaction strength is of comparable magnitude for all four in-plane phonon branches and must be considered simultaneously. Moreover, the calculated scattering rates suggest an acoustic phonon contribution that is much weaker than previously thought, revealing the role of optical phonons even at low energies. Accordingly it is predicted, in good agreement with a recent measurement, that the intrinsic mobility of graphene may be more than an order of magnitude larger than the high values reported in suspended samples.Comment: 12 pages, 4 figure

Mt. Etna Volcanic Aerosol and Ash Retrievals using MERIS and AATSR Data

Envisat MERIS and AATSR data have been acquired in the framework of the Eurorisk-Preview project. The project addresses European civil protections and proposes to develop, at the European scale, new information services to support the risk management. In Italy one of the most important natural risks is due to the presence of volcanoes. Mt. Etna in Sicily, displays persistent activity, periodically interrupted by eruptions, which emit volcanic aerosol and ash to different altitudes in troposphere affecting the central Mediterranean area. In order to test the use of MERIS and AATSR data to derive emitted particles parameters as optical depth, effective radius and the ash mass of particles, the already developed remote sensing techniques has been adapted. MERIS and AATSR data acquired during the Mt. Etna 2002-2003 volcanic eruption has been chosen. The use of VIS and TIR bands of the two sensor demonstrates the potential to derive useful information on plume particles and to monitor the volcanic plume during eruption if frequent and high resolution data is available in near real time

Bottlenose Dolphins Mom-Calf Interactions over the First and Second Year of Life

As both wild and captive dolphin calves develop, they spend less time with their mothers and more time engaged in independent activities. In this study, the social development of six captive dolphin calves (Tursiops truncatus) were examined over the first and second year of life. Focal animal behavioral ethogram data were collected using a 30 second scan sampling technique. The predominant swim position and individual behaviors were recorded. There were a number of general developmental patterns: (1) an increase in the percentage of time that the calves engaged in solo swimming, (2) a decrease in infant position, and (3) a decrease in echelon position. The shift in primary swim position and increase in independent (solitary) behaviors exhibited over the study is consistent with past research on calf development. The basis for the difference each calf’s behavior could be a result of the experience or type of mother, the unique personalities in the calves, or a combination of both

Beluga Whales Socio-Sexual Interactions and Behaviors (Delphinapterus leucas)

Cetaceans are known for developing social relationships with each other by displaying various social and contact behaviors. Few studies have investigated the social interactions and types of contact behavior between belugas (Delphinapterus leucas). The present study focused on the frequencies of many social behaviors observed among four belugas (three males and one female) in the care of humans and the changes in behavior over an extended period of time. Continuous data were collection via video recordings over a four year period and were coded for social interactions. Preliminary analysis revealed that Male C was the most likely to initiate social interactions in this social group. It appears that the social interactions among the individuals may be somewhat stable over time. The findings of this study have implications for better understanding beluga social interactions of whales that are living under managed care