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Search Results: 1 - 10 of 96 matches for " Phaedon Avouris "
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Phonon and Electronic Non-radiative Decay of Excitons in Carbon Nanotubes
Vasili Perebeinos,Phaedon Avouris
Physics , 2008, DOI: 10.1103/PhysRevLett.101.057401
Abstract: We investigate theoretically the rates of non-radiative decay of excited semiconducting nanotubes by a variety of decay mechanisms and compare with experimental findings. We find that the multi-phonon decay (MPD) of free excitons is too slow to be responsible for the experimentally observed lifetimes. However, MPD lifetimes of localized excitons could be 2-3 orders of magnitude shorter. We also propose a new decay mechanism that relies on a finite doping of nanotubes and involves exciton decay into an optical phonon and an intraband electron-hole pair. The resulting lifetime is in the range of 5 to 100 ps, even for a moderate doping level.
Electrical and Mechanical Properties of Twisted Carbon Nanotubes
Alain Rochefort,Phaedon Avouris
Physics , 1999, DOI: 10.1103/PhysRevB.60.13824
Abstract: We have evaluated the energies required to twist carbon nanotubes (NTs), and investigated the effects of these distortions on their electronic structure and electrical properties. The computed distortion energies are high, indicating that it is unlikely that extensive twisting is the result of thermal excitation. Twisting strongly affects the electronic structure of NTs. Normally metallic armchair $(n,n)$ NTs develop a band-gap which initially scales linearly with twisting angle and then reaches a constant value. This saturation is associated with a structural transition to a flattened helical structure. The values of the twisting energy and of the band-gap are strongly affected by allowing structural relaxation in the twisted structures. Finally, we have used the Landauer-B{\"u}ttiker formalism to calculate the electrical transport of the metal-NT-metal system as a function of the NT distortion.
Exciton Ionization, Franz-Keldysh and Stark Effects in Carbon Nanotubes
Vasili Perebeinos,Phaedon Avouris
Physics , 2007, DOI: 10.1021/nl0625022
Abstract: We calculate the optical properties of carbon nanotubes in an external static electric field directed along the tube axis. We predict strong Franz-Keldysh oscillations in the first and second band-to-band absorption peaks, quadratic Stark effect of the first two excitons, and the field dependence of the bound exciton ionization rate for a wide range of tube chiralities. We find that the phonon assisted mechanism dominates the dissociation rate in electro-optical devices due to the hot optical phonons. We predict a quadratic dependence of the Sommerfeld factor on the electric field and its increase up to 2000% at the critical field of the full exciton dissociation.
Inelastic Scattering and Current Saturation in Graphene
Vasili Perebeinos,Phaedon Avouris
Physics , 2010, DOI: 10.1103/PhysRevB.81.195442
Abstract: We present a study of transport in graphene devices on polar insulating substrates by solving the Bolzmann transport equation in the presence of graphene phonon, surface polar phonon, and Coulomb charged impurity scattering. The value of the saturated velocity shows very weak dependence on the carrier density, the nature of the insulating substrate, and the low-field mobility, varied by the charged impurity concentration. The saturated velocity of 4 - 8 x 10^7 cm/s calculated at room temperature is significantly larger than reported experimental values. The discrepancy is due to the self-heating effect which lowers substantially the value of the saturated velocity. We predict that by reducing the insulator oxide thickness, which limits the thermal conductance, the saturated currents can be significantly enhanced. We also calculate the surface polar phonon contribution to the low-field mobility as a function of carrier density, temperature, and distance from the substrate.
Electron Interference Effects on the Conductance of Doped Carbon Nanotubes
Alain Rochefort,Phaedon Avouris
Physics , 2000,
Abstract: We investigate the effects of impurity scattering on the conductance of metallic carbon nanotubes as a function of the relative separation of the impurities. First we compute the conductance of a clean (6,6) tube, and the effect of model gold contacts on this conductance. Then, we compute the effect of introducing a single, two, and three oxygen atom impurities. We find that the conductance of a single-oxygen-doped (6,6) nanotube decreases by about 30 % with respect to that of the perfect nanotube. The presence of a second doping atom induces strong changes of the conductance which, however, depend very strongly on the relative position of the two oxygen atoms. We observe regular oscillations of the conductance that repeat over an O-O distance that corresponds to an integral number of half Fermi-wavelengths ($m\lambda_F/2$). These fluctuations reflect strong electron interference phenomena produced by electron scattering from the oxygen defects whose contribution to the resistance of the tube cannot be obtained by simply summing up their individual contributions.
Current Saturation and Surface Polar Phonon Scattering in Graphene
Vasili Perebeinos,Phaedon Avouris
Physics , 2009,
Abstract: We present a study of transport in graphene devices on polar insulating substrates using a tight-binding model. The mobility is computed using a multiband Boltzmann treatment. We provide the scaling of the surface polar phonon contribution to the low-field mobility with carrier density, temperature, and distance from the substrate. At high bias, we find that graphene self-heating effect is essential to account for the observed saturated current behavior. We predict that by optimizing the device cooling, the high bias currents can be significantly enhanced.
Graphene Plasmonics for Terahertz to Mid-Infrared Applications
Tony Low,Phaedon Avouris
Physics , 2014, DOI: 10.1021/nn406627u
Abstract: In recent years, we have seen a rapid progress in the field of graphene plasmonics, motivated by graphene's unique electrical and optical properties, tunabilty, long-lived collective excitation and their extreme light confinement. Here, we review the basic properties of graphene plasmons; their energy dispersion, localization and propagation, plasmon-phonon hybridization, lifetimes and damping pathways. The application space of graphene plasmonics lies in the technologically significant, but relatively unexploited terahertz to mid-infrared regime. We discuss emerging and potential applications, such as modulators, notch filters, polarizers, mid-infrared photodetectors, mid-infrared vibrational spectroscopy, among many others.
Impact Excitation by Hot Carriers in Carbon Nanotubes
Vasili Perebeinos,Phaedon Avouris
Physics , 2006, DOI: 10.1103/PhysRevB.74.121410
Abstract: We investigate theoretically the efficiency of intra-molecular hot carrier induced impact ionization and excitation processes in carbon nanotubes. The electron confinement and reduced screening lead to drastically enhanced excitation efficiencies over those in bulk materials. Strong excitonic coupling favors neutral excitations over ionization, while the impact mechanism populates a different set of states than that produced by photoexcitation. The excitation rate is strongly affected by optical phonon excitation and a simple scaling of the rate with the field strength and optical phonon temperature is obtained.
Mobility in semiconducting carbon nanotubes at finite carrier density
Vasili Perebeinos,J. Tersoff,Phaedon Avouris
Physics , 2005, DOI: 10.1021/nl052044h
Abstract: Carbon nanotube field-effect transistors operate over a wide range of electron or hole density, controlled by the gate voltage. Here we calculate the mobility in semiconducting nanotubes as a function of carrier density and electric field, for different tube diameters and temperature. The low-field mobility is a non-monotonic function of carrier density, and varies by as much as a factor of 4 at room temperature. At low density, with increasing field the drift velocity reaches a maximum and then exhibits negative differential mobility, due to the non-parabolicity of the bandstructure. At a critical density $\rho_c\sim$ 0.35-0.5 electrons/nm, the drift velocity saturates at around one third of the Fermi velocity. Above $\rho_c$, the velocity increases with field strength with no apparent saturation.
Interaction of solid organic acids with carbon nanotube field effect transistors
Christian Klinke,Ali Afzali,Phaedon Avouris
Physics , 2007, DOI: 10.1016/j.cplett.2006.08.090
Abstract: A series of solid organic acids were used to p-dope carbon nanotubes. The extent of doping is shown to be dependent on the pKa value of the acids. Highly fluorinated carboxylic acids and sulfonic acids are very effective in shifting the threshold voltage and making carbon nanotube field effect transistors to be more p-type devices. Weaker acids like phosphonic or hydroxamic acids had less effect. The doping of the devices was accompanied by a reduction of the hysteresis in the transfer characteristics. In-solution doping survives standard fabrication processes and renders p-doped carbon nanotube field effect transistors with good transport characteristics.
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