Crosstalk between nanotube devices: contact and channel effects

At reduced dimensionality, Coulomb interactions play a crucial role in determining device properties. While such interactions within the same carbon nanotube have been shown to have unexpected properties, device integration and multi-nanotube devices require the consideration of inter-nanotube interactions. We present calculations of the characteristics of planar carbon nanotube transistors including interactions between semiconducting nanotubes and between semiconducting and metallic nanotubes. The results indicate that inter-tube interactions affect both the channel behavior and the contacts. For long channel devices, a separation of the order of the gate oxide thickness is necessary to eliminate inter-nanotube effects. Because of an exponential dependence of this length scale on dielectric constant, very high device densities are possible by using high-k dielectrics and embedded contacts

Phase ordering and roughening on growing films

We study the interplay between surface roughening and phase separation during the growth of binary films. Already in 1+1 dimension, we find a variety of different scaling behaviors depending on how the two phenomena are coupled. In the most interesting case, related to the advection of a passive scalar in a velocity field, nontrivial scaling exponents are obtained in simulations.Comment: 4 pages latex, 6 figure

Interferometric determination of the s- and d-wave scattering amplitudes in 87^{87}Rb

We demonstrate an interference method to determine the low-energy elastic scattering amplitudes of a quantum gas. We linearly accelerate two ultracold atomic clouds up to energies of 1.2 mK and observe the collision halo by direct imaging in free space. From the interference between $s$- and $d$- partial waves in the differential scattering pattern we extract the corresponding phase shifts. The method does not require knowledge of the atomic density. This allows us to infer accurate values for the $s$- and d-wave scattering amplitudes from the zero-energy limit up to the first Ramsauer minimum using only the Van der Waals $C_{6}$ coefficient as theoretical input. For the $^{87}$Rb triplet potential, the method reproduces the scattering length with an accuracy of 6%.Comment: 4 pages, 3 figure

New biostratigraphic and chronostratigraphic data from the Sautou formation and adjacent strata (Cambrian, Givonne inlier, Revin group, Northern France) and some lithostratigraphic and tectonic implications

In the western part of the Givonne Inlier, the “Falizette” and the “Claire-Terne de la Borne” rivers exhibit sections described as belonging, in ascending order, to the La Chapelle (Rv2), Illy (Rv3) and Sautou (Rv4) Formations. The “Falizette” section yielded acritarchs of zone 4 (locally 4b) similar to assemblages observed earlier (Vanguestaine, 1978) in the “Givonne” and “ Hatrelle” valleys of the Givonne Inlier. In the “Terne de la Borne” section, the strata described as belonging to the Illy Formation and most part of the Sautou Formation, the latter in its type locality, provided acritarchs of zone 2 (and possibly 1) and do not correlate therefore with the Rv3 and the Rv4 of the Rocroi Inlier but with Rv2 (and possibly Rv1) of the same area. This correlation is reinforced by the observation in the sequence of a roo? ng slate seam, previously undescribed, a possible equivalent of the Peureux Member, characterizing the upper part of Rv1 in the Rocroi Inlier. Besides specimens pointing to an acritarch biozone 2 assemblage, the richest sample of the Sautou Formation also yielded rare examples of acritarch species which have not previously been recorded in Belgium or the surrounding areas. They are Adara alea, Celtiberium geminum, possibly Eliasum llaniscum, Multiplicisphaeridium martae and Retisphaeridium postae. The probable metazoan Ceratophyton vernicosum has also been observed. Compared to the well dated Newfoundland Cambrian succession, acritarch biozones 2 assemblages indicates a mid Middle Cambrian age. This new chronostratigraphic result not only allows a better calibration of the Belgian acritarch zonation with respect to the acritarch and trilobite international zonations but also con? rms our interpretation of the lithostratigraphic succession

Lifetime of dynamic heterogeneity in strong and fragile kinetically constrained spin models

Kinetically constrained spin models are schematic coarse-grained models for the glass transition which represent an efficient theoretical tool to study detailed spatio-temporal aspects of dynamic heterogeneity in supercooled liquids. Here, we study how spatially correlated dynamic domains evolve with time and compare our results to various experimental and numerical investigations. We find that strong and fragile models yield different results. In particular, the lifetime of dynamic heterogeneity remains constant and roughly equal to the alpha relaxation time in strong models, while it increases more rapidly in fragile models when the glass transition is approached.Comment: Submitted to the proceedings of the 6th EPS Liquid Matter Conference, Utrecht 2-6 July 200

Properties of short channel ballistic carbon nanotube transistors with ohmic contacts

We present self-consistent, non-equilibrium Green's function calculations of the characteristics of short channel carbon nanotube transistors, focusing on the regime of ballistic transport with ohmic contacts. We first establish that the band lineup at the contacts is renormalized by charge transfer, leading to Schottky contacts for small diameter nanotubes and ohmic contacts for large diameter nanotubes, in agreement with recent experiments. For short channel ohmic contact devices, source-drain tunneling and drain-induced barrier lowering significantly impact the current-voltage characteristics. Furthermore, the ON state conductance shows a temperature dependence, even in the absence of phonon scattering or Schottky barriers. This last result also agrees with recently reported experimental measurements.Comment: Nanotechnology, in pres