Seven zero nine zero computer program for determination of precision lattice constants

Computer program for calculation of lattice parameters for cubic, tetragonal, and hexagonal crystals - magnesium oxide and aluminum oxid

XTH acts at the microfibril-matrix interface during cell elongation

Sulphorhodamine-labelled oligosaccharides of xyloglucan are incorporated into the cell wall of Arabidopsis and tobacco roots, and of cultured Nicotiana tabacum cells by the transglucosylase (XET) action of XTHs. In the cell wall of diffusely growing cells, the subcellular pattern of XET action revealed a 'fibrillar' pattern, different from the xyloglucan localization. The fibrillar fluorescence pattern had no net orientation in spherical cultured cells. It changed to transverse to the long axis when the cells started to elongate, a feature mirroring the rearrangements of cortical microtubules and the accompanying cellulose deposition. Interference with the polymerization of microtubules and with cellulose deposition inhibited this strong and 'fibrillar'-organized XET-action, whereas interference with actin-polymerization only decreased the intensity of enzyme action. Epidermal cells of a mutant with reduced cellulose synthesis also had low XET action. Root hairs (tip-growing cells) exhibited high XET-action over all their length, but lacked the specific parallel pattern. In both diffuse- and tip-growing cell types extraction of the incorporated fluorescent xyloglucans by a xyloglucan-specific endoglucanase reduced the fluorescence, but the 'fibrillar' appearance in diffuse growing cells was not eliminated. These results show that XTHs act on the xyloglucans attached to cellulose microfibrils. After incorporation of the fluorescent oligosaccharides, the xyloglucans decorate the cellulose microfibrils and become inaccessible to hydrolytic enzymes

First measurements of the index of refraction of gases for lithium atomic waves

We report here the first measurements of the index of refraction of gases for lithium waves. Using an atom interferometer, we have measured the real and imaginary part of the index of refraction $n$ for argon, krypton and xenon, as a function of the gas density for several velocities of the lithium beam. The linear dependence of $(n-1)$ with the gas density is well verified. The total collision cross-section deduced from the imaginary part is in very good agreement with traditional measurements of this quantity. Finally, as predicted by theory, the real and imaginary parts of $(n-1)$ and their ratio $\rho$ exhibit glory oscillations

Nanotrench for nano and microparticle electrical interconnects

We present a simple and versatile patterning procedure for the reliable and reproducible fabrication of high aspect ratio (10 4 ) electrical interconnects that have separation distances down to 20 nm and lengths of several hundreds of microns. The process uses standard optical lithography techniques and allows parallel processing of many junctions, making it easily scalable and industrially relevant. We demonstrate the suitability of these nanotrenches as electrical interconnects for addressing micro and nanoparticles by realizing several circuits with integrated species. Furthermore, low impedance metal-metal low contacts are shown to be obtained when trapping a single metal-coated microsphere in the gap, emphasizing the intrinsic good electrical conductivity of the interconnects, even though a wet process is used. Highly resistive magnetite-based nanoparticles networks also demonstrate the advantage of the high aspect ratio of the nanotrenches for providing access to electrical properties of highly resistive materials, with leakage current levels below 1 pA. © 2010 IOP Publishing Ltd

Improved setup for producing slow beams of cold molecules using a rotating nozzle

Intense beams of cold and slow molecules are produced by supersonic expansion out of a rapidly rotating nozzle, as first demonstrated by Gupta and Herschbach. An improved setup is presented that allows to accelerate or decelerate cold atomic and molecular beams by up to 500 m/s. Technical improvements are discussed and beam parameters are characterized by detailed analysis of time of flight density distributions. The possibility of combining this beam source with electrostatic fields for guiding polar molecules is demonstrated

Structure and conductance histogram of atomic-sized Au contacts

Many experiments have shown that the conductance histograms of metallic atomic-sized contacts exhibit a peak structure, which is characteristic of the corresponding material. The origin of these peaks still remains as an open problem. In order to shed some light on this issue, we present a theoretical analysis of the conductance histograms of Au atomic contacts. We have combined classical molecular dynamics simulations of the breaking of nanocontacts with conductance calculations based on a tight-binding model. This combination gives us access to crucial information such as contact geometries, forces, minimum cross-section, total conductance and transmission coefficients of the individual conduction channels. The ensemble of our results suggests that the low temperature Au conductance histograms are a consequence of a subtle interplay between mechanical and electrical properties of these nanocontacts. At variance with other suggestions in the literature, our results indicate that the peaks in the Au conductance histograms are not a simple consequence of conductance quantization or the existence of exceptionally stable radii. We show that the main peak in the histogram close to one quantum of conductance is due to the formation of single-atom contacts and chains of gold atoms. Moreover, we present a detailed comparison with experimental results on Au atomic contacts where the individual channel transmissions have been determined.Comment: 11 pages, 10 figures, version to be published in Phys. Rev. B. The paper has been thoroughly revised and several figures have been replaced by new one

Cluster-based density-functional approach to quantum transport through molecular and atomic contacts

We present a cluster-based density-functional approach to model charge transport through molecular and atomic contacts. The electronic structure of the contacts is determined in the framework of density functional theory, and the parameters needed to describe transport are extracted from finite clusters. A similar procedure, restricted to nearest-neighbor interactions in the electrodes, has been presented by Damle et al. [Chem. Phys. 281, 171 (2002)]. Here, we show how to systematically improve the description of the electrodes by extracting bulk parameters from sufficiently large metal clusters. In this way we avoid problems arising from the use of nonorthogonal basis functions. For demonstration we apply our method to electron transport through Au contacts with various atomic-chain configurations and to a single-atom contact of Al.Comment: 18 pages, 13 figure

Tilt-angle landscapes and temperature dependence of the conductance in biphenyl-dithiol single-molecule junctions

Using a density-functional-based transport method we study the conduction properties of several biphenyl-derived dithiol (BPDDT) molecules wired to gold electrodes. The BPDDT molecules differ in their side groups, which control the degree of conjugation of the pi-electron system. We have analyzed the dependence of the low-bias zero-temperature conductance on the tilt angle phi between the two phenyl ring units, and find that it follows closely a cos^2(phi) law, as expected from an effective pi-orbital coupling model. We show that the tilting of the phenyl rings results in a decrease of the zero-temperature conductance by roughly two orders of magnitude, when going from a planar conformation to a configuration in which the rings are perpendicular. In addition we demonstrate that the side groups, apart from determining phi, have no influence on the conductance. All this is in agreement with the recent experiment by Venkataraman et al. [Nature 442, 904 (2006)]. Finally, we study the temperature dependence of both the conductance and its fluctuations and find qualitative differences between the examined molecules. In this analysis we consider two contributions to the temperature behavior, one coming from the Fermi functions and the other one from a thermal average over different contact configurations. We illustrate that the fluctuations of the conductance due to temperature-induced changes in the geometric structure of the molecule can be reduced by an appropriate design.Comment: 9 pages, 6 figures; submitted to Phys. Rev.

Electronic and atomic shell structure in aluminum nanowires

We report experiments on aluminum nanowires in ultra-high vacuum at room temperature that reveal a periodic spectrum of exceptionally stable structures. Two "magic" series of stable structures are observed: At low conductance, the formation of stable nanowires is governed by electronic shell effects whereas for larger contacts atomic packing dominates. The crossover between the two regimes is found to be smooth. A detailed comparison of the experimental results to a theoretical stability analysis indicates that while the main features of the observed electron-shell structure are similar to those of alkali and noble metals, a sequence of extremely stable wires plays a unique role in Aluminum. This series appears isolated in conductance histograms and can be attributed to "superdeformed" non-axisymmetric nanowires.Comment: 15 pages, 9 figure