Desorption kinetics and interaction of Xe with single-wall carbon nanotube bundles

We present a study on the kinetics of xenon desorption from single-wall carbon nanotube (SWNT) bundles using thermal desorption spectroscopy (TDS). TD-spectra from SWNT samples show a broad desorption feature peaked at significantly higher temperature than the corresponding low-coverage desorption feature on graphite. The observations are explained using a coupled desorption-diffusion (CDD) model, which allows the determination of the low-coverage Xe binding energy for adsorption on SWNT bundles, 27 kJ/mol. This energy is about 25% higher than the monolayer binding energy on graphite, 21.9 kJ/mol. By comparison with molecular mechanics calculations we find that this increase of the binding energy is consistent with adsorption in highly coordinated groove-sites on the external bundle surface.Comment: 8 pages, 5 figure

The Study of Charge Transport through Organic Thin Films: Mechanism, Tools, and Applications

Theoretical and experimental issues are still a probelems in molecular electronics. Different model for electron transport are discussed. Molecular junctions of different geometry are compared

Microfabricated Teflon Membranes for Low-Noise Recordings of Ion Channels in Planar Lipid Bilayers

We present a straightforward, accessible method for the fabrication of micropores with diameters from 2 to 800 μm in films of amorphous Teflon (Teflon AF). Pores with diameters ≤40 μm made it possible to record ion fluxes through ion channels in planar bilayers with excellent signal characteristics. These pores afforded: i), stable measurements at transmembrane voltages up to 460 mV; ii), recordings at low noise levels (0.4 pA rms at 4.3 kHz bandwidth); iii), recordings at high effective bandwidth (10.7 kHz); and iv), formation of multiple planar lipid bilayers in parallel. Microfabricated pores in films of Teflon AF made it possible to examine, experimentally and theoretically, the influence of the pore diameter on the current noise in planar bilayer recordings. Reducing the pore diameter below 40 μm mainly increased the stability of the planar bilayers, but had only a small effect on the level of the current noise. The low-noise properties of bilayer recordings on micropores in Teflon AF films were exploited to record the smallest conductance state of alamethicin (24 pS) at an unprecedentedly high bandwidth of 10.7 kHz

The Influnce of Defects in the Electrical Characteristics of Mercury Drop-Junctions: A Study of Self Assembled Monolayers (SAMs) of n-Alkanethilate on Rough and Smooth Silver

This paper compares the structural and electrical characteristics of self-assembled monolayers (SAMs) of n-alkanethiolates, SCn (n = 10, 12, 14), on two types of silver substrates: one used as-deposited (AS-DEP) by an electron-beam evaporator, and one prepared using the method of template-stripping. Atomic force microscopy showed that the template-stripped (TS) silver surfaces were smoother and had larger grains than the AS-DEP surfaces, and reflectance-absorbance infrared spectroscopy showed that SAMs formed on TS substrates were more crystalline than SAMs formed on AS-DEP substrates. The range of current densities, J (A/cm2), measured through mercury-drop junctions incorporating a given SAM on AS-DEP silver was, on average, several orders of magnitude larger than the range of J measured through the same SAM on TS silver, and the AS-DEP junctions failed, on average, 3.5 times more often within five current density-voltage (J-V) scans than did TS junctions (depending on the length of the alkyl chains of the molecules in the SAM). The apparent log-normal distribution of J through the TS junctions suggests that, in these cases, it is the variability in the effective thickness of the insulating layer (the distance the electron travels between electrodes) that results in the uncertainty in J. The parameter describing the decay of current density with the thickness of the insulating layer, , was either 0.57 Å-1 at V = +0.5 V (calculated using the log-mean of the distribution of values of J) or 0.64 Å-1 (calculated using the peak of the distribution of values of J) for the TS junctions; the latter is probably the more accurate. The mechanisms of failure of the junctions, and the degree and sources of uncertainty in current density, are discussed with respect to a variety of defects that occur within Hg-drop junctions incorporating SAMs on silver