Determining concentration depth profiles in fluorinated networks by means of electric force microscopy

By means of electric force microscopy, composition depth profiles were measured with nanometric resolution for a series of fluorinated networks. By mapping the dielectric permittivity along a line going from the surface to the bulk, we were able to experimentally access to the fluorine concentration profile. Obtained data show composition gradient lengths ranging from 30 nm to 80 nm in the near surface area for samples containing from 0.5 to 5 wt. % F, respectively. In contrast, no gradients of concentration were detected in bulk. This method has several advantages over other techniques because it allows profiling directly on a sectional cut of the sample. By combining the obtained results with x-ray photoelectron spectroscopy measurements, we were also able to quantify F/C ratio as a function of depth with nanoscale resolution.     

Simulating the formation of sodium:electron tight-contact pairs: watching the solvation of atoms in liquids one molecule at a time

The motions of solvent molecules during a chemical transformation often dictate both the dynamics and the outcome of solution-phase reactions. However, a microscopic picture of solvation dynamics is often obscured by the concerted motions of numerous solvent molecules that make up a condensed-phase environment. In this study, we use mixed quantum/classical molecular dynamics simulations to furnish the molecular details of the solvation dynamics that leads to the formation of a sodium cation-solvated electron contact pair, (Na(+), e(-)), in liquid tetrahydrofuran following electron photodetachment from sodide (Na(-)). Our simulations reveal that the dominant solvent response is comprised of a series of discrete solvent molecular events that work sequentially to build up a shell of coordinating THF oxygen sites around the sodium cation end of the contact pair. With the solvent response described in terms of the sequential motion of single molecules, we are then able to compare the calculated transient absorption spectroscopy of the sodium species to experiment, providing a clear microscopic interpretation of ultrafast pump-probe experiments on this system. Our findings suggest that for solute-solvent interactions similar to the ones present in our study, the solvation dynamics is best understood as a series of kinetic events consisting of reactions between chemically distinct local structures in which key solvent molecules must be considered to be part of the identity of the reacting species.     

Low-temperature exfoliation of multilayer-graphene material from FeCl3 and CH3NO2 co-intercalated graphite compound

Microwave induced rapid decomposition of nitromethane at low temperature exfoliates the graphene sheets from the FeCl(3) and CH(3)NO(2) co-intercalated graphite compound without creating many defects and functional groups. This approach provides a scalable method for high-quality graphene materials via low-temperature exfoliation of graphite under mild chemical conditions.     

Nanochannel confinement: DNA stretch approaching full contour length

Fully stretched DNA molecules are becoming a fundamental component of new systems for comprehensive genome analysis. Among a number of approaches for elongating DNA molecules, nanofluidic molecular confinement has received enormous attentions from physical and biological communities for the last several years. Here we demonstrate a well-optimized condition that a DNA molecule can stretch almost to its full contour length: the average stretch is 19.1 μm ± 1.1 μm for YOYO-1 stained λ DNA (21.8 μm contour length) in 250 nm × 400 nm channel, which is the longest stretch value ever reported in any nanochannels or nanoslits. In addition, based on Odijk's polymer physics theory, we interpret our experimental findings as a function of channel dimensions and ionic strengths. Furthermore, we develop a Monte Carlo simulation approach using a primitive model for the rigorous understanding of DNA confinement effects. Collectively, we present a more complete understanding of nanochannel confined DNA stretching via the comparisons to computer simulation results and Odijk's polymer physics theory.     

Anomalous Phases in Cavity-Free 240 GHz Pulsed ENDOR Spectra of 1.44 GeV Xe-Irradiated LiF

Paramagnetic centers generated by swift heavy ion irradiation of LiF crystals could be identified as electrons trapped at regular anion vacancy sites (F centers). Well-resolved electron-nuclear double resonance (ENDOR) spectra resulting from the hyperfine interaction with ⁷Li and ¹⁹F nuclei located in six different shells could be recorded. In order to preserve the millimeter-sized crystals, a cavity-free setup was used for the ENDOR experiments at an electronic Larmor frequency of 240 GHz. Apparently even under conditions of extremely high local energy loss in the ion track, the local density of persistent F centers is still sufficiently low to prevent distortions of the ionic crystal. The spread of hyperfine coupling constants was less than 5 %. Neither in electron paramagnetic resonance (EPR) nor in ENDOR spectra there was evidence for different types of paramagnetic centers. When performing ENDOR by applying the radiofrequency pulse directly after the 3-pulse Mims-type microwave sequence, an anomalous ENDOR effect was observed. The observed “positive” and “negative” ENDOR response can be attributed to efficient hole and anti-hole formation in the inhomogeneously broadened EPR spectrum and can be used to determine the sign of hyperfine coupling constants.     

IndecomposableA-module summands inH * V which are unstable algebras

Letp be a prime and denote byA the modp Steenrod algebra. We determine the indecomposableA-module summands ofH*((ℤ/p)) ^d ;F _p which admit the structure of an unstableA-algebra. In fact, it turns out that this is equivalent to the problem of determining those indecomposableA-module summands which arise as the modp cohomology of a space (or even a classifying space of a finite group). We reduce this problem to one in modular representation theory, namely for whichd andp is the projective cover of the trivial one dimensional GL(d,F _p ) representationF _p a permutation module. Our solution of this latter problem makes use of the classification of subgroups of GL(d,F _p ) acting transitively on (F _p ) ^d \{0} and hence depends on the classification of finite simple groups (on Feit-Thompson's odd order theorem ifp=2).     

Self-assembled monolayers for liquid crystal alignment: simple preparation on glass using alkyltrialkoxysilanes

A simple procedure for the preparation of octadecylsiloxane self-assembled monolayers (SAMs) on float glass substrates is described. The method utilizes commercial octadecyltriethoxysilane, OTE: n-C₁₈H₃₇Si(OCH₂CH₃)₃, as the SAM precursor, with deposition accomplished in toluene solution using n-butylamine as catalyst. This synthetic approach obviates the use of the problematic trichlorosilanes typically required for the preparation of high quality SAMs, and is characterized by a wide 'process window,' utilizing off-the-shelf reagents without special handling.     

Partially Coherent Waves in Nonlinear Periodic Lattices

We study the propagation of partially coherent (random-phase) waves in nonlinear periodic lattices. The dynamics in these systems is governed by the threefold interplay between the nonlinearity, the lattice properties, and the statistical (coherence) properties of the waves. Such dynamic interplay is reflected in the characteristic properties of nonlinear wave phenomena (e.g., solitons) in these systems. While the propagation of partially coherent waves in nonlinear periodic systems is a universal problem, we analyze it in the context of nonlinear photonic lattices, where recent experiments have proven their existence.     

Studies on the determination of multiple numbers of experimental parameters 1. Preliminary study

Expressions are given for analytical extraction of parameters for polynomial and single relaxation experiments, and an indication is given of the application of the technique to multiple relaxation experiments. Examples are given for the cases of single and double relaxations. Hypothetical reference is made to time domain reflectometry.