In-situ transmission electron microscopy observations and molecular dynamics simulations of dislocation-defect interactions in ion-irradiated copper

An in-situ transmission electron microscopy straining technique has been used to investigate the dynamics of dislocation-defect interactions in ion-irradiated copper and the subsequent formation of defect-free channels. Defect removal frequently required interaction with multiple dislocations, although screw dislocations were more efficient at annihilating defects than edge dislocations were. The defect pinning strength was determined from the dislocation curvature prior to breakaway and exhibited values ranging from 15 to 175 MPa. Pre-existing dislocations percolated through the defect field but did not show long-range motion, indicating that they are not responsible for creating the defect-free channels and have a limited contribution to the total plasticity. Defect-free channels were associated with the movement of many dislocations, which originated from grain boundaries or regions of high stress concentration such as at a crack tip. These experimental results are compared with atomistic simulations of the interaction of partial dislocations with defects in copper and a dispersed-barrier-hardening crystal plasticity model to correlate the observations to bulk mechanical properties.     

Characterizing unusual metal substrates for gap‐mode tip‐enhanced Raman spectroscopy

In this article, the electromagnetic (EM) field in gap‐mode tip‐enhanced Raman spectroscopy (TERS) is investigated theoretically and experimentally for a range of commonly used and unusual metal and nonmetal substrates. By approaching a metal tip to a substrate, both form a coupled system that confines the EM field created at the tip apex. The influence of the substrate onto the EM field enhancement is observed in a top‐illumination gap‐mode TERS setup for different metal substrates. These include Au, the most commonly used substrate, and also a wide range of rarely or previously unused TERS substrates (Cu, Ag, Al, Pd, Pt, Ni, Ti, Mo, W, stainless steel, Al₂O₃, SiO₂). Self‐assembled monolayers of thiols and brilliant cresyl blue thin film samples are investigated experimentally on nine metal substrates, all showing considerable TERS enhancement. With finite difference time domain and finite element simulations used, the article provides a good estimate of the EM field enhancement for a wide range of substrates for users to estimate how well a substrate of choice will perform in a gap‐mode TERS experiment. The reduction in EM field strength |E²| compared with Au is less than an order of magnitude for many metals (Calculations: Cu 92%, Ag 81%, Ni 53%). This article experimentally shows that a wide variety of conductive substrates can be used, when one is willing to trade a fraction of the EM field enhancement. TERS was seen on all metal substrates including stainless steel, yet quantification was not always possible. These qualitative results were complemented with intensities from calculations. The wider variety of substrates will increase the applicability of TERS and evolve it one step further towards use in standard analytics. Copyright © 2012 John Wiley & Sons, Ltd.     

Aqueous Electrochemical Reduction of Carbon Dioxide and Carbon Monoxide into Methanol with Cobalt Phthalocyanine

Conversion of CO₂ into valuable molecules is a field of intensive investigation with the aim of developing scalable technologies for making fuels using renewable energy sources. While electrochemical reduction into CO and formate are approaching industrial maturity, a current challenge is obtaining more reduced products like methanol. However, literature on the matter is scarce, and even more for the use of molecular catalysts. Here, we demonstrate that cobalt phthalocyanine, a well‐known catalyst for the electrochemical conversion of CO₂ to CO, can also catalyze the reaction from CO₂ or CO to methanol in aqueous electrolytes at ambient conditions of temperature and pressure. The studies identify formaldehyde as a key intermediate and an unexpected pH effect on selectivity. This paves the way for establishing a sequential process where CO₂ is first converted to CO which is subsequently used as a reactant to produce methanol. Under ideal conditions, the reaction shows a global Faradaic efficiency of 19.5 % and chemical selectivity of 7.5 %.     

Development of an OPO system at 1.57 μm for integrated path DIAL measurement of atmospheric carbon dioxide

Active remote sensing is a promising technique to close the gaps that exist in global measurement of atmospheric carbon dioxide sources, sinks and fluxes. Several approaches are currently under development. Here, an experimental setup of an integrated path differential absorption lidar (IPDA) is presented, operating at 1.57 μm using direct detection. An injection seeded KTP-OPO system pumped by a Nd:YAG laser serves as the transmitter. The seed laser is actively stabilized by means of a CO₂ reference cell. The line-narrowed OPO radiation yields a high spectral purity, which is measured by means of a long path absorption cell. First measurements of diurnal variations of the atmospheric CO₂ mixing ratio using a topographic target were performed and show good agreement compared to simultaneously taken measurements of an in situ device. A further result is that the required power reference measurement of each laser pulse in combination with the spatial beam quality is a critical point of this method. The system described can serve as a testbed for further investigations of special features of the IPDA technique. PACS  42.65.Yj; 42.68.Wt; 92.60.hg     

On the Integration of Dielectrometry into Electrochemical Impedance Spectroscopy to Obtain Characteristic Properties of a Dielectric Thin Film

We demonstrate a novel impedimetric approach providing unprecedented insight into characteristic properties of dielectric thin films covering electrode surfaces. The concept is based on the joint interpretation of electrochemical impedance spectroscopy (EIS) together with dielectrometry (DEM) whose informative value is mutually interconnected. The advantage lies in the synergistic compensation of individual shortcomings adversely affecting conventional impedimetric analysis strategies relying exclusively on either DEM or the traditional EIS approach, which in turn allows a reliable determination of thickness and permittivity values. The versatility of the method proposed is showcased by an in-situ growth-monitoring of a nanoporous, crystalline thin film (HKUST-1) on an interdigitated electrode geometry.     

Chiral Ligands in Hypervalent Iodine Compounds: Synthesis and Structures of Binaphthyl-Based λ3-Iodanes

Several novel binaphthyl-based chiral hypervalent iodine(III) reagents have been prepared and structurally analysed. Various asymmetric oxidative reactions were applied to evaluate the reactivities and stereoselectivities of those reagents. Moderate to excellent yields were observed; however, very low stereoselectivities were obtained. NMR experiments indicated that these reagents are very easily hydrolysed in either chloroform or DMSO solvents leading to the limited stereoselectivities. It is concluded that the use of chiral ligands is an unsuccessful way to prepare efficient stereoselective iodine(III) reagents.