Flow-Assisted Self-Organization of Hybrid Membranes

Microfluidic flows are a powerful tool to drive reactions far from equilibrium and, thus, induce chemical selforganization. Studies of membrane formation in microfluidic devices have been limited to non-redox and purely inorganic reactions. Here, the formation of hybrid membranes at the interface of AgNO₃ and 3,3′,5,5′-tetramethylbenzidine solutions, which are steadily co-injected into a microfluidic device, is reported. The membrane thickening occurs in both directions and reveals oscillatory dynamics. The hybrid membrane mainly consists of hair-like Ag microstructures, Ag nanowires, and unbranched TMB–TMB²⁺ microfibers. Branched dendrite-like fibers form on the TMB side when the flow is stopped. These components were characterized with techniques including micro-Raman and energy dispersive X-ray spectroscopy as well as scanning electron microscopy. The effects of initial concentration ratios on the membrane thickening speed and its opaqueness were also studied.     

Discrete optimization methods for group model selection in compressed sensing

Mathematical Programming - In this article we study the problem of signal recovery for group models. More precisely for a given set of groups, each containing a small subset of indices, and for...     

A Re-evaluation of Factors Controlling the Nature of Complementary Hydrogen-Bonded Networks

The energy profiles of hydrogen-bonded heterocyclic aromatics have been decomposed into atomistic energy contributions using the Interacting Quantum Atoms (IQA) method. The resulting energy contributions have been sequenced by the Relative Energy Gradient (REG) approach to determine their influence upon the shape of these energy profiles. The results show inadequacies in Jorgensen's secondary interaction hypothesis (SIH). A novel method of finding a condensed analogy for the interaction between the molecules is presented. The findings of this work further doubt the validity of the SIH, and reinforce previous warnings against its misguided use.     

Imaging surfaces of nano‐scale roughness by atomic force microscopy with carbon nanotubes as tips: a comparative study

Accurate knowledge of the nanoroughness of surfaces is crucial for many applications related to optics, electronics or tribology. Although atomic force microscopy (AFM) can image surfaces with a nanometre spatial resolution, the finite size of standard tips means that pores, pits or grooves with dimensions similar to or smaller than the tip apex will not be accurately imaged. Furthermore, standard tips are made of silicon or silicon nitride and are prone to wear. Mitigation may arise from the availability of AFM tips with a carbon nanotube (CNT) at their foremost end. This study compares the imaging performance of ultrasharp Si tips, CNT AFM tips prepared by a Langmuir‐Blodgett (LB) technique, and of CNT AFM tips prepared by a chemical vapour deposition (CVD) technique. The free length of the CNT AFM tips is in the range 80–200 and 600–750 nm, respectively. A polycrystalline niobium film surface is imaged that shows nanoroughness. The measurements demonstrate that CNT AFM tips allow excellent imaging if the scan parameters are adjusted very carefully. Nevertheless, in some cases distortions are found. The measured average grain diameter is 19.9 ± 3.6 nm in the case of a CNT AFM tip made by the LB technique, and 18.0 ± 3.3 nm in the case of a CNT AFM tip made by CVD. In addition to cross‐sections of topography images, also the power spectral density (PSD) is analyzed. An empirical approach for the readout of the characteristic length is suggested that involves the first derivative of the decadic logarithm of the PSD. Copyright © 2011 John Wiley & Sons, Ltd.