Large-scale fabrication of wafer-size colloidal crystals, macroporous polymers and nanocomposites by spin-coating

This paper reports a simple spin-coating technique for rapidly fabricating three types of technologically important materials--colloidal crystal, macroporous polymer, and polymeric nanocomposite, each with high crystalline qualities and wafer-scale sizes. Dispersion of monodisperse silica colloids in triacrylate monomers is spin-coated onto a variety of substrates. Shear-induced ordering and subsequent polymerization lead to the formation of three-dimensionally (3D) ordered colloidal crystals trapped inside a polymer matrix. The thickness of as-synthesized colloidal crystal-polymer nanocomposite is highly uniform and can be controlled simply by changing the spin speed and time. Selective removal of the polymer matrix and silica spheres lead to the formation of large-area colloidal crystals and macroporous polymers, respectively. The wafer-scale process is compatible with standard semiconductor microfabrication, as multiple micrometer-sized patterns can be created simultaneously for potential device applications. Normal-incidence transmission spectra in the visible and near-infrared regions show distinct peaks due to Bragg diffraction from 3D ordered structures. The spin-coating process opens a new route to the fundamental studies of shear-induced crystallization, melting and relaxation.     

Time-independent point-spread function for NMR microscopy.

The resolution of NMR microscopy is analyzed in terms of the point-spread function, PSF(r), and the equivalent k space modulation transfer function, MTF(k). The analysis is developed for NMR spin warp and projection reconstruction imaging experiments; however, the framework provided is quite general. Incoherent spin motion is analyzed to predict what limits, if any, on spatial resolution are imposed by diffusion. Previous estimates of diffusion limits at 1-5 microns were developed for specific imaging techniques, typically using a mean displacement argument. Although qualitatively correct, the quantitative predictions represent practical rather than fundamental limits. It is shown that diffusion-dependent "blurring" can be made arbitrarily small and that the practical limits are less stringent than previously thought. A major point illustrated by the PSF-MTF formulation is that the irreversible loss of coherence by randomly diffusing spins occurs faster than the physical displacement, thereby reducing their effect considerably on the frequency or phase of the net detected signal. The irreversible loss of signal due to diffusive motion will contribute to and possibly dominate the signal-to-noise limit of resolution. The resolution as measured by the width of the PSF and MTF for diffusion is shown to be independent of the signal acquisition time, and their functional forms allow selection of microscopic imaging parameters. An example of a three-dimensional spin-warp image of a green algae cell is shown with resolution of approximately 16 microns x 13 microns x 10 microns.     

MNDO calculations on boron–nitrogen derivatives of nonbenzenoid aromatics: I. The two fully boron–nitrogen-alternating isomers of “inorganic azulene”

Modified neglect of diatomic overlap (MNDO) calculations have been used to investigate the ground state properties of the two fully boron-nitrogen-alternating isomers of “inorganic azulene”: 1,3,4,6,8-pentaaza-2,3a, 5,7, 8a-pentaboraazulene ( 1 , 1,3,4,6,8-PAPBAZ) and 2,3a,5,7,8a-pentaaza-1,3,4,6,8-pentaboraazulene ( 2 , 2,3a,5,7,8a-PAPBAZ). Both molecules optimize to planar structures, have exothermic heats of formation (−194.4 kcal/mol and −161.4 kcal/mol, respectively), and exhibit some bond delocalization. The relationship of these two PAPBAZ isomers to their organic parent molecule, azulene, is discussed.     

Periodic orbits, damped transitions and targeted energy transfers in oscillators with vibro-impact attachments

We study complex damped and undamped dynamics and targeted energy transfers (TETs) in systems of coupled oscillators, consisting of single-degree-of-freedom primary linear oscillators (LOs) with vibro-impact attachments, acting, in essence, as vibro-impact nonlinear energy sinks (VI NESs). First, the complicated dynamics of such VI systems is demonstrated by computing the VI periodic orbits of underlying Hamiltonian systems and depicting them in appropriate frequency–energy plots (FEPs). Then, VI damped transitions and distinct ways of passive TETs from the linear oscillators to the VI attachments for various parameter ranges and initial conditions are investigated. As in the case of smooth stiffness nonlinearity [Y. Lee, G. Kerschen, A. Vakakis, P. Panagopoulos, L. Bergman, D.M. McFarland, Complicated dynamics of a linear oscillator with a light, essentially nonlinear attachment, Physica D 204 (1–2) (2005) 41–69], both fundamental and subharmonic TET can be realized in the VI systems under consideration. It is found that the most efficient mechanism for VI TET is through the excitation of highly energetic VI impulsive orbits (IOs), i.e., of periodic or quasiperiodic orbits corresponding to zero initial conditions except for the initial velocities of the linear oscillators. In contrast to NESs with smooth essential nonlinearities considered in previous works, VI NESs are capable of passively absorbing and locally dissipating significant portions of the energies of the primary systems to which they are attached, at fast time scale. This renders such devices suitable for applications, like seismic mitigation, where dissipation of vibration energy in the early, highly energetic regime of the motion is a critical requirement.     

Automated electrochemical synthesis and photoelectrochemical characterization of Zn1-xCo(x)O thin films for solar hydrogen production

High-throughput electrochemical methods have been developed for the investigation of Zn1-xCo(x)O films for photoelectrochemical hydrogen production from water. A library of 120 samples containing 27 different compositions (0 相似文献