Ultrahigh Aspect Ratio Copper-Nanowire-Based Hybrid Transparent Conductive Electrodes with PEDOT:PSS and Reduced Graphene Oxide Exhibiting Reduced Surface Roughness and Improved Stability.

Copper nanowires (CuNWs) with ultrahigh aspect ratio are synthesized with a solution process and spray-coated onto select substrates to fabricate transparent conductive electrodes (TCEs). Different annealing methods are investigated and compared for effectiveness and convenience. The CuNWs are subsequently combined with the conductive polymer poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) ( PEDOT: PSS) or with reduced graphene oxide (rGO) platelets in order to reduce the surface roughness and improve the durability of the fabricated TCEs. Our best-performing PEDOT: PSS/CuNW films have optical transmittance T550 = 84.2% (at λ = 550 nm) and sheet resistance Rs = 25 Ω/sq, while our best CuNW/rGO films have T550 = 84% and Rs = 21.7 Ω/sq.

Fluctuating hydrodynamics of multi-species reactive mixtures.

We formulate and study computationally the fluctuating compressible Navier-Stokes equations for reactive multi-species fluid mixtures. We contrast two different expressions for the covariance of the stochastic chemical production rate in the Langevin formulation of stochastic chemistry, and compare both of them to predictions of the chemical master equation for homogeneous well-mixed systems close to and far from thermodynamic equilibrium. We develop a numerical scheme for inhomogeneous reactive flows, based on our previous methods for non-reactive mixtures [Balakrishnan , Phys. Rev. E 89, 013017 (2014)]. We study the suppression of non-equilibrium long-ranged correlations of concentration fluctuations by chemical reactions, as well as the enhancement of pattern formation by spontaneous fluctuations. Good agreement with available theory demonstrates that the formulation is robust and a useful tool in the study of fluctuations in reactive multi-species fluids. At the same time, several problems with Langevin formulations of stochastic chemistry are identified, suggesting that future work should examine combining Langevin and master equation descriptions of hydrodynamic and chemical fluctuations.

Polarization microscope using a near infrared full-Stokes imaging polarimeter.

This paper presents a polarization microscope using an infrared (IR) full-Stokes imaging polarimeter. The IR polarimeter utilizes an optimized interference-based micropolarizer design, and provides full-Stokes images with resolution of 1608 × 1208 at 35 frames/second. The device fabrication, instrument calibration, performance evaluation, and measurement results are presented. The measurement error of the imaging polarimeter is less than 3.5%, and the standard deviations are less than 2%.

Graphene Q-switched Ho(3+)-doped ZBLAN fiber laser at 1190 nm.

We report Q-switched pulse operation of holmium (Ho(3+))-doped ZrF(4)-BaF(2)-LaF(3)-AlF(3)-NaF (ZBLAN) at ∼1190 nm in an all-fiber ring laser by using a fiber-optic graphene saturable absorber, which was fabricated by depositing graphene onto the flat surface of a side-polished D-shaped fiber. Stable Q-switched operation was established at a pump power of 180 mW with a repetition rate of 24 kHz and pulse width of 5.7 µs. When the pump power was increased to 1125 mW, 0.44 µJ Q-switched pulses with a repetition rate of 111 kHz and a pulse width of 0.8 µs were generated.

Infrared liquid crystal polymer micropolarizer.

The ability to create arbitrary patterned linear and circular infrared (IR) liquid crystal polymer (LCP) polarizers is demonstrated. The operating wavelength of the thin-film polarizer ranges from 700 to 4200 nm. The linear micropolarizer is fabricated using IR dichroic dye as a guest in LCP host with feature size as small as 4 µm. The circular micropolarizer is fabricated using cholesteric LCPs with feature size as small as 6.2 µm.

Tunable light emission from co-assembled structures of benzothiadiazole molecules.

Co-assembled structures possessing tunable light emission from 510-690 nm have been prepared using various compositions of two different 4,7-substituted benzothiadiazole molecules, 1 and 2. The preferential incorporation and co-localization of 1 and 2 to produce co-assemblies are possible because of structural similarities and allow for tuning of morphology and light emission.

Full-Stokes imaging polarimeter using an array of elliptical polarizer.

In this paper, a full-Stokes imaging polarimeter operating at 580 nm using an array of elliptical polarizers is presented. The division-of-focal-plane polarimeter utilizes a set of four optimized measurements which represent a regular tetrahedron inscribed in the Poincaré sphere. Results from the device fabrication, instrument calibration and characterization are presented. The performance of the optimized full Stokes polarimeter, as defined by size of the standard deviation of the degree of circular polarization, is found to be approximately five times better than the performance of the simple full-Stokes polarimeter.

Fluctuating hydrodynamics of multispecies nonreactive mixtures.

In this paper we discuss the formulation of the fluctuating Navier-Stokes equations for multispecies, nonreactive fluids. In particular, we establish a form suitable for numerical solution of the resulting stochastic partial differential equations. An accurate and efficient numerical scheme, based on our previous methods for single species and binary mixtures, is presented and tested at equilibrium as well as for a variety of nonequilibrium problems. These include the study of giant nonequilibrium concentration fluctuations in a ternary mixture in the presence of a diffusion barrier, the triggering of a Rayleigh-Taylor instability by diffusion in a four-species mixture, as well as reverse diffusion in a ternary mixture. Good agreement with theory and experiment demonstrates that the formulation is robust and can serve as a useful tool in the study of thermal fluctuations for multispecies fluids.

Supercapacitor operating at 200 degrees celsius.

The operating temperatures of current electrochemical energy storage devices are limited due to electrolyte degradation and separator instability at higher temperatures. Here we demonstrate that a tailored mixture of materials can facilitate operation of supercapacitors at record temperatures, as high as 200°C. Composite electrolyte/separator structures made from naturally occurring clay and room temperature ionic liquids, with graphitic carbon electrodes, show stable supercapacitor performance at 200°C with good cyclic stability. Free standing films of such high temperature composite electrolyte systems can become versatile functional membranes in several high temperature energy conversion and storage applications.

Graphene Q-switched 2.78 µm Er3+-doped fluoride fiber laser.

We report a diode-pumped 2.78 µm Er3+-doped ZBLAN fiber laser passively Q switched by a graphene saturable absorber, which was directly deposited onto a fiber dichroic mirror by the method of optically driven deposition. Stable Q-switched operation with a pulse duration of 2.9 µs and a pulse energy of 1.67 µJ was achieved in a 10 m long gain fiber. The pulse duration was reduced to 1 µs when the gain fiber length was shortened to 2 m. This Letter demonstrates that graphene is a promising and reliable saturable absorber for mid-infrared pulse generation at 3 µm.

One-dimensional self-assembly of a water soluble perylene diimide molecule by pH triggered hydrogelation.

A water soluble perylene diimide molecule has been fabricated into nanofibers via a pH triggered hydrogelation route. The one-dimensional self-assembly is dominated by the intermolecular π-π stacking interactions in concert with the hydrogen bonding between the carboxylic acid side chains. The anisotropic electronic and optical properties observed for the nanofibers are consistent with the one-dimensional intermolecular π-π arrangement.

Patterned cholesteric liquid crystal polymer film.

Herein, the ability to create arbitrarily patterned circular polarized optical devices is demonstrated by using cholesteric liquid crystal polymer. Photoalignment with polarized ultraviolet light is utilized to create aligned cholesteric liquid crystal films. Two different methods, thermal annealing and solvent rinse, are utilized for patterning cholesteric liquid crystal films over large areas. The patterned cholesteric liquid crystal films are measured using a Mueller matrix imaging polarimeter, and the polarization properties, including depolarization index, circular diattenuation (CD), and circular retardance are derived. Patterned nonlinearly polarized optical devices can be fabricated with feature sizes as small as 20 µm with a CD of 0.812±0.015. Circular polarizing filters based on polymer cholesteric liquid crystal films have applications in three-dimensional displays, medical imaging, polarimetry, and interferometry.

Multi-mode waveguides from ultra-long self-assembled hexagonal faceted microtubules of a benzothiadiazole molecule.

Length controlled (µm-mm-cm) self-assembly of hexagonal faceted microtubules has been achieved using a phase-transfer solution processing approach from . The self-assembled structures exhibit both polarized light emission and multi-mode waveguide properties over large length scales. The multi-mode waveguide characteristics are analyzed using a combination of experiment and finite-difference-time-domain calculations.

Ultrafine nanofibers fabricated from an arylene-ethynylene macrocyclic molecule using surface assisted self-assembly.

Large area uniform nanofibers have been fabricated from a hexameric arylene-ethynylene macrocycle (1) through in situ self-assembly on a glass substrate during solvent evaporation. The fibril morphology is controlled by the solvophilic core of 1, in conjunction with the interfacial interactions between the side chains of 1 and the substrate.

Synthesis of iron nanoparticles from hemoglobin and myoglobin.

Stable iron nanoparticles have been synthesized from naturally occurring and abundant Fe-containing bio-precursors, namely hemoglobin and myoglobin. The formation of stable iron nanoparticles was achieved through a one-pot, single-phase chemical reduction approach. The reduction of iron ions present in the bio-precursors was carried out at room temperature and avoids the use of harsh chemical reagents. The size distribution of the product falls into the narrow 2-5 nm range and the particles were found to be crystalline. This method can be a valuable synthetic approach for producing bio-conjugated nanoparticle systems for biological applications.

Controlled, Stepwise Reduction and Band Gap Manipulation of Graphene Oxide.

Graphene oxide (GO) has drawn tremendous interest as a tunable precursor in numerous areas, due to its readily manipulable surface. However, its inhomogeneous and nonstoichiometric structure makes achieving chemical control a major challenge. Here, we present a room-temperature based, controlled method for the stepwise reduction of GO, with evidence of sequential removal of each organic moiety. By analyzing signature infrared absorption frequencies, we identify the carbonyl group as the first to be reduced, while the tertiary alcohol takes the longest to be completely removed from the GO surface. Controlled reduction allows for progressive tuning of the optical gap from 3.5 eV down to 1 eV, while XPS spectra show a concurrent increase in the C/O ratio. This study is the first step toward selectively enhancing the chemical homogeneity of GO, thus providing greater control over its structure, and elucidating the order of removal of functional groups and hydrazine-vapor reduction.

Chemical reaction mediated self-assembly of PTCDA into nanofibers.

Uniform and crystalline nanofibers of perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA), an insoluble organic semiconducting molecule, have been achieved by self-assembling the molecules using chemical reaction mediated conversion of an appropriately designed soluble precursor, perylene tetracarboxylic acid (PTCA) using carbodiimide chemistry.

Flexible ZnO-cellulose nanocomposite for multisource energy conversion.

Materials with the ability to harness multiple sources of energy from the ambient environment could lead to new types of energy-harvesting systems. It is demonstrated that nanocomposite films consisting of zinc oxide nanostructures embedded in a common paper matrix can be directly used as energy-conversion devices to transform mechanical and thermal energies to electric power. These mechanically robust and flexible devices can be fabricated over large areas and are capable of producing an output voltage and power up to 80 mV and 50 nW cm(-2) , respectively. Furthermore, it is shown that by integrating a certain number of devices (in series and parallel) the output voltage and the concomitant output power can be significantly increased. Also, the output voltage and power can be enhanced by scaling the size of the device. This multisource energy-harvesting system based on ZnO nanostructures embedded in a flexible paper matrix provides a simplified and cost-effective platform for capturing trace amounts of energy for practical applications.

Ultrathin planar graphene supercapacitors.

With the advent of atomically thin and flat layers of conducting materials such as graphene, new designs for thin film energy storage devices with good performance have become possible. Here, we report an "in-plane" fabrication approach for ultrathin supercapacitors based on electrodes comprised of pristine graphene and multilayer reduced graphene oxide. The in-plane design is straightforward to implement and exploits efficiently the surface of each graphene layer for energy storage. The open architecture and the effect of graphene edges enable even the thinnest of devices, made from as grown 1-2 graphene layers, to reach specific capacities up to 80 µFcm(-2), while much higher (394 µFcm(-2)) specific capacities are observed multilayer reduced graphene oxide electrodes. The performances of devices with pristine as well as thicker graphene-based structures are examined using a combination of experiments and model calculations. The demonstrated all solid-state supercapacitors provide a prototype for a broad range of thin-film based energy storage devices.