We explore the impact of monovalent counter-ions on the molecular conformation of highly charged flexible polyelectrolytes for a range of molecular topologies (linear chains, stars, and unknotted and trefoil rings) by molecular dynamics simulations that include an explicit solvent having short range interaction with the polyelectrolyte. In particular, we investigate how the counter-ions near the polyelectrolytes with variable mass influence the average molecular shape. We also characterize the interfacially “bound” counter-ions by calculating the time-averaged number of interfacial counter-ions, as well as the degree to which the polyelectrolytes wrap around the counter-ions by calculating the number of contacts between the counter-ions and the polyelectrolyte.

The temperature dependence of the forward and reverse current voltage characteristics of circular Al+ implanted 4H-SiC p-i-n vertical diodes of various diameters, post implantation annealed at 1950 °C/5 min, have been used to obtain the thermal activation energies of the defects responsible of the generation and the recombination currents, as well as the area and the periphery current component of the current voltage characteristics. The former have values compatible with those of the traps associated to the carbon vacancy defect in 4H-SiC. The hypothesis that only these traps may justify the trend of the current voltage characteristics of the studied diodes has been tested by simulations in a Synopsys Sentaurus TCAD suite.

Bentonite is used as one of the materials for engineered barrier systems in a radioactive waste repository. Since the major clay mineral constituent of bentonite is montmorillonite, its physico-chemical properties are important. Basal spacing of water-saturated Na-montmorillonite is reported to decrease with increasing Na-montmorillonite density. This paper presents a thermodynamic model to calculate change in the interlayer space of Na-montmorillonite based on the relative partial molar Gibbs free energy (dG) of interlayer water as contacted with a solution of an arbitrary salinity (NaCl concentration). Directly change in montmorillonite density (ρdm) against salinity was calculated by the thermodynamic model. The dG of interlayer water as contacted with a solution of an arbitrary salinity can be calculated by dG = dGH2O+ dGS (dGH2O: relative partial molar Gibbs free energy of interlayer water, dGS: that of water in a solution of an arbitrary salinity). The author previously reported an empirical correlation of dGH2O vs. water content for Na-montmorillonite. The dependence of ρdm on salinity was calculated by replacing dGH2O in the empirical correlation with dG. ρdm increased with salinity. Concretely, initially the ρdm-values of 0.5 and 1.0 Mg/m3 increased to 1.05 and 1.16 Mg/m3 under 0.5 m-NaCl, respectively. Interlayer space vs. salinity was estimated based on the measured results of basal spacing vs. ρdm by XRD and the average density of montmorillonite vs. salinity calculated by this model.

We demonstrate an alternative route to synthesize functionalized silica nanoparticles through incorporation of alcohol compounds in the Stöber process. The Stöber process has been widely utilized for the synthesis of silica nanoparticles due to its simplicity and reliability. Silane based compounds have been incorporated in this process in order to tailor surface properties of the silica nanoparticles. These compounds do, however, have limitations in their utility due to side reactions with water and intermolecular polymerization. In this article, we report the incorporation of alcohol based reagents in the Stöber process as an alternative means of synthesis and functionalization of silica nanoparticles. In particular, choline chloride was chosen as an exemplary alcohol to be incorporated in the process for tuning overall surface charge of the silica nanoparticles. These silica nanoparticles with incorporated choline chloride were characterized by atomic force microscopy (AFM), zeta potential measurements, and X-ray photoelectron spectroscopy (XPS) in comparison with silica nanoparticles synthesized from the traditional Stöber process. While the size and shape of the nanoparticles exhibited little difference between the two synthetic routes, the zeta potential of the choline chloride incorporated nanoparticle was ∼10 mV higher than that of the traditional silica nanoparticles. Composition of the choline chloride containing silica nanoparticles was verified by XPS with the observation of strong N1s and C1s signals. The methods introduced in this article could be expanded to incorporate a range of alcohol containing compounds including choline chloride for the synthesis of silica nanoparticles with a tuned surface chemistry.

We are reporting an approach to prepare bulk foils of α″-Fe16N2 that can be directly obtained from a melt spinning process. The diffraction peaks from α″-Fe16N2 phase were found in X-ray diffraction spectrum of the foil, for which a nitrogen composition of 8.7at% was found by Auger electron spectroscopy. The microstructure of this melt spun foil was analyzed. We found 600 nm subgrains inside 8 μm grains for this foil. The coercivity of the α″-Fe16N2 foil was found as 222 Oe with a saturation magnetization of 223 emu/g. We analyzed the coercivity based on the microstructure and proposed a model to explain how to further improve it in melt spun FeN foils.

Recent advances in studies of local mechanical properties of polymers with different atomic force microscopy techniques (contact, Hybrid and amplitude modulation modes) are described in interplay between experiment and theory. Analysis of force curves and time dependencies of probe response to sample compliance, which were recorded on a number of polymer materials at various temperatures, leads to quantitative mapping of specific mechanical properties (elastic modulus, work of adhesion, etc). High spatial resolution of elastic modulus mapping (10-20 nm) is illustrated in measurements of lamellar structures of several polymers. Challenges of examination of viscoelastic properties are pointed out and a possible solution is presented.

Charge transport properties of pentacene have been investigated by a joint experimental and theoretical study. The growth of pentacene on the substrates shows mainly two different polymorphic phases, a bulk phase and a thin-film phase. The thin-film phase is crucial for the charge transport in two-terminal and three-terminal devices such as organic Schottky diodes and organic thin film transistors, respectively. Experimentally, mobility in two-terminal devices is less by five orders of magnitude than that in three-terminal devices. We show here that this difference can be explained on the basis of strong electronic coupling between molecular dimers located in the ab-plane and relatively weak coupling between the planes (along the c-axis).

Perovskite based photovoltaics have recently emerged as the forerunner in the next generation photovoltaic technology because of the rapid increase of power conversion efficiency (PCE). However, it is well recognized that the exposure to moisture, heat and light causes the degradation of perovskite [1] (especially for methylammonium lead iodide (CH3NH3PbI3) which is the most commonly used perovskite material). It makes stability a main issue for the commercialization of perovskite based photovoltaics. Hence, an advanced encapsulation method is one of the keys to improve the stability. Here we present a comparison study between different encapsulation methods. Perovskite based photovoltaics devices were encapsulated using UV epoxy resin, with or without the addition of desiccant and the deposition of SiO2 layer. By minimizing the ingress of moisture and oxygen, devices with storage in ambient air under one sun continuous illumination could retain 94 % of the initial performance (PCE around 13%) after two days.

In the highly-correlated electronic system Ca1-x PrxMnO3 having the simple perovskite structure, it has beenreported that there exists the C-type orbital-ordered (COO) state accompanyingan antiferromagnetic ordering for 0.10 ≤ x≤ 0.25. According to the previous studies concerning orbital-orderedstates in simple perovskite manganites, the COO state was understood to becharacterized by a spatial array of (3z2-r2)-type orbitalsfor 3d electrons in Mn ions. The notable feature of the COO state inCa1-x PrxMnO3 is that the state with the monoclinic-P21/msymmetry appears as a result of the structural transition from the disorderedstate with the orthorhombic-Pnma symmetry. Compared with the COO-state formationfrom the cubic-Pm $\overline 3$m state, however, the formation from the disordered-Pnma statehas not been understood yet. We have thus examined the crystallographic featuresof the formation of the COO state in Ca1-x PrxMnO3, mainly by x-ray powder diffraction and transmissionelectron microscopy. In the case of x = 0.16, forinstance, the COO state was found to appear from the disordered-Pnma statearound 90 K on cooling. The notable feature of the formation is that, in thePnma state just before the COO-state formation, characteristic diffusescattering appeared around each reflection in electron diffraction patterns,together with the splitting of the 200c reflection in x-ray powder diffractionprofiles in the pseudo-cubic notation. Based on these experimental data, it isunderstood that the formation of the COO state in Ca1-x PrxMnO3 accompanies remarkable fluctuations of the C-type orbitalordering in the disordered-Pnma state.

In Belgium, Eurobitum bituminized radioactive waste is an important intermediate-level long-lived waste form that contains, besides bitumen and radionuclides, large amounts of soluble salts (mainly NaNO3). Geological disposal in a water-saturated sedimentary formation will induce swelling of Eurobitum due to water uptake by the hygroscopic salts embedded in a highly efficient semi-permeable bitumen membrane. Initially, while there is still free space in the primary waste containers, free swelling will occur. To improve our understanding of the water uptake processes under free swelling conditions, water uptake and leaching tests are being performed in which inactive Eurobitum was contacted at the top with 0.1 M KOH (simplified representation of young cement water) without effective stress on the sample. Under these test conditions, the evolution of the water uptake and NaNO3 leaching processes shows several stages: (1) initial fast ingress of water into and leaching of NaNO3 from pores close to the surface; (2) slower progression of the hydration front, the swelling and the leaching of NaNO3, but behaving linearly with the square root of time, indicating that these processes are controlled by diffusion; (3) after more than 2 to 3 years, the leaching, hydration and swelling rates re-increase, attributed to the formation of interconnecting pores and (micro)cracks in the bitumen matrix in response to its increasing deformation.

Discovery of superconductivity in BiS2 layers based systems has attracted tremendous interest of both experimentalists and theoreticians from condensed matter physics community. In this article, a review of our high pressure studies on BiS2 based superconductors is given. The pressure effects on magnetic, transport properties and superconducting transitions are discussed for different types of doped and undoped BiS2-based compounds such as Bi4O4S3 and ReO/FBiS2 (Re = rare-earth). Pressure tends to decrease the magnetic transition temperature in the undoped or only slightly doped compounds. The superconducting Tc increases with low pressure for under doped BiS2 based compounds, remains approximately constant for optimal doping, and decreases linearly in the overdoped range. Under pressure, the semiconducting behavior in the normal state is suppressed markedly and monotonically, whereas the evolution of Tc is nonlinear, the superconductivity in the BiS2 layer favors the Fermi surface at the boundary between the semiconducting and metallic behaviors. However, strong suppression of the semiconducting and induced metallic behavior without doping in ReO/FBiS2 suggests that the Fermi surface is located in the vicinity of some instability. Furthermore, notable properties under pressure in the BiS2 family are reported. The prospects for raising Tc in this family are proposed on the basis of experimental and theoretical studies.

In this work, we propose a model to quantify strain induced conductordiscontinuities based on measuring electrical resistance while applying tensilestrain to metal-polymer systems. Under strain, changing conductor geometry andinduced conductor discontinuity increase electrical resistance. On Kaptonsubstrates strained to ε = .07, evaporated gold films did notdeform and resistance increase was only caused by geometry change. Conversely,discontinuity caused 31% and 72% of the resistance increase in evaporated andprinted silver films at the same strain. On PDMS substrates, the same magnitudeof discontinuity, causing 31% of the resistance increase, occurred at onlyε = .024 in evaporated silver films. At the same strain,discontinuity caused 86% of the resistance increase in evaporated gold films.Printed silver films were inelastic. The results suggest that traditionalfabrication techniques may be more suitable to flexible hybrid electronicsapplications than additively manufactured conductors.

Graphene-based field effect transistors (GFETs) were assessed when interfaced with well separated and precisely placed core/shell CdSe/ZnS semiconductor quantum dot (QD) arrays. The QDs were imbedded in a hexagonal hole-array, which was formed in a layer of anodized aluminum oxide on Si/SiO2 substrates. Graphene (single, or two layers), grown by chemical vapor deposition (CVD) on Cu foils, was transferred and placed on top of the QDs imbedded films and served as the transistor channel. Electrical characteristics under white-light illumination at various biasing conditions revealed that the photo current was decreasing upon increasing biasing. The device's photoluminescence (PL) as a function of both the drain-source and gate-source potentials also reduced as a function of the potential biases. We observed two maxima in the PL data while tilting the sample with respect to the incident laser beam. We attributed it to the optimal coupling between the incident and the emission wavelengths to resonating surface modes.

The past few years have seen the introduction of a number of 3D and 4D printingtechniques used to process tough hydrogel materials. The use of‘color’ 3D printing technology where multiple inks areused in the one print allows for the production of composite materials andstructures that can further enhance the mechanical performance of the printedhydrogel. This article reviews a number of 3D and 4D printing techniques forfabricating functional hydrogel based devices.

Heterogeneous catalytic materials and electrodes are used for (electro)chemical transformations, including those important for energy storage and utilization.1, 2 Due to the heterogeneous nature of these materials, activity measurements with sufficient spatial resolution are needed to obtain structure/activity correlations across the different surface features (exposed facets, step edges, lattice defects, grain boundaries, etc.). These measurements will help lead to an understanding of the underlying reaction mechanisms and enable engineering of more active materials. Because (electro)catalytic surfaces restructure with changing environments,1 it is important to perform measurements in operando. Sub-diffraction fluorescence microscopy is well suited for these requirements because it can operate in solution with resolution down to a few nm. We have applied sub-diffraction fluorescence microscopy to a thin cell containing an electrocatalyst and a solution containing the redox sensitive dye p-aminophenyl fluorescein to characterize reaction at the solid-liquid interface. Our chosen dye switches between a nonfluorescent reduced state and a one-electron oxidized bright state, a process that occurs at the electrode surface. This scheme is used to investigate the activity differences on the surface of polycrystalline Pt, in particular to differentiate reactivity at grain faces and grain boundaries. Ultimately, this method will be extended to study other dye systems and electrode materials.

Graphene-based nanomaterials (graphene nanosheets/graphene nanoribbons) decorated with vanadium pentoxide (V2O5) nanobelts (i.e. GVNBs) were synthesized via one-step low-temperature facile hydrothermal/solvothermal method as high-performance electrochemical composite electrodes. VNBs were formed in the presence of graphene oxide (GO), a mild oxidant, which transforms into reduced GO (rGOHT) assisted in enhancing the electronic conductivity with mechanical strength for GVNBs. From surface sensitive electron microscopy and spectroscopy structural characterization techniques and analyses, rGOHT nanosheets/ nanoribbons appear to be inserted into and coated with the layered crystal structure of VNBs, which further confirmed the enhanced electrical conductivity of VNBs. The electrochemical energy storage capacity of GVNBs is investigated using electrochemistry and the specific capacitance Cs are determined from both the cyclic voltammetry (CV) with scan rate and galvanostatic charge/discharge V-t profiles with varying current density. The GVNBs having rGO-rich composite V1G3 (V2O5/GO = 1:3) showed superior performance followed by V2O5-rich V3G1 (V2O5/GO = 3:1) as compared with V1G1 (V2O5/GO = 1:1) composites besides pure component (rGOHT and V2O5) materials. Moreover, V1G3 and V3G1 composites showed excellent cyclic stability and the capacitance retention of > 80% after 200 cycles. Furthermore, by performing extensive simulations and modeling of electrochemical impedance spectroscopy data, we determined various circuit parameters (charge transfer and solution resistance, double layer and low frequency capacitance). These findings highlight the comparative performance of nanocomposite hybrid electrode materials.

Secondary electron transmission measurements are used to examine the electron diffusion and thermalization processes in B-doped nanocrystalline diamond membranes of thickness 2.3 μm and 650 nm. Specifically, transmitted energy spectra are measured following impact by an electron beam that penetrates deeper in the membrane as the beam energy Eo increases. A fully-thermalized emission peak is observed for Eo ≤ 16 keV and Eo ≤ 7 keV from the 2.3-μm-thick and 650-nm-thick films, respectively, with a small high-energy tail beginning to emerge at higher Eo. These measurements are analyzed using Monte Carlo simulations that generate constant-energy contour lines (down to 0.05 Eo) as a function of beam depth into the film. From these simulations, we deduce that secondary electrons have a minimum thermalization length of ∼ 630 nm and ∼ 260 nm in the 2.3-μm-thick and 650-nm-thick films, respectively. Further insight into the secondary-electron transport behavior is gained from the analysis, and this understanding is applied to the design of a transmission electron-current amplifier device.

Recently, commercial home electric appliances with bactericidal/viral inactivation function of room air have been widely available. Most of these home appliances equip discharge devices which possibly generate reactive oxygen and nitrogen oxides. However, these effects are still controversial problem. To elucidate the inactivation effect of these devices at molecular level, we have been considering large DNA molecules as a biomarker to be used. By exposing DNA solution to the gas containing the chemical species, oxidative damage to DNA such as strand breaks can be induced. We have conducted the single-molecule-based evaluation method of DNA strand break using large linear DNA molecules. The obtained breakage rate could possibly be used for evaluation of reactivity of radicals generated by the discharge devices.

Insulating silicon dioxide (SiO2) films can be produced by hydrolysis of metal alkoxide tetraethylorthosilicate (TEOS) in the presence of an acid catalyst in supercritical fluid CO2 (sc-CO2). In this study, SiO2 films are formed on different substrates using TEOS as a source of silicon, and acetic acid (HAc) as a catalyst. Water required for the hydrolysis reaction is from in situ generation of esterification and condensation reactions involving HAc and the alcohol produced. The acid catalyzed deposition reaction actually starts at room temperature but produces decent films in sc-CO2 at moderately high temperatures (e.g. 50 °C). Supercritical fluid CO2 is known to have near zero surface tension and provides an ideal medium for fabrication of SiO2 films. Formation of SiO2 films via hydrolysis reaction in sc-CO2 is more rapid compared to the traditional hydrolysis reaction at room temperature. In general, metal alkoxide hydrolysis reactions carried out in a closed sc-CO2 system is not affected by moisture in air compared with traditional open-air hydrolysis systems. Using sc-CO2 as a reaction medium can eliminate undesirable organic solvents utilized in traditional alkoxide hydrolysis reactions.

X-ray diffraction (XRD) and electron diffraction (ED) measurements demonstrated that the SiO2 films produced are amorphous. Energy dispersive spectroscopy (EDS), attenuated total reflectance-Fourier transform infrared (ATR-FTIR) and X-ray photoelectron (XPS) spectroscopy show elemental compositions of the films formed on the substrate surfaces to be SiO2. Film thickness formation by controlling the amount of the catalyst is discussed.

Powders of La2O3 were mixed with mechanical ball-milling technique (MA) adding TiO2, to improve the electrochemical performance as a storage material. Microstructures, morphologies and electrochemical results were investigated using TEM, X-ray diffraction (XRD), Cyclic Voltammetry and Potentiodynamic studies. Results showed that, the samples with TiO2 content affected the capacity of response. The alloys exhibit a superior capacity and stability adding TiO2. The milling ball to powder weight ratio was kept 5 to 1 for all experimental runs. Milling intervals were 0, 2 and 4 hrs; using alternate cycles of 30 minutes milling and 30 min resting. The nanostructure TiO2 powder, improves the samples to design a better electrode. TiO2 has significant influence on electrochemical performance of electrodes. Electrochemical experiments were performed on ACM Instruments Gill AC and a typical three electrode setup was constructed to measure the electrochemical properties of the working electrode. Here, platinum was used as the counter electrode and calomel was used as the reference electrode. Structures of the samples were analyzed by digital image tools.