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.

We demonstrated the fabrication of 10 emitters InGaN laser diode array of themaximum output power of 9 W at 420 nm. The device as a whole has thedifferential efficiency of above 1 W/A. The maximum output power is limited to 9W (pulse operation) by catastrophic mirror damage or to around 5 W in CWoperation by thermal roll-over. Larger arrays with stripes width of around 15µm and numbers of emitters up to 20 should enable reaching 20 W, whichis suitable for light engine of desktop projectors and a building block ofcinema theater projectors.

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.

Recently, metal-halide perovskites have demonstrated an extraordinarily rapid advance in single junction cell efficiency to over 20%, while still offering potentially low costs. Since the bandgap is larger than the ideal single-junction value, perovskite-based tandem cells can theoretically offer even higher efficiencies. Instead, however, the record tandem cell performance in experiments to date has come in slightly below that of record single junctions, although slightly higher than the same single junctions. In this work, we consider both how this disconnect can be explained quantitatively, and then devise experimentally feasible, variance-aware approaches to address them. The first stage of our approach is based on reconfiguring dielectric front coatings to help reduce net reflected power and balance junction currents by reshaping the reflection peaks. This method could be applied to post-fabrication stage of perovskite/c-Si tandem cells, and also applicable to cell and module level structures. In the second stage of our approach, we can almost entirely eliminate Fresnel reflection by applying a conformal periodic light trapping structure. In the best case, a short circuit current (Jsc) of 18.0 mA/cm2 was achieved, after accounting for 4.8 mA/cm2 of parasitic loss and 1.6 mA/cm2 reflection loss. Further improvements may require a change in the baseline materials used in perovskite cells.

The Supercontainer is the reference concept for the post-conditioning of vitrified high-level radioactive waste and spent fuel in Belgium. It consists of a prefabricated concrete buffer that completely surrounds a carbon steel overpack. In this highly alkaline environment (pH ∼ 13.6) and under normal conditions (i.e. without the ingress of aggressive species), the carbon steel overpack will be protected by a passive oxide film, which is believed to result in very low uniform corrosion rates.

This paper gives an overview of the status of the uniform corrosion, pitting corrosion and stress corrosion cracking behaviour of carbon steel expected during the waste disposal period.

Decorin is a small leucine-rich repeat proteoglycan supporting collagen fibril formation by controlling the rate of collagen fibrillogenesis and fibril dimensions. Peptides derived from the inner surface of decorin have been shown to bind to collagen, while peptides derived from the outer surface do not display such binding affinity. As typical secondary structural elements such as β-sheets and α-helical regions were found in the decorin X-ray crystal structure, here it was investigated by Circular Dichroism (CD) spectroscopy in solution, whether the same structural elements can be found in the derived peptides. Here it is shown that the peptide derived from decorin’s outer surface has the propensity to adopt helical conformation, as it was found in the crystal structure. The results were more pronounced in 80 vol% TFE solution, which led to an increase in the number as well as the length of helices. In contrast, peptides derived from the inner surface had a higher tendency to adopt β-sheet conformation, also in TFE, which corresponds to the conformation of the original sequence in the crystal structure of decorin. This suggests that the peptides derived from decorin adopt the structures present in the native protein.

We present a new concept applicable to the epitaxial growth of dislocation-free semiconductor structures on a mismatched substrate with a thickness far exceeding the conventional critical thickness for plastic strain relaxation. This innovative concept is based on the out-of-equilibrium growth of compositionally graded alloys on deeply patterned substrates. We obtain space-filling arrays of individual crystals several micrometers wide in which the mechanism of strain relaxation is fundamentally changed from plastic to elastic. The complete absence of dislocations at and near the heterointerface may pave the way to realize CMOS integrated SiGe X-ray detectors.

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.