Synthesis at the nanoscale of ZnO into poly(methyl methacrylate) and its characterization

In this paper, PMMA/ZnO nanocomposites have been prepared by a very simple, facile and versatile chemical approach. The prepared PMMA/ZnO nanocomposites possess no color, high transparency, good thermal stability, UV-shielding capability, luminescence and homogeneity. The chemical process involved solution mixing of ZnO nanoparticles dispersed in DMAc with the Polymethylmethacrylate (PMMA) matrix dissolved in the same solvent. The effect of ZnO content on the physical properties of the PMMA matrix is investigated by X-ray diffraction, field emission scanning electron microscopy, thermogravimetric analysis, UV–Vis absorption and photoluminescence spectroscopy. It was found that pure hexagonal ZnO nanoparticles with an average particle size of 4–8 nm were homogeneously dispersed in the PMMA matrix. A significant improvement in thermal properties was observed with the incorporation of 1.0 wt% ZnO nanoparticles. The prepared nanocomposite films are highly transparent and a clear excitonic peak is observed in their absorption spectra. Measurement of room temperature photoluminescence spectra shows intensive near-band edge emission peak at 3.28 eV without any structural defects for a nanocomposite film with a filler content of 1.0 wt%.     

THz photomixer with milled nanoelectrodes on LT-GaAs

A terahertz (THz) photomixer: (i) a meander type antenna with integrated nanoelectrodes on (ii) a low temperature grown GaAs has been fabricated and characterized. It was designed for spectral range of 0.3–0.4 THz where molecular fingerprinting and sensing are performed. By combination of electron beam lithography with post-processing using focused ion beam (FIB), milling the THz emitter was successfully fabricated. Nanogaps as small as 40 nm width in the active area of photomixer were milled by FIB. Nanocontacts enhance electric fields of the illuminated and THz radiation and contribute to a better collection of photo-electrons. THz emission was obtained and spectrally characterized.     

An in silico protocol for identifying mTOR inhibitors from natural products

The mammalian target of rapamycin (mTOR) is an anti-cancer target. In this study, we propose an in silico protocol for identifying mTOR inhibitors from the ZINC natural product database. First, a three-dimensional quantitative structure–activity relationship pharmacophore model was built based on known mTOR inhibitors. The model was validated with an external test set, Fischer’s randomization method, a decoy set and pharmacophore mapping conformation testing. The results showed that the model can predict the mTOR inhibition activity of the tested compounds. Virtual screening was performed based on the best pharmacophore model, and the results were then filtered using a molecular docking approach. In addition, molecular mechanics/generalized born surface area analysis was used to refine the selected candidates. The top 20 natural products were selected as potential mTOR inhibitors, and their structural scaffolds could serve as building blocks in designing drug-like molecules for mTOR inhibition.     

From the crust to the core of neutron stars on a microscopic basis

Within a microscopic approach the structure of Neutron Stars is usually studied by modelling the homogeneous nuclear matter of the core by a suitable Equation of State, based on a many-body theory, and the crust by a functional based on a more phenomenological approach. We present the first calculation of Neutron Star overall structure by adopting for the core an Equation of State derived from the Brueckner-Hartree-Fock theory and for the crust, including the pasta phase, an Energy Density Functional based on the same Equation of State, and which is able to describe accurately the binding energy of nuclei throughout the mass table. Comparison with other approaches is discussed. The relevance of the crust Equation of State for the Neutron Star radius is particularly emphasised.     

Laser generated Ag and Ag–Au composite nanoparticles for refractive index sensor

Localized surface plasmon resonance (LSPR) wavelength of metal nanoparticles (NPs) is highly sensitive to size, shape and the surrounding medium. Metal targets were laser ablated in liquid for preparation of spherical Ag and Ag@Au core–shell NP colloidal solution for refractive index sensing. The LSPR peak wavelength and broadening of the NPs were monitored in different refractive index liquid. Quasi-static Mie theory simulation results show that refractive index sensitivity of Ag, Ag–Au alloy and Ag@Au core–shell NPs increases nearly linearly with size and shell thickness. However, the increased broadening of the LSPR peak with size, alloy concentration and Au shell thickness restricts the sensing resolution of these NPs. Figure-of-merit (FOM) was calculated to optimize the size of Ag NPs, concentration of Ag–Au alloy NPs and Au shell thickness of Ag@Au core–shell NPs. The refractive index sensitivity (RIS) and FOM were optimum in the size range 20–40 nm for Ag NPs. Laser generated Ag@Au NPs of Au shell thickness in the range of 1–2 nm showed optimum FOM, where thin layer of Au coating can improve the stability of Ag NPs.     

Solution-processed P3HT-based photodetector with field-effect transistor configuration

In this paper, we presented a solution-processed photodetector with a configuration of field-effect transistor Au/poly(3-hexylthiophene) (P3HT)/poly(methyl methacrylate) (PMMA)/Al, in which P3HT acts as the active layer and PMMA as dielectric layer, and the drain and source electrodes (Au) were fabricated through a shadow mask. Using the top-gate bottom-contact configuration and employing orthogonal solvent to avoid “solution corrosion”, the devices with three different thicknesses (38, 150 and 223 nm) of the P3HT layer were investigated, and all of them showed typical transistor properties and their drain–source current can be controlled by the gate voltage. The photocurrent of the device Au/P3HT(223 nm)/PMMA(930 nm)/Al shows an obvious increment over a broad range of wavelengths from 350 to 650 nm, giving a maximum photo-to-dark current ratio of 2,404 with a photoresponsivity of 22.71 mA/W under the incident 350 nm light at V _DS = ?5 V.     

SERS scaling rules

We demonstrate the qualitative analysis of surface-enhanced Raman scattering (SERS) intensity and optical extinction by experimentally and numerically. This analytical methods are well matched not only the simple square lattice array of nanostructures, but also the rectangular lattices. We also demonstrate SERS selectivity of modes controlling the optical extinction of excitation and scattering wavelength. Both square lattice and rectangular lattice have similar tendency, but the rectangular lattice structures have much higher selectivity of SERS modes.     

The phase behavior of gamma and laser irradiated polytetrafluorine

By using thermomechanical spectroscopy, an amorphous and three crystalline (high melting, intermediate, and low melting forms) blocks of the topological structures of polytetrafluoroetylene (PTFE) were characterized and their behavior under γ-radiation up to 2420 kGy was explored. The influence of γ-radiation on the powder and sheet of PTFE is essentially the same leading to formation of amorphous character. The glass transition and melting point temperatures of PTFE continuously decreased with increasing dose of irradiation. On exposure to continuous CO₂ laser radiation, PTFE degrades at a high rate and its clusters have a fibrous form. Initial γ-irradiation of PTFE enhances the laser ablation process.     

Effect of SiO2–metal–SiO2 plasmonic structures on InGaAs/GaAs quantum well intermixing

Dielectric–metal–dielectric sandwich structures have been fabricated on top of an InGaAs/GaAs single quantum well (QW) structure to enhance atomic interdiffusion across the QW interfaces at elevated temperature during rapid thermal annealing using a halogen lamp as the heating source. The QW intermixing enhancement is realized during rapid thermal annealing. By placing a properly designed SiO₂–Ag–SiO₂ structure on top of the QW sample, a blueshift in photoluminescence emission from 920 to 882 nm was observed, larger than that obtained in a SiO₂-capped QW annealed at the same condition. Finite-difference time-domain simulation and optical reflectance measurements showed that the enhanced QW intermixing is due to the plasmonic resonance-enhanced light absorption and suppressed light reflection from the SiO₂–Ag–SiO₂ structure.     

Label Free Fluorometric Characterization of DNA Interaction with Cholate Capped Gold Nanoparticles Using Ethidium Bromide as a Fluorescent Probe

We demonstrated label free ethidium bromide assisted characterization of DNA interaction with cholate capped AuNPs. Interactions between ss/ds DNA and AuNPs with two different lengths (0.5 and 0.85 kb) were analyzed through fluorescence spectrophotometer and agrose gel electrophoresis analysis. Further results were confirmed by UV–globally visible spectrophotometer, DLS and TEM. As 0.5 and 0.85 kb of ssDNA effectively interacted with AuNPs through the van der Waals interaction which consequently led to the prevention of salt induced aggregation, EtBr intercalations as well as fluorescence shift with less binding constant 0.098 and 0.108 μM, respectively. On the contrary, the same length of dsDNA (0.5 and 0.85 kb) not interacted with AuNPs which led to the NPs aggregation, EtBr intercalation as well as fluorescence shift with increased binding constant 0.166 and 0.599 μM, respectively. This approach helped to understand the mode of interactions of DNA with cholate capped AuNPs without any modifications in a simple method and the results could be readout through the naked eye under the UV transilluminator. Figure

Fluorometric characterization of interaction of different lengths of ss/dsDNA with cholate capped AuNPs using EtBr as fluorescence probe     

On the thickness-dependent diffusion coefficient of perfluoropolyether lubricants on a thin diamond-like film

Diffusion of perfluoropolyethers (PFPEs) lubricants on a hard disk surface is an important self healing characteristic to replenish PFPEs lubricants on their uncovered surface. In the present paper, we study the diffusion coefficients of non-functional PFPE Z and PFPE Zdol with functional end groups as a function of lubricant film thickness on a thin DLC (diamond-like) film. Diffusion coefficients of PFPE Z and PFPE Zdol molecules on a DLC film are calculated using the equation of Einstein’s law of diffusion (Guo et al. J. Appl. Phys 93:8707, 2003; Guo Ph.D. thesis, 2006; Chung et al. IEEE Trans. Magn. 45:3644, 2009) considering the movement of their center of mass to reach their equilibrium positions from their original configurations. And it is averaged with the film thickness to show the thickness dependence on the diffusion of PFPEs lubricants on a DLC substrate. Firstly diffusion coefficients of sub-monolayer of partially coverage PFPE Z and PFPE Zdol on a DLC substrate are studied briefly and secondly the diffusion coefficient of monolayer PFPE Zdol on a DLC substrate is also studied elaborately. To support our results, we compare our thickness-dependent diffusion coefficients of PFPE Z and PFPE Zdol with those of published theoretical (Guo Ph.D. thesis, 2006; Chung et al. IEEE Trans. Magn. 45:3644, 2009) and experimental results (Chung et al. Tribol. Lett. 32:35, 2008; Ma et al. Tribol. Lett. 10:203, 2001). Here we study how lubricant film thickness plays an important role on its diffusion. Effects of polar end bead functionality, lubricant film thickness enhance the anisotropic behavior of diffusion coefficients of PFPE Zdol on the DLC substrate. But in the present analysis we consider hard disk carbon overcoat as a thin DLC film and we include all of their atoms within the force cut-off distance with PFPEs lubricant molecules for the interactions to study the thickness dependence on their diffusion coefficients.     

Investigation of various transmission properties and launching techniques of plastic optical fibres suitable for transmission of high optical powers

The significant parameters for plastic fibres with various core/cladding combinations are given: refractive index, numerical aperture, critical angle of total internal reflection at the core/cladding interface and maximum angle of aperture. The output power of a plastic fibre (PS/PMMA) was measured as a function of the angle of incidence. The results are interpreted using the ray optical fibre transmission model. Various launch-loss-reducing optical end-face working procedures are compared. We also investigated a method to avoid Fresnel reflection losses by a Brewster angled fibre input end-face for a linearly polarized light beam. The transverse and longitudinal intensity distribution of the output beam of a PS/PMMA fibre was measured. We conclude that a single large core clad plastic fibre is a promising alternative to a multi-glass fibre bundle for some applications.     

Stimulation of neurite growth under broadband pulsed THz radiation

The effect of low-intensity broadband pulsed THz radiation in the range from 0.05 to 1.2 THz, with power from 0.25 to 11.6 µW, on the growth of neurites of spinal ganglia of (10–12)-day chick embryos has been investigated. An analysis of the 3-min irradiation with powers in this range has demonstrated both stimulating and suppressive effects of THz radiation on the proliferative activity of neurites. This effect manifests itself with a decrease in the THz radiation power.     

Continuous-wave 2.52 Terahertz Gabor inline compressive holographic tomography

Continuous-wave (CW) 2.52 Terahertz (THz) 3D tomographic images were obtained by numerically reconstructing a single Gabor inline digital hologram based on modified compressive sensing reconstruction algorithm. Three metallic copper samples which are separately adhered to three Teflon plate were used as the targets. The actual axial resolution achieved was higher than 6 mm, and the lateral resolution was higher than 0.4 mm. Similarly, a paper clip and a handwritten character sample on a white paper were also imaged. Numerical simulation and experimental results verified the preferable reconstruction characteristics of the proposed modified algorithm. The feasibility of CW THz Gabor inline compressive holographic tomography is confirmed by adding barriers such as Teflon boards and thermal paper to block the samples.     

Enhanced effect of side-Ohmic contact processing on the 2DEG electron density and electron mobility of In0.17Al0.83N/AlN/GaN heterostructure field-effect transistors

From the capacitance–voltage curves and current–voltage characteristics of the In_0.17Al_0.83N/AlN/GaN heterostructure field-effect transistors (HFETs) with side-Ohmic contacts and normal-Ohmic contacts, two-dimensional electron gas (2DEG) electron mobility was calculated. It is found that the polarization Coulomb field scattering (PCF) is closely related to the normal-Ohmic contact processing, and the PCF was weakened by side-Ohmic contact processing in In_0.17Al_0.83N/AlN/GaN HFETs, similar to that in AlGaN/AlN/GaN HFET devices. Further, due to the stronger spontaneous polarization in the thinner In_0.17Al_0.83N barrier layer, the influence of the gate bias on the PCF in In_0.17Al_0.83N/AlN/GaN HFETs is greater than that in AlGaN/AlN/GaN HFETs. As a result, the PCF in In_0.17Al_0.83N/AlN/GaN HFETs with side-Ohmic contacts is stronger than that in AlGaN/AlN/GaN HFETs with side-Ohmic contacts. Moreover, the 2DEG electron density in the In_0.17Al_0.83N/AlN/GaN HFETs with side-Ohmic contacts is increased by more than twice compared with the 2DEG electron density in the In_0.17Al_0.83N/AlN/GaN HFETs with normal-Ohmic contacts.     

Optimized AC conductivity correlated to structure,morphology and thermal properties of PVDF/PVA/Nafion composites

Polyvinylidene fluoride (PVDF) and polyvinyl alcohol (PVA) composites were prepared by controlled loading of Nafion (5 to 15 wt%) by solution casting using water and dimethylformamide (DMF) as a solvent. The surface morphology of composite analyzed by atomic force microscopy (AFM) reveals the presence of Nafion ionomers. The increase in interlayer spacing of modified PVDF/PVA polymer system as a function of Nafion was detected by X-ray diffraction (XRD). The major change in Fourier transform infrared (FTIR) spectroscopy confirms the chemical bond C=O stretching around 1,700 cm^?1 due to Nafion. Differential scanning calorimetry (DSC) demonstrates the thermal stability of polymer composites and the decrease in melting temperature (T _m). The optimized AC conductivity (σ) of the prepared composite was evaluated by using an impedance analyzer as a function of temperature (40 to 150 °C) at constant 30-MHz frequency. The highest conductivity of 1.3?×?10^?2 S m^?1 was observed at 80 °C for 10 wt% of Nafion and correlated with structure, morphology and thermal properties of modified PVDF/PVA/Nafion composites. The experimental results may be useful for sensors, fuel cells and battery application domains.     

Interaction of One Anthraquinone Derivative with ctDNA Analyzed by Spectroscopic and Modeling Methods

The interaction of one anthraquinone derivative (AOMan) with calf thymus deoxyribonucleic acid (ctDNA) was systematically investigated at physiological pH 7.4 by fluorescence spectroscopy and molecular modeling. Binding constants of ctDNA with AOMan were calculated at different temperatures. Thermodynamic parameters, enthalpy and entropy changes were calculated according to Van’t Hoff equation, which indicated that the reaction was spontaneous and predominantly enthalpically driven. The increasing viscosity of ctDNA indicated that AOMan could intercalate into the base pairs of ctDNA. This conclusion was also demonstrated by the results obtained from KI quenching, denatured DNA studies and fluorescence polarization experiment. Furthermore, the molecular modeling results showed that anthraquinone ring tended to slide into the G–C rich region of ctDNA through the hydrogen bond, which are consistent with the results from experimental methods. Studying the binding interaction of target anthraquinones with DNA is one of the key steps in their DNA-changing action and the design of new drugs.     

Fabrication and performance of polymer–nanocomposite anti-reflective thin films deposited by RIR-MAPLE

Design of polymer anti-reflective (AR) optical coatings for plastic substrates is challenging because polymers exhibit a relatively narrow range of refractive indices. Here, we report synthesis of a four-layer AR stack using hybrid polymer:nanoparticle materials deposited by resonant infrared matrix-assisted pulsed laser evaporation. An Er:YAG laser ablated frozen solutions of a high-index composite containing TiO₂ nanoparticles and poly(methyl-methacrylate) (PMMA), alternating with a layer of PMMA. The optimized AR coatings, with thicknesses calculated using commercial software, yielded a coating for polycarbonate with transmission over 97 %, scattering <3 %, and a reflection coefficient below 0.5 % across the visible range, with a much smaller number of layers than would be predicted by a standard thin film calculation. The TiO₂ nanoparticles contribute more to the enhanced refractive index of the high-index layers than can be accounted for by an effective medium model of the nanocomposite.     

Plasmonic enhancement of optical absorption of UV radiation by Au nanoparticles dispersed on ZnO thin film

Ultraviolet photoconductivity in sol gel-derived ZnO thin film loaded with gold (Au) nanoparticle (NPs) is investigated. Au-NPs loaded ZnO thin film (Au-NPs/ZnO) is found to exhibit high photoconducting gain (K) of about 4.12 × 10³ as compared to the bare ZnO thin film-based photodetector (4.9 × 10¹). The enhanced photoconductive gain of Au-NPs/ZnO detector has been achieved due to simultaneous lowering of dark current which occurs due to Schottky barrier effect originated after dispersing the Au NPs on the surface of ZnO thin film. The enhancement in photocurrent upon UV illumination is due to trapping of UV radiation via plasmonic effect caused by Au-NPs and subsequently coupling of absorbed light with the optical modes of underlying semiconducting ZnO surface.     

Looking at hydrogen motions in confinement

Why in a barren and hot desert, clays can contain a significant fraction of water? Why does concrete crack? How can we demonstrate that complexation of a drug does not alter its conformation in a way that affects its functionality? In this paper we present results on various studies using Quasi-Elastic Neutron Scattering aimed at clarifying these questions. To allow for a better understanding of neutron scattering, a brief introduction to the basics of its theory is presented. Following the theoretical part, experimental results dealing with the effects of confinement on the water dynamics caused by the interfaces in clays and the nano- and micro-pores of concrete are reviewed in detail. At the end, recent Quasi-Elastic Neutron Scattering investigations on the complexation of the local anesthetics Bupivacaine (BVC.HCl, C₁₈H₂₈N₂₀.HCl.H₂O) and Ropivacaine (RVC.HCl, C₁₇H₂₆N₂₀.HCl.H₂O) into the cyclic β-cyclodextrin oligosaccharide are presented. To conclude, the perspectives that the European Spallation Source brings to this subject are discussed.