Disposable Injection‐Moulded Cell‐on‐a‐Chip Microfluidic Devices with Integrated Conducting Polymer Electrodes for On‐Line Voltammetric and Electrochemiluminescence Detection

This work reports the construction and characterization of plastic electrochemical micro‐flow‐cells with integrated injection‐moulded polymer electrodes. The three electrodes (working, auxiliary, and reference) were fabricated by injection‐moulding from a conducting grade of polystyrene loaded with carbon fibers. On‐chip reference electrodes were prepared by coating one of the conducting polymer electrodes with a Ag/AgCl layer (implemented either by e‐beam evaporation of Ag followed by electrochemical formation of AgCl or by applying a Ag/AgCl paste). Working electrodes were either polymer electrodes coated with Au by e‐beam evaporation or bare conducting polymer electrodes. The electrodes were integrated into the micro‐flow‐cells by an over‐moulding process followed by ultrasonic welding. The devices were characterized by optical and electrochemical techniques. Studies by cyclic voltammetry (CV), anodic stripping voltammetry (ASV) and electrochemiluminescence (ECL) demonstrate ‘proof–of‐principle’ of the micro‐flow‐cells as electrochemical sensors.     

Analysis of thermal parameters and factors acting on thermal conduction of low‐k films

The thermal properties of a silicon oxide‐based low‐k film and a thermally oxidized silicon film were investigated using the 3‐omega and laser thermo‐reflectance (LTR) methods. Thermal conductivity and effusivity were successfully estimated by the 3‐omega and LTR methods, respectively. It was confirmed that the combination of thermal effusivity and conductivity can successfully provide the heat capacity and thermal diffusivity of the films. The thermal parameters thus obtained suggested that the lower thermal conductivity of the examined low‐k film comes mainly from the rather low level of thermal diffusivity. Based on an analysis of the X‐ray diffraction profiles of the films, it was found that the low thermal diffusivity of the low‐k film can be attributed to the discontinuity of the network structure of their clusters. The heat resistance at the interface between the film and Si substrate was also evaluated. We found that the low‐k film exhibited, interestingly, negative interfacial heat resistance, although interfacial heat resistance should have a positive value in general. In order to determine the origin of the negative interfacial heat resistance, the interface state of the films was analyzed in detail on the basis of X‐ray reflectivity (XRR) measurements. The XRR results showed clearly that a thin, high‐density layer was present at the interface of the low‐k films. This high‐density layer presumably promoted heat flow to the substrate, resulting in the apparent negative interfacial heat resistance. Copyright © 2008 John Wiley & Sons, Ltd.     

2‐Aminobenzenethiol‐Functionalized Silver‐Decorated Nanoporous Silicon Photoelectrodes for Selective CO2 Reduction

A molecularly thin layer of 2‐aminobenzenethiol (2‐ABT) was adsorbed onto nanoporous p‐type silicon (b‐Si) photocathodes decorated with Ag nanoparticles (Ag NPs). The addition of 2‐ABT alters the balance of the CO₂ reduction and hydrogen evolution reactions, resulting in more selective and efficient reduction of CO₂ to CO. The 2‐ABT adsorbate layer was characterized by Fourier transform infrared (FTIR) spectroscopy and modeled by density functional theory calculations. Ex situ X‐ray photoelectron spectroscopy (XPS) of the 2‐ABT modified electrodes suggests that surface Ag atoms are in the +1 oxidation state and coordinated to 2‐ABT via Ag?S bonds. Under visible light illumination, the onset potential for CO₂ reduction was ?50 mV vs. RHE, an anodic shift of about 150 mV relative to a sample without 2‐ABT. The adsorption of 2‐ABT lowers the overpotentials for both CO₂ reduction and hydrogen evolution. A comparison of electrodes functionalized with different aromatic thiols and amines suggests that the primary role of the thiol group in 2‐ABT is to anchor the NH₂ group near the Ag surface, where it serves to bind CO₂ and also to assist in proton transfer.     

Direct Correlation Between Electric and Structural Properties During Solidification of Poly(3‐hexylthiophene) Drop‐Cast Films

Structural and electrical properties of semicrystalline P3HT cast films onto Si/SiO₂ surface are studied during the solidification under applied electric field in lateral OFET geometry. During evaporation of the solvent, the formation of P3HT crystallites is monitored simultaneously by time‐resolved X‐ray diffraction and by source‐drain current measurements. The electrical current is reaching its maximum in two pronounced regimes already before complete solidification of the polymer as detected by X‐ray diffraction intensities. The monitored complex time dependence of current and X‐ray intensities reveals a highest conducting level for the gel‐like state.     

Ag/Au Alloy LSPR Engineering by Co‐deposition of RF‐Sputtering and RF‐PECVD

Silver‐Gold alloy/diamond like carbon (Ag‐Au/DLC) nanocomposite films were prepared by co‐deposition of RF‐sputtering and RF‐PECVD on glass substrates by using acetylene gas and silver‐gold target. The deposition process was carried out at room temperature in one minute with the variable parameters of initial pressures and RF powers. X‐ray diffraction analysis demonstrated the formation of Ag/Au alloy nanoparticles with a face‐centered cubic (FCC) structure. Localized surface plasmon and optical properties of Ag‐Au alloy nanoparticles were studied by UV‐visible spectrophotometry which showed that increasing RF power and initial pressure cause a redshift in all samples. Moreover, the effect of RF power and initial pressure on the size and shape of nanoparticles were studied by 2D Atomic force microscopy images. Energy dispersive X‐ray spectroscopy revealed the formation of Ag‐Au/DLC nanoparticles and the percentages of C, Ag, Au and O in all samples. The applied method for Ag/Au alloy preparation is the one step and low‐cost method which makes the samples ready for sensing application.     

Super structure formation in a wholly aromatic copolyester fiber

The structure of a wholly aromatic copolyester fiber containing 60 mol% p‐hydroxybenzoic acid (PHB), 20 mol% 4−4′‐dihydroxydiphenyl, 15 mol% terephthalic acid and 5 mol% isophthalic acid was studied by means of electron microscopy and wide‐angle X‐ray diffraction. The X‐ray diffraction pattern of the wholly aromatic copolyester fibers showed two sets of diffractions: one set was composed of sharp spots which arose from relatively high crystalline phase. The crystal structure analyzed by these spots was orthorhombic and the lattice dimensions were a = 0.869 nm, b = 0.510 nm, c = 1.20 nm and ρ = 1.50 g/cm³. Another set was characteristic of streaks on the meridian extending parallel to the equator. X‐ray scattering intensity distribution on the meridian was calculated as the square of Fourier transform of random chain model. Comparison of this intensity distribution with the observed meridional maxima concluded that the streaks were due to rather disordered chains with a PHB content of less than 50%. Dark field image (DFI) taken from the meridional 002 reflection showed that slender crystallites were distributed over the whole visual field, oriented parallel to the fiber axis. On DFI from the equatorial 200 reflection, some of these crystallites were also observable, forming groups that distributed randomly in the field. All crystallites belonging to the same group co‐oriented in a*‐ and c*‐axis directions, though disordered parts intervened among the crystallites. This is attributed to the fact that, though the content of PHB in the segments of disordered parts was only 50%, these PHB held the co‐orientation among the slender crystallites within one group. Heat treatment induced the development of block segment and subsequent crystallite growth with fiber. This reorganization improved the thermostability and the mechanical properties. Copyright © 2000 John Wiley & Sons, Ltd.     

Investigation of a‐Si (N+)/c‐Si (P) hetero‐junction solar cell through AFORS‐HET simulation

In this paper, a TCO/a‐Si(N⁺)/a‐Si(i)/c‐Si(P)/Al‐BSF(P⁺) structure hetero‐junction (HJ) cell model is developed. With AFORS‐HET V3.0, we investigate the influence of amorphous silicon (a‐Si) emitter and amorphous silicon (a‐Si)/crystalline silicon (c‐Si) interface defects on the HJ cell performance. Through modulating a‐Si(N⁺) emitter doping concentration and band offset at a‐Si/c‐Si interface, a maximum width value of 103 nm inversion layer is observed in the c‐Si(P) side. For 1 Ω.cm c‐Si (P) substrate, emitter doping of over 1 × 10²⁰ cm^?3 is necessary for achieving a high‐efficiency a‐Si/c‐Si HJ cell. Furthermore, defects at a‐Si(N⁺)/c‐Si(P) interface severely affect the open circuit voltage (Voc) and short circuit current density (Jsc) of the cell. Meanwhile, simulation indicates that Voc is more sensitive to interface defect density (Dit) than Jsc. A thin a‐Si(i) layer between a‐Si(N⁺) and c‐Si(P) does induce great improvement in Voc of TCO/a‐Si(N⁺)/a‐Si(i)/c‐Si(P)/Al‐BSF(P⁺) cell. As a result, high cell efficiency of 22.27% is achieved for a‐Si(N⁺)/c‐Si(P) HJ Cell with optimized parameters. Copyright © 2010 John Wiley & Sons, Ltd.     

In Situ Study of the Surface Oxidation of FeCr Alloys Using Grazing Incidence X‐ray Absorption Spectroscopy (GIXAS)

The surface oxidation of FeCr alloys with 18, 28, and 43 mass‐% Cr was investigated in situ using grazing‐incidence X‐ray absorption spectroscopy (GIXAS) at the chromium and iron K‐edges. Oxidation in air was monitored in situ in the temperature range from 290 K to 680 K. The standard GIXAS data analysis is extended for the treatment of a single layer model in order to estimate the chromium concentrations of the oxide layer and of the near‐interface substrate as well as the oxide layer thickness. XANES analysis shows transitions from b.c.c. Fe to corundum type Fe₂O₃ and from b.c.c. Cr to corundum type Cr₂O₃. The initial oxide layers are 1.1‐1.4 nm thick and contain 60‐90 mass‐% chromium, while the near‐interface substrate is depleted in Cr. During heating, iron oxide growth dominates up to 560‐600 K. Then the chromium oxide layer loses its passivation effect and Cr oxidation sets in.     

Direct Electrochemistry of Cytochrome c at Modified Si(100) Electrodes

This paper demonstrates the direct electron transfer between the heme moiety of horse hearth cytochrome c and a pyridinyl group on self‐assembled‐monolayer‐modified Si(100) electrodes. Self‐assembled monolayers (SAMs) containing the putative receptor ligand were prepared by a step‐wise procedure using “click” reactions of acetylene‐terminated alkyl monolayers and isonicotinic acid azide derivatives. Unoxidized Si(100) electrodes, possessing either isonicotinate or isonicotinamide receptor ligands, were characterized using X‐ray photoelectron spectroscopy, contact‐angle goniometry, cyclic voltammetry, and electrochemical impedance spectroscopy. The ability of isonicotinic acid terminated layers to coordinatively bind the redox center of cytochrome c was found to be restricted to pyridinyl assemblies with a para‐ester linkage present. The protocol detailed here offers an experimentally simple modular approach to producing chemically well‐defined SAMs on silicon surfaces for direct electrochemistry of a well‐studied model redox protein.     

X‐ray diffraction study of low‐energy carbon‐ion implanted Si(001)

In the search for Si‐ and C‐based crystalline phases in low‐energy ion implanted and electron‐beam annealed Si surface layers, X‐ray diffraction (XRD) measurements were performed at grazing incidence on samples of large SiC nanocrystals grown on a 90 nm thick Si layer containing C atoms. Diffraction patterns and reciprocal space maps did not reveal XRD patterns originating from the nanocrystals or the implanted layer, but did show that distortions of the Si crystal structure were introduced into the implanted layer. After annealing, the strain in the implanted layer is reduced, possibly by carbon atoms that have moved to locations close to dislocations and dislocation loops. This investigation underpins the growth theory of the SiC nanocrystals on Si, with carbon atoms migrating to form the nanostructures. Copyright © 2007 John Wiley & Sons, Ltd.     

A Comparative Study of Modifying Gold and Carbon Electrode with 4‐Sulfophenyl Diazonium Salt

A comparison of the reductive adsorption behavior of 4‐sulfophenyl diazonium salt and subsequent electrochemical reactivity on gold relative to carbon was studied with some significant differences observed. The ability of the 4‐sulfophenyl layer adsorbed onto gold to block access of the redox probe ferricyanide to the underlying electrodes, as determined via cyclic voltammetry was inferior to the same layers formed on glassy carbon electrodes thus indicating a more open, porous layer formed on gold. More significantly, the 4‐sulfophenyl layers are shown to be far less electrochemically stable on gold than on glassy carbon. Electrochemical and X‐ray photoelectron spectroscopy (XPS) evidence suggests the instability is due to cleavage of the bond between sulfonate functional group and phenyl ring. These results provide further evidence that although aryl diazonium salt layers are relatively stable on gold surfaces compared with alkanethiol based self‐assembled monolayer (SAMs), the stability is not as high as is observed on carbon.     

High‐Performance Platinum‐Free Dye‐Sensitized Solar Cells with Molybdenum Disulfide Films as Counter Electrodes

By using a radio‐frequency sputtering method, we synthesized large‐area, uniform, and transparent molybdenum disulfide film electrodes (1, 3, 5, and 7 min) on transparent and conducting fluorine‐doped tin oxide (FTO), as ecofriendly, cost‐effective counter electrodes (CE) for dye‐sensitized solar cells (DSSCs). These CEs were used in place of the routinely used expensive platinum CEs for the catalytic reduction of a triiodide electrolyte. The structure and morphology of the MoS₂ was analyzed by using Raman spectroscopy, X‐ray diffraction, and X‐ray photoemission spectroscopy measurements and the DSSC characteristics were investigated. An unbroken film of MoS₂ was identified on the FTO crystallites from field‐emission scanning electron microscopy. Cyclic voltammetry, electrochemical impedance spectroscopy, and Tafel curve measurements reveal the promise of MoS₂ as a CE with a low charge‐transfer resistance, high electrocatalytic activity, and fast reaction kinetics for the reduction of triiodide to iodide. Finally, an optimized transparent MoS₂ CE, obtained after 5 min synthesis time, showed a high power‐conversion efficiency of 6.0 %, which comparable to the performance obtained with a Pt CE (6.6 %) when used in TiO₂‐based DSCCs, thus signifying the importance of sputtering time on DSSC performance.     

Forensic Applications of Portable X‐ray Fluorescence Spectrometer: Glass Samples

Portable X‐ray Fluorescence Spectrometer (PXRF) is a qualitative and semi‐quantitative elemental analysis method. Recently, many researches using PXRF in the elemental analysis of materials have been reported. However, PXRF has not been extensively applied in forensic science, thus this study is devoted to demonstrate the utility of this technique through a rapid elemental analysis of glass samples for preliminary glass discrimination. Major elements such as Si, O, Ca, Al, and Na, as well as traces of Sr, Rb, K, Fe and Sn, in 25 glass samples were analyzed by PXRF. The amounts of some elements, such as Fe, K, Zr, and Sr, vary in different samples, while other elements, such as Th, are consistent in most tested glass samples. The results show that we can discriminate 98.31 % of 7,500 pair‐wise comparisons created from 25 glass samples. This study establishes PXRF as a new rapid method for the preliminary elemental analysis of glass, which shows a potential to be further applied for discrimination of glass samples in forensic field.     

X‐ray microanalysis in STEM of short‐term physicochemical reactions at bioactive glass particle/biological fluid interface. Determination of O/Si atomic ratios

Short‐term physicochemical reactions at the interface between bioactive glass particles and biological fluids are studied and we focus our attention on the measurements of O/Si atomic ratio. The studied bioactive glass is in the SiO₂? Na₂O? CaO? P₂O₅? K₂O? Al₂O₃? MgO system. The elemental analysis is performed at the submicrometre scale by scanning transmission electron microscopy associated with energy‐dispersive x‐ray spectroscopy (EDXS) and electron energy‐loss spectroscopy (EELS). We previously developed an EDXS quantification method based on the ratio method and taking into account local absorption corrections. In this way, we use EELS data to determine, by an iterative process, the local mass thickness, which is an essential parameter for correcting absorption in EDXS spectra. After different immersion times of bioactive glass particles in a simulated biological solution, results show the formation of different surface layers at the bioactive glass periphery. Before 1 day of immersion, we observe the presence of an already shown (Si,O,Al)‐rich layer at the periphery. In this paper, we demonstrate that a thin ‘electron dense’ (Si,O)‐layer is formed on top of the (Si,O,Al)‐layer. In this (Si,O)‐layer, depleted in aluminium, we point out an increase of oxygen weight concentration that can be interpreted by the presence of Si(OH)₄ groups, which permit the formation of a (Ca,P)‐layer. Aluminium plays a role in the glass solubility and may inhibit apatite nucleation. After the beginning of the (Ca,P)‐layer formation, the size of the ‘electron dense’ (Si,O)‐layer decreases and tends to disappear. After 2 days of immersion, the (Ca,P)‐layer grows in thickness and leads to apatite precipitation. Copyright © 2004 John Wiley & Sons, Ltd.     

Surface and interface analysis of electrochemically synthesized ferromagnetic/semiconducting Ni/GaAs(001) thin film

Thin film of ferromagnetic (FM) metal (Ni) on a semiconducting substrate (GaAs), i.e. Ni/GaAs(001), has been synthesized using electrochemical method. The structural, chemical and magnetic properties at the surface and interface have been investigated using X‐ray diffraction (XRD)/grazing incidence X‐ray reflectivity (GIXRR), X‐ray photoelectron spectroscopy (XPS) and magneto‐optical Kerr effect (MOKE) techniques, respectively. A crystalline peak observed at 44.4º in the XRD pattern, corresponding to Ni(111) Bragg peak, confirms the monocrystalline nature of the film. The atomic force microscopy image shows small‐sized spherical crystallites uniformly deposited over the substrate. The fitted GIXRR pattern confirms a smooth Ni/GaAs(001) film surface with roughness of less than ~5 ± 0.4 Å. The micro‐structural parameters, such as film thickness, surface and interface roughness, and electron density, are found to be ~230 ± 5 Å, ~4.5 ± 1 Å, ~0.5 ± 0.02 Å and ~6.38 ± 0.5 (Å^?2), respectively. The chemical nature of the film at the surface and interface, investigated using a depth profile XPS technique, shows no diffusion of metallic Ga and As into Ni layer or vice versa, confirming a sharp FM/semiconducting Ni/GaAs(001) interface. The magnetization behavior investigated using MOKE technique at room temperature shows a soft FM nature of the film with coercivity of ~75 Oe at the film surface. However, coercivity was found to be ~35 Oe at the interface. In addition, the saturation magnetization is also found to decrease at the interface with decreasing Ni layer thickness. The observed magnetization behavior is correlated with structural and chemical changes that occur at the interface of Ni/GaAs(001) film. Copyright © 2013 John Wiley & Sons, Ltd.     

Plasma and chromic acid treatments of polycarbonate surface to improve coating–substrate adhesion

The influence of Ar/O₂ plasma activation and chromic acid etching of polycarbonate (PC) surface on the adhesion of coating to substrate was systematically studied by cross‐cut and tape peel methods through temperature‐shock aging tests. The differences between the wettabilities and elemental compositions of plasma‐treated and chromic acid‐treated PC surfaces prior to coating deposition were evaluated by contact angle measurements and X‐ray photoelectron spectroscopy. To elucidate the adhesion failure of the coatings, nanoindentation technique was employed for the quantitative assessment of the nanomechanical changes of coating depositions on PCs after temperature‐shock aging tests. The two surface treatments can significantly improve the hydrophilicity and polarity of the PC surface, resulting in excellent adhesion of the coating on the PC substrate. Temperature‐shock aging tests reveal that the adhesion of coating on plasma‐modified substrates is superior to that of chromic acid‐etched substrates. We propose that the improved adhesion of the coating on the plasma‐modified PC can be attributed to the higher wettability and more cross‐linking of C–O–Si bonds at the coating–substrate interface. Copyright © 2013 John Wiley & Sons, Ltd.     

Characterization of nano‐organized multilayers constituted by successive inorganic (gold) and organic (alkylthiols) layers

Nanostructured multilayers constituted by alternate metallic (gold) and organic (alkyldithiol) layers, and grafted onto glass or silicon substrates are prepared and analysed. Such complex layers could be of interest as a new type of surfaces but also as localized dissipative zones particularly in the field of adhesion science. The formation and the structure of these model systems are examined using a number of techniques such as atomic force microscopy (AFM), wetting analysis (contact angles), X‐ray photoelectron spectroscopy (XPS) and conductivity measurements. It is shown that, in terms of electrical conductivity, gold layers exhibit a percolation transition from an insulating granular structure to a conductive worm‐like structure at a threshold thickness of about 5 nm. XPS (and wettability) analyses clearly indicate that the fractional coverage of the gold surface is about 30% with alkyldithiol and that these molecules are either grafted in a stand‐up position or in the form of a loop. Moreover, a partial electrical connection between two successive gold layers is observed, confirming that the confined organic layer of alkyldithiol between them is too loosely organized to play the role of an insulating barrier. Copyright © 2007 John Wiley & Sons, Ltd.     

A new cross‐linked system of silicone rubber based on silicone‐polyurea block copolymer

A new cross‐linked system of silicone rubber (SR) was obtained from silicone‐polyurea block copolymers that was synthesized with aminopropyl terminated polydimethylsiloxane and (4‐isocyanatocyclohexyl)‐methane. SR possessed self‐reinforced and physical cross‐linked structure. It had better mechanical properties that the hardness, the tensile strength, and the elongation at break could reach 65 Shore A, 3.78 MPa, and 458% with the polyurea segment content ranging from 2.01% to 9.13% by weight . The hydrogen bond that led to the physical cross‐linked structure was proved byFourier transform infrared spectroscopy. The microphase separated structure that caused the self‐reinforcement was illustrated by scanning electron microscopy, X‐ray diffraction analysis, and dynamic mechanical analysis. Fourier transform infrared spectroscopy results showed the hydrogen bond formation between the polyurea units. Scanning electron microscopy, dynamic mechanical analysis, and X‐ray diffraction analysis results proved the microphase separation existed between polyurea units and ―Si―O―Si― chains. The increase of polyurea contents enhanced the binding of hydrogen bond and improved the extent of microphase separation. Accordingly, it decreased the thermal properties and lowered the glass transition temperature (T_g) from −108°C to −114°C. Also, the increase of polyurea contents increased the hydrophobicity of SR that the surface free energy could reach to −24.81 mN/m.     

Surface analysis of epitaxially grown GeSn alloys with Sn contents between 15% and 18%

Metastable Germanium–tin (GeSn) layers with rather high Sn content between 15% and 18% grown on Si substrates by molecular beam epitaxy were analyzed for the morphological changes on a surface before and after reaching critical layer parameters (thickness, Sn content, and growth temperature) for surface roughening. Atomic‐force microscopy investigations were performed as a function of thickness and separately for varying Sn concentrations in the GeSn layer. Epitaxial growth of metastable, uniform GeSn (15% Sn content) layers is obtained up to a critical thickness which increases from about 80 to above 200 nm by reducing the nominal growth temperature from 160 to 140 °C. Phase separation of the complete layer into tin‐rich surface protrusions and a Ge‐rich matrix takes place beyond the critical thickness. This surface roughening via phase separation was not observed in earlier investigations with lower Sn concentrations (<6%). Tin depletion in the GeSn matrix was confirmed by using energy‐dispersive X‐ray spectroscopy measurements showing residual Sn concentration below 5%. Additionally, creation of droplets with high concentration of tin on the surfaces was confirmed by energy‐dispersive X‐ray spectroscopy. Copyright © 2016 John Wiley & Sons, Ltd.     

Introduction of Ag/CuO/MCM‐48 as an efficient catalyst for the one‐pot synthesis of novel pyran‐pyrrole hybrids

Bimetallic silver and copper incorporated mesoporous MCM‐48 (Ag/CuO/MCM‐48) was synthesized by simple wet‐impregnation method. The knowledge about its structural properties was gathered by means of Fourier transform‐infrared, energy‐dispersive X‐ray, X‐ray diffraction, field emission‐scanning electron microscopy, transmission electron microscopy and Brunauer–Emmett–Teller analyses. The catalytic activity of Ag/CuO/MCM‐48 was examined in the one‐pot three‐component reaction of 3‐(1‐methyl‐1H‐pyrrol‐2‐yl)‐3‐oxopropanenitrile, malononitrile and various aromatic aldehydes leading to novel pyran‐pyrrole hybrid derivatives in reduced reaction times (5–10 min) and excellent yields (88–97%). Application of Ag/CuO/MCM‐48 as a potent heterogeneous catalyst with good reusability up to five times, use of ethanol as an eco‐compatible medium and chromatography‐free work‐up are some crucial green aspects of this procedure.