Potassium ion-selective electrodes based on valinomycin/PVC overlayered solid substrates

In this work, permutations of plasticized PVC membranes with incorporated valinomycin are coated over various substrate metallizations. Characterization of the resulting potassium electrodes includes measurement of sensitivity, short- and long-term potential drift, dissolved oxygen induced potential transients and probe lifetime. Results using the best performing metallizations compare favorably with those obtained using identical membranes in the symmetrical solution contact configuration. Prospects for use of this approach as the ion-sensing layer of ISFET (Ion-Sensitive Field-Effect Transistor) devices are considered.     

The ammonia sensitivity of platinum-gate MOSFET devices: dependence on gate electrode morphology

The response to ammonia of silicon-based Metal Oxide Semiconductor Field Effect Transistor (MOSFET) devices having either evaporated or sputtered Pt gate electrodes has been studied. A substantial difference in ammonia sensitivity was observed between these two types of device, which is thought to be related to differences in morphology between the two types of gate electrode; devices having evaporated Pt gate electrodes, which are non-continuous, are very ammonia sensitive, whereas devices having sputtered Pt gates, which are continuous, are not ammonia sensitive. However, both the evaporated and sputtered gate devices exhibit a similar response to hydrogen (typically, changes in threshold voltage (V_T) of approximately -420 mV and -350 mV respectively to 500 ppm hydrogen at 150 °C). The ammonia sensitivity of the evaporated Pt-gate MOSFET is dependent on both temperature and ageing effects; the optimum operating temperature of this device is 175 °C, and a burn-in period of approximately 48 h at 200 °C is necessary before the maximum response to ammonia is observed. The humidity response of both evaporated and sputtered Pt-gate MOSFET devices has been studied at 175 °C; a change from 20 to 95% r.h. does not produce a significant response from either of these devices (ΔV_T is typically -35 mV and -5 mV respectively).     

Preparation of high quality electrical insulator self-assembled monolayers on gold. Experimental investigation of the conduction mechanism through organic thin films

Self-assembled monolayers (SAMs) form highly ordered, stable dielectrics on conductive surfaces. Being able to attach larger-area contacts in a MIM (metal-insulator-metal) diode, their electrical properties can be determined. In this paper, the electrical conduction through thiolate SAMs of different alkyl chain lengths formed on gold surfaces were studied and discussed. The influence of the headgroup with respect to the surface quality and prevention of short circuits is investigated. Phenoxy terminated alkanethiols were found to form high quality SAMs with perfect insulating properties. Synthesis of the required terminally substituted long chain thiols have been developed. The I(V) characteristics of MIM structures formed with these SAMs are measured and simulated according to theoretical tunneling models for electrical conductivity through thin organic layers. SAM based electronic devices will become especially important for future nanoscale applications, where they can serve as insulators, gate dielectric of FETs, resistors, and capacitor structures.     

Optimisation of an electronic amplifier applied to electrolyte/insulator/semiconductor structure

This paper reports on the final development of a MOSFET-based amplifier for the electrical characterisation of chemical field-effect capacitors (ChemFEC) based on electrolyte/insulator/semiconductor (EIS) capacitive structure. Experimental demonstration is performed through the study of SiO₂/Si₃N₄ ion sensitive field-effect capacitor (ISFEC) sensors for pH measurement. This study deals with the amplification's properties according to the ISFEC and MOSFET electrical characteristics. Thus, the ISFEC transition from the accumulation to the inversion regime is shown to be responsible for a non-linear phenomenon. Nevertheless, thanks to a compromise between the ISFEC flat-band voltage and the MOSFET threshold voltage, linear responses are evidenced on the [2-12] pH range. Thus, the non-linear phenomenon observed in previous works is clarified. The detection structure evidences linear responses, which is an essential parameter for sensors. Finally, high detection sensitivities are obtained on a small pH range due to this non-linearity.     

Sensitive Detection of Small Molecule–Protein Interactions on a Metal–Insulator–Metal Label‐Free Biosensing Platform

The need to develop label‐free biosensing devices that enable rapid analyses of interactions between small molecules/peptides and proteins for post‐genomic studies has increased significantly. We report a simple metal–insulator–metal (MIM) geometry for fabricating a highly sensitive detection platform for biosensing. MIM substrates consisting of an Au–PMMA–Ag nanolayer were extensively studied using both theoretical and experimental approaches. By monitoring reflectivity changes at the normal incidence angle, we observed molecular interactions as the thickness of the biolayer increased on the substrate surface. These interactions included the adsorption of various proteins (Mw=6–150 kD) and interactions between small molecules (Mw≤2 kD) and the immobilized proteins. The interaction of designed monosaccharide‐modified designed peptides with various lectins was also clearly detected. These interactions could not be detected by the conventional Au‐only substrate. Thus, the MIM approach affords a powerful label‐free biosensing device that will aid our understanding of protein interactions and recognition.     

Review of oxide formation in a plasma

The physical processes occurring at the surface and in the bulk of an oxide during plasma oxidation or anodization are discussed. It is shown that (i) the majority of oxygen ions used in the growth are formed by electron-assisted surface processes, (ii) the nature of the oxide surface and especially the presence of electrode contamination can have a determinant role in the oxygen exchange between the plasma and the oxide, and (iii) ion space charge can control the anodization kinetics. Two applications (formation of the insulating barrier of Josephson junctions, and GaAs MOSFET devices) are presented.     

Molecular imprinted membrane biosensor for pesticide detection: Perspectives and challenges

Polymers are crucial component for modern sensor devices. However, comprehensive research on polymer sensor technology is still going strong. Molecular imprinted membrane (MIM) is a great design that demonstrates acceptable recognition ability when integrated with a sensing transducer. Generally, the detection technique that has been widely and sparingly used for pesticide is mass spectrometry merged with gas and/or liquid chromatography. Nevertheless, this review focuses not on these common methods but on the specific methodology of MIM biosensor for the analysis of pesticides. Finally, the transduction schemes of the MIM sensor are reviewed. The interest of this article is sketched to the trends and challenges present in this field of study.     

Electrical detection of hepatitis C virus RNA on single wall carbon nanotube-field effect transistors

We report the unambiguous detection of a sequence of Hepatitis C Virus (HCV) at concentrations down to the fractional pM range using Single Wall Carbon Nanotube (SWNT) Field Effect Transistor (FET) devices functionalized with Peptide Nucleic Acid (PNA).     

Surface characterization of functionalized imidazolium-based ionic liquids

The surface composition of oligo(ethylene glycol) ether functionalized bis(trifluoromethylsulfonyl)imide ionic liquids has been studied by means of X-ray photoelectron spectroscopy (XPS). For [Me(EG)MIM][Tf 2N], [Et(EG) 2MIM][Tf 2N], and [Me(EG) 3MIM][Tf 2N], which vary by the number of ethylene glycol (EG) units (from 1 to 3), we have shown that the stoichiometry of the surface near region is in excellent agreement with the bulk stoichiometry, which confirms the high purity of the ionic liquid samples investigated and rules out pronounced surface orientation effects. This has been deduced from the experimental observation that the angle-resolved XP spectra of all elements present in the IL anions and cations (C, N, O, F, S) show identical signals in the bulk and surfaces sensitive geometry, i.e., at 0 degrees and 70 degrees emission angle, respectively. The relative intensity ratios of all elements were found to be in nearly perfect agreement with the nominal values for the individual ILs. In contrast to these findings, we identified surface-active impurities in [Me(EG)MIM]I, which is the starting material for the final anion exchange step to synthesize [Me(EG)MIM][Tf 2N]. Sputtering of the surface led to a depletion of this layer, which however recovered with time. The buildup of this contamination is attributed to a surface enrichment of a minor bulk contamination that shows surface activity in the iodide melt.     

Dielectric Properties Investigation of Metal–Insulator–Metal (MIM) Capacitors

This study presents the construction and dielectric properties investigation of atomic-layer-deposition Al₂O₃/TiO₂/HfO₂ dielectric-film-based metal–insulator–metal (MIM) capacitors. The influence of the dielectric layer material and thickness on the performance of MIM capacitors are also systematically investigated. The morphology and surface roughness of dielectric films for different materials and thicknesses are analyzed via atomic force microscopy (AFM). Among them, the 25 nm Al₂O₃-based dielectric capacitor exhibits superior comprehensive electrical performance, including a high capacitance density of 7.89 fF·µm⁻², desirable breakdown voltage and leakage current of about 12 V and 1.4 × 10⁻¹⁰ A·cm⁻², and quadratic voltage coefficient of 303.6 ppm·V⁻². Simultaneously, the fabricated capacitor indicates desirable stability in terms of frequency and bias voltage (at 1 MHz), with the corresponding slight capacitance density variation of about 0.52 fF·µm⁻² and 0.25 fF·µm⁻². Furthermore, the mechanism of the variation in capacitance density and leakage current might be attributed to the Poole–Frenkel emission and charge-trapping effect of the high-k materials. All these results indicate potential applications in integrated passive devices.     

Comparison of an Electronic Nose with the Sensory Evaluation of Food Products by “Triangle Test”

In this paper a novel approach for performing discriminative test in food quality control is reported. The method is based on the use of an electronic nose equipped with 10 Metal Oxide Semiconductor Field Effect Transistor (MOSFET) sensors, 12 Metal Oxide Semiconductor (MOS) sensors and one humidity sensor. The pattern of the sensor responses generated by the electronic nose has been used for performing “objective” triangle tests in several food products. The results were compared with the data obtained by using standard methodology (triangle test) of sensory analysis (UNI ISO 4120 Norm). The e‐nose is able to classify correctly all the samples under study, while the sensory panel is able to correctly perform the test only in 50% of the cases. As compared with the sensory test, the electronic nose methodology is simple, rapid and results suggest that it can be useful tool for performing discriminative testing.     

[C14MIM]Br离子液体对聚丙烯超临界CO2发泡性能的影响

本文对PP/[C₁₄MIM]Br体系的熔融过程和对CO₂的吸收, 以及[C₁₄MIM]Br在PP基体中的分散状态进行了研究, 并初步考察了[C₁₄MIM]Br对PP发泡性能的影响.     

Electrical characteristics and chemical stability of non-oxidized, methyl-terminated silicon nanowires

Silicon nanowires (Si NWs) modified by covalent Si-CH3 functionality, with no intervening oxide, show atmospheric stability, high conductance values, low surface defect levels, and allow for the formation of air-stable Si NW Field-Effect Transistors (FETs) having on-off ratios in excess of 105 over a relatively small gate voltage swing (+/-2 V).     

Polypyrrole: Synthesis and electronic device application

A Ta solid electrolytic capacitor using conducting polypyrrole as a counter electrode has been developed by means of the direct film formation of electrochemical and chemical polymerization methods. Two-step electrochemical polymerization at a rapid and gentle rate yields a polypyrrole film on the dielectric surface of the capacitor. On the other hand, the homogeneous mixture dissolving pyrrole and oxidant under −70 °C allows chemical polymerization at elevated temperature, which also produces polypyrrole film on the dielectric surface. The capacitors produced by these methods demonstrate the improved characteristics, i.e., a high capacitance, low inner resistance and small leakage current, that correspond to the high-speed electronic devices.     

Transient Optical Characteristics of Broad Absorption Band Excitons Modulated by Micro-cavity

The understanding of light-matter interaction within micro-cavity lays the basic groundwork for many future photon-related technologies and applications. We prepared low quality metal-insulator-metal(MIM) micro-cavity consisting massive two-level broad absorption band dye(Nile Red) excitons, which randomly dispersed in SU-8 polymer negative resist matrix and measured their optical characteristics. New binate transmission peaks with large energy separation(so-called Rabi-splitting phenomenon) and their angular anti-crossing behavior in consequence of the interaction between dye excitons and confined photons were observed. It was also confirmed that the separated energy can be tuned by changing the doped exciton concentrations. Time-resolved transient absorption measurements showed that such an interaction is indeed a coherent one but rather a strong coupling one and one can modulate such a coherent mechanism by easily adjusting the detuning between dye excitons and confined cavity photons. This work may provide a comprehensive and deep understanding for such massive broad absoprtion band excitons-doped MIM micro-cavities and represent a further step to realize optical cavity-modulated devices in future.     

Fabrication and biocompatibility of cell outer membrane mimetic surfaces

The surface design used for improving biocompatibility is one of the most important issues for the fabrication of medical devices.For mimicking the ideal surface structure of cell outer membrane,a large number of polymers bearing phosphorylcholine(PC) groups have been employed to modify the surfaces of biomaterials and medical devices.It has been demonstrated that the biocompatibility of the modified materials whose surface is required to interact with a living organism has been obviously improved by introducing PC groups.In this review,the fabrication strategies of cell outer membrane mimetic surfaces and their resulted biocompatibilities were summarized.     

Electronic excitations induced by hydrogen surface chemical reactions on gold

Associated with chemical reactions at surfaces energy may be dissipated exciting surface electronic degrees of freedom. These excitations are detected using metal-insulator-metal (MIM) heterostructures (Ta-TaOx-Au) and the reactions of H with and on a Au surface are probed. A current corresponding to 5×10(-5) electrons per adsorbing H atom and a marked isotope effect are observed under steady-state conditions. Analysis of the current trace when the H atom flux is intermitted suggests that predominantly the recombination reaction creates electronic excitations. Biasing the front versus the back electrode of the MIM structure provides insights into the spectrum of electronic excitations. The observed spectra differ for the two isotopes H and D and are asymmetric when comparing negative and positive bias voltages. Modeling indicates that the excited electrons and the concurrently created holes differ in their energy distributions.     

Parallel processing in the isoelectric focusing chip

Investigation of isoelectric focusing (IEF) kinetics has been performed to provide the theoretical basis for miniaturization of classical IEF in immobilized pH-gradients. Standard IEF demands colinearity of the electric field and pH-gradient directions (serial devices). It is shown that the IEF separation process based on a continuous, serial pH gradient is incompatible with miniaturization of separation devices. The new realization of the IEF device by a parallel IEF chip is suggested and analyzed. The main separation tool of the device is a dielectric membrane (chip) with conducting channels that are filled by Immobiline gels of varying pH. The membrane is held perpendicular to the applied electric field and proteins are collected (trapped) in the channels whose pH are equal to the pI of the proteins. The pH value of the surrounded aqueous solution is not equal to any channel's pH. The fast particle transport between different channels takes place due to convection in the aqueous solution. The new device geometry introduces two new spatial scales to be considered: the scale of transition region from a solution to the gel in a channel and a typical channel size. The corresponding time scales defining the IEF process kinetics are analyzed and scaling laws are obtained. It is shown both theoretically and experimentally that parallel IEF accelerates the fractionation of proteins by their pI down to several minutes and enables possible efficient sample collection and purification.     

Amplified potentiometric determination of pK(00), pK(0), pK(l), and pK(2) of hydrogen sulfides with Ag(2)S ISE

The chemical capacitor theory has been applied to accurately determine dissociation constants of H(2)S with the Ag(2)S ion-selective electrode (ISE). The theory's principle is based on the measurement of the change in electrode charge density as a result of protonated or unprotonated sulfide adsorbed on the electrode surface. This charge density is related to the potential. Connection of each individual capacitor in series amplifies the potential according to the equation, E(total)=E(1)+E(2)+E(3)+cdots, three dots, centeredE(n). As the charges of individual capacitors are concentrated to one capacitor area, the charge density rises, and the potential increases. The pK(00), pK(0), pK(1), and pK(2) are reported as 1.8, 2.12, 7.05, and 12.0, respectively. The pK(00) and pK(0) are reported here for the first time. The pK(1) agrees well with the literature values; however, the pK(2) differs from those reported recently under extreme conditions. Reasons for disproving the unreasonably high pK(2)>17-19 values are given based on calculations. Mainly, when pK(2)>17-19, the experimental results do not fit the equilibrium equations, pH=(pK(1)+pK(2))/2, pK(1)=(pK(0)+pK(2))/2, and pH=pK(2)+log(HS(-))/(S(2-)).