Jiří Janata

Electrochemical study of gold electrodes with anodic oxide films—I. Formation and reduction behaviour of anodic oxides on gold

Abstract Up to three types of oxide are formed during anodic polarization of gold. The first formed oxides (oxides I and II, surface oxides, inner oxides) can be selectively electrochemically reduced and reformed in the presence of the last formed oxide (oxide III, bulk oxide, outer oxide). It is shown that a second type of oxide (oxide II) is not formed before oxide I reaches a thickness of two monolayers, ie 1.5 mC cm −2 oxide charge. This critical limit is independent of pH, electrolyte, ionic strength, buffer, buffer capacity or surface roughness. A severe influence of insufficient buffer capacity in potentiodynamic surface oxide formation and reduction is experimentally shown, discussed and explained. It is suggested that the onset of oxide II formation can be used for surface roughness determinations.

Polyaniline-Gold Nanocomposite System

Nanostructured composite materials of polyaniline (PANI) with gold clusters of different sizes and amounts have been produced. PANI films of the same thickness were grown electrochemically on platinum substrates. Then nucleation of gold clusters in the PANI film was initiated by chemical reduction of tetrabromoaurate ion in acidic solution. The spontaneous process of gold cluster formation was evaluated using UV-vis spectroscopy, scanning electron microscopy, and the Kelvin probe. It was found that the amount and size distribution of gold clusters vary with immersion time. The measured work function of the PANI/Au composite changes its magnitude according to the changes in composition of the materials. Despite the fact that the preparation method makes the gold cluster growth difficult to control in size and in distribution, it is of interest to applications for solid-state potentiometric sensors, batteries, supercapacitors, or catalysis since it modifies the electron affinity of the synthesized conducting polymer/gold composite.

Chemically sensitive field-effect transistors.

Sometimes unjustified, but nonetheless ever present need for more information continues to stimulate the development of new sensors and detectors. One of the more recent additions to the armory of these devices is the chemically sensitive field effect transistor (chemfet). It was born in the early seventies out of two very successful technologies: solid state integrated circuits and ion-selective electrodes (ise). It is still in its infancy but already out of the teething stage and with a very bright prospect ahead.

Development and Calibration of Field-Effect Transistor-Based Sensor Array for Measurement of Hydrogen and Ammonia Gas Mixtures in Humid Air

A sensor array for analyzing hydrogen and ammonia gas mixtures in humid air has been developed, built into a rugged system, and calibrated for laboratory testing. The sensor array is comprised of four chemically sensitive field-effect transistors (CHEMFETs). Chemically sensitive layers for the sensors were developed and tested using a Kelvin probe. A combination of catalytic and noncatalytic thin layers (palladium and polyaniline) was selected for the four-sensor array. The work function responses of the CHEMFET sensor array to mixtures of hydrogen, ammonia, and humid air were measured. Chemometric multivariate methods, linear and nonlinear partial least squares, were used for the calibration of the sensor array using gas mixtures in the concentration range from 0 to 10 000 ppm hydrogen and ammonia in humid air. The sensor array for ammonia showed good sensitivity, selectivity, response time, and stability and is recommended for field deployment. In contrast, the sensor array for hydrogen, though highly sensitive to hydrogen, demonstrated inadequate stability, requiring further development before deployment is recommended.

A critical evaluation of the mechanism of potential response of antigen polymer membranes to the corresponding antiserum

Abstract A critical evaluation of the potentiometric response of polymer-based electrodes to proteins is described. Despite the rather poor reproducibility of some of these measurements, it was established that the interface at a PVC membrane containing cardiolipin, lecithin and cholesterol with electrolyte solutions is non-polarized. It is suggested that the observed changes of potential are due to the changes of exchange current densities of individual ions which participate in the ion-exchange process and establish a mixed potential at that interface. Although some degree of immunochemical coupling is present, these sensors would be difficult to utilize as immunoelectrodes.

Ion-selective field effect transistors with polymeric membranes

The construction and operation of ion-selective field effect transistors (ISFET) with polymeric membranes are described, and their electrical and chemical performance are discussed. The H+, K+, and Ca2+ ISFETs all show responses similar to those of the corresponding ion-selective electrodes, with t95% response times of approximately 40 ms and accurate ion activity measurements for periods up to one month.

A field effect transistor as a solid-state reference electrode

Abstract The construction and performance of an integrated on-chip reference field-effect transistor is described. It is shown that excellent temperature and noise compensation can be obtained with this arrangement. The reference FET was used in conjunction with a pH ISFET and K + ISFET.

Combination of flow injection analysis and voltammetry

Abstract The flow injection analyzer for students, teaching and research (FIAstar) is used in conjunction with a new micropool mercury flow-through electrode, to explore the possibilities offered by using d.c. polarography, rapid scan and amperometric titrations on a dispersed sample zone in motion. The work outlines the principles of the use of a scanning detector for investigation of the concentration gradients and chemical reactions taking place during the dispersion of sample solution within a carrier stream. The data, which are collected in real time, are displayed in three-dimensional diagrams.

Effect of Morphology on the Response of Polyaniline-Based Conductometric Gas Sensors: Nanofibers vs. Thin Films

Mixtures of methanol with increasing fractions of formic acid were used to progressively transform the morphology of polyaniline starting from nanofibers to compact conventional films. It was demonstrated that the methanol/formic acid mixture could be used as a viable solvent system for nanostructured polyaniline to achieve sufficient processability while maintaining its microstructure. The effects of morphology on the response of polyaniline-based conductometric sensors to neutral gas molecules were also examined. Although the nanofiber films demonstrated faster responses, they exhibited lower sensitivity than conventional thin films. Creating high surface area nanofibril structures in polyaniline film does not appear to effectively enhance sensor sensitivity due to the relatively open structure inherent to many polymeric materials and the adverse contribution from the interfibrillar contact resistance associated with nanofiber films.

Historical review. Twenty years of ion-selective field-effect transistors

Ion sensitive field-effect transistors have been researched for over twenty years. Several hundred papers have been written about them and they are beginning to appear on the commercial market. The evolution of this field and perennial issues concerning these sensors are reviewed from the authors perspective.