In this study, we determined the Pd(II) chlorocomplex species that has the most favorable interaction with an electropolymerized and protonated polyaniline (PANI) film. This study was completed with the intent to use this species to electrochemically build atomic palladium clusters in the PANI matrix. Varying amounts of NaCl were added to a K2PdCl4/HClO4 solution to result in three species studied: PdCl2(H2O)2, PdCl3(H2O)−, and PdCl42–. UV–vis spectroscopy was used to confirm the speciation, and Raman spectroscopy, X-ray photoelectron spectroscopy, and cyclic voltammograms were used to probe the interaction between the Pd species and PANI. It was determined that PdCl3(H2O)− most effectively interacts with PANI as a result of the charge balance between the anion and the protonated nitrogen-containing groups in the polymer. It has been also found that some fraction of inserted Pd(II) cannot be reduced to Pd(0).

A sorption process of RuCl3 in phosphate buffer by polyaniline (PANI) powder chemically synthesized from phosphoric acid was spectrophotometrically monitored as a function of time. It was determined that the sorption process follows the Langmuir and Freundlich isotherms, and their constants were evaluated. It was determined that chemisorption was the rate-controlling step. By conducting detailed studies, we assigned the chemisorption to Lewis acid based interactions of the sorbent electron pair localized at the benzenoid amine (−NH2) and quinoid imine (═NH) groups, with the sorbate, RuCl3, as the electron acceptor. The stability of the interaction over a period of ∼1 week showed that the presence of the Ru(III) in the PANI matrix reverses its state from emeraldine base to emeraldine salt, resulting in a change of conductivity. The partial electron donor based charge transfer is a slow process as compared to the sorption process involving Brønsted acid doping.

The space–charge region of an organic semiconductor (OS)–insulator interface is probed by analyzing the spontaneous, thermally driven drain current fluctuations of a field-effect transistor in which the OS forms the gate electrode. This so called “excess drain current noise” is the outcome of local fluctuations of the Fermi level, resulting from stochastic exchange of electrons between traps near the Fermi level. The power spectral density of this noise is characteristic of a Lorentzian process with a distribution of time constants, which is attributed to the disorder in the OS film. Furthermore, this disorder leads to local inhomogeneity of the work function in the film and a finite correlation length of the work function fluctuations. The measurement of work function noise is only possible within a correlation length of the OS–insulator interface. Through systematic variation of gate voltage, primary doping and secondary doping levels, the correlation length, disorder, and the trapping/de-trapping time constant are examined on polyaniline as a representative OS. A model is proposed for local work function variations and spontaneous charge-carrier fluctuations within polyaniline films with consequences for organic electronics using organic semiconductors.

Survey of cyclic voltammograms of lower aliphatic alcohols in 1 M KOH recorded at electrodes containing atomic gold is presented. The atomically structured gold is placed in polyaniline, which is deposited on a platinum electrode. The electrochemical behavior of these atomic gold electrodes (AGE) is compared with Pt/polyaniline electrode without gold and with Pt/polyaniline electrode containing “unstructured” nanoclusters of Au. The conditions were identical for all of the experiments. This allows direct visual comparison of the effect of atomic structuring. The electrochemical activity of the AGEs is dominated by the odd–even pattern of reactivity, and it is superimposed on specific electrochemical behavior of individual alcohols.

Our atom-by-atom deposition method has been used to prepare hetero-tri-atomic clusters of Au1Pd2 and Au2Pd1 in polyaniline as isolation matrix. The sequence in which individual atoms are added affects the final structure of the cluster. Because of the uniquely defined point of attachment of the cluster to the PANI, isomers such as PANI-Pd–Au–Pd, PANI–Au–Pd–Pd and PANI–Pd–Pd–Au have been created. It is shown that the latter has much higher activity towards electrooxidation of n-propanol in alkaline medium than the first two. In fact, its activity is even higher than that of the most active homo-clusters PANI–Au6 and PANI–Pd2. The observed results are in good agreement with few available theoretical calculations of the HOMO–LUMO gap energy of these structures.

The effect of addition of one atom of palladium to n atoms of gold (n = 1–5) dispersed in polyaniline electrodes, for the electrooxidation of methanol and ethanol in alkaline solution has been investigated. For comparison, oxidation at pure atomic metal electrodes, Pt/PANI–Aun=2–7 and Pt/PANI–Pdn=2–6, was performed. It is shown that the one added Pd atom affects the oxidation peak currents and makes a significant difference in selectivity. Similar to our previous studies, the electrocatalytic activity has been correlated with the theoretically predicted HOMO–LUMO gap energies for the atomic metal alloys.

The previously described cyclic pathway method for deposition of atomic metals has been used to create Pd1–6 atomic clusters and Au1–5Pd1 and Au1–4Pd2 bimetallic atomic clusters in polyaniline (PANI). The controlled deposition of predetermined atomic size clusters of metals has been examined by testing the electrochemical oxidation of n-propanol in 1 M NaOH. The oxidation peak currents from the cyclic voltammograms were found to follow the same trend as the changes of the calculated HOMO–LUMO gap energies. The FTIR signature of PANI for these films also followed the calculated trend. This study also looks at the effects of atomic arrangement in the atomic structure on the support matrix of PANI. The results presented here have shown that the cyclic pathway is a versatile method for the atomic deposition of single metal, bimetallic, or even trimetallic atomic clusters in PANI.

Under precisely controlled conditions, atomic gold electrodes with even or odd number of Au atoms per polyaniline repeat unit (Pt/PANI/AuN for 0 < N < 7) were prepared. The electrochemical behavior of these new electrodes is compared with that of macro gold and PANI coated platinum electrodes by testing electrochemical oxidation of n-propanol and iso-propanol. This study allowed us to separate the behavior dominated by that of macroscopic gold in strongly alkaline medium and by that of the quantized odd–even effect of atomic gold. Within this overarching scope, there is a specific oxidation pattern attributable to the structural differences between the two isomers of propanol. The significance of this research lies in the recognition of high specific catalytic activity of atomic gold, which is at least three orders of magnitude higher than that of bulk gold for the oxidation of alcohols. It points to a substantial saving of the precious metal without the loss of catalytic activity, which is important in fuel cells and in other energy conversion device applications.

Here we report the fabrication of two types of microirradiators, consisting of a recessed disk and protruding wire with low-β-energy radionuclide Ni-63 electrodeposited onto a 25 μm diameter Pt wire. Ni-63 is constricted to a small surface area of the microelectrode; hence, this tool provides a means of delivery of localized, large dose density of β radiation to the object but a minimal dose exposure to the user. The activity levels of Ni-63 emitted from the recessed disk and protruding wire are 0.25 and 1 Bq, respectively. The corresponding β particles flux levels emitted from the recessed disk and protruding wire are 51 and 11 kBq/cm2, respectively. These values, measured experimentally using liquid scintillation counting, fit very well the expected values of activity for each microirradiator, calculated considering the self-absorption effect, typical for low-energy β particles. In order to determine the optimal configuration the dose rates for varying distances from the object were calculated.

Solid-state potentiometric sensors based on the chemical modulation of the work function of organic semiconductors are discussed. The theory of the chemical work function modulation is briefly reviewed. There are several sensor configurations, in which this transduction principle can be employed. First is the Kelvin probe, second is the chemically sensitive field-effect transistor in which the conventional metal gate of the silicon-based transistor has been replaced by an organic semiconductor. Chemical modulation of work function enters also into the operation of the third type of sensor discussed in this review, on “organic field-effect transistor”. It is shown that in reality such sensors are “field-modulated chemiresistors”, rather than potentiometric sensors.

A sensing layer for a chemically sensitive field-effect transistor (CHEMFET) based on a composite of camphorsulfonic acid (CSA)-doped polyaniline (PANI) and the room-temperature ionic liquid (IL) 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)-imide, BMI(Tf2N), has been developed and characterized for the sensing of ammonia gas. The work function responses of the cast films with and without IL were analyzed by “stepwise” changes of ammonia gas concentration from 0.5 to 694 ppm in air as a function of the mole fraction of IL to PANI. The PANI·CSA/BMI(Tf2N) layers showed enhanced sensitivities, lower detection limits, and shorter response times. There is experimental evidence that PANI forms a charge-transfer complex with imidazolium cation.

Polyaniline forms a strong complex with chloroaurate at the protonated imine sites. Here we report on an electrochemical procedure that allows preparation of gold clusters by adding gold atoms one-by-one (“bottom–up” approach). It is contrasted with the “top–down” approach in which the growth of multi-atom Au clusters was also controlled electrochemically. Our results confirm that both the amount and the size of gold clusters affect the properties of the composite material.

Very slow changes in solvation taking place in water-saturated nitrobenzene have been observed and studied by nuclear magnetic resonance (NMR), Fourier transform infrared, and inelastic neutron scattering spectroscopy. These changes are most likely caused by the rearrangement of the hydrogen-bonded water network. Lithium salts used as the “reporter” species in the 7Li NMR experiments accelerate this reorganization. Results of this work are important for electrochemical studies of the nitrobenzene–water interface.

In this paper are addressed two important, but seemingly unrelated issues: long term performance of a gas sensing array and performance of an air purification unit. It is shown that when considered together, the system can be regarded as a “smart filter”. The enhancement is achieved by periodic differential sampling and measurement of the “upstream” and “downstream” gases of a filter. The correctly functioning filter supplies the “zero gas” from the downstream for the continuous sensor baseline correction. A key element in this scheme is the synthetic jet that delivers well-defined pulses of the two gases. The deterioration of the performance of the “smart filter” can be diagnosed from the response pattern of the sensor. The approach has been demonstrated on removal/sensing of ammonia gas from air.

Dynamics of solvation of lithium salts in “wet” nitrobenzene was studied by 7Li NMR and by FTIR. Well-resolved NMR peaks corresponding to various solvatomers of Li have been observed in solution of LiClO4 in nitrobenzene saturated with water. It has been found that the solvation equilibria are dominated by slow kinetics involving mixed solvatomer Li(nitrobenzene/water). At the glass wall this solvatomer decomposes slowly, over period of many hours, to fully hydrated Li(water) solvatomer. On the other hand, no such decomposition is observed at the Teflon/nitrobenzene interface and the Li(nitrobenzene/water) even more slowly converts to solvatomer Li(nitrobenzene), solvated mostly by nitrobenzene. The effect of the anion on the “free” OH stretch at 3583 and 3672 cm−1, respectively, has been studied by the FTIR.

The amount of electronic charge transferred between gold particles and polyaniline depends not only on the electron affinity of the two materials but also on the size of the gold particles. As measured by X-ray photoelectron spectroscopy, for particles < ∼5 nm the binding energy of the electrons is size dependent. This “nano-effect” has its origin in the electrostatics of particles. It is demonstrated as a measurable shift of the binding energy of the Au4f7/2 photoelectrons emitted from Au particles embedded in a polyaniline matrix. Gold nanoparticle size was evaluated by high resolution transmission electron microscopy.

The controlled growth of gold nanoclusters in polyaniline is predicated by the ability of PANI to switch from conducting to insulating form and by the fact that imine nitrogens form a strong complex with chloroaurate anions. The principal technique used in this study has been chronopotentiometric stripping. The chronopotentiograms indicate that the electrochemical interface for the Pt/Au/polyaniline/electrolyte shifts back and forth from the solution/PANI interface to Au/PANI interface. By adjusting experimental conditions the size and the size distribution of Au clusters can be controlled.

A method for determination of the volatile compounds present in new and used petroleum oils was developed. The identification of the new and used oils was based on the abundance of volatile compounds in headspace above the oils. Multivariate analysis based on principal component analysis (PCA), and hierarchal cluster analysis was used to evaluate the degradation compounds found in used engine oil. The gas phase of new and used petroleum oils was analyzed using a time of flight mass spectrometer (TOF MS) and sensor arrays. The samples included used engine oil, up to 35,500 miles. The principal components identified by PCA were volatile constituents of the oils. New and used oils were also differentiated using multivariate analysis of the results from these gas phase detection methods. The identification of the origin of volatile samples in the used oils has been studied by spiking newer oil samples with a complex mixture of volatile compounds. These samples were then analyzed with the sensor array. Results from the spiked samples correlated better with the older, more used oil samples, confirming that the previously identified volatile compounds can be used to classify new and used engine oils. Using chemometrics, the used oils were differentiated into categories using metal oxide semiconductor (MOS) and quartz crystal microbalance (QCM) sensor arrays or mass spectrometry. The QCM sensors were able to better differentiate the new and used oil samples compared to the metal oxides. In the mass spectrometry and sensor array analysis the new oils were clustered into groups and separated by mileages. The older, more used oils were clearly distinguished from the newer oils.

Four polymeric materials were tested for developing high-aspect ratio photomask on silicon wafer. A 166 μm thick mask was successfully made using spin-on epoxy. It showed good adhesion to silicon dioxide, good chemical stability towards common organic solvents and excellent mechanical strength. A procedure for removing it from the wafer has been also developed.

The mechanism of electrochemical doping in poly(phenylenesulfidephenyleneamine) (PPSA) was investigated by in situ spectro-electrochemical methods. Our results indicate that the doping level in PPSA can be quantitatively adjusted by controlling the charge injection through regulating the applied oxidation potential and the duration of the doping. Due to the stabilization of the dopant ions, the oxidation state of the doped polymer can be permanently adjusted to desirable levels. It is demonstrated that a dry PPSA film with defined work-function (WF) values can be reproducibly prepared. The WF of the doped PPSA varies logarithmically with the amount of doping charge, in analogy with the changes in the Fermi level over impurity concentration observed in conventional semiconductors during doping.

The space–charge region of an organic semiconductor (OS)–insulator interface is probed by analyzing the spontaneous, thermally driven drain current fluctuations of a field-effect transistor in which the OS forms the gate electrode. This so called “excess drain current noise” is the outcome of local fluctuations of the Fermi level, resulting from stochastic exchange of electrons between traps near the Fermi level. The power spectral density of this noise is characteristic of a Lorentzian process with a distribution of time constants, which is attributed to the disorder in the OS film. Furthermore, this disorder leads to local inhomogeneity of the work function in the film and a finite correlation length of the work function fluctuations. The measurement of work function noise is only possible within a correlation length of the OS–insulator interface. Through systematic variation of gate voltage, primary doping and secondary doping levels, the correlation length, disorder, and the trapping/de-trapping time constant are examined on polyaniline as a representative OS. A model is proposed for local work function variations and spontaneous charge-carrier fluctuations within polyaniline films with consequences for organic electronics using organic semiconductors.