Przemysław Kwolek

Arithmetic Device Based on Multiple Schottky-like Junctions

Photoelectrodes containing cadmium sulfide deposited as powders and crystalline thin layers combined with semi-solid ionic liquid electrolyte behave like Schottky photodiodes. Appropriate connection of these devices results in simple optoelectronic logic gates (AND, XOR) and enables construction of an optoelectronic binary half-adder.

BixLa1−xVO4 solid solutions: tuning of electronic properties via stoichiometry modifications

BixLa1-xVO4 solid solutions were obtained in the form of fine powder via a microwave-assisted hydrothermal route. The presence of a solid solution in the studied system was confirmed using X-ray diffraction (XRD) and optical spectroscopy techniques. Pure BiVO4 and LaVO4 were obtained in the monoclinic form, whereas solid solutions in the tetragonal, zircon-type structure. The optical band gap dependence on the composition of the solid solution is parabolic, thus there is a possibility to tune this parameter in a wide concentration range, from 2.4 to 4.0 eV. An absorption coefficient maximum is also concentration-dependent, possibly, due to the structural disorder of the samples. Solid solutions with Bi(3+) concentration between 11.94 and 32.57 at.% exhibit intense, green luminescence. This indicates the presence of Bi-originated electronic states within the band gap. The value of the conduction band edge potential, measured by both electrochemical impedance spectroscopy and work function measurements, is concentration-independent. Moreover, solid solutions exhibit a photoelectrochemical photocurrent switching effect, thus they may be promising materials for molecular electronics and as dioxygen activators.

Photoelectrochemistry of n-type antimony sulfoiodide nanowires

In the presented work the photoelectrochemical properties of SbSI along with the electronic structure (i.e. conduction and valence band edge potentials as well as conductivity type) of sonochemically obtained nanowires are discussed for the first time. The spectroscopic investigations indicate interesting optical properties, including surface isotope effect and excitonic emission. The photoelectrochemical investigation of SbSI revealed the occurrence of the photoelectrochemical photocurrent switching effect. It may be defined as a change in photocurrent direction (generated at the illuminated semiconducting electrode immersed in electrolyte) due to an appropriate polarization of the electrode versus the reference electrode. It is often observed for semiconductors as a result of the reduction of molecular oxygen dissolved in the electrolyte. However, in the case of SbSI, the photocurrent switching was recorded regardless of the presence of molecular oxygen in the electrolyte, probably due to the reduction of triiodide species formed at anodic polarization of the SbSI electrode, in an iodide-containing electrolyte. The switching potential (i.e. the potential where anodic-to-cathodic photocurrent transition occurs) equals to ca. 0.4 V versus standard hydrogen electrode, which is close to the formal potential of the I(-)/I3(-) redox couple. Therefore, this semiconducting material is of potential interest for the construction of new photovoltaic systems, novel optoelectronic switches and logic devices.

Lead molybdate – a promising material for optoelectronics and photocatalysis

The growing interest in the use of light as an information and energy carrier has led to an increasing demand for new materials, characterised by particular photoelectrochemical properties. The aim of this work is to introduce a wide band gap semiconductor – PbMoO4 with a detailed description of its synthesis procedure and product characterisation. The emphasis was put on its electronic structure and photoelectrochemical properties in order to evaluate the mechanism of the photoelectrochemical photocurrent switching effect (the PEPS effect). This phenomenon may be utilized in the construction of simple logic devices (e.g. logic gates or switches) or more complex optoelectronic circuits. Lead molybdate in the form of fine powder was obtained via a microwave assisted hydrothermal route. It was found that the composition of the reaction mixture (i.e. the ratio between lead and molybdate ions) influences the morphology and the electronic structure of the semiconductor. The photoelectrochemical characterization revealed that PbMoO4 in the presence of the Ce4+/Ce3+ redox couple exhibits the PEPS effect regardless of the presence of oxygen in the electrolyte. This may be explained in terms of oxidation/reduction processes of cerium(III)/cerium(IV) species. An attempt to modify the surface via the adsorption of alizarin onto PbMoO4 was also made. The spectroscopic characterization and DFT calculations performed for such an organic–inorganic hybrid material revealed that the dye binds to MoVI centres which are exposed on the surface. Alizarin adsorbed onto PbMoO4 strongly enhances the cathodic photocurrent generation. At the same time, however, the anodic photocurrent diminishes. Therefore, literally no switching effect occurs for such a system. Nonetheless, the generation of intense cathodic photocurrent may be utilized in photocatalysis, e.g. during the photoreduction of metal ions or the generation of reactive oxygen species and/or solar fuels.

Acoustic wave sensing devices and their LTCC packaging

The paper presents the relevant results of manufacturing LTCC packages intended for chip assembly as well as the RF behavior of SAW and FBAR structures used as temperature and, respectively, humidity sensing devices. Packaged SAW-based temperature sensors were characterized in a cryostat set-up, while the packaged FBAR-based humidity sensors were measured in a small enclosure with controlled humidity. Linear behaviour of the frequency shift vs. temperature and, respectively, relative humidity was evidenced.

Unconventional Computing Realized with Hybrid Materials Exhibiting the PhotoElectrochemical Photocurrent Switching (PEPS) Effect

Increasing demand for high computational power and high density memories enforces rapid development of microelectronic technologies. However, classical, silicon-based electronic elements cannot be miniaturized infinitely. Therefore, in order to sustain rapid development of information processing devices, new approaches towards future computing devices are needed. These approaches encompass either search for new material technologies or new information processing paradigms. In this chapter we present our contribution to the field including both approaches. We introduce classical, Boolean logic devices based on different materials and nanoscale implementations of ternary logic, fuzzy logic and neuromimetic computing.

The Influence of Sodium Molybdate on the Rate of Corrosion of Aluminum in Phosphoric(V) Acid

Corrosion rates of aluminum in phosphoric (V) acid solutions were determined gravimetrically in a presence of sodium molybdate which acts as an inhibitor. Inhibition efficiencies were calculated. The most effective corrosion inhibition was observed for 0.5 M H3PO4 and 100 mM of Na2MoO4. Since insoluble corrosion products precipitated onto specimens and influenced the determined corrosion rates, an analysis of a morphology of the specimens was performed by using a scanning electron microscope. The corrosion products are composed of Mo, P, Al and O. An Mo/P atomic ratio varied between 0.8 and 1.6 depending on the concentrations of phosphoric (V) acid and sodium molybdate. For three concentrations of H3PO4, the concentration ranges of sodium molybdate, where the gravimetric method may be applied were determined.

The replacement of chromate by molybdate in phosphoric acid-based etch solutions for aluminium alloys

ABSTRACT Corrosion inhibition of aluminium alloys in the acidic solutions is important in the aluminium finishing industry (stripping solutions for anodic films). Sodium molybdate is a potential replacement for chromate-containing species used in the stripping solutions. It was tested as the corrosion inhibitor of 2024 aluminium alloy in orthophosphoric acid solutions. A corrosion rate of the alloy as a function of an initial concentration of sodium molybdate and temperature was determined by using gravimetric and gasometric methods. The corrosion rate was significantly lower in the solutions containing over 5 mM of sodium molybdate when compared to the uninhibited solution. The inhibition efficiency decreased with the increase of the temperature for the constant concentration of sodium molybdate. Sodium molybdate reduced the corrosion of the alloy by adsorption as well as formation of insoluble corrosion products on the alloy.