Kacper Pilarczyk

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.

Organotitania-based nanostructures as a suitable platform for the implementation of binary, ternary and fuzzy logic systems

Titanium dioxide nanocomposites were synthesized in hierarchical architectures through the use of a 1,4-dihydroxyanthraquinone photosensitizer. In the first step, the dye was either incorporated into the TiO2 core or adsorbed on its surface. In the subsequent phase, both structures were covered with an outer layer of titanium dioxide. The structure, morphology, aggregation, spectroscopic, and electrochemical properties of the synthesized TiO2 -based materials are presented with emphasis on the photosensitization and the photocurrent switching phenomena, which are also discussed within the context of the optical logic gates implementation and fuzzy logic systems operation. We present three different interpretations of the photocurrent action spectra yielding binary, ternary, or fuzzy logic circuits.

Tuning of electronic properties of fullerene-oligothiophene layers

Electronic properties of fullerene derivatives containing oligothiophene pendant chain (1–3 thiophene moieties) were investigated using the Kelvin probe technique and quantum chemistry methods. For electrochemical examination of these systems, Langmuir–Blodgett (LB) layers were prepared by the deposition on a gold substrate. The analysis of the experimental data shows that the value of the work function depends strongly on the length of oligothiophene chain. Similar dependence was also found for the surface photovoltage measurements conducted for the layers consisting of multiple LB films of the examined compounds deposited on gold surfaces. The assumption has been made that these changes are associated with the influence of oligothiophene chain on the electrostatic potential distribution near the surface of the sample. The hypothesis was confirmed by the results of DFT calculations, which revealed that the value of Fermi level energy shifts in the opposite direction to the determined work function. The key highlights of this study are as follows: electronic structure tuning by oligothiophene side chain; DFT calculation on fullerene-thiophene system; work function measurements of thin molecular layers.

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.

Heavy pnictogen chalcohalides: the synthesis, structure and properties of these rediscovered semiconductors

This review focuses on the synthesis, properties and selected applications of heavy pnictogen chalcohalides, i.e. compounds of the MQX stoichiometry, where M = As, Sb, and Bi; Q = O, S, Se, and Te; and X = F, Cl, Br and I. The first section focuses on their synthesis and crystal structures, and the second section discusses the electronic structure on the basis of quantum chemical modelling and selected experimental data. Finally, the third section discusses their electrical, photoelectrochemical and photocatalytic properties and applications. In contrast to perovskites, chalcopyrites and kesterites, chalcohalides have attracted relatively less attention, but their structure and properties are well suited for numerous applications.

Tuning of the Seebeck Coefficient and the Electrical and Thermal Conductivity of Hybrid Materials Based on Polypyrrole and Bismuth Nanowires

The growing demand for clean energy catalyzes the development of new devices capable of generating electricity from renewable energy resources. One of the possible approaches focuses on the use of thermoelectric materials (TE), which may utilize waste heat, water, and solar thermal energy to generate electrical power. An improvement of the performance of such devices may be achieved through the development of composites made of an organic matrix filled with nanostructured thermoelectric materials working in a synergetic way. The first step towards such designs requires a better understanding of the fundamental interactions between available materials. In this paper, this matter is investigated and the questions regarding the change of electrical and thermal properties of nanocomposites based on low-conductive polypyrrole enriched with bismuth nanowires of well-defined geometry and morphology is answered. It is clearly demonstrated that the electrical conductivity and the Seebeck coefficient may be tuned either simultaneously or separately within particular Bi NWs content ranges, and that both parameters may be increased at the same time.

Charge transfer tuning in TiO2 hybrid nanostructures with acceptor–acceptor systems

An interesting interplay between two different modifiers and the surface of titanium dioxide leads to a significant change in the photoelectrochemical properties of the designed hybrid materials. The semiconductor is photosensitized by one of the counterparts and exhibits the photoelectrochemical photocurrent switching effect due to interactions with graphene oxide – the second modifier mediates charge transfer processes in the system, allowing us to design the materials response at the molecular level. Based on the selection of molecular counterpart we may affect the behaviour of hybrids upon light irradiation in a different manner, which may be useful for the applications in photovoltaics, optoelectronics and photocatalysis. Here we focus particularly on the nanocomposites made of titanium dioxide with graphene oxide combined with either 2,3,5,6-tetrachlorobenzoquinone or 2,3-dichloro-5,6-dihydroxybenzoquinone – for these two materials we observed a major change in the charge transfer processes occurring in the system.