Agnieszka Podborska

Nanoscale optoelectronic switches and logic devices

The photoelectrochemical photocurrent switching (PEPS) effect, in the beginning regarded as a scientific curiosity, has become a field of extensive study for numerous research groups all over the world. This unique effect can be utilized for nanoscale switching and information processing, furthermore, is can serve as an interface between molecular information processing and macroscopic electronics. This review summarizes recent efforts in understanding photocurrent switching effects and their application for the construction of nanoscale switches and logic devices. Furthermore, some future prospects concerning the development of electronic/optoelectronic devices based on photoactive semiconducting hybrid materials are presented.

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.

Towards 'Computer-on-a-Particle' Devices: Optoelectronic 1:2 Demultiplexer Based on Nanostructured Cadmium Sulfide

Nanocrystalline sulfur-doped cadmium sulfide (CdS) prepared by microwave synthesis was investigated. Photoelectrochemical and optical characteristics of sulfur-doped CdS exhibit the photoelectrochemical photocurrent switching effect. Depending on the wavelength and applied bias, the anodic and/or cathodic photocurrent was observed. The unusual behaviour of nanocrystalline CdS allowed the construction of a combinatorial logic system from this material.

Application of spectroscopic methods for identification (FT-IR, Raman spectroscopy) and determination (UV, EPR) of quercetin-3-O-rutinoside. Experimental and DFT based approach.

Vibrational (FT-IR, Raman) and electronic (UV, EPR) spectral measurements were performed for an analysis of rutin (quercetin-3-O-rutinoside) obtained from Rutaofficinalis. The identification of rutin was done with the use of FT-IR and Raman spectra. Those experimental spectra were determined with the support of theoretical calculations based on a DFT method with the B3LYP hybrid functional and 6-31G(d,p) basis set. The application of UV and EPR spectra was found to be a suitable analytical approach to the evaluation of changes in rutin exposed to certain physicochemical factors. Differences in absorbance observed in direct UV spectra were used to monitor changes in the concentration of rutin in degraded samples. Spectra of electron paramagnetic resonance allowed studying the process of free-radical quenching in rutin following its exposure to light. The molecular electrostatic potential (MEP) and frontier molecular orbitals (LUMO-HOMO) were also determined in order to predict structural changes and reactive sites in rutin.

Nanoparticles with logic and numeracy: towards 'computer-on-a-particle' optoelectronic devices

The review focuses on semiconductor nanoparticles and hybrid materials obtained by immobilisation of various molecular species on nanoparticulate semiconductors. These materials constitute unique systems combining collective properties of solids with structural diversity of molecules which show distinctive photoelectrochemical properties. Theoretical models of electronic interactions between molecules and semiconductor surfaces have been presented. Additionally, the review summarises the idea of small particles that can work as electronic devices. These devices are able to sense the environment and communicate with other devices and with the user. The devices are based on surface modified wide-band gap semiconductors and the photoelectrochemical photocurrent switching effect. This effect has created a new platform for novel chemical switches, logic gates and other information processing devices. The mechanism of photocurrent switching is discussed with respect to the type of surface complex-support interaction. Photoelectrochemical properties of multicomponent photoelectrodes based on wide band gap nanocrystaline semiconductors modified with various molecules were investigated. The review presents some examples of hybrid materials working as logic devices, including reconfigurable ones and simple arithmetic systems together with mechanistic problems related to nanoscale information processing.

Application of vibrational spectroscopy supported by theoretical calculations in identification of amorphous and crystalline forms of cefuroxime axetil.

FT-IR and Raman scattering spectra of cefuroxime axetil were proposed for identification studies of its crystalline and amorphous forms. An analysis of experimental spectra was supported by quantum-chemical calculations performed with the use of B3LYP functional and 6-31G(d,p) as a basis set. The geometric structure of a cefuroxime axetil molecule, HOMO and LUMO orbitals, and molecular electrostatic potential were also determined by using DFT (density functional theory). The benefits of applying FT-IR and Raman scattering spectroscopy for characterization of drug subjected to degradation were discussed.

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.

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.

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.

Novel information processing devices: A material odyssey

Along with photocatalytic properties and applications in solar energy harvesting, wide band gap semiconductors offer a universal and versatile platform for the construction of unconventional information processing devices. Here, we present an overview of different materials and formal approaches towards information processing in optoelectronic systems based on nanostructured and molecular materials.