Table of contents

PREFACE

We are pleased to introduce the Proceedings of the 20th JUBILEE INTERNATIONAL SCHOOL ON CONDENSED MATTER PHYSICS "Physics and Applications of Advanced and Multifunctional Materials (20^th ISCMP). The school was held from September 3rd to September 7th, 2018 in Varna, Bulgaria. It was organized by the Institute of Solid State Physics of the Bulgarian Academy of Sciences (ISSP-BAS), and took place at one of the fine resorts on the Bulgarian Black sea "Saints Constantine and Helena".

The aim of this international school is to bring together top experimentalists and theoreticians, with interests in interdisciplinary areas, with the younger generation of scientists, in order to discuss current research and to communicate new forefront ideas. This year special focus was given to advanced organic and inorganic materials and their application in biophysics and sensors. Traditionally covered areas, such as characterization of nanostructured materials and thin films were also discussed. Participants from 16 countries presented 26 invited lectures, 28 short oral presentations and 60 posters.

The hope of the organizing committee is that the 20^th ISCMP provided enough opportunities for direct scientific contacts, interesting discussions and interactive exchange of ideas between the participants. The nice weather certainly helped a lot in this respect. The editors would like to thank all authors for their high-quality contributions and the members of the international program committee for their commitment.

The papers submitted for publication in the Proceedings were refereed according to the publishing standards of the Journal of Physics: Conference Series. The Editorial Committee members are very grateful to the Journal's staff for the continuous fruitful relations and for giving us the opportunity to present the work from the 20^th ISCMP.

Prof. DSc Hassan Chamati, Prof. DSc Doriana Dimova-Malinovska, Assoc. Prof. Dr. Julia Genova Prof. DSc Diana Nesheva, and Prof. DSc Albena Paskaleva

List of Organising Committee are available in this PDF.

All papers published in this volume of Journal of Physics: Conference Series have been peer reviewed through processes administered by the proceedings Editors. Reviews were conducted by expert referees to the professional and scientific standards expected of a proceedings journal published by IOP Publishing.

The aim of this paper is to discuss the possibility of theoretically engineering multifunctional nanomaterials. The calculations were performed for 1D and 2D nanomaterials by using results obtained within the Hubbard model (HM). The main results of the HM are briefly reviewed. The conclusion is that the approach taken in this paper is a distinct improvement over those in the literature.In the present paper results of applications of the HM are directly used in examples of engineering nanomaterials. On the other hand, in the literature calculations were performed by ab initio methods and then fitted to the form of the Hamiltonian of the HM.

We phenomenologically investigate the phase diagram of some ferrimagnetic materials on the basis of two bilinearly coupled Heisenberg models sitting on two interpenetrating simple magnetic cubic lattices. Computations were performed with the help of the Landau free energy obtained through applying the Hubbard-Stratonovich transformation to the initial microscopic Heisenberg Hamiltonian. The transitions to the magnetically ordered phases within the model are found to be of second order with the occurrence of a compensation point at lower temperatures for some values of the system's parameters. It is found that the main stable phase is a two-sublattice collinear ferrimagnet in addition to a metastable non-collinear phase. The numerical results give a detailed description of temperature dependence of magnetization on the strength of intersublattice interaction and the difference between the effective exchanges of two ferromagnetically ordered sublattices. Our results are in qualitative agreement with the experimental results on Y₃Fe₅O₁₂ in the strong coupling limit and the compounds ErFe₂ and GdCo₁₂B₆ for weak couplings.

The optical and carrier transport properties of GaInNAs layers grown by molecular beam epitaxy on n-GaAs substrates are studied by surface photovoltage (SPV) spectroscopy combined with photoluminescence (PL) measurements data. The SPV spectra clearly show a red shift of the band gap energy with respect to the band gap of GaAs, which is in line with the PL results. The combined analysis of the SPV amplitude and phase spectra has allowed determining the residual doping type in the layer. The minority carrier diffusion length was assessed by means of the method called "constant SPV".

The weak links effects are one of the main challenges for effective power applications of high temperature superconducting materials. Studies of these effects help for their better understanding and subsequent improvement. An overview analysis of the intergranular properties of cuprate (Y₀.8Ca_0.2Ba₂Cu₃O_7-δ) and iron-based chalcogenide (FeSe_0.5Te_0.5) polycrystalline samples was carried out, by means of series of electro-transport experiments at different magnetic fields. The temperature evolution of the Josephson coupling and intrinsic superconductivity effects for the both systems was constructed. The FeSe_0.5Te_0.5 compound shows very stable and superior behavior compared to Y_0.8Ca_0.2BCO up to the highest magnetic fields (14T) used. We have explored FeSe_0.5Te_0.5 Josephson weak links influence (as a non-linear process) over the resistive transition using different AC current amplitudes and applying the sensitive AC transport third harmonics technique.

The impact of substrate temperature on surface and grain boundary reflection is studied as a function of thickness of chromium nanofilms in the range, 10-80 nm. Substrate temperature happens to be one of the important and crucial deposition parameters, which regulates many physical properties of evaporated thin films. Hence, we have deposited the chromium nanofilms at four different substrate temperatures (Ts = 22, 100, 150 & 1800C) in order to study and analyze its effect on surface and grain boundary reflections and other electrical properties. In this work a qualitative analysis of both surface and grain boundary reflections of thin chromium nanofilms with independent variation of thickness is reported. The grain boundary reflection coefficients (R) have been calculated by estimating the resistivity data of the chromium nanofilms using Mayadas-Shatzkes and Fuchs-Sondheimer models. The substrate temperature dependent resistivity of chromium films exhibit an unusual behavior.

The present work incorporates a study on nucleation, and growth due to the changes in the nano-structural properties as a function of thickness and grain boundary reflection in tin thin nanofilms Thickness happens to be one of the important and crucial nanofilm preparative parameters which dictates majority of properties like, nano-structure, electrical, optical and morphological texture of evaporated tin nanofilms. Hence, we have selected tin nanofilms in the thickness range 20-160 nm, in order to study the thickness dependence of their nano structural and electrical properties, in the temperature range 77-450 K, in detail. All the films were grown in a conventional vacuum coating unit under a pressure of ∼10-6 Torr at room temperature of 22 0C, onto cleaned glass substrates. The tin film nano-structure was analyzed by Transmission Electron Microscope(TEM). The nano structural properties can be tuned to the desired level and application by the proper choice or proper combination of deposition parameters. And it is found to depend upon the nature of the substrate material, environment and the binding force between the substrate material and evaporated tin atoms.

Over the years several new effects in fluorescently labelled Langmuir monolayers or Langmuir-Blodgett (LB) films, deposited on solid support plates, have been reported. Mostly layers from Dipalmytoyl Phosphatidyl Ethanolamine head labelled with Nitrbenzoxadiazole (DPPE-NBD) have been studied. This molecule behaves exactly as the DPPE molecule which is part of biological membranes. So it is expected that DPPE-NBD molecules can serve as an appropriate matrix for implementation of selectively reacting proteins or enzymes while preserving their function. This combination can act as an active layer in biosensor applications for operation in either gas or liquid environments and this molecule could further increase the system sensitivity in such applications. Addition of the chromophore NBD head group also stabilizes the film and allows for multilayer deposition which is not possible for phospholipids. In this study, LB monolayers were deposited on glass substrates at different surface pressures and with or without Cadmium ions in the water subphase. They were studied using fluorescence spectroscopy and Atomic Force Microscopy (AFM). In view of possible biosensor applications, LB layer by layer deposition was performed on Rayleigh Surface Acoustic Wave (SAW) resonant devices working at 440 MHz. These can effectively be used to transduce the biosensor signal from the active layer by providing a mass proportional frequency output. Layers from DPPE-NBD that might also be suitable for possible SAW based biosensor applications were deposited at a surface pressure of 10 mN/m. AFM spectroscopy reveals the phase coexistence of liquid and solid phases as well as higher bilayer nanosized cylinders. Fluorescence intensity was strongly self-quenched at this pressure and fluorescence lifetime spectroscopy shows a complex behaviour with a 3-rd order exponential decay. A frequency downshift of 10 KHz per monolayer was measured with the coated SAW device which results in a deposited mass of about 1 ng/monolayer.

An analysis of the methods for measuring the characteristic length of the cooperative molecular dynamics in glass-forming liquids is submitted. The equations and methods for measuring the size of the cooperatively rearranging regions in post Adam-Gibbs theories are compered, and it is proved that they give one and the same number, but with different interpretation for the relaxed molecular units. The interpretation that the rearranging units defined by Wunderlich are smallest structural units, named beads, is supported by the predicted "universal" value for the cooperatively rearranging range at the glass-transition temperature, as well as from a precise modeling for the relaxations by the generalized entropy theory. It has been found that the characteristic length estimated by random first order transition theory, as well as by the "four-point" dynamic susceptibility method, measured as the number of the bead's diameters coincide with the length of the cooperatively rearranging region in Adam-Gibbs theory extended at the molecular level.

Graphene oxide (GO), the water soluble form of 2D graphene, has received much attention because of its attractive properties for a wide range of applications and products. Surface modification with different functional groups can improve GO biocompatibility for further biomedical applications. In the present study we have evaluated genotoxicity of pristine and ammonia-modified graphene oxide (GO-NH₂) nanoparticles (NPs) in a human lung epithelial cell line, A549, exposed for 24 h to different concentrations of NPs (0.1, 1, 10, 20 and 50 μg/ml). Quantification of reactive oxygen species (ROS) indicated that exposure to higher concentrations of both types of NPs resulted in enhanced ROS generation. The observed comet tail migration in the method of Single Cell Gel Electrophoresis in the cells treated with 20 and 50 μg/ml GO and GO-NH₂ indicated presence of damages in DNA. Cell cycle analysis showed that after treatment of A549 cells with increasing concentrations of NPs for 24h the percentage of cells in G0/G1 phase of the cell cycle decreased while the percentage of cells in G2/M increased. The presented results suggest that ammonia-modified GO NPs applied at concentrations higher than 20 μg/ml induced stronger toxicity effect in A549 cells compared to pristine GO and that the use of low concentrations of GO and GO-NH₂ NPs is important to avoide adverse biological effects.

We present a brief review of application of a model-independent analysis of X-ray refleetometry data to our recent investigations of thin films of phospholipids DSPC and DMPS on a surfaces of water and colloidal silica hydrosol. Comparison of the results against analytical models of phospholipid membranes known in literature allowed us to extract more extensive information on the samples in question. The effect of spontaneous ordering of lipid films on a surface of colloidal silica is discussed. We also demonstrate the possibilities to influence the structure of prepared membranes by enriching the substrate with alkali ions.

Thin films of CBAMINE were deposited at air-water interface by the method of Langmuir-Blodgett (LB) technique onto a suitable substrate. Atomic force microscopy technique was used to characterize its thin film properties. The results indicate that a uniform LB film monolayer from the water surface to a glass or quartz crystal substrates deposited with a transfer ratio of over 96 %. Gas sensing properties and thickness of the LB thin films of CBAMINE were investigated using Surface plasmon resonance (SPR) technique. Its vapour sensing properties were investigated for different volatile organic compounds. Reversible changes in the optical behaviour were observed and thin films of this material are highly selective for chloroform vapour with fast response and recovery times.

Pyrazolo[3,4-b]quinolines are fascinating compounds of great importance. They reveal not only a range of very interesting biological activities, but also have been applied as optical brighteners, in organic light emitting diodes (OLED), in polymer light emitting diodes (PLED), sensors, in nonlinear optics, solar cells and many others. Recently, two interesting scaffolds emerged from the basic ring system, the first group comprises analogues of azafluoranthenes, the second one contains a seven-member ring embedded in the main framework, which can give rise to chiral compounds to be used to the production of diodes emitting circularly polarized light (CPL).

Polymer electrets are one of the most important types of electrets, which are widely used both in academic research and industrial applications. The effect of trapped charges on dielectric properties of the polymer electrets is crucial for more intelligent utilization of these materials. The aim of the present paper is to investigate the lyophilization effect on electret and dielectric properties of polymer films. The properties of one synthetic polymer (polystyrene – PS) and two biopolymers (polylactic acid – PDLA and poly-ε-caprolactone – PεC) were investigated and compared. The samples were analyzed by means of dielectric relaxation spectroscopy in the range of 20 Hz – 1 MHz using QuadTech 1910 Inductance Analyzer. The frequency dependences of the impedance magnitude and the phase angle were measured. Regarding the electret properties, the samples were charged in a conventional three-electrode corona system. Positive and negative 5 kV voltage was applied to the corona electrode and 600 V voltage with the same polarity was applied to the grid as to the corona electrode. The results showed that the lyophilization increases time relaxation of the trapped charges. It was established that the samples charged in a positive corona are more stable than those charged in a negative corona.

Additional three-site exchange interactions, naturally arising, e.g., in the strong-coupling expansion of the two-band Hubbard model and in various effective spin Hamiltonians, may stabilize various exotic spin phases which are not typical for the pure Heisenberg models on frustrated lattices and/or with extra biquadratic exchange terms. The reason is hidden in some specific features of the isotropic three-site exchange interactions, such as the promotion of collinear spin configurations as well as the reinforcing tendency towards clustering of the quantum spins on the shortest exchange bonds. As a result, systems with integer and half­integer composite spins in the unit cell might be expected to support different quantum phase diagrams. In this work, we study this phenomenon by comparing the quantum phase diagrams of two Heisenberg chains with extra three-site exchange terms and two different alternating pairs of site spins S and σ [(S, σ) = $(1,\frac{1}{2})$ and ($(\frac{3}{2},\frac{1}{2})$], resulting in half-integer and integer cell spins S + σ, respectively.

The entropy and the specific heat of a quantum spherical model with a long-range interaction (decreasing at large distances r as r^–d–σ where d is the space dimensionality and 0 < σ ≤ 2) are studied in the quantum critical region at the upper quantum critical dimension d = 3σ/2. The problem of obtaining the temperature-dependent corrections to the ground state free energy involves the solution of a transcendental equation, the exact solution of which is expressed in terms of the Lambert W-function. The free energy, the entropy and the specific heat in the quantum critical region are derived in terms of the Lambert W-function. For systems in real physical dimensions (chains, thin layers, i.e. films and three-dimensional systems) the exact results for the entropy and the specific heat obtained in terms of the Lambert W-function and the leading asymptotic ones are compared on the basis of the calculated relative errors. It can be concluded that for a class of quantum models at the upper critical dimension the Lambert W-function is a very effective tool for an exact computation of low-temperature critical properties, especially in the finite-temperature quantum critical region.

The interaction between solitons, propagating in a magnetic chain, with a qubit is studied. The spin chain is described by the Heisenberg model in a nearest-neighbour approximation with anisotropy. The quantum bit (qubit) is modeled by a two level quantum system. The equation for the evolution of the qubit is obtained. The role of the parameters of the soliton for the quantum bit dynamics is investigated. The results are analyzed using a geometrical representation for the qubit as a Bloch sphere.

The propagation of soliton excitations in a system of two magnetic chains with impurities is studied. The inhomogeneous chains coupled through ferromagnetic interaction between the opposite spins are described by a Heisenberg model in the nearest-neighbor approximation. The presence of the impurities leads to linear perturbing terms in the evolutionary equations. We investigated numerically the influence of the soliton parameters, the interchain coupling and the defect strength on the soliton dynamics. The conditions of perfect soliton switching are obtained.

We suggest and experimentally demonstrate a broadband polarization rotator. Our device consist of a Fresnel's rhomb retarder and a composite broadband half-wave plate with relative rotation α between their fast polarization axis. Such a optical device rotate the polarization plane of a linearly-polarized light at angle 2α over a wide range of wavelengths.

Thirty – five samples of red wines from different geographic regions have been characterised according to 14 basic optical and chemical characteristics - colour parameters, content of anthocyanins and antioxidant activity. The goals of this study is to compare the tested wines using different statistical methods. Conducting hierarchical cluster analysis the samples have been divided into 4 clusters according to their difference and similarity. The result is presented graphically by a dendrogram. It could be concluded that the optical parameters and related chemical indicators are more decisive for the division of wines based on the region of production than on the basis of the predominant grape variety. The total number of studied parameters was reduced to 4 factors by factor analysis using Principle Component Analysis (PCA). These new factors explained 86.75% of the entire variation. The first factor contained chemical parameters and color coefficients in SIELab colorimetric system. The second one was connected with the quality characteristics of wine, which were important for consumers such as brilliance of red, color intensity. The third and the fourth factors were related with the Hues angles, color parameter b and saturation for the red wines.

The effect from the inclusion of nematic liquid crystal (LC) E8 into the polymer poly(ethylene oxide) (PEO) was inspected by studying of structural and electrical properties of PEO-E8 composites at weight percentage of E8 ranging from 10 % to 50 %. Flexible PEO-E8 films with a thickness of 0.1 mm were structurally characterized by X-ray diffraction and X-ray photo-electron spectroscopy. The results obtained by our analyses indicate that a polymer-LC intermolecular complex is formed by inclusion of E8 LC molecules in the PEO host at a certain their concentration level. The structural properties of PEO-E8 composites were correlated with their electro-conducting properties as depending on the E8 LC concentration. By the amount of the LC fraction one can achieve a controlled modification of the structural and electro-conducting properties of the PEO-E8 material. As compared to PEO, the inclusion of E8 LC in the PEO polymer matrix can lead to a considerably enhanced electrical conductivity of PEO-E8 composites.

We report results from our continued investigations on a finite-size chain (molecule) of L spin-$\frac{1}{2}$ spins with XY spin exchange interaction coupled at an arbitrary spin site to a single mode of an electromagnetic field via the Jaynes-Cummings model. Here we study the energy spectra in the case of an arbitrary photon fill number n, as compared to the n = 1 limit in our previous work [J. Phys.: Conf. Ser. 682 (2016) 012032] and [J. Phys.: Conf. Ser. 764 (2016) 012017]. By building the appropriate combinations of basis product states involving the photon as well as the up down spins it is possible to simplify the systems that are necessary to diagonalize from n × 2^L to at most 2^L . This results are in tune with those reported in the recent paper by N. Wu [Phys. Rev. B 97 (2018) 014301], and may prove to be useful for the quantum computing aficionados.

MOS structures with two-layer insulator, SiO₂/SiO_x, are tested for switching between high and low resistance state. Part of the structures were annealed at 1000 °C for 60 min in N₂ in order to form silicon nanocrystals (Si NCs) in a SiOx matrix. Cross-sectional transmission electron microscopy revealed that after the high temperature annealing phase separation takes place and nanocrystals with size of ∼ 4–5 nm are formed. Direct current–voltage measurements showed that bipolar switching occurs only in the annealed c–Si/SiO₂/SiO_x/Al structures and not in the control samples. A model explaining the resistance change by electric field formation of conductive pathway in the SiO_x-Si NCs layer at negative gate voltages and current driven destruction of the conductive filament at positive voltages was verified by high frequency capacitance-voltage (C-V) measurements. From the C-V results the dielectric constant of non-annealed SiO_x films with x = 1.3 was calculated to be ε_SiOx = 4.6.

Layers of ZnSe (50, 110 and 160 nm thick) are deposited at room substrate temperature by thermal evaporation of ZnSe powder in vacuum. As-deposited and relaxed layers are investigated by spectroscopic ellipsometry to get information about their optical properties, porosity and surface roughness. The obtained data indicate that all layers are nanocrystalline and the lattice relaxation causes a porosity decrease and surface roughness increase. Ethanol sensing experiments are carried out at room temperature in air and results show an increase of the layers sensitivity with decreasing thickness while the relaxation causes sensitivity decrease. The sensitivity behavior is discussed considering the changes in the films porosity and the ethanol related decrease of the potential barriers at the nanocrystallite interfaces.

Thin films consisting of a sol-gel Nb₂O₅ matrix doped with fly ash zeolites in different volume fractions were deposited by the method of spin-coating. Zeolites of Na-X phase were prepared by long-term alkaline atmospheric conversion of coal ash collected from the electrostatic precipitators in TPP "AES Galabovo" supplied by lignite coal from the "Maritza East" basin using two different molarities of alkaline activator (NaOH). The surface morphology and structure of zeolite powders and films were studied by scanning electron microscopy and X-ray diffraction, respectively. Optical constants (refractive index and extinction coefficient) along with thickness of the films were calculated using a previously developed procedure comprising two steps of nonlinear minimization of the discrepancies between the measured and calculated reflectance spectra of films deposited on silicon substrates. The liquid adsorption and vapor sensing ability of fly ash zeolites were tested by measuring the reflectance spectra of the films prior to and after exposure to probe acetone molecules. The application of zeolites from fly ash for optical sensing is demonstrated and discussed.

Leakage currents of Al₂O₃/HfO₂ multilayer stacks deposited by atomic layer deposition in the low voltage region (0 ÷ ±4V) are investigated in dependence on Al₂O₃ sublayers thickness and the post-deposition annealing in two ambients (O₂, N₂,). The stacks with 5cy of Al₂O₃ show highest current, compared to structures with lower (2cy) and higher (10cy) Al₂O₃ content. Oxygen treatment does not affect significantly the leakage current at low voltages, while annealing in nitrogen definitely increases it. The current follows power law dependence, Vⁿ, with n varying in the interval of about 0.6 to ∼1. The application of ±12V pulses shift the leakage curves towards higher or lower current values depending on the polarity of the pulse. Leakage curves after the pulse stress are described either with Vⁿ or (V-V_t)ⁿ relations depending on both pulse and measurement bias polarity. The results are found consistent with a model similar to the collective transport in array of small metal dots model in which the current is limited by the available sites for charge carriers to move on.

In order to enlighten the in-depth organization of thin tellurium films, deposited by the frequency assisted thermal evaporation in vacuum (FATEV) approach, morphological, structural and spectroscopic investigations were performed. Spectroscopic ellipsometry (SE) and cross-section scanning electron microscopy (SEM) showed a change of the growth mechanism upon application of higher vibrations' input frequencies during the films deposition. The films, deposited by conventional thermal evaporation in vacuum with no vibrations applied, as well as these, deposited by FATEV with application of 50 Hz vibrations, were characterized by initial densification followed by 2D nanoparticles growth when a certain threshold thickness was reached. On the other hand, the high-frequency vibrations of 4 and 10 kHz preconditioned growth of tellurium nanoribbons oriented towards the z-axis from the very beginning of the film formation. The topography changes, observed by atomic force microscopy (AFM) and scanning electron microscopy, showed highly porous surfaces (with high root mean square surface roughness) formed by distinct nanoblades for the films, deposited at low input frequencies, while the films, deposited under the impact of vibrations in the kilohertz range, were much more ordered, and hence their surface was significantly smoother. The structural parameters of the samples were investigated by X-ray diffraction (XRD) analysis.

The functional characteristics of thin film planar solar cells are very sensitive to the presence of pores, voids or holes. Thus deposition of compact, dense and uniform layers is essential in that technology. These issues are especially important in organometalic perovskite solar cells where the active layers are in the nano metric scale. In this emerging technology the reduction of cost-efficiency ratio is a serious barrier for commercialization. In this work we have investigated different parameters of the process of deposition of SnO₂ thin films by spin coatings which influence its compactness and impenetrability. Influences of the thermal treatments on the properties of the films were investigated by UV – vis spectrometry, X-ray diffractometry (XRD), Scanning Electron Microscopy (SEM), Atomic Force Microscopy AFM), X-Ray Photo-electron spectroscopy (XPS) and Spectral Elipsometry (SE). Finally the coverage ability of the SnO₂ films was checked by Cyclic Voltammetry (CV) in aqueous redox solution.

With the advantage of ultrashort pulse width and ultrahigh peak power, subpicosecond lasers can provide extremely precise machining, and therefore has been widely applied in micro and nanoscale manufacturing. We present the results of the experimental parametric study on efficiency, accuracy and quality of subpicosecond laser micromachining of materials, that have a potential for application in innovative devices and technologies. The laser micromachining process was performed with a Yb:KYW subpicosecond laser and a Ti:S femtosecond laser. The study contains a comparison between the two methods, and results analysis using advanced metrology techniques, such as 3D microscopy.

In this work, chitosan/hydroxyapatite (Ch/HAp) thin composites were synthesized and examined before and after femtosecond laser irradiation in order to investigate the substrate response and surface changes occurring during the process. The zones of interaction formed after treatment by fs laser pulses were analysed by scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). The results revealed that the laser processing of Ch/HAp thin films leads to generation of well-defined laser-induced periodic surface structures (LIPSS) for a laser fluence F = 2.07 J/cm² at 800 nm wavelength with pulse durations in the range of 130 fs. It is demonstrated experimentally that the femtosecond interaction regime results in the formation of ripples beneficial for the functionalization of biopolymer/ceramic samples for further tissue engineering applications. In the transmittance spectra, profile variations for the non-treated and laser-processed surfaces were noticed depending on the number of pulses applied.

Polyelectrolyte multilayers (PEMs) are widely used as drug delivery systems, but still remain challenging for their small drug immobilizing capacity. One way to increase the immobilized drug amount may be crosslinking of the PEMs, which stabilize them and increase their porosity. The aim of the present study is fabrication and characterization of chitosan/casein PEMs, which are crosslinked with different crosslinking agents – glutaraldehyde, sodium tripolyphosphate, CaCl₂ and combinations of two of them. XPS method was used to prove the PEMs crosslinking. SEM was used to observe film morphology and its variation due to cross­linking. Water capacity of PEMs in 100 % relative humidity was investigated. Release of model drug Benzydamine Hydrochloride was monitored spectrophotometrically at 306 nm. The crosslinking improves the PEMs stability and causes formation of porous surface. After crosslinking the amount of the immobilized drug increased several times.

Thin (7 μm) layers of nanocomposites from graphene nanoflakes (GrFs) dispersed at concentrations of 10⁻³ wt.% into the nematic liquid crystal (NLC) E7 were characterized by various investigation techniques, such as Raman spectroscopy, impedance measurements and dielectric spectroscopy, as well as by electro-optical measurements (optical transmittance of the NLC layers versus the voltage of the applied external AC electric field). Conducting behaviour, dielectric permittivity and electric energy loss of our planar-aligned NLC layers at room temperature were analysed as a function of frequency in the range from 0.5 Hz to 1 MHz. The analysis of experimental data indicates that the molecular alignment through GrFs/NLC surface interactions is responsible for the reduction of the ionic conductivity of E7 NLC in the presence of GrFs. As compared to pure LC E7, this leads to improved characteristics for the studied nanocomposites, necessary in their practical applications in electro-optics.

The change in electrical conductivity and dielectric response of liquid crystal (LC) E7 by doping with graphene nanoparticles was experimentally studied by complex electrical impedance and dielectric spectroscopy over the frequency range from 0.1 Hz to 1 MHz of the applied electric field. In the measured graphene/E7 nanocomposite films (7 μm-thick, with planar orientation), graphene nanoflakes were dispersed in the nematic E7 at the concentration of 10⁻³ wt.%. Graphene nanodopants lead to a change of both electrical transport and dielectric permittivity of the LC E7 which should render improved electro-optic response of the considered room-temperature nanocomposite nematic films.

Recent advances in supercapacitor technology reveals new opportunities for energy storage devices for application in electro-transportation and renewable energy sectors. In this paper results on device fabrication are reported. A low-cost screen-printing technology to obtain electrodes of supercapacitor has been applied. The device structure is based on Cu plate/hydrocarbon ink electrodes and gel electrolyte. Carbon ink is prepared from naturally occurring not full carbonized particles in the chimney's soot. The cyclic charge/discharge measurements confirm supercap behaviour and specific capacitance around 5 F/g at discharge current of 0.62 A/g. The flat configuration of the supercaps allows easy connection in series and adjustment to DC loads. A pack of four supercaps driving conventional LED has been thoroughly tested for more than 100 cycles.

Flexible supercapacitors are attractive devices for portable applications including those integrated in clothes. Highly conducting flexible electrodes can easily be fabricated by graphene powder and PE polymer foil but reliable fabrication of supercapacitor structure is still a challenge. A promising solution could be the incorporation of conducting polymer as polyaniline (PANI) intended to stabilize the mesoporous carbon and graphene plates, to form a conductive porous composite and to increase the capacitance. Low-cost aqueous electrolyte (1V) supercapacitor devices based on graphene/PANI composite were developed, tested in series configurations and compared in electrical performance. Preliminary applications in portable solar chargers are discussed.

Electronic transport properties of methylammonium lead iodide perovskite single crystals prepared by inverse temperature crystallisation have been investigated using dark current, steady state and transient photocurrent measurements. Above 250 K the dark conductivity at electric fields below 100 V/cm is thermally activated, with single activation energy 0.7 eV and magnitude 4×10⁻⁸ S/cm at 300 K. At higher electric fields, conductivity increases as a power law suggesting space charge limitation. Steady state photoconductivity exhibits a roughly linear dependence on photon flux below 10¹⁵ cm⁻²s⁻¹ and square root dependence above this, consistent with trap-limited and band-to-band recombination mechanisms respectively. Photocurrent overshoot and undershoot on a timescale of 10-100 s are observed on application and removal of a steady light source. Transient photocurrent measurements with temperature reveal a peak in the localised density of states 0.26 eV into the band gap, with an attempt to escape frequency of 10¹¹ s⁻¹. Deeper states are distributed exponentially with characteristic energy 54 meV, decreasing towards mid-gap.