III-nitrides (III-Ns) semiconductors and their alloys have shown in the last few years high potential for interesting applications in photonics and electronics. III-Ns based heterostructures (HS) have been under wide investigation for different applications such as high frequency transistors, ultraviolet photodetector, light emitters etc. In the present contribution a III-Ns based heterostructure, in particular the nearly lattice matched Al1-xInxN/AlN/GaN HS will be discussed. The formation of the two dimensional electron gas (2DEG), its origin, its electrical and optical properties, the confined subband states in the well and its effect on the conduction mechanisms have been studied. Moreover, extended defects and their effect on the degradation phenomena of the 2DEG have been analyzed.

The high resolution X ray diffraction (HR-XRD) diagrams have been studied in the GaAs /InxGa1-xAs /In0.15Ga0.85As/GaAs quantum wells with embedded InAs quantum dots (QDs) in dependence on the composition of the capping InxGa1-xAs layers. The parameter x in capping InxGa1-xAs layers varied from the range 0.10-0.25. These technological changes have been accompanied by the variation non-monotonously of InAs QD emission. Numerical simulation of HR-XRD results has shown that the level of elastic strains and the composition of quantum layers vary none monotonously in studied QD structures. Simultaneously it was revealed that the process of Ga/In inter diffusion at the InxGa1-xAs/InAs QD interface are characterized by the dependence non monotonous versus parameter x in capping InxGa1-xAs layers. The physical reasons of the mentioned optical and structural effects in studied structures have been discussed.

We examine the microwave reflection from the high mobility GaAs/AlGaAs two-dimensional electron system (2DES). Strong correlations have been observed between the microwave induced magnetoresistance oscillations and the microwave reflection oscillations in a concurrent measurement of the microwave illuminated magnetoresistance and the microwave reflection from the 2DES. The correlations were followed as a function of the microwave frequency and the microwave power dependent. Different existing theories are considered to explain the results.

Microwave-induced zero-resistance states appear when the associated B-1-periodic magnetoresistance oscillations grow in amplitude and become comparable to the dark resistance of the two-dimensional electron system (2DES). Existing theories have made differing predictions regarding the influence of the microwave polarization in this phenomenon. We have investigated the effect of rotating, in-situ, the polarization of linearly polarized microwaves relative to long-axis of Hall bars. The results indicate that the amplitude of the magnetoresistance oscillations is remarkably responsive to the relative orientation between the linearly polarized microwave electric field and the current-axis in the specimen. At low microwave power, P, experiments indicate a strong sinusoidal variation in the diagonal resistance Rxx vs. θ at the oscillatory extrema of the microwave-induced magnetoresistance oscillations. Interestingly, the phase shift θ0 for maximal oscillatory Rxx response under photoexcitation is a strong function of the magnetic field, the extremum in question, and the magnetic field orientation.

In this work we report on the characteristics of GaAs/AlGaAs heterostructures with a symmetric double two-dimensional electron gas (D-2DEG). Optical characterization was made by room temperature photoreflectance (PR) spectroscopy as well as electrical properties were determinated using the quantum Hall effect measurements at 2K. In order to study the surface effects on the conduction band profile, three samples with different GaAs cap layer thickness (25, 60 and 80 nm) were grown by the molecular beam epitaxy. Photoreflectance spectra at room temperature show the wide-period Franz-Keldysh oscillations between 1.42 and 1.70 eV originated by the surface electric field. The analysis of these oscillations shows that the surface electric field varies from 503 to 120 kV/cm whereas the thickness of the cap layer increases that was produced by the reduction of the depletion zone near the surface. Using QHE measurements we found that electron density increases if the surface electric field decreases.

The many-body correlation effects in the spatially separated electron and hole layers in the coupled quantum wells (CQW) are investigated. A special case of the many-component electron-hole system is considered, ν>>1 being the number of the components. Keeping the main diagrams in the parameter 1/ν allows us to justify the selection of the RPA diagrams. The ground state of the system is found to be the electron-hole liquid with the energy smaller than the dense exciton gas phase. The possible connection is discussed between the results obtained and the experiments in which the inhomogeneous state in the CQW is found.

The photoluminescence (PL), its temperature dependence and X-ray diffraction (XRD) have been studied in MBE grown GaAs/AlGaAs/InGaAs/AlGaAs /GaAs quantum wells (QWs) with InAs quantum dots embedded in the center of InGaAs layer in the freshly prepared states and after the thermal treatments during 2 hours at 640 or 710 °C. The structures contained two buffer (Al0.3Ga0.7As/In0.15Ga0.85As) and two capping (In0.15Ga0.85As / Al0.3Ga0.7As) layers. The temperature dependences of PL peak positions have been analyzed in the temperature range 10-500K with the aim to investigate the QD composition and its variation at thermal annealing. The experimental parameters of the temperature variation of PL peak position in the InAs QDs have been compared with the known one for the bulk InAs crystals and the QD composition variation due to Ga/Al/In inter diffusion at thermal treatments has been detected. XRD have been studied with the aim to estimate the capping/buffer layer compositions in the different QW layers in freshly prepared state and after the thermal annealing. The obtained emission and XRD data and their dependences on the thermal treatment have been analyzed and discussed.

The results of correlated electron paramagnetic resonance (EPR) and photoluminescence (PL) study of obliquely deposited porous SiOx films after step-by-step 15 min annealing within 105 min in vacuum at 950°C are presented. The low intensity symmetrical and featureless EPR line with a g-value g=2.0044 and a linewidth of 0.77 mT has been detected in as-sputtered films and attributed to dangling bonds (DB) of silicon atoms in amorphous SiOx domains with x=0.8. Successive annealing results in decreasing this line and the appearance of an intense EPR line with g=2.0025, linewidth of 0.11 mT and a hyperfine doublet with 1.6 mT splitting. According to the parameters this spectrum has been attributed to the EX center, a hole delocalized over four non-bridging oxygen atoms grouped around a Si vacancy in SiO2. The impact of chemical treatment before annealing and duration of anneals on the defect system, and a correlation of the PL intensity with decreasing of the DB EPR signal are discussed.

In this work, the metallic element Ru is introduced into a-Si:H. The structural and electrical properties of the films doped with Ru have been investigated. Raman spectra reveal that the addition of Ru disarranges further the intrinsically disordered amorphous network and generates more coordinated defects. Meanwhile, a new paramagnetic signal, associated with the holes localized in valence band tail, has been observed. Moreover, the conductivity increases by about nine orders of magnitude with the increase of doping concentration, and the temperature coefficient of resistance (TCR) results show that this material may have a potential application in the infrared detectors.

The conventional method to fabricate porous silicon with n-type substrates requires light assisted generation of holes used in the electrochemical reaction. Recently, two different methods have been proposed to fabricate some similar structures: Hall effect [1] and lateral electrical field [2]. Hall effect assisted etching involves the application of a perpendicular electric and magnetic field to achieve the concentration of holes at the HF/silicon interface to assist the electrochemical reaction, while the other involves the application of a lateral electrical field across the silicon wafer. In this work, the electrochemical etching of high resistivity n-type silicon wafers under the combined effect of magnetic and lateral electrical field to produce photoluminescent macroporous structures under dark conditions, is reported. A lateral gradient in pore sizes as well as in light emission is observed. Optical and structural properties were studied for their possible applications as a biosensor.

Microstructral and charge-trap properties of single Hf-silicate dielectric films are presented versus annealing treatment. The as-grown films were found to be homogeneous and amorphous. It is shown that annealing treatment results in the formation of alternated Hf-rich and Si-rich layers. The mechanism responsible for this phenomenon is found to be surface directed spinodal decomposition. The increase of annealing temperature up to 1000-1100°C resulted in the crystallization of Hf-rich phase. The stability of its tetragonal phase caused an enhancement of film permittivity was observed. The evolution of charge trapping properties of the films results in the memory effect which nature was discussed.

The present work deals with the comparative investigation of Si-ncs embedded in SiO2 and Al2O3 dielectrics grown by RF magnetron sputtering on fused quarts substrate. The effect of post-deposition processing on the evolution of microstructure of the films and their optic and luminescent properties was investigated. It was observed that photoluminescence (PL) spectra of Six(SiO2)1-x films showed one PL band, which peak position shifts from 860 nm to 700 nm when the x decreases from 0.7 to 0.3. It is due to exciton recombination in Si-ncs. For Six(Al2O3)1-x films, several PL bands peaked at about 570-600 nm and 700-750 nm and near-infrared tail or band peaked at about 800 nm were found. Two first PL bands were ascribed to different oxygen-deficient defects of oxide host, whereas near-infrared PL component is due to exciton recombination in Si-ncs. The comparison of both types of the samples showed that the main radiative recombination channel in Six(SiO2)1-x films is exciton recombination in Si-ncs, while in Six(Al2O3)1-x films the recombination via defects prevails due to higher amount of interface defects in the Six(Al2O3)1-x caused by stresses.

The effect of thermal annealing on the optical properties of Al2O3 films with different Si content was investigated by the photoluminescence method. Si-rich Al2O3 films were prepared by RF magnetron co-sputtering of the silicon and alumina targets on long quarts glass substrates. Photoluminescence (PL) spectra of freshly prepared Si-rich Al2O3 films are characterized by three PL bands with the peak positions at 2.97-3.00, 2.25-2.29 and 1.50 eV. The thermal annealing of the films at 1150 °C during 30 min stimulates the formation of Si nanocrystals (NCs) in the film area with Si content exceeded 60%. After the thermal annealing the PL intensity of all mentioned PL bands decreases and the new PL band appears with the peak position at 1.67 eV. The new PL band is attributed to the photo currier recombination inside of Si NCs. The size of NCs estimated from the PL peak position 1.67 eV of Si NC emission is about ∼-4.5-5.0 nm.

The temperature dependences of PL spectra of Si-rich Al2O3 films have been studied in the range of 10-300K with the aim to reveal the mechanism of recombination transitions for mentioned above PL bands 2.97-3.00, 2.25-2.29 and 1.50 eV in freshly prepared films. The thermal activation of PL intensity and permanent PL peak positions in the temperature range 10-300K permit to assign these PL bands to defect related emission in Al2O3 matrix.

Structural, optical and luminescent properties of Si-rich HfO2 films fabricated by RF magnetron sputtering were investigated versus annealing treatment. Pronounced phase separation process occurred at 950-1100°C and resulted in the formation of hafnia and silica phases, as well as pure silicon clusters. An intense light emission of annealed samples in visible spectral range was obtained under broad band excitation. It was ascribed to exciton recombination inside silicon clusters as well as host defects. To confirm the formation of Si clusters, the structures were co-doped with Er3+ ions and effective light emission at 1.54µm was obtained under non-resonant excitation due to energy transfer from Si clusters towards Er3+ ions. The interaction of Si clusters, host defects and Er3+ ions under is discussed.

Photoluminescence (PL), scanning electronic microscopy (SEM) and Raman scattering have been studied in crystalline ZnO nanosheets with different sizes after the thermal annealing at 400 °C for 2 hours in ambient air. ZnO nanosheets were created by the electrochemical (anodization) method using the variation of the etching durations with obtained ZnO nanosheet sizes from the range 40-360 nm. Earlier it was shown using the X ray diffraction (XRD) method that thermal annealing performed the ZnO oxidation and crystallization with the creation of the wurtzite crystal lattice. Four PL bands are revealed in PL spectra with the PL peaks at 1.60, 2.08, 2.50 and 3.10 eV. Size decreasing of ZnO nanosheets stimulates tremendous changes of ZnO optical parameters. It is shown that decreasing the ZnO nanosheet sizes is accompanied by the intensity increase of a set of Raman peaks and the surface defect related PL bands. The reasons of emission transformation and the nature of optical transitions have been discussed as well.

In this work a simple method to produce the ZnO nanosheets (NSs) with inclusions of Cu nanocrystals by means of electrochemical etching without the necessity of any surfactant has been presented. The Raman spectroscopy demonstrates that the amorphous samples of ZnO-Cu present appreciable changes in its vibrational behavior after the thermal treatment at 400°C in ambient atmosphere. The study of Photoluminescence (PL) shows monotonous increasing the bands centered in 3.07, 2.41, 2.03 and 1.57 eV versus etching time in freshly prepared samples. The intensity variation of the PL bands, the changes in vibrational behavior, as well as the impact of the copper content and preparation conditions allow identifying emission inside the visible spectral range related to the surface defects that is interesting for the future possible application this ZnO system in room temperature “white” light-emitting diodes.

Kinetics of the microstructural evolution in ZnO and NiO black powder mixture during prolonged mechanical processing (MP) was investigated by Scanning electron microscopy (SEM), Laser Particle Sizer (LPS), X-ray diffraction, electron paramagnetic resonance (EPR), infrared absorption (FTIR) and UV-Visible diffuse reflection methods.

The photoluminescence, its temperature dependences, as well as structural characteristics obtained by the method of Scanning electronic microscopy (SEM) have been studied in ZnO:Ag nanorods prepared by the ultrasonic spray pyrolysis (USP). PL spectra of ZnO:Ag NRs in the temperature range from 10 K to 300 K are investigated. Three types of PL bands have been revealed: i) the near-band-edge (NBE) emission, ii) defect related emission and iii) IR emission. It is shown that IR emission corresponds to the second-order diffraction of near-band-edge (NBE) emission bands. The study of NBE PL temperature dependences reveals that the acceptor bound exciton (ABE) and its second-order diffraction peak disappeared at the temperature higher than 200 K. The attenuation of the ABE peak intensity is ascribed to the thermal dissociation of ABE with appearing a free exciton (FE). The PL bands, related to the LO phonon replica of FE and its second-order diffraction, dominate in the PL spectra at room temperature that testify on the high quality of ZnO:Ag films prepared by the USP technology.

A green and mild synthesis of colloidal zinc oxide nanocrystals in ethanol/dimethylformamide mixtures was introduced which allows to produce stable crystalline ZnO particles and tailor their average size in the range of 2.8−4.5 nm by varying temperature and duration of post-synthesis ageing. An increase in dimethylformamide fraction in the mixture results in acceleration of ZnO nanocrystals ripening. Colloidal ZnO nanocrystals emit broadband photoluminescence in the range of 2−3 eV with the quantum yields of up to 12 %.

Cystic fibrosis (CF) is an inherited childhood-onset life-shortening disease. It is characterized by increased respiratory production, leading to airway obstruction, chronic lung infection and inflammatory reactions. The most common bacteria causing persisting infections in people with CF is Pseudomonas aeruginosa. Superparamagnetic Fe3O4 iron oxide nanoparticles (NPs) conjugated to the antibiotic (tobramycin), guided by a gradient of the magnetic field or subjected to an oscillating magnetic field, show promise in improving the drug delivery across the mucus and P. aeruginosa biofilm to the bacteria. The question remains whether tobramycin needs to be released from the NPs after the penetration of the mucus barrier in order to act upon the pathogenic bacteria. We used a zero-length 1-ethyl-3-[3-dimethylaminopropyl] carbodiimide hydrochloride (EDC) crosslinking agent to couple tobramycin, via its amine groups, to the carboxyl groups on Fe3O4 NPs capped with citric acid. The therapeutic efficiency of Fe3O4 NPs attached to the drug versus that of the free drug was investigated in P. aeruginosa culture.