Showing papers in "Lithuanian Journal of Physics in 2011"

Generation of metal nanoparticles by laser ablation

Abstract: The process of nanoparticle generation during nanosecond and picosecond laser ablation of various metals (Ni, Al, W and stainless steel) in ambient air and argon gas was investigated. The number concentration of nanoparticles generated by laser ablation in argon gas was up to 100 times higher compared to the concentration in ambient air. Three stable separate size peaks of nucleation, Aitken and accumulation modes of nanoparticles were observed in case of argon gas, while in ambient air particles of a wide size spectrum (8–200 nm) were generated. The natural precursors in ambient air can have an effect on size spectrum of the particles composed of various chemical compounds with target material during the ablation process. The influence of laser process parameters and properties of investigated metals on the number concentration and size distribution of nanoparticles generated during ns- and ps-laser ablation was observed. Keywords: nanoparticles, nanosecond and picosecond laser ablation, metals, size distribution, number concentration, ambient air, argon gas

Ultraviolet light emitting diodes

Abstract: The paper presents a review of the recent development of III-nitride based deep UV light emitting diodes (LEDs). Main applications of the deep UV LEDs are introduced. Review of material issues is focused on the lattice mismatch between the substrate and the active layer and at heterojunctions in multiple quantum well structures forming the active layer, the localization of nonequilibrium carriers, the material properties limiting the internal quantum efficiency, and the effect of efficiency droop at high density of nonequilibrium carriers. AlGaN is currently the semiconductor of choice for development of deep UV LEDs, so this material is the most discussed one in this review, though some information on AlInGaN is also provided. Keywords: light emitting diodes, ultraviolet light sources, III-nitride semiconductors, AlGaN

FLUENCE DEPENDENT VARIATIONS OF BARRIER CHARGING AND GENERATION CURRENTS IN NEUTRON AND PROTON IRRADIATED Si PARTICLE DETECTORS

Abstract: The stability of the potential barrier is an essential characteristic in high energy particle detector operation under irradiation conditions. In this work a technique for barrier evaluation by linearly increasing voltage (BELIV) is presented, based on analysis of current transients measured at reverse biasing. The technique has been applied to diodes irradiated by neutrons and protons with fluences in the range of 1012–1016 cm–2 in 1 MeV neutron equivalent. Fluence and temperature dependent characteristics of the diode barrier capacitance as well as of generation current are discussed. Keywords: charge extraction currents, junction barrier, generation current, radiation defects

SPECTROSCOPIC INVESTIGATIONS OF CdTe QUANTUM DOT STABILITY IN DIFFERENT AQUEOUS MEDIA

Abstract: For the successful use of quantum dots (QDs) in biomedicine their chemical and optical stability is of great importance. In this study the changes of photoluminescence parameters of CdTe QDs coated with mercaptopropionic acid (MPA) dependently on time and environment are presented. The presence of salt ions in the QD water solution decreases photoluminescence band intensity and induces red shift. The pH value of the solution also influences spectroscopic properties of QDs. In the pH range from 2.5 to 9 a decrease of photoluminescence intensity is observed. The fastest one, leading to the complete luminescence bleaching, occurs in the most acidic medium. Changes of QD spectral properties in cell growth media were studied as well. The results imply that spectroscopic changes of CdTe‐MPA QDs are caused by the interactions between the ions present in the solution and ligand coating of QDs. The model of possible processes is proposed.

Optical resistance and spectral properties of anti-reflective coatings deposited on LBO crystals by ion beam sputtering

Abstract: The nonlinear LBO (LiB3O5) crystal is widely used in many Nd : YAG, Yb : KGW and Nd : YLF lasers in order to generate higher optical harmonics. However, the most limiting factor in such applications is the optical resistance of their coated surfaces described by the so-called Laser Induced Damage Threshold (LIDT) parameter. In this work we investigate the “fatigue” (multi-pulse) behaviour of LIDTs in LBO crystals coated with different types of (single AR@355 nm and triple AR@355+532+1064 nm wavelength) anti-reflective coatings while optimising the refractive index designs and selecting appropriate sub-layer materials. All the coatings were produced of different oxide materials (ZrO2, Al2O3, SiO2) and ZrO2-SiO2 mixtures by using the ion beam sputtering (IBS) deposition technique. The optical damage resistance of both fixed and transient refractive index coatings is of special interest. Besides the spectral properties, the resistance to laser irradiation is characterised at the wavelength of 355 nm with laser pulses of nanosecond duration. The conclusions are drawn about the AR coated LBO with the most successful designs by the means of optical resistance.

Simulation of thermal conversion of solid fuel by the discrete particle method

Abstract: We introduce the discrete particle method (DPM) that derives from the discrete element method (DEM). This is an advanced numerical simulation tool that takes into account both motion and chemical conversion of granular material, such as coal or biomass, in furnaces in conjunction with computational fluid dynamics (CFD). However, predictions of solely motion or conversion in a decoupled mode are also applicable. The DPM uses object oriented computational techniques that support objects representing three-dimensional particles of various shapes, size, and physical properties of particle material. This makes DPM a highly versatile tool in dealing with a variety of problems related to different industrial applications of granular matter. A review of literature concerning different approaches to mass and heat transfer in packed beds is presented. Keywords: dicrete particle method (DPM), numerical modelling, combustion, moving bed, forward acting grate

Dielectric studies on binary mixtures of formamide with ethanolamine using the time domain technique

Abstract: Dielectric relaxation measurements on formamide (FA) – ethanolamine (ETA) solvent mixtures have been carried out across the entire concentration range using time domain reflectometry technique at 15, 25, 35, and 45 0C over the frequency range from 10 MHz to 10 GHz. The mixtures exhibit a principle dispersion of the Davidson–Cole relaxation type at microwave frequencies. Bilinear calibration method is used to obtain complex permittivity e*(ω) from complex reflection coefficient ρ*(ω) over the frequency range 10 MHz to 10 GHz. The excess permittivity eE, excess inverse relaxation time (1/τ)E, Kirkwood correlation factor geff , and thermodynamic parameters such as Gibbs energy of activation ΔG and molar enthalpy of activation ΔH are also calculated to study the solute–solvent interaction. Keywords: activation energy, excess parameters, Kirkwood correlation factor, time domain reflectometry

Investigations of intermolecular interactions between 2-methoxyethanol and nitrobenzene through dielectric relaxation study

Abstract: Complex dielectric spectra e*(ω) = e' − ie" of binary mixture of 2-methoxyethanol with nitrobenzene were obtained in the frequency range of 10 MHz to 20 GHz over the volume fraction range 0 < v < 1 and at different temperatures of 288, 298, 308, and 318 K using the time domain reflectometry (TDR) technique. The static dielectric constant "s and relaxation time have been obtained. These values are used to obtain the excess permittivity eEs , excess inverse relaxation time (1/τ)E, Kirkwood correlation factor geff , Bruggeman factor fB, and thermodynamic parameters. On the basis of above parameters, intermolecular interaction and dynamics of molecules at molecular level are predicated. Keywords: dielectric relaxation, excess parameters, Kirkwood correlation factor, thermodynamic parameters, time domain reflectometry

Trends of atmospheric heavy metal deposition in lithuania

Abstract: The results of long-term measurements of heavy metal (Pb, Zn, Cr, Ni, Cu, Mn, Cd, Fe, As, Hg) concentrations carried out at the Aukstaitija and Žemaitija integrated monitoring stations (IMS) are presented in this work. The average annual concentrations of heavy metals in the air in 2007–2008 and in precipitation over the period 2006–2010 are analysed. A higher deposited amount of heavy metals on the Earth’s surface was determined in the western part of lithuania (Žemaitija IMS) compared with the eastern part of lithuania (Aukstaitija IMS). Different deposited amounts of heavy metals are related to higher concentration of heavy metals in the air and higher amounts of precipitation in the western part of lithuania. A decreasing trend of Pb concentration in precipitation and an increasing trend for Cr, Ni and Cu in precipitation and deposited amounts were observed at both stations. Common correlating groups of element concentrations for both stations were established: As–Cd, Ni–Cr–Cu, and Mn–Cu. These groups are probably typical of the entire territory of lithuania and are caused by long-range transfer of air masses.

Dielectric dispersion in 1,2-diaminopropane- dimethylaminoethanol mixtures as a function of composition and temperature

Abstract: The dielectric dispersion e' and dielectric loss e" of binary mixture of 1,2-diaminopropane–dimethylaminoethanol were measured by employing the time domain reflectometry technique over a frequency range from 10 MHz to 20 GHz at 288, 298, 308, and 318 K temperatures. The accuracy in the measurement of the e' and e" values obtained from this technique is within ±5%. To evaluate various dielectric parameters, the frequency dependents complex permittivity (e*(ω) = e' – ie") data, viz., static permittivity e0, relaxation time τ, and permittivity at high frequency e∞ were fitted by the nonlinear least-squares fit method to Debye expression. Temperature dependent e0, τ, Kirkwood correlation factor g, free energy of activation ΔG, and enthalpy of activation ΔH have been determined and discussed in terms of the effect of –NH2 and –CH3 side-group on molecular dynamics and intermolecular hydrogen bonds. The dielectric behaviour of 1,2-diaminopropane and dimethylaminoethanol liquid molecules and their conformations as well as molecular dynamics of the system can be explored only by comparing the dielectric data of the mixture system with the dielectric data of the individual molecules and their dynamics.

Characterization of aerosol sources at urban and background sites in Lithuania

Abstract: Size and composition real-time measurements of atmospheric submicron aerosol (PM1) were conducted in the Lithuanian background and urban areas during several months (April–July, 2008) using the Quadrupole aerosol mass spectrometer (QAMS). The average mass concentration of non-refractory PM1 ranged within 8–13 μgm−3. Organic compounds of PM1 were the most abundant constituent ranging from 70 to 83%, nitrate made up 4.0–7.7%, ammonium 1.7–3.9%, sulfate 11–21%, and chloride less than 1%. While sulfate concentrations were comparable at the urban and background sites, concentrations of organic compounds and nitrate in Vilnius city were almost twice as high as those at the background site (Rūgsteliskis). The average aerodynamic diameter for nitrate and organics was about 300 nm at both sampling sites – in Vilnius city and at Rūgsteliskis background site. The average aerodynamic diameter for ammonium was about 355 nm and for sulfate about 400 nm. The main source of organics and nitrates in the city was emission from traffic, however the main source of sulfates at urban and background sites was long-range transport. Positive matrix factorization (PMF) analysis of the unit mass-resolution (UMR) spectra was used to identify sources of organic matter in the urban (Vilnius) and background (Rūgsteliskis) aerosol. Organic aerosol components were identified from AMS spectra for both sites: primary anthropogenic emissions – hydrocarbonlike organic aerosol (HOA), aged oxygenated low volatility organic aerosol (LV-OOA), and less oxygenated, presumably, semivolatile organic aerosol (SV-OOA) at the urban site (Vilnius city) as well as biomass burning organic aerosol (BBOA), aged oxygenated low volatility organic aerosol (LV-OOA), and semivolatile biogenic secondary organic aerosol (SV-OOA) at the background site (Rūgsteliskis). Keywords: atmospheric submicron aerosol, urban and background sites, concentration, composition, size distribution, sources

Photoluminescence characterisation of GaAs/AlGaAs structures designed for microwave and terahertz detectors

Abstract: The photoluminescence (PL) spectra of GaAs/AlGaAs structures designed for microwave and terahertz detectors were investigated. Detailed experimental results of PL were obtained both before and after etching of the heavily doped layers. Possible mechanisms of carrier recombination are discussed and certain emphasis is put on the up to 20 times enhancement of the PL intensity observed in these detector structures.

Distribution of artificial radionuclides in the Baltic seaside environment

Abstract: Investigation on 137Cs and 239,240Pu activity concentration was undertaken in a coastal zone of the Baltic Sea on the Lithuanian territory to study the vertical distribution of radionuclides (down to 30 cm). The Baltic seaside is one of the regions where the highest radionuclide concentrations after the Chernobyl NPP accident were detected. Moreover, this area is a significant recreational zone, therefore, peculiarities of radionuclide spreading in the environmental ecosystem are important from the radioecological point of view. The obtained results of vertical distribution of 137Cs and 239,240Pu in sand and forest soil suggest that the radionuclide downward migration depends on the structure of matrix and its chemical composition. Besides, the results of radionuclide distribution on the stripe between the Baltic Sea and the Curronian Lagoon indicate that the sea is a possible source of radioactive contaminants. Keywords: plutonium, radiocesium, activity concentration, sand, forest soil, migration, organic matter

Parallelism between charge redistribution and delocalization. Applications to organic reactions

Abstract: The study is devoted to interrelations between two perturbative expansions for molecules and molecular systems, namely between terms of power series for one-electron density matrices on the one hand, and those for respective representation matrices of non-canonical (localized) molecular orbitals (MOs) on the other hand, as well as to the relevant implications. As the most outstanding example of the latter, simple proportionalities are established between alterations in populations of basis orbitals due to chemical interaction and delocalization coefficients of respective localized MOs (LMOs). The proof of these proportionalities is valid for members of power series to within the fifth order inclusive that were shown previously to be sufficient for investigations of the most important organic reactions. As a result, classical interpretations of early stages of these reactions in terms of shifts of respective localized pairs of electrons (cf. the so-called ‘curly arrow chemistry’) acquire a quantum-chemical support. Moreover, the results of the present study allow comparisons of relative extents of delocalization of LMOs for alternative routes of the same process. On this basis, predominant (allowed) routes of organic reactions are shown to be characterized by enhanced delocalization of respective principal pairs of electrons as compared to alternative (forbidden) routes. Raktažodžiai: localized molecular orbitals, Brillouin theorem, organic reactions, delocalization, curly arrow chemistry

Multibeam pumping of opa by radiation of fibre amplifiers

Abstract: The results of effective optical parametric amplification in KTP crystal pumped by three beams delivered by fibre amplifiers are presented. The second harmonic of three 1.2 ns and 200 µJ pulses each extracted from fibre amplifier have been used to pump optical parametric amplifier (OPA) simultaneously. The conversion efficiency of pump radiation into a signal beam was close to 25%.

Fabrication influence on the surface morphology and structure of vapour etched porous silicon

Abstract: The structure and properties of porous silicon produced applying vapour-phase chemical etching of Si in HF : HNO3 acid mixture are analysed. Experimental layers of different porosity with pores of different size and shape corresponding to different active surface areas, were formed by varying the etching parameters. The fabricated structures were investigated using the X-ray diffractometry (XRD), Raman spectroscopy (RS), infrared spectroscopy (FTIR) and photoluminescence spectrometry (PL) methods. SEM imaging was used for the visualization of the produced structures. The refractive index of the experimental layers was evaluated by optical ellipsometry measurements and used for layer porosity estimation. The crystallite size in the fabricated porous structures was estimated taking into account the presence of porous (p-Si), crystalline (c-Si) and amorphous (a-Si) structures in the experimental layers. The size of crystallites in the porous Si layers was found to vary from 3.1 nm to 4.3 nm, and layer porosity varied from 61.4 to 86.7% in different samples. Fabrication of mesoporous silicon structures containing nanosized crystallytes, achieved by controlling vapour-phase chemical etching parameters, is discussed on the basis of the obtained results. Keywords: vapour-phase etching, porous Si, nanocrystalline, mesoporous structure

Electron transport in modulation-doped InAlAs/InGaAs/InAlAs and AlGaAs/InGaAs/AlGaAs heterostructures

Abstract: The possibilities of enhancing the electron mobility and high-field drift velocity in channels of modulation-doped InAlAs/InGaAs and AlGaAs/InGaAs quantum wells by tuning interaction of electrons with interface phonons are tested and reviewed. A large increase in the mobility is achieved in a novel metamorphic In0.7Al0.3As/In0.8Ga0.2As structure with the high InAs content in the InAlAs barrier layer as well as in the AlxGa1-xAs/In0.2Ga0.8As structure with the low AlAs content in the AlGaAs barrier layer. An enhancement in the electron mobility by inserting thin InAs layers into the In0.52Al0.48As/In0.53Ga0.47As quantum well is obtained. The electron drift velocity saturates at high electric fields of 1.5–5 kV/cm and achieves a maximal value of 2.5 . 107 cm/s in the InGaAs quantum well with the thin InAs and GaAs inserts.

UV spectral features of poly(propylene imine) dendrimers

Abstract: The UV optical spectra of amine terminated poly(propylene-imine) (PPI) dendrimers of generatons G1 to G5 were investigated experimentally. The occurrence of double band at (270–290) nm in absorption spectra of amine terminated dendrimer and the dependence of the spectra on the generation number and concentration in dichloromethane solution were discussed. The lineshape of double band was similar in the sequence G1 to G5, though some redistribution of the intensity of components was observed. A linear dependence of the absorbance in the double band was determined in the solutions at low concentrations of order 1x10–5 M. Experimental data have indicated that double band is caused by several optical transitions related to the core electronic excitations. A significant Rayleigh light scattering was found for higher dendrimer generations. Keywords: PPI NH2-terminated dendrimers, optical absorbance, light scattering

Influence of aerosol particle concentration on volumetric activities of indoor radon progeny

Abstract: The influence of aerosol particle concentration on changes of volumetric activities of radon short-lived decay products was investigated. Volumetric activities of radon short-lived products in accommodations under various living conditions were measured. Concentrations of aerosol particles in the air, equilibrium factors, and unattached fraction were determinated under normal living conditions and by increasing the concentration of aerosol particles in the air of the accommodations. An increase of radon short-lived decay products attached to aerosol particles was obtained during a candle or frankincence burn, in smokefilled compartments, or in steamy kitchen conditions, therefore larger volumetric activity of the alpha particles was registered. Negative correlation coefficient between unattached fraction and the radioactive equilibrium factor, as well as positive correlation coefficient between the radioactive equilibrium factor and aerosol particle concentration in the air of accommodations has been determined. Seasonal changes of the radioactive equilibrium factor are presented.

Sensitivity improvement in porous silicon microwave detector

Abstract: Attempts to use microporous silicon structures in detection of microwave radiation were investigated. Point-contact-like samples containing microporous silicon layers were manufactured using traditional technique of electrochemical etching of p-type crystalline silicon. The response of the structures to microwave radiation of 10 GHz frequency was studied. It is shown that the microporous silicon containing samples exhibited sensitivity by several orders higher than that of similar detectors having no porous layers. The results were analysed within the model of hot carrier effects.

Enhanced light emission in nanostructures

Abstract: The enhancement of light emissive processes in different quantum nanometric systems is presented in this review. The plasmonic enhanced photoluminescence (fluorescence) of metals and metal nanoparticles, molecules and semiconductor nanostructures, as well as surface-enhanced Raman scattering is initially considered. The enhancement of excitonic photoluminescence intensity in semiconductor confined systems such as quantum wells, quantum wires and quantum dots, and microcavities are then discussed. Finally, the experimental results of the enhanced exciton photoluminescence from GaAs homojunctions, δ-doped GaAs structures, GaAs/AlGaAs selectively doped and AlInN/GaN heterostuctures is presented. These results can be applied to enhance the emission of light-emitting diodes, as well as to increase the efficiency of solar cells.

Dielectric relaxation of dihydric alcohol-1,4-dioxane mixtures using time domain technique

Abstract: Complex dielectric permittivity measurements of 1,2-propanediol–1,4-dioxane mixtures has been carried out at different concentration and in the frequency range of 10 MHz to 20 GHz using time domain reflectometry (TDR). The least squares fit method has been used to obtain the static dielectric constant, relaxation time, and Bruggeman factor for binary mixtures. The Kirkwood–Frohlich theory is applied to compute the dielectric constant for the mixtures. It adequately reproduces the experimental values of static dielectric constants for the 1,2-propanediol–dioxane mixtures. The excess parameters confirm that the heteromolecular hydrogen bonding interactions between 1,2-propanediol and dioxane molecules vary significantly in the mixture. The Bruggeman model for the nonlinear case has been fitted to the experimental dielectric data for mixtures. Keywords: dielectric relaxation, time domain reflectometry, alcohols

Dependence of Z-scan measurements on the spatiotemporal pulse parameters

Abstract: We report the experimental results obtained by the closed-aperture Z-scan technique where Nd:YAG minilaser short pulses with different temporal pulse shapes have been used. It is shown that the nonlinear refractive index coefficient n2 of fused silica (one of the smallest among the condensed media) can be successfully measured using the pulses with durations of about 1 ns and energies less than 1 mJ. Very good compatibility between the values for the same samples of fused silica is obtained only if the temporal shapes of the used SBS-compressed, single longitudinal or multi longitudinal mode pulses are properly taken into account. It is also shown that spatial properties of the used beams should be taken account of properly. By these experiments we emphasize the significance of taking into account the temporal pulse shape profile for accurate determination of the nonlinear refractive index by the Z-scan technique. Keywords: Z-scan, pulse shape, nonlinear refractive index, fused silica

Electrical properties of nonstoichiometric In2O3-x thin films

Abstract: Thin films of indium oxide were grown heteroepitaxially by dc magnetron sputtering onto (110) faces of crystalline yttriastabillized zirconia. Resistance versus temperature of the films was measured in situ in a wide temperature range during film heating and cooling under various oxygen pressure conditions. Insulator–metal (I–M) phase transition induced in the nonstoichiometric oxide material with oxygen content variation has been indicated. The characteristic activation energy of oxygen diffusion in the material has been estimated by analysing temperature and oxygen content-dependent resistance kinetics. Keywords: In2O3 films, electroresistivity, magnetron sputtering, oxygen diffusion, insulator–metal transition

An explicit basis of lowering operators for irreducible representations of unitary groups

Abstract: The representation theory of the unitary groups is of fundamental significance in many areas of physics and chemistry. In order to label states in a physical system with unitary symmetry, it is necessary to have explicit bases for the irreducible representations. One systematic way of obtaining bases is to generalize the ladder operator approach to the representations of SU(2) by using the formalism of lowering operators. Here, one identifies a basis for the algebra of all lowering operators and, for each irreducible representation, gives a prescription for choosing a subcollection of lowering operators that yields a basis upon application to the highest weight vector. Bases obtained through lowering operators are particularly convenient for computing matrix coefficients of observables as the calculations reduce to the commutation relations for the standard matrix units. The best known examples of this approach are the extremal projector construction of the Gelfand–Zetlin basis and the crystal (or canonical) bases of Kashiwara and Lusztig. In this paper, we describe another simple method of obtaining bases for the irreducible representations via lowering operators. These bases do not have the algebraic canonicity of the Gelfand–Zetlin and crystal bases, but the combinatorics involved are much more straightforward, making the bases particularly suited for physical applications. Keywords: unitary group, special unitary group, irreducible representations, lowering operators, spin-free quantum chemistry, many-body problem

Dielectric properties of Pb(Fe1/2Ta1/2)O3ceramics over 70–300 K temperature range

Abstract: The studies of dielectric response in ferromagnetic lead ferrotantalate Pb(Fe1/2Ta1/2)O3 are reported over a wide range of temperature under the applied bias field. The features of dielectric nonlinearity deduced from behaviour of reverse e'(E=) curves at different temperatures, including regions of ferroelectric phase transition and vicinity of the Neel point, are examined. Obtained results indicate a substantial broadening of the ferroelectric phase transition. The results are discussed with respect to effects of ferroelectric ordering in relaxor materials of such kind.

Control of two-dimensional electron spin by an abrupt change of physical parameters of a quantum well

Abstract: We apply Clifford algebra to investigate 2D electron spin reflection off and transmission through a stepped discontinuity of physical parameters in semiconducting quantum well. The discontinuity may be due to change of spin-orbit interaction constants, effective masses, or electrostatic potential. In the paper the posed problem has been solved exactly. It is shown that the reflected electronic beam has identical spin polarization as the incident one. However, the transmitted beam suffers spin flipping and in general case consists of a mixture of up and down spin states. Optimal conditions for total reversion of 2D electron spin polarization are found. Special attention is paid to correct boundary conditions in the presence of spin-orbit interaction. A simple formula that connects spin polarization of the transmitted beam and SO interaction constants is presented. Keywords: Clifford algebra, geometric algebra, semiconductors, spintronics, spin polarization, spin flipping, quantum well

GROWTH, PROPERTIES AND SENSOR APPLICATIONS OF LOW TEMPERATURE GROWN ZnO NANORODS

Abstract: ZnO nanorods with the average diameter of about 60–300 nm have been grown by the low temperature aqueous chemical growth technique. The impact of growth time and reactant concentration on the morphology on ZnO structures was tested by scanning electron microscopy and photoluminescence spectroscopy. High optical quality of obtained ZnO nanorod films was evidenced by dominating free exciton transitions. The reduction of surface to volume ratio by increasing the diameter of ZnO nanorods resulted in a linear increase of excitonic luminescence intensity with respect to the defect related emission. Excellent photoluminescence properties and high surface area of ZnO nanorods can be used for the detection of organic contaminants dissolved in water. The quenching of both excitonic and defect luminescence was observed upon exposure of ZnO nanorod films to various organic contaminants.

InAlGaN laser diodes grown by plasma assisted molecular beam epitaxy.

Abstract: We present recent progress in the growth of nitride-based laser diodes (LDs) made by plasma assisted molecular beam epitaxy (PAMBE). This technology is ammonia-free, and nitrogen for the growth is activated by RF plasma source from nitrogen molecules. The demonstration of continuous wave blue-violet InGaN LDs has opened a new perspective for PAMBE in optoelectronics. We demonstrate the laser diodes grown by PAMBE operating at the range from 410 nm to 455 nm. The key factors which allow us to extend the lasing wavelength to 455 nm are (a) improvements in the growth of InGaN quantum wells with high nitrogen flux in PAMBE, and (b) design of the laser diode structure. We also report on optically pumped lasing at 501 nm on InGaN laser structures which show that there are no intrinsic limitations in PAMBE technology for the growth of green LDs.

Time-resolved fluorescence spectroscopy of the heart tissues

Abstract: During the heart surgery there is a possibility to harm the conduction system of the heart (HCS), which may cause dangerous obstruction of the heart functionality. The muscular origin makes it complicated to distinguish HCS from the surrounding tissues; therefore, there is an immense necessity to visualise HCS during the operation time. Optical methods carry information about intrinsic properties of the tissue and provide the unique possibility to study the objects non-invasively. The experiments were performed on the human heart tissue specimens ex vivo. HCS, myocardium (MC), and connective tissue (CT) were preliminary marked by a pathologist and histologically approved after the spectral measurements. The spectrometer FLS920 (Edinburgh Instruments) was used for steady state and time-resolved fluorescence registration. Fluorescence was exited using a 405 nm pulsed laser. Spectral analysis revealed that at least three fluorophores are responsible for the emission in the region of 430–550 nm. According to the lifetimes, the fluorescing constituents in all tissues should be the same. The fractional components of fluorescence intensity revealed a similar composition of MC and HCS; however, quantitative differences were observed between HCS and CT.