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Journal of materials science / Materials in electronics 34, 651-9 (2023). doi:10.1007/s10854-023-10026-4, The oxide glass-ceramics is a promising class of solid state materials because they are based on thermally stable and chemically inert glass oxide matrices. Development of such efficient glass matrices suitable for creation of glass-ceramic materials for several purposes is an important practical task. The xLi$_2$O-yV$_2$O$_5$-(100-x-y)B$_2$O$_3$ undoped glass and 47Li$_2$O-$_2$V$_2$O$_5$-50B$_2$O$_3$-1La$_{0.3}$Eu$_{0.7}$VO$_4$ glass samples with crystalline nanoinclusions were synthesized and investigated using XRD, IR and UV-Vis spectroscopy and UV band-to-band excitation of luminescence. The synthesized glass samples are characterized by wide band photoluminescence emission with maximum at 570 nm and intensity increased with increase of Li$_2$O concentration. The excitation spectra consist of three bands with maxima located at 270, 320 and 365 nm. The observed concentration dependencies of spectral distributions in the absorption and excitation spectra are explained by influence of the lithium ions on a ratio between triborate and tetraborate groups in the glass networks. The assumption is made that the observed wide band photoluminescence emission of the glass matrix can appear as a result of recombination processes between the defects in borate networks and the broken vanadate groups. The crystalline component in the doped glass samples is found to not affect the luminescence properties of the glass matrix. Intensity of narrow band photoluminescence emission of the crystalline component is up to 10 times more intense than that of the glass matrix wide band emission. The synthesized type of the glass matrices has promising characteristics for the use of developed materials in lighting devices, as it allows improving the spectral distribution of light emission towards the white light., Published by Springer Science + Business Media B.V, Dordrecht [u.a.]

Co-doped with Ca2+ and Er3+ ions LаVO4:Eu crystalline nanoparticles are synthesized and investigated with a goal to clarify the mechanisms of Ca2+ and Er3+ impurities effects on Eu3+ ions luminescence and to find compositions with enhanced luminescence intensity. The XRD analysis reveals dependence of crystal structure on dopants concentration: monoclinic crystal phase is observed for low dopant concentrations and content of tetragonal crystal phase increases with dopant concentrations increase. The SEM investigation reveals formation of nanoparticles with two types of shapes. Photoluminescence spectra consist of lines caused by f-f transitions in the Er3+ and Eu3+ ions. It has been shown that dependence of the Eu3+ ions luminescence intensity on the Er3+ and Ca2+ concentrations is caused by cumulative effects of dopants on crystal lattice structure, on defects in the first coordination sphere of the Eu3+ ions and on efficiency of excitation energy transfer. The maximal luminescence intensity is found for the Lа0.8Er0.05Eu0.05Ca0·1VO4 composition. The corresponded intensity is as much as 19 ± 2 and 8 ± 2 times higher than luminescence intensity of the Lа0.95Eu0.05VO4 and Lа0.9Eu0.05Ca0·05VO4 compounds, respectively. Conclusion is made that Er3+ and Ca2+ ions co-doping is a promising way to increase luminescence efficiency of the Eu3+ ions in the LaVO4 nanocrystals.

High pressure studies of monoclinic yttrium aluminum oxide single crystals (Y4Al2O9 -YAM) doped with Ce3+ ions grown by micro-pulling-down method are reported. The results of absorption measurements in the mid-infrared prove the existence of four different sites in which Ce3+ ions substitute Y ions, in accordance with the crystallographic structure of YAM. The lowest 5d level of Ce3+ is located very close to the bottom of the conduction band for two of four Ce3+ related centers at ambient pressure, which results in strong temperature quenching of their luminescence. Two other Ce3+ centers do not emit at ambient pressure since their 5d levels are resonant with the conduction band. Application of high pressure above 11 GPa restores their luminescence. Consequences of such energy structure of various Ce3+ sites in YAM for the Dorenbos theory are discussed. The bandgap energy of YAM is found to be 5.93 eV, which is the smallest out of the three yttrium aluminum oxides. High-pressure synchrotron angle dispersive x-ray diffraction and Raman scattering measurements identify a phase transition occurring at pressures between 8 and 11 GPa, which has martensitic character. The second phase transition to another structure (likely with hexagonal symmetry) occurs at a pressure around 16 GPa.

Water-soluble upconversion nanoparticles (UCNPs), based on polyvinylpyrrolidone (PVP)-coated NaYF4:Er3+,Yb3+,Gd3+, with various concentrations of Gd3+ ions and relatively high upconversion efficiencies, were synthesized. The internalization and cytotoxicity of the thus obtained UCNPs were evaluated in three cell lines (HeLa, HEK293 and astrocytes). No cytotoxicity was observed even at concentrations of UCNPs up to 50 μg ml-1. The fate of the UCNPs within the cells was studied by examining their upconversion emission spectra with confocal microscopy and confirming these observations with transmission electron microscopy. It was found that the cellular uptake of the UCNPs occurred primarily by clathrin-mediated endocytosis, whereas they were secreted from the cells via lysosomal exocytosis. The results of this study, focused on the mechanisms of the cellular uptake, localization and secretion of UCNPs, demonstrate, for the first time, the co-localization of UCNPs within discrete cell organelles.

Ca9Nd(VO4)7 single crystal was grown by the Czochralski method in inert atmosphere. The crystal structure and chemical composition were studied. Polarized absorption and luminescence spectra were investigated in details. It was found that the Ca9Nd(VO4)7 crystals belongs to self-activated laser materials with a weak concentration quenching of luminescence. Judd-Ofelt analysis was performed. The emission cross-sections spectra for 4F3/2 → 4I9/2, 4I11/2, 4I13/2 transitions were determined. For the first time Raman spectra of the Ca9Nd(VO4)7 single crystal were recorded and interpreted.

Pure and Nd-doped Ca 10 Li(VO 4 ) 7 single crystals were grown by the Czochralski method. The structure of Ca 10 Li(VO 4 ) 7 single crystal was refined starting from a model of Ca 10 K(VO 4 ) 7 using the powder diffraction data collected at a laboratory high-resolution diffractometer. The defect structure of the single crystal was studied with the use of both, high-resolution diffraction using a laboratory instrument and X-ray topographic techniques employing synchrotron radiation at the Hasylab laboratory (Hamburg). Polarized absorption and luminescence spectra of Nd-doped Ca 10 Li(VO 4 ) 7 crystal were investigated in details. The laser oscillation was obtained under flash lamp pumping and the slope efficiency of 0.87% was achieved in the free-running mode. Preliminary examination of lasing properties points that Ca 10 Li(VO 4 ) 7 :Nd crystal can be a highly efficient solid state laser medium. Crystals of this kind are expected to be suitable for application as efficient non-linear optics materials.

We study the nature of the intensity parameter Ω2 and the associated line strength S of the 4I9/2 → 4G5/2 hypersensitive transition in the series of Nd3+ doped Ca9Ln(VO4)7 and Ca10A(VO4)7 double calcium orthovanadate crystals. It has been shown that the covalence of neodymium – ligand bonds has a weak effect on Ω2 and S. They are mainly determined by the symmetry of the local environment of the neodymium ions, which lowers from yttrium ion to lanthanum ion for Ca9Y/La/Nd(VO4)7 crystals and from potassium ion to lithium ion in a series of Ca10K/Li(VO4)7 crystals.

We present the results of structural characterization of Cd1 � xMnxGeAs2 chalcopyrite-type crystals with low Mn content x varying from 0 to 0.037. High resolution X-ray powder diffraction method of measurements and Rietveld refinements procedure used for analysis of obtained diffraction patterns revealed high crystal quality of the samples. The substitutional alloying of Cd1 � xMnxGeAs2, with Mn ions at Cd sites, has been confirmed. The analytical equations describing the linear reduction of the lattice parameters with increase of Mn content were deduced and compared with the literature results of theoretically estimated lattice parameters of compounds of the same kind. Copyright © 2015 John Wiley & Sons, Ltd.

Gallium nitride is studied at ambient and nonambient temperatures by powder X-ray diffraction followed by Rietveld refinement of the structure. The structure is reported for the ambient temperature on the basis of laboratory data. The diffraction data collected using a synchrotron beam serve for derivation of the lattice parameter and thermal expansion dependencies on temperature. The variation of unit-cell size on temperature was studied in detail in a broad range 11 K

The aim of the present work is to study the magnetic properties of ZrO2(Fe) nanocrystals prepared by the wet chemistry method. The microwave assisted hydrothermal synthesis was used. The detailed structural characterization was performed by means of X-ray diffraction and TEM studies. 57 Fe Mossbauer spectra were recorded at room temperature for all samples. The isomer shift and quadrupole splitting indicate the presence of Fe 3+ ions. The systematic measurements of AC magnetic susceptibility up to 350 K and magnetization as a function of magnetic field (up to 9 T) and temperature were performed. Depending on the nominal concentration of magnetic dopant different types of magnetic behavior, were observed. 2015 Elsevier B.V. All rights reserved.

Upconverting Gd2O3 nanoparticles (NPs) doped 1% Er3+ and 18% Yb3+ permits one to perform optical imaging. Because of the presence of Gd3+ they are useful in MRI. The main challenge is to enhance the NPs upconversion efficiency. As a result of co-doping the NPs with Zn2+ ions, achieved using microwave-induced solution combustion synthesis, we obtained optimal upconversion quantum yields (UQYs). The breakdown of the local crystal field symmetry around the rare earth ions, maximal in the presence of 5% of zinc, may be responsible for the highest observed UQY. The upconversion of IR light results in emission of visible red light mainly at 660 nm and at 550 nm. Optimized red photoluminescence of the samples observed in an organic environment was examined as a function of the laser power density to explain the mechanism of the upconversion emission. Paramagnetic properties of the NPs were determined by superconducting quantum interference device measurements. The non-functionalized nanoparticles incubated with HeLa cells were endocytosed and imaged by confocal laser scanning microscopy. We investigated their localization inside HeLa cells for various incubation times and NPs concentrations. PrestoBlue toxicity assay was performed to test the NPs bio-efficacy.

Water-soluble upconversion nanoparticles (UCNPs), based on polyvinylpyrrolidone (PVP)-coated NaYF

Understanding the origin of the strong difference of electrical parameters between as grown and annealed undoped ZnO films prepared at a temperature range of 100–200 °C by thermal atomic layer deposition is essential for their future applications. In this paper, we show that the conductivity drop by up to 4 orders of magnitude as effect of post-growth annealing is accompanied by multiple simultaneous effects like a two orders of magnitude decrease of hydrogen impurity content, a strong width reduction of the luminescence peaks, and an increase of crystallite sizes influencing the carrier scattering. We show that a level of structural and optical improvement as well as the final electrical parameters of annealed films strongly depend on the previously employed growth temperature, which is related to transition from oxygen- to zinc-rich conditions influencing a type and concentration of native point defects. The growth temperature does not only influence the bandgap energy but also the binding energies of existing donors and the relative ratio between the number of donors and acceptors; hence, it determines the final electrical characteristics of the films. This means that electrical properties of undoped ZnO-atomic layer deposition films can be tuned by native defects engineering.

The work describes results of Mn-doped YAlO 3 (YAP) nanocrystalline materials synthesized by the solution combustion method using urea as a fuel. The materials were characterized by X-ray powder diffraction, scanning electron microscopy and luminescence techniques. The combustion synthesis method with codoping with Hf 4+ ions allows to obtain highly efficient YAP:Mn 2+ phosphor with negligible emission from Mn 4+ ions that can be applicable for thermoluminescent dosimetry of ionizing radiation. Namely, the phosphor has a single dominating thermal glow peak at about 200 °C with the green emission near 530 nm related to Mn 2+ (Y) ions.

Spatially resolved X-ray diffraction techniques provide useful quantitative information on the defect structure distribution for single crystals, thin films or nanowires. In this study, high-resolution X-ray diffraction is used at a laboratory X-ray source, to study the defect structure of undoped and Yb doped needle-shaped PrVO 4 crystals grown by the slow cooling method, and to observe the effect of Yb doping on crystal structure and quality. General information on the defect structure is derived from reciprocal lattice-point maps at several selected points. Details of the defect structure are obtained with the use of mapping of triple axis rocking curves and of 2 θ / ω diffraction curves. Combining these techniques provided useful information on the variation of defect nature and distribution along the crystals. There is no particular difference between the undoped and doped crystals. They are typically single crystalline, some of them are built from several blocks with misorientation angles up to several hundred arcsec. The full width at half maximum (FWHM) at the central part of the crystals is as low as about 10–12 arcsec. There is a tendency of FWHM to increase close to the crystal tips, demonstrating that the crystals are of lower crystalline quality at these regions. The mappings performed for (100) and (010) faces show that one of faces exhibits a small curvature (the lattice tilt being smaller than 2 arcsec/mm), whereas the other is characterized by a larger curvature (the tilt by at least three times larger). Unexpectedly, the reciprocal lattice-point maps for (100) and (010) crystal faces include an additional reciprocal lattice point of weak intensity. Its possible origin is discussed.

Genetic algorithms (GAs) are a tool used to solve high-complexity computational problems. Apart from modelling the phenomena occurring in Nature, they help in optimization, simulation, modelling, design and prediction purposes in science, medicine, technology, and everyday life. They can be adapted to the given task, be joined with other ones (this leads to combined or hybrid methods), and can work in parallel on many processors. The uses of GAs reported in literature represent a wide variety of approaches and led to solving of numerous computational problems of high complexity. In materials science and related fields of science and technology the GAs open possibilities for materials design, studies of their properties, or production at industrial scale. Here, the recent use of GAs in various domains connected to materials science, solid state physics and chemistry, crystallography, biology, and engineering is reviewed. The listed examples taken from recent literature show how broad the use of these metho...

Crystal growth and thermal properties of binary borates, Ca3RE2(BO3)4 (RE = Y, Gd, Nd), are considered promising crystals for laser applications. These single crystals were grown by the Czochralski method. The crystal and defect structure were characterized. Volumetric chemical methods without prior separation of the components were developed and applied for the determination of the dependence of chemical compositions of the crystals on the growth conditions. The thermal conductivity was investigated in the 50–300 K range. The character of the temperature dependence of thermal conductivity was found to be similar to that of glass. The possible reasons of the observed features of the thermal conductivity were analyzed.

The $$\hbox {Ca}_{9}\hbox {RE}(\hbox {VO}_{4})_{7}$$ (RE $$=$$ La, Nd, Gd) and $$\hbox {Ca}_{10}\hbox {M}(\hbox {VO}_{4})_{7}$$ (M $$=$$ Li, Na, K) single crystals have been grown by the Czochralski method. The binary vanadates are isostructural to “whitlockite” mineral (rhombohedral symmetry, R3c space group). Their thermal conductivity has been investigated in the range 50 K–300 K parallel to the c axis. For $$\hbox {Ca}_{9}\hbox {Gd}(\hbox {VO}_{4})_{7}$$ crystals, the thermal conductivity has been investigated in the range 300 K–550 K also. Additionally, for the $$\hbox {Ca}_{10}\hbox {M}(\hbox {VO}_{4})_{7}$$ (M $$=$$ Li, Na, K) crystals the heat capacity has been studied in the temperature range 80 K–300 K. The character of the temperature dependence of thermal conductivity is close to that of glasses. The possible reasons of the observed features of the thermal conductivity have been analyzed. Raman spectra of $$\hbox {Ca}_{10}\hbox {M}(\hbox {VO}_{4})_{7}$$ (M $$=$$ Li, Na, K) crystals have been measured and discussed. The spectral lines were broad and similar to polycrystalline or amorphous solids. These crystals are expected to be suitable for application as efficient nonlinear optic and laser materials.

Knowledge on the defect and electronic structure allows for improved modeling of material properties. A short literature review has shown that the information on defect structure of rare earth orthovanadate single crystals is limited. In this paper, defect and electronic structure of a needle-shaped Yb:LuVO 4 single crystal grown by the slow cooling method have been studied by means of X-ray diffraction topography employing white synchrotron beam, high-resolution diffraction (HRD) and photoelectron spectroscopy (XPS) techniques. Topographic investigations show that the crystal is composed of two blocks disoriented by about 1.5° and separated by a narrow deformed region. Some contrasts observed within the crystal volume may be attributed to glide bands and sector boundaries. The contrasts appearing in the vicinity of the surface may be interpreted as due to the presence of small inclusions. The HRD study indicates, in particular, that among point defects, the vacancy type defects dominate and that the density of other defects is small in comparison. The XPS measurements enabled, despite highly insulating properties of the studied crystal, an analysis of its bulk electronic structure, including the main core-levels (O 1 s , V 2 p , Lu 4 f ) as well as the valence band range.

We present the results of structural investigation by XRD and optical microscopy methods of films II-VI as a dependence on technological parameters. The presented films consist of microcrystallites from nanosized blocks. It is elucidated that sizes of blocks do not depend on technological factors. The dependences between size of microcrystallites and temperatures of chamber and evaporated cell are presented. The results of calculation of currentvoltage characteristics show that the main mechanism of current charge is multi step tunneling. This result makes a forecast of development of resonance - tunneling structure on the base of films of group II-VI

Atomic layer deposition (ALD) was used to fabricate transparent and conductive thin films of ZnO. Two hundred-nano metre thick ZnO films were deposited on glass substrates at low growth temperatures varied between 120 and 240 °C. As zinc and oxygen precursors we used diethylzinc (DEZn) and deionized water, respectively. To find optimal film parameters, the structure, surface morphology, optical and electrical measurements were carried on. The films obtained at 200 °C show the highest carrier concentration (~10 20 cm -3 ) and the lowest resistivity (2 x 10 -3 Ω cm). The films exhibit mobilities up to 37 cm 2 /Vs that we associate to the process technology used. An important point of our approach was that the films studied were not intentionally doped (with Al or other group III elements) but the high electrical conductivity was achieved by playing with the sample stoichiometry and growth conditions.

The lattice parameter for polycrystalline diamond is determined as a function of temperature in the 4–300 K temperature range. In the range studied, the lattice parameter, expressed in angstrom units, of the studied sample increases according to the equation a = 3.566810(12) + 6.37(41) × 10−14T 4 (approximately, from 3.5668 to 3.5673 Å). This increase is larger than that earlier reported for pure single crystals. The observed dependence and the resulting thermal expansion coefficient are discussed on the basis of literature data reported for diamond single crystals and polycrystals

The bone fragments of the Australopithecus Africanus from the dolomitic cave in the Cradle of Humankind in South Africa have been studied by the use of several spectral techniques. The aim was to establish their degree of preservation and possibilities of inferring the life conditions from them. X-ray diffraction studies revealed the transformation of the mineral components partially into fluoroapatite form with addition of goethite, birnessite and quartz phases and with surprisingly well preserved collagen remains. Several important chemical elements were detected by using the electron (EPMA) and synchrotron-based X-ray fluorescence (XRF) microprobes. Among them, Sr and Zn were distributed in a way following the distribution of Ca, the main element of the bones. We suspect the immanent crystallographic substitution of Ca in this case in native bone. Iron followed the distribution of Sr but while Sr is distributed in a continuous way in more rigid locations, iron occurs mainly in the edge zones of the bones and in spot-like inclusions inside. Some part of the spots located in a very edge of bone is also filled with Mn and Cu. It suggests that the porosity and fracture of bones plays a more significant role in the localization of Fe, Mn and Cu. They also form a rigid thin layer (100–250 μm) avoiding further penetration. As (as AsO43−?) distribution pattern is unique and seems to occur in those locations where the concentrations of Sr are small. The conditions for bone penetration as determined from Eh-pH diagrams suggest that is rather impossible to preserve the organic matter in locations of Mn and also that Mn and Fe hardly can meet in the same spots.

GaMnAs layers on (0 0 1)-oriented GaAs substrates were grown by the molecular beam epitaxy (MBE) method. Structural properties of samples processed at up to 920 K under hydrostatic Ar pressure up to 1.1 GPa were investigated by X-ray, secondary ion mass spectroscopy and atomic force microscopy methods. The sign of strain (compressive or tensile) of the GaMnAs layers, related to a creation of MnAs nanoclusters, is found to be dependent on processing conditions and on primary structure defects, whereas it was independent of Mn concentration. An influence of the defects structure in as-grown samples on the strain state of processed GaMnAs layers is discussed. (C) 2009 Elsevier Ltd. All rights reserved.

The article presents preliminary investigation results on the near-surface damage produced by single pulses of XUV free-electron laser in the amorphous α-SiO 2 , the monocrystalline silicon and the epitaxial films of gold. The irradiation was delivered with single pulses of only 25 fs at a wavelength of 32.5 nm and of energy up to 10 μJ. Structural modifications induced by irradiation were characterized by X-ray microdiffraction, as well as by the AFM and optical microscopy. Ablation craters of well-defined edges with smooth interiors and outer embankments surrounding the crater edges were found in the materials. Polycrystalline phases were revealed in Si and Au film samples, in the embankments and in central parts of some craters. In α-SiO 2 , a diffraction pattern typical of an amorphous material was observed without any traces of irradiation-initiated crystallization. A step-like, complete removal of gold film was evidenced inside craters, with only small gold residues in central part of craters exposed to higher fluences.

In this paper we report observation of highly efficient Pr3+ 4f–4f emission in ZrO2 (0.5 mol.% Pr3+) fine nanocrystals stabilized by Y2O3 (7 mol.%). The nanocrystals were obtained via a hydrothermal microwave-driven process followed by heat treatment at 1200 °C. The samples excited by 266 or 297 nm light exhibit a remarkable sensitizing of Pr3+ photoluminescence. The chromaticity analysis indicates the usability of the studied material as a red luminescent phosphor.

A genetic algorithm aiming for finding the global minimum and multiple deep local minima of a function exhibiting a complex landscape is studied. A feedback dynamic penalty function is used as a means to direct the algorithm to look for new local minima. The penalty is applied in close vicinity of all minima found before the current search stage. The last one, where the population tends to be trapped in, is treated smoothly. The penalty becomes progressively active there causing that the population progressively transfers outside the trapping area. The method ascertains that, unlike in more classical approaches, after finding the global minimum and a number of local ones on the way, the algorithm continues the exploration and identifies new local minima. Performance tests are described for a task of indexing of a powder diffraction pattern. The presented way of constructing the penalty function is to some extent problem specific, but the applied scheme may be adapted to other global search and optimisation problems, in particular to those requiring identification of multiple deep local minima.

We report on properties of low-temperature (LT) ZnO films grown by the atomic layer deposition method with diethylzinc (DEZn) precursor. It is shown that the ZnO thin film crystallographic orientation, quality of the surface, and optical properties depend on the main growth parameters like temperature, pulsing, and purging time and thus can be varied in controllable manner. All the presented results were obtained for ZnO layers grown at temperature between 90 and 200 degrees C. (C) 2008 Elsevier B.V. All rights reserved.

ZnO thin films were grown by atomic layer deposition method at extremely low temperature using a reactive diethylzinc as a zinc precursor. Optical properties, electrical properties and surface morphology were examined by photoluminescence, Hall effect and atomic force microscope. The study shows correlation between optical, electrical properties and surface morphology in a series of samples of different thickness.

We report on growth of MnTe layers by molecular beam epitaxy on Al2O3 substrates and of ZnTe layers on hybrid MnTe/Al2O3 substrates. The aim of our work was to prepare hexagonal phases of epitaxial thin films of these two materials. In the case of MnTe, the hexagonal NiAs-type phase was prepared by depositing the film directly on Al2O3 substrates. On the other hand, the crystal structure of ZnTe layers grown on hybrid MnTe/Al2O3 substrates was found to depend on the layer thickness: layers thinner than 0.05 μm grew in a metastable hexagonal wurtzite structure, but with further increases of the thickness, the cubic zinc blende phase of ZnTe tended to appear. The structural properties of MnTe and ZnTe layers were characterized by high energy electron and X-ray diffraction methods. Electrical properties of MnTe films were assessed by the Hall effect measurements. The topography and microstructure were analyzed by atomic force microscope. The Neel temperature and magnetic domains structure of antiferromagnetic hexagonal MnTe layers were obtained from neutron experiments.

Lattice absorption of Zn 1-x-y Be x Mg, Se and Cd 1-x-y Be x Zn y Se mixed crystals grown by a high pressure Bridgman method has been investigated by infrared spectroscopic ellipsometry in the wave number range from 230 cm to 5000 cm -1 . Ellip-sometric spectra of Cd 1-x-y Be x Zn y Se crystals display features in the spectral range 350-550 cm associated with BeSe-type phonon modes. In the optical spectra of Zn 1-x-y Be x Mg y Se crystals both BeSe-type and MgSe-type: lattice absorption bands are detected. The MgSe-like modes are located at approximately 300 cm -1 . The frequencies and oscillator strengths of optical phonon modes depend strongly on the alloy composition.

A method of controlling a preferred orientation of ZnO thin films grown by Atomic Layer Deposition (ALD) is discussed. The results for ALD films grown at low temperature with zinc acetate as a zinc precursor are presented. We demonstrate that to control a preferential growth mode one has to correlate growth temperature and separation time (so-called purging time) between pulses of precursors.

International audience; The apparently universal 1-bond2-mode percolation behavior in the Raman spectra of zincblende semiconductor alloys is generally observed for the short bond only, and not for the long one. In this work we perform a combined high-pressure-backward/near-forward Raman study of the leading percolation-type (Zn,Be)Se alloy (50at.% Be), which exhibits a distinct percolation doublet in the spectral range of its short Be?Se bond, in search of a Zn?Se analogue. The high-pressure-backward insight is not conclusive per se, but clarifies the perspective behind the near-forward Raman study. The latter reveals an unique Zn?Se phonon-polariton. Its fair contour modeling depending on the scattering angle is achieved within the linear dielectric approach, based on ellipsometry measurement of the ZnBeSe refractive index. Somewhat surprisingly this reveals that the phonon-polariton in question is a fractional' one in that it carries only half of the available Zn?Se oscillator strength, as ideally expected in case of a BeSe-like bimodal Raman behavior of the long Zn?Se bond.

ZnO thin films were grown on silicon substrate by atomic layer deposition method. We explored double-exchange chemical reaction and used very volatile and reactive diethylzinc as a zinc precursor. These enables us to obtain zinc oxide thin films of high quality at extremely low growth temperature (90−200◦C). The films are polycrystalline as was determined by X-ray diffraction and show flat surfaces with roughness of 1–4 nm as derived from atomic force microscopy measurements. Photoluminescence studies show that an edge emission of excitonic origin is observed even at room temperature for all investigated ZnO layers deposited with the diethylzinc precursor.

Zinc oxide (ZnO) is a wurtzite-type II-VI compound semiconductor with a wide, direct band-gap (3.37 eV) and has an exciton binding energy of 60 meV, larger than thermal energy at room temperature (RT) of kBT ~ 25 meV. By alloying with CdO, which has a cubic NaCltype structure and a narrower direct band gap of 2.3 eV, the band gap of ZnO can be redshifted to a blue or even a green spectral range. Therefore, ZnO [1] and ZnCdO [2] nanowires have attracted significant attention as promising “building blocks” for nanometerscale optoelectronic devices operating in the green to UV spectral region. We report on the photoluminescence (PL) studies of ZnO and Zn1-xCdxO (x~0.02-0.05) nanowires grown at different temperatures (435, 535, 570°C) by non-catalyst solid-vapor technique on SiO2/Si substrates. X-ray diffraction (XRD) and transmission electron microscopy (TEM) measurements show that the structure of ZnO and Zn1-xCdxO nanowires is of wurtzite-type with good crystal perfection. Surface morphology of samples was determined by scanning electron microscopy (SEM). The PL spectra of as-grown nanowires, nanowires extracted from the substrate and deposited onto Si wafer, and nanowires dispersed in ethanol solution by sonication were collected using 325 nm (He-Cd) or 351 nm (Ar + ) laser lines. The measurements were performed at temperatures from 10 K to 300 K. The temperature dependence of photoluminescence emitted by ZnO and Zn1-xCdxO nanowires was measured and analyzed. The low-temperature PL spectra for ZnO (Zn1-xCdxO) as-grown nanowires are dominated by the emission peak at 3.359 eV (3.361 eV) originating from the radiative recombination of donor-bound excitons (DX). At temperatures 80-100 K, a small peak at 3.369 eV (3.337 eV) assigned to the free-exciton (FX) recombination starts to appear. The FX peak redshifts with increasing temperature, its intensity increases and finally FX line dominates the spectrum at RT. Additionally at low temperature we observed the peak at 3.311 eV (3.328 eV) which most probably is due to a two-electron satellite (TES). In spite of the narrowing of band gap in Zn1-xCdxO, a blueshift (of about 2 meV) of the near-band edge (NBE) emission was observed in the PL spectra. It might be caused by a spinodal decomposition. In order to study PL from a small number of individual nanowires we either dispersed them in ethanol solution by sonication or extracted them from the substrate and deposited onto Si wafer. We present the dependence of PL spectra of Zn1-xCdxO nanowires in ethanol solution on excitation power. Also we measured polarization properties of emitted light. The comparison at RT of μ-PL measurements performed on several (~10) Zn1-xCdxO nanowires resting on Si wafer with the macro-PL of as-grown nanowires shows also a blueshift of the NBE emission. This effect is probably a consequence of selective transfer of nanowires, having smaller diameter, onto the silicon substrate. The research was partially supported by the Ministry of Science and Higher Education (Poland) through grant N515 015 32/0997 and by the Network "New materials and sensors for optoelectronics, information technology, energetic applications and medicine".

Extensive studies of physical properties and growth process of ZnO crystals are motivated by unique electrical and optical properties of this material. In the present work, the defect-structure characteristics of a bulk zinc oxide crystal grown by Contactless Chemical-Vapour-Transport method are studied. The macromosaic spread is found to be of the order of 1°. The values of lattice parameters and axial ratio in the main part of the crystal perfectly agree with literature data. Changes of the colour observed along the crystal correlates with intentional vapour pressure variation during the growth.

X-ray diffraction, resistivity, and susceptibility measurements are used to examine the effects of film thickness d (from 17 to 250 nm) on the structural and superconducting properties of La1.85Sr0.15CuO4 films grown by pulsed laser deposition on SrLaAlO4 substrates. For each d the film sgrow with a variable strain, ranging from a large compressive strain in the thinnest films to a negligible or tensile strain in thick films. Our results indicate that the tensile strain is not caused by the off-stoichiometric layer at the substrate–film interface. Instead, it may be caused by the extreme oxygen deficiency in some of the films.

The Cr/Gd multilayers (substrate/Mo/Crx/Gd30, where x = 10, 20, 30 A) were deposited on 200 A thick Mo buffer using molecular beam epitaxy (MBE) UHV technique. Two different types of monocrystalline substrates were used—MgO (1 0 0) and Al2O3 (1 1 −2 0). It was shown that the roughness of the Cr/Gd interface strongly depends on the type of the substrate—the samples grown on the sapphire substrate were smoother than those grown on MgO. A strong influence of substrate temperature on Cr/Gd interface formation was also observed—samples grown at room temperature have smoother interfaces than samples grown at 250 °C. The strong in-plane anisotropy has been observed from the hysteresis loop analysis. The magnitude of coercivity field was found to increase with increasing the Cr layer thickness. The Curie temperature dependence on Cr layer thickness was also investigated.

X-ray photoelectron (XPS) studies of core-levels in Sn1−xMnxTe (x Te bond; (2) occurrence of low BE component in the Mn 2p spectrum, indicative of clean-surface species containing reduced-valence Mn ions (i.e. Mnq+, where 0

A detailed optical characterization of three wurtzite-type Cd1–x–yBexZnySe mixed crystals has been carried out by using contactless electroreflectance (CER) and photoreflectance (PR) in the temperature range of 15 to 400 K. The samples were grown by the modified high pressure Bridgman method. The transition energies of the A, B and C features of Cd1–x–yBexZnySe are determined via a lineshape fit to the CER and PR spectra. The parameters that describe the temperature dependence of the interband transition energies of the features A and C are evaluated and discussed. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)