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A description of the hydrogen occupation site in LiNbO3 and LiTaO3 is made based on theoretical structural models and validated by measured OH− stretching vibrational modes.

Journal of synchrotron radiation 28(1), 158 - 168 (2021). doi:10.1107/S1600577520014344, Many scientific questions require X-ray experiments conducted at varying temperatures, sometimes combined with the application of electric fields. Here, a customized sample chamber developed for beamlines P23 and P24 of PETRA III at DESY to suit these demands is presented. The chamber body consists mainly of standard vacuum parts housing the heater/cooler assembly supplying a temperature range of 100 K to 1250 K and an xyz manipulator holding an electric contact needle for electric measurements at both high voltage and low current. The chamber is closed by an exchangeable hemispherical dome offering all degrees of freedom for single-crystal experiments within one hemisphere of solid angle. The currently available dome materials (PC, PS, PEEK polymers) differ in their absorption and scattering characteristics, with PEEK providing the best overall performance. The article further describes heating and cooling capabilities, electric characteristics, and plans for future upgrades of the chamber. Examples of applications are discussed., Published by Wiley-Blackwell, [S.l.]

Lithium tantalate (LiTaO3) has large technological importance due to numerous applications, especially for motion sensors, radiation detectors, and optical waveguides. In some manufacturing processes temperature treatments are applied to obtain the desired structure or composition. However, the temperature treatment influences the optical and electrical properties of the material due to the incorporation of defects. Unfortunately, the exact nature and concentration of these defects are only insufficiently known. In the present study, temperature-induced defect incorporation in congruent LiTaO3 crystals under vacuum at 1224 K is investigated. Inelastic neutron spectra are measured in situ to identify the point defects and separate them from further contributions of structural phase transition as well as ferroelectric domain structure. Inelastic neutron scattering data are analysed with respect to small defect concentrations by comparing with density functional theory results. The influence of ferroelectric domains is analysed by Raman and FT-IR spectroscopy. Combining the results of the different techniques, we will elucidate the role of and vacancies during the annealing of congruent LiTaO3.

Hydrogen incorporation during crystal growth or other treatment has attracted research interest for a long time, but the diffusion paths and the role of additional defect sites within the lithium metal oxides (LiMO3 with M = Nb, and Ta) are still not fully understood. We investigated the hydrogen diffusion by crystal orientation- and light polarization-resolved FT-IR spectroscopy. The OH− stretching vibration is modified by the out- and in-diffusion of hydrogen using appropriate temperature and atmosphere conditions. An isotropic out- and in-diffusion in the congruent as-grown materials was observed. For C-LiNbO3 a higher diffusion rate and a lower activation energy than in C-LiTaO3 were found. In comparison to C-LiTaO3, a possible reason could be the Ta interstitial defect cluster, which limits the diffusion through the empty octahedral sites. The in-diffusion coefficients of reduced crystals are almost two orders of magnitude higher compared to those of the as-grown materials. Obviously, the hydrogen diffusion is promoted by the presence of oxygen and lithium vacancies. Since the defect sites are decorated with hydrogen, the hydrogen saturation concentration depends on the defect concentration. Finally, the same diffusion rate is observed for reduced LiTaO3 and LiNbO3. Consequently, vacancy formation is lifting the diffusion blocking by Ta interstitial defects.

Pyroelectrocatalysis is the conversion of thermal energy directly into chemical energy. On the background of renewable energies and the need for efficient industrial processes, the conversion of waste heat into hydrogen is of special relevance. Since the reported thermodynamic cycles for pyroelectric energy harvesting do not fit the conditions encountered in a reactive medium such as water appropriately, we describe a new thermodynamic charge-voltage-cycle characterised by fixed upper and lower potentials. These threshold potentials comprise the redox potential of the reaction of interest - here the hydrogen evolution reaction - as well as an overpotential mainly dictated by the temperature-induced bending of electronic bands in the pyroelectric semiconductor. Because polarisation changes below the threshold are useless for chemical reactions, material properties as well as process conditions have to be chosen accordingly. In particular the particle size along with the temperature difference are shown to determine the conversion efficiency.

Large single crystals of GdCa4O(BO3)3 (space group Cm) were grown by the Czochralski method. Dielectric, piezoelectric and elastic coefficients at room temperature as well as specific heat capacity, thermal expansion and cation disorder were studied employing a variety of methods including resonant ultrasound spectroscopy, differential scanning calorimetry, dilatometry and X-ray diffraction techniques. The electromechanical parameters (4 dielectric, 10 piezoelectric and 13 elastic stiffness coefficients) obtained on different samples are in excellent agreement indicating high internal consistency of our approach, whereas the values reported in literature differ significantly. The elastic behaviour of GdCa4O(BO3)3 resembles the one of structurally related fluorapatite, i.e. the elastic anisotropy is relatively small and the longitudinal effect of the deviations from Cauchy-relations exhibit a pronounced minimum along the direction of the dominating chains of cation polyhedra. GdCa4O(BO3)3 exhibits a maximum longitudinal piezoelectric effect of 7.67 × 10−12 CN−10, a value in the order of that of langasite-type materials. Significant changes of the calcium/gadolinium distribution on the 3 independent cation sites accompanied by characteristic anomalies of heat capacity and thermal expansion suggest processes of nonconvergent cation ordering above about 900 K in GdCa4O(BO3)3.

The formation of oxide grains with pronounced inhomogeneous elemental distribution of Cr and Fe is reported for AISI 316 L stainless steel during the early stages of oxidation at 800 °C. Each oxide grain essentially consists of consecutive Cr-rich and Fe-rich layers parallel to the surface. Local elemental distribution, interplanar spacing and absence of grain boundaries or misorientation were characterized by state-of-the-art TEM. The oxide grains exhibit mainly corundum-type structure. Aspects of the oxide formation mechanism are discussed considering earlier findings, indicating a broader relevance of the new observations regarding the early stages of oxidation of austenitic stainless steel.

We have investigated ferroelectric charged domains in polycrystalline hexagonal yttrium manganite thin films (Y1Mn1O3, Y0.95Mn1.05O3, Y1Mn0.99Ti0.01O3, and Y0.94Mn1.05Ti0.01O3) by scanning electron microscopy (SEM) in secondary electron emission mode with a small acceleration voltage. Using SEM at an acceleration voltage of 1.0 kV otherwise homogenous surface charging effects are reduced, polarization charges can be observed and polarization directions (±Pz) of the ferroelectric domains in the polycrystalline thin films can be identified. Thin films of different chemical composition have been deposited by pulsed laser deposition on Pt/SiO2/Si structures under otherwise same growth conditions. Using SEM it has been shown that different charged domain density networks are existing in polycrystalline yttrium manganite thin films.

β-Chitinous scaffolds isolated from the skeleton of marine cephalopod Sepia officinalis were used as a template for the in vitro formation of ZnO under conditions (70 °C) which are extreme for biological materials. Novel β-chitin/ZnO film-like composites were prepared for the first time by hydrothermal synthesis, and were thoroughly characterized using numerous analytical methods including Raman spectroscopy, HR-TEM and XRD. We demonstrate the growth of hexagonal ZnO nanocrystals on the β-chitin substrate. Our chitin/ZnO composites presented in this work show antibacterial properties against Gram positive bacteria and can be employed for development of inorganic–organic wound dressing materials.

In our experiments, the icing temperature of small water volumes placed on different pyroelectric single crystals (SrxBa1−xNb2O6, LiNbO3, and LiTaO3) was determined using two measurement setups: (1) the sessile droplet and (2) ring system method. In the first method, a free-standing water droplet was exposed to several external factors in the air environment. This was found to lead to higher icing temperatures compared to the second method where the water was more isolated from external factors such as evaporation. In the second method, the material of the ring system was found to be an important factor determining the freezing temperature of the enclosed water. A recommendation for the application of both methods is given, their advantages and disadvantages depending on the purpose of measurement, and their reproducibility for practical applications. In addition to this, the correlation between pyroelectricity and icing temperature, with regard to several types of internal and external factors affecting water freezing, is also discussed in the paper.

Large single crystals of rare-earth calcium oxoborates RCa4O(BO3)3 with R=Er, Y, Dy, Gd, Sm, Nd, La ( RCOB) were grown by the Czochralski method. Complete sets of dielectric, piezoelectric stress, and elastic stiffness coefficients of the RCOB crystal species were determined at ambient conditions using a combination of resonant ultrasound spectroscopy and the substitution method. The results are inherently consistent and reveal clear crystal chemical trends, with the size of the trivalent cation playing an important role. In particular, the longitudinal and shear aggregate elastic stiffnesses, c11iso and c44iso, decrease from about 165 to 154 GPa and, respectively, 45 to 41 GPa from the smallest to the largest R3+ cation of the investigated crystal species, while the dielectric coefficients ϵ22 and ϵ33 increase. However, the maximum longitudinal piezoelectric effect peaks with 8.6pCN−1 at NdCOB, the species where the radius of R3+ best matches the one of Ca2+. Increasing differences in the size of R3+ and Ca2+ lead to anisotropic stresses in the crystal lattice, which are partially relaxed by an increasing degree of cation disorder.

A complex concentrated Co-Cr-Fe-Mn-Ni-Si alloy with increased configurational entropy and contents of Cr, Mn, and Si corresponding to those in 316L stainless steel was studied with respect to its oxidation behavior. Early-stage oxidation was investigated for annealing at 400 °C and 800 °C. In addition to Cr, considerable amounts of Fe, Co, and Ni were found in the oxide, and nodules formed at 800 °C. In contrast to 316L, on which a protective corundum-type oxide forms during oxidation, the formation of spinel-type oxide was observed to dominate both at low and high temperature.

The ferroelectric phase transition of copolymers of vinylidene fluoride (VDF) with trifluoroethylene (TrFE) is well known and related to conformational changes in the polymer chain. Contrary to the expected paraelectric behaviour in the high temperature phase a pyroelectric investigation of the phase transition in the range from 0°C to 130°C combined with X-ray diffraction indicate the copolymer as ferroelectric when prepared and polarised in the high-temperature phase. Based on this finding the orthorhombic space-group Fmm2 is proposed for the polar high-temperature phase. Above the Curie temperature the material exhibits pyroelectricity with inverted sign, whose origin is interpreted as flexoelectricity.

This work presents an extreme biomimetics route for the modification of the surface of fibre-based scaffolds of poriferan origin by the creation of novel nanostructured multiphase biocomposites. The exceptional thermal stability of the nanostructured sponge chitin allowed for the formation of a novel nanocrystalline chitin-(Ti,Zr)O2 composite with a well-defined nanoscale structure under hydrothermal conditions (160 °C). Using a combination of experimental techniques, including X-ray diffraction, scanning electron microscopy, high resolution transmission electron microscopy, EDX mapping and near-edge electron loss spectroscopy (ELNES) in TEM and thermogravimetry/differential scanning calorimetry coupled with mass spectrometry; we showed that this bioorganic scaffold facilitates selective crystallization of TiO2, predominantly in form of anatase, over the monoclinic zirconium dioxide (baddeleyite). The control of the crystal morphology through the chitin templates is also demonstrated. Obtained samples were characterized in terms of their photoluminescent properties and photocatalytic performance. These data confirm the high potential of the extreme biomimetics approach for developing a new generation of multiphase biopolymer-based nanostructured materials.

This study demonstrates a new preparation method for single-crystal X-ray diffraction samples using a focused ion beam. The results of the structure determination and electron density maps with differently prepared samples are discussed, to evaluate this new method., High-quality single-crystal X-ray diffraction measurements are a prerequisite for obtaining precise and reliable structure data and electron densities. The single crystal should therefore fulfill several conditions, of which a regular defined shape is of particularly high importance for compounds consisting of heavy elements with high X-ray absorption coefficients. The absorption of X-rays passing through a 50 µm-thick LiNbO3 crystal can reduce the transmission of Mo Kα radiation by several tens of percent, which makes an absorption correction of the reflection intensities necessary. In order to reduce ambiguities concerning the shape of a crystal, used for the necessary absorption correction, a method for preparation of regularly shaped single crystals out of large samples is presented and evaluated. This method utilizes a focused ion beam to cut crystals with defined size and shape reproducibly and carefully without splintering. For evaluation, a single-crystal X-ray diffraction study using a laboratory diffractometer is presented, comparing differently prepared LiNbO3 crystals originating from the same macroscopic crystal plate. Results of the data reduction, structure refinement and electron density reconstruction indicate qualitatively similar values for all prepared crystals. Thus, the different preparation techniques have a smaller impact than expected. However, the atomic coordinates, electron densities and atomic charges are supposed to be more reliable since the focused-ion-beam-prepared crystal exhibits the smallest extinction influences. This preparation technique is especially recommended for susceptible samples, for cases where a minimal invasive preparation procedure is needed, and for the preparation of crystals from specific areas, complex material architectures and materials that cannot be prepared with common methods (breaking or grinding).

Hydrogen incorporation into lithium niobate and lithium tantalate during crystal growth has attracted research interest for a long time, but the diffusion paths and defect sites within the materials are only partially understood. In the present study, the hydrogen defect is investigated by crystal orientation and light polarization resolved FT-IR spectroscopy. The OH − absorption band is splitting in two sub-bands, which are significantly affected by intrinsic defects. We attribute the line broadening of both band components to the antisite defect cluster, which is decorated by hydrogen. LiNbO3 and LiTaO3 although, isomorphic in crystal and defect structure, differ significantly in their antisite defect cluster concentration and, as we show, also in the occupation of hydrogen bonding sites in the structure.

Defect engineering is an effective tool to manipulate material properties and produce completely new ones that are symmetry-forbidden in a defect-free crystal. For example, single crystals of SrTiO 3 form, as a long-term reaction to external static electric fields, a strained near-surface layer through the migration of oxygen vacancies out of the area beneath the positively charged electrode. It was previously shown that this near-surface phase exhibits pyroelectric and piezoelectric properties, which are symmetry-forbidden in centrosymmetric bulk SrTiO 3. In the present paper, different approaches have been used to better understand the nature of this reaction. In situ XRD measurements were carried out to investigate the dynamics of the lattice distortion during the formation and relaxation of this phase. Interferometry measurements were carried out to determine the piezoelectric thickness change of the samples and to indirectly investigate the polar property of the unit cell before, during, and after electroformation. We observe the instantaneous formation of a polar strontium titanate unit cell at room temperature, explainable by electrostriction, and the expected additional contribution after a long-term field application.

Ferroelectricity in hafnium oxide thin films is known to be induced by various doping elements and in solid-solution with zirconia. While a wealth of studies is focused on their basic ferroelectric properties and memory applications, thorough studies of the related pyroelectric properties and their application potential are only rarely found. This work investigates the impact of Si doping on the phase composition and ferro- as well as pyroelectric properties of thin film capacitors. Dynamic hysteresis measurements and the field-free Sharp-Garn method were used to correlate the reported orthorhombic phase fractions with the remanent polarization and pyroelectric coefficient. Maximum values of 8.21 µC cm−2 and −46.2 µC K−1 m−2 for remanent polarization and pyroelectric coefficient were found for a Si content of 2.0 at%, respectively. Moreover, temperature-dependent measurements reveal nearly constant values for the pyroelectric coefficient and remanent polarization over the temperature range of 0 °C to 170 °C, which make the material a promising candidate for IR sensor and energy conversion applications beyond the commonly discussed use in memory applications.

Essential to the quality of X-ray analysis in crystallography, such as diffractometry and spectrometry, is a stable and reproducible X-ray source. Commonly, different optical elements are utilized to provide a dedicated X-ray beam. The stable alignment of all these components is a prerequisite in order to reduce aberrations and to achieve high signal-to-noise ratios. Besides such aberrations and electronically induced variations of the X-ray primary beam intensity, the environmental conditions are of particular importance, most prominently the barometric pressure, humidity and temperature. In a qualitative as well as quantitative study, the influence of the environmental conditions on the primary beam intensity of a sealed tube with a Cu anode and their correlations are determined. For a common setup, utilizing a scintillation counter, laboratory as well as external conditions are monitored simultaneously for 28 d. Their individual influence on the X-ray intensity and their correlations are evaluated by statistical analysis including time lag. By this comprehensive study, experimental intensity variations of up to ΔI/I= 1.153 ± 0.001% are determined during density of air changes of Δρ/ρ = 3.7 ± 0.6%. This is interpreted in terms of air transmission variations of up toTX-ray= 1.137 ± 0.001% for a typical X-ray analysis setup due to ambient barometric pressure, temperature and humidity changes for natural mid- and long-term variations. Significant correlations with respect to daily and weekly cycles and in particular with ambient conditions are determined. These results are used for a time-dependent absorption correction of the measured intensity, which reduces the standard error by about 25%.

The disinfection of bacteria by thermally excited pyroelectric materials in aqueous environments provides opportunities for the development of new means of sanitization. However, little is known about the formation of reactive oxygen species (ROS) at the surface of the thermally excited pyroelectric materials. To investigate the pyroelectrically driven ROS generation we performed OH radical specific measurements of thermally stimulated barium titanate nanoparticles in contact with palladium nanoparticles. Through electron spin resonance measurements with the spin trap BMPO (5-tert-butoxycarbonyl 5-methyl-1-pyrroline n-oxide) and fluorescence spectroscopy of 7-hydroxycoumarin, OH radical generation was detected, which confirms the hypothesis of pyroelectric ROS production. Since pyroelectric potential changes are insufficient for direct electrochemical OH radical generation, we propose a two-step charge-transfer model facilitated by intermittent contact between the palladium and the pyroelectric nanopartic...

This work presents an extreme biomimetics route for the creation of nanostructured biocomposites utilizing a chitinous template of poriferan origin. The specific thermal stability of the nanostructured chitinous template allowed for the formation under hydrothermal conditions of a novel germanium oxide-chitin composite with a defined nanoscale structure. Using a variety of analytical techniques (FTIR, Raman, energy dispersive X-ray (EDX), near-edge X-ray absorption fine structure (NEXAFS), and photoluminescence (PL) spectroscopy, EDS-mapping, selected area for the electron diffraction pattern (SAEDP), and transmission electron microscopy (TEM)), we showed that this bioorganic scaffold induces the growth of GeO2 nanocrystals with a narrow (150–300 nm) size distribution and predominantly hexagonal phase, demonstrating the chitin template’s control over the crystal morphology. The formed GeO2–chitin composite showed several specific physical properties, such as a striking enhancement in photoluminescence exceeding values previously reported in GeO2-based biomaterials. These data demonstrate the potential of extreme biomimetics for developing new-generation nanostructured materials.

The atomic layer deposition (ALD) of stoichiometric SrTiO 3 as well as layers with either Sr or Ti excess from the commercial precursors Bis(tri-isopropylcyclopentadienyl)-strontium Sr( i Pr 3 Cp) 2 , Tetrakis-(dimethylamido)titanium(IV) Ti[N(CH 3 ) 2 ] 4 and H 2 O on a commercial ALD system is demonstrated. The influence of the stoichiometry on the optical layer properties was investigated. Spectroscopic ellipsometry shows that all Sr x Ti y O z layers are transparent up to the optical gap energy, which amounts to 3.87 eV for stoichiometric SrTiO 3 . A direct correlation between the Sr content, optical properties, layer density and the growth per cycle value was determined. X-ray photoelectron spectroscopy after Ar ion cluster sputtering indicates that the layers are free of carbon. After ex situ annealing under atmospheric conditions we observed a change in microstructure from amorphous to polycrystalline starting at 545 °C by atomic force microscopy and grazing incidence X-ray diffraction. Electrical I–V measurements show very small leakage currents confirming the insulating character of the Sr x Ti y O z layers.

Nitrogen ion implantation into strontium titanate single crystals causes a slight shift of the Ti-K edge position compared to pristine SrTiO3 and a strong increase of the second pre-edge peak in X-ray absorption near-edge spectroscopy (XANES) using grazing incidence geometry. Calculations by a finite difference method demonstrate that the strong increase of the second pre-edge feature in the defect distorted phase can be attributed to a static displacement of the Ti atom relative to the surrounding oxygen octahedron.

Strontium titanate is a promising insulator material in resistance switching random access memories. Strontium titanate thin films are prepared by atomic layer deposition from bis(tri-isopropylcyclopentadienyl)-strontium (Sr(iPr3Cp)2), Tetrakis-(dimethylamido)titanium(IV) (Ti[N(CH3)2]4) and water at a substrate temperature of 300 °C. The layer stoichiometry is analyzed by X-ray fluorescence spectroscopy for the main element composition and by X-ray photoelectron spectroscopy to detect light element contamination. A significant carbon contamination is found whereas nitrogen is not detected. These results are discussed with possible decomposition reactions of the Sr(iPr3Cp)2 molecule at the given deposition temperature. The film microstructure is characterized by grazing incidence X-ray diffraction. Optical and electrical characterizations show that the strontium titanate layers are transparent up to an optical gap of 3.85 eV and insulating.

Diffraction Anomalous Fine Structure (DAFS) combines the long-range, crystallographic sensitivity of X-ray diffraction with the short-range sensitivity of X-ray Absorption Spectroscopy (XAS). In comparison to other spectroscopic methods, DAFS can additionally distinguish phases of different translational symmetry by choice of momentum transfer, or isolate spectra from chemically identical atoms on various Wyckoff sites of a crystal's structure using crystallographic weights. The Anisotropy of Anomalous Scattering (AAS) extends the concept of isotropically scattering atoms to a more general case, where the atom's scattering characteristics depend on the polarization as well as the wavevector of the incident and scattered X-rays. These can be written as tensors that reflect the local site symmetries of the resonant atom. Forbidden Reflection Near-Edge Diffraction (FRED) is an elegant way to measure AAS by using reflections that are extinguished in the special case of isotropically scattering atoms. They can only be observed due to the non-isotropic contributions at photon energies in the vicinity of an absorption edge where electronic transitions occur. Combining the site selectivity of DAFS with the information accessible through AAS allows probing the short-range order and local orbitals of selected atoms in a crystal structure of a chosen phase. The present condensed review gives a brief overview on the pioneer work, the theory and sensitivities as well as selected recent applications of these powerful and promising Resonant X-ray Diffraction (RXD) methods. Additionally, some recent work of the authors is included exemplarily for the model structure rutile TiO2 presenting the progress in measurement and interpretation.

The magnetooptical (MO) response of Ru/Py/Ta thin film stacks with 4, 8, and 17 nm thick Ni81Fe19 permalloy (Py) films on a SiO2/Si and a ZnO substrate was measured by vector magnetooptical generalized ellipsometry. The MO response from VMOGE was modelled using a 4 × 4 Mueller matrix algorithm. The wavelength-dependent, substrate-independent and thickness-independent complex MO coupling constant ( Q ) of Py in the Ru/Py/Ta thin film stacks was extracted by fitting Mueller matrix difference spectra in the spectral range from 300 nm to 1000 nm. Although the composition-dependent saturation magnetization of Ni x Fe1−x alloys (x = 0.0…1.0), e.g. of Ni81Fe19, is predictable from the two saturation magnetization end points, the MO coupling constant of Ni x Fe1−x is not predictable from the two Q end points. However, in a small alloy range (0.0 x x Q of Ni x Fe1−x can be interpolated from a sufficiently high number of analyzed Ni x Fe1−x alloys. The available complex MO coupling constants of six different Ni x Fe1−x (x = 1.0 to 0.0) alloys were used to interpolate MO response of binary Ni x Fe1−x alloys in the range from x = 0.0 to x = 1.0.

We report unipolar resistive switching in polycrystalline, hexagonal yttrium manganite thin films grown on unpatterned Pt metal coated SiO2/Si substrates with circular Al top electrodes. Electroforming-free or electroforming-based resistive switching is observed, depending on the chemical composition (Y1Mn1O3, Y0.95Mn1.05O3, Y1Mn0.99Ti0.01O3, and Y0.94Mn1.05Ti0.01O3). The number of loading cycles measured at room temperature for samples with Y1Mn1O3 and Y0.95Mn1.05O3 composition is larger than 103. The dominant conduction mechanism of the metal–insulator–metal structures between 295 K and 373 K in the high resistance state is space charge limited conduction and in the low resistance state is ohmic conduction. Activation energies in Ohm's law region in the high resistance state are calculated from the Arrhenius equation and are evaluated to be 0.39 ± 0.01 eV (Y1Mn1O3), 0.43 ± 0.01 eV (Y0.95Mn1.05O3), 0.34 ± 0.01 eV (Y1Mn0.99Ti0.01O3), and 0.38 ± 0.02 eV (Y0.94Mn1.05Ti0.01O3).

The triboelectric effect describes electrical charging when bringing different materials into contact. We report on the generation of hard X-ray radiation by peeling various adhesive tapes under medium vacuum conditions. Beside vacuum housing and pumps as instrumentation only an electric motor, two rolls and a metal foil as target material are necessary. The spectral distribution of generated X-rays was analyzed using an energy-dispersive detector. Depending on peeling speed, pressure and choice of material combination, electrons with energies sufficient to excite emission in the hard X-ray region are produced. The results are discussed in terms of triboelectric separation of charge carriers.

The atomic layer deposition (ALD) of TiO 2 from tetrakis(dimethylamino)titanium (TDMAT) and water was studied in the substrate temperature ( T S ) range of 120 °C to 330 °C. The effect of deposition temperatures on the resulting layer microstructure is investigated. Based on the experimental results, possible interaction mechanisms of TDMAT and H 2 O precursor molecules and the TiO 2 surface at different temperatures are discussed. The TiO 2 layers were characterized with respect to microstructure, composition and optical properties by glancing angle x-ray diffraction and reflectometry, x-ray fluorescence analysis, photoelectron spectroscopy and spectroscopic ellipsometry. A constant layer growth with increasing number of ALD cycles was achieved for all investigated deposition temperatures, if the inert gas purge time after the H 2 O pulse was increased from 5 s at temperatures below 250 °C to 25 s for T S ≥ 320 °C. In the investigated temperature range, the growth per cycle varies between 0.33 and 0.67 A/cycle with a minimum at 250 °C. The variations of the deposition rate are related to a change from a surface determined decomposition of TDMAT to a gas phase decomposition route above 250 °C. At the same temperature, the microstructure of the TiO 2 layers changes from amorphous to predominately crystalline, where both anatase and rutile are present.

Oxygen migration in perovskites is well known to occur via vacancies along the TiO

International audience; Diatoms are considered unicellular eukaryotic organisms exclusively depositing biogenic silica. Heretofore there has been no report of calcification by these algae. Here it is shown that calcium carbonate within the stalks of Didymosphenia geminata, a nuisance species that has prolifically colonized streams and rivers globally, is biogenic in origin and occurs as a network of calcite nanofibers. The nanofibrous framework in the mineralized polysaccharide matrix imparts mechanical support to the stalks, providing stability in variable flow conditions. The results demonstrate that D. geminata possesses cellular and periplasmic carbonic‐anhydrases that contribute to carbon fixation and biomineralization, respectively. The activity of external carbonic‐anhydrase was more than 50% of the total activity, which points to its role in anchoring this bioeroding diatom on hard surfaces. The first evidence of multiphase biomineralization by diatoms that deposit both biogenic silica and crystalline biogenic calcite which are imparting distinct functional advantage to the organism is provided.

Electrical properties of SrTiO3 single crystal samples treated by an anisotropic surface annealing technique under reducing conditions have been investigated in the temperature range of 35 K–300 K. Optical and atomic force microscopy show that annealing gives rise to polycrystallization and the formation of colored dendritic structures. Carrier concentrations and mobilities determined by Hall measurements as well as resistivities detected by van der Pauw measurements show the expected metallic behavior due to oxygen vacancy doping. Moreover, the temperature dependent resistivities indicate a cubic-to-tetragonal phase transition, which to our knowledge has not been reported before. Additionally, the transition occurred up to 53 K above the known bulk transition temperature TC at 105 K with a hysteresis up to a temperature of 220 K. Both phenomena possibly arise from dislocations and associated strain fields introduced by surface annealing that are assumed to lower the free energy of the tetragonal phase and simultaneously pin tetragonal domains. Thus, microregions of the tetragonal phase persist above TC causing the hysteresis in resistivity up to ∼12%. This effect possibly provides new chances for future oxide based non-volatile data-storage devices.

Polycrystalline YMnO3 thin films sandwiched between an un-patterned bottom electrode (Pt or Pt/Ti) and a circular top electrode (Au or Al) reveal an electroforming-free, unipolar resistive switching. We report YMnO3 resistive switching devices endurance depending on the bottom electrode and the top electrode. The number of loading cycles of the Al/YMnO3/Pt resistive switch is larger than 103. The resistance ratio between the high resistance (OFF) and the low resistance (ON) state is larger than 104, which can be further increased to 105 by decreasing the diameter of the Al top electrode.