Ultrafast photoinduced reflectivity transients in (Nd0.5Sr0.5)MnO3(Nd_{0.5}Sr_{0.5})MnO_3

The temperature dependence of ultrafast photoinduced reflectivity transients is reported in Nd$_{0.5}$Sr$_{0.5}$MnO$_{3}$ thin film. The photoinduced reflectivity shows a complex response with very different temperature dependences on different timescales. The response on the sub-ps timescale appears to be only weakly sensitive to the 270K-metal-insulator phase transition. Below $\sim 160$ K the sub-ps response displays a two component behavior indicating inhomogeneity of the film resulting from the substrate induced strain. On the other hand, the slower response on the 10-100 ps timescale is sensitive only to the metal-insulator phase transition and is in agreement with some previously published results. The difference in the temperature dependences of the responses on nanosecond and $\mu$s timescales indicates that thermal equilibrium between the different degrees of fredom is established relatively slowly - on a nanosecond timescale

MOCVD of rhenium-containing complex oxides with the new thd-precursor

Complex oxides containing rhenium, for instance, magnetoresistive double perovskites and Re-stabilised Hg high Tc superconductors, attract a significant attention. We developed a volatile rhenium compound compatible with the thd-complexes of metals by reaction of the product of the metal electrolysis with 2,2,6,6-tetramethylheptan-3,5-dion at the elevated temperature. The details of crystal structure of the compound are discussed. The blocks [ReO(thd)2](ReO4) form layered molecular structure. The compound was used in the single source MOCVD together with thd-complexes of different metals (Ba, La, Ho) producing films of the double oxides. The Restabilised Rex(Ba,Sr)2Ca2Cu3Oy (x=0.1-0.3) precursor films with high composition homogeneity and surface smoothness were deposited to be saturated with Hg under the high pressure

Perovskite heterostructures grown by MOCVD

We have deposited epitaxial perovskite heterostructures including nickelates RNiO3 (R=Pr, Nd) on the top of CMR manganites (La1-xPrx)0.7Ca0.3MnO3, (x=0-1) and antiferromagnetic ferrites RFeO3 (R=Nd, Eu). The heterostructures were characterised by XRD, SEM, EDX, HREM, electric and magnetic measurements. Particular attention is paid to the lattice strain in the layers and the structure of their interfaces. A 60 K shift of the metalinsulator transition temperature as well as suppression of the electrical resistivity hysteresis were found for the nickelate film on the ferrite layer. The effects are believed to be due to the strain and magnetic coupling of the layers

Volatile surfactant assisted MOCVD of oxide materials

a new approach to improve the crystalline quality of MOCVD derived oxide films is proposed. The approach is to deposit the films in the presence of volatile surfactants, thus it is named Volatile Surfactant Assisted MOCVD (VSA MOCVD). The surfactants are low melting volatile oxides, particularly, PbO and Bi2O3, which have been used in our work. The approach was examined in the deposition of BaTiO3, LaAlO3, MgAl2O4, CeO2, and ZrO2 (Y2O3) epitaxial films. Improved crystallinity and surface morphology of the VSA MOCVD derived films in comparison with the films deposited using thermal MOCVD were evidenced with XRD, HREM, AFM, EDX and RBS characterizations. Also the effects of surfactants on film composition and deposition rate were studied and discussed. A model of the process is proposed

Розширення функціональних можливостей резонаторних апертурних датчиків для НВЧ діагностики малорозмірних об'єктів

У роботі розглядаються основні принципи функціонування резонаторних датчиків з рухомим зондоутворюючим центральним провідником і підходи, спрямовані на оптимізацію їх вимірювальних характеристик. Показано внесок втрат, пов'язаних із виникненням хвильового поля, неузгодженістю умов поширення в обсязі резонансного вимірювального перетворювача (РВП), а також прийоми, спрямовані на виключення їх впливу. Представлені кількісні дані, що характеризують роботу сенсору, що перебудовується, в межах кожного з двох розглянутих режимів функціонування, а також переконують у необхідності оптимізації геометрії конструктиву резонаторного зонда (РЗ). Наведено порівняльний аналіз використання як РВП зондів конусного та циліндричного типів. Показано, що екранування зразків має набагато більший сенс для використання циліндричного конструктиву при діагностиці об'єктів з низьким тангенсом кута втрат. Отримана інваріантність гібридного сигналу (δQ/Q)/(δf/f) до впливу заважаючих факторів, обумовлених зміною геометрії апертурного вузла сенсора при переміщенні вістря зонда, та ступеня включення об'єкта в електромагнітне поле резонатора.The paper discusses the basic principles of functioning of resonator sensors with a movable probeforming central conductor and approaches aimed at optimizing their measuring characteristics. The effectiveness of changing the coefficient of inclusion of an object in the electromagnetic field of the resonator is shown by introducing a mechanism into the sensor design that provides axial movement of the central conductor of the coaxial. This design allows the probing tip to be positioned both coplanar with the end aperture and displaced inside or outside the coaxial. It is shown that in order to diagnose objects with low dielectric losses, the probing tip must be pulled out of the coaxial, thereby transferring the probe to the mode of a monopole antenna. When the object has high dielectric losses, the required sensitivity of the sensor is achieved by shifting the probing tip into the inside of the coaxial, and the shortened capacitance mode is implemented. Quantitative data are presented that characterize the operation of the tunable sensor within each of the two modes of operation considered, as well as convincing of the need to optimize the geometry of the resonator probe (RP) construct. The contribution of losses associated with the appearance of a wave field, the mismatch of propagation conditions in the volume of a resonant measuring transducer (RMT), as well as techniques aimed at eliminating their influence is shown. A comparative analysis of the use of conical and cylindrical probes as RMT is presented. It is shown that the shielding of samples makes much more sense for the use of a cylindrical construct in the diagnostics of objects with a low loss tangent. It is shown that it is possible to significantly reduce the influence of interfering factors caused by a change in the geometry of the sensor aperture assembly when the probe tip is moved, by using a hybrid signal (δQ/Q)/(δf/f)

Perovskite heterostructures grown by MOCVD

3d-metal perovskites are promising thin film materials with a great variety of electrical and magnetic properties. We have deposited the epitaxial heterostructures including different combinations of CMR manganites (La1-xPrx)0,7Ca0,3Mn0,3, (x=0-l), metallic nickelates RNiO3 (R=Pr, Nd, Sm) with sharp metal-insulator transition and antiferromagnetic insulators RFeO3 (R=Nd, Eu) . The heterostructures were characterised by XRD, SEM, EDX, HREM, RBS, electric and magnetic measurements. Particular attention is paid to the lattice strain in the layers and the structure of their interfaces. The prototype electronic devices based on the heterostructures are discussed

Epitaxial ferroelectric capacitors obtained by MOCVD

Thin films of metallic oxides La0.5Sr0.5CoO3, La NiO3, [La0.5Sr0.5CoO3]l-x[LaNiO3]x and ferroelectrics PbZrxTi1-xO3 were deposited by single source MOCVD using M(thd)n compounds. After the deposition conditions of individual layers were optimized, the epitaxial capacitors LaNiO3/PbTiO3/LaNiO3, [La0.5Sr0.5CoO3]0.5[LaNiO3]0.5/PbTiO3/[La0.5Sr0.5CoO3]0.5[LaNiO3]0.5 and La0.5Sr0.5CoO3/PbTiO3/La0.5Sr0.5CoO3 were prepared on MgO single crystal substrates. The materials obtained were characterized by XRD, SEM, EDX, AFM, HREM and Raman spectrometry. For ferroelectric measurements on each wafer the series of capacitors with common bottom electrode and separate top electrode plates (200 to 200 mkm2) were formed by standard photolithography. Remnant polarization of obtained capacitors reached 5-10 mkC/cm2. Crucial effect of morphological and microstructural deffects of capacitor layers on reproducibility of polarization was noted. Keywords : MOCVD, metallic oxide, ferroelecirics, heterostructures

Evolution of ( La 1 - y Pr y ) 0.7 Ca 0.3 MnO 3 crystal structure with A-cation size, temperature, and oxygen isotope substitution

PACS. 75.30.Vn Colossal magnetoresistance – 61.12.Ld Single-crystal and powder diffraction,

Phase relations in thin epitaxial films of complex oxides prepared by MOCVD

The composition and orientation of the phases nucleating on a single crystalline substrate during MOCVD of complex oxides are governed by thermodynamics, growth kinetics, the structures of the substrate material and growing compounds. We demonstrate the importance of the formation of coherent interfaces for the stabilization of otherwise non-equilibrium oxide phases. The systematic analysis of experimental results (e.g. HREM study of coherent R2O3 inclusions in RBa2Cu3O7 epitaxial films, epitaxial BaCu3O4 films on perovskite substrates of various orientations) shows that equilibrium relations in epitaxial thin films of complex oxides could remarkably differ from those of ceramics