In this paper we report the results of synthesis and study of both ceramic samples and thin films of electronically doped La_{0.7}Pr_{0.3}MnO_3 and related heterostructures composed of La_{0.7}Pr_{0.3}MnO_3 and p-type La_{0.67}Ca_{0.33}MnO_3. The ceramic La_{0.7}Pr_{0.3}MnO_3 samples were prepared by a conventional solid state reaction technique. Single phase La_{0.7}Pr_{0.3}MnO_3 thin films and La_{0.7}Pr_{0.3}MnO_3/La_{0.67} Ca_{0.33}MnO_3 heterostructures were grown on lattice-matched perovskite NdGaO_3 substrates by pulsed laser deposition. Electron doping was indicated both for ceramic La_{0.7}Pr_{0.3}MnO_3 samples and thin films from thermopower data. Both ceramic samples and thin films of La_{0.7}Pr_{0.3}MnO_3 demonstrated resistivity of about 10 mΩ cm at 300 K and semiconductor-like resistance vs. temperature behavior with cooling down to 78 K. Meanwhile, the resistance of the La_{0.7}Pr_{0.3}MnO_3/La_{0.67}Ca_{0.33}MnO_3 interface showed an anomalous peak at 185 K. A series of post-deposition annealing experiments demonstrated a crucial role of annealing temperature and ambience on both electrical and magnetic properties of La_{0.7}Pr_{0.3}MnO_3 material and the heterostructures.
We report preparation and investigation of p -n heterostructures based on Fe₃O₄ thin films grown on semiconductor Si and GaAs substrates. Fe₃O₄ films with thickness ranging from 60 to 300 nm were grown at 350÷450°C using dc magnetron sputtering technique. The measurement of X-ray diffraction and reflection high energy electron diffraction revealed polycrystalline microstructure of thin Fe₃O₄ films deposited on both Si and GaAs substrate. Investigation of surface composition by X-ray photoelectron spectroscopy showed that Fe 2p peak consists of three main peaks, namely, metallic iron Fe(0), Fe(II), and Fe(III). Transport measurements of Fe₃O₄/n-(Si, GaAs) heterostructures demonstrated nonlinear current-voltage (I -V) dependences in the temperature range from 300 K to 78 K.
We report fabrication and electrical characterization of the organic-inorganic semiconductor diode structures formed by evaporating thin films of three novel low molecular mass organic compounds on n-type Si substrates. The organic compounds containing carbazole and triphenylamine structural units, namely: 9,9'-bis(4-butylphenyl)-3,3'-bicarbazolyl (BPBC), 4-(1H-perimidin-2-yl)-N,N-diphenylbenzenamine (PER) and 9,9'-diethyl-3,3'-bicarbazolyl (EBC) have been synthesized. The current-voltage characteristics of the Au/(BPBC, EBC, PER)/n-Si diode structures measured at T = 295 K revealed rectifying behavior with a potential barrier height values of 0.71 eV, 0.73 eV, 0.76 eV, respectively.
We report the fabrication and investigation of p-n diode structures based on thin hole-doped La_{2/3}Ca_{1/3}MnO_3 films grown on n-type silicon substrates. La_{2/3}Ca_{1/3}MnO_3 films with typical thickness of about 400 nm were prepared using pulsed laser deposition. Reflection high-energy electron diffraction measurements revealed polycrystalline quality of La_{2/3}Ca_{1/3}MnO_3 thin films on Si substrates. The surface roughness of La_{2/3}Ca_{1/3}MnO_3 films investigated by atomic force microscopy was found to be in the range of 25÷30 nm. Studies of electrical properties showed that La_{2/3}Ca_{1/3}MnO_3/Si heterostructures exhibit nonlinear asymmetric I-V characteristics both at room temperature and at 78 K. Furthemore, it was shown that these I-V dependences are sensitive to magnetic field, especially at lower voltages.
We present new experimental evidence indicating the importance of magnetic field component of microwave field (f=9.4 GHz) for magnetoresistive properties of polycrystalline La_{0.7}Ca_{0.3}MnO_3 films. The microwave measurements revealed a different character of the temperature-dependent electrical resistance of polycrystalline La_{0.7}Ca_{0.3}MnO_3 films placed in the centre (maximal amplitude of H_{10} wave vector) and at a narrow wall of the wave-guide (reduced H_{10} amplitude). Theoretical estimations of the influence of substrate onto distribution of microwave electric and magnetic fields in the waveguide were performed using the finite-difference time-domain method.
Current and electrical field-induced electroresistive effects were investigated for La_{0.67}Ca_{0.33}MnO_3/MgO thin films demonstrating nanosized electrical inhomogeneities. Two different models based on enhanced conductivity of intergrain boundaries by injecting spin-polarized carriers from ferromagnetic grains and electrical field-enhanced hopping of carriers in high resistance intergrain media were carried out to explain nonlinear electrical properties of the films.
We report on an overgrowth of quantum structures consisting of diluted magnetic semiconductor CdMnTe quantum wells with non-magnetic barriers made of CdMgTe or ZnTe on ferromagnetic MnAs and GaMnAs films by molecular beam epitaxy. Atomic force microscopy images of the quantum structures grown on MnAs demonstrated the existence of two types of regions on the surface: protruded islands with micrometric sizes, surrounded by areas of small-scale roughness. Magnetic force microscopy study of these samples revealed a magnetic domain structure only on the above mentioned islands. The (II,Mn)VI quantum wells grown on GaMnAs films exhibited relatively smooth surface, but no magnetic force microscopy signal was measurable either before or after magnetizing the sample. In the luminescence spectra of all our quantum structures the emission attributed to CdMnTe quantum wells was observed. The influence of magnetization on the luminescence line position was investigated.
We report heteroepitaxial growth of multiferroic BiFeO_3 thin films by RF magnetron sputtering on lattice-matched SrTiO_3 substrates, as well as preparation and electrical properties of the heterostructures formed by growing BiFeO_3 thin films on highly conductive LaNiO_3 films and n-Si substrates. Nonlinear and rectifying current-voltage (I-U) characteristics were revealed for the heterojunctions in a wide temperature range (T=78-300 K).
We report valence states of ions in La_{0.7}Ce_{0.3}MnO_3 thin films grown by a reactive dc magnetron sputtering. The measurements were performed by means of high-energy X-ray photoelectron spectroscopy using synchrotron radiation. It was found that Ce ion in the compound is either in tetravalent or trivalent chemical state, manganese is in divalent, trivalent and tetravalent states, while La ion existing in oxide and hydroxide chemical species is in trivalent state.
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