A. Abrutis

Magnetoresistant La1−xSrxMnO3 films by pulsed injection metal organic chemical vapor deposition: effect of deposition conditions, substrate material and film thickness

Abstract High quality epitaxial La 1− x Sr x MnO 3 films were deposited by pulsed injection metal organic chemical vapor deposition, using as precursor materials metal-2,2,6,6-tetramethyl-3,5-heptandionates dissolved in monoglyme. The influence of various deposition conditions, substrate material and film thickness on film properties was investigated. The best films were deposited on LaAlO 3 substrates at 825 °C: films exhibited a sharp semiconductor–metal transition and high magnetoresistance (∼40%) at a close-to-room temperature and in a rather low field of 1.5 T. In-situ or ex-situ high-temperature annealing in oxygen increased the temperature of semiconductor–metal transition, but decreased the magnetoresistance and the temperature coefficient of resistance. Biaxial strain imposed by the lattices’ mismatch was clearly observed in thinner La 1− x Sr x MnO 3 films on perovskite substrates. Tensile strain was present in the films on SrTiO 3 and compressive strain in the films on LaAlO 3 (and less clearly on NdGaO 3 ). Both tensile and compressive strains decreased the temperature of electric transition and the values of magnetoresistance. The strain was completely relaxed in the films more than ∼100 nm thick.

Annealing effect on magnetic and electrical properties of epitaxial La0.8MnO3−δ thin films grown by chemical vapor deposition

A new liquid source metalorganic chemical vapor deposition process has been developed in order to control precisely the amount of precursors vapors that is produced. Films of self-doped La0.8MnO3−δ have been deposited on LaAlO3 (012) substrates. X-ray diffraction measurements reveal an epitaxial growth. The as-deposited films exhibit both a ferromagnetic (Tc=200u2009K) and a metal–insulator (Tρ=130u2009K) transition. Postannealing experiments have been carried out and the results indicate the resistivity is considerably reduced, the temperature of transitions is raised to 320 K, and a magnetoresistance Δρ/ρ0=20% per tesla is obtained at 300 K in the 0–2u2002T range.

Investigation of thickness-dependent stress in PbTiO3 thin films

X-ray diffraction (XRD) and Raman spectroscopy were used to investigate stress dependence on thickness in PbTiO3 (PTO) films grown by pulsed liquid injection metalorganic chemical vapor deposition on a LaAlO3 (001) substrate (LAO). Films on sapphire substrate (R plane) were used as the polycrystalline film reference. Epitaxial PTO films with a dominant c domain structure are grown on LAO substrate, whereas the films on sapphire are polycrystalline. A detailed investigation of the PTO/LAO film microstructure by XRD gives evidence of PTO twinning. Both techniques reveal that PTO films are under tensile in-plane stresses. The study of the film thickness dependence of microstrains, grain size, volume fraction of a domains, as well as surface morphology of PTO/LAO films indicates that these parameters are clearly correlated. A change in the relaxation mechanism between 65 and 125 nm of film thickness has been evidenced. A c parameter gradient occurs throughout the film depth; it originates in stress relaxation...

In-situ heteroepitaxial growth of CeO2/YBa 2Cu3O7 films on sapphire by injection CVD

Abstract A new principle for stable generation of precursors from volatile vapours in a CVD reactor was developed for in-situ deposition of bilayers CeO 2 /YBa 2 Cu 3 O 7 on sapphire (11¯02) substrates. This principle is based on computer controlled injection of precise microdoses of liquid precursors or solutions of solid precursors in an organic solvent in an evaporator of CVD reactor, “flash evaporation” and rapid vapour transport to the deposition zone. Application of several injections sources permits in-situ deposition of multilayered oxide structures. Heteroepitaxially grown CeO 2 (≈ 0.2 μm)/YBa 2 Cu 3 O 7 (0.5–1 μm)/Al 2 O 3 structures exhibited a sharp superconducting transition at about 90 K (Δ T = 0.6-1 K) and had a critical current density of about 10 5 A/cm 2

Deposition of Ta2O5/SiO2 multilayer films by a new process “injection MOCVD”

Abstract Ta 2 O 5 and SiO 2 multilayer stacks have been deposited on silicon (100) substrate at 850 °C and 550 °C by a new process, which consists of injecting small and accurate quantities of precursor into an LPCVD reactor. Injections of the metalorganic precursors of tantalum and silicon have been achieved with two high speed electro-valves. AFM and TEM characterizations show that Ta 2 O 5 thin film deposited at 850 °C has a very rough surface, whereas at 600 °C it presents a smooth surface. From the TEM images of the multilayers, a similar behavior is observed.

Ferroelectric nanodomains in epitaxial PbTiO3 films grown on SmScO3 and TbScO3 substrates

Domain structures of 320 nm thin epitaxial films of ferroelectric PbTiO3 grown by MOCVD technique in identical conditions on SmScO3 and TbScO3 perovskite sub- strates have been investigated by Raman spectroscopy and piezoresponse force microscopy techniques. Phonon frequency shifts and typical domain structure motifs are discussed. The results reveal strikingly different domain structure architecture: domain structures of the PbTiO3 film grown on SmScO3 have dominantly a-domain orientation while strongly preferential c-domain orientation was found in the PbTiO3 film grown on the TbScO3 substrate. Differences between the two cases are traced back to the film-substrate lattice mismatch at the deposition temperature.

Electric transport properties of YBa2Cu3O7−δ thin-film bridges with laser-written channels of easy vortex motion

Electric properties of YBa2Cu3O7−δ (YBCO) superconducting thin-film bridges with artificial 5-μm-wide channels for easy motion of Abrikosov vortices have been investigated. Vortex channels have been laser written into the bridge constrictions by means of heat-induced, partial depletion of oxygen from the laser-illuminated areas. Insertion of the channel into a bridge structure increases its resistivity in the normal state, broadens the superconducting transition, and dramatically reduces the critical current density. Experimentally observed features have been ascribed to the vortex channeling mechanism, which reduces the pinning efficiency of the extended growth defects in YBCO.

Thin YBCO films on (001) substrates grown by injection MOCVD

YBCO thin (about ) films were deposited at on (001) by single-source injection CVD. Precisely controlled microamounts of organometallic -diketonates dissolved in an organic solvent were injected sequentially into the evaporator by means of a computer-driven injector and the resultant vapour was transported into the deposition zone. The influence of the vapour phase composition on films properties was investigated. A mixture of and -oriented YBCO crystallites exists in all deposited films and its ratio depends on the vapour phase composition. For both a and c perpendicular crystallites only in-plane orientation with respect to substrate axes was found. Bidirectional twinning was established in the crystallites of both types. of the films (about 90 K) was almost independent of the vapour phase composition in the studied range. However, the critical current density depended clearly on the vapour phase composition in relation to the ratio variation. of the films varied in the range .

High quality YBa2Cu3O7 films grown on LaAlO3 by single source pulsed metalorganic chemical vapor deposition

Abstract The possibilities of a new single source injection metalorganic chemical vapor deposition technique were demonstrated for in situ growth of YBa 2 Cu 3 O 7 films of very high crystalline and transport quality. Precisely controlled microamounts of organometallic β-diketonates dissolved in an organic solvent were injected sequentially into the evaporator by means of a computer-driven injector and the resultant vapor was transported into the deposition zone. Accuracy of microdosing (within 5%) and nonselective flash-like evaporation of the precursors were the main factors for obtaining a reproducible vapor phase composition in spite of poor stability of the Ba precursor. The influence of vapor phase composition on film properties was investigated. After the optimisation of deposition conditions, the YBa 2 Cu 3 O 7 films with very high critical current density up to (6–7)×10 6 xa0A/cm 2 at 77xa0K were reproducibly grown on LaAlO 3 (0xa00xa01).

Synthesis and characterisation of YBCO thin films grown by injection-MOCVD

Abstract Epitaxial YBCO thin films have been grown on MgO, SrTiO 3 and NdGaO 3 substrates by a new process (injection MOCVD). Droplets (few μ1) of a solution of Y, Ba and Cu β-diketonates in monoglyme are injected into an evaporator through a fast micro electro-valve driven by a computer. Growth rates more than ten times higher than those obtained by the conventional MOCVD process have been obtained in this first step of experiments (>3 μ m h −1 ). The best films obtained so far have T c >90 K and J c >3×10 6 A cm −2 .