V. Kubilius

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.

Modified graphitized carbon black as transducing material for reagentless H2O2 and enzyme sensors

Direct electron transfer between redox enzymes and electrodes is the basis for the third generation biosensors. We established direct electron transfer between quinohemoprotein alcohol dehydrogenase (PQQ-ADH) and modified carbon black (CBs) electrodes. Furthermore, for the first time, this phenomenon was observed for pyrroloquinoline quinone (PQQ)-dependent glucose dehydrogenase (PQQ-GDH). Reagentless enzyme biosensors suitable for the determination of ethanol, glucose and sensors for hydrogen peroxide were designed using CB electrodes and screen-printing technique. Aiming to create an optimal transducing material for biosensors, a set of CB batches was synthesized using the matrix of Plackett-Burman experimental design. Depending on the obtained surface functional groups as well as the nano-scale carbon structures in CBs batches, the maximal direct electron transfer current of glucose and ethanol biosensors can vary from 20 to 300 nA and from 30 to 6300 nA for glucose and ethanol, respectively. Using modified CB electrodes, an electrocatalytic oxidation of H(2)O(2) takes place at more negative potentials (0.1-0.4V versus Ag/AgCl). Moreover, H(2)O(2) oxidation efficiency depends on the amount and morphology of fine fraction in the modified CBs.

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

Metal-organic chemical vapour deposition of mixed-conducting perovskite oxide layers on monocrystalline and porous ceramic substrates

Perovskite oxide layers, i.e. manganites La1−x(Sr,Ca)xMnO3, ferrates La1−xSrxFe1−yCoyO3, gallates La1−xSrxGa1−y(Co,Ni,Fe)yO3 of a thickness of 0.8–2 μm, were deposited by pulsed injection MOCVD (metal-organic chemical vapour deposition) on various monocrystalline and porous ceramic substrates. The layers were characterised by X-ray diffraction, scanning electron microscopy, wavelength dispersion spectroscopy and by electrical measurements of the total conductivity vs. temperature. Such oxides are known as mixed electronic–ionic conductors and are largely studied as materials for the fabrication of oxygen permeable membranes. One of the aims of this work was to estimate the suitability of the pulsed injection MOCVD technique for the preparation of dense perovskite layers for their use as membranes for oxygen.

Effect of deposition conditions on the stoichiometry and structural properties of LiNbO3 thin films deposited by MOCVD

Epitaxial LiNbO3 thin films were deposited on C-sapphire substrates by pulsed injection metal organic chemical vapor deposition and atmospheric pressure metal organic chemical vapor deposition. The effect of deposition conditions, such as the ratio of Li/Nb precursors in solution and the deposition pressure, on the phase composition, Li nonstoichiometry, texture, epitaxial quality, residual stresses and formation of twins in LiNbO3 films was studied by means of X-ray diffraction and Raman spectroscopy. It was found that the deposition pressure played an important role in the incorporation of Li2O in the film and the formation of in-plane and out-of-plane twins.

YBa2Cu3O7–x Thin Films and YBa2Cu3O7–x/CeO2 Heteroepitaxial Structures Grown on YSZ Substrates by Pulsed Injection CVD†

The in situ synthesis of thin YBa2Cu3O7–x (YBCO) films and YBCO/CeO2 heterostructures was carried out on (001) Zr(Y)O2 (YSZ) substrates from the organometallic vapor phase by a new pulsed injection CVD technique. The secondary ion mass spectrometry (SIMS) concentration profiles revealed a diffusion of Zr from the unbuffered substrate to the films. The films had a dominating (001) texture and a dominating 45° in-plane orientation, but other orientations (0°, 9°, 36°) were also not infrequent in the films. The vapor phase composition was found to have a great influence on the film microstructure and critical parameters. The critical temperatures (Tc) of the best YBa2Cu3O7–x films were about 90 K, the critical current densities (Jc) being ∼4 × 105 A cm−2 at 77 K. A thin epitaxial CeO2 layer grown in situ before YBCO deposition stopped the Zr diffusion from the substrate and dramatically improved the epitaxy and critical parameters of YBCO films. The Tc (ΔTc) and Jc of the deposited YSZ/CeO2/YBCO heteroepitaxial structures equaled ∼90 K (∼0.3 K) and ∼4 × 106 A cm−2 at 77 K. This result shows that a simple deposition of an intermediate CeO2 layer before the growth of YBCO makes YSZ substrates very competitive with perovskite substrates.

Chemical vapor deposition and characterization of high-k BaHf1−xTixO3 dielectric layers for microelectronic applications

Possibilities to grow high-k BaHf1−xTixO3 layers were investigated by pulsed liquid injection metal-organic chemical vapor deposition technique. Ba(thd)2 (thd=2,2,6,6-tetramethylheptane-3,5-dionate), Hf(thd)4, and Ti(OiPr)2(thd)2 were used as precursors, toluene as solvent, and Si(100) as substrate. The influence of solution composition and deposition temperature on crystallization and elemental and phase compositions of Ba–Hf–Ti–O layers was investigated. BaHf1−xTixO3 layers with x∼0–0.5 may be obtained at 600–650 °C, whereas the lower deposition temperature (500–550 °C) resulted in crystallization of the dominating orthorhombic BaCO3 phase in deposited films. Films were characterized by x-ray diffraction, atomic force microscopy, and scanning electron microscopy. Electrical measurements were performed for deposited thin films in view of storage capacitor applications of BaHf1−xTixO3 films in dynamic random access memories.

MgO by Injection CVD

Abstract Epitaxial YBa 2 Cu 3 O 7 layers with 45° in-plane orientation have been grown by Injection CVD on MgO substrates polished off-axis to within 1.4–1.9° of the [100] direction. This new single-source CVD process is based on computer-controlled injection of precise microdoses of a metal–organic precursor solution into a CVD reactor. A wide range of solution compositions was tested to investigate compositional effects on phase purity, surface morphology, texturing and superconducting properties of the prepared films. The highest quality films with pure 45° texture had a smooth surface, zero resistance T c ( R =0) of 88–89 K, and critical current density J c (77 K) above 10 6 A/cm 2 .

Properties of Al-doped ZnO films grown by atmospheric pressure MOCVD on different orientation sapphire substrates

ABSTRACT Al-doped ZnO films were grown on different orientation sapphire substrates (sapphire-R, C, M, A) at 400–600 °C via the atmospheric pressure aerosol-assisted MOCVD technique. The influence of deposition temperature and orientation of sapphire substrate on the microstructure, electrical and optical properties of ZnO-Al films was investigated. Epitaxial films grown on sapphire-R substrates exhibited the best electrical properties: carrier mobility was 50–60 cm2 V−1 s−1, resistivity <10−3 Ω cm. The conditions of post-deposition treatment of films (gas atmosphere during film cooling after deposition, ex-situ annealing) had a marked influence on the electrical properties of films.

On the possibility to grow zinc oxide-based transparent conducting oxide films by hot-wire chemical vapor deposition

Hot-wire chemical vapor deposition (HW-CVD) was applied to grow zinc oxide (ZnO)-based transparent conducting oxide (TCO) films. Indium (In)-doped ZnO films were deposited using a cold wall pulsed liquid injection CVD system with three nichrome wires installed at a distance of 2 cm from the substrate holder. The wires were heated by an AC current in the range of 0–10 A. Zn and In 2,2,6,6-tetramethyl-3,5-heptanedionates dissolved in 1,2-dimethoxyethane were used as precursors. The hot wires had a marked effect on the growth rates of ZnO, In-doped ZnO, and In2O3 films; at a current of 6–10 A, growth rates were increased by a factor of ≈10–20 compared with those of traditional CVD at the same substrate temperature (400 °C). In-doped ZnO films with thickness of ≈150 nm deposited on sapphire-R grown at a wire current of 9 A exhibited a resistivity of ≈2 × 10−3 Ωcm and transparency of >90% in the visible spectral range. These initial results reveal the potential of HW-CVD for the growth of TCOs.