Metalorganic Deposition Process Research Articles

Non-hysteretic metal–insulator transition of VO2 films grown by excimer-laser-assisted metal organic deposition process

We examined the correlation between thickness of an epitaxial VO2 phase grown on a TiO2 (001) substrate by the excimer-laser-assisted metal organic deposition (ELAMOD) process and the metal–insulator transition (MIT) property of it. The abrupt and hysteretic MIT was observed for the epitaxial films (thickness: t≥6nm), and the epitaxial film (t≤4nm) showed semiconductor behavior. When an amorphous VOx layer was prepared on the ultrathin epitaxial phase (t≤4nm) by the ELAMOD, a non-hysteretic MIT was successfully observed. The non-hysteretic MIT was found to be owing to roughened interface between the epitaxial phase and the amorphous phase, where there would be a number of structural defects.

Optical waveguide and nonlinear properties of Bi3NdTi3O12 thin films

Neodymium-substituted bismuth titanate (Bi3NdTi3O12, BNT) thin films were prepared on quartz substrates by a metal-organic solution deposition process. The crystalline structure was evaluated by X-ray diffraction. Waveguide property was investigated by using prism coupling technique and optical transmittance measurement. The optical nonlinearities of the film were measured by the top-hat Z-scan techniques and a large positive nonlinear refractive index, nonlinear refractive coefficient and two-photon absorption coefficient were determined to be 3.84 × 10−7 esu, 0.7523 cm2/GW and 4.81 × 104 cm/GW, respectively. These results reveal that the BNT film may be a kind of new multifunctional materials.

TiO xN y coatings grown by atmospheric pressure metal organic chemical vapor deposition

Titanium oxynitride coatings were deposited on various substrates by an original atmospheric pressure metal organic chemical vapor deposition (MOCVD) process using titanium tetra- iso-propoxide as titanium and oxygen precursors and hydrazine as a nitrogen source. The films composition was monitored by controlling the N 2H 4 mole fraction in the initial reactive gas phase. The variation of the N content in the films results in significant changes in morphological, structural and mechanical properties. When a large excess of the nitrogen source is used the resulting film contains ca 17 at % of nitrogen and forms dense and amorphous TiO xN y films. Growth rates of these amorphous TiO 1.5N 0.5 coatings as high as 14 μm/h were obtained under atmospheric pressure. The influence of the deposition conditions on the morphology, the structure, the composition and the growth rate of the films is presented. For the particular conditions leading to the growth of amorphous TiO 1.5N 0.5 coatings, first studies on the mechanical properties of samples grown on stainless steel have revealed a high hardness, a low friction coefficient, and a good wear resistance in unlubricated sliding experiments against alumina which make them very attractive as protective metallurgical coatings.

Epitaxial growth of La 0.7Sr 0.3CoO 3 thin films on SrTiO 3 substrates by metal–organic deposition

La 0.7Sr 0.3CoO 3 thin films have been epitaxially grown on SrTiO 3 (0 0 1) single-crystal substrates by metal–organic deposition process. Crystallinity and morphology of the obtained films were examined in detail using X-ray diffraction and transmission electron microscopy. The evolution of the out-of-plane lattice parameter with film thickness is investigated. The critical thickness for strain relaxation is found in the 60–80 nm range. The electrical properties of the obtained films in various conditions have been investigated. By increasing the annealing temperature to 1000 °C and the film thickness to 120 nm, the electrical resistivity was decreased by several orders of magnitude. We measured a resistivity of approximately 5 × 10 −4 Ω cm in a wide interval of temperature 77–320 K, making this material a promising candidate for a variety of applications.

The structural and electrical properties of oriented [formula omitted] films prepared by metal organic deposition method

Strontium titanate films with high a -axis orientation [ a ( 100 ) = 94.1 % ] and random orientation were deposited on (111) Pt/Ti/ SiO 2/Si substrates by a concentration controlling of the precursor solution during the metal organic deposition process. Topography of samples was investigated by atomic force microscopy after annealing at 800 °C. X-ray diffraction found that the degree of a -axis orientation increased with increasing annealing temperature. The leakage current and the dielectric property were strongly dependent on the film orientation, and the possible causes of orientation dependence were discussed.

Effect of argon ion activity on the properties of Y 2O 3 thin films deposited by low pressure PACVD

Yttrium oxide thin films are deposited by microwave electron cyclotron resonance (ECR) plasma assisted metal organic chemical vapour deposition process using an indegeneously developed Y(thd) 3 {(2,2,6,6-tetramethyl-3,5-heptanedionate)yttrium} precursor. Depositions were carried out at two different argon gas flow rates keeping precursor and oxygen gas flow rate constant. The deposited coatings are characterized by X-ray photoelectron spectroscopy (XPS), glancing angle X-ray diffraction (GIXRD) and infrared spectroscopy. Optical properties of the films are studied by spectroscopic ellipsometry. Hardness and elastic modulus of the films are measured by load depth sensing nanoindentation technique. Stability of the film and its adhesion with the substrate is inferred from the nanoscratch test. It is shown here that, the change in the argon gas flow rates changes the ionization of the gas in the microwave ECR plasma and imposes a drastic change in the characteristics like composition, structure as well as mechanical properties of the deposited film.

High temperature coefficients of resistance of VO 2 films grown by excimer-laser-assisted metal organic deposition process for bolometer application

With bolometer application in mind, we prepared VO 2 films on TiO 2 (001) substrates by an excimer-laser-assisted metal organic deposition process at 300 °C or less. A metal-to-insulator transition of VO 2 is expected to induce high temperature coefficient of electrical resistance (TCR) useful for high-performance infrared sensors, but the practical use of crystalline VO 2 films has been prevented due to the accompanied wide hysteresis. In this study, by forming the epitaxial phase only near the substrate interface, the transition of the film was successfully broadened and the hysteresis disappeared. The maximum TCR of the film was more than –10%/°C near room temperature, and the temperature range in which TCR was higher than –4%/°C was very wide (280–320 K).

Doping of Tin-oxides pinning centers into YBCO films by MOD method

Tin-oxides were doped into YBCO films as pinning centers to improve Jc properties in a magnetic field. YBCO films were grown by a metal organic deposition process using tri-fluoroacetates starting solutions which contains tin compounds such as SnO2 particles or tin-acetylacetonate salts for pinning centers. Jc of the YBCO films were enhanced by introducing pinning centers both SnO2 and tin-acetylacetonates in the wide range of the magnetic angle. Especially, Jc of YBCO film grown by the solution with tin-acetylacetnates increased in all magnetic field angles. XRD analysis and TEM observation revealed the existence of BaSnO3 particles with the size of about 30 nm in the YBCO film grown by the solution with tin-acetylacetnates. The BaSnO3 nano particles were distributed randomly in the film and were considered to act as 3-dimentional pinning centers.

Effects of uniaxial constant pressures on the joint properties of REBCO coated conductors

We studied the effects of uniaxial constant pressures by using some weights on the properties of the diffusion joints using Ag stability layers of REBa2Cu3O7−X (REBCO, RE=Y, Gd) coated conductors. Two tapes were stuck in a face to face manner with Ag surfaces in contact, and were pressed uniaxially during the joining under a constant pressure at 673K in a pure oxygen atmosphere. The Ag area at the joint was 6×5 mm2 for YBCO coated conductors produced by modified metal-organic deposition (MOD) process using precursor solution of trifluoroacetates (TFA) for Y and Ba and F-free salt for Cu. A very low resistance of about 10 nΩcm2 across the joint was achieved by the diffusion joining under the pressure of 10 MPa. The relations between the joint resistance, the joint structure and the joint pressure were investigated.

High-Jc GdBa2Cu3O7−δ films fabricated by the metal–organic deposition process

We report a successful fabrication of high-Jc GdBa2Cu3O7−δ (GdBCO) films by the metal–organic deposition process on the LaAlO3 (LAO) (001) substrates. The coating solution was prepared by mixing Gd, Cu fluorine-free sources with Ba trifluoroacetate. Samples were dip-coated, pyrolized within 3h at the temperature up to 400°C in a humid oxygen atmosphere, and finally fired at various high temperatures in 100ppm Ar/O2 atmosphere. The GdBCO films fired at 775 and 800°C exhibited Jc values of ∼2.1MA/cm2 at 77K in a self-field, which are attributable to both high Tc,zero values of ∼89K and high in-plane textures of 1.3–1.4°. Above 800°C, however, the superconducting properties of GdBCO films are degraded due to the thermal decomposition of GdBCO film in 100ppm Ar/O2 atmosphere.

Effects of tin-compounds addition on Jc and microstructure for YBCO films

Tin-compounds were doped into YBa2Cu3O7−δ (YBCO) films as pinning centers to enhance Jc in magnetic fields. YBCO films were grown by a metal organic deposition process using tri-fluoroacetates starting solutions. Tin-acetylacetonate salts were then dissolved into the starting solution as pinning centers. Jc of the YBCO films with tin-acetylacetonates were enhanced in all magnetic field angles. Transmission electron microscopy (TEM) and TEM-EDS (Energy Dispersive X-ray Spectroscopy) observations revealed the existence of tin-compound particles with the size of about 30nm in the YBCO film. These nano particles were distributed randomly in the film and were considered to act as 3-dimentional pinning centers.

Thick homoepitaxial GaN with low carrier concentration for high blocking voltage

High voltage GaN Schottky diodes require a thick blocking layer with an exceptionally low carrier concentration. To this aim, a metal organic chemical vapor deposition process was developed to create a (14 μm) thick stress-free homoepitaxial GaN film. Low temperature photoluminescence measurements are consistent with low donor background and low concentration of deep compensating centers. Capacitance–voltage measurements performed at 30 °C verified a low level of about 2×10 15 cm −3 of n-type free carriers (unintentional doping), which enabled a breakdown voltage of about 500 V. A secondary ion mass spectrometry depth profile confirms the low concentration of background impurities and X-ray diffraction extracted a low dislocation density in the film. These results indicate that thick GaN films can be deposited with free carrier concentrations sufficiently low to enable high voltage rectifiers for power switching applications.

Microwave ECR plasma CVD of cubic Y2O3 coatings and their characterization

Abstract Yttrium oxide (Y2O3) thin films are deposited by microwave electron cyclotron resonance (ECR) plasma assisted metal organic chemical vapour deposition (MOCVD) process at a substrate temperature of 350 °C using indigenously developed metal organic precursors (2,2,6,6-tetra methyl-3,5-heptane dionate) yttrium, commonly known as Y(thd)3 synthesized by ultrasound method. The deposited coatings are characterized by X-ray photoelectron spectroscopy, glancing angle X-ray diffraction, scanning electron microscopy, EDS and infrared spectroscopy. The characterization results indicate that it is possible to deposit non-porous coatings with excellent uniformity of a single phase cubic Y2O3 on various substrates by this process at reasonably low substrate temperature that is desirable in various manufacturing processes.

Preparation of Dispersed Platinum Nanoparticles on a Carbon Nanostructured Surface Using Supercritical Fluid Chemical Deposition

We have developed a method of forming platinum (Pt) nanoparticles using a metal organic chemical fluid deposition (MOCFD) process employing a supercritical fluid (SCF), and have demonstrated the synthesis of dispersed Pt nanoparticles on the surfaces of carbon nanowalls (CNWs), two-dimensional carbon nanostructures, and carbon nanotubes (CNTs). By using SCF-MOCFD with supercritical carbon dioxide as a solvent of metal-organic compounds, highly dispersed Pt nanoparticles of 2 nm diameter were deposited on the entire surface of CNWs and CNTs. The SCF-MOCFD process proved to be effective for the synthesis of Pt nanoparticles on the entire surface of intricate carbon nanostructures with narrow interspaces.

Structural and electrical properties of ZnO nanorods and Ti buffer layers

Vertically-well-aligned ZnO nanorods were synthesized on Ti buffer layers by a metal-organic chemical-vapor deposition process. Structural analyses demonstrated that the ZnO nanorods were well-aligned in the c-axis and ab-plane. Transmission electron microscopy (TEM) showed that the Ti buffer layer was amorphous and interdiffused into the ZnO nanorods. Energy-dispersive spectroscopy (EDS) analysis revealed the Ti buffer layers to be slightly oxide. Extended x-ray absorption fine structure confirmed the TEM and EDS results. The I-V characteristic measurements showed a 20-fold increase in current density with the Ti buffer layer, suggesting excellent electrical contact between the Ti buffer layer and ZnO nanorods.

Effective Connection of Phase-Separated Metallic Pathways under Low Magnetic Fields in Charge-Ordered Insulators of Micropatterned Perovskite Manganite Thin Films

We investigated the probe size dependence of the electrical transport properties of perovskite manganite La 0.67 Ca 0.33 MnO 3 (LCMO) films with electronic phase separation (EPS) between ferromagnetic metal and charge-ordered insulator phases. A micropatterned wire was fabricated by an excimer-laser-assisted metal organic deposition process. A patterned wire of an LCMO film with a width of 10 µm had a higher insulator–metal transition temperature associated with the ferromagnetic transition than that of an LCMO film with a large probe size. Moreover, a low-magnetic-field magnetoresistance (LFMR) effect was observed for the micropatterned wire film; the resistivity decreased only from H ⊥ c > 0.02 T. The origin of this LFMR effect is thought to be the effective connections of the ferromagnetic metal domains between the probe contacts with small dimensions similar to the size of the phase-separated metal and insulator domains. These properties were qualitatively explained by numerical simulations of resista...

Preparation of polycrystalline VO2 films on glass and TiO2/glass substrates by means of excimer laser assisted metal organic deposition

An excimer laser assisted metal organic deposition process for the preparation of vanadium dioxide (VO2) films is described. When a precursor film grown on a silica glass substrate by preheating at 300°C was irradiated with a KrF laser at room temperature in air, the film was crystallized into polycrystalline VO2 phases. Generally, the preparation of VO2 films requires strict atmosphere control, but in this process, the polycrystalline VO2 films were successfully prepared without it. Moreover, it was revealed that crystallization into the VO2 phases was promoted by a TiO2 buffer layer placed on the glass substrate. This means that the photochemical reaction induced by the TiO2 absorbing the laser participates in the crystallization. The electrical resistivity of the film grown on the TiO2/glass substrate was lowered compared to that of the film grown on the glass substrate due to improvement of the film uniformity. The crystallinity of the obtained film was dependent on the irradiation time. With the improved crystallinity of the film, the resistivity drop through the metal-insulator transition became large.

Formation mechanism of BaZrO3 nanoparticles in Y1−xSmxBa2Cu3Oy-coated conductors derived from trifluoroacetate metal–organic deposition

Grains of BaZrO3 (BZO) in REBa2Cu3Oy (REBCO) films exhibit microstructural differences, depending on whether they weredeposited by pulsed-laser deposition (PLD) or metal–organic deposition (MOD). In orderto understand the origins of these differences, we examined the formation mechanism ofBZO nanoparticles in the MOD process with detailed observations of the quenchedfilms by transmission electron microscopy. The BZO nanoparticle was found toform in the precursor during the temperature ramp prior to the formation of theY1−xSmxBa2Cu3Oy (YSmBCO) crystals. The YSmBCO grew layer by layer while entrapping the BZOparticles, which resulted in random dispersion of the BZO particles in the YSmBCO layer.Consequently, uniformly dispersed BZO nanoparticles were formed in the YSmBCO matrixderived from the TFA-MOD process. These findings indicate that a key factor in achievingfine dispersion of BZO nanoparticles in the superconducting matrix is strongly related tonucleation of the BZO phase crystals in the precursor before growth of the YSmBCO layer,which is unique to the MOD process. In subsequent testing, YSmBCO-coatedconductors with uniformly dispersed and densely concentrated BZO nanoparticlesshowed striking isotropic magnetic-field angular dependence of critical currents.

Zr-doped YBCO Film Prepared by Fluorine-reduced MOD Method

Through replacing copper Tri-fluoroacetate by copper α-methacrylic in Metal Organic Deposition(MOD) process,the total amount of fluorine in YBCO precursor solution was reduced by about 50%.As a result,the calcination period for YBCO precurse film was dramatically reduced.The calcination time was reduced to 2h,only one seventh of that in all-Fluorine MOD process.X-ray diffraction and scanning electronic microscope(SEM) measurements show that YBCO films have strong YBCO(00l) peaks and crack-free surface.The critical temperture(Tc) and critical current density(Jc at self-field,77K) are 90K and 2.84MA/cm2,respectively.Furthermore,the property of YBCO film prepared by the fluorine-reduced MOD method is enhanced greatly by incorporating 6mol% Zr element into the film.

Characterization of metal-supported Al 2O 3 thin films by scanning electrochemical microscopy

In this paper, physiochemical properties of amorphous alumina thin films, grown by the metal organic chemical vapour deposition process on the surface of platinum (Pt/Al 2O 3) and stainless steel (SS/Al 2O 3), were investigated in aqueous media. The study was performed by the use of scanning electrochemical microscopy (SECM), which allowed obtaining information on uniformity, topography and chemical stability/reactivity of the alumina coatings with high spatial resolution. In particular, the effects due to local acid, base and fluoride ions attack on alumina layers of thickness of about 250 nm (in the Pt/Al 2O 3 sample) and 1000 nm (in the SS/Al 2O 3 sample) were investigated. In the acid and base attack, high concentrations of H 2SO 4 and KOH were electrogenerated locally by the use of a 25 μm diameter platinum microelectrode. The latter was also used as SECM tip to monitor the chemical effect on the alumina layers. It was found that, regardless of the thickness of the film, alumina provided good resistance against local attack of concentrated H 2SO 4; instead, the film dissolved when subjected to KOH attack. The dissolution rate depended on several experimental parameters, such as SECM-tip to substrate distance, electrolysis time and alumina film thickness. The alumina layer proved also relatively poor resistance to etching in 0.1 M NaF solutions.