| Chemical Vapor Deposition (CVD) involves the dissociation and/or chemical reactions of gaseous reactants in an activated (heat, light, plasma) environment, followed by the formation of a stable solid product. It is a widely used materials-processing technology, which involves electronic, optoelectronic, surface modification, ceramic fibre production and CMC applications. This thesis focuses on a novel CVD technique (Aerosol Assisted CVD, AACVD), with its development and applications.SOFCs, an energy conversion device, possess many advantages such as high energy conversion efficiency, less pollution and convenience. But it still failed to reach commercial viability due to its high operating temperature (>1000℃). Decrease the thickness of solid electrolyte is one of the key steps for intermediate temperature SOFC operated in 600-800℃. In this thesis, assembled AACVD apparatus were used to prepare: electrolyte thin films, including YSZ (yttria stabilized zirconia), SDC (samarium doped ceria); interconnect and electrode materials, LaCrO3 based materials. Simultaneously, systematic research has been done, including selection and preparation of metalorganic precursors, design and assembly of AACVD apparatus, growth kinetics, deposition mechanism, film morphologic zone models, and film properties testing. The present research also gave a well-knit academic and experimental base in the in-situ continuous growth and fabrication of all components of SOFCs in the future development.In the first part of chapter 1, several AACVD techniques developed in last two decades have been reviewed, including AAMOCVD, AA-PCVD, AACCVD, AACVD, ESAVD. Some science aspects in AACVD have been reviewed, such as selection of precursors, generation and transportation of aerosol droplets. The application of AACVD has also been reviewed systematically.In chapter 2, the working principle and materials of SOFCs were reviewed. Various manufacturing processes for SOFCs thin films were also reviewed, including physical methods (physical vapor deposition), chemical methods (EVD, AACVD) and ceramic powder processes (screen painting, casting).In chapter 3, precursors, M(DPM)3 (DPM=dipivaloylmethanate, M=Sm, Mn, Cr, Co, Fe) were synthesized from HDPM, NaOH/NaAc/CO(NH2)2 and inorganic salts and characterized by elemental analyses, X-ray diffraction, thermogravimetry-differential thermal analysis, nuclear magnetic resonance spectroscopy and fourier transform infrared spectroscopy. These compounds have been identified with high purity and anhydrous.All the compounds exhibit high volatility. They volatize and decompose completely below 300℃. The decomposition process is sensitive to the ambient gases. The decomposition and oxidation of the M(DPM)3 are occurred at lower temperature in air than in N2, which suggests that O2 and CO2 facilitates the two processes. in air makes the formation of Sm2(CO3)3 by-product by heating. The kinetic parameters of activation energy, frequency factor were computed using different models and thereinto D2 model best adjusted the experimental isothermal thermogravimetric data of Mn(DPM)3 and Cr(DPM)3.The results of infrared spectroscopy and mass spectroscopic spectroscopy indicated that the chemical bonds in these compounds dissociate generally following the sequence of C-O>M-O>C-C(CH3)3>C-C and C-H at elevated temperatures. The decomposition processes of M(DPM)n are strongly influenced by the coordination number and central metal ion radius.In chapter 4, cold-wall AA-MOCVD were assembled and successfully employed to fabricate YSZ films on NiO-SDC anode substrates from M(DPM)n precursors, with substrate temperature 400-960℃and reactor pressure 0.1 atm.YSZ thin films with amorphous microstructure were obtained at the substrate temperature 400℃and mixture phase of cubic and monoclinic structures at 550-700℃, which were all changed into full cubic microstructure after annealing treatment at 1100℃. Thin films exhibited full cubic phase at the substrate temperature higher than 800℃. Film morphologies were changed from uniform, smooth and laminated structure to columnar structure and then to coarse but dense surface with increasing of substrate temperatures. At substrate temperature 400-800℃, YSZ film growth was diffusion controlled with growth rate 0.6-1.5μm/h and Ea<22 kJ/mol. The Y/Zr and Gd/Ce ratios in the films were found to be smaller than those in the source solution. YSZ film was prone to porous cluster with increasing of source concentration. Kinetic model shown that the growth rate of YSZ film was proportional to quarter root of substrate temperature, square root of carrier flow rate and source concentration.In chapter 5, Samarium-doped ceria (SDC) thin films were prepared from Sm(DPM)3 and Ce(DPM)4 using the AAMOCVD method.α-Al2O3 and NiO-YSZ disks were chosen as substrates in order to investigate the difference in the growth process on the two substrates. Single cubic structure could be obtained on eitherα-Al2O3 or NiO-YSZ substrates at deposition temperatures above 450℃; the similar structure between YSZ and SDC results in matching growth compared with the deposition onα-Al2O3 substrate. A typical columnar structure could be obtained at 650℃onα-Al2O3 substrate and a more uniform surface was produced on NiO-YSZ substrate at 500℃. The composition of SDC film deposited at 450℃is close to that of precursor solution (Sm:Ce=1:4), higher or lower deposition temperature will both lead to sharp deviation from this elemental ratio. The different thermal properties of Sm(DPM)3 and Ce(DPM)4 may be the key reason for the variation in composition with the increase of deposition temperature.With Y(DPM)3 and Zr(DPM)4 as precursors, YSZ thin films were deposited onto NiO-SDC substrates using a modified AAMOCVD apparatus, where high power halogen lights were used as assisted heaters. Cubic structured YSZ was obtained when the films were deposited at 650℃. The cubic YSZ transformed to tetragonal structure after annealed at 1100℃for 3h, possibly due to crystallite growth. Y/Zr mole ratio of the deposited film depends on the Y/Zr ratio of the precursors, indicating that the thin film composition can be effectively controlled. Scanning electron microscopy (SEM) analysis showed a strong bonding between the films and substrates. Thickness of the film was estimated to be about 9 urn with a high growth rate of 50 nm/min, which inferring the AAMOCVD is very effective in synthesis of YSZ films. AC impedance analyses showed that the ionic conductivity of the YSZ film is 0.034 S/cm at 800℃, which is slightly less than that of bulk YSZ, and the conduction activation energy (Ea) changed from 80.8 kJ/mol to 138.8 kJ/mol at 640℃with decreasing temperature.In chapter 6, LaCrO3 thin films on electrolyte yttria-stabilized zirconia (YSZ) substrates were prepared by ultrasonic AACVD technique in the temperature range of 600～750℃using lanthanum and chromium nitrates as precursors. Thin films obtained at 600～650℃appear to be a mixture of cubic La(OH)CrO4 and cubic LaCrO4 phases, which transforms to pure cubic LaCrO4 with the substrate temperature increasing to 700～750℃. After annealed at 900℃for 2h, all films convert to single cubic LaCrO3 phase. The change of Cr2p spectra in X-ray photoelectron spectroscopy (XPS) analysis shows the similar phase transformation process. Reaction processes with respect to the substrate temperature were proposed according to X-ray diffraction (XRD) and XPS analysis. The surface morphology of the films was found to depend strongly on the substrate temperature, which would be the deciding factor of film growth mechanisms.The deposition of La0.7Ca0.3CrO3-δ (LCC) thin films was studied in detail by electrostatic AACVD process, considering the functions of deposition temperature, substrate material and solvent composition. The microstructures of LCC films, varied from porous reticulated model, cage-like particles to interconnect nanowire structure, can be effectively assembled. With increasing substrate temperature, the porosity decreases considerably; the pore and pore wall sizes both became smaller. When changing the substrate material from nickel, aluminum, and alumina substrates to copper substrate, the microstructure of LCC film converted from porous reticulated model to cage-like particle model. It may be interpreted by the bigger contact angle on the copper substrate than that on other substrates. A qualitative mechanism involved in the formation of various microstructures was presented. Moreover, by changing the solvent composition, the layer morphology may also be significantly modified, from porous reticulated model to interconnect nanowire structure.
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