Chemical Solution Deposition Process Research Articles

ChemInform Abstract: UV‐Assisted Nucleation and Growth of Oxide Films from Chemical Solutions

AbstractReview: 50 refs.

Photoelectric properties of BiVO4 thin films deposited on fluorine doped tin oxide substrates by a modified chemical solution deposition process

BiVO4 films deposited on Fluorine doped tin oxide glass substrates were successfully prepared by a modified chemical solution deposition process. Structure and optical spectrum analysis show that the resultant BiVO4 films consist entirely of monoclinic scheelite structure and have a narrow band gap of ～2.66 eV. The films were investigated by photoelectrochemical and photovoltaic measurements with regard to hydrogen production and solar energy conversion under visible light. The BiVO4 photoanodes show significantly higher visible light induced photoelectrochemical performance (～1.1 mA/cm2 at 1.0 V vs. Ag/AgCl) than those reported ones, which is very promising for splitting water to H2 and O2. A Schottky BiVO4 solar cell was also investigated for comparison with photoelectrochemical measurements. The correlation between the photoelectrochemical and photovoltaic behavior for BiVO4 was explained. Our research should provide important support for the applications of BiVO4 films or its modified forms such as doping and nanocomposite in heterojunction photoelectrochemical cells and solar cells with suitable energy level alignment at the interface.

Fabrication of thin-film gadolinia-doped ceria (GDC) interdiffusion barrier layers for intermediate-temperature solid oxide fuel cells (IT-SOFCs) by chemical solution deposition (CSD)

A dense gadolinia-doped ceria (GDC) interdiffusion barrier layer as thin as 300nm was successfully fabricated on a rigid anode/electrolyte bilayer substrate using the chemical solution deposition (CSD) process for intermediate temperature solid oxide fuel cells (SOFCs). Drying-related macro-defects were removed by employing drying control chemical additives (DCCA), which effectively relieved drying stresses. The major process flaws caused by the constraining effects of the rigid substrate were completely eliminated by the addition of GDC nanoparticles into the chemical solution, which suppressed the generation of microstructural anisotropy by mitigating the predominant bi-axial substrate constraints. As a consequence, a thin film GDC interlayer was successfully deposited with a high volumetric density, effectively preventing the chemical interaction between the electrolyte and cathode during the fabrication process and subsequent operation. The cell test and microstructural analysis confirmed excellent electrochemical performance and structural and chemical stability. The CSD process presented in this paper is considered to be a promising technology for the practical preparation of GDC thin film barrier layers for intermediate temperature SOFCs based on the film quality, processing costs and potential for large-scale production.

Observation of high dielectric constant of Bi-Nb-O<sub>x</sub> thin-film capacitors fabricated by chemical solution deposition process

Observation of high dielectric constant of Bi-Nb-O<sub>x</sub> thin-film capacitors fabricated by chemical solution deposition process

UV-assisted nucleation and growth of oxide films from chemical solutions

The fabrication of thin oxide films at low temperatures using simple processes has been a significant challenge associated with expanding the potential applications of these materials. Recent developments have demonstrated that the photo-assisted chemical solution deposition (PACSD) process offers a promising means of solving these difficulties, allowing high volume, on-demand production of variable sample sizes using an advantageous wet process. A better understanding of the crystal growth phenomena associated with this process, however, is required to enable various oxide thin films to be prepared using this new concept. Under pulsed ultraviolet (UV) laser irradiation, crystal growth has been confirmed to proceed by near-instantaneous photothermal heating and photochemical effects at the reaction interface. Vacuum UV lamp irradiation is also a useful means of generating oxide nuclei, since it results in effective chemical bond cleavage and simultaneously produces reactive oxidant (O3/O((1)D)) species. In this review, the nucleation and growth mechanisms which occur during the PACSD process are introduced and discussed and we examine the future possible applications of this process.

Chemical solution growth of ferroelectric oxide thin films and nanostructures

Chemical solution deposition (CSD) provides a low-cost, versatile approach for processing of thin and ultrathin ferroelectric films, as well as short and high aspect ratio ferroelectric nanostructures. This review discusses the state of the art in the processing of ferroelectric oxide thin films and nanostructures by CSD, with special emphasis on nucleation and growth phenomena. The effects of choice of precursor solution, substrate and bottom electrode stack, and thermal treatment conditions on the nucleation and growth are examined. Furthermore, methods to control ferroelectric thin film's microstructure, including phase content, texture, grain size and chemical homogeneity, are reviewed. Lastly, current CSD-based methods for processing of ferroelectric oxide nanostructures are presented with special consideration of the structural development, as well as advantages and shortcomings associated with each method. Lead zirconate-titanate, Pb(ZrxTi1-x)O3 (PZT), and barium titanate, BaTiO3 (BT), are used throughout the discussion, as specific examples for CSD processing of perovskite ferroelectrics.

Fabrication of YBCO/CeO2/YBCO multilayer films through an all chemical solution deposition approach

In this paper, the growth characteristics and superconducting properties of YBCO/CeO2/YBCO multilayer films derived from an all chemical solution deposition process layer by layer are investigated. X-ray diffraction results show that the c-axis epitaxial growth feature of the bottom YBa2Cu3O7-δ (YBCO) film was perfectly inherited. Alternating epitaxial growth of YBCO/CeO2/YBCO multilayer films was confirmed by high resolution transmission electron microscopy in combination with selected area electron diffraction, which will lay the groundwork for preparation of SIS-type Josephson junctions. In addition, nanosized BaCeO3 particle rather than BaCeO3 transition layer was observed in the interface between YBCO and CeO2. The superconductivity measurement results show that the proposal method gives better superconducting properties only for high magnetic field and at low magnetic field it deteriorates the superconducting properties.

Observation of 57Fe-Enriched BiFeO3 Thin Films Using Mössbauer Spectroscopic Microscope

57Fe-enriched BiFeO3 (BFO) thin films were produced from a stoichiometric precursor solution by chemical solution deposition process. The perovskite BFO thin film fabricated at 550 °C on a Pt/Ti/SiO2/Si substrate showed saturated polarization–electric field (P–E) hysteresis loops. The remanent polarization Pr and the coercive field Ec at room temperature were 89 µC/cm2 and 365 kV/cm, respectively. The Mössbauer spectra consisted of the antiferromagnetic perovskite BFO and a paramagnetic component at a fraction in the range of 11 to 14%. The secondary component was supposed to be due to Bi2Fe4O9 and/or an amorphous component, influencing the ferroelectric property at room temperature. The Bi2Fe4O9 thin film was also fabricated at 700 °C on a SiO2/Si substrate. Furthermore, we tried to measure the mapping images corresponding to the perovskite BFO and Bi2Fe4O9 components separately using a Mössbauer spectroscopic microscope. A mapping image showed the distribution of the perovskite BFO component on the film.

Mössbauer Spectra of <sup>57</sup>Fe-Enriched BiFeO<sub>3</sub> Thin Films Fabricated on SiO<sub>2</sub>/Si Substrates by Chemical Solution Deposition Process

sup>57Fe-enriched BiFeO3 (BFO) thin films were fabricated on SiO2/Si substrates from a stoichiometric precursor solution by chemical solution deposition process. The Bi/Fe molar ratio of the thin films decreased from 0.95 to 0.80 with increase in the sintering temperature. A perovskite phase and flat surface were obtained in the BFO thin films sintered at 500 and 600 °C. However, the 57Fe Mössbauer spectra showed a mixture phase due to amorphous and/or Bi2Fe4O9 phases in the BFO thin films. The valence state of Fe ions of the BFO thin films was confirmed to be only Fe3+ by the Mössbauer spectra.

Surface morphology and ferroelectric properties of compositional gradient PZT thin films prepared by chemical solution deposition process

A series of PbTiO3/PbZrxTil−xO3 (PT/PZT) and PbZrO3/PbZrxTil−xO3 (PZ/PZT) compositional gradient thin films are obtained by chemical solution decomposition (CSD) method. The influences of buffer layers on surface morphology are investigated. Thin films with buffer layer are able to maintain the perovskite structure with (111)-preferred orientation. The surface microstructure and ferroelectric properties of the PZT thin films differs significantly depending on the use of PT or PZ buffer layers. When the PT buffer layer has five layers, the root mean square roughness (RMS) [17.7nm] and remnant polarization (Pr) [35.83μC/cm2] are maximized. On the other hand, when PZ buffer layer has one layer, the RMS [3.67nm] and Pr [26.08μC/cm2] are also maximized. The down-graded (Zr composition varying from 0.6 at the bottom surface to 0.4 at top surface) thin films exhibit larger surface roughness and better ferroelectric property than up-graded (Zr composition varying from 0.4 at the bottom surface to 0.6 at top surface) thin films. Therefore, different buffer layer determines different surface morphology. It is concluded that the ferroelectric property of the gradient thin films not only depends on its composition structure, but can also be controlled by the surface morphology. The results indicate that the PZT films with better ferroelectric property should have larger surface roughness.

In situ measurement of crystallization of oxide thin films during irradiation with pulsed UV laser in chemical solution deposition process

The epitaxial and polycrystalline growth of lanthanum strontium manganite films on single crystalline strontium titanate and lanthanum aluminate substrates, respectively, under the irradiation with XeCl lasers in the excimer laser-assisted metal organic deposition (ELAMOD) process have been previously reported. In order to investigate the growth phenomena, we monitored the thermal radiation from the sample surfaces irradiated with a pulsed ultraviolet laser in situ with near-infrared sensors. The cooling of the lanthanum strontium manganite films on strontium titanate substrates was significantly slower than that of films on lanthanum aluminate substrates. A similar behavior was also observed by the numerical simulation study. This difference in the cooling decay curves may play an important role in the mode by which crystal growth occurs in the ELAMOD process.

Preparation of perovskite Fe-doped Na0.5Bi0.5TiO3 thin film from polyethylene glycol-modified solution precursor on LaNiO3/Si substrate

A (100)-oriented Fe-doped NBT Na0.5Bi0.5TiO3 (NBTFe) thin film was fabricated on LaNiO3(100)/Si substrate using a chemical solution deposition process, in which the solution precursor was modified by polyethylene glycol with a molecular weight of 600 (PEG600). The effects of PEG600 for crystalline structure, morphology, and electrical properties of NBTFe thin film were characterized. It is observed that with the PEG600 additive, phase-pure perovskite can be obtained for NBTFe thin film at a relatively lower annealing temperature of 500°C. Moreover, in NBTFe thin film with PEG600 modification, enhanced ferroelectricity is achieved with a larger remanent polarization (Pr) of 21.9μC/cm2, and the values of the dielectric constant and dissipation loss at 100kHz are estimated to be 411 and 0.153, respectively.

Enhanced ferroelectric properties of highly (100) orientedPb(Zr0.52Ti0.48)O3thick films prepared by chemical solution deposition

Ferroelectric Pb ( Zr0.52Ti0.48) O3(PZT) thick films with highly (100) preferential orientation have been prepared by chemical solution deposition process on Pt / Ti / SiO2/(100) Si substrates and pyrolyzed at 350°C–450°C, then annealed at 650°C. The typical thickness of the films is 3.9 μm. Effects of the pyrolysis temperature and excess PbO on the orientation, dielectric and ferroelectric properties of PZT thick films have been discussed. Domain switching and depoling process were studied by piezoelectric force microscopy. (100) oriented PZT films exhibit enhanced electrical properties. The dielectric constant and loss tangent of the films are 1444 and 0.022 at 1 kHz, respectively. The remnant polarization increases from 27.6 to 34.6 μC/cm2, and the coercive field decreases from 61.4 to 43.5 kV/cm, when the orientation of the films changes from the random orientation to the preferential (100) orientation. The leakage current density is 10-8A/cm2at dc field of 0.25 kV/cm, and then increases to 10-6A/cm2at 40 kV/cm. The piezoelectric response of the oriented films is investigated by Piezoelecric Force Microscopy (PFM).

Raman spectroscopy of nanocrystalline Mn-doped BiFeO3 thin films

Enhancement of magnetic and electric properties in multiferroic Mn-substituted BiFeO3 thin films (BiFe1− x Mn x O3 with x = 0.00–0.05) grown via the low-temperature chemical solution deposition process on low-cost substrates like indium tin oxide (ITO)/glass and silicon is reported in this work. A detailed structural analysis by high-resolution X-ray diffraction and Raman spectroscopy indicates that the grown films exhibit rhombohedral distorted perovskite structure without any impure phase. Raman spectroscopic analysis shows all 13 Raman active (4A1 + 9E) phonon modes corresponding to distorted rhombohedral BFO R3c structure. BFO thin film with 5% Mn substitution showed maximum saturation and remnant magnetisation (M s = 16.70 emu/g and M r = 2.58 emu/g) and remarkably reduced leakage current due to distortion in the spin cycloid structure and suppression of oxygen vacancies due to partial replacement of Fe3+ ion by Mn3+ ion, respectively. These enhanced multifunctional properties highlight the potential applications of BFMO system in thin film devices which can couple magnetic and ferroelectric order parameters.

Evolution of low fluorine solution in decomposition and crystallization for YBa2Cu3Oy film growth

A new chemical solution deposition process for YBCO films based on a low fluorine content solution has been developed. The total content of fluorine in this solution is about 50% of that in all TFA solution, the amount of corrosive fluorine-containing gas released can be greatly reduced and the acute decomposition in a short time can be suppressed. A smooth and homogeneous surface have been achieved at the heating rate of 5K/min by using this low fluorine solution. During the crystallization process, the composition of intermediated phases (BaYF, CuO) are changed with the annealing temperature. The reaction of nanocrystal Y2O3 and CuO is accompanied with the nucleation of YBCO phase, which indicates that there may be less second phase formation in the crystallization process. The traces of intermediate phase (BaYF–Ba(O,F)2) are observed. It demonstrates that the growth mechanism of the low fluorine solution is still “ex situ BaF2” process. The YBCO films with a fast pyrolysis process has been demonstrated high performance with Jc (77K, self field)=∼3.2MA/cm2.

Epitaxial Growth of LZO Film on NiW Substrate

La2Zr2O7 (LZO) oxide film is a good choose for buffer layer of coated conductors, especially for Chemical Solution Deposition route to fabricate coated conductors. In this paper, the influences of process parameters on texture of LZO films deposited by chemical solution deposition process on NiW substrate were studied, and results indicated that the heat-treatment temperature, dwell time and the oxygen content in the heat-treatment atmosphere were important to obtain a cube textured LZO film on NiW substrate. Based on our results, it was believed that inhibition of crystallite growth of LZO grains on the top layer of LZO film was the key to understand the epitaxial growth of LZO film on NiW substrate.

Effect of excess Pb on epitaxial growth of Pb(Mg<sub>1/3</sub>Nb<sub>2/3</sub>)O<sub>3</sub> thin films prepared by chemical solution deposition process

Effect of excess Pb on epitaxial growth of Pb(Mg<sub>1/3</sub>Nb<sub>2/3</sub>)O<sub>3</sub> thin films prepared by chemical solution deposition process

Thermal conductivity of nano-grained SrTiO3 thin films

We measure the thermal conductivities of nano-grained strontium titanate (ng-SrTiO3) films deposited on sapphire substrates via time-domain thermoreflectance. The 170 nm thick oxide films of varying grain-size were prepared from a chemical solution deposition process. We find that the thermal conductivity of ng-SrTiO3 decreases with decreasing average grain size and attribute this to increased phonon scattering at grain boundaries. Our data are well described by a model that accounts for the spectral nature of anharmonic Umklapp scattering along with grain boundary scattering and scattering due to the film thickness.

Thin Film Yttria-Stabilized Zirconia (YSZ) Electrolyte Fabricated by a Novel Chemical Solution Deposition (CSD) Process for Solid Oxide Fuel Cells (SOFCs)

Thin Film Yttria-Stabilized Zirconia (YSZ) Electrolyte Fabricated by a Novel Chemical Solution Deposition (CSD) Process for Solid Oxide Fuel Cells (SOFCs)

Characterization of 57Fe-Enriched BiFeO3 Thin Films by Mössbauer Spectroscopy

57Fe-enriched BiFeO3 (BFO) thin films were fabricated on Pt/Ti/SiO2/Si substrates from a stoichiometric precursor solution by chemical solution deposition process. The Bi/Fe molar ratio of the BFO thin films was about 0.93. The crystallinity and surface morphology of the BFO thin films were improved by using a single-sintering technique. Mössbauer spectra of the BFO thin films were measured at room temperature, and the valence state of Fe ions was confirmed to be Fe3+ only. One of the BFO thin films fabricated by single-sintering at 550 °C showed a relatively saturated P–E hysteresis loop. The remanent polarization Pr and the coercive field Ec at 10 kHz were 59 µC/cm2 and 327 kV/cm, respectively, at room temperature.