Anxiang Kuang

Sol-gel-derived c-axis oriented ZnO thin films

c-Axis oriented zinc oxide thin films were prepared by sol-gel process on fused quartz substrates. The structure, optical and electrical properties of ZnO films were investigated. Growth of the thin films strongly depends on heat-treatment conditions. The c-axis lattice constants of the thin films and the band gap are a little bigger than that of ZnO crystal. The differences between the thin film and crystal might be attributable to the grain boundaries and imperfections in thin films.

Synthesis and optical properties of highly c-axis oriented Bi4Ti3O12 thin films by sol-gel processing

Abstract Highly c -axis oriented Bi 4 Ti 3 O 12 thin films have successfully been prepared on fused quartz substrates by sol-gel processing. The orientation degree of the thin film was about 87%. The thin film exhibits good optical transmission. The optical-absorption properties of the thin films have been measured. The variation of bandgap with annealing temperature is studied.

X-RAY PHOTOELECTRON SPECTROSCOPY STUDY ON COMPOSITION AND STRUCTURE OF SOL-GEL DERIVED PBTIO3 THIN FILMS

The surface states of sol‐gel derived PbTiO3 thin films on Si substrates before and after Ar+ sputtering were studied by x‐ray photoelectron spectroscopy (XPS). The results showed that there was no residual carbon or other impurity element in the films except some carbon surface contamination due to specimen handling or pumping oil. A large amount of absorbed oxygen was near the surfaces of the films. The chemical composition of the films was found to be stoichiometric, as proved by inductively coupled plasma results. The valence states of the ions indicated that the films were PbTiO3 with perovskite structure. The XPS spectra of the films after Ar+ sputtering for 10 min differed greatly from those of as‐prepared films. This probably results from the preferred sputtering of lead atoms and the production of many new dangling bonds during Ar+ bombardment.

Preparation of KTa0.65Nb0.35O3 thin films by a sol-gel process

Abstract Crack-free and transparent potassium tantalate niobate (KTN) KTa 0.65 Nb 0.35 O 3 thin films of perovskite structure were prepared through spin-coating using a sol-gel process. A homogeneous and stable precursor solution was obtained from K(OC 2 H 5 ), Ta(OC 2 H 5 ) 5 , and Nb(OC 2 H 5 ) 5 in absolute ethanol without any additives. Infrared absorption spectra indicate the existence of a complex reaction resulting in the formation of double metal alkoxides KNb(OC 2 H 5 ) 6 and KTa(OC 2 H 5 ) 6 in solution. The precursor powder crystallized to pyrochlore at 600°C, and then completely transformed to perovskite at 750°C. Highly oriented KTN films possessing a perovskite structure were successfully prepared on R -plane sapphire substrates at 750°C and on SrTiO 3 (100) substrates at 650°C. The chemical composition of the KTN films is in good agreement with the atomic ratio of the starting materials.

Reactions in preparing Bi4Ti3O12 ultrafine powders by sol-gel process

Abstract Bismuth titanate powders around the nanometer range have been synthesized using sol-gel process with bismuth nitrate and titanium butoxide as raw materials. The formation mechanism of sol, gel and the reactions in heat treatment process have been studied. It was found that a chelate reaction occurred in solution. In heat treatment process, the gel started to crystallize into mixture phases at 400°C; at 700°C, formed four phases, at 850°C, finally transformed to single layered perovskite structure. The particle size of powders increased with calcination temperature.

Synthesis and ferroelectric properties of c‐axis oriented Bi4Ti3O12 thin films by sol‐gel process on platinum coated silicon

c‐axis oriented Bi4Ti3O12films have been prepared on Pt/Ti/Si(111) substrates by sol‐gel process. Crack‐free films of 0.5 μm thickness were fabricated using a multilayer spinning technique and calcination at 600 °C for 30 min. The average grain size of the film is about 0.15 μm. The film exhibits ferroelectric hysteresis with remanent polarization Pr=4.8 μc/cm2 and coercive field Ec=70 kV/cm. The measured dielectric constant and loss factor at a frequency of 100 kHz are 170 and 0.02 respectively.

Growth of layered perovskite Bi4Ti3O12 thin films by sol–gel process

Abstract Ferroelectric Bi 4 Ti 3 O 12 thin films were prepared on SrTiO 3 crystal substrates by a sol–gel process. A homogeneous and stable precursor solution was obtained from Bi(NO 3 ) 3 and Ti(OC 4 H 9 ) 4 . Stability of solution was determined by its pH value, which directly affects the growth behaviour and orientation of the thin films. The single-phase Bi 4 Ti 3 O 12 polycrystalline thin films were grown at 500°C by using a pH 2.5 solution, which turns into highly c -axis orientation at 550°C. Completely c -axis oriented thin film was prepared by using a solution of pH 3.5.

XPS study on composition and structure of epitaxial KTa1−xNbxO3 (KTN) thin films prepared by the sol-gel process

Epitaxial KTN (x=0.35) thin films were prepared on (100) SrTiO3 substrates by the sol-gel process. In this paper, wide and narrow scans of XPS analysis were studied on the surface of the KTN thin films before and after Ar+ sputtering for 10 min. The results show that no impurity or residual carbon was observed in the films, except for some carbon contamination caused by handling and pumping oil on the surface of the films. The chemical composition of the films is in good agreement with the stoichiometry of the starting materials, as demonstrated by the ICP results. The valence states of the ions indicated that the films are KTN with a perovskite structure. XPS spectra of the films after Ar+ sputtering differ considerably from those of the as-grown films, which may be attributable to the preferred sputtering of potassium and to new valence states produced during the Ar+ bombardment. In addition, it was confirmed by the angle resolution XPS results that the chemical composition was well-distributed and that no other phase was observed apart from KTN in the near surface region of the films.

SOL-GEL derived ferroelectric lead titanate thin films on doped silicon substrates

Abstract PbTiO3 thin films were fabricated by the spinning method in the sol-gel process. Films with thickness of 0.15 μm to 4.0μm were coated on doped silicon substrates, using a multiple deposition process. The processing yields highly reliable crack-free films with easy control of crystal structure and composition at firing temperature of 550 to 750 °C. The very fine grain size in PbTiO3 films was studied as a function of firing temoperature. The ferroelectric and dielectric properties of the films were investigated using metal-ferroelectric-semiconductor configaration, and were strongly dependent on the film thickness and the firing temperature. Good ferroelectric properties can be obtained in the films of thickness more than 2μm fired at 600-650 °C.

Preparation of highly oriented KTN/SrTiO3(111), KTN/SrTiO3(100) thin films by Sol-Gel method

Abstract Abstarct Highly oriented perovskite KTN/SrTiO3(100)thin films were perpared by Sol-Gel method from KOCOCH3, Ta(OC2H5)5 and Nb(OC2H5)5. The crystallization process of KTN thin films on SrTiO3 substrate was studied by XRD. Some technical parameters such as the solution concentration, viscoaity, catalyst, heat treatment temperature, heating and cooling rate, and O2 flow were determined by the experiments, at the same time, the lattice constant, thermal expansion coefficient and chemical stability of substrate which influenced the structure and quality of KTN films were also discussed