Fabrication And Physical Properties Of Interface Engineered Functional Oxide Thin Films

This research is to utilize the interface engineered nanotechnique to build up a solid foundation on the development of new multifunctional materials with designable and controllable physical properties. In this thesis, the main new findings are summarized below:1. Highly epitaxial (LaBa)Co2O5.5+δ, LBCO) thin films have been successfully deposited on four different substrates, namely, LaAlO3, SrTiO3, NdGaO3, and MgO, by pulsed laser ablation. The LBCO films have excellent epitaxial behavior, single crystallinity, and sharp atomic interfaces. The transport property studies indicate that the transport behaviors of the films are highly dependent upon the interface strain energies. Specifically, the lattice mismatch can significantly influences the resistivity, magnetoresistance, and magnetic moment of the LBCO films, which suggests that the electrical and magnetic properties of the highly epitaxial LBCO thin films can be engineered with interface. High temperature transport property measurements indicate that the LBCOfilms have extraordinary sensitivity to reducing-oxidizing environment and the exceedingly fast surface exchange rate. It is indicating that the LBCO films have the potential application in the area of oxygen sensor devices for harsh environments at high temperature.2. La0.67Ca0.33MnO3 thin films were epitaxial grown on miscut (001) MgO substrates by using pulsed laser deposition. Electrical transportant property measurements indicate that the electrical resistance and the metal-insulator transition temperatures were highly dependent upon the miscut angles, which can be attributed to be the difference in residual strain. Especially, an anomalous magnetoresistance effect (-1010) has been observed with the value about four orders higher than the previous reported record.3. Pure and additional Mn doped Ba0.6Sr0.4TiO3 (0.5%,2%) (Mn:BST) thin films were epitaxially grown on the LaAlO3 by using pulsed laser deposition. Microstructural characterizations reveal that the as-grown thin films have excellent single crystallinity and epitaxial nature with atomically sharp interface. Microwave dielectric property measurements indicate that the additional Mn doping can significantly enhance the microwave dielectric properties of the BST films. The best value of the dielectric loss tangent (0.0227) can be obtained at the 0.5% Mn doping BST films at the microwave frequency of-15.6GHz, which are promised for the development of room temperature microwave elements. 4. Environmental friendly ferroelectric relaxor Ba(Zr0.2Ti0.8)O3 thin films with additional 2% Mn dopant (Mn:BZT) were epitaxially grown on MgO substrates by pulsed laser deposition. The as-grown films are c-axis oriented with an atomic sharp interface. The room temperature dielectric measurements reveal that the films have excellent dielectric properties. At the frequency of 1MHz, the film has a high dielectric tunability value of 53.4% at 800 Kv/cm with a large dielectric constant of 190 and an extra low dielectric loss value of 0.006. In the range of microwave frequency from 15GHz-18GHz, the average value of relative dielectric constant and the loss tangent is approximately 267 and 0.047, respectively, with large tunability values of 44.4%-48.0%.5. Environment friendly dielectric (Mn:BST//Mn:BZT)2 multilayered thin films were epitaxially deposited on (001) MgO substrates by pulsed laser deposition with different combinations of Mn:BST over Mn:BZT,2.5:7.5; 1:1; and 7.5:2.5. The as-grown multilayered films are c-axis oriented. The high-frequency microwave (15.5-18 GHz) dielectric property characterizations show that the dielectric constant, dielectric loss, and tunabilities of the multilayered thin films are highly dependent upon the sequences of Mn:BST to Mn:BZT. The optimized dielectric tunability with a low loss tangent was found to be 58.1%-74.4% under the combination ratio of 1:1 for Mn:BST to Mn:BZT.6. Interface engineered (BTO0.4//STO0.6)N heterostructures were designed and fabricated on MgO substrates by pulsed laser deposition. The heterostructures have highly epitaxial quality with c-axis oriented and atomic sharp interfaces. However, the high-frequency microwave (-18 GHz) dielectric property characterizations reveal that the dielectric constants and dielectric losses of the heterostructures are highly dependent upon the stacking period number (layer thickness) and designed structures. The optimized dielectric performance was found to be 0.02 for the dielectric loss tangent and 1320 for the dielectric constant, respectively, in the heterostructure of (BTO0.4//STO0.6)16.We subsequently investigated the dielectric properties of the (BTO0.5//STO0.5)16/MgO multilayered thin films. The average values of relative dielectric constant and dielectric loss tangent are found to be approximately 407 and 0.024, respectively, with large dielectric tunabilities of 11.8% to 35.9% for the frequencies varying from 5 GHz to 18 GHz. It is indicating that the BTO//STO multilayered thin films are promised for the development of room temperature microwave elements.7. High crystalline quality BaTiO3//SrTiO3 multilayered thin films were fabricated on polycrystalline Ni metal tapes by pulsed laser deposition. Transmission electron microscopy studies reveal that the multilayered BTO/STO thin films have good textured structures or good single-crystal nature. The dielectric property measurements show that the multilayered thin films have very low loss tangent in the range of 1 kHz to 1MHz where the average loss is about 0.0085, especially at 1MHz, the loss tangent is only 0.0073. This excellent result suggests that the BTO/STO heterostructures can be developed for the supercapacitance device applications.8. ZnO films embedded with Ag nano-particles are deposited at 750℃with reactive radio-frequency magnetron sputtering. The films are found to have a large enhancement in the intensity of photoluminescence emission and in the extinction of incident light. The enhancement is assigned to be from the interaction between the localized surface plasmons in the Ag nano-particels and the light. The surface plasmons in the films can be excited in a wide range, from ultraviolet to near infrared wavelength of light.