| 1. |
- Wang, Xin, et al.
(författare)
-
Composition, structure, and dielectric tunability of epitaxial SrTiO3 thin films grown by radio frequency magnetron sputtering
- 1999
-
Ingår i: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films. - : American Institute of Physics (AIP). - 0734-2101 .- 1520-8559. ; 17:2, s. 564-570
-
Tidskriftsartikel (refereegranskat)abstract
- Epitaxial (001) oriented SrTiO3 films have been deposited on LaAlO3(001) substrates by off-axis radio frequency magnetron sputtering in Ar:O-2 gas mixtures at substrate temperatures ranging from 650 to 850 degrees C. For the deposition conditions used, stoichiometric targets yielded 20% Sr-deficient films, whereas Sr-enriched targets (Sr1.1TiO0.9O3.0) resulted in stoichiometric films. The Sr-deficient films had a mosaic structure and a larger lattice parameter in comparison to bulk SrTiO3. The stoichiometric films on the other hand had a much higher crystalline quality in the as-deposited condition. The mosaicity of the latter films was primarily limited by the crystalline quality of the LaAlO3 substrates. The lattice parameters of the stoichiometric films were also smaller than the Sr-deficient ones and closer to the bulk value. The dielectric properties of the stoichiometric films were superior to the Sr-deficient films. For films with a thickness of similar to 300 nm, the typical dielectric constants as measured at similar to 77 K and I MHz were determined to be 820 and 500, for the stoichiometric and Sr-deficient films, respectively. Also the capacitance change, as a direct current bias voltage was applied to an interdigital capacitor, was higher for the stoichiometric film, 27.3% as compared to 8.6% when applying a bias of 300 V at 77 K. We also demonstrate the effectiveness of thermal annealing in improving both crystalline quality and dielectric properties, especially for the Sr-deficient films. (C) 1999 American Vacuum Society. [S0734-2101(99)010002-7].
|
|
| 2. |
- Wang, Xin, et al.
(författare)
-
Dietary factors influence the recovery rates of Helicobacter pylori in a BALB/cA mouse model
- 1998
-
Ingår i: Zentralblatt für Bakteriologie: Ternational Journal of Medical Microbiology: Medical Microbiology, Virology, Parasitology, Infectious Diseases. - 0934-8840. ; 288:2, s. 195-205
-
Tidskriftsartikel (refereegranskat)abstract
- The aim of this study was to assess the ability of different mouse diets to sustain an H. pylori infection in BALB/cA mice. Four commercially available mouse diets were compared. Experiment 1: Mice were fed the four diets for seven days before infection, infected three times at two-day intervals with 0.1 ml of 10(9) colony-forming units/ml H. pylori cells. H. pylori strains (n = 4) were cultured on GAB-Camp agar for 2 days, harvested and suspended in PBS. All animals were sacrificed at 2 and 4 weeks post inoculation. Experiment 2: Mice infected for 8 weeks were fed RM2, changed to the different diets for 10 days and sacrificed. Stomachs were collected, cultured on GAB-Camp agar to estimate H. pylori growth and stomach biopsies were analyzed by PCR. There were significant differences between diets in their ability to sustain growth of H. pylori. The range was from a few hundred colonies to no growth at all on the GAB-Camp agar. PCR signals showed good correlation with the culture results. All H. pylori-infected mice gave a significantly higher inflammation score compared to non-infected mice. The diet RM2, having the highest number of culturable H. pylori in the mouse stomach, also showed the highest inflammation. These results suggest that the dietary factors affect the amounts of H. pylori in an infection of BALB/cA mice.
|
|
| 3. |
|
|
| 4. |
- Wang, Xin
(författare)
-
Structure and Properties of Perovskite SrTiO3 and Na0.5K0.5NbO3 Thin Films Fabricated by rf Magnetron Sputtering
- 1998
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Functional oxide thin films are getting more and more attention due to their unique dielectric, piezoelectric, ferroelectric, magnetic, superconducting properties. This thesis focuses on the growth, compositional control, and structure-property relationships of SrTiO3 and Na0.5K0.5NbO3 thin films. These films were prepared by rf reactive magnetron sputtering. Structure-property investigations were performed by Rutherford backscattering spectroscopy, high resolution x-ray diffraction, scanning electron microscopy, atomic force microscopy, transmission electron microscopy methods, and dielectric, ferroelectric and piezoelectric measurements. Information from the structureproperty relationship studies was then used as input to improve the quality and properties of the thin-layers. High quality SrTiO3 and Na0.5K0.5NbO3 films suitable fortunable microwave dielectric components were developed. SrTiO3 thin films with relatively high dielectric constant were also deposited on commercial substrates for the goal of integrating by-pass capacitors into multi-module chips. Ferroelectric and piezoelectric properties of Na0.5K0.5NbO3 thin films were also studied for the technological goal of fabricating piezoelectric sensors. The relative materials performance characteristics of these films under important operational variables as devices were also tested.Epitaxial (001) orientated SrTiO3 films have been deposited on LaA1O3(001) substrates using off-axis sputtering. Stoichiometric targets yielded 20 % Sr-deficient films, whereas Sr-enriched targets (Sr1.1 Ti0.9O3.0) resulted in stoichiometric films. For stoichiometric SrTiO3 film the domain structure of the substrate was exactly copied into the film as revealed by the ω-ω/20 map and ω-Φ maps. On the other hand Sr deficient film exhibited a large degree of mosaicity. The lattice parameters of the stoichiometric films were also smaller than the Sr-deficient ones and closer to the bulk value. The dielectric properties of the stoichiometric films were superior to the Sr-deficient films.To further investigate the influence of deposition conditions on film composition and structure, SrTiO3 thin films have also been grown on LaA1O3(001) byon-axis sputtering. Epitaxial growth of SrTiO3 films on LaA1O3(001) single crystal substrates has been realized at growth temperatures as low as 350 °C. In the growth temperature range below 350 °C, films are polycrystalline showing three different orientations (100), (110), and (111).Utilizing high dielectric constant thin film for integrated capacitors is one important factor in downsizing microelectronic devices and systems. In the present work SrTiO3 thin films have been grown on Cu-coated glass fiber laminate substrates at ambient temperature. The obtained films have low crystallinity. The dielectric constants of the films were found to spread between 40-70 and the dissipation factors decreased with frequency down to 8x10-4 at 1 MHz.Room temperature tunable dielectric thin films are attractive for many types ofmicrowave components in telecommunication industry. For this purpose Na0.5K0.5NbO3 thin films have been grown on LaA1O3(001) substrates. XRD showed that the films are epitaxial of good quality (mosaic broadening as narrow as 0.044°). The dielectric properties of these interdigital capacitors were measured at 1 MHz from roomtemperature down to 50 K. The capacitor showed a high tunability (35 %) at room temperature and a low loss tangent of 0.007 without de bias applied.
|
|
