Jose M. Mir

Epitaxial nonlinear optical films of LiTaO3 grown on GaAs in waveguide form

Nonlinear optical films of LiTaO3 were epitaxially grown on (NH4)2Sx‐treated (111) GaAs using e‐beam evaporated MgO as intermediate layers. The MgO lattice was found to rotate by 180° about the [111] surface normal with respect to the GaAs substrate. The laser‐ablated LiTaO3 film grew epitaxially in the preferred [0001] direction and formed a waveguide with its underlying buffer layer of MgO.

Optical thin films for waveguide applications

The development of optical thin films for waveguide applications will enable a variety of new and highly useful optoelectronic functions. Many difficulties must be overcome, however, before optical films can be used in photonics applications. Properties such as polycrystallinity, surface topography, and refractive‐index homogeneity can affect the performance of optical thin film waveguides to a much greater extent than in other thin film applications because of the long optical interaction lengths. Even a small degree of polycrystallinity in anisotropic media, for example, can be a significant source of optical scattering. We review recent results of epitaxial lithium tantalate thin films grown as waveguide structures on sapphire and gallium arsenide substrates. Highly oriented crystalline structures with useful optical properties have been demonstrated. Although many challenges still remain before optical thin films are used widely as waveguides, modern thin film technology is beginning to provide the to...

Growth of superconducting Bi2Sr2CaCu2O8+x films on alumina, silicon, and fused quartz

Interactions between superconducting Bi2Sr2CaCu2O8+x films and substrates were investigated by ion backscattering, x‐ray diffraction, and four‐point probe resistivity measurements. During annealing at temperatures above‐ 800 °C, Bi2Sr2CaCu2 oxide films rapidly reacted with alumina, Si, Si covered with SiO2, and quartz, resulting in catastrophic failure. Zr‐based barrier layers were used to minimize film‐substrate interactions. When a single ZrO2 layer was interposed between the superconducting oxide film and the underlying substrate, the Bi2Sr2CaCu2 oxide films showed a large‐grained polycrystalline microstructure and exhibited the orthorhombic structure. Films on sapphire showed transitions to the superconducting state beginning near 100 K with zero resistance achieved at 70 K. Films on Si and thermally grown SiO2 showed a similar drop in resistance around 95 K, whereas the transition was broad and the zero resistance state was not reached. For films on quartz, high thermal stress caused cracking of the ...

Superconducting Y1Ba2Cu3O7-y thick films from nitrate pastes

A novel technique for forming superconducting Y1Ba2Cu3O7-y, thick films by screen printing pastes made from spray-dried nitrate powders on alumina and magnesia is described. Manufacture and characterization of nitrate powders are discussed. A model based on dissolution of yttrium nitrate is proposed to explain the rheological and film-forming properties of the nitrate pastes. Low-viscosity pastes are found to give better performance in terms of printability and quality of prints. Barium carbonate formation can be avoided by use of the nitrate pastes and by firing in an oxygen atmosphere. Superconducting thick films were achieved on single-crystal (1 0 0) MgO (T0=77 K) and on polycrystalline alumina with a prereacted barrier layer (T0=55 K).