John A. Agostinelli

Epitaxial LiTaO3 thin films by pulsed laser deposition

Epitaxial LiTaO3 thin films having excellent crystalline properties have been achieved on (0001)‐sapphire substrates using the technique of pulsed laser deposition. X‐ray diffraction analysis revealed that completely single‐phase c‐oriented LiTaO3 films were produced. X‐ray rocking curve analysis showed that the range of misalignment of the c‐axis direction was about 0.2°. Ion channeling studies indicated a minimum backscattering yield of only 4.9%. Channeling also revealed an improvement in crystalline perfection as a function of distance above the interface with the sapphire substrate. Optical waveguiding with losses on the order of 1 dB/cm was demonstrated.

Superconducting thin films in the BiSrCaCuO system by the decomposition of metallo-organic precursors

Abstract Thin films in the BiSrCaCuO system have been produced using the metallo-organic decomposition (MOD) technique. Multiphase films having the stoichiometries BiSrCaCu 3 O 6.5+ y andBiSrCaCu 2 O 5.54 were fabricated on single crystal MgO substrates and were found to have superconducting resistance behaviors. The superconducting phase was identified to be Bi 2 Sr 2 CaCu 2 O 8+ x . Highly c -axis-oriented films of Bi 2 Sr 2 CaCu 2 O 8+ x were achieved on MgO and SrTiO 3 substrates. SEM, EDS, and XRD analysis of these films detected only a single phase. Superconducting onset temperatures above 100 K and zero resistivity states at 84 K were observed.

Laser processing of carbon‐implanted Cu, Ni, and Co crystals: An attempt to grow diamond films

Carbon films have been prepared by laser‐pulse treatment of single crystals of copper, nickel, and cobalt, which have been previously implanted at room temperature with 50 keV carbon ions to a fluence of 1×1018 cm−2. Characterization using Raman scattering, Auger spectroscopy, and transmission electron microscopy showed that the films consisted of amorphous carbon and microcrystalline graphite but not diamond. In addition, an appreciable amount of substrate material was found present embedded in the carbon films.

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...

Epitaxially oriented YBa2Cu3O7−x thin films on 〈100〉 MgO prepared by metallo‐organic decomposition

Superconducting thin films of YBa2Cu3O7−x were prepared by metallo‐organic decomposition. Both ion channeling and x‐ray diffraction measurements showed that the oxide films grown on 〈100〉 MgO are epitaxially oriented in structure. The minimum yield of metal components varied from 0.58 to 0.32 in channeling measurements with the analyzing beam at energies ranging from 4.5 to 1.0 MeV. All x‐ray diffraction lines corresponded to the (00l) reflections of the superconducting phase. The film exhibited complete superconductivity at 79–80 K with a transition width of 2.5 K.

Solid state reactions in the formation of YBa2Cu3O7−δ high Tc superconductor powders

Abstract The synthesis of high Tc superconducting YBa2Cu3O7−δ powders obtained by three different schemes has been i investigated. The decomposition of metal carboxylates, mixed metal oxalates, and the conventional ceramic method of mixed oxide/carbonate are contrasted. Thermal analysis (TGA, DTA) results as well as X-ray diffraction data are used to follow the progress of the decomposition and solid state reactions leading to the formation of the required perovskite. The effect of cation mixing at the molecular level in the carboxylates and oxalates is compared to the physical mixing of coarser particles in the conventional approach. In the case of the carboxylates and mixed oxalate it is suggested that Ba and Y form a double carbonate that decomposes into barium carbonate and yttrium oxide in the progress of the reaction.

A cubic phase in the Y-Ba-Cu-O system and heteroepitaxial orthorhombic/cubic thin film structures

Abstract The metastable “cubic-123” phase in the Y-Ba-Cu-O system is discussed and its use in multilayer heteroepitaxial structures incorporating the high T c YBa 2 Cu 3 O 7−δ and the cubic material is described. Both SNS type sandwich layers and superlattice structures containing the two materials have been fabricated. The cubic material offers the possibility of an all Y-Ba-Cu-O Josephson junction.

YBCO-based ramp-edge Josephson junctions and DC SQUIDs with a cubic-YBCO barrier layer

Abstract Recently, the discovery of a nonsuperconducting metastable cubic phase of YBa 2 Cu 3 O 7 (YBCO) has been reported. Because of the structural, chemical, and depositional compatibility of cubic-YBCO with superconducting YBCO, it is an excellent candidate for use in heteroepitaxial structures. Such structures involving superconducting YBCO/cubic YBCO/superconducting YBCO ramp-edge proximity-effect Josephson junctions were fabricated on MgO substrates. Junctions having critical current densities of ≈8×10 4 A/cm 2 and I c R n products as high as 0.8 mV at 15 K were produced. Shapiro steps were seen in the presence of RF radiation. DC SQUIDs were fabricated with these junctions and showed periodic critical current modulation with applied magnetic field to temperatures in excess of 77 K.

Epitaxial growth of oxides on semiconductors using fluorides as a buffer layer

The success in epitaxial growth of oxides on Si using an intermediate fluoride layer largely depends on the reactivity of the fluoride with the oxide and the stability of the fluoride against oxidation. The fluoride‐oxide reaction was studied by Rutherford backscattering spectrometry and x‐ray diffractometry. It is found that a large number of oxides are stable on CaF2, while some containing K, Li, and Ba react with CaF2. The results are consistent with thermodynamic predictions, and correlate well with the equalized electronegativity of the oxides. The stability of bare CaF2 on Si is found to be strongly related to the ambient. The CaF2 surface remains intact after annealing at 650 °C in 25% O2/N2, although Ca‐silicate formation takes place at the Si‐CaF2 interface. When annealing is conducted in air, Ca‐carbonate is readily formed at the surface. The results provide guidelines for epitaxial growth of oxides on semiconductor/fluoride structures. The potential application of using fluorides as buffer laye...

High-resolution autostereoscopic immersive imaging display using a monocentric optical system

An autostereoscopic display system was designed and constructed. The design, which uses pupil imaging with a curved mirror, is described. It employs a monocentric configuration to enable a wide field of view and large pupils while keeping the lens diameters small to fit them within the interoccular separation. For each eye, image formation was accomplished using 1920 x 1200 liquid crystal on silicon (LCOS) spatial light modulators in a 3-panel configuration. The design employs custom curved diffusers, which were developed to optimize throughput, contrast, and pupil illumination uniformity.