Q.Y. Ying

Time-resolved resonant absorption study of 532-nm laser-generated plumes over YBa2Cu3O7 targets

The number densities n(t) of the atomic species produced by pulsed‐laser (532‐nm) interaction with YBaCuO targets were measured using time‐resolved resonant absorption spectroscopy. At ∼5 J/cm2 fluence and 0.8 mm above the target, the peak n(t) ranged from 1013 to 1015 cm−3. The distributions of the normal z‐velocity component could be modeled by Gaussian functions, in agreement with the theory of supersonic nozzle beams and the more recent theory of Knudsen layer formation. Such theoretical fits gave most probable z velocities in the km/s range and Mach numbers as high as 7. Ba‐ion z velocities were better fitted by a 4:7 mix of fast (∼3‐km/s) and slow (∼2‐km/s) components.

Laser patterning and critical current measurements of submicrometer lines of Y-Ba-Cu-O

Superconducting strips of 0.6 μm width were fabricated by direct laser writing on mirror‐like Y‐Ba‐Cu‐O thin films on various substrates. These films were grown by laser deposition without post‐annealing. Laser ablation etching had no effect on the Tc and Jc until the lines were <1 μm wide. The 0.6‐μm‐wide strip showed some degradation of Tc. The critical current densities for all patterned lines were measured to be ∼4×106 A/cm2 at 20 ° K.

Noise measurement of YBa2Cu3O7−x and Ti2Ba2Ca2Cu3O10−x thin films

The noise of YBa2Cu3O7−x and Tl2Ba2Cr2Cu3O10−x thin films in the frequency range from 0.5 Hz to 100 kHz was studied. In the normal state, it was found that 1/f noise dominated, with a magnitude strongly dependent on temperature. In the superconducting state, the noise was only observable at frequencies below 5 Hz with our present setup. Equilibrium thermal fluctuation noise was not observed in these films.

Electrical properties of the interface between YBa2Cu3Ox films and various substrates

The electrical properties of the interfacial layers between YBCO films and various substrates were studied using {ital in} {ital situ} resistivity measurements. It was found that this method is sensitive to even a 10-A-thick interface layer. Moreover, it yields the resistivity of the interfacial layer and the YBCO film during deposition. For yttria-stabilized zirconia, the interface has a very low resistivity. For MgO and sapphire the interface has a high resistivity; SrTiO{sub 3} falls between these two cases. Sapphire shows a large reaction layer and evidence for nucleated growth, which are probably responsible for its relatively poor superconducting properties.

Physics Of In-Situ Laser Deposition Of Superconducting Thin Films

The physics of the in-situ laser deposition process is reviewed. Emphasis will be placed on the use of excimer lasers, and the deposition of YBCO thin films. It will be shown that the laser target interaction conditions, and the properties of the laser generated plume are inducive to the formation of high quality films. In addition to the formation of energetic atomic beams, laser deposition is also highly compatible with reactive deposition which make it suitable for oxide and nitride films. An in-situ diagnostic technique is introduced which is capable of detecting the inter-facial boundary layer between the film and the substrate. It is also shown that post-deposition in-situ oxidation is necessary for the formation of superconducting films.

Laser Induced Deposition of YBa 2 Cu 3 O 7−x Thin Films

We describe here the deposition of the YBaCuO superconducting thin films by the laser evaporation technique. The characterization of this process, and possible optimization with regards to wavelength and pulse duration of the laser will be discus sed.

Y-Ba-Cu-O thin films as high-speed IR detectors

Y-Ba-Cu-O thin film infrared detectors were fabricated and studied with various lasers. Operation of the detector in both the bolometric and nonbolometric modes was investigated at 10 microns with a CO2 laser. In the bolometric mode, the detectivity of the detector at 90 K was 2.1 x 10 to the 8th cm sq rt Hz/W with a response time of 15 microsec, corresponding to a bandwidth of 70 KHz. The speed of the detector in the nonbolometric mode was much faster and was beyond the instrument resolution. With a picosecond N2 laser, the output showed an instrument limited duration of 2 ns. The detectivity could not be determined in the nonbolometric mode due to the extremely low noise. The superconducting film quality is critical to the performance of these detectors.

Plasma-Assisted Laser Deposition of Superconducting Thin Films — A Basic Study

An experimental study of the process of plasma-assisted laser deposition was described. It was found that atomic beams of Y,Ba,Cu, and O were inportant for the in-situ growth of superconducting films. These atomic beams could be modelled very well by a supersonic expansion mechanism. The atomic kinetic energies and their spatial dependence were measured and correlated to the thin film properties.

Laser Evaporation Deposition Of Superconducting And Semiconducting Thin Films

We describe here the deposition of superconducting and semiconducting thin films by the laser evaporation technique. The, characterization of this process, and possible optimization with regards to wavelength and pulse duration of the laser will be discussed. Results of laser interaction experiments will also be described.

Growth of Highly Oriented Cds X Se 1 . X Thin Films By Uv Laser Evaporation Deposition

CdS x Se 1−x thin films have been grown by uv laser-evaporation deposition in a clean vacuum environment. The films have their c-axis perpendicular to the surface, and are optically smooth and homogeneous. These high quality films should be useful in nonlinear integrated optics applications.