Fabrication of Organic Dye-Coated High-TC Superconductor Optical Devices: Interface Chemistry and Properties
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751 Mat. Res. Soc. Symp. Proc. Vol. 328. @1994 Materials Research Society
increases the responsivity of the device to light relative to that of the uncoated superconductor element. Response enhancements are greatest at those wavelengths which are absorbed most strongly by the dye6 . Since a large number of dyes can be deposited onto the high-Tc structures, a variety of systems can be prepared with tailored spectral response characteristics. In this regard, we have prepared dye/superconductor systems that respond selectively to red, green, and blue light. In order to further develop this important new area of research, it is now necessary to study issues related to the chemical compatibility of the molecular compounds with the high-Tc materials. Although it has been known for some time now that cuprate phases degrade rapidly when in the presence of water, carbon dioxide, carbon monoxide, and acidsl 0 ' 1 1, very little information is known regarding the chemical compatibility of molecular and superconductor materials. Thus, the focus of the paper will be placed on analysis of dye/superconductor interface reactions which occur during the fabrication of dye/superconductor optical sensors. EXPERIMENTAL Thin films of YBa2Cu3O7-8 were deposited on polished MgO substrates using the laser ablation method 1 2,13 . Microbridge or "meandering path" junctions were patterned on the YBa2Cu3O7-8 thin films either by laser ablation etching 14 or by diamond scribe etching. The organic dyes, chloroaluminum phthalocyanine[Strem], H2-phthalocyanine [Strem], and H2octaethylporphyrin [Aldrich], were purified by acid pasting or sublimation and were deposited onto the junction area by sublimation. Electrical measurements were made using the Van der Pauw geometry (i.e. 4 contacts at the corners of the film) with gold, palladium, or silver contacts, which were sputter-coated onto the films. The optical and electrical measurements were carried out in a closed-cycle helium cryostat equipped with a quartz optical window. Optical measurements were completed using a mechanically chopped monochromatic light beam which originated from either a quartz-tungsten-halogen lamp or a xenon arc lamp. Using a dc biased current close to the critical current, the in-phase voltage that developed across the junction was sensed with a lock-in amplifier. RESULTS In order to create molecular dye/HTSC optical sensors the steps outlined in Figure 1 were utilized. Important for the fabrication of such systems is the avoidance of interface reactions between the dye and the superconductor components. In the first step, a YBa2Cu3O7-5 film is deposited onto a clean MgO (100) substrate using the laser ablation method. By varying the number of laser pulses, film thickness values in the range of 500 to 2000A are obtained. After deposition, the film must be patterned to create regions of weak electrical contact in the superconductor film. Superconductivity is more easily modulated in these weak link structures making the system more sensitive to the influence of light. Th
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