A NEW TECHNIQUE FOR HIGH TEMPERATURE SUPERCONDUCTING THIN FILM PRODUCTION: PULSED ELECTRON BEAM EVAPORATION IN A PLASMA ENVIRONMENT

THIS PROJECT INVOLVES A NOVEL APPROACH TO PULSED ELECTRON BEAM (E-BEAM) EVAPORATION IN THE PRESENCE OF AN OXYGEN PLASMA FOR THE DEPOSITION OF HIGH TEMPERATURE SUPERCONDUCTING (HTS) THIN FILMS. RECENTLY REPORTED WORK SHOWED THAT SMOOTHER THIN FILMS OF YBA2CU3OX CAN VE DEPOSITED USING PULSED LASER EVAPORATION. INDEPENDENT WORK USING MOLECULAR BEAM EPITAXY TECHNIQUES DEMONSTRATED THAT THE PRESENCE OF ATOMIC OXYGEN IN SITU DURING FILM DEPOSITIONIS ONE KEY TO LOWERING THE REQUIRED SUBSTRATE AND ANNEAL TEMPERATURES FROM THE 850 DEGREES TO 900 DEGREES CENTIGRADE RANGE. THIS PROJECT ADOPTS A NOVEL APPROACH. IT WILL USE APULSED E-BEAM THAT IS ALREADY OPERATIONAL AND HAS 75 KV BEAMENERGY, UP TO 1,000 A CURRENT, AND 1 US PULSE WIDTH (WITH BEAM DIAMETER ON TARGET OF UNDER 1 CM YIELDING ABOUT 100 J/CM(2) OR 10(8) W/CM(2)) TO FLASH EVAPORATE YBA2CU3OX PELLETS FOR DEPOSITION ON HEATED SUBSTRATES. THIS POWER DENSITY IS COMPARABLE TO THAT REPORTED USING LASERS FOR PULSED EVAPORATION. THE E-BEAM SYSTEM IS EFFICIENT (ABOUT 80%), THE ELECTRONS HAVE LONG RANGE (10 TO 20 UM) COMPARED TO LASERS, AND THE COUPLING EFFICIENCY TO THE MATERIAL TARGET IS ESSENTIALLY 100%. THE GREATER RANGE SHOULD RESULT IN A SMOOTHER EVAPORATION PROCESS AS COMPARED TO THE "EXPLOSIVE" EVAPORATION REPORTED UNDER CERTAIN CONDITIONS OF LASER ABLATION. OTHER KEY ADVANTAGES OF THIS APPROACH INCLUDE PULSED EVAPORATION OF THE MATERIAL IN THE PRESENCE OF PLASMA; THIS IN TURN PRODUCES ATOMIC OXYGEN ATOMS AND IONS (AS WELL AS O2). PHASE I WILL DEVELOP THE OPERATION OF THIS UNIQUE PULSED E-BEAM PLUS A PLASMA ARRANGEMENT TO EVAPORATE HTS MATERIAL AND FORM THIN FILMS ONSUBSTRATES. THE FILMS WILL BE CHARACTERIZED BY RUTHERFORD BACKSCATTERING SPECTROMETRY TO DETERMINE THE STOICHIOMETRY. AFTER AN ANNEAL, THE RESISTIVITY VERSUS TEMPERATURE WILL BE DETERMINED WITH A FOUR-POINT PROBE.