IMPROVEMENTS IN THE PROPERTIES OF ELECTRON-BEAM DAMAGE YBA2CU3O7-DELTA JUNCTIONS

We have considerably improved the properties of our electron beam dama ge junctions by using a smaller condenser aperture. The better defined beam results in a more concentrated damage profile, Consequently, the junctions have a more resistive barrier and higher current density co mpared to junctions fabricated with a large aperture, We can now obtai n an IcRn value of 2 mV up to a temperature of 50 it. The improved jun ctions have barriers with T-cn=0 K, and consequently operate over a mu ch wider temperature range. Using the small aperture we have varied th e length of the barrier while keeping its resistivity constant. The ex ponential variation of the critical current of these junctions with le ngth shows that they have an SNS-character with the decay length varyi ng between 3 and 4 nm.