SURFACE MODIFICATION OF YBA2CU3O7-DELTA THIN-FILMS USING THE SCANNING TUNNELING MICROSCOPE - 5 METHODS

We have investigated using the scanning tunneling microscope (STM) as a tool for surface modification of YBa2Cu3O7-delta (YBCO) thin films and have identified five distinct methods whereby the STM tip can modify the superconductor surface. (i) By lowering the tunneling resistance we make the tip scratch or 'mill' the sample surface mechanically. (ii) By increasing the bias voltage above about 4 V we can modify the surface by an apparent electron beam damaging process. (iii) By increasing the bias voltage above 10 V and raising the tunneling current, we can cause a more dramatic effect which is probably due to a thermal process. (iv) By operating the STM in a damp carbon dioxide atmosphere we can cause the STM tip to etch the surface electrochemically. (v) Finally, we have some preliminary data suggesting that the high field under an extremely sharp tip displaces the oxygen atoms in the YBCO lattice. Examples of each of these techniques are shown and discussed.