The development of quantum electronics depends
mainly on the development of nano-processing.
STM has been a powerful tool for nano-processing.
Before, the exposure of PMMA with STM could only
be done in unltra high vacuum. The problem for
exposure of PMMA under ambient condition is the
unstability of the tip at tunnel condition. We used
two measures to attack the problem:(l)adopted special
procedure to prepare the W tip. After the formation
of the tip, the tip was further etched for Is;(2)first let
the system go into tunnel condition at lower voltage
then raised the voltage to exposure value gradually.
After these two mwasures, the tip could be stablized
under ambient condition. Afterwards, we used three
set of labels to approach gradually from large area to
small area to locate the exposure region. Finally, we
have exposed 20nm thick of PMMA under ambient
cdndition with STM and have obtained lines of 300nm
linewidth.