Exposure of PMMA with STM under ambient condition

The development of quantum electronics depends mainly on the development of nano-processing. STM is a powerful tool for nano-processing. Before, the exposure of PMMA with STM could only be done in ultra high vacuum. The problem for exposure of PMMA under ambient conditions is the instability of the tip at tunnel conditions. We used two measures to attack the problem: (1) We adopted a special procedure to prepare the W tip. After the formation of the tip, it was further etched for 1s; (2) We first let the system go into tunnel condition at lower voltage then raised the voltage to exposure value gradually. After these two measures, the tip could be stabilized under ambient conditions. 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 20 nm thick PMMA layers under ambient conditions with STM and have obtained lines of 300 nm linewidth