Control of a micro tunneling unit under atomic force

We have previously reported the development and operation of a lateral tunneling unit (LTU), a micromachined device which can control the magnitude of a tunneling current passing through a vacuum gap by adjusting the distance of the gap. The amplitude of the actuator driving voltage necessary to vary the current certain range was much larger than the theoretically expected value. Its cause has been left unclear. We carried out experiments in the air and in ultrahigh vacuum (UHV), in order to determine the mechanism of the disagreement. The results of them indicated that an atomic force affects the behavior of the LTU. The estimated magnitude of the force was so large as not to be neglected compared with the actuation force of the LTU. We increased the rigidity and actuation force over 50 times and achieved stabilization. A guide to design a stable LTU and its controller will be given based on the experimental results