Direct observation of a vacuum tunnel gap in a tunneling microscope using a transmission electron microscope

This article reports the observation of the vacuum tunnel gap between two conductors using a high resolution transmission electron microscope. A 2.5-mm-sq micromachined tunneling microscope chip has been fabricated with a minimum feature size of 0.4 μm. The chip fits into a modified side-entry transmission electron microscope holder. The electrostatic actuators and springs are designed to produce a large force which is linear with applied voltage to overcome the forces between the tip and sample. The tunnel gap is controlled by a purpose-built feedback controller. One-dimensional micromachines work reliably during observation of the tip apex in a transmission electron microscope, allowing the voltage and current to be changed while the tunnel gap is observed. Two-dimensional machines that can scan the tip have also been tested and shown to be functional.