X-ray calibrated tunneling system utilizing a dimensionally stable nanometer positioner

Abstract

To determine to what extent tunneling probes can be used for metrology or as position-sensitive transducers on the atomic scale, accurate characterization of tunneling current as a function of distance must be ascertained. This report describes a system for making such characterizations and observing their repeatability in air. Also, it is often necessary to position two objects to within nanometers in order to perform precision measurements. Included in the narrative, a dimensionally stable screw-wedge-lever system is described for manually moving a tunneling probe to within 15 nm of a conducting surface. The conducting surface is translated via a magnetically actuated single crystal flexure system previously calibrated through direct x-ray interferometry over a 20-nm range. This limited calibration range dictated dimensional positioning below 15 nm. Also, tunneling current measurements demanded dimensional stability below one nanometer. The complete system is demonstrated to hold the relative probe-surface separation to within 1 nm over a 15-minute duration. Also, the vibrational resonance of the structure is determined using the power spectrum analysis during electron tunneling. Resulting data using platinum, palladium, and silver tips in conjunction with a carbon surface show that current-displacement values vary from run to run with a positional difference of up to 1 nm for a given current. These variations suggest limitations for using tunneling probes in air to perform angstrom metrology.