Submicron deformation field measurements: Part 1. Developing a digital scanning tunneling microscope

A new experimental method has been developed for studying deformations of micromechanical material systems at the submicron scale. To that end, a special digital scanning tunneling microscope (STM) was designed to be coupled to a mechanically deforming specimen. Operating in constant current mode, this digitally controlled STM records detailed topographies of specimen surfaces with a resolution of 10 nm in-plane and 7 nm out-of-plane over a 10 μ × 10 μ area. Three-dimensional displacement field information is extracted by comparing topographies of the same specimen area before and after deformation by way of a modified digital image correlation algorithm. The resolution of this (combined) displacement measuring method was assessed on translation and uniaxial tensile tests to be 5 nm for in-plane displacement components and 1.5 nm for out-of-plane motion over the same area. This is the first paper in a series of three in which the authors delineate the main features of this specially designed microscope and describe how it is constituted, calibrated and used with the improved version of the digital image correlation method to determine deformations in a test specimen at the nanoscale.