Feedback control for scanning tunnel microscopes

Abstract

A feedback control system for enhancing the feedback loop characteristics of a vertical axis control in a scanning tunneling microscope or the like, including a tip member for positioning relative to a surface for measuring the topography of the surface. A horizontal control coupled to the tip for providing a plurality of adjacent horizontal scans across the surface. A vertical control coupled to the tip for providing a vertical control of the tip during the plurality of adjacent horizontal scans. A local error signal produced in accordance with the vertical position of the tip relative to the surface in real time during the plurality of adjacent horizontal scans. A storage member responsive to the local error signal for storing the local error signal for producing a delayed error signal representing the vertical position of the tip relative to the surface at an earlier time, and a vertical tip control signal coupled to the vertical control and formed by combining the local error signal and the delayed error signal for enhancing the control of the vertical position of the tip.