An ultra-precision interference comparator for dimensional measurements using two tunnelling microscopes as probes

作者：Koenders L^*; Harms CH; Waltereit E; Wilkening G

来源：Measurement Science and Technology, 2003, 14(7): 943-952.

DOI：10.1088/0957-0233/14/7/307

• scanning tunnelling microscope
• interference comparator
• gauge block

A new kind of high resolution, high accuracy comparator for dimensional measurements and its application for the measurement of the thickness of gauge blocks is presented. This comparator consists of two scanning tunnelling microscopes (STMs) whose tips probe the opposite sides of a sample. The STM tips are fixed on two high quality mirrors that are moved by piezoelectric actuators. The positions of the mirrors are measured by a high resolution laser interferometer, thereby coupling the length measurements to the unit of length. The detection of the sample's surface is performed by the STM probes and utilizes the high dependence of the tunnelling current on the tip-to-sample distance, which follows an exponential function and reaches about 1 nA at a tip-to-sample distance of less than 1 nm. This technique allows one to determine the position of the surface with a higher degree of accuracy than is possible using mechanical or optical probes.
The determination of a distance consists of two consecutive displacement measurements by laser interferometer without and with the sample between the two tunnelling tips. The difference of these measurements corresponds to the object's length once environmental conditions such as temperature and refractivity are taken into account.
In this paper we describe the construction and alignment of the instrument, the optimization of various components and experimental investigations of some parts of the measuring process, show first experimental results of the complete comparator obtained on thin gauge blocks and discuss the uncertainty budget.

• 出版日期2003-7