Calibration of nanosensors with direct traceability to the meter

Abstract

Nanosensors are a new class of sensors that has recently appeared. These sensors are characterized by nanometer or sub-nanometer resolution over a range of at least several micrometers. The most well known examples are capacitive and inductive sensors but also laser interferometers, holographic scales, and scanning probe microscopes (SPM's) belong to the class of nanosensors. The accuracy of these nanosensors is not necessarily of the same level as the resolution. Effects like sensitivity errors, non-linearity, hysteresis and drift may cause deviations of many nanometers. In order to determine these errors in a traceable way, a new measuring instrument was developed. The heart of the system is a Fabry-Perot interferometer, which consists of two parallel mirrors separated by a distance L from each other. Light of a so-called slave laser is directed into this Fabry-Perot cavity and stabilized to the cavity length L. When one of the mirrors of this cavity is displaced the frequency of the slave-laser will follow its movement. The frequency of this slave-laser is then compared to the frequency of a primary length standard. In this way the displacement of the mirror is measured. When a nanosensor is placed on top of the mirror it will also follow the movement of the mirror. In this way the nanosensor is calibrated. The range of the instrument is 300 micrometers and the uncertainty is approximately 1 nm. Measurements of different sensors, such as an inductive and a capacitive sensor as well as a laserinterferometer will be presented. A detailed description of the uncertainty budget will also be given.