Optical Fingerprint of Flat Substrate Surface and Marker-free Lateral Displacement Detection with Angstrom-level Precision

TL;DR

This paper introduces a novel optical fingerprinting method using speckle patterns from flat substrates, enabling marker-free, high-precision lateral displacement detection with 0.22 nm accuracy, useful for nanotechnology and microscopy.

Contribution

It presents a new approach to generate and utilize optical fingerprints from speckle patterns for reproducible position identification and ultrasensitive displacement measurement.

Findings

Reproducible optical fingerprints can identify specific substrate areas.

Displacement detection precision achieved is 0.22 nm.

Method applicable to semiconductor and super-resolution microscopy.

Abstract

We report that flat substrates such as glass coverslips with surface roughness well below 0.5 nm feature notable speckle patterns when observed with high-sensitivity interference microscopy. We uncover that these speckle patterns unambiguously originate from the subnanometer surface undulations, and develop an intuitive model to illustrate how subnanometer non-resonant dielectric features could generate pronounced interference contrast in the far field. We introduce the concept of optical fingerprint for the deterministic speckle pattern associated with a particular substrate surface area and intentionally enhance the speckle amplitudes for potential applications. We demonstrate such optical fingerprints can be leveraged for reproducible position identification and marker-free lateral displacement detection with an experimental precision of 0.22 nm. The reproducible position identification allows us to detect new nanoscopic features developed during laborious processes performed outside of the microscope. The demonstrated capability for ultrasensitive displacement detection may find applications in the semiconductor industry and super-resolution optical microscopy.