A step-by-step workflow to extract the genuine circular dichroism of thin films

TL;DR

This paper introduces a two-step workflow combining sample rotation and flipping to accurately measure genuine circular dichroism in anisotropic thin films, addressing artifacts from optical anisotropy and instrument imperfections.

Contribution

It presents a novel, reliable method and a custom sample stage to isolate true CD signals in thin films, with detailed setup and Python code provided.

Findings

Workflow effectively suppresses anisotropy-induced artifacts

Demonstrated on chiral molecules on metallic surfaces

Validated on metal halide perovskite samples

Abstract

Circular Dichroism (CD) spectroscopy has evolved from a purely solution based method towards a powerful tool in the analysis of chiral thin films. Although a straightforward technique, the genuine CD signal is often accompanied by artifacts arising from optical anisotropy and instrumental imperfections. This tutorial presents a two-step workflow that reliably isolates the orientation invariant CD response for anisotropic thin films by combining azimuthal sample rotation with sample flipping. For this purpose, a home-built sample stage was developed, which enables systematic suppression of many anisotropy-induced artifacts in commercial CD spectrophotometers. Both a detailed description of the setup itself as well as the needed python script are provided. The reliability of the workflow is demonstrated on two selected samples from different research fields: chiral molecules attached to metallic surfaces as well as metal halide perovskites incorporating chiral spacer molecules