THz time-domain spectroscopic investigations of thin films

TL;DR

This paper advances THz time-domain spectroscopy techniques for analyzing ultra-thin films, focusing on high-precision measurement and data analysis methods for layered samples, including applications in cultural heritage.

Contribution

It introduces a novel experimental and data analysis procedure for accurately characterizing thin films using THz spectroscopy, applicable to both single and multi-layer samples.

Findings

Successful measurement of micrometric thin films

Effective disentangling of multiple reflections in data

Extraction of material parameters with high accuracy

Abstract

THz time domain spectroscopy is a powerful technique enabling the investigation of different materials in the far-infrared frequency range. Even if nowadays this technique is well established, its application to very thin films remains particularly difficult. We investigated the utilization of THz spectroscopy on samples of micrometric thickness with the aim to disentangle multiple reflections and to measure with high accuracy the absolute values of the material parameters. We implemented an experimental and data analysis procedure that can be applied to free-standing single-layers or multi-layers samples. Specifically, we report on the experimental investigation by THz time domain spectroscopy of two samples: a test sample made of two layers of known thickness and materials; and a second sample, that is of a great interest for cultural heritage studies, made of a thin film of ink layered on a thicker support. Moreover, we describe in details the data analysis and fitting procedures needed to extract the material parameters from the experimental results.