# Air tightness of hBN encapsulation and its impact on Raman spectroscopy of van der Waals materials

## TL;DR

This study demonstrates that hBN encapsulation effectively prevents oxidation of van der Waals materials during Raman spectroscopy, highlighting the importance of proper encapsulation for non-invasive characterization.

## Contribution

It provides new insights into how hBN encapsulation impacts the preservation of van der Waals materials during Raman analysis, emphasizing the need for full encapsulation.

## Key findings

- Oxidation occurs in ambient conditions during Raman spectroscopy.
- Full hBN encapsulation prevents oxidation of NbSe2.
- Partial encapsulation is insufficient to block oxygen diffusion.

## Abstract

Raman spectroscopy is a precious tool for the characterization of van der Waals materials, e.g. for the determination of the layer number in thin exfoliated flakes. For sensitive materials, however, this method can be dramatically invasive. In particular, the light intensity required to obtain a significant Raman signal is sufficient to immediately photo-oxidize few-layer thick metallic van der Waals materials. In this work we investigated the impact of the environment on Raman characterization of thin NbSe$_2$ crystals. We show that in ambient conditions the flake is locally oxidized even for very low illumination intensity. On the other hand, we observe no degradation if the Raman measurements are performed either in vacuum or on fully hBN-encapsulated samples. Interestingly, we find that covering samples deposited on the usual SiO$_2$ surface only from the top is not sufficient to prevent diffusion of oxygen underneath the layers.