# Minimizing Extrinsic Effects in High-Pressure Raman of Monolayer WSe2 through Substrate and Pressure-Transmitting Medium Control

## TL;DR

This study shows how to reduce substrate and pressure medium effects when measuring Raman spectra of monolayer WSe2 under high pressure.

## Contribution

The study introduces diamond as a substrate to minimize strain transfer and isolates intrinsic vibrational responses in monolayer WSe2.

## Key findings

- LA-related second-order modes only enhance above 15 GPa with diamond substrates, due to weaker strain coupling.
- Non-uniform strain from non-hydrostatic PTM intensifies these modes rapidly.
- Wrinkles after decompression activate the B2g mode due to local symmetry breaking.

## Abstract

We present a comprehensive study of the Raman spectra
of monolayer
WSe2 under high pressure up to 40 GPa, focusing on the
influence of both the substrate and the pressure-transmitting medium
(PTM). By using diamond as the substrate, which minimizes strain transfer
compared to conventional Si/SiO2, we isolate the intrinsic
vibrational response of monolayer WSe2 from substrate-induced
effects. Our results show that the enhancement of LA-related second-order
modes occurs only at pressures >15 GPa, much higher than in Si/SiO2-supported samples, reflecting the weaker strain coupling
to diamond. However, once the PTM loses hydrostaticity, non-uniform
strain rapidly intensifies these modes. The role of strain-induced
disorder is further evidenced by the appearance of wrinkles after
decompression, which lead to local symmetry breaking and activate
the normally forbidden B2g
mode. Density
functional theory (DFT) calculations indicate that the K-Λ valley
crossover in the conduction band occurs at higher pressures than previously
reported, but still much lower than those required to tune the second-order
modes, thus suggesting that their intensification is predominantly
driven by strain-induced disorder rather than electronic transitions.
These findings provide practical guidelines for minimizing substrate-
and PTM-related artifacts, thereby enabling more accurate and reproducible
high-pressure Raman characterization of two-dimensional materials.