Ultrafast Laser Ablation, Intrinsic Threshold, and Nanopatterning of Monolayer Molybdenum Disulfide

TL;DR

This paper investigates femtosecond laser ablation of monolayer MoS₂, revealing substrate effects, proposing an intrinsic ablation threshold, and demonstrating high-resolution patterning with potential for scalable manufacturing.

Contribution

It uniquely shows that ablation is an adiabatic process unaffected by substrate thermal coupling, introduces an intrinsic threshold, and demonstrates rapid, high-resolution patterning of monolayer MoS₂.

Findings

Ablation is an adiabatic process with negligible heat transfer.

Substrate effects are due to the etalon effect, not thermal coupling.

Femtosecond laser patterning achieves sub-micron resolution at mm/s speeds.

Abstract

Laser direct writing is an attractive method for patterning 2D materials without contamination. Literature shows that the femtosecond ablation threshold of graphene across substrates varies by an order of magnitude. Some attribute it to the thermal coupling to the substrates, but it remains by and large an open question. For the first time the effect of substrates on femtosecond ablation of 2D materials is studied using MoS$_{2}$ as an example. We show unambiguously that femtosecond ablation of MoS$_{2}$ is an adiabatic process with negligible heat transfer to the substrates. The observed threshold variation is due to the etalon effect which was not identified before for the laser ablation of 2D materials. Subsequently, an intrinsic ablation threshold is proposed as a true threshold parameter for 2D materials. Additionally, we demonstrate for the first time femtosecond laser patterning of monolayer MoS$_{2}$ with sub-micron resolution and mm/s speed. Moreover, engineered substrates are shown to enhance the ablation efficiency, enabling patterning with low-power femtosecond oscillators. Finally, a zero-thickness approximation is introduced to predict the field enhancement with simple analytical expressions. Our work clarifies the role of substrates on ablation and firmly establishes femtosecond laser ablation as a viable route to pattern 2D materials.