Nanomechanical absorption spectroscopy of 2D materials with femtowatt sensitivity

TL;DR

This paper introduces a highly sensitive nanomechanical spectroscopy method for 2D materials, achieving femtowatt sensitivity and simplifying the process, enabling detailed optical absorption measurements at nanoscale with practical advantages.

Contribution

The authors develop a protocol for nanomechanical spectroscopy of 2D materials with two orders of magnitude improved sensitivity and simplified experimental setup using electrical actuation and low-stress membranes.

Findings

Achieved femtowatt sensitivity in nanomechanical absorption spectroscopy.

Successfully characterized WS₂, CrPS₄, and gold nanoparticle supercrystals.

Demonstrated advantages over conventional optical methods in 2D material analysis.

Abstract

Nanomechanical spectroscopy (NMS) is a recently developed approach to determine optical absorption spectra of nanoscale materials via mechanical measurements. It is based on measuring changes in the resonance frequency of a membrane resonator vs. the photon energy of incoming light. This method is a direct measurement of absorption, which has practical advantages compared to common optical spectroscopy approaches. In the case of two-dimensional (2D) materials, NMS overcomes limitations inherent to conventional optical methods, such as the complications associated with measurements at high magnetic fields and low temperatures. In this work, we develop a protocol for NMS of 2D materials that yields two orders of magnitude improved sensitivity compared to previous approaches, while being simpler to use. To this end, we use electrical sample actuation, which simplifies the experiment and provides a reliable calibration for greater accuracy. Additionally, the use of low-stress silicon nitride membranes as our substrate reduces the noise-equivalent power to $NEP = 890 fW/\sqrt{Hz}$, comparable to commercial semiconductor photodetectors. We use our approach to spectroscopically characterize a two-dimensional transition metal dichalcogenide (WS$_2$), a layered magnetic semiconductor (CrPS$_4$), and a plasmonic supercrystal consisting of gold nanoparticles.