Intrinsic properties of suspended MoS2 on SiO2/Si pillar arrays for nanomechanics and optics

TL;DR

This study investigates the intrinsic properties of suspended MoS2 membranes on pillar arrays, demonstrating control over strain and doping, high-quality optomechanical resonators, and methods for tuning optical and mechanical properties at the nanoscale.

Contribution

It introduces a novel approach to control and analyze strain, doping, and optical emissions in suspended 2D MoS2 on periodic pillar arrays, enabling reproducible nanomechanical and optoelectronic devices.

Findings

High-quality resonators with Q-factor of 600 at room temperature.

Strong strain-induced band-gap reduction and direct-to-indirect transition.

A simple method to extract local strain from Raman spectra.

Abstract

Semiconducting 2D materials, such as transition metal dichalcogenides (TMDs), are emerging in nanomechanics, optoelectronics, and thermal transport. In each of these fields, perfect control over 2D material properties including strain, doping, and heating is necessary, especially on the nanoscale. Here, we study clean devices consisting of membranes of single-layer MoS2 suspended on pillar arrays. Using Raman and photoluminescence spectroscopy, we have been able to extract, separate and simulate the different contributions on the nanoscale and to correlate these to the pillar array design. This control has been used to design a periodic MoS2 mechanical membrane with a high reproducibility and to perform optomechanical measurements on arrays of similar resonators with a high-quality factor of 600 at ambient temperature, hence opening the way to multi-resonator applications with 2D materials. At the same time, this study constitutes a reference for the future development of well-controlled optical emissions within 2D materials on periodic arrays with reproducible behavior. We measured a strong reduction of the MoS2 band-gap induced by the strain generated from the pillars. A transition from direct to indirect band gap was observed in isolated tent structures made of MoS2 and pinched by a pillar. In fully suspended devices, simulations were performed allowing both the extraction of the thermal conductance and doping of the layer. Using the correlation between the influences of strain and doping on the MoS2 Raman spectrum, we have developed a simple, elegant method to extract the local strain in suspended and non-suspended parts of a membrane. This opens the way to experimenting with tunable coupling between light emission and vibration.