Direct and Scalable Chemical Vapor Deposition of Ultrathin Low-Noise MoS2 Membranes on Apertures

TL;DR

This paper introduces a novel substrate-free, reagent-limited chemical vapor deposition method for directly growing ultrathin, low-noise MoS2 membranes across apertures, enabling contamination-free 2D crystal fabrication with high quality.

Contribution

It presents a new substrate-free growth mechanism for 2D MoS2 membranes, allowing direct, selective, and contamination-free fabrication across apertures without transfer processes.

Findings

Successful direct growth of freestanding MoS2 membranes across apertures

Membranes exhibit atomic-layer thickness and high structural quality

Low-noise ion-current recordings demonstrate membrane suitability for nanopore applications

Abstract

We show that atomically thin molybdenum disulfide (MoS2) crystals can grow without any underlying substrates into free-standing atomically-thin layers, maintaining their planar 2D form. Using this property, we present a new mechanism for 2D crystal synthesis, i.e. reagent-limited nucleation near an aperture edge followed by reactions that allow crystal growth into the free-space of the aperture. Such an approach enables us, for the first time, the direct and selective growth of freestanding membranes of atomically thin MoS2 layers across micrometer-scale pre-fabricated solid-state apertures in SiNx membranes. Under optimal conditions, MoS2 grows preferentially across apertures, resulting in sealed membranes that are one to a few atomic layers thick. Since our method involves free-space growth and is devoid of either substrates or transfer, it is conceivably the most contamination-free method for obtaining 2D crystals reported so far. The membrane quality was investigated using atomic-resolution transmission electron microscopy, Raman spectroscopy, photoluminescence spectroscopy, and low-noise ion-current recordings through nanopores fabricated in such membranes.