Fabrication and characterisation of inorganic monolayers for semiconductors and devices

Abstract

Monolayers derived from layered materials exhibit electrical, magnetic and optical properties radically different to the bulk. Therefore, industrially-viable methods for fabrication of layered materials from precursors will find application in fields as diverse as electronics, fuel cells and light technology. In this thesis, several new avenues for 2D materials synthesis are explored.

A novel synthetic method for highly-crystalline micron-sized domains of monolayers of phase-pure MoS2 by liquid atomic layer deposition (ALD). Single-crystalline MoS2 with domain sizes up to 100 μm (among the largest reported) and an area of ~5,000 μm2 is demonstrated and proved by optical and electron microscopy, Raman spectroscopy and photoluminescence (PL) characterisation. The new process combines liquid chemistry with discrete, layer-by-layer deposition of precursors for the first time. The quality of MoS2 is comparable to that obtained by chemical vapour deposition (CVD). Hence, this method for MoS2 production potentially provides a low-cost and large-scale route to 2D materials. An application for the technique is presented, involving development of an MoS2—WS2 heterostructure, aiming to exploit the unique optical properties of heterostructured materials in type II band alignment. A high-quality heterostructure is demonstrated, exhibiting good vertical coverage of the overlayer, as shown by XRD and Raman spectroscopy.

Hydroxide-mediated liquid exfoliation of SnS2 is presented as a safe, high-quality alternative to lithium-ion intercalation. The resulting SnS2 nanoflakes are shown to be monolayer and of good crystallinity, by optical microscopy (OM), Raman spectroscopy and x-ray diffraction (XRD).

The application of AFM to fundamental study of interlayer van der Waals (vdW) forces in layered materials is explored by combining the technique with liquid exfoliation.

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Identifiers

ORCID for Iris S. Nandhakumar: orcid.org/0000-0002-9668-9126

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