Coexisting 1T/2H polymorphs, reentrant resistivity behavior, and charge distribution in MoS2-hBN 2D/2D composite thin films

TL;DR

This study demonstrates the growth and characterization of MoS2-hBN composite thin films exhibiting coexisting polymorphs, reentrant resistivity behavior, and enhanced charge transfer, revealing their potential for novel electronic applications.

Contribution

It introduces a new nanocomposite thin film with coexisting 1T/2H MoS2 polymorphs and unique electrical behaviors, advancing the understanding of 2D material heterostructures.

Findings

Presence of coexisting 1T and 2H MoS2 polymorphs confirmed by Raman, XPS, and HRTEM.

Observation of reentrant semiconductor-metal-insulator transition in the composite.

Enhanced charge transfer and output voltage in nanogenerator devices using the composite film.

Abstract

In view of their immensely intriguing properties, two dimensional materials are being intensely researched in search of novel phenomena and diverse application interests, however, studies on the realization of nanocomposites in the application-worthy thin-film platform are rare. Here we have grown MoS2-hBN composite thin films on different substrates by the pulsed laser deposition technique and made comparative studies with the pristine MoS2 and hBN films. The Raman, XPS and HRTEM confirm the concomitant presence of both the 1T (conducting) and 2H (semiconducting) polymorphs of MoS2 in the composite film. Interestingly, a peculiar reentrant semiconductor-metal-insulator transition is seen in the composite film which is absent in the MoS2 film, and it correlates well with the signatures of phonon softening seen in temperature-dependent Raman spectroscopy. Furthermore, electrostatic force microscopy reveals the presence of three distinct regions (metallic, semiconducting, and insulating) in the composite film with differing contact potentials and enhanced propensity for charge transfer with respect to pristine MoS2. A triboelectric nanogenerator device containing biphasic composite film as an electron acceptor exhibits more than twofold (sixfold) enhancement in peak-to-peak output voltage as compared to the pristine MoS2 (hBN) film. These observations bring out the potential of nanocomposite thin films for unfolding emergent phenomena and technological applications.