The influence of crystal thickness and interlayer interactions on the properties of heavy ion irradiated MoS2. (7th May 2020)

• Record Type: Journal Article
• Authors: Isherwood, Liam H; Hennighausen, Zachariah; Son, Seok-Kyun; Spencer, Ben F; Wady, Paul T; Shubeita, Samir M; Kar, Swastik; Casiraghi, Cinzia; Baidak, Aliaksandr
• Is Part Of: 2D materials. Volume 7:Number 3(2020)
• Publication Date: 2020-05-07
• Subjects: two-dimensional materials -- transition metal dichalcogenides -- nanomaterials -- ion irradiation -- radiation damage -- crystallographic defects -- defect-engineering -- Raman spectroscopy -- x-ray photoelectron spectroscopy -- transmission electron microscopy -- electron diffraction; Graphene -- Periodicals; Materials science -- Periodicals; Nanostructured materials -- Periodicals; 620.115
• DOI: 10.1088/2053-1583/ab817b
• Languages: English
• ISSNs: 2053-1583

Abstract

Abstract: Ion irradiation is a versatile tool to introduce controlled defects into two-dimensional (2D) MoS2 on account of its unique spatial resolution and plethora of ion types and energies available. In order to fully realise the potential of this technique, a holistic understanding of ion-induced defect production in 2D MoS2 crystals of different thicknesses is mandatory. X-ray photoelectron spectroscopy, electron diffraction and Raman spectroscopy show that thinner MoS2 crystals are more susceptible to radiation damage caused by 225 keV Xe + ions. However, the rate of defect production in quadrilayer and bulk crystals is not significantly different under our experimental conditions. The rate at which S atoms are sputtered as a function of radiation exposure is considerably higher for monolayer MoS2, compared to bulk crystals, leading to MoO3 formation. P-doping of MoS2 is observed and attributed to the acceptor states introduced by vacancies and charge transfer interactions with adsorbed species. Moreover, the out-of-plane vibrational properties of irradiated MoS2 crystals are shown to be strongly thickness-dependent: in mono- and bilayer MoS2, the confinement of phonons by defects results in a blueshift of the A 1 g mode. Whereas, a redshift is observed in bulk crystals due to attenuation of the effective restoring forces acting on S atoms caused by vacancies in adjacent MoS2 layers. Consequently, the A 1 g frequency of tri- and quadrilayer crystals is statistically invariant on account oft competition between phonon confinement effects and interlayer interactions. The A 1 g linewidth is observed to decrease in bi- and trilayer crystals after low dose irradiation and is attributed to layer decoupling. This work shows that there is a complex interplay between defect production, crystal thickness and interlayer interactions in MoS2 . Our results demonstrate that ion irradiation is an effective tool to modulate the electronic, vibrational and structural properties of MoS2, which may prove beneficial for practical applications.