Open AccessThe influence of crystal thickness and interlayer interactions on the properties of heavy ion irradiated MoS2
Author(s) -
Liam H. Isherwood,
Zachariah Hennighausen,
SeokKyun Son,
Ben F. Spencer,
P. Wady,
S. M. Shubeita,
Swastik Kar,
Cinzia Casiraghi,
Aliaksandr Baidak
Publication year - 2020
Publication title -
2d materials
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.702
H-Index - 72
ISSN - 2053-1583
DOI - 10.1088/2053-1583/ab817b
Subject(s) - materials science , ion , crystal (programming language) , irradiation , raman spectroscopy , analytical chemistry (journal) , spectroscopy , crystallography , chemistry , optics , physics , organic chemistry , chromatography , quantum mechanics , computer science , nuclear physics , programming language
Ion irradiation is a versatile tool to introduce controlled defects into two-dimensional (2D) MoS 2 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 MoS 2 crystals of different thicknesses is mandatory. X-ray photoelectron spectroscopy, electron diffraction and Raman spectroscopy show that thinner MoS 2 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 MoS 2 , compared to bulk crystals, leading to MoO 3 formation. P-doping of MoS 2 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 MoS 2 crystals are shown to be strongly thickness-dependent: in mono- and bilayer MoS 2 , 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 MoS 2 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 MoS 2 . Our results demonstrate that ion irradiation is an effective tool to modulate the electronic, vibrational and structural properties of MoS 2 , which may prove beneficial for practical applications.