Electronic Properties of MoS₂ Nanoparticles

Abstract

We present a first principle, theoretical study of MoS2 nanoparticles that provides a unified explanation of measured photoluminescence spectra and recent STM measurements as a function of size. In addition, our calculations suggest ways to engineer the electronic properties of these systems so as to obtain direct band gap 3D layered nanoparticles or Mo doped metallic nanowires. In particular, we show that single sheet MoS2 nanoparticles up to ∼3.4 nm show no appreciable quantum confinement effects. Instead, their electronic structure is entirely dominated by surface states near the Fermi level. In 3D nanoparticles, we found a strong dependence of their electronic properties on layer stacking and distance, and we suggest that the observed photoluminescence variation as a function of size originates from the number of planes composing the system. The number of these planes and their distance can be tuned to engineer clusters with direct band gaps, at variance with the bulk. Our results also suggest ways to take advantage of surface states to design metallic nanowires with novel catalytic and thermoelectric properties.

Origin of Indirect Optical Transitions in Few-Layer MoS2, WS2, and WSe2

“…This trend leads to indirect-to-direct gap crossover at a large interlayer spacing. 29 Similar to reducing the number of layers, increasing interlayer spacing results in upshift of the Λ valley and downshift of the Γ hill. These regions of the band structure describe wave functions that decay slowly outside the plane of MX 2 sandwich.…”

Electronics and optoelectronics of two-dimensional transition metal dichalcogenides

“…Many TMDCs have band structures that are similar in their general features, as shown by first principles and tight-binding approximations 25,[80][81][82][83][84][85] and measured using a variety of spectroscopic tools 31,32,[86][87][88][89] . In general, MoX 2 and WX 2 compounds are semiconducting whereas NbX 2 and TaX 2 are metallic 25,[80][81][82][83][84] .…”

“…In general, MoX 2 and WX 2 compounds are semiconducting whereas NbX 2 and TaX 2 are metallic 25,[80][81][82][83][84] . The band structures of bulk and monolayer MoS 2 and WS 2 calculated from first principles are shown in Fig.…”

“…The change in the band structure with layer number is due to quantum confinement and the resulting change in hybridization between p z orbitals on S atoms and d orbitals on Mo atoms 31,32,81 . The electronic distributions are also spatially correlated to the atomic structure 32 .…”

Graphene is not alone

“…They have a very similar appearance to graphite and have applications primarily in solid lubricants. In the single-layer form some of these materials, such as molybdenum disulphide (a ball-and-stick model is shown; molybdenum, blue; sulphur, yellow), are direct bandgap semiconductors 3,4 , which could have important implications for their use in electronic devices.…”