Kavli Affiliate: Ke Wang
| First 5 Authors: Aleksandar Radic, Nick von Jeinsen, Ke Wang, Yiru Zhu, Ismail Sami
| Summary:
Sulfur vacancy defects mediate a wide range of optoelectronic properties in
MoS2, with precise control of defect density allowing for tuneable
optoelectronic devices. However, accurate measurement of defect density in
monolayer and few-layer samples poses a challenge due to their small scattering
cross-sections to photon or electron probes. Conventional lab-based techniques
such as Raman and photoluminescence can infer approximate defect density in
micro-scale samples via optoelectronic properties, but they require validation
using stoichiometric beam-line XPS. We introduce an ultra-low energy (~64 meV)
and non-intrusive lab-based technique to quantify the surface defect density in
micron-scale monolayer MoS2. Here we show that a recently developed technique,
helium atom micro-diffraction (referred to as scanning helium microscopy (SHeM)
in literature), can be used to directly measure vacancy-type defect density in
2D materials by performing atom diffraction from a microscopic spot. SHeM uses
a neutral, inert, and thermal energy probe of helium-4 atoms to measure ordered
and disordered atom-surface scattering allowing the level of surface order to
be inferred. The presented method enables rapid, non-damaging, and
material-agnostic lab-based quantification of defect density in 2D materials, a
crucial step towards the wider adoption of 2D semiconductors in devices.
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