Kavli Affiliate: Ke Wang
| First 5 Authors: Chenyang Zhao, Chenyang Zhao, , ,
| Summary:
Two-dimensional (2D) transition metal dichalcogenides (TMDs), such as MoS2,
have the potential to be widely used in electronic devices and sensors due to
their high carrier mobility and tunable band structure. In 2D TMD devices,
surface and interface cleanness can critically impact the performance and
reproducibility. Even sample surfaces prepared under ultra-high vacuum (UHV)
can be contaminated, causing disorder. On such samples, trace levels of
submonolayer contamination remain largely overlooked, and conventional surface
characterisation techniques have limited capability in detecting such
adsorbates. Here, we apply scanning helium microscopy (SHeM), a non-destructive
and ultra-sensitive technique, to investigate the surface cleanness of 2D MoS2.
Our measurements reveal that even minute amounts of adventitious carbon induce
atomic-scale disorder across MoS2 surfaces, leading to the disappearance of
helium diffraction. By tracking helium reflectivity over time, we quantify the
decay of surface order across different microscopic regions and find that flat
areas are more susceptible to contamination than regions near edges. These
findings highlight the fragility of surface order in 2D materials, even under
UHV, and establish SHeM as a powerful tool for non-damaging microscopic 2D
material cleanness characterisation. The approach offers a new route to
wafer-scale characterisation of 2D material quality.
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