Aerospace & Defense Technology - December 2023 - 34

Tech Briefs
three samples of graphene grown on copper
substrate. For the graphene grown on
the nickel substrate, we exposed the irradiation
dose of 100 krad (1.0 kGy) and
250 krad (2.5 kGy) on sample number
one and two, respectively. On graphene
grown on the copper substrate, we
exposed 125 krad (1.25 kGy), 175 krad
(1.75 kGy), and 265 krad (2.65 kGy) irradiation
on sample number one, two, and
Flow rate
Controllers
Ar
H2
CH4
Reaction Chamber
Pressure Gauge
Heater Stage
Figure 1: A schematic of cold wall resistive heater type CVD system.
Figure 1. Schematic of gas flow in graphene nanoCVD reactor
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three, respectively. These irradiation
doses were used for the first set of irradiations.
Raman spectroscopy and Xray photoelectron
spectroscopy studies were performed
on all samples (unexposed and
exposed). After that, same amount of irradiation
dose was subjected to samples
and Raman spectroscopy and XPS studies
were performed again in order to observe
effect of accumulated irradiation dose.
Purge Gas
To Pump
Purge
Valve
We investigated gamma irradiation
Pressure
Control
Valve
effects on a monolayer of MoS2. We studied
the changes in the physical properties
of MoS2 using Raman spectroscopy and
XPS. The results showed that S defects
dominate at lower irradiation, while Mo
defects appear at higher irradiation doses.
The shifting of Mo 3d and S 2p peaks in
the XPS spectra confirmed the presence
of S and Mo point defects. DFT studies
suggest that, as the gamma irradiation
dose increases, the bandgap decreases,
which implies that gamma radiation-induced
defects degrade the electronic conductivity
of MoS2 monolayer.
This work was performed by Chintan
P. Chavda and Georgios Veronis for
Louisiana State University and the Air
Force Research Laboratory Space Vehicles
Directorate. For more information,
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under the
Materials category.
Process Gasses

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Aerospace & Defense Technology - December 2023

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