Optoelectronic and thermal properties of metallic transition metal dichalcogenides
Author(s)
Advisor
Kasırga, Talip SerkanDate
2020-11Publisher
Bilkent University
Language
English
Type
ThesisItem Usage Stats
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Abstract
After the successful isolation of graphene monolayer from its bulky counterpart,
there has been tremendous advancement in the field of 2D material. Transition metal dichalcogenides(TMDCs) is family of 2D materials comprising of a
transition metal atom sandwiched between two chalcogen atoms. Photoresponse
of semiconducting TMDCs has been studied extensively in literature. However,
photoresponse from metallic TMDCs is unprecedented and hence has not been
studied to explore which mechanism might prevail. Among our findings, we discovered that photocurrent generation through metallic TMDCs is possible and
has a photo-thermal origin. Using scanning photo-current microscopy, we were
able to obtain spatial photocurrent maps for both, zero biased and biased samples. At zero applied bias, the photocurrent generation is localized to metal-metal
junction and governed by Seebeck effect. At finite applied bias, photocurrent
from the whole crystal is observed and is due to photobolometric effect. As
Photo-bolometric effect relies on photo-thermally induced resistance change of
the material, we extended our study to extract thermal conductivity of metallic TMDCs via bolometric effect. As contact of crystal with substrate act as a
heat sink, we used suspended crystals over a hole to thermally isolate it from
any heat sink. Resistance change via laser induced heating is experimentally
measured at the center of the suspended part of crystal. Measured resistance
change is matched with expected resistance change which is calculated using thermal conductivity(κ) as a fitting parameter via commercially available finite element method package(COMSOL). This way, thermal conductivity of the metallic
TMDCs is calculated with very high accuracy and precision.
Keywords
Opto-electronicsPhoto-current
Seebeck effect
Photo bolometric effect
TMDCs
Thermal conductivity