Temperature and power dependent photothermal properties of single-layer MoS2
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ix, 57 pages
DepartmentTowson University. Department of Physics, Astronomy, and Geosciences
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The discovery of graphene, nearly a decade ago [1, 2, 3], has since given interest into other atomically thin, two-dimensional (2D) crystals. One such material is mono-layer molybdenum disulphide (MoS2). Electronic device manufactures in particular have found 2D materials such as MoS2 interesting because of the physical and electronic properties. MoS2 can be fashioned into electronic components such as field-effect transistors (FETs) or logic gates easily and are particularly thin. This interest means MoS2 must be understood from an electronic and physical perspective before it can fully be integrated into electronic devices. To understand MoS2 better a comprehensive power and temperature dependent study on MoS2 was done using both Raman and photoluminescent spectroscopies. Mechanical ex-foliation of MoS2 from bulk provides single-layer flakes, which are then transferred either to sapphire substrates or suspended over holes in Si/Si3N4. We measure temperature dependence from ~~100K to 400K and power dependence from ~~6 uW to ~~7mW using an Argon laser at 514.5nm and a HeNe laser at 632.8 nm. Raman spectroscopy was used for initial identification of a single-layer flake of MoS2. In MoS2 when the two Raman peaks, the A1g and E1 2g are less than 18 cm-1 the flake is considered single layer. The thermal conductivity of MoS2 was experimentally extracted from Raman temperature and power measurements using linear coefficients, xT and xP , for temperature and power dependence of the peak position respectively. This value of thermal conductivity K was calculated to be ~~34.5 Wm-1 K-1. Temperature and power dependent photoluminescent (PL) spectroscopy was used to explore the band-gap and energy transitions of MoS2. The PL spectrum exhibits a main exitonic peak (A) at ~~1.87 eV, which consist of both neutral excitons and charged trions (A-or A+). The photothermal properties of a material are important when a material is going to be used in electronic devices. The materials thermal conductivity is important for proper heat management in a device. This work reports thermal conductivity along with important insight into the band-gap. All of this information about the photothermal reaction of the material is necessary before MoS2 can be implemented into electronic devices.