This paper reports a comprehensive study of temperature dependence of fluorescence spectroscopy of graphene quantum dots at different excitation wavelengths. Very significant (more than 50%) and similar decrease of normalized spectrum intensity is observed within temperature range less than 80 °C for excitation wavelengths of 310 nm, 340 nm and 365 nm. Besides, the temperature dependence of the red-shift of spectrum peak shows different wavelength dependence characteristic with coefficient as high as 0.062 nm K(-1) for the same temperature range, which gives us a hint about selecting the right excitation wavelength by compromising the excitation efficiency for fluorescence intensity and the temperature coefficient for peak shift in thermal applications. Temperature dependence of peak width is in a weakly linear relationship with a coefficient of 0.026 nm K(-1). Regarding the excellent stability and reversibility during thermal measurement, graphene quantum dot is a good candidate for the implementation in the nanoscale thermometry, especially in the bio-thermal field considering its superior biocompatibility and low cytotoxicity.

Graphene has been highlighted as a great potential material in wearable devices, owing to its extraordinary properties such as mechanical softness, high electrical conductivity and ultra-thin thickness. However, there are remaining challenges in thermal dissipation of graphene under such complicated conditions, which significantly affect the performance of portable electronics. Using molecular dynamics simulations, we have performed systematic analysis of thermal performance for the application in wearable devices in terms of graphene with defects, under uniaxial tensile strain, and vertical stress. Three kinds morphology of defects (horizontal line defect, circular defect, and vertical line defect) are constructed by deleting atoms on the pristine graphene plane. The thermal conductivity is related to the projected defected area perpendicular to the direction of the heat current. The relative thermal conductivity displays a cubic decreasing trend with the increase of uniaxial tensile strain. Besides, the thermal conductivity of graphene is not only related to the deformation quantity, but also related to the type of compression region. Our results show that the thermal conductivity decreases a lot under local stress with larger vertical deformation, while no obvious decline is observed under the global stress. This study aims to provide guidelines and ballpark estimates for experimentalists fabricating flexible devices from graphene.

Most conventional Raman thermometry for thermal properties measurement is on steady-state basis, which utilizes either Joule heating effect or two lasers configurations coupled with increased complexity of system or measurement uncertainty. In this work, a new comprehensive approach including both transient and steady-state Raman method is proposed for thermal properties measurement of micro/nanowires. The transient method employs a modulated (pulsed) laser for transient heating and Raman excitation, and is termed time-domain differential Raman. The average elevated temperature during the transient heating period is probed simultaneously based on Raman thermometry. Thermal diffusivity can be readily determined by fitting normalized temperature rise against heating time with a transient heat conduction model. On the other hand, thermal conductivity can be obtained in the steady-state measurement by adjusting modulation settings. To verify this method, a carbon nanotube (CNT) fiber is measured with the thermal diffusivity of 0.20 5 0.20

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