Jin Hui Liu

Thermal Transport Across the Interface Between a Suspended Single-Walled Carbon Nanotube and Air

The heat transfer coefficients of several individual single-walled carbon nanotubes (SWCNTs) were measured using a micro-Raman spectroscopy technique in an atmosphere environment. A 514 nm laser was focused in the middle of a suspended SWCNT and the local temperature rise was measured by monitoring the downshifts of the G-band frequency. The heat transfer coefficient can be extracted from the measured midpoint temperature rise. Because there are no temperature drops at the ends of SWCNTs, the thermal contact resistance can be ignored. A detailed kinetic model was developed to predict the heat transfer coefficient quantitatively from the free molecular regime to the continuum regime. The theoretical prediction agrees well with the experimental data. Based on the present model, a maximum heat transfer coefficient occurs in the transition regime at a diameter of several nanometers, which is the competition result of the thermal resistances of the noncontinuum layer and continuum layer. The maximum value agrees with the prediction of kinetic theory of gases. The noncontact Raman measurement technique and prediction model will benefit the thermal design of carbon nanotube-based heat spreaders.

Heat transfer between an individual carbon nanotube and gas environment in a wide knudsen number regime

Applications of carbon nanotube (CNT) and graphene in thermal management have recently attracted significant attention. However, the lack of efficient prediction formula for heat transfer coefficient between nanomaterials and gas environment limits the further development of this technique. In this work, a kinetic model has been established to predict the heat transfer coefficient of an individual CNT in gas environment. The heat dissipation around the CNT is governed by molecular collisions, and outside the collision layer, the heat conduction is dominant. At nanoscales, the natural convection can be neglected. In order to describe the intermolecular collisions around the CNT quantitatively, a correction factor 1/24 is introduced and agreeswellwith the experimental observation. The prediction of the present model is in good agreement with our experimental results in free molecular regime. Further, a maximum heat transfer coefficient occurs at a critical diameter of several nanometers, providing guidelines on the practical design of CNT-based heat spreaders.

Optical absorptance measurement of an individual multiwall carbon nanotube using a T type thermal probe method.

Optical absorptance is an important property of carbon nanotubes for practical applications but has rarely been accurately measured. We developed a T type thermal probe method to measure the optical absorptance of an individual multiwall carbon nanotube. In this method, one end of the carbon nanotube (CNT) is attached to the center of a platinum nanofilm in a T shape and the Pt nanofilm acts as a thermometer. A laser beam irradiates at the CNT and the absorbed laser power can be determined by measuring the average temperature rise of the Pt nanofilm based on the temperature dependence of the electric resistance. Experimental results showed that a 100-nm-diameter multiwall CNT could absorb 13.2% of the 514-nm-wavelength laser power with the laser spot diameter being 1 μm. This method is useful for determining the optical absorptance of CNTs and other one-dimensional nanostructures such as Si/Ge nanowires for various optical wavelengths in their photovoltaic, photoelectrolysis and other optical applications.