Physics Letters A 374 (2010) 4144–4151 Contents lists available at ScienceDirect Physics Letters A www.elsevier.com/locate/pla Thermal transport in multiwall carbon nanotube buckypapers Yanan Yue, Xiaopeng Huang, Xinwei Wang ∗ Department of Mechanical Engineering, 2025 Black Engineering Building, Iowa State University, Ames, IA 50011-2161, USA article info abstract Article history: Received 8 April 2010 Received in revised form 18 June 2010 Accepted 12 August 2010 Available online 17 August 2010 Communicated by R. Wu A steady-state electro-Raman-thermal (SERT) technique is developed to characterize the thermal transport in multiwall carbon nanotube (MWCNT) buckypapers. This SERT technique involves steady-state joule heating of a suspended sample and measuring its middle point temperature based on Raman shift intensity. The thermal conductivity is determined from linear fitting of the temperature against heating power. Combined with the transient-electro-thermal technique, the thermophysical properties of two MWCNT buckypapers are characterized as 1.19 and 2.92 W/(m K) for thermal conductivity, 3.65 × 10 −6 and 7.58 × 10 −6 m 2 /s for thermal diffusivity, 459 and 543 kg/m 3 for density. Detailed discussion and analysis are provided about the uncertainty of the SERT technique and its capacity for measuring wires down to sub-μm length. The low thermal conductivity of the buckypaper indicates its thermal transport is determined by the thermal contact resistance between MWCNTs. These contact points feature low thermal conductance. The mean distance between two adjacent contact points is estimated in the order 45–450 μm and 93–933 μm for the two samples, indicating low-density contacts within the buckypaper.  2010 Elsevier B.V. All rights reserved. 1. Introduction As the promising material in micro-electro-mechanical sys- tems (MEMS) and nano-electro-mechanical systems (NEMS), one- dimensional micro/nanoscale materials such as carbon nanotubes (CNTs), are attracting significant interest for their superior mechan- ical and electrical characteristics. Extensive work has been devoted for characterizing their thermophysical properties which are tightly related to their structure and are important for their industrial ap- plications. Several non-contact techniques have been established successfully on thermal transport study of micro/nanoscale materi- als: the 3ω method, the microfabricated device method, the optical heating electrical thermal sensing (OHETS) technique, the tran- sient electrothermal (TET) technique, the transient photo-electro- thermal (TPET) technique, and the pulsed laser-assisted thermal relaxation (PLTR) technique [1–8]. These techniques have great capacity for thermophysical prop- erty characterization of micro/nanowires while each of them has certain limitations. Physically, the 3ω method detects the 3ω signal in the specimen during the self-joule heating to study the resis- tance change, which is used to determine thermal diffusivity [1]. Despite its simple experimental principle, the 3ω technique suf- fers from poor signal to noise ratio and is vulnerable to various noises in the power source and environment. The OHETS method * Corresponding author. Tel.: +1 515 294 2085; fax: +1 515 294 3261. E-mail address: xwang3@iastate.edu (X. Wang). tracks the temperature evolution and phase shift difference be- tween temperature and laser beam during under periodical laser heating. This technique overcomes the drawback of the 3ω method and features significantly improved signal-to-noise ratio and ease of experiment conduction. The experimental time of this technique is much shorter than that of the 3ω method [4]. The other three techniques like TET, TPET and PLTR probe the temperature evolu- tion during step electrical/laser heating or after pulsed laser heat- ing to evaluate the thermal diffusivity. The time required for these three techniques is significantly shorter than that for the 3ω and OHETS techniques. In these three transient techniques, the ther- mal relaxation time of the sample is ∼ l 2 /α, where l is the sample length and α is its thermal diffusivity. For samples of very short length and high thermal diffusivity, the characteristic heat transfer time would be very short and it becomes difficult to employ the transient techniques. Besides, all the techniques reviewed above have no capacity for direct temperature measurement, which is a critical requirement for analyzing the heat transfer process in ma- terials and determining thermal conductivity [5–8]. To overcome the challenges mentioned above, the Raman spec- troscopy is adopted in this work for temperature measurement and heat transfer analysis. Based on the Raman spectra’s depen- dence on temperature, Raman thermometry is an compelling tech- nique for non-contact temperature probing and has been applied successfully on the silicon and CNTs analysis [9–12]. For the par- ticular structure of CNTs, there are three vibration modes which appear as three peaks in the Raman spectrum within the Ra- man shift range from 100 cm −1 to 2000 cm −1 : radial breathing 0375-9601/$ – see front matter  2010 Elsevier B.V. All rights reserved. doi:10.1016/j.physleta.2010.08.034