Electrical and thermal characterization of carbon nanotube films
(Color online) Scheme of multilayer sample used as demonstrator to measure either electrical conductivity with four gold contacts (a) or thermal conductivity with a continuous titanium layer (b). The barrier layer is either insulating for transverse electrical measurements or conductive (TiN) for axial electrical measurements. From bottom to top: the Si substrate is covered with a barrier layer (about 170 nm) then the catalyst layer (initially of 9 nm in thickness); the MWCNT film is between 20 and thick, and the final metallic layer is about 500 nm.
(Color online) Scheme of the reactor used for the three-step CNT growth process as described in the text. For the PLD process (a), the arm supporting the target was introduced in front of the sample for catalyst layer deposition and then moved back. For the PECVD process (b), the arm supporting the plasma source was introduced without venting the chamber.
Cross-section SEM image of the gold deposited on the top of the MWCNT film for electrical measurements. The deposited thickness of the gold is 500 nm.
Cross-section SEM image of the titanium layer deposited on the top of the MWCNT film for thermal measurements. The CNT film was stressed when the sample was broken for SEM analysis and some nanotubes are detached from the substrate (white lines in the foreground of the image).
(Color online) Pictures of the gold contacts (left) on the top of the MWCNT and of the electrical probes (right). On the left picture, the impact of the probes can be seen on the gold contacts.
SEM images of the impact of the probes upon the Au/MWCNT carpet after measurement, top view (a) and side view (b). On the left image, the limit of the gold spot can be seen on the left; on the right image, the cross-section is not symmetrical because the break in the sample did not pass through the exact center of the gold contact; it is clear from this SEM image that compression of the CNT film did not break or damage the tubes themselves.
(Color online) Top view of the infrared pyrometry experimental set-up used for thermal characterization of CNTs.
SEM images of the MWCNT film cross-section grown on an substrate at different magnifications. Height is . Whiter lines are parts of the film which were scratched during breaking and handling of the sample.
SEM image of the MWCNT carpet cross section grown on a TiN/Si substrate. Height is . Whiter lines are parts of the film which were scratched during breaking and handling of the sample.
HRTEM images of MWCNT from the film grown on an substrate.
(Color online) Raman spectra of the MWCNT film grown on (bold line) and on TiN/Si (light line) substrates. The RF plasma power is 25 W to grow the carpet on the insulating barrier layer and is 200 W to grow the carpet on the TiN conductive barrier layer. No radial breathing modes (RBM) are visible in the low wavenumbers.
(Color online) curves obtained from transverse measurements on the CNT carpet grown on the insulating barrier layer (the current flows perpendicularly to the axis of CNTs). Comparison between measurements done without (a) and with (b) a thin gold layer on the top of the CNT carpet. The two curves without gold were measured in the same place on the sample, the light one after the bold one.
(Color online) curves of a MWCNT carpet grown on a conductive TiN barrier layer. The bold curve gives the result for the transverse measurement (the current flows perpendicularly to the axis of CNTs) and the light curve gives the result for axial measurements (the current flows along the axis of CNTs).
(Color online) Temperature variation for the Ti/CNT surface grown on insulating barrier layer, from room temperature, versus time at laser fluence. The numerical model (stars) compared with experimental results (continuous line).
Thermal properties of a CNT carpet compare to titanium thin film.
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