Nondestructive characterization of Carbon Nanotubes by Photothermal Techniques

Carbon nanotubes (CNT) are multifunctional materials commonly used in a large number of applications in electronics, sensors, nanocomposites, thermal management, actuators, energy storage and conversion, and drug delivery. Despite recent important advances in the development of CNT purity assessment tools and atomic resolution imaging of individual nanotubes by scanning tunnelling microscopy and high-resolution transmission electron microscopy, the macroscale assessment of the overall surface qualities of commercial CNT materials remains a great challenge. The lack of quantitative measurement technology to characterize and compare the surface qualities of bulk manufactured and engineered CNT materials has negative impacts on the reliable and consistent nanomanufacturing of CNT products In this paper we show how photothermal and photoacoustic techniques represent useful non-destructive tools to study the thermal properties of carbon nanotubes films. The photoacoustic spectroscopy (PAS) is used for a direct measurement of the absorbance spectra of CNT showing many advantages with respect to the standard optical spectra measurements which are usually affected by relevant scattering phenomena. We applied PAS in the UV/VIS range from 250 to 650 nm by using 400 W Arc Xe lamp. On the other side photothermal radiometry (PTR) has been applied by using an Ar++ pump laser beam, modulated at a frequency in the range 1Hz -100 kHz, and a MCT infrared detector, in order to measure the effective thermal parameters, the IR emission properties from CNT thin films, and evaluate the average thermal boundary resistances at the film/bulk interface. We investigated two set of CNT; in the first group the nanostructures are aligned (“forest”) and deposited onto a silicon substrate. The diameter of the nanotubes ranges from 20-50nm, and the total thickness of the CNT film ranges from m tom. In the second group the CNT are randomly oriented in plane, and the CNT film is deposited on different transparent substrate (PET and quartz). Experimental results show how both PAS and PTR represent an excellent tool for quantitative measurement of the thermal properties of CNT thin films.