Raman spectroscopy-based detection of as-grown suspended carbon nanotubes for integration into sensors

Abstract. The localization of individual suspended as-grown carbon nanotubes is crucial for their integration into sensor devices that use carbon nanotubes, such as carbon-nanotube field-effect transistors for gas sensing. The detection yield of Raman spectroscopy was determined with respect to SEM imaging. Raman spectroscopy was conducted using two different excitation laser wavelengths, 488 and 514 nm, on a sample set of 1676 carbon nanotubes. The resulting measurements were analyzed using the G and D* carbon-nanotube (CNT) Raman bands. For the 514 nm excitation laser wavelength, Raman spectroscopy achieved a detection yield of 90.3 %. Similarly, when the 488 nm excitation laser wavelength was used, a CNT detection yield of 89.4 % was observed. When combining the detection results of two laser wavelengths (514 and 488 nm), the overall detection yield increased significantly to 96.4 %. The experimentally obtained detection yield results are compared to theoretically expected yields for individual excitation wavelengths, as well as to expected detection yields with the two above-mentioned excitation laser wavelengths. The possibility to further increase the Raman spectroscopy detection yield by using an additional laser wavelength was explored by determining the visibility of another smaller subset of suspended CNTs with a 785 nm laser in addition to the other two wavelengths. A slight increase of up 2.5 % in the detection yield was achieved. These findings highlight the efficacy of multi-wavelength Raman spectroscopy for detecting chemical vapor deposition (CVD)-grown suspended carbon nanotubes, demonstrating its value in advancing carbon-nanotube-based sensors.