Sensors based on carbon nanotubes and germanium nanowires for explosive detection

TNT belongs to the class of nitroaromatic explosives which represent large part of the most common explosives. Semiconducting nanowires can detect TNT down to a detection limit of ~1x10-6 ppt by proper surface functionalization with an electron-rich amino-silane which binds the explosive molecules of TNT through charge-transfer donor-acceptor interactions causing sharp changes in the conductance of MW [1]. Carbon nanotubes (CNT) are highly responsive to their physical and chemical environment. CNT are unique among nanoscale sensor platforms in their ability to detect the adsorption of as few as a single molecule of an analyte [2]. CNT based chemiresistors display promising performance in explosive sensing. The hot wall vapour phase epitaxy using iso-butil-germane and gold nanoparticle colloids was used to grow Ge NWs. First attempts to functionalize the NWs surface have been performed by long chain alkanethiols terminating with an amino group. The electron-rich amino groups provide the passivation of the NWs surface and bind the electron-deficient explosive molecules of TNT through charge-transfer donor-acceptor interactions, affecting the conductance of the NWs. Single NWs were contacted to Au electrodes with Pt deposited by focused ion beam. I-V characteristics showed the ohmic nature of Pt-NW contacts and electrical resistivity values in the 0.05 - 0.5 ohm cm range Aerosol-assisted CVD and arc-discharge methods have been used for synthesizing single wall carbon nanotubes. Cyclohexane and hexane, metallocenes have been used as carbon sources and catalyst, respectively. For the functionalization of CNTs with amino groups different approaches have been followed: -Preliminary oxidation of the CNT surface by treatment with H2SO4/HNO3 to generate carboxylic acid moieties that are subsequently exploited to anchor the sensing group through the formation of ester or amide bonds. -"Prato reaction" [3] as a method of functionalization of nanostructures alternative to the above described sequence oxidation-condensation sequence. First characterizations of the successful functionalization of nanostructures are reported. [1] A. Lichtenstein, E. Havivi, R. Shacham, E. Hahamy, R. Leibovich, A. Pevzner, V. Krivitsky, G. Davivi, I. Presman, R. Elnathan, Y. Engel, E. Flaxer and F. Patolsky, Nature Comm., 5 (2014) 4195. [2] L. Cognet, D. A. Tsyboulski, J. D. R. Rocha, C. D. Doyle, J. M. Tour, R. B. Weisman. Science 316 (2007) 1465-1468. [3] V. Georgakila, K. Kordatos , M. Prato, DM. Guldi, M. Holzinger, A. Hirsch (2002). J. Am. Chem. Soc. 124 (5): 760-761