Direct Synthesis and Integration of Individual, Diameter-Controlled Single-Walled Nanotubes (SWNTs)

We present a robust and versatile approach for the reproducible and controllable growth of single-walled carbon nanotubes (SWNTs) through a self-assembled monolayer (SAM) technique coupled with an atomic hydrogen (Hat) pretreatment to control the catalytic metallic nanoparticles size and density. The nanoparticles are obtained from a self-assembled monolayer of metal complexes or salts on a SiO2 substrate using a two-step strategy. The oxide is first functionalized by silanization with a coordinating ligand leading to the formation of an anchoring SAM on the substrate. Then, metallic complexes such as ruthenium porphyrin (RuTPP) or metallic salts (FeCl3, RuCl3) are assembled by coordination bonds on the preformed organic SAM. Pyrolysis under radical hydrogen atmosphere of the as-prepared SAM yields metallic nanoparticles whose size and density are controlled and tuned. Using the as-formed nanoparticles as catalysts, SWNTs are grown by double hot-filament-assisted chemical vapor deposition (d-HFCVD). They exhibit a remarkably good crystalline quality, with a diameter (and type) strongly dependent on the nature of the initial catalyst precursor and its preparation. Field-effect transistors (FETs) with excellent characteristics were obtained using such in-place grown SWNTs. The electronic properties of the SWNTs can be tuned: the transistors obtained from Ru­(TPP) and FeCl3 exhibit I ON/I OFF current ratio up to ∼109, indicative of the direct growth of a high proportion of semiconducting nanotubes over than 98%. Such elevated I ON/I OFF values have been reported essentially for CNT-FETs devices based on individual semiconducting SWNTs, so far. By contrast, devices obtained from the RuCl3 salt display I ON/I OFF current ratio well below 102, indicating the direct growth of SWNTs highly enriched in metallic specimens.