Electron transport in very clean, as-grown suspended carbon nanotubes

Single- walled carbon nanotubes have shown a wealth of quantum transport phenomena thus far(1-11). Defect- free, unperturbed single- walled carbon nanotubes with well behaved or tunable metal contacts are important for probing the intrinsic electrical properties of nanotubes. Meeting these conditions experimentally is non- trivial owing to numerous disorder and randomizing factors. Here we show that similar to 1-mu m- long fully suspended single- walled carbon nanotubes grown in place between metal contacts afford devices with well defined characteristics over much wider energy ranges than nanotubes pinned on substrates. Various low- temperature transport regimes in true- metallic, small- and large- bandgap semiconducting nanotubes are observed, including quantum states shell-filling, - splitting and - crossing in magnetic. fields owing to the Aharonov - Bohm effect. The clean transport data show a correlation between the contact junction resistance and the various transport regimes in single- walled- carbon- nanotube devices. Furthermore, we show that electrical transport data can be used to probe the band structures of nanotubes, including nonlinear band dispersion.