  Single walled carbon nanotubes (SWNT) have displayed a wealth of quantum
transport phenomena thus far. Defect free, unperturbed SWNTs with wellbehaved
or tunable metal contacts are important to probing the intrinsic electrical
properties of nanotubes. Meeting these conditions experimentally is nontrivial
due to numerous disorder and randomizing factors. Here we show that ~ 1 um long
fully suspended SWNTs grown-in-place between metal contacts afford SWNT devices
exhibiting 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 for medium conductance devices. The clean transport data reveals a
correlation between the contact junction resistance and the various transport
regimes in SWNT devices. Further, we show that electrical transport data can be
used to probe the band structures of nanotubes including nonlinear band
dispersion.
