Structural imaging of a thick-walled carbon microtubule

Abstract

We analyze the structure of a thick-walled carbon microtubule based on direct electron beam imaging of the graphitic cylinders comprising the fiber. Clearly resolved six-fold symmetry of basal planes overlying the fiber core indicate zero overall fiber helicity and alignment of individual cylinders. Sidewall measurements calibrated from the {100} core fringes show uniform spacings of about 0.375 nm, which are larger than those reported for other microtubules or for crystalline graphite (0.335 nm). Short zones of local 3o helicity are observed along the fiber. Structural transitions which alter the helicity are characterized by extra atomic planes and other defects, including nested sub-tubules. We discuss implications for the fiber's growth and electrical properties.