STRUCTURAL IMAGING OF A THICK-WALLED CARBON MICROTUBULE

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 {1010BAR} 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 3-degrees 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.