We describe interlayer force measurements during prolonged, cyclic telescoping motion of a multiwalled carbon nanotube. The force acting between the core and the outer casing is modulated by the presence of stable defects and generally exhibits ultralow friction, below the measurement limit of 1:4 10 ÿ15 N=atom and total dissipation per cycle lower than 0:4 meV=atom. Defects intentionally introduced in the form of dangling bonds lead to temporary mechanical dissipation, but the innate ability of nanotubes to self heal rapidly optimizes the atomic structure and restores smooth motion.

We have created insulated C60 nanowire by packing C60 molecules into the interior of insulating boron nitride nanotubes (BNNTs). For small-diameter BNNTs, the wire consists of a linear chain of C60 molecules.With increasing BNNT inner diameter, unusual C60 stacking configurations are obtained (including helical, hollow core, and incommensurate) that are unknown for bulk or thin-film forms of C60.C60 in BNNTs thus presents a model system for studying the properties of dimensionally constrained "silo" crystal structures. For the linear-chain case, we have fused the C60 molecules to form a single-walled carbon nanotube inside the insulating BNNT.

We introduce carbon onto boron sites in MgB 2. The resulting changes in crystal lattice constants and superconducting transition temperature T c are characterized by x-ray-diffraction, magnetic susceptibility, and electrical resistance measurements. The consequence of approximately 10% carbon doping of boron sites is a 1% contraction of the intraplane lattice dimension ͑with no appreciable change in the interplane dimension͒ and a lowering of T c by approximately 7 K. The relative contributions to the shift in T c from lattice contraction and charge transfer are evaluated.