High resolution electron microscopy of Al-Cu-Fe quasicrystals: atomic structure and modeling
High quality Al-Cu-Fe quasicrystals have been studied at the atomic level with a high resolution microscope operating at 400 kV. When the incident beam is parallel to the fivefold axis, experimental bright-field images in thin regions of the specimen are found to be of two types, depending on the electron optical parameters employed. One of these images is of greater contrast than the other, but both types yield decagon-like image features. Close agreement is found between both types of contrast-enhanced micrographs and microscope image simulations of a realistic atomic model.
Energetics of negatively curved graphitic carbon
BY analogy with the positively curved carbon networks that comprise the fullerenes1-3, it has been suggested4 that negative curvature might be possible in graphitic carbon sheets, giving rise to extended structures corresponding to periodic minimal surfaces5 that divide space into two disjoint labyrinths. Whereas the positive curvature of fullerenes results from the presence of five-membered rings, negative curvature would derive from seven-membered rings. Here we present calculations of the cohesive energy and bulk moduli of two such hypothetical, negatively curved carbon networks.
String theory of the roton
An effective string theory of vortex ring excitations in a boson superfluid can in principle be derived using the coherent-state functional integral. The details of this derivation are complicated but lead unambiguously to the existence of a purely imaginary term in the string's effective action. This term is responsible for stabilizing a microscopic vortex ring against collapse if its momentum is sufficiently great. © 1992.
Experimental and theoretical determination of the magnetic susceptibility of C60 and C70
THE magnetic susceptibility of C60 and the possibility of magnetic-field-induced π-electron ring currents in this carbon spheroid have been of interest since the initial experiments on carbon clusters1. If the molecule is regarded as a sphere with a radius of 3.5 Å, on which 60 electrons are free to move, the Pauling ring-current model predicts a ring-current diamagnetic susceptibility 41 times the π-electron ring-current magnetic susceptibility of benzene with the field normal to the plane of the six-membered ring2,3.
Icosahedral C60 revisited: An aromatic molecule with a vanishingly small ring current magnetic susceptibility
In a previous publication we conclude that: "Although planar aromatic hydrocarbons and graphite have provided appropriate points of analogy for the π-electron energy structure of C60, it is clear that the magnetic response of C60 is unlike that of any other molecule yet encountered". In a recent Letter, Fowler, Lazzeretti and Zanasi (FLZ), report ab initio calculations on the magnetic susceptibility of icosahedral C60. FLZ conclude that C60 possesses "... the strong diamagnetism expected of an aromatic system".