This week’s item is Science Express paper “Dislocation-Driven Nanowire Growth and Eshelby Twist ” by Michael Bierman et al. (doi:10.1126/science.1157131). By growing PbS nanowires using chemical vapor deposition (CVD) they observe hyper-branched structures, similar to the pine trees with a trunk and multiple branches. The spiral growth pattern is due to the existence of a single screw 
dislocation within the trunk of the nanoscale “pine tree”. The authors test the theory of screw dislocations developed by Eshelby in 1950ies, in particular his prediction of the “Eshelby twist”, an angular twist in the lattice, with twist per unit length proportional to Burgers vector of the dislocation and inversely proportional to the radius of the structure. Because of small radii of the grown PbS nanostructures, nanowires present an excellent testing ground for expected Eshelby twist. The authors find that the fit to Eshelby theory produces Burgers vector on the order of 6 Angstroms, comparable to the expected value of a single unit cell, 5.94 Angstroms.
