17 research outputs found
The development and applications of ultrafast electron nanocrystallography
We review the development of ultrafast electron nanocrystallography as a
method for investigating structural dynamics for nanoscale materials and
interfaces. Its sensitivity and resolution are demonstrated in the studies of
surface melting of gold nanocrystals, nonequilibrium transformation of graphite
into reversible diamond-like intermediates, and molecular scale charge
dynamics, showing a versatility for not only determining the structures, but
also the charge and energy redistribution at interfaces. A quantitative scheme
for three-dimensional retrieval of atomic structures is demonstrated with
few-particle (< 1000) sensitivity, establishing this nanocrystallographic
method as a tool for directly visualizing dynamics within isolated
nanomaterials with atomic scale spatio-temporal resolution.Comment: 33 pages, 17 figures (Review article, 2008 conference of ultrafast
electron microscopy conference and ultrafast sciences
Utilizing total scattering to study the Jahn-Teller transition in La1-xCaxMnO3
Total scattering based atomic pair distribution function (PDF) analysis, with the advent of high data throughput neutron powder diffractometers, helps understanding the nature of the Jahn-Teller (JT) phase transition in La 1-xCaxMnO3 colossal magnetoresistive (CMR) manganites. The JT distortion of the MnO6 octahedra, is long-range ordered in the orthorhombic (O) phase, but disappears in the pseudo-cubic (O') phase crystallographically. An anomalous unit cell volume contraction occurs at the transition. The PDF study indicates that the distortion persists locally deep in the O' phase, contrary to the crystallographic view. Simultaneously, local structural features observed in PDF at 10.3 Å, sensitive to the oxygen sublattice changes, evolve dramatically across the transition. The same effect is observed irrespective of the way the O-O' phase boundary is crossed: it is seen both in the temperature series data for x=0, and in the doping series data at 310 K and at 550 K. © by Oldenbourg Wissenschaftsverlag