Quantifying Molecular Disorder in Tri-Isopropyl Silane (TIPS) Pentacene Using Variable Coherence Transmission Electron Microscopy.

Structural disorder in molecular crystals is a fundamental limitation for achieving high charge carrier mobilities. Quantifying and uncovering the mechanistic origins of disorder are, however, extremely challenging. Here we use variable coherence transmission electron microscopy to analyze disorder in tri-isopropyl silane pentacene films, utilizing diffuse scattering that is present both as linear streaks and as a slowly varying, isotropic background. The former is due to thermal vibration of the pentacene molecules along their long axis, while the latter is due to static defects kinetically frozen during film deposition. The thermal vibrational amplitude is ∼0.4 Å, while the static displacement parameter in our simplified analysis is much larger (1.0 Å), because it represents the cumulative scattering of all defect configurations that are frozen in the film. Thin film fabrication therefore has an important effect on crystallinity; our technique can be readily used to compare samples prepared under different conditions.

Ultrafast electron diffraction pattern simulations using GPU technology. Applications to lattice vibrations.

Graphical processing units (GPUs) offer a cost-effective and powerful means to enhance the processing power of computers. Here we show how GPUs can greatly increase the speed of electron diffraction pattern simulations by the implementation of a novel method to generate the phase grating used in multislice calculations. The increase in speed is especially apparent when using large supercell arrays and we illustrate the benefits of fast encoding the transmission function representing the atomic potentials through the simulation of thermal diffuse scattering in silicon brought about by specific vibrational modes.

Is precession electron diffraction kinematical? Part I: "Phase-scrambling" multislice simulations.

Results from multislice simulations are presented which demonstrate that diffracted intensities obtained using precession electron diffraction are less sensitive to the phases of structure factors compared to electron diffraction intensities recorded without precession. Since kinematical diffraction intensities depend only on the moduli of the structure factors, this result supports previous research indicating that the application of precession leads to electron diffraction intensities becoming more kinematical in nature.

Is precession electron diffraction kinematical? Part II A practical method to determine the optimum precession angle.

A series of experiments was undertaken to investigate the kinematical nature of precession electron diffraction data and to gauge the optimum precession angle for a particular system. Kinematically forbidden reflections in silicon were used to show how a large precession angle is needed to minimise multi-beam conditions for specific reflections and so reduce the contribution from dynamical diffraction. Small precession angles were shown to be detrimental to the kinematical nature of some low-order reflections. By varying precession angles, precession electron diffraction data for erbium pyrogermanate were used to investigate the effect of dynamical diffraction on the output from structure solution algorithms. A good correlation was noted between the precession angle at which the rate of change of relative intensities is small and the angle at which the recovered structure factor phases matched the theoretical kinematical structure factor phases.

Synthesis and characterization of ultra-small superparamagnetic iron oxide nanoparticles thinly coated with silica.

Ultra-small superparamagnetic iron oxide nanoparticles (SPIOs) were synthesized by co-precipitation of iron chloride salts with ammonia and then encapsulated with thin (~2nm) layers of silica. The particles have been characterized for size, diffraction pattern, surface charge, and magnetic properties. This rapid and economical synthesis has a number of industrial applications; however, the silica-coated particles have been optimized for use in medical applications as MR contrast agents, biosensors, DNA capturing, bioseparation and enzyme immobilization.