Nanosecond electron pulses in the analytical electron microscopy of a fast irreversible chemical reaction.

We show how the kinetics of a fast and irreversible chemical reaction in a nanocrystalline material at high temperature can be studied using nanosecond electron pulses in an electron microscope. Infrared laser pulses first heat a nanocrystalline oxide layer on a carbon film, then single nanosecond electron pulses allow imaging, electron diffraction and electron energy-loss spectroscopy. This enables us to study the evolution of the morphology, crystallography, and elemental composition of the system with nanosecond resolution. Here, NiO nanocrystals are reduced to elemental nickel within 5 µs after the laser pulse. At high temperatures induced by laser heating, reduction results first in a liquid nickel phase that crystallizes on microsecond timescales. We show that the reaction kinetics in the reduction of nanocrystalline NiO differ from those in bulk materials. The observation of liquid nickel as a transition phase explains why the reaction is first order and occurs at high rates.

Raman scattering of magnetoelectric gallium ferrite thin films.

Gallium ferrite, Ga(2-x)Fe(x)O(3) (GFO), is a promising magnetoelectric material as it exhibits both magnetic and electric orders close to room temperature. Here, we report a temperature-dependent investigation of GFO thin films with x = 1.0 and 1.4 by using Raman scattering. Our investigation suggests the absence of a structural phase transition of both films in the investigated 90-500 K temperature range, which is similar to earlier observations on bulk samples. We note, however, the occurrence of weak anomalies in the temperature-dependent band position of some phonons, which we attribute to spin-phonon coupling as the anomalies occur close to the Néel temperature of the materials.