Technology for observation of redox reactions in SEM
The hardware requirements comprise the atomic hydrogen source (here), which is a thermal cracker source for generation of atomic hydrogen radicals. The additional harware requirements comprise the gas inlet, cooling circuit (both part of the atomic source) and sample heating stage, mounted to an SEM. The atomic hydrogen technology allows studying the reduction reactions at lower temperature compared to reduction by molecular hydrogen, because the molecules are pre-dissociated by the source. A proof-of-concept experiment is the nickel redox cycle shown in the figure below.
The sample, as prepared by high temperature annealing (top and image 1), is oxidized by exposure to air at higher pressure (30 Pa) at elevated temperature (580 °C). The procedure results in drastic change in image contrast (2) due to formation of thin oxide layer. For reduction experiment, the temperature is lowered to 540 °C. Exposure to atomic hydrogen (by applying 36W to the dissociation capillary for 60 minutes) results in restoration of the contrast to the state before the oxidation, thus proving a complete reduction of the nickel oxide formed in the oxidation step. The redox cycle can be repeated.