Reversible gas–solid reaction in an electronically-stimulated palladium nanogap

We investigated a nanogap between a pair of palladium electrode tips with gas (nitrogen, hydrogen, and oxygen) and a biasing voltage using in situ atomic resolution environmental transmission electron microscopy (ETEM). We found an unexpected gas-solid (nitrogen-palladium) reaction that occurs on the surface of the positive electrode tip. A palladium nitride compound was synthesized with gaseous nitrogen at low pressure at room temperature. The nitridation of palladium was previously reported and predicted to occur only under high pressure and at high temperature. The reaction in ETEM apparatus was reversible with the change in the magnitude of an electric field in the nanogap. Additionally, the asymmetrical surface dynamics on the pair of electrode tips in gas (nitrogen, hydrogen, and oxygen) were revealed by ETEM observation. It is likely that the electrons in the gap induce the reversible reaction. This study has opened a new route toward creating nanoscale materials because the creation, stabilization, and annihilation of the material in a nanogap can be controlled electrically and electronically on demand for various applications.