In situ observation of the melting and sintering of submicron-sized bismuth particles

The sintering and melting of submicron-sized bismuth particles were studied in situ via scanning electron microscopy. The relevant bismuth particles were prepared via a polyol-mediated synthesis, which results in spherical and non-agglomerated particles, about 250 nm in size. The samples as well as suitable references were deposited on a heater stage assembly inside a scanning electron microscope. Both were investigated up to temperatures of 480 degrees C. Surprisingly, sample areas continuously scanned by the electron beam showed neither sintering nor melting of submicron-sized bismuth, whereas melting was observed at temperatures between 250 and 270 degrees C in non-scanned areas. This behavior was ascribed to an electron-beam-induced decomposition of organic stabilizers that adhered on the bismuth particles to form a thin layer of amorphous carbon. For experimental verification of this hypothesis, controlled carbon coating of submicron-sized bismuth particles was conducted.