In-situ cobalt nanocrystal synthesis by intense electron beams in TEM

We report the synthesis of cobalt nanoparticles of a range of sizes from raw cobalt fluoride powder using high intensity focused electron beams and their characterisation in-situ in a TEM. A variety of beam intensities with different focussing level in a JEOL JEM 3010 TEM at an acceleration voltage of 300 kV is used. Depending on the beam intensity either a distribution of a large number of nanoparticles of 1-150 nm size or singular/a small number of fine metal particle(s) of ∼150 nm up to micron size can be produced. Mechanisms of the nanoparticle formation are discussed. This simple, organic precursor free, non-hazardous and oxide-free fabrication method offers great potential for basic research, as it allows the fabrication of fresh particles 'on demand' in a location with a distribution as required. As the size range is tuneable, the full magnetic properties from superparamagnetic, over single domain ferromagnetic, to multi-domain are covered.