<i>In situ</i> tuning of crystallization pathways by electron beam irradiation and heating in amorphous bismuth ferrite films

The sculpting of crystalline materials from amorphous films by electron beam irradiation in transmission electron microscopy (TEM) offers an effective way for fabrication of nanostructure and devices. However, the synthesis of multifunctional complex oxide and related composites for possible device application is difficult to achieve. Here, we show that the crystallization pathways of amorphous bismuth ferrite films could be tuned by controlled electron beam irradiation and in situ heating in TEM. The results show that Bi segregates from amorphous films and then aggregates into crystalline nanoparticles (the particle size can be tuned by electron dose rates) under electron beam irradiation below 100 °C, while Bi2Fe4O9 nanocrystals are observed at boundary areas between quasi-liquid Bi nanoparticles at 300 °C due to the cooperative effect of electron beam irradiation and thermal heating. Moreover, the Bi/Bi2Fe4O9 metal/semiconductor solid state heterostructure with nearly atomically sharp interfaces emerges when cooling down to room temperature. This finding expands the variety of nanostructures synthesized by electron bombardment and offers a new way to fabricate complex architectures and possible functional devices at the nanometer scale with direct in situ TEM observation and monitoring.