Room temperature synthesis of UO2+x nanocrystals and thin films via hydrolysis of uranium(IV) complexes

Methods for the straightforward, room temperature synthesis of UO2+x nanoparticles and thin films using solution processable, molecular uranium(IV) compounds is described. Ultra-small uranium dioxide nanoparticles are synthesized from the hydrolysis of either U(ditox)(4) (ditox = (-OCHBu2)-Bu-t) (1) or U(CH2SiMe2NSiMe3)[N(SiMe3)(2)](2) (2) via addition of water to stirring solutions of the compounds in non-polar solvents to give UO2-1 and UO2-2, respectively. The structural characteristics of the uranium dioxide nanoparticles were characterized using powder X-ray diffraction (pXRD), high-resolution transmission electron microscopy (HRTEM), and Raman spectroscopy. The pXRD results affirm the cubic fluorite structure expected for UO2 nanoparticles. The nanocrystallinity of UO2-1 and UO2-2 were substantiated by bright-field HRTEM images and fast Fourier transform (FFT) patterns. The HRTEM analysis also shows the nanoparticles fall within the ultra-small regime possessing sizes of similar to 3 nm with uniform distribution. Additionally, we demonstrate the versatility of 1 as a uranium dioxide precursor, showing that it can be readily sublimed onto glass or silicon substrates and subsequently hydrolyzed to give UO2+x thin films.