Metal oxides has attracted great attention due to the widely applications, which are commonly used in semiconductor industry due to their excellent physical and chemical properties. Also, it exhibits variety of structures. Among various metal oxides, cuprous (Cu₂O, copper (I) oxide) is regarded as one of the most promising materials. It is cheap, earth-abundant, and nontoxic; therefore, it can be applied in catalysis, sensor, solar cell and p-type semiconductor. However, the redox reaction of cuprous is still uncertain, which strongly influent its size, morphology, and nanostructure.

In this work, the growth and dissolution of cuprous were observed via in situ liquid cell transmission electron microscopy (TEM). The study of cuprous nanoparticles formation, such as kinetics analysis, nucleation, growth, and reduction reaction in liquid phase can be achieved. In the cuprous growth, dendrite shape agglomeration dispersed everywhere inside the chip at the beginning. Few minutes later, the accumulation of copper ions resulted in a rapidly growth of cuprous nanostructures. The results indicated that the electron beam reduced the precursor which led the copper ions transfer into copper (I) oxide. Whereas in the cuprous dissolution, the cubic shape dissolved in specific {100} planes, and finally fully disappeared. The dissolution is resulted from the higher dose of electron exposure, the radiation-damage-caused vacancies accumulated and formed porous checkerboard-like nanostructure. The growth/dissolution results were systemically analyzed through the viewpoint of kinetics and dynamics. The direct observation of the dynamic process sheds light on the preparation of metal oxide by redox reaction method and extends the study of reaction kinetics.