Room temperature mushrooming of gallium wires and its growth mechanism

Spontaneous growth of Ga wires at high rate (∼200 nm/s) from a composite system of Cr2GaC (a MAX phase) and Ga is presented. A Ga wire growth mechanism based on a catalysis model, which involves fractured Cr2GaC grains as the catalyst, is proposed. Regarding the morphologies and the incubation time of the Ga wires, this system shares most features with metal/alloy substrates, such as tin and zinc, where the whiskering phenomenon has been well established and has resisted interpretation for 60+ years. The same growth mechanism is thus considered to operate across different substrates, including the composite one in this study. However, the experimental findings in this composite system oppose the popular stress-based mechanism for the whisker growth with metal/alloy substrates, and provide new sights on this phenomenon. In addition, compelling evidences strongly indicate that fractured Cr2GaC grains produced by ball milling initiated the growth of Ga wires, like a 'catalyst', and the pristine Cr2GaC grains do not have the catalytic effect on Ga wire growth. The new findings on Ga wire growth from Cr2GaC-Ga composite and the proposed mechanism would shed new light on uncovering the myths of the general whiskering phenomena.