A team of scientists at Missouri University of Science and Technology, Rolla, developed a one-step approach to growing germanium nanowires from an aqueous solution. They say that their process may lead to a simpler, less expensive way to use germanium in lithium-ion batteries.

Scanning electron micrograph image of germanium nano wires electrodeposited onto an indium-tin oxide electrode from an aqueous solution. (Credit: Jay A. Switzer/Missouri University of Science and Technology)

As a semiconductor material, germanium is superior to silicon, they explain. However, it is more expensive to process for widespread use in batteries, transistors, and other applications.

They modified an electrodeposition process found to produce germanium nanowires using liquid metal electrodes. That process, developed by University of Michigan researchers and known as the electrochemical liquid-liquid-solid process (ec-LLS), uses a metallic liquid that performs two functions: acting as an electrode to cause electrodeposition, and as a solvent to recrystallize nanoparticles.

The Rolla team applied the ec-LLS process by electrochemically reducing indium-tin oxide (ITO) to produce indium nanoparticles in a solution containing germanium dioxide, or Ge(IV). The indium nanoparticle in contact with ITO acts as the electrode to reduce Ge(IV) and dissolves the reduced Ge into the particle, the team reports. The germanium then begins to crystallize out of the nanoparticle, which allows the growth of the nanowire.

The researchers tested the effect of temperature for electrodeposition by growing the germanium nanowires at room temperature and at 95°C. They found that the nanowires grown at room temperature had smaller diameters, but otherwise there was no significant difference in the quality of the nanowires.