The Missouri S&T researchers describe the process as a “simple, one-step method to grow nanowires of germanium from an aqueous solution.
As a semiconductor material, germanium is superior to silicon, explained Dr. Jay A. Switzer, the Donald L. Castleman/Foundation for Chemical Research Professor of Discovery at Missouri S&T. Germanium was used in the first transistors. It is more expensive to process for widespread use in batteries, solar cells, transistors and other applications.
Switzer and his team have had success growing other materials at the nanometer scale through electrodeposition a process that Switzer likens to growing rock candy crystals on a string. In a 2009 Switzer and his team reported that they had grown zinc oxide ‘nanospears’ each hundreds of times smaller than the width of a human hair on a single-crystal silicon wafer placed in a beaker filled with an alkaline solution saturated with zinc ions.
But growing germanium at the nano level is not so simple. In fact, electrodeposition in an aqueous solution such as that used to grow the zinc oxide nanospears is thermodynamically not feasible, according to Switzer.
So the Missouri S&T researchers took a different approach. They modified an electrodeposition process found to produce germanium nanowires using liquid metal electrodes. That process, developed by University of Michigan researchers led by Dr. Stephen Maldonado and known as the electrochemical liquid-liquid-solid process (ec-LLS), involves the use of a metallic liquid that performs two functions: It acts as an electrode to cause the electrodeposition as well as a solvent to recrystallize nanoparticles.
Switzer and his 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 the ITO acts as the electrode for the reduction of Ge(IV) and also dissolves the reduced Ge into the particle, reports the Missouri S&T team. The germanium then starts to crystallize out of the nanoparticle allowing the growth of the nanowire.
The Missouri S&T researchers tested the effect of temperature for electrodeposition by growing the germanium nanowires at room temperature and at 95 degrees Celsius (203 degrees Fahrenheit). They found no significant difference in the quality of the nanowires, although the nanowires grown at room temperature had smaller diameters. Switzer believes that the ability to produce the nanowires at room temperature through this one-step process could lead to a less expensive way to produce the material.
The high conductivity (of germanium nanowires) makes them ideal for lithium-ion battery applications, explained Switzer.
The Missouri S&T researchers describe their method in a paper entitled ‘Electrodeposited Germanium Nanowires’ published on the website of the journal ACS Nano. Their one-step approach could lead to a simpler, less expensive way to grow germanium nanowires.
Source: http://www.electronics-eetimes.com/en/germanium-nanowire-process-could-improve-lithium-ion-batteries.html?cmp_id=7&news_id=222922234&vID=209&page=0
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