Graphene is worth lots more than cookies.
By Gail Flower
In August 2011, Mike Williams of Rice University’s news staff wrote an article about how graduate students at Houston, TX-based Rice showed local Girl Scouts how a shortbread cookie could serve as a carbon source for graphene. And graphene is worth lots more than cookies.
How did they do it? When Girl Scout Troop 25080 came to Rice’s Smalley Institute for Nanoscale Science and Technology (YouTube video: http://tinyurl.com/3tngrnk), Rice graduate students Gedeng Ruan, Zengzong Sun, Zhiwei Peng, and their professor, James Tour, showed the girls that graphene can be made from any carbon source, including the cookies they were then eating. The commercial rate for pristine graphene runs at $250 for a 2-in. square, making an entire box of traditional shortbread cookies worth about $15 billion in profit after processing.
The researchers made high-quality graphene by carbon deposition on copper foil. The crumbled cookie took 15 minutes to re-cook in a furnace flowing with argon and hydrogen gas at a temperature of 1050°C. When it came out, it looked like a small, clear piece of flexible material. As the cookie cooked, a single-atom-thick layer of graphene formed on the oppositeside of the foil, leaving other residues on the original side.
If you can make bulk graphene, you might be able to make graphene-based transparent electrodes by combining graphene with a fine metallic mesh. And if you can do that, you might have a challenging product for replacing indium tin oxide as a necessary element for flat-panel and touchscreen displays, solar cells, and LED lighting.
But first, you have to back up a bit to what it takes to make indium. ITO (tin-doped indium tin oxide) is a transparent conducting film that is deposited on surfaces using electron beam, physical vapor deposition, or a range of sputter-deposition techniques. It is widely used, limited in supply, and expensive to deposit because it traditionally requires the use of vacuum techniques. If you want lots of indium, you commonly get it as a byproduct of processing zinc, and then you must purify it. It’s complicated.
Enter graphene. It’s based on carbon—the most common element around. Researchers at Rice University have made graphene out of cockroaches, chocolate, grass, and many other unusual, carbon-based sources. Results were the same. A tiny film of graphene formed on the opposite side of copper foil. The advantage is that graphene makes for a transparent, flexible product that’s close to the end use. Therefore, solar cells need not be made of glass, and printing on flexible, roll-to-roll substrates can make the end product for a lower price.
By the time the Girl Scouts of Troop 25080 make it to Rice University, chances are they’ll have made cookies at some point rather than graphene; however, they won’t long forget the point that physical things can change forms and that research is fun. I’d be willing to bet that each will own devices with flat-panel displays using graphene in the future. I’ll bet you that based on the cost of a cookie—before processing, please.
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