Wednesday, January 21, 2009

Graphene Sheets and Arthur C. Clark Space Elevators

This is more of the graphene revolution rushing toward us. Complaints aside, we are not far at all from been able to produce large sheets. A comment has also been made that this material is approaching the electrical behavior of a room temperature super conductor.

Now imagine a printed circuit of this stuff layered with insulation and metglas materials and you are on the way to utterly unbelievable capability. I do not think we have ever seen a technology emerge so fast.

With any luck we can take a continuously produced sheet and slice it into thin strips to produce the world’s strongest rope ala Arthur C. Clark. The produced thin strip will form a slowly twisting tube that is then wound around its sisters to form the strongest rope possible. How many are needed to make a space elevator has to still be answered, but this is certain to meet the strength requirements. And we will have fiber continuity from ground to geostationary position.

I considered the possibility of a space elevator as completely unlikely, when I read Clark’s novel. I have to hand him another kudo for prescience. By the way, he wrote a book predicting future technology about forty years ago that I will still recommend. He got a lot right and we are now filling in his last blanks in the battery business.

It sounds as though this may be produced from vapor form onto a chilled wheel some way or the other. For our space rope, it can be several layers thick.

The key point that I am making is that the continuous production of a uniformly thick sheet of graphene with multiple splits is the topological equivalent of a rope. It is also a manufacturing process that can be incrementally improved until we have our space cable.

Shares anyone? This will really work and the initial capability is maybe a year away.

Bigger, Stretchier Graphene

High-quality, clear graphene films are a leap toward bendable OLED displays.
By Prachi Patel-Predd

Big and bendy: A transparent graphene film, two centimeters on each side, stretches and flexes when transferred to a rubber stamp. The stamp can be used to deposit the film on any substrate. Credit: Ji Hye Hong

Korean researchers have found a way to make large graphene films that are both strong and stretchy and have the best electrical properties yet. These atom-thick sheets of carbon are a promising material for making flexible, see-through electrodes and transistors for flat-panel displays. Graphene could also lead to foldable organic light-emitting diode (OLED) displays and organic solar cells. However, it has not been easy finding a way make large, high-quality sheets of graphene.

Researchers from the Sungkyunkwan University and the Samsung Advanced Institute of Technology, in Suwon, Korea, have made centimeters-wide graphene films that are 80 percent transparent and can be bent and stretched without breaking or losing their electrical properties. Others have made large graphene films using
simpler techniques, but the new films are 30 times more conductive. In addition, it is easy to transfer the new films onto different substrates. "We have demonstrated that graphene is one of the best materials for stretchable transparent electronics," says Byung Hee Hong, who led the work, which is published in Nature.

Graphene is an excellent conductor, and it transports electrons tens of times faster than silicon does. It could replace the brittle indium tin oxide (ITO) electrodes that are currently used in displays, organic solar cells, and touch screens. Graphene transistors could also
replace silicon thin-film transistors, which are not transparent and are hard to fabricate on plastic.

The easiest way to make tiny flakes of high-quality graphene is to peel off graphene layers from graphite (which is, essentially, just a stack of graphene sheets). Last year, a group led by Rutgers University materials-science and engineering professor
Manish Chhowalla devised a method for making centimeters-scale pieces for practical applications. The researchers dissolved graphite oxide in water, creating a suspension of individual graphene-oxide sheets, which they deposited on top of a flexible substrate.

The Korean researchers use a method called chemical vapor deposition. First, they deposit a 300-nanometer-thick layer of nickel on top of a silicon substrate. Next, they heat this substrate to 1,000 CÂș in the presence of methane, and then cool it quickly down to room temperature. This leaves behind graphene films containing six to ten graphene layers on top of the nickel. By patterning the nickel layer, the researchers can create patterned graphene films.

Others, such as MIT electrical-engineering professor
Jing Kong, are working on similar approaches to making large graphene pieces. But the Korean researchers have taken the work a step further, transferring the films to flexible substrates while maintaining high quality. The transfer is done in one of two ways. One is to etch away the nickel in a solution so that the graphene film floats on its surface, ready to be deposited on any substrate. A simpler trick is to use a rubber stamp to transfer the film.

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