

Graphene creates electricity when struck by light - kennjason
http://www.extremetech.com/extreme/98941-graphene-creates-electricity-when-struck-by-light

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jws
Original MIT description: [http://www.mit.edu/newsoffice/2011/graphene-
thermoelectric-1...](http://www.mit.edu/newsoffice/2011/graphene-
thermoelectric-1007.html)

Current had previously been seen in response to light, but was assumed to be a
photovoltaic effect. This new work says it is a "hot-carrier" response.

 _"The material’s electrons, which carry current, are heated by the light, but
the lattice of carbon nuclei that forms graphene’s backbone remains cool. It’s
this difference in temperature within the material that produces the flow of
electricity."_

It is interesting because it is a response to temperature differences and
responds to wide frequencies and power ranges of light.

Don't sell your coal mine stock yet, _"It is still unclear if it could be used
for efficient energy generation. It’s too early to tell."_

~~~
jcfrei
>Don't sell your coal mine stock yet, "It is still unclear if it could be used
for efficient energy generation. It’s too early to tell."

isn't graphene made from coal? maybe this discovery might even further
increase coal demand?

~~~
sp332
Coal is made of carbon molecules, and so is graphene. But then again so is
diamond, and graphite (pencil lead). So it's not easy to convert
coal->graphene (though it's probably not as hard as graphite->diamond :)

[https://secure.wikimedia.org/wikipedia/en/wiki/Allotropes_of...](https://secure.wikimedia.org/wikipedia/en/wiki/Allotropes_of_carbon)

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jpdoctor
Can anyone with an actual background in thermoelectrical effects tell us why
this is not just a consequence of graphene's Seebeck coefficient?

As near as I can tell:

1\. They used 850nm to heat one side of the graphene pn junction

2\. Photons have an absorption depth, so the side facing the laser heats more
than the side away from the laser.

3\. Seebeck effect manifests.

~~~
sp332
They didn't heat one side, they heated all of it. The electrons became mobile
and moved from the n-side to the p-side. What's interesting is that the
electrons got exited but the nuclei did not. So the nuclei stay in their
pattern while the electrons flow.

Edit: all I know is what I read in the press release :) Here's the actual
paper <http://arxiv.org/abs/1108.3826>

~~~
jpdoctor
> What's interesting is that the electrons got exited but the nuclei did not.

This statement can't be right. If the temperature of the material went up,
then the nuclei became exited. And if they didn't, then the result is
identical to the photoelectric effect.

Edit: By the way, what you've described corresponds to "freeze-out" in old-
fashioned semiconductor terms. As you drop the temperature of a diode, the
free electrons and holes fall back to their low energy state and it turns back
into a vanilla semiconductor. Heating it up makes them mobile again.

Edit2: > Edit: all I know is what I read in the press release :)

Yeah, it was clear that the PR was not written by someone knowledgeable. I'm
sure there are MIT folks on this board so I'm hoping one of them pokes the
right colleague so that we get a clearer answer, because it sure sounds like
there's something interesting going on there.

Thanks for the arxiv pointer, I'll try to look this weekend.

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Cushman
Am I the only one who wishes we could give these folks a few billion dollars
so they could stop issuing press releases and just _make_ something already?

~~~
mrsebastian
The graphene researchers from yesterday got $2 mil at least!
<http://news.ycombinator.com/item?id=3080058>

But yeah, money going into graphene research will certainly be on the rise
over the next few years :)

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sp332
This effect was seen before, but had been dismissed as a photoelectric effect.
[http://www.mit.edu/newsoffice/2011/graphene-
thermoelectric-1...](http://www.mit.edu/newsoffice/2011/graphene-
thermoelectric-1007.html) And here's the actual paper:
<http://arxiv.org/abs/1108.3826>

------
meow
"Since its discovery in 2004 (by pulling a thin layer off a piece of pencil
graphite using sticky tape)"

So can I just do that and get a layer of graphene ? I mean is it really that
simple ?

~~~
sp332
You'll get a bunch of graphite and some microscopic bits of graphene. But
yeah, it's the easiest way to get some for experimenting.
[https://secure.wikimedia.org/wikipedia/en/wiki/Graphene#Draw...](https://secure.wikimedia.org/wikipedia/en/wiki/Graphene#Drawing_method)

------
ck2
So could a space elevator in theory be self-powering from the cable?

I mean there is going to be 36,000km of it.

~~~
sp332
Maybe. But they'll have to deal with the fact that a space elevator would
effectively "ground" the ionosphere first.

~~~
jsmcgd
I guess you don't actually need to ground it. The Earth end of it could hover
above the ground or it could be attached to some insulator.

