Graphene Studies

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webolife
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Re: Graphene Studies

Unread post by webolife » Thu Jan 12, 2012 11:45 am

Help me with a mental roadblock...
If telluric currents are in the crust, yet the crust is largely non-conductive...
there seems to be a paradox or a contradiction here...
Sorry if this is off thread... it will help me understand graphene better if I can get this out of my head...
Truth extends beyond the border of self-limiting science. Free discourse among opposing viewpoints draws the open-minded away from the darkness of inevitable bias and nearer to the light of universal reality.

seasmith
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Re: Graphene Studies

Unread post by seasmith » Thu Jan 12, 2012 3:20 pm

Telluric currents
Web,
Really haven't spent much time on the subject yet, but guess the quickndirty answere is that the name is an old one. "Tellurics" have since been shown to permeate the seas and magmas as well, and as most of the crust contains H2O and various salts, apparently conductivity is there also.
A harebrained notion of my own is that, on a global scale, the crustal zones with their myriad mixes of elements, minerals and compounds, may act in some areas as 'doped' transistors too, in response to atmospheric emf's

edit: of course that was meant to be orthorhombic Crystal, not crustal in previous post...

mharratsc
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Re: Graphene Studies

Unread post by mharratsc » Mon Feb 27, 2012 8:06 am

webolife wrote:Help me with a mental roadblock...
If telluric currents are in the crust, yet the crust is largely non-conductive...
there seems to be a paradox or a contradiction here...
Sorry if this is off thread... it will help me understand graphene better if I can get this out of my head...
Everything is dielectric at some power level, if you think about it. The Earth is a semiconductor, like any silicon-based IC chip.
Mike H.

"I have no fear to shout out my ignorance and let the Wise correct me, for every instance of such narrows the gulf between them and me." -- Michael A. Harrington

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webolife
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Re: Graphene Studies

Unread post by webolife » Wed Feb 29, 2012 11:59 am

That's more at my thinking... so here's my next question: Does the pressure on the semi-conductor transform it into a conductor? And if so, does this not make a direct correlation between mechanical pressure and voltage?
Truth extends beyond the border of self-limiting science. Free discourse among opposing viewpoints draws the open-minded away from the darkness of inevitable bias and nearer to the light of universal reality.

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starbiter
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Re: Graphene Studies

Unread post by starbiter » Wed Feb 29, 2012 7:42 pm

The link below shows how heat and pressure increase the conductivity of rock [a semiconductor].

http://mars.mines.edu/pub/76EPropertiesRocks.pdf

This process would allow current to possibly penetrate rock to depth.

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seasmith
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Re: Graphene Studies

Unread post by seasmith » Sat Mar 17, 2012 9:05 am

~
Engineered piezoelectric graphene

[how to make conductors di & piezo electric]
They modeled graphene doped with lithium, hydrogen, potassium and fluorine, as well as combinations of hydrogen and fluorine and lithium and fluorine on either side of the lattice. Doping just one side of the graphene, or doping both sides with different atoms, is key to the process as it breaks graphene's perfect physical symmetry, which otherwise cancels the piezoelectric effect.
The results surprised both engineers.
"We thought the piezoelectric effect would be present, but relatively small. Yet, we were able to achieve piezoelectric levels comparable to traditional three-dimensional materials," said Reed. "It was pretty significant."
Designer piezoelectricity
"We were further able to fine tune the effect by pattern doping the graphene—selectively placing atoms in specific sections and not others," said Ong. "We call it designer piezoelectricity because it allows us to strategically control where, when and how much the graphene is deformed by an applied electrical field with promising implications for engineering."
Image

http://pubs.acs.org/doi/abs/10.1021/nn204198g

http://www.nanowerk.com/news/newsid=246 ... oo%21+Mail


All of which sort of ties in with of the postings here about Telluric effects, mharratsc's and my comments on dielectrics and semi-conductor doping above.

~

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Re: Graphene Studies

Unread post by seasmith » Thu May 31, 2012 6:56 pm

Posted: May 31st, 2012
Graphene in a highly non-linear state

Wang explained that linear optical properties only transmit light – one light signal comes into a material and one comes out. "The non-linear property can change and modulate the signal, not just transmit it, producing functionality for novel device applications."
"We were the first group to break new ground, to start looking at it in a highly excited state consisting of extremely dense electrons – a highly non-linear state. In such a state, graphene has unique properties."
Wang's group started with high-quality graphene monolayers grown by Hupalo and Tringides in the Ames Laboratory. The researchers used an ultrafast laser to "excite" the material's electrons with short pulses of light just 35 femtoseconds long (35 quadrillionths of a second). Through measurements of the photo-induced electronic states, Wang's team found that optical conductivity (or absorption) of the graphene layers changed from positive to negative – resulting in the optical gain – when the pump pulse energy was increased above a threshold.
The results indicated that the population inverted state in photoexcited graphene emitted more light than it absorbed. "The absorption was negative. It meant that population inversion is indeed established in the excited graphene and more light came out of the inverted medium than what entered, which is optical gain," Wang said. "The light emitted shows gain of about one percent for a layer a mere one atom thick, a figure on the same order to what's seen in conventional semiconductor optical amplifiers hundreds of times thicker."
http://www.nanowerk.com/news/newsid=254 ... oo%21+Mail

Sparky
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Re: Graphene Studies

Unread post by Sparky » Thu May 31, 2012 9:02 pm

Well, there you go again.... :!: Bending my mind... :D
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webolife
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Re: Graphene Studies

Unread post by webolife » Sat Jun 02, 2012 9:26 am

Emitted... do they just mean "reflected" or is it "transmitted" [as through a filter], since the graphene surface was "photoexcited"?
Truth extends beyond the border of self-limiting science. Free discourse among opposing viewpoints draws the open-minded away from the darkness of inevitable bias and nearer to the light of universal reality.

seasmith
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Re: Graphene Studies

Unread post by seasmith » Sun Jun 03, 2012 1:44 pm

Emitted... do they just mean "reflected" or is it "transmitted" [as through a filter], since the graphene surface was "photoexcited"?
Web,

I've read a related article in the print version Nature Nanotechnology, which is covered up with arcane formulii and theoretical terms, but i think it would be more properly be re-emitted.
The mechanism is an equivalent of 'surface plasmon resonance'
http://en.wikipedia.org/wiki/Surface_plasmon_resonance
(also discussed a bit in the "Extraordinary Light" thread")
tho that term seems to have fallen out of favor lately as different research facilities vie for their own patents.

These folks, and IBM in the print article, are combining different electro-molecular resonances & structures (here stacked like Tesla's cascading capacitor discharge plates ?) and observing the results with the new bevy of electro-scanning microscopes (who knows how They affect nano-tranitions ??), to see what happens.

garbage in, biofuels out,
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seasmith
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Re: Graphene Studies

Unread post by seasmith » Wed Jul 11, 2012 6:56 pm


Graphene Repairs Holes By Knitting Itself Back Together, Say Physicists

Image

Enter Konstantin Novoselov at the University of Manchester and a few pals who have spent more than a few hours staring at graphene sheets through an electron microscope to see how it behaves.

Today, these guys say they've discovered why graphene appears so unpredictable. It turns out that if you make a hole in graphene, the material automatically knits itself back together again.

Novoselov and co made their discovery by etching tiny holes into a graphene sheet using an electron beam and watching what happens next using an electron microscope. They also added a few atoms of palladium or nickel, which catalyse the dissociation of carbon bonds and bind to the edges of the holes making them stable.

They found that the size of the holes depended on the number of metal atoms they added--more metal atoms can stabilise bigger holes.

But here's the curious thing. If they also added extra carbon atoms to the mix, these displaced the the metal atoms and reknitted the holes back together again.

Novoselov and co say the structure of the repaired area depends on the form in which the carbon is available. So when available as a hydrocarbon, the repairs tend to contain non-hexagonal defects where foreign atoms have entered the structure.
http://www.technologyreview.com/view/42 ... 2012-07-11


http://arxiv.org/abs/1207.1487

seasmith
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Re: Graphene Studies

Unread post by seasmith » Mon Jul 23, 2012 7:58 pm

~
Carbon nanotube rope stimulates neural stem cells

Image
SEM image of the interaction of NSCs on CNT rope. The majority of neurites extend along the ridgelike structure of the spiral topography. Inset: low-magnification image of the CNT rope structure. (Reprinted with permission from Wiley-VCH Verlag)
Reporting their work in the July 2, 2012 online edition of Small
"Carbon Nanotube Rope with Electrical S ... tem Cells"
a team led by Tzu-Wei Wang, an assistant professor in the Department of Materials Science and Engineering at National Tsing Hua University, found that neural stem cells plated on carbon nanotube rope were not only boosted towards differentiated neurons but also promoted their neurite elongation when compared to conventional tissue culture plate via the analysis of neuronal specific gene and protein expressions.
These NSCs were fluorescently transfected and cultured on the CNT twisted rope-like structure. This CNT rope device provides a platform for the possibility to in situ observe the real-time response of these stem cells on an eletroconductive substrate after electrical stimulation.
http://onlinelibrary.wiley.com/doi/10.1 ... 8DD.d03t01

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webolife
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Re: Graphene Studies

Unread post by webolife » Mon Jul 23, 2012 8:59 pm

Ok, I will take "re-emitted" as a description of reflection. This is relevant to the discussion in that it is likely only a characteristic of the electrical quasi-surfaces of graphene that are involved in the behavior of the light.
Truth extends beyond the border of self-limiting science. Free discourse among opposing viewpoints draws the open-minded away from the darkness of inevitable bias and nearer to the light of universal reality.

Michael V
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Re: Graphene Studies

Unread post by Michael V » Tue Jul 24, 2012 3:36 am

webolife,

I confess I am not too interested in the graphene thing, but if it helps:
The nature of light is solved. A single "photon" is only emitted once, subsequent "re-emissions" from other electrons are causal though not inevitable. The re-emission is not the same photon, even if the newly caused photon has similar characteristics.

Michael

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webolife
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Re: Graphene Studies

Unread post by webolife » Tue Jul 24, 2012 9:48 pm

Not wishing to go far offthread, Michael, could you clarify for me whether you believe that the nature of any reflection is "re-emission" [regardless of our differences about the nature of "photon"]?
Truth extends beyond the border of self-limiting science. Free discourse among opposing viewpoints draws the open-minded away from the darkness of inevitable bias and nearer to the light of universal reality.

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