Graphene Studies

[seasmith]

Graphene's 'quantum leap' takes electronics a step closer

The reason for such unique electronic properties is that electrons in this material are very different from those in any other metals. They mimic massless relativistic particles – such as photons.
Due to such properties graphene is sometimes called 'CERN on a desk' – referencing the Large Hadron Collider in Switzerland. This is just one of the reasons why the electronic properties are particularly exciting and often bring surprises.

In contrast to the single-particle picture, the real spectrum of graphene is profoundly nonlinear so that the Fermi velocity describing the spectral slope reaches ~3x10^6 m/s at n <10^10 cm^-2, three times the value commonly used for graphene.

http://arxiv.org/abs/1104.1396

[seasmith]

~
Graphene for 2D Plasmons

n two-dimensional graphene, electrons have a tiny rest mass and respond quickly to electric fields. A plasmon describes the collective oscillation of many electrons, and its frequency depends on how rapidly waves in this electron sea slosh back and forth between the edges of a graphene microribbon. When light of the same frequency is applied, the result is "resonant excitation," a marked increase in the strength of the oscillation – and simultaneous strong absorption of the light at that frequency. Since the frequency of the oscillations is determined by the width of the ribbons, varying their width can tune the system to absorb different frequencies of light.

The strength of the light-plasmon coupling can also be affected by the concentration of charge carriers – electrons and their positively charged counterparts, holes. One remarkable characteristic of graphene is that the concentration of its charge carriers can easily be increased or decreased simply by applying a strong electric field – so-called electrostatic doping.

The Berkeley team measured prominent absorption peaks at room temperature.

Source: Berkeley Lab


This ES effect brought to mind the NPA lecture today by A Assis: 'The Electric Force of a Current" {a revival of W. Weber's )1804-1891} work on ES/EM interactions.

viewtopic.php?f=3&t=4284&start=90

While there are now many dozens of ED-related, reviewed paper$ in the journals, i could not find one cogent explanation of the elementary physics of 'Electrostatic Doping'.
Perhaps one of T'bolt's kind and talented contributers could help here.

If one needs to allocate a numerical value to "voltage", rather than "voltage difference", then a reference zero must be defined. The most useful system of referencing takes body "B" as the Earth, and sets µB=0 and VB=0. In circuit analysis this is achieved by attaching a "Ground" symbol to some appropriate point of the circuit.

In this context, it must be clearly understood that the term "voltage difference" always relates to differences in electrochemical potential that occur inside conductors. The term "voltage difference" should never be used to refer to differences in electrostatic potential, whether these occur inside electrical conductors or in space outside them (even though such differences are also normally measured in volts).

http://en.wikipedia.org/wiki/Fermi_level

[webolife]

Just a little sound bite from me... my view defines light as the delta-voltage caused by the decrease in the electrons PE [electron drops to a lower "energy level"], not as something emitted by that process from the atom.

[Jarvamundo]

thanks for the updates sea

Just a little sound bite from me... my view defines light as the delta-voltage caused by the decrease in the electrons PE [electron drops to a lower "energy level"], not as something emitted by that process from the atom.

[like button]

[seasmith]

Nov 17, 2011
Graphene goes Magnetic

So say researchers in Japan who have observed room-temperature ferromagnetism in the graphene nanopore arrays, caused by, they believe, electron spins localized at the zigzag-shaped atomic-structured nanopore edges. The phenomenon, only predicted by theory until now, might help make magnets that are rare-element free, extremely light, transparent and flexible, as well as novel spintronics devices that exploit edge-polarized spins.

Magnetic flux exists in probably all atomic structures, but only some atomic structures/geometric forms
release the flow to surrounding space.
'Edges' are naturally orthogonal planes, a bit like antennas .

Magnets and spintronics devices
According to Haruyama, the graphene arrays could be used as single-layer magnets that are rare-element free, extremely light, transparent and flexible. They might also be used to make novel spintronics devices that utilize edge-polarized spins.

http://nanotechweb.org/cws/article/tech/47854

[seasmith]

"These are electronic stripes, called "charge density waves," on the surface of a graphitic superconductor."

The LCN team donated extra electrons to a graphene surface by sliding calcium metal atoms underneath it. One would normally expect these additional electrons to spread out evenly on the graphene surface, just as oil spreads out on water. But by using an instrument known as a scanning tunneling microscope, which can image individual atoms, the researchers have found that the extra electrons arrange themselves spontaneously into nanometer-scale stripes. This unexpected behavior demonstrates that the electrons can have a life of their own which is not connected directly to the underlying atoms.

Matter waves ?


http://www.nature.com/nphys/journal/v1/ ... s0010.html


http://www.nanowerk.com/news/newsid=235 ... oo%21+Mail

[mharratsc]

I say - think of corn starch and water on a speaker:

Collins Lab: DIY Cymatics


It's all about the vibrations, I think... the question is: at that scale, where do the vibrations come from? o.O

[seasmith]

PIEZOELECTRIC GRAPHENE:

Piezoelectric substances generate electricity in response to physical pressure, and vice versa, and scientists can use these materials for applications such as energy harvesting and artificial muscles, as well as to make precise sensors. Graphene itself is not naturally piezoelectric. But the Houston engineers reasoned that if they took either a semiconducting or insulator form of graphene, punched triangle-shaped holes into it, and applied a uniform pressure to the material, they could make that material act as though it were piezoelectric.

The team's calculations showed that triangular holes did indeed result in piezoelectric behavior, while circular holes – as they predicted – did not. They also found that graphene's pseudo-piezoelectricity was almost as strong as that of well-known piezoelectric substances such as quartz. The authors suggest that triangular pores could be created in real graphene using electron-beam radiation in a lab, which means these calculations can be tested using existing methods. "Nature has dealt humankind … a very limited choice of effective electromechanical materials" that exhibit piezoelectricity, write the authors in their paper, accepted to the AIP's Applied Physics Letters. Adding graphene to the list "could potentially open new avenues" of use, both for graphene and for applications that rely on piezoelectricity.

Source: American Institute of Physics

[webolife]

This triangular hole behavior would appear to be a confirmation of the fundamental geometric properties of matter.
I'm wondering if they found if square holes also work?

[seasmith]

I'm wondering if they found if square holes also work?
-webo

Don't know, but my conclusion was about the same. Square is pretty close to circle, ie stable~ whereas has been discussed previously, triangular and hexagonal forms being natural modes of propagation.
Have a background with piezoelectricity, but have no idea if say rocksalt (squarish crystal) is a good transducer.
Is there a science teacher in the house ?


http://www.nanowerk.com/news/newsid=238 ... oo%21+Mail

[webolife]

Quartz is classic piezoelectric crystal. The harder crystals also work well.
I think pure halite is too soft to be a good piezocandidate, but apparently some salts do work.
Interestingly only non conductors are piezoelectric! That is an interesting idea I hadn't pondered.
How might this affect the topic of telluric currents?

[seasmith]

Well sure, but quartz is definitely not square:



Although some of its related compounds probably are.

[mharratsc]

Quartz is a good piezoelectric. It is one of the 'growing' crystals that will extrude in a hexagonal form. Do other similarly 'growing' crystals exhibit good piezoelectric characteristics?

[seasmith]

Interestingly only non conductors are piezoelectric! That is an interesting idea I hadn't pondered.
How might this affect the topic of telluric currents?
-webolife

The effects would probably be minimal, on a global scale.

Piezo materials, including crystals and ceramics generate a voltage in response to an applied mechanical stress. In what is known as the inverse piezoelectric effect, these same materials will lengthen or shorten in response to an applied voltage.

Both effects entail high frequency oscillations and very small currents. Although quarts and feldspar are the two most common elements in the Earth's crust, either effect is more likely to be of a local nature.

Telluric currents (low frequency) are probably of an more inductive nature, ie moving EM fields penetrating a conductive crust and/or flowing conductors like oceans and magmas traversing Earth's magnetic field, though the book is far from written.

Many modern piezo-transducers are manufactured semiconductors, and with natural quartz being used to 'seed' the beds for silicon wafer stock. It seems, in a broad sense, that the 'doped' semiconductors are mimicking a condition of charge mobility that is produced naturally by certain crystal geometries?

My work was with UT and the use of piezoelectrics, not the manufacture of transducers...

[seasmith]

I should go back some on the "high frequency" bit above. HF is characteristic of most modern and UT apps, but early phonograph cartridges did use piezo crystals and ceramics to transmit low frequencies, which are then amplified electronicly.
[Also a common crystal used was Rochelle Salt, which has some version of an orthorhombic crustal structure.]

So, strong LF-EM fluxes could conceivably make the mountains hum, or LF grinding of geo-faults could make the mountains glow. Local anomalies on the geo-magnetic maps may well have a piezoelectric component.


http://www.co-bw.com/Audio_Turntables_A ... ges.htm#tc