Could Graphene Become the Next Silicon?

[sanman]

Interesting article I read on how the highly-conductive graphene also begins to exhibit some semiconductive properties at very narrow dimensions:

http://www.technologyreview.com/Nanotech/20119/

http://physicsworld.com/cws/article/news/32539

Gee, I wonder if this could keep Moore's Law going?

 

[sanman]

Yet another breakthrough on graphene production:

http://www.rsc.org/chemistryworld/News/2008/January/28010802.asp

 

[Gokul43201]

how the highly-conductive graphene also begins to exhibit some semiconductive properties at very narrow dimensions

Did you mean to say "graphite" above? Graphene is defined as a monoloayer sheet of graphite, and to my knowledge, the linear dispersion with the Dirac points exists independent of sheet dimensions.

 

[dst]

Did you mean to say "graphite" above? Graphene is defined as a monoloayer sheet of graphite, and to my knowledge, the linear dispersion with the Dirac points exists independent of sheet dimensions.

The links say graphene ribbon.

 

[Gokul43201]

The links say graphene ribbon.

Yes, I didn't read the article fully. Apparently, there's something about on/off ratios in very narrow ribbons. I have no idea what that means - perhaps something to do with the drop in conductivity upon gating?

 

[jpr0]

Did you mean to say "graphite" above? Graphene is defined as a monoloayer sheet of graphite, and to my knowledge, the linear dispersion with the Dirac points exists independent of sheet dimensions.

Nano-ribbons (quasi-1D graphene wires) generally have a gap between the conduction and valence bands at the Dirac point. Also, the band structure of bilayer graphene looks parabolic around the Dirac point.

 

[jpr0]

Didn't Geim already make a "lossless" transistor from graphene nano-ribbons? I guess the difference here is that the sample by Geim was obtained "by chance", whereas the above articles focuses mainly on the fact that GNRs can be made in a controlled way.

This is an article about the Geim transistor:

http://www.rsc.org/chemistryworld/News/2007/February/28020703.asp

 

[sanman]

I believe researchers at Max Planck Institute also created windowpane electrodes from graphene for solar windowpanes.

Graphene devices seem to currently underperform silicon ones despite graphene's superior carrier mobility, so I assume there's a lot of room for optimization/improvement to get the most out of the material.

Now that simple alkaline solutions can be used to make graphene, I wonder how long it will be before we see the manufacture of very large wafers for microprocessors, solar panels, and perhaps even TV displays?

 

[staf9]

Nano-ribbons and nanotubes (both graphite) have both been used as diodes, you can make nano-radios with them. It definitely looks like they have some application in the future of computing.

 

[sanman]

We've all heard about strained silicon:

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

What about strained graphene? What properties would that likely exhibit?
Normal graphene already has an extremely high electrical conductivity. But just as strained silicon has a higher conductivity than ordinary silicon, would strained graphene show any particular improvement?

 

[sanman]

Since graphene has to be whittled down to ~10nm scale in order to become more semiconductive for less leaky gates, then maybe a technology like this one could help achieve that:

http://focus.aps.org/story/v21/st6

 

[sanman]

Could graphene circuits do 1 Terahertz or better?

http://www.technologyreview.com/Infotech/20242/?a=f

Incidentally, this article is part of MIT Technology Review's Special Report on

http://www.technologyreview.com/specialreports/specialreport.aspx?id=19

 

[sanman]

http://nanotechweb.org/cws/article/tech/32967

from the article:

The bandgap of a graphene ribbon strongly depends on its geometry, and in particular its width. Now, Salim Ciraci of Bilkent University in Ankara together with students Haldun Sevincli and Mehmet Topsakal have found that when ribbons of different widths or compositions are joined together, multiple-quantum-well structures form. Electrons confined in the wells mediate several interesting phenomena, like resonant tunnelling, quantum ballistic transport and spin valve effects.

Even more interesting is the finding that superlattices made from zigzag ribbons cause electrons with one direction of spin to be localized in the well region while electrons with opposite spin directions continue to propagate. This way electronic and magnetic states of the quantum structure can be modulated in real space.

Looks like graphene can do all sorts of interesting things that silicon can't.

 

[sanman]

Oh beloved graphene, is there anything you cannot do?

http://physicsworld.com/cws/article/news/33080

 

[sanman]

Fujitsu creates new CNT-graphene hybrid composite material:

http://sst.pennnet.com/display_arti...itsu-touts-lower-temp-CNT-graphene-composite/

 

[sanman]

Bilayered Graphene is capable of reducing noise, resulting in an improved signal-to-noise ratio in comparison to other materials at the nanoscale:

http://www.eetimes.com/news/latest/showArticle.jhtml?articleID=206902149

http://www.semiconductor.net/article/CA6538892.html?desc=topstory

The graphene age comes closer! I hope it's soon!

 

[sanman]

Graphene Using Fewer Electrons More Efficiently

More on graphene, the next big wonder material!

https://www.newsdesk.umd.edu/scitech/release.cfm?ArticleID=1621

 

[sanman]

Graphene for Optical Displays

Graphene is great for optical displays too!

http://physicsworld.com/cws/article/news/33522

ar 27, 2008
Graphene makes for better optical displays

Graphene
Transparent carbon

Graphene may be just one atom thick, but the wonder material has yet another application to add to its mounting stack of potential applications. According to the same group of researchers that first fabricated the 2D sheets of carbon nearly four years ago, graphene has the ideal optical properties to form the transparent electrodes in liquid crystal displays (LCDs). The researchers have also developed a technique that overcomes the traditional problems with manufacturing sizable quantities of graphene.

LCDs typically contain an array of many “cells”, each of which consists of a thin layer of liquid crystal sandwiched between a pair of polarizers crossed at 90° to each other. Light entering from behind a cell gets polarized in one direction when it passes through the first polarizer, so when it reaches the second it cannot get through. This makes the cell appear dark. To make the cell bright, the light must pass through the second polarizer, which requires the intervening liquid crystal to rotate the light’s polarization.

To do this, an electric field is applied across the polarizers and this twists the orientation of the long molecules in the liquid crystal. The polarization of the light is guided along the twist of the molecules, and by the time it reaches the second polarizer it has rotated through 90° so that it can pass.

Of course, the electric field has to be applied using electrodes, and these have to be both transparent and good electrical conductors. For such qualities engineers usually turn to indium tin oxide (ITO). However, this material has its drawbacks: indium is rare and therefore expensive; and ITO can release both indium and oxygen ions, which prevent the liquid crystal from aligning correctly. Now, a team including Andre Geim and Kostya Novoselov from the University of Manchester in the UK and Sergey Morozov from the Institute for Microelectronics Technology in Chernogolovka in Russia have found that graphene is generally more transparent than ITO, but with seemingly no drawbacks (arXiv:0803.3031).
Many applications

Graphene comprises a rippled sheet of carbon just one atom thick, rather like a single layer from a crystal of graphite. Indeed, graphene is often fabricated by ripping a layer off a thin piece of graphite with sticky tape, a process known as micromechanical cleavage (or the “Scotch tape method”). Since Geim and colleagues discovered graphene in 2004, researchers have found no end of desirable properties for the material — it can be an excellent electrical and thermal conductor, an equally good semiconductor, and a sensitive mass detector.

A benefit of using graphene for LCD electrodes is that, unlike ITO, it is stable. This prevents it from releasing ions into an “alignment layer”, which is sometimes applied onto LCD electrodes to encourage the liquid-crystal molecules to align properly. Such stray ions can reduce the effectiveness of the alignment layer, causing undesirable “image sticking”. Perhaps more importantly, however, graphene trumps ITO for transparency. Geim’s team used micromechanical cleavage to deposit flakes of graphene onto a glass slide, which they put under an optical microscope. They found that graphene had an optical transmission of about 98%, significantly higher than the 82–85% of standard ITO.

What is doubly impressive about graphene is that it can achieve high optical transmission with a corresponding sheet resistance (a 2D measure of resistivity) of just 6 kΩ. With an added alignment layer of polyvinyl alcohol, which has the side effect of reducing resistance, this figure drops to 400 Ω. Further chemical doping can reduce the sheet resistance to 50 Ω. ITO, on the other hand, has to trade resistance for transparency. Indeed, if an ITO electrode is made thin enough to rival the transparency of graphene, its sheet resistance skyrockets.
Faster production

The one downside with graphene is that, in the past, it has been difficult to produce. Micromechanical cleavage can only produce a few flakes at a time, and is therefore unlikely to ever be employed commercially. However, Geim’s team have developed a new production technique that can reap larger quantities.

They begin by placing crystals of graphite in a bath of dimethylformamide (DMF) and then sonicate it with ultrasound for over three hours. Graphite is hydrophobic which means it tends to clump together in water, but in DMF the sonication allows it to “dissolve” into flakes. Next, the researchers centrifuge the mixture for 10 minutes to remove thick flakes from the monolayer flakes of graphene, which they subsequently spray onto a glass slide. Finally, they anneal the slides for two hours at 250 °C amid hydrogen and argon gas. Although the thickness is not consistent over the slide — it varies between one and four layers of graphene — the optical properties match those of graphene produced by micromechanical cleavage.

Geim’s team are not planning to commercialize graphene electrodes themselves. Novoselov told physicsworld.com that they have had “interest” from the LCD industry, although he could not name the companies to which he was referring. The team will shortly be publishing more fundamental results on graphene’s optical properties.

 

[sanman]

Couldn't graphene be similarly useful as an electrode for solar cells? If it could be similarly manufactured in very large dimensions for that purpose, then perhaps it could bring down the cost of solar power.

 

[sanman]

Muons in Graphene

Graphene is said to affect its electrons in such a way so as to make them effectively "massless"

http://www.sciencedaily.com/releases/2008/04/080403140918.htm

I'd like to then ask how other heavier leptons, like muons, would behave in graphene?

What would muons do? Would they also behave masslessly?

If so, could this property be usefully exploited for experimental purposes, for example to even probe the nature of graphene or of muons themselves?

 

[sanman]

Just as so many are scrambling to incorporate the word "nano" into the names of their products, it seems like manufacturers of graphitic products are all trying to change the name to "graphene", in keeping with the excitement around the material:

http://www.smalltimes.com/display_a...ene-platelets-outperform-other-nanomaterials/

Is this "nano-graphene" or is it graphite?

 

[sanman]

Also, could buckyballs improve flash memory?

http://community.zdnet.co.uk/blog/0,1000000567,10007899o-2000331777b,00.htm

 

[sanman]

May 12, 2008
http://physicsworld.com/cws/article/news/34159"

Wow, this is cool.

 

[Gokul43201]

There was a paper recently that reported measuring the quantum Hall effect in graphene...at room temperature!

(I'll add a citation later)

 

[will.c]

Was that by any chance talked about in Ivar Martin's presentation at OSU? I'm up in Akron until I get an apartment in Columbus, but I really wanted to crash that seminar, since my undergraduate research was on graphene.

 

[f95toli]

There was a paper recently that reported measuring the quantum Hall effect in graphene...at room temperature!

(I'll add a citation later)

Yes, there is even a project about that where I work. However, from a purely practical point of view (e.g. resistance standards) this is probably only good as a selling point for graphene; you still need a >10 Tesla and the only way to achieve that is with a superconducting magnet in helium meaning you might as well cool the sample as well.

 

[sanman]

Growing High-Quality Graphene

A means of growing high-quality graphene has been achieved:

http://www.physorg.com/news129980833.html

One by one, the obstacles to the graphene age are falling.

I, for one, welcome our new sp2-hybridized overlords.

 

[Gokul43201]

Was that by any chance talked about in Ivar Martin's presentation at OSU? I'm up in Akron until I get an apartment in Columbus, but I really wanted to crash that seminar, since my undergraduate research was on graphene.

No, it wasn't in Martin talks, but there was a mention of it in Ben Hu's talk about a month ago.

Yes, there is even a project about that where I work. However, from a purely practical point of view (e.g. resistance standards) this is probably only good as a selling point for graphene; you still need a >10 Tesla and the only way to achieve that is with a superconducting magnet in helium meaning you might as well cool the sample as well.

They can make these big fields at room temperature in the High Magnetic Field labs, where for instance, this work was done.

Link to the paper in Science: http://www.sciencemag.org/cgi/content/full/sci;315/5817/1379

 

[sanman]

http://www.physorg.com/news131123209.html

 

[sanman]

Graphene Surprises

http://www.physorg.com/news132151987.html

 

[sanman]

Here is a summary of a paper submitted on making a graphene balloon:

http://eprintweb.org/S/article/cond-mat/0805.3309

The PDF is linked on that page.

 

[sanman]

Ultra-Dense Storage from Graphene-based Memory Devices:

http://www.telecomskorea.com/index.php?option=com_content&task=view&id=5855&Itemid=2

The POSTECH professor said tests have shown that the efficiency level of the magnetoresistance of graphene nanoribbons reaches into the million-percent range, compared to few hundred percent for devices created in the past.

Greater efficiency in magnetoresistance translates into smaller memory devices that can store more data.

 

[arw75]

Chirality as well as width

I don't know if this came out in the copious number of articles cited, but it's not just the width of GNRs that determines bandgap, but also the chirality of the cut.

So if you have a graphene sheet, and cut a strip along the zig-zag direction, then along the armchair direction (60deg from memory), then another along the zig zag again, you've made a semiconductor, metal, semiconductor ... I want to say heterojunction, but whatever.

If the cutting method can be implemented, then an electrical circuit could potentially be "stamped" out of a graphene sheet.

If the ballistic transport predictions are as useful as they look, and the electron phonon and electron electron interactions don't bugger things up, then graphene is looking very exciting.

Anyone going to ICSNN in Brazil this Aug? Graphene will be a hot issue...

 

[arw75]

oh and thanks to Sanman for making me laugh:

"I, for one, welcome our new sp2-hybridized overlords. "

 

[sanman]

Hi, what you've said makes sense, as we all know that armchair-vs-zigzag nanotubes make the difference between metallic vs semiconducting nanotubes. So it seems natural for the same thing to apply to sheet graphene.

But for practical chip-making purposes, I'd wonder if we've have to carve out the GNRs for our conductive circuit wires from the armchair direction on one sheet, and then separately carve out our semiconductive gates from the zigzag direction on another sheet, and then use chemical self-assembly to graft all the GNRs into the right places.

That amazing conductivity might make it all worth it, of course.