Talk:Graphene

From Wikipedia, the free encyclopedia

	Chemistry Portal Graphene is within the scope of WikiProject Chemicals, a daughter project of WikiProject Chemistry, which aims to improve Wikipedia's coverage of chemicals. To participate, help improve this article or visit the project page for details on the project.
Article Grading: The article has not been rated for quality and/or importance yet. Please rate the article and then leave comments here to explain the ratings and/or to identify the strengths and weaknesses of the article..

Contents 1 Allotrope? 2 2D Crystal? 3 Electron Transport 4 Properties 5 Minimal conductivity 6 Finite thickness 7 Graphene's thickness 8 Developments happening quickly 9 Translation into english? 10 who should be credited for the discovery of graphene? 11 When did Wikipedia discover graphene? 12 Lowest Resistivity? 13 Graphene by liquid-phase exfoliation 14 Graphene Nanoribbons

[edit] Allotrope?

From the article:

"It is not an allotrope of carbon because the sheet is of finite size and other elements appear at the edge"

For that matter, the same occurs for diamond and graphite. Diamond is merely a matrix of carbon atoms bonded in a tetrahedral shape. Graphite is series of benzene rings. In both allotropes, each carbon atom has a total of four bonds, assuming that the matrix is unbounded (in graphite, there are two single bonds and one double bond per atom). When the matrix ends, the carbon atoms typically bond to hydrogen atoms at their surface to terminate the extra loose bonds. And yet, the two are still considered allotropes.

It is not, then, for this reason that graphene is not a new allotrope.

From my reading, graphene is similar to graphite in that it is a single layer of a graphite matrix. See here (IUPAC). Note that graphene is a singular sheet of graphite, just as goose is the singular of geese. For this reason, graphene is not an allotrope, because graphene and graphite are the same.

Also, note that graphite is a 'quasi-infinite' matrix.

Kris Kerwin

Graphene is chemically and structurally quite different from graphite. For example, it is a semi-conductor and it is prevented from melting by micrometer-scale random corrugations. Whether it is different enough to be an allotrope is tricky, but I'd say it is. I completely agree that the finiteness of graphene is irrelevant and should not be mentioned. Even other allotropes of carbon are finite in some or all dimensions, including nanotubes and buckyballs. --Alistair

A quick search on Google for "graphene allotope" seems to point to classification of graphene as a carbon allotrope. These include pages from the University of Conneticut (http://www.phys.uconn.edu/Seminars/2007Spring/20070319hsc.html), a peer-reviewed article in Nature Physics (http://www.nature.com/nphys/journal/v2/n9/full/nphys384.html - Nature Physics 2, 620 - 625 (2006)), and an article in C&E News (The news magazine of the American Chemical Society - http://pubs.acs.org/cen/science/84/8416sci1a.html) On the minus column is an article in The Hindu (http://www.hindu.com/seta/2006/04/06/stories/2006040600971700.htm - "It is however not an allotrope because (a) the sheet is finite in size and (b) it contains at least one more element, namely hydrogen at the edges."), and an entry in nanoscienceworks.org's Nanopedia (http://www.nanoscienceworks.org/nanopedia/graphene - "It is not an allotrope of carbon because the sheet is of finite size and other elements appear at the edge in nonvanishing stoichiometric ratios"). Those are just the results from the first 30 entries. At any rate, the current claim that it is not an allotrope is inconsistent with the WP page on allotropes, because the latter does not refer to thickness as a criteria. One or the other page should be fixed. -- 14:27, 26 July 2007 (UTC)

[edit] 2D Crystal?

Is graphene really a 2D crystal???, graphene is not , strictly speaking, a crystal in the full sense of the word, since I don't think you can speak of "translational symmetry" because that would mean you could consider its dimentions to be much , much larger than the unit cell , which is definitely not the case for graphene. --85.138.18.55 18:07, 12 April 2006 (UTC) Pedro

It certainly makes sense to say graphene is a 2D crystal - it has two distinct translation symmetries. Similarly, a carbon nanotube is a 1D crystal. --Alistair

[edit] Electron Transport

In the section on electron transport, it might be more accurate to say that the "charge carriers" obey a Dirac equation, not the electrons. That way, the statement includes holes too, but excludes non-conduction electrons. However, this should be checked with somebody who actually knows about the electronic structure! --Alistair

I would second the amendment of "electrons" to "charge carriers": this is the terminology used in Novoselov et al. Science 306 2004. The discussion of whether or not graphene is an allotrope of carbon is flawed (the 'thickness' of a material is irrelevant, an allotrope is a structurally different form of the same element) and boils down to semantics in the end; more importantly I don't believe that this is the best way to start what is supposed to be an informative article. When we give talks we normally start with the dimensionality aspects: i.e. 0D = quantum dots, atoms etc., 1D = nanowires, nanotubes, 3D = diamond, graphite etc., and now 2D = monolayer graphene, monolayer hexagonal boron nitride etc. which places the discovery in context (note that dimensionality in this sense refers to electronic transport properties and not the structure itself). Graphene is not just a singular noun, Kris, and graphene and graphite are most definitely not the same - they differ in terms of band structure (graphene is a zero-gap semimetal), transport properties (ballistic conduction at room temperature in graphene), crystal structure (graphite has a c unit cell parameter) etc. The discussion of defects is interesting, but again not necessarily the best way to start the article in my opinion. - T. Booth Mbcx0tjb 13:19, 24 March 2007 (UTC)

[edit] Properties

Any details of graphene's melting point, breaking strength, stretchability, electrical conductivity and heat conductivity? If they direction dependent please give all values. Andrew Swallow 22:30, 11 July 2007 (UTC)

[edit] Minimal conductivity

Should the minimal conductivity mentioned in the article not be e²/h instead of e²/ hbar ? Sorry I am not quite sure. Can someone please correct the entry and delete this from discussion?

Minimal conductivity in Novoselov et al. work is 4e²/h - 4 coming from the two pseudospins times two valley indices. However, recently there have been indications that this value is not universal, i.e., it depends on the actual strength of disorder in the material. For ballistic samples, the theoretical prediction for the conductivity is rather 4e<up>2/π. Anyway - I did not find a mentioning of this minimal conductivity in the main article, and as it is still a bit controversial, it should probably be left out. --80.220.143.51 19:41, 9 August 2007 (UTC)

[edit] Finite thickness

The article says "It is not an allotrope of carbon because the sheet is of finite thickness." How does that follow? Any sheet of any material is of "finite thickness". Matt 00:42, 8 August 2007 (UTC).

• I see now that this sentence was also queried above by others. I've removed it. It makes no sense as written, and if it's supposed to mean something then it needs to be explained better. Matt 13:56, 8 August 2007 (UTC).

[edit] Graphene's thickness

Hi you all! Perhaps there's an error at the end of "Chemical modification" paragraph: it's written that graphene's layers are 5,3 angstroms thick. But in Princeton's PDF, at page 16, it's written that a graphene's flake is 3,34 angstroms thick. I think you should write 3,5 instead of 5,3 angstroms in the article. What do you think? Let me know on [1]. Bye.--87.2.174.81 21:20, 1 September 2007 (UTC)

[edit] Developments happening quickly

Graphene Gazing Gives Glimpse Of Foundations Of Universe

"I was rather pessimistic about graphene-based technologies coming out of research labs any time soon. I have to admit I was wrong. They are coming sooner rather than later."

Shenme (talk) 08:16, 4 April 2008 (UTC)

[edit] Translation into english?

Alot of the material, especially in the subsections under "properties", are deeply techincal and seem to make no attempt to reahc a reader who is not a qunatum physiscist and would probably know all this stuff anyway. For example, under electronic properties, there is a statement: "Thus, the Hall conductivity is [some martian giberish], where N is the Landau level index and the double valley and double spin degeneracies give the factor of 4. This remarkable behavior can even be measured at room temperature." If you don't happen to know what Hall conductiviy and Landau level indices are the only thing "remarkable" about this is that anyone believes more than 2% of the Wikipedia readers will understand it at all ;-)

But serioulsy, if anyone really does understand what all this means, it would be nice to ADD some statements saying something like "this means such and such" without actually dumbing down the article or removing any of the important facts and figures. A good example, under the mechanical properties, is the statement "These high values make Graphene very strong and rigid." I may not know what the Mermin-Wagner theorem is but, I do know what strong and rigid mean. Rich.lewis (talk) 17:14, 7 April 2008 (UTC)

[edit] who should be credited for the discovery of graphene?

If Iijima is often considered as the discoverer of carbon nanotubes, would not then it be fair to give the credit for graphene as it was suggested by Carbophiliac?

"This discovery should be attributed to Andre Geim who is the corresponding author in the first few graphene papers.^[1][2] His priority seems to cause no controversy, unlike the hotly-debated discovery of carbon nanotubes. Indeed, there have been a number of earlier efforts to make very thin films of graphite by mechanical exfoliation (just like the Manchester group did) but nothing thinner than 50 to 100 layers came out, and no proof for the existence of free-standing layers of 2D crystals was given before 2004.

Further credits for the discovery of graphene go to Kostya Novoselov (Geim's associate; the first author in most of the Manchester papers) and Philip Kim from Columbia University whose group was first to confirm and extend Geim's discovery."

Let me add that I followed refs given by UMDNANO and found that Geim was one of the two corresponding authors of Nature 2007 that was first to report graphene in the suspended state. In my opinion, it is actually not important as the area took off after his Science 2004 and the back-to-back Nature papers in 2005.

YZhangfirst (talk) 21:59, 24 April 2008 (UTC)

Two points that might help here:

(i) I'm not sure about benchmarks in the manufacture of large free-standing sheets, although electron microscopists have I think had methods for making very thin supports for transmission study of single heavy atoms for some time. It might be worthwhile to check further into that literature on that, and in that context I will ask around.

(ii) Concerning the existence of atom-thick graphene sheets in bulk, we've known now since the mid 1990's that unlayered graphene (density near 2g/cc) is manufactured in abundance in the atmosphere of late-stage red giant stars. Laboratory samples of presolar materials show this clearly by more than one analysis technique. How asymptotic giant branch stars pull it off, and how in turn we might similarly make composites of unlayered graphene on earth, is still a mystery and the subject of ongoing research. Thermochap (talk) 22:38, 24 April 2008 (UTC)

Thanks for this. I do not really know about graphene around red giants but, surely, so-called nanographenes (a few nm large sheets of graphene) should be there too, next to a plenty of buckyballs and carbon nanotubes. I also read that chemists can make graphene molecules consisting of up to 222 atoms (10 or so benzene rings in diameter). Still, there is a sea of difference between nanocrystals and macroscopic crystals that you can touch, measure and even look through. 81.104.93.72 (talk) 23:01, 24 April 2008 (UTC)

Thank you both for your thoughtful comments. I agree there seems to be nothing new under the sun. But I do believe that the size does matter (at least, my girlfriend says so ;-).

YZhangfirst (talk) 23:11, 24 April 2008 (UTC)

I do not really understand why UMDNANO argues against Geim. Someone has to be credited for the discovery of graphene and he is a single focal point for this. Of course, there were bits and pieces known before but the breakthrough came from his group, as even UMDNANO agrees. In any case, this is a done deal. Geim got the Mott prize for "the discovery of graphene" (I just added this to Andre Geim page). One can of course argue that this is a British prize and they can be biased (but probably less than one guy called UMDNANO). I googled further and found that Geim's associate Kostya Novoselov got a young scientist European prize (Kurti or something) for "his part in the discovery of graphene". Novoselov also listed as a 2008 prize winner from "International Union of Applied and Pure Physics". I did not find the citation line there but it is probably similar.

So whom should we trust? British, Europeans, Internationals or UMDNANO? Let us return the Discovery page to the original state of Carbophiliac (I have no time now - please do).

DrWhoever (talk) 11:54, 25 April 2008 (UTC)

I'll comment on this. It is abundantly clear that Andre Geim has discovered something, but this is science, so we should be careful about defining what he discovered. Certainly Geim made the first electrical transport measurements on graphene, and these measurements were instrumental in showing that graphene's electronic properties were those described by Wallace in 1947 (i.e. massless Fermions). Geim's 2004 paper is also incontrovertably the work that started the explosion of interest in graphene. However, Geim no more "discovered graphene" than Bednorz and Müller discovered superconductivity. Bednorz and Müller still won the Nobel prize, and Andre Geim still might.

It is clear that the concept "graphene" existed theoretically and experimentally well before 2004. The IUPAC definition of "graphene" dates to 1995! And surface scientists were studying graphene for years (there are literally dozens of paper on this, by some very prominent scientists, this is not some obscure stuff that no one knows about). Also, Walt de Heer's group has shown that graphene on silicon carbide, which has been studied since 1975, has the same massless Dirac Fermion properties as Geim's graphene. So, is graphene on SiC still "graphene"? Did Geim discover it? I think the answer to the first has to be yes, and the second, no. Yet, Geim was the first to show that graphene on SiO2 really behaves like graphene, by doing electrical measurements, and he beat de Heer to this.

It appears to me that the Mott prize committee tried to solve this problem by awarding Geim the prize for "For his discovery of a new class of materials: free-standing two-dimensional crystals, in particular graphene." The key word is "free-standing". What does it mean? It seems to refer to graphene free of any substrate, which Geim could possibly get the credit for, but only in 2007 (and the prize was announced in October, 2006!) So "free-standing" graphene needs a definition, and none is provided by the Mott prize citation. I would say "free-standing" graphene is graphene that is only weakly bound to a substrate, such that its electrical properties are similar to the isolated 2D crystal. Within this definition, Geim be be properly said to have "discovered free-standing graphene".

I'd be happy with any changes to the History/Discovery section that reflect this.

Umdnano (talk) 14:14, 25 April 2008 (UTC)

This is much better. Sounds like a genuine disagreement rather than a grudge.

Let me comment on this. I wrote a thesis on graphene, and it contained a long section on history of graphene and I continue to be interested in who, why and how in this story. It might be biased as most information comes from the articles Geim co-authored (Geim&Novoslov, Nature Mat 2007; Geim&McDonald, Physics Today 2007; Geim&Kim, Scientific American this year; one can download the copies from www.graphene.org as I did). But all the papers should have been refereed I believe, MacDonald is a famous theorist and Kim is Geim's arch-competitor. There is also Physics World by Neto, Guinea and Peres. I know Paco Guinea, and he is not a guy who would compliment everyone.

Those articles clearly say that graphene was known before as 1) an idealized system for theorists (like Wallace and Semenoff); 2) within chemically exfoliated soot/sludge; 3) as large molecules (PAH) or nano-graphenes; 4) as epitaxial layers. However, no one ISOLATED individual graphene layers (either microscopic or macroscopic); they all remained in bulk or on top and frankly no one was bothered at all about THOSE graphene layers. If people bother about them now and revisit the earlier studies (sometimes claiming hindsightedly how clever they are), then only because graphene has become interesting, AFTER Geim showed that it was a beautiful system.

Look at "graphene oxide" papers. Now it seems so straighforward to take graphite oxide known for more than 100 years and dissolve it in water to get monolayers. I doubt that the several groups now studying graphene oxide papers, films, etc. would be bothered to search for monolayers without being prompted by Geim's research.

It is not important whether graphene is suspended (as in references UMDNANO cites) or placed on another substrate. In both cases, it is isolated. This was not the case of (1),(2) and (3). I argue that it is not the case of (4) either. Graphene is chemically bound to either Ni, Ir or SiC. In the latter case, there is so-called first or dead layer which is not s-p^2 bonded and not conductive. Next layers resemble graphene or, maybe, graphite, I do not know. It is still debated, despite 4 years after Geim's Science paper. I doubt that anyone would be inteested in debating this without knowing how good graphene could be.

I also want to mention that in the case of Geim it seems to be not a straightforward, incremental step (this is why I agree with Carbophiliac who gave the guy such a nice credit). Both Geim and Kim previously referred to several efforts of mechanical splitting of graphite into thin layers. If I remember correctly, it was a Japanese group who first reported 100 layers in 1996 (in some very obscured journal). In their latest paper in Scientific American 2008, Geim&Kim apparently found a German group who did the same even earlier (1990 or so - there is no reference and I did not look for the paper yet). In any case, if you compare this with both Kim's PRL 2005 and McEuen's Nanoletter 2005, you find that there was little progress during the 15 years. Moreover, when Geim found the way of isolating graphene, he did not sit on the technology but disclose it widely. I doubt that this is common. My former boss would certainly kill all PhD students just in case they might leak a word (;-) I know first hand that Geim invited people to visit his lab for "tutorials on making graphene". Many groups did learn the trick directly in Manchester. This fact remains unacknowledged anywhere in literature (not everyone is as generous). This is why I vote for the Nobel for Geim. He deserves it, especially for "human reasons" (;-).

However, "discover" is indeed a very contentious word. I do understand the problems of UMDNANO with this word. Remember Columbus who discovered America, didn't he? Or was it discovered before him? or it was never discovered as natives lived there all the time. Technically, Geim was first to isolate graphene. "the isolator of graphene" (;-) - does not sound right. I would be also careful with word "discoverer" but in this particular case I feel the guy deserved it.

This is probably all I know and can add to the discussion. Pity that this "memoir" cannot be added to the graphene article. All the best to you guys who can be bothered to read this.

DrWhoever (talk) 20:51, 25 April 2008 (UTC)

This was interesting to read. I am located in Manchester and know people from the group of Prof Geim. As for me, Dr Who? is more or less right. And indeed the graphene tutorials still go on.81.104.93.72 (talk) 23:00, 25 April 2008 (UTC)

I tried my best to accommodate this discussion in the main article.

YZhangfirst (talk) 15:09, 27 April 2008 (UTC)

• I think the "Occurrence" and "History" sections should be combined into one section: there is a significant overlap. "Occurrence" is the wrong word anyway; this section is about the discovery/isolation/fabrication, whatever you want to call it. 81.157.196.227 (talk) 02:12, 28 April 2008 (UTC)

I agree but because Carbophiliac's entry caused such a negative reaction of Umdnano, I would rather wait for a few weeks for the dust to settle. I feel that Carbophiliac writes better than me, and maybe he could do this eventually. —Preceding unsigned comment added by YZhangfirst (talk • contribs) 09:56, 28 April 2008 (UTC)

I am more-or-less fine with the way this is shaping up, but there's one thing that still bothers me. I believe that the argument against 2D crystals being possible was put forth ex post facto. That is, I don't think anyone expressed the idea that the impossibility of 2D crystals was responsible for the failure to isolate graphene before 2004, and there is ample evidence that many groups were working on this (McEuen, Ruoff, Kim, de Heer, etc.). (As an aside, several groups were inspired by the successful isolation of single-layer crystals of transition metal dichalcogenides, though this work never gained much attention, and probably can't be used to discount the 2D argument, since these crystals are three atoms thick.) This sounds like a rewrite of history to match a cliche: "..the lone scientist doesn't heed the skeptics who say it can't be done, and succeeds to do the impossible..."

So, can anyone produce evidence that isolated graphene was thought impossible before 2004?

Umdnano (talk) 13:47, 28 April 2008 (UTC)

Let me try to answer this.

There is so-called Mermin-Wagner theorem that rigorously forbids the existence of perfect 2D matter (see section Mechanical properties). It goes even further back in history to Landau and Peierls in 30th. Thermal fluctuations are too powerful in 2D and induce defects at a finite temperature. This is it, from the point of view of theory.

People still argue why graphene exists. I witnessed a confrontation at a 2006 conference when a speaker (theorist) told that graphene would be unstable without a Si substrate, referring to the theorem. When someone from the audience mentioned then-unpublished results by Meyer et al (Nature 2007), the speaker answered that they should be wrong. In this paper, Meyer and Geim argue that ripples help to stabilize graphene crystals because not completely flat 2D matter becomes more stable (see section Mechanical properties). Another line of thinking (which sounds more reasonable for me)is that the crystals used in experiments are too small for the theorem to work at room temperature (there should be a critical size at which dislocations start appear). However, graphene should become unstable at higher temperatures, well below the melting temperature of bulk graphite. No one has studied this physics so far.

I will comment on the earlier experimental efforts, and the cliche tomorrow.

DrWhoever (talk) 10:41, 29 April 2008 (UTC)

I am quite familiar with Mermin's result and previous work, and the argument against the existence of 2D crystals. My point (which is illustrated nicely by your anecdote of the conference speaker) is that the Mermin's result has nothing to say about graphene on a SiO2 substrate as discovered by Geim in 2004. There is a reasonable argument to be made that many expected graphene without a substrate not to exist on the basis of the Mermin-Wagner theorem, but I cannot see how this can be applied to graphene on a substrate, which was already known to exist in 1975, and is what was reported by Geim in 2004.

I agree that the graphene crystals studied this far are quite possibly too small for the Mermin-Wagner theorem to apply. Mermin states in Phys. Rev. 176, 250 (1968) "Note that the exact bound (26) may well be so weak as to allow two-dimensional systems of less than astronomic size to display crystalline order."

Umdnano (talk) 19:50, 29 April 2008 (UTC)

In my opinion, the argument against 2D crystals is slightly more than ex post facto as you put it. First, the theory indeed has never argued against the existence of isolated (free-standing) graphene but it argues against its growth. The latter requires high temperatures at which the Mermin-Wagner theorem is quite valid without "astronomic sizes" involved. This is why the 222 carbon structure seems to be the very limit for graphene molecules. Anything much larger is simply impossible to grow. Second, the growth on metallic substrates and SiC is 3D and requires a matching crystal lattice. In my opinion, graphene cannot be called isolated in this case. Certainly not for the metal subsrates. SiC is a bit special, more complicated case but anyway graphene is isolated much less than in Geim's case. There is this "dead" layer that looks like graphene but 100% bound to the SiC substrate. "Epitaxial graphene" is what is grown on top of the dead layer, like new graphene layers can be grown on top of graphite. In this sense, "isolated graphene" was also found on bulk graphite (see A. M. Affoune et al, Chem Phys Lett 348, 17 (2001)). Third, Meyer et al referred to the Mermin-Wagner theorem in order to explain the observed non-flatness of suspended graphene. I know that it is hotly debated whether this non-flatness is intrinsic but if it is this would prove the impossibility of strictly 2D matter post ex post facto, which would be interesting. Enough for today.

I believe that most people assume term graphene to be 100 years old (or at least 50). The ref to the 1987 paper is very helpful.

DrWhoever (talk) 09:49, 30 April 2008 (UTC)

Here is my final word in defence of Geim who discovered graphene, at least from an experimentalist's point of view. Umdnano refers to Bednorz and Müller who "discovered high-Tc superconductors". Of course, those compounds were known and even electrically studied earlier but no one put them in a helium cryostat before. Similarly, de Heer took graphitized SiC (the technique known since 1975) and measured for the first time its electrical properties. An incremental step one may say but it was important and would probably bring him fame if the graphitic layers showed as nice properties as those of Geim's graphene. No one would notice de Heer's "epitaxial graphene", if not for real graphene.

Geim's group did much much more than just measured electrical properties of a previously known material (as Umdnano implies). They introduced a new experimental system from scratch. Although no one seems to have argued that a single atomic plane of graphite is impossible to exist (there are many things impossible - why bother?), no one isolated graphene or was even close (leaving aside studies of graphene).

The first cited report of micromechanically thinned graphite was in 1990 (Seibert et al, PRB 42, 2842). It was a film of ~ 100 layers in thickness (optical studies). Then came a Japanese experimentalist Y Ohashi in Tanso 180, 235 (1997). The graphite films were even thicker but those were the first electrical measurements of thin graphite. There were also many observations of thin graphitic films on top of graphite. The one that stands out is by Ebessen & Hiura, Adv. Mater. 7, 582, 1995 (~10 layers) and the one that does not (but often cited) is by Ruoff's group who showed a few SEM images of very thick graphite pancakes (APL 75, 193, 1999). In 2005, Kim's and McEuen's groups reported electrical measurements on graphite films of ~30 layers in thickness (they were not aware yet of Geim's work). As one can clearly see, there was little progress during the two decades until Geim's group came up single-handedly with monolayer graphene in 2004 and not only observed but measured it too.

There is nothing new under the sun but in this case Geim's step was not as incremental as by say Iijima or, for the matter, Bednorz and Müller and many other Nobel winners.

DrWhoever (talk) 11:13, 4 May 2008 (UTC)

This probably won't get noticed, but I should point out that I actually said that saying Geim "discovered graphene" was like saying Bednorz and Müller "discovered superconductivity", not "high-Tc superconductors", which they did, in fact, discover.

Umdnano (talk) 21:43, 19 May 2008 (UTC)

There is a difference between discovering something and discovering a way to isolate it. Geim should be credited with developing the method of extracting graphene, but I and probably many others learned in school that graphite is made of layers of carbon (which werent called graphene but were exactly the same thing) and it was also explained how the layers are not bound to themselves and how they slide against one another and leave chunks (not graphen) behind when you write with graphite. Not only it sounds silly It makes the scientists look bad for overstating his achievement (which is a serious crime for a scientists) although he might not be the one who propagates this.

I removed the part of the quote which said Geim managed to "fool" nature, people who think they can fool nature are only fooling themselves, lets not propagate their childish way of thinking.195.242.255.83 (talk) 11:38, 4 May 2008 (UTC)

My intention has been to defend people like Geim (and de Heer too) against other people who have a strong hindsight bias and, after being explained, start thinking that they actually knew everything from school.

DrWhoever (talk) 14:18, 4 May 2008 (UTC)

Wow! People were busy during the last 2 weeks - it took time to read all this. Why so much agression?! Relax - it is not your discovery anyway ... even if it is a discovery. Actually, in their review article (Nature Materials 2007) Novoselov and Geim called it "experimental discovery of graphene" (first page). Of course, you would not expect from them to diminish their own achievements, would you? So, there is no point for Dr Whoever to go further than Geim suggests. In my opinion, "experimental discovery" sounds fair and, nota bene, this notion passed through referees and editors who I admit should probably understand more than at least I do. Carbophiliac (talk) 14:57, 4 May 2008 (UTC)

Actually, the full phrase that you quote from Geim's article is "2D materials were presumed not to exist, until 2004, when the common wisdom was flaunted by the experimental discovery of graphene7 and other free-standing 2D atomic crystals (for example, single-layer boron nitride and half-layer BSCCO)8." It is clear that "free-standing" must also modify graphene here. This is further clarified in the same article later: "On the other hand, single- and few-layer graphene have been grown epitaxially by chemical vapour deposition of hydrocarbons on metal substrates28,29 and by thermal decomposition of SiC (refs 30–34)... Epitaxial growth of graphene offers probably the only viable route towards electronic applications and, with so much at stake, rapid progress in this direction is expected." This makes it clear that epitaxial graphene is graphene. So Geim should be credited with the "experimental discovery of free-standing graphene", which is in accordance with his citation for the Mott Medal in 2007. "Free-standing graphene" is defined as graphene isolated electronically to a degree that its electronic properties are well described by those of a single graphene sheet.

In any case, to maintain a neutral point of view, an authoritative source written by other than Geim should be used to reference the acceptance by the scientific community that Geim is the discoverer of whatever it is he discovered. The Mott Medal citation should be sufficient, and hence Geim should be credited with the "experimental discovery of free-standing graphene". Note that publication in a scientific journal is not enough; please see the discovery of carbon nanotubes. In that case, hundreds of papers have referred (incorrectly) to Iijima as the discoverer of carbon nanotubes.

Umdnano (talk) 16:24, 13 May 2008 (UTC)

Is there any fairness in this world? Iijima is often credited with "the discovery of carbon nanotubes", but he can maybe argue that he saw a single-wall nanotube first. Nothing else! Geim has done much more. Can one argue against his discovery of graphene being conductive and high quality? He was certainly first there. About the anomalous quantum Hall effect and non-vanishing conductivity in graphene? About the [experimental] discovery of Dirac fermions in graphene? The discovery of chiral quasiparticles with mass in a bilayer? What about the fine structure constant seen through graphene using a microscope? Come on, guys.

Whatever you say, Geim is a single focus point in the whole area and he opened it single-handedly. It is a human nature to lessen other people's achievements [as well as exaggerate your personal achievements]. Don't be like lawyers. Someone has to be credited with the discovery of graphene, and I cannot see anyone else who would even marginally deserve such a credit. —Preceding unsigned comment added by 213.174.113.122 (talk) 09:46, 17 May 2008 (UTC)

By your logic, Richard Smalley discovered the single-walled carbon nanotube, and Stuart Parkin discovered GMR, and Donald Eigler invented the scanning tunneling microscope.

Umdnano (talk) 21:34, 19 May 2008 (UTC)

It seems to me that who discovered graphene should be a matter of fact, not of fairness. I agree with many of the statements by 213.174.113.122 above. All of the following seem reasonable to add to the history section in some form or another:

"Geim made the first electrical transport measurements on graphene, showing it to have high carrier mobility"

"Geim and Kim discovered the anomalous quantum Hall effect in graphene"

"Geim and Kim discovered massless Dirac Fermions in graphene"

"Geim discovered massive chiral quasiparticles and an anomalous quantum Hall effect in bilayer graphene"

"Geim discovered that the transparency of graphene measures the fine structure constant"

But I don't understand the argument that because Geim has done so much pioneering work in the field, we should decide "out of fairness" that he discovered the material. I also don't agree that "someone has to be credited with the discovery of graphene", certainly there are plenty of materials for which no one is particularly honored for the discovery. I think that its quite clear that (without cooking up an extremely tortured definition of "graphene") that graphene was already around and being studied before Geim, but it was Geim that showed how interesting it is. For that, he quite possibly deserves to win a Nobel prize. But I don't see why we need to rewrite history. I mean, there were review articles written on the subject of graphene before Geim, for heaven's sake! Idosp2 (talk) 02:28, 22 May 2008 (UTC)

What reviews? There were no such reviews. You probably mean Dresselhauses' review on graphite or several others on carbon nanotubes or a couple on aromatic molecules? Nothing closer than this. Please do not confuse people.

As for the above statements that graphene is well known to children to exist within graphite, we also know that all crystals consist of atomic planes. Say, NaCl crystals can be cleaved along crystallographic directions. We do learn this at school. However, does anyone around dare to predict that a monolayer of NaCl can be isolated similar to graphene? Can SiC be cleaved to one atomic plane? It may be harder but is this possible? As already commented by someone, people can predict many things with the benefit of hindsight. I have recently read an article from a Berkeley group who doubt that Geim made a monolayer of BN in his 2005 PNAS paper. They could not make it and hence doubted. Graphite and BN are very similar materials with respect to their crystal structures. I do not care about electronic properties but

"Geim was first to prove that individual atomic planes can exist outside bulk crystals"

Carbophiliac (talk) 17:45, 22 May 2008 (UTC)

For a review, see Oshima and Nagashima, J. Phys.: Condens. Matter 9, 1 (1997). Epitaxial graphene is graphene (even Geim calls it graphene in his Nature Materials review article). In many cases, it was shown by ARPES (well before 2004) to have the electronic structure of graphene (i.e. massless dispersion relation). There is simply no definition of graphene except the most tortured that can include graphene bound to a silicon dioxide substrate but exclude graphene bound to, say, titanium carbide, where it has been shown that the electronic structure of the carbon monolayer is that of graphene.

The statement "Geim was first to prove that individual atomic planes can exist outside bulk crystals" could only be true by a technicality, i.e. Geim showed that graphene could exist tied to an amorphous substrate (SiO2) rather than a crystalline substrate. This was the state of things until 2007, when possibly two groups could claim to have been the first to make graphene free of any substrate (Siegmar Roth's group, and Paul McEuen's group).

As I pointed out above, there are many well-defined firsts to which Geim can claim credit. I think rather than coming up with some tortured definition of graphene so that Geim can lay claim to discovering it, it would be more appropriate to use language such as "Geim is the father of modern graphene research" or somesuch to describe Geim's role.

Idosp2 (talk) 23:47, 22 May 2008 (UTC)

NB As I mentioned above, it was NOT the work by "Siegmar Roth's group". Geim is a corresponding author on this paper, and Roth is not. Geim was in exactly the same position on the author list in Science 2004. But this is really a technicality. Even if he was not, it is more than obvious that this paper as well as McEuen's one were initiated by Geim's earlier findings. In my opinion, suspended graphene was an obvious next step after finding it on SiO2, and both mentioned papers used the cleavage technique. YZhangfirst (talk) 09:52, 25 May 2008 (UTC)

The first author of the paper (Meyer) was a graduate student in Roth's group. The last author is Roth. The technique was pioneered by Roth's group, to suspend carbon nanotubes. All the experiments were carried out in Roth's group by Meyer. My statement that Roth's group could lay claim to being the first to suspend graphene is correct.

And, are you really suggesting that Geim should get the credit for McEuen's nanomechanical resonator work, on which Geim is not even a co-author?

Idosp2 (talk) 02:03, 26 May 2008 (UTC)

First, I cannot trust the anonym who claims that all the work was done by Meyer. I would like to know what the 5 other authors think about this claim. Second, I rely on facts rather than rumors. And the fact is that the first 2 authors in Nature 2007 are both corresponding. This normally means that they contributed equally or at least comparably. If Geim only supplied samples to Meyer, his student would be the second author. If for a moment we believe the statement that Meyer did all the experiments, this would mean that Geim approached him with the idea to do them. This would explain the author list. I have also noticed that Geim is not always a corresponding author even in the papers coming from his own group. He would certainly have an opportunity to fix his place as desired. This means that he tries to keep things fair (NB much more fair than many professors). Third, in Science 2004 someone called Firsov is the last author. Does this mean that the experiments were done in his group? And finally, I did not try to take away any credit from McEuen's group. It s a great group. All I said was that for people dealing with suspended nanotubes it was reasonably obvious to apply the developed techniques to graphene after it was discovered. If McEuen did not do those experiments, Zettl, Roukes or others would have eventually done. It is like with the fractional quantum Hall effect, someone will surely report it in graphene soon. It is a too obvious direction, without taking any credit from the person who will see it first. YZhangfirst (talk) 13:09, 1 June 2008 (UTC)

[edit] When did Wikipedia discover graphene?

Apparently the first Wikipedia entry for graphene is dated 19 August 2004, before the publication of Geim's paper in Science. (OK, so Wikipedia didn't discover graphene, but my point is that there is an interest in having an encyclopedic entry regarding graphene even as it existed before Geim's work.)

Umdnano (talk) 16:09, 6 May 2008 (UTC)

To be fair. The first entry defines graphene as "a typical graphene would have the chemical formula C₆₂H₂₀. Graphenes are aromatic". How many people agree with this definition? The second entry on Oct 22 2004 adds a link to the BBC World article[2] which tells us that "a new class of material ... has been discovered by scientists", referring many times to Prof Geim who "leads the research team". —Preceding unsigned comment added by Absolutef (talk • contribs) 23:07, 7 May 2008 (UTC)

[edit] Lowest Resistivity?

(Moved from top of page to new section)

Is there any reference to the mentioned value of resistivity (caliming that is less than the resistivy of Silver) in the article? If yes, the reference should be provided. —Preceding unsigned comment added by 192.174.37.51 (talk) 20:58, 14 May 2008 (UTC)

This is in the press release at https://newsdesk.umd.edu/scitech/release.cfm?ArticleID=1621, but can be calculated from the information in the article itself: the sheet resistivity due to acoustic phonon scattering in graphene at room temperature is 30 Ohms/square. This is a 3D resistivity of 30 Ohms/square*3.4 Angstroms = 1.02x10^-6 Ohm-cm, compared to about 1.62x10^-6 Ohm-cm for silver. 3.4 Angstroms is the thickness of the graphene sheet.

I will update the reference on the main page.

Umdnano (talk) 14:54, 27 May 2008 (UTC)

[edit] Graphene by liquid-phase exfoliation

There is a report posted on ArXiv.org of production of graphene from graphite with 12% yield by mass using a liquid-phase technique[3]. (They have obtained single suspended sheets of graphene as imaged directly by TEM.) This is unpublished (for now) and hence probably shouldn't be part of the Wikipedia entry yet, but it points out a problem with the current organization of the "graphene" page: the Occurrence and History and Discovery sections are redundant, and don't really reflect their titles. I believe Occurrence should be renamed Synthesis and Occurrence, and list the current techniques for producing graphene (mechanical exfoliation, epitaxial growth, solution techniques) as well as the natural occurrences of graphene (in soot, in presolar onions and red-giant stars, etc.). These should probably have individual sub-heads. The historical information in Occurrence is already reflected in the History and Discovery section.

Opinions?

Umdnano (talk) 15:18, 27 May 2008 (UTC)

I noticed this too. In my opinion, it is the same micromechanical cleavage but on industrial scale (ultrasound instead of scotch tape). What puzzles me is that no one did it before, despite 100 years of intercalation. Someone should have done this and, because it is so important, we will soon hear claims that it was well known ;-) I cannot believe that it remained undiscovered before the snowball started by Geim's group. Occurrrence is an ugly word in my opinion. YZhangfirst (talk) 13:44, 1 June 2008 (UTC)

I hate to defend the Manchester group again but I try keep this discussion fair. They reported the same ultrasound exfoliation technique in organic liquids earlier[4]. Already published as I saw a press release too. —Preceding unsigned comment added by Absolutef (talk • contribs) 20:20, 1 June 2008 (UTC)

[edit] Graphene Nanoribbons

Graphene nanoribbons are distinct from Graphene. There are serious changes in the electronic structure such as a finite bandgap, excitonic effects, and chiral dependence to properties. Therefore, this class of materials deserves its own page.

I moved the above unsigned comment (from History, it was written by Tm2008 on 14:57, 14 June 2007) from the top of the page to this new section, rather than simply delete it. It seems to be orphaned.

The point is apparently now moot, since there is a Wikipedia page for Graphene nanoribbons.

Idosp2 (talk) 02:03, 28 May 2008 (UTC)