nanoREV.

Graphene vs Carbon Nanotubes

Trouble is brewing and the carbon wars have begun. It’s “sheets” versus “tubes”, 2-D vs 3-D, graphene versus nanotubes. Man your battlestations, toss in your bets, and start your research!

Because of some recent news regarding graphene, in this post I will attempt to highlight some of the patentability issues relating to novelty and obviousness of simple substitution of known materials in known devices. Specifically, I will attempt to describe how the substitution of graphene into devices in which the use of carbon nanotubes has been disclosed may stand up to USC 35 102 and USC 103 rejections at the US Patent and Trademark Office. Two initial questions that I will try to answer are:

• Are graphene and carbon nanotubes, in the eyes of the USPTO, essentially the same thing?
• Do scientific extrapolations based on experimental data perpetuate the very “predictable results” that post-KSR rationales determine to be obvious?

Thanks to these recent developments in graphene research, specifically by A.K. Geim et al. in the UK, these single sheets of carbon may prove viable for use in electronics, such as single-electron transistors. Actually, a recent article reports that Geim’s group “calculated that pure graphene should allow electrons to travel more easily than in any other material, including gold, silicon, gallium arsenide, and carbon nanotubes” which would therefore make this material absolutely perfect for electronics. Keyword: “calculated”.

In fact, in their most recent publication, Geim et al. show that the intrinsic mobility of their graphene may potentially have a value of about 200,000 cm²/V-s, which coincidentally exceeds that for any other semiconductor! But what about carbon nanotubes? Weren’t nanotubes, with their >100,000 cm²/V-s intrinsic mobilities supposed to be the be-all end-all to overcome switching issues plaguing silicon based semiconductors at room temperature? (That’s also not a bad number to simply act as a conductor either). All eyes on graphene and good-bye carbon nanotubes?

Maybe it’s a bit premature to discount carbon nanotubes altogether. Graphene’s still expensive as hell. For example, if you want a micromachined graphene crystallite smaller than the thickness of a human hair then be prepared to spend more than $1000 a pop. On the other hand, you’re now looking at $250/kg for carbon nanotubes, but that figure is dropping every year as production around the world increases. So, while graphene apparently has the electronic advantage, carbon nanotubes have the economical edge. I’m not expecting this to be a quiet fight because a lot of investors, not yet wise to these new developments, have already poured their hopes and dreams (read: wallets) into a carbon-nanotube-based-electronics future.

Well, the trouble isn’t so much that there’s a new awesome material with great electrical properties. The problem may be trying to patent a device that uses this known material as a substitute instead of carbon nanotubes in say, transistors, to do the exact same thing. As I mentioned above, one major question that will have to be answered is whether an array of carbon atoms laid out flat in a single sheet (i.e., graphene) is equivalent to an array of carbon atoms rolled into a tube (er, a nanotube) . According to the US Patent and Trademark Office, Class 977/734 covers:

Subject matter wherein the nanostructure is formed of caged, curved, or planar graphene or wherein the nanostructure is formed or caged, curved or planar graphene, or hexagon ring structure which constitutes either a non-carbon-based composition, e.g., WS2 or MoS2, etc., or substantially a non-carbon-based, e.g., planar C3N4, etc. (1) Note. Graphene is the name given to a single layer of (most commonly) carbon atoms densely packed into a hexagon ring structure; it is widely used to describe properties of many materials including graphite, soot, fullerenes having a caged molecular structure, e.g., buckyballs, nanotubes, and nanococoons, etc.; fullerenes having a curved or partially caged molecular structure, e.g., nanohorns and nanoscrolls, etc.; and fullerenes having a planar molecular structure (although planar graphene itself has been historically presumed to be unstable and typically not existing in the free state).

If you look closely at this class definition, you’ll see that apparently in the nanotechnology arts, “graphene” is a generic term for pretty much all forms of carbon including “carbon atoms densely packed into a hexagon ring structure” and “nanotubes”. Meanwhile, indented under this subclass is Class 977/742 for carbon nanotubes. So carbon nanotubes are a subset of graphene? This seems to be the counter-intuitive case, because carbon nanotubes have benefited from early research and development, accelerated product introduction and good promotion. So does this mean that carbon nanotubes and graphene are equivalent? Another point of interest is the small blurb about graphene not existing in the free state.

The other issue is whether a patent examiner can reject a claim which substitutes “graphene” where “carbon nanotube” has earlier appeared in prior art based on post-KSR 103(1) rejection rationale B: “Simple substitution of one known element for another to obtain predictable results”? Now I call your attention back to the word “calculated” from the beginning of this post. It appears that the 200,000 cm²/V-s value for graphene’s intrinsic mobility was partially attained by a calculation. This calculation is partially based on evidence showing weak temperature dependence of electron transport in the material as a result of little or no temperature-dependent phonon scattering. The group also eliminated the possibility of flexural phonons, electron-electron scattering and umklapp scattering by comparing empirical data. So in essence, the group has perpetuated a “predictable result”: graphene (at least in the form/purity in which they created it) shall and always will have such a high electron mobility at room temperature. Therefore it may be fair to say that simply substituting graphene to do the job that carbon nanotubes have also been shown to do, may be obvious and therefore unpatentable.

By the way, Gleim’s group registered the domain name graphene.org