Klaus Müllen and a team from the Max Planck Institute for Polymer Research in Mainz have now introduced a new method for the synthesis of long, narrow graphene ribbons with defined dimensions in the journal Angewandte Chemie.
Previously, graphene ribbons were mainly cut out of larger graphene sheets or were obtained by slitting open carbon nanotubes lengthwise. However, with these methods it is impossible to produce ribbons that have a precisely established ratio of width to length as well as defined edges. These details are important because they determine the electronic properties of the ribbons. The search has thus been on for a method that allows controlled production of very narrow graphene ribbonsan extremely difficult challenge. The German researchers working with Müllen are now well on the way to overcome it. They are not starting with large structures to cut up (top-down); instead they are building their ribbons from smaller components (bottom-up).
The building blocks selected by Müllen and his team are long chains of aromatic six-membered carbon rings called polyphenlyenes. In contrast to previous approaches, they did not produce straight chains; instead they made them with a flexible, zigzagging, bent backbone. Furthermore, they attached hydrocarbon side-chains to the backbone to increase the solubility in organic solvents, which allows the compounds to be synthesized and processed in solution.
The next step is a reaction that splits off hydrogen (dehydrogenation). This causes a ring-closing reaction in each pointy tip of the zigzag, forming a new aromatic six-membered carbon ring that shares a side with three neighboring ringsthe chain transforms in to a narrow ribbon.
In this way, the team was able to produce a series of different nanoribbons with lengths reaching over 40 nm. The width of the ribbon was defined by the size of the points of the polyphenylene precursor. The resulting ribbons are free of defects and soluble in common organic solvents.
We have been the first to demonstrate that structural perfection can be achieved by the classical bottom-up synthesis of defined graphene nanoribbons, says Müllen. The solubility of the ribbons is an important requirement for the large-scale production of electronic components.
Explore further:
Nanoribbons for graphene transistors
More information:
Klaus Müllen, Graphene Nanoribbons by Chemists: Nanometer-Sized, Soluble, and Defect-Free, Angewandte Chemie International Edition, Permalink to the article: dx.doi.org/10.1002/anie.201006593
nuge
PinkElephant
You can think of it as a sheet of benzene rings, except the classical definition of a benzene ring is a hexagon of C with H atoms at each corner. In graphene, there is no H, only pure C. And it's just one continuous sheet of C. You can visually parse it into "rings", but there are no distinct rings in the sheet (each C atom belongs equally to 3 adjacent "rings".) The chemistry is a bit different, because of this: the different affinity of valence electrons toward C vs. H in benzene, compared to uniform and symmetric affinity in a pure-C sheet.
Similar to buckyballs and nanotubes, a graphene sheet is just one big holistic macromolecule. You can parse it into a collection of hexagonal rings, just like you can parse a buckyball into a bunch of hexagons and pentagons. But in the end, it's a single entity, and its electronic properties derive from its integrated structure (rather than any artificially delineated substructure.)
nuge
PinkElephant
So in graphene, on average at any given instant 3 of the 4 valence electrons on each C atom are binding it covalently to its 3 neighboring C atoms, while the 4th electron is randomly migrating through the molecule.
nuge
PinkElephant
Though as opposed to metals, in graphene, due to the structure of the molecule, electrons can only migrate along the 2D plane of the graphene sheet (they cannot easily jump from sheet to sheet in bulk graphite.) So conductivity really depends on how well-aligned the electric field is with the graphene sheet's plane. It also depends on orientation of the sheet: current travels easier in some directions than in others along the sheet, due to how the bond axes align with the electric field.
The conductivity of isolated graphene is excellent. At room temperature it can be more conductive than any metal, when it is suspended in vacuum. However, when laid against a substrate, at room temperature the thermal vibration modes induced by the substrate can reduce carrier mobility significantly; by how much depends on the substrate.
yoatmon
1) Graphene = 5700
2) Silver = 66.5
3) Copper soft / hard = 57 / 56
4) Aluminum = 35
5) Brass = 15 - 19
Values are derived x = 1 : specific resistance.
yoatmon
yoatmon
Researchers at MIT were the first to successfully grow multiwalled CNTs on a graphene sheet. This enables the electrons to move just as easily in the 3rd dimension as in the other two within one plane.
antialias
A surface (albeit a toridal one in the case of a CNT) is still topologically a 2D surface.
yoatmon
That may well be; it doesn't make my statement less viable.
kcameron
100X copper conductivity would revolutionize many fields; especially electric motors and inductors. Unfortunately, it doesn't look like it's feasible.
nuge
And another thing, what is the magnetic behaviour of graphene like?
yoatmon
Ref. to wikipedia:
//en.wikipedia.org/wiki/Graphene
Ref. to Berkeley News Bulletin:
//newscenter.lbl.gov/news-releases/2010/07/29/graphene-under-strain/
StandingBear
kcameron
1.7X would still be pretty good. Given the greatly reduced density and ability to withstand much higher temperatures, graphene wires may someday lead to substantially improved electric motors, etc.
kcameron
Given graphene's greatly reduced density and ability to withstand high temperatures, it would still make for a substantial improvement to motors, etc.
kcameron
Given graphene's greatly reduced density and ability to withstand high temperatures, it would still make for a substantial improvement to motors, etc.
kcameron
nuge
yoatmon
"Copper resistivity is about 1.7x10-6 Ω·cm. So graphene's conductivity is about 1.7X that of copper; a far cry from 100X."
------------------------------------------------------
Check out e. g. : (http//www)
.electronicsweekly.com/Articles/2009/08/05/46677/georgia-tech-claims-100x-copper-conductivity-for-graphene-interconnect.htm
kcameron
Here's the relevant excerpt from that article:
"This makes them very robust in resisting electromigration and should greatly improve chip reliability. The current carrying capacity is at least two orders of magnitude higher than copper at these size scales"
Again: current carrying capacity != conductivity.