Following yesterday’s post is yet another reason why transmission electron microscopy (TEM) is becoming an increasingly useful nanotech tool. The recently demonstrated ability to visualize individual atoms of carbon and hydrogen on a graphene surface opens new avenues for studying the behavior of hydrocarbon chains. From nanotechweb.org, written by Hamish Johnston (requires free registration) “Graphene substrate reveals hydrogen atoms“:
Physicists in the US claim to have used a transmission electron microscope (TEM) to see a single hydrogen atom — the first time that a TEM has been used to image such a light atom. The breakthrough was made by supporting the atom on graphene — a sheet of carbon just one atom thick. The team has also been able to watch hydrocarbon chains move across the graphene surface, suggesting that the technique could be used to study the dynamics of biological molecules.
There is nothing new in using TEMs to see individual atoms, but until now such instruments could only be used to image heavy atoms. One reason is that a TEM creates an image by shining an electron beam on a sample and measuring how much it is deflected by atoms of interest. Lighter atoms deflect electrons less than heavier atoms, which means that only the latter show up on an image.
Another problem is that a sample in a TEM has to be supported on a substrate that is durable enough not to be damaged by the electron beam, but thin enough for most of the electrons to pass straight through. Thin metal films or semiconductor foils are usually chosen as substrates, but these are still much thicker than single atoms and contain atoms heavier than carbon or hydrogen. Scattering from the substrate therefore tends to swamp the already weak signal from lighter atoms.
Now, however, Jannik Meyer, Alex Zettl and colleagues at the University of California, Berkeley have found a way around this problem by using graphene, the thinnest and toughest known material, as a TEM substrate (Nature abstract).
The team came up with the idea while using a TEM to study defects in graphene. However, they also discovered that they could identify individual carbon and hydrogen atoms — as well as hydrocarbon chains — that had contaminated the surface of the graphene.
…Zettl told physicsworld.com that the team is particularly interested in using the technique in the development of functionalized nanostructures — tiny objects that are engineered to perform a specific function. These are often hybrid materials — say a carbon nanotube decorated with biologically active molecules — and Zettl believes that TEM could be used to understand the real-time chemical binding or molecular dynamics processes that make such materials function.
We can hope the improved ability to study hydrocarbon molecules on a surface will aid the development of diamondoid mechanosynthesis, for example as envisioned by the theoretical work of Freitas and collaborators.
—Jim
