May 31, 2013
Powerful Technique Captures Pictures Of Molecules Before And After Reacting With Each Other
Rebekah Eliason for redOrbit.com — Your Universe Online
One of the hottest topics in chemical research right now is the study of graphene. This cutting edge compound, composed of a single layered sheet of hexagonal carbon atoms linked together, could be the next step in designing nanostructures for electronics and next-generation computers.Graphene nanostructures have the potential to form transistors, logic gates, and other parts for use in tiny electronic devices, but scientists have yet to discover an easy and reliable method of producing graphene.
Felix Fischer of the U.S. Department of Energy's Lawrence Berkeley National Laboratory (Berkeley Lab) has been actively studying the process of building graphene.
Fischer and his colleagues set out to engineer graphene, but in the process they discovered a powerful technique to capture pictures of molecules before and after they reacted with each other.
According to Fischer, “We weren't thinking about making beautiful images; the reactions themselves were the goal, but to really see what was happening at the single-atom level we had to use a uniquely sensitive atomic force microscope in Michael Crommie's lab. Nobody has ever taken direct, single-bond-resolved images of individual molecules, right before and immediately after a complex organic reaction.”
The specific microscope technique used was noncontact atomic force microscopy (nc-AFM). In nc-AFM a tiny probe with a sharp tip moves across the surface of the molecule registering the bumps and dips on the surface.
Fischer described nc-Afm by stating that “a carbon monoxide molecule adsorbed onto the tip of the AFM 'needle' leaves a single oxygen atom as the probe. Moving this ℠atomic finger´ back and forth over the silver surface is like reading Braille, as if we were feeling the small atomic-scale bumps made by the atoms.”
The nc-AFM technique is particularly useful because a chemist may not always know what the product of a specific reaction is.
Fischer further explains: “In chemistry you throw stuff into a flask and something else comes out, but you typically only get very indirect information of what you have. You have to deduce that by taking nuclear magnetic resonance, infrared or ultraviolet spectra. It is more like a puzzle, putting all the information together and then nailing down what the structure likely is. But it is just a shadow. Here we actually have a technique at hand where we can look at it and say, this is exactly the molecule. It's like taking a snapshot of it.”
Fischer and his colleague Michael Crommie, a UC Berkeley professor of physics, devised a method to capture images using nc-AFM of carbon molecules before and after they reacted in an effort to understand the mechanism of graphene reactions as well as to decipher if graphene had been made.
First they placed molecules on a silver surface they designed to cool down to 4 Kelvin, which is about 270 degrees Celsius below zero. This super cold temperature keeps molecules from wiggling around and reacting with one another. Once the first images were taken, the surface was heated until molecules reacted and then chilled down to 4 Kelvin again. Fischer and Crommie were surprised the reaction did not produce what they had intuitively predicted, but instead produced two different types of molecules.
Nc-AFM not only shows the position of specific atoms, but it also provides pictures of the electronic bond forces between them distinguishing even between single, double and triple bonds. Fischer was amazed by the images stating, “Even though I use these molecules on a day to day basis, actually being able to see these pictures blew me away. Wow! This was what my teachers used to say that you would never be able to actually see, and now we have it here.”
This microscope technique should enable further advance of graphene nanostructures but Fischer noted, “The implications go far beyond just graphene.” Before many more advances in graphene nanostructures are discovered, Fisher is sure that “Large discoveries lie ahead.”