With this award, funded by the Chemical Measurement and Imaging Program of the Division of Chemistry, Professor Gruebele and his students will develop single molecule absorption spectroscopy detected by a scanning tunneling microscope. In this experiment, a laser beam excites a single molecule deposited on a semiconductor or metal surface, and a nanometer-sized metal tip detects the change of the molecular shape caused by the laser excitation. The laser wavelength is then scanned to measure an absorption spectrum of the molecule, while simultaneously visualizing the shape of the molecule's excited state. The technique will also be used to study complex surfaces with defects, such as conductive glasses. Absorption spectroscopy allows for the measurement and visualization of molecules that do not fluoresce, and that cannot be detected by single molecule fluorescence techniques.
The broader goal of this research is to understand how the excited states of large molecules used in molecular electronics are tuned by defects and by a complex surface environment. The carbon nanotubes, quantum dots and metallic glasses studied in this project have applications ranging from displays to cell phone shells; however, much of the fundamental physical chemistry needed to harness the properties of these materials remains to be discovered. The undergraduate and graduate students supported by this research project will acquire the knowledge and hands-on skills needed to advance U.S. chemical technology and teaching in the area of nanodevices.
We studied two things during the grant period: chemical electronics, and glass. Computers are getting faster all the time. This is achieved by making the switches in them smaller so signals travel faster. Ultimately, computing will go down to the level of single atoms or molecules. We use a technique called scanning tunneling microscopy combined with lasers to look at how a single molecule or 'nanostructure' changes structure ('switches') when exposed to light. We were able to directly observe how much room is occupied by a single electron in a carbon nanotube. Glass is a common but mysterious substance: it feels like s solid, but its atomic structure is like a liwuid. So why is it not liquid? This question has plagued researchers for 100 years, and we have seen the answer: by making movies with a resolution of 0.00000005 inches, we can see what makes a glass move - very slowly. Clusters of atoms, just a few atoms wide, hop back and forth on the surface of glasses between just two states, a very different kind of motion than in liquids. Glasses have many practical applications, such as the rims around cell phones, and of course windows. Understanding how glass flows at a nanoscopic scale could improve our ability to make new glasses with 'designer' properties. And seeing how single molecules switch does not make a computer, but can tell us whether molecules or nanostructures are robus enough to even be usable as pieces in a molecular computer. The work required a lot of high tech equipment, most of it manufactured in the USA by companies like Stanford Research Systems, or MDC Vacuum. Several students were trained, and are now professors, or work at high tech US companies like Intel, making the next generation of microschips. The local Illinois economy also benefits form this influx of science students, who need glassblowers and electronic shops in town to help with their work. The principal investigator brings this research experience into his classroom, and participated in an outreach program to Viet Nam, a former enemy state, but now turning into an ally that looks to the US for how to build its economic and science infrastructure. Image: A single carbon nanotube on a semiconductor surface (purple), with a gap in its absorption signal (golden) indicating an open 'switch'.
