Spotlight on Research:
Surface Physicist Liz Seiberling 
Explores Uncharted Territory


photos by Patrick Leonard 
Liz Seiberling  
     Liz Seiberling is a trailblazer.  As the first female faculty member hired by the UF Department of Physics ten years ago, she broke gender barriers. As the building committee chair of the new Physics Building, she helped shaped the future of her department.  And as a surface physicist, she probes the unknown microscopic make-up of matter. "I have no idea what I'm going to find when I look at a new material," explains Seiberling.  "It's what the pioneers must have felt when they first set foot on new land...it's all uncharted territory."  

Liz Seiberling (right) and the Scanning Tunneling Microscope (STM). 

     Surface physicists like Seiberling examine atoms on a clean well-ordered surface in order to study the behavior and properties of these tiny particles.  For years, Seiberling used an accelerator to examine atoms through a process called ion scattering, and with her expertise in this technique, she developed a way to very sensitively measure the position of atoms on the surface.  

     More recently, though, Seiberling has been using an instrument called a Scanning Tunneling Microscope (STM), a fairly new invention (only about 12 years old).  The STM is basically an extremely sharp, tiny tip that moves along the surface, going up and down depending on whether it comes close to an atom or not.  Via a small, regulated electric current which hops across the gap between the tip and the studied surface, the STM probes and traces the atoms--or actually, the electronic structure of the atoms.  The movements of the tip are controlled and recorded by a high-powered computer, which translates the data into amazingly detailed images.  
STM  
The STM's tiny tip can actually move and rearrange individual atoms (left). 

     "With the STM we can look at where atoms sit on a surface, and we can explore whether or not we can influence where they sit," says Seiberling.  "Maybe we heat the surface or maybe we shine a laser on the surface--we can even nudge atoms around with the tip of the STM.  When looking at a picture of manipulated atoms [see molecule man, below] it's astounding to think about the fact that those are individual atoms that someone has just reached down and moved."  

     But Seiberling isn't content with just rearranging atoms. "I'm more interested in trying to form molecules or react atoms," she explains.  "What we might do is pull an atom over here and then add another next to it.  Then the question is, are they now a molecule, or are they just two atoms sitting next to each other?"  The STM can help answer this question because it can 'see' the electron cloud which indicates whether the atoms have formed a molecule or not.  "Another thing we might do is put several atoms next to each other," Seiberling continues, "and see if we can build a molecule that would normally not occur in nature."  
row of atoms  

Seiberling looks along a row of atoms in a model of silicon (right).  Silicon, a semiconductor, is the backbone of the computer and communications industry.  
 

     When asked about the potential applications of her work, Seiberling is cautious: "I think the realm of application is a ways off, as it always is in basic research.  More interesting in the immediate future is testing theories of why or whether certain metastable systems exist or why certain molecular forms don't exist.  Sometimes such forms are theoretically predicted, but chemists can't find them.  So, if we go down and build one, can it exist?  Is it metastable?  If I heat it, is it going to spring into some other state?"  

     Despite Seiberling's modesty, STM technology has a quite important (and lucrative) future.  "Moving individual atoms represents the end-point of computer miniaturization," she admits.  "Based on our present understanding, the smallest possible binary state involves changes on an atomic scale.   Thus, research like ours could eventually lead to much smaller and faster computers."  Scanning surfaces on such a minute scale can be tedious--Seiberling says "it's like searching through the desert with a fine-toothed comb"--but unexpected discoveries make the detailed work worthwhile.  "I usually--and this is what I advise my students to do--go into an experiment telling myself, 'Well, it's either going to be A or B, and almost invariably it's C.  Nature is unpredictable."  

 

Liz Seiberling (left) looks into the main vacuum chamber that houses the STM. 

     Recently, one of her undergraduate students proved Seiberling's point on the unpredictability of nature.  While using the STM, he made a potentially important find:  he noticed a strange alteration in a previously mysterious interference pattern on a graphite surface.  Certain atoms have unusual clustering effects, which can be examined with STM, but this interference pattern didn't correspond with what the group already knew about the clustering effect of the carbon they were examining.  After careful study, Seiberling thinks the student found a tear in the surface, which slightly rotated overlapping layers of carbon atoms just enough to produce a "moiré pattern" (an optical effect that occurs when two repetitive patterns are superimposed on each other and then rotated.  On a larger scale, anyone noticing the strange geometric effects caused by viewing two overlapping porch screens, has seen a moiré pattern).  "After successfully reproducing the patterns with computer simulations, we think the interference pattern is indeed a moiré pattern," says Seiberling.  "Physicists had published pictures of such patterns with other explanations, but none of their theories were able to be reproduced.  Now, because of my student's discovery, we may take a large step forward in understanding the STM and its interaction with matter."  

Jia 
Jinfeng Jia (above), Seiberling's post-doctoral research associate, uses  the computer attached to the STM to control the microscope's movements and to record and view its findings.  Jia, an expert in STM and surface physics, is visiting from Beijing University in China. 

     Hai-Ping Cheng, the only another female physics professor at UF (she joined the faculty in 1994), is a theorist and expert on clusters.  "We've written a proposal together," Seiberling explains.  "We're hoping that sometime soon we will be able to collaborate.  I can do the experiments and she can do the theory."  

     Has Seiberling ever felt uncomfortable being one of few women in her field?  "I didn't really think about it a whole lot," she says of her early days as a grad student and young physicist.  " I always felt I fit in pretty well.  But I think as I've gotten older, I've become aware that my way of thinking of things is different, and that there is a benefit to having a woman's perspective."