The Art Is In The Tip


by Skip Derra

Science is serious stuff, but that doesn't mean you can't 
have fun with it. And if there is anyone who has fun with 
science, it's associate professor of chemistry Marc Porter.

Porter, who also is an Ames Laboratory associate scientist 
and director of the Institute for Physical Research and 
Technology's Microanalytical Instrumentation Center, leads a 
group of 21 people into the arcane world of chemical 
interfaces -- the boundary between a solid and a liquid or a 
solid and a gas. Porter and his colleagues explore these 
interfaces atom by atom and molecule by molecule in work that 
has the potential for enormous benefits.

For example, one of the group's projects could lead to a 
coating for body implants that minimizes bacterial growth and 
reduces the body's rejection of the implant. Another project 
could lead to more powerful microelectronics, a third could 
significantly shrink the size of chemical sensors, and a 
fourth could lead to new ways of separating complex chemical 
compounds used as drugs. 

While trying to understand the complexities of how a ceramic 
molecule interacts with human tissue is daunting, the 
atmosphere in Porter's group is relaxed and collegial. Group 
members, mostly grad students, have as good a time with their 
work as Porter has directing them. 

"This is science," Porter simply says. "It's supposed to be 
fun." 

The science, and fun, is give and take. For instance, 
Porter's office nameplate has a new addition, compliments of 
the members of his group. It reads: 

Marc Porter

does the work of three men ... 

Moe, Larry and Curly.


"Truth is, I'm the Moe of this group," Porter admits. "But 
I'm like everyone else here. I really want to be Curly."

Porter says his mentors, professors Ted Kawana at Ohio State 
(now at Kansas) and Gordon Skinner at Wright State, Dayton, 
Ohio (now retired), were "masters at getting people 
interested in science and in creating new opportunities.

"I feel you can start students on a project and kind of point 
them in the right direction," he added. "Our students are 
talented enough and hard-working enough that they will take 
the project places you didn't figure they'd go."

Overall, Porter's group is engaged in more than 20 projects 
that range from fundamental to applied chemistry. And while 
they tackle serious science, they also incorporate new and 
entertaining twists to their research. One example is the 
work Porter is doing on atomic force microscopy with 
postdoctoral resident Mark McDermott and graduate student 
John-Bruce Green.

Atomic force microscopy, a somewhat new and exotic technique, 
has the potential to "see" surfaces down to molecular levels. 
An atomic force microscope has a minute probe shaped like a 
spring. The back of the spring is mirrored and a small prism-
shaped tip protrudes just beyond the end of it. The 
researchers lower the probe until it barely touches the 
surface of a material. 

The tip hovers along the surface much the same way a 
phonograph needle glides over a record, "experiencing" some 
of the atomic and molecular forces between tip and surface. 
Laser beams measure the minute up and down motion of the 
spring as the surface attracts and repels the tip. 

The resulting image is a "topographical map" of the molecular 
peaks and valleys of the surface with an accuracy within less 
than a billionth of a meter.

To get information on the composition of the surface, Porter, 
Green and McDermott ran the microscope in a "force frictional 
mode," in which the tip measures the resistance it encounters 
as it crosses different types of chemicals on a surface. 

To test their technique, the researchers scratched an ISU 
"microemblem" into a surface with two chemically different 
layers on it (one high friction, one low friction). The ISU 
monogram, arguably the smallest ever, measures only 275 
nanometers across, or about one-hundred-thousandth of an 
inch. 

The team was successful in "seeing" the microemblem. In fact, 
their force friction  microscopy method has a resolution down 
to 10 nanometers, a record, according to Porter. The work 
shows that the technique can map a surface's chemical 
composition down to molecular levels. 

The team now plans to make its microscope even more powerful 
by sharpening the tips. "The art is in the tip," Porter said. 
"If you can't make good tips, you can't see squat." 

In fact, the trio is so tip-enamored that they set up a "tip 
hall of fame" to honor those tips that rise above the call of 
duty. 

Porter said experimental data suggest they can resolve down 
to tens of angstroms with the right tip (an angstrom is one 
hundred-millionth of a centimeter), so there's a good chance 
they might try making an even smaller ISU monogram. 

A scientific paper on their work was published in the Journal 
of Physical Chemistry (July 6) and they are writing a second 
paper on the force friction work. It has a working title of 
Pulp Friction.

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contact:  Skip Derra, News Service, (515) 294-4917
updated:  7-28-95