#181 from R&D Innovator Volume 4, Number 10          October 1995

A Lesson in Collaboration
by Chad A. Mirkin, Ph.D., and John T. McDevitt, Ph. D.

Dr. Mirkin is associate professor of chemistry at Northwestern University, Evanston, Illinois.  Dr. McDevitt is associate professor of chemistry at the University of Texas, Austin.  This article is written from Mirkin's vantage point.

How would it be to have inexpensive, hand-held magnetic resonance imaging equipment in every hospital and doctor‘s office, powerful supercomputers on your desktop, and easily accessible mobile telephone stations in every town?  The secret to constructing many of these devices relies on understanding how to effectively use and process superconducting materials--ones that exhibit zero resistivity below a critical temperature, Tc.

Although many applications based on superconductors were, a decade ago, thought to be impractical because of the need to cool the materials to temperatures close to absolute zero (-273°C), the recent discovery of high-temperature superconductors has opened up the possibility for a number of important applications.  Mother nature was kind to reveal her secrets that allowed scientists to make materials that conduct electricity with zero resistance, at temperatures close to those achievable with relatively simple refrigeration methods.  But she wasn’t kind in terms of the challenges that need to be surmounted to make practical devices from these "superconducting" compounds.  My collaborator, John T. McDevitt, and I have made a discovery that could hasten the development of high-temperature superconducting materials and devices for various applications.             

Small Talk

The genesis of the idea arose from a 1994 Office of Naval Research review meeting organized by our program officer, John C. Pazik.  These meetings are typically long, grueling sessions where each participant is evaluated for past accomplishment and potential future contributions to the program.  The purpose of these meetings is not only to update the sponsors as to each lab’s progress, but also to stimulate collaborative efforts between participating scientists.  Naturally, everyone wants to continue to be considered for future funding allocations, so there’s a fair bit of pressure, and the scientists are constantly thinking of ways to impact the program through their research endeavors.

At the end of each day, many of the participants congregate in the local bar and discuss what they have heard.  I happened to end up across a table from John McDevitt, and we began to discuss each others' projects.  Our group's expertise, as synthetic chemists, lies in preparing and characterizing chemically modified interfaces, while John works on the inorganic chemistry, electrochemistry, and corrosion reactivity of superconductors.

Typically, solid-state inorganic and synthetic chemists don’t have a lot to talk about with regard to interests in science.   So after a few minutes into the conversation, after we had exhausted common areas of scientific interest, we began thinking about ways to merge the two important fields and the ramifications of doing so.  I asked John if anyone had tried to chemically modify the surface of superconductors with molecule-based reagents.  Trying to covalently attach molecules to superconductors seemed like a reasonable thing to do since the other important classes of electronic materials, metals, semiconductors, and insulators, had been extensively studied in this regard.  He told me that although there had been numerous ways to chemically modify the solid-state materials through ion-substitution reactions (e.g., substituting Ca2+ for Ba2+), methods for covalently attaching molecules to this class of ionic materials were, at the time, unrealized.                                                           

As it turned out, both of us had independently considered the possibilities that would arise from chemically modifying high-temperature superconductors; but each group was missing one of the two key materials to carry out the necessary studies: the appropriate molecules and the superconducting substrates. 

John, who had recently written a comprehensive review article, was familiar with some of the prior unsuccessful attempts to modify superconductor surfaces, and relayed the disappointing details to me as we each tossed down another beer.  A few drinks later, the obstacles seemed significantly less daunting, and we began to discuss plans to attack the problem in a systematic manner.  Through the evening and following day, we continued discussing all of the marvelous things that could be done with superconductors, provided that methods for controlling their surface properties could be developed.  Like many good ideas that are catalyzed by liquor and small talk at conferences, they were quickly filed away after leaving the conference.    

Upon returning to our universities, neither of us acted on any of these ideas.  However, about two months later, John invited me to Texas to give a seminar.  After the seminar, the topic of       chemically modifying superconductors came up again.  We decided that, with the molecules we had synthesized for other studies and the superconducting substrates John routinely prepares in his laboratory, we could quickly probe and determine the coordination chemistry of the superconductor.  Because our molecules are all redox-active and the superconductor is a metal at room temperature and can be used as an electrode, we decided that we could easily probe the efficiency of the adsorption process (if it occurred) by electrochemistry.      

A Success                                            

I soon received a package from John with several superconducting substrates.  I asked my postdoctoral associate, Kaimin Chen, to go to the shelf and collect every redox-active molecule that could possibly bind to Y, Ba, Cu, or O in the superconductor.  Being inorganic coordination chemists, we first tried N- and S-containing reagents that we expected would bind to Cu in the superconductor.  Kaimin tried an initial reaction between a superconducting substrate and a redox-active ferrocenylamine.  He came to me the following day with a big smile on his face, and exclaimed, "It worked!"  He showed me the data.  It was significantly better than what we expected.  The molecules attached to the surface in a very efficient manner to form a stable monolayer film.               

I quickly called John to tell him the good news and to discuss our next steps.  We decided that it was important to determine whether or not the superconducting properties of the chemically modified material remained intact; so the samples were sent back to Texas, and John and his co-workers confirmed that the Tc for the superconductor had not changed as a result of its chemical modification.               

Great Results!                                            

Later, I found out that John was initially skeptical of the discovery, as it happened too fast and seemed too good to be true, but after receiving and testing a small amount of the sample      compound for himself, the "doubting Thomas" (his true middle name) became convinced that the chemistry worked.  This all happened in about a week, and we were all overwhelmed with the possibilities for this chemistry.           

One consequence of modifying the superconductor with the monolayers of redox-active agents was its resistance to corrosion.  Copper oxide superconductors normally corrode in air via a reaction with water to form barium hydroxide, which reacts further with carbon dioxide to form barium carbonate.  Having studied the mechanism of corrosion of high-Tc systems, John and his coworkers were equipped to study the influence of the monolayers on the corrosion reaction.  We thought that the monolayer might be acting as a barrier layer that inhibited the corrosion reaction, and we decided that there may be ways to enhance this corrosion resistance by designing and synthesizing molecules that pack better on the superconductor surface than the molecules chosen for our initial studies.                                             

We decided to try linear hydrocarbons and fluorocarbons because they’re known to form densely packed structures on other types of surfaces.  Furthermore, we thought that the fluorinated hydrocarbons would form a water-resistant layer comparable to Teflon polymers.

We synthesized several molecules, used them to modify superconducting substrates, and sent them to John for corrosion analysis.  Again, the results were spectacular.  We were able to show that the modified substrates, under conditions that quickly corroded the unmodified substrates, are resistant to corrosion.      

Possible Applications

This had "industrial process" written all over it, so we immediately contacted our respective technology-transfer offices and filed a patent application.  Since our initial discovery, we’ve shown that superconducting substrates can be tailored with this monolayer chemistry to improve adhesion between polymeric materials and the superconductor, pattern organic conducting polymers on the surface of the superconductor, and control etching of the superconductor.  The substrates can also make insulating barrier layers of controlled thickness, which may be useful to prepare more sensitive SQUID devices for detecting magnetic fields (these have applications in the human health industry for cardiovascular assessment, and in the petroleum industry for detecting large oil deposits in the earth's crust).                               

As with many important scientific discoveries, this one involved the combination of two disciplines that in the past have had very little overlap.  It’s a lesson in collaboration and persistence.  It has opened up exciting personal opportunities for us, as we have recently begun to work with several superconductor start-up companies to help them develop their high-performance products. We currently are searching for additional funding to develop this important area of research.   

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