The almost deafening buzz about nanotechnology and its implications for the world economy would be but the barest whisper, were it not for the scanning tunneling microscope. In 1986, Gerd Binnig and Heinrich Rohrer received the Nobel Prize in physics for inventing the STM at IBM's Zurich Research Laboratory five years before. Now, nearly 20 years later, Binnig may be leading the way to creating the smallest digital memory ever devised, with a descendent of the STM.
For the first time, the STM allowed researchers to see surface features smaller than an atom. The instrument exploits a phenomenon known as tunneling, which causes electrons to leap from surface atoms to the tip of an ultrasharp electrode suspended a few angstroms above. Measuring the amount of tunneling that occurs as the tip scans the sample provides the data necessary to plot a picture of the surface.
The same year that he received the Nobel Prize for the STM, Binnig took the concept one step further to invent atomic force microscopy. AFM maps the surface of a material by recording the vertical displacement necessary to maintain a constant force on the cantilevered probe tip as it scans a sample's surface. Whereas STMs can be used to study only electrically conductive surfaces, AFMs can probe insulating surfaces as well.
Now, in an IBM research effort called the Millipede project, Binnig and his colleagues are putting thousands of AFM probes together in arrays to create a new kind of data storage device. The unit will have an astounding 155-gigabits-per-square-centimeter density--enough to store 50 DVDs on something the size of a credit card. Ones and zeros are stored by making microscopic depressions in a polymer film.
I traveled to Switzerland in February to see the Millipede project up close and to talk with Binnig about STM, AFM, and the process of invention.
Did you immediately see commercial value in the scanning tunneling microscope?
I was an exception in the physics group in that I wrote quite a few patents. Most of my colleagues at the IBM Zurich lab in the late 1970s didn't even think about patents. They were just interested in asking questions like "How does matter behave?" I was interested in how nature behaves, too, but also in what I could invent to understand it even better. So it was natural for me to write patents [to cover the STM and other topics].
What prompted you to begin developing the STM?
Heinrich Rohrer defined the problem by saying it would be interesting to look at inhomogeneities on surfaces, on the atomic, or close to, the atomic level. At the time, physicists thought only in terms of regular arrays of atoms, crystals.
I started looking through all the equipment that existed to study materials around the atomic scale. There was nothing, so we had to invent something.
The intention was to make a microscope to do spectroscopy [on individual atoms]. For a tunneling experiment, we'd apply a voltage to two electrodes and ramp it up and look at how the current behaved--from this we could conclude what the chemistry of the material was. As a side effect, we got a microscopic image of the topography of the surface.
How did you translate the concept into a working prototype?
That was a relatively slow process, with many iterations. I learned how to move the probe tips around very precisely. I first wanted to do that with quartz, but then I realized quartz doesn't move that far and we switched to piezoelectric ceramics.
Then we went into a very primitive vacuum chamber just to see if the microscope worked. Things don't have to be perfect at the beginning. But you have to first find a way to make it work even a little.
In a way, this process is just like Columbus going from Europe to America: on the way there, he has no clue that he is coming closer. We were in exactly the same situation because the instrument never worked. You have no clue what to do, what knobs to turn to make it work better, because it simply does not work at all. You can't be sure whether you are close to a solution or not. That forces you to try many different things and all you can do is think about what could have prevented the instrument from working. Only then do you find new ideas.
What was it like to finally get it to work?
That was the most impressive moment I have had in my scientific career, even more so than getting the phone call from [the Nobel committee in] Stockholm. I was not sure whether I should laugh or cry.
I think it was three o'clock in the morning and I was alone in the lab. I was trying all kinds of tricks, but in the end it was pure luck. Because the microscope has a tip which has a few atoms on it, some of the atoms in the tip could be mobile. You have to be absolutely patient, but suddenly one atom was sitting right in the front of the tip and I got atomic resolution. That's the way to success, not giving up.
I knew it was a very important moment. I was trying to image a sample that I had tried to image many times before without any success. Suddenly, the microscope's like [making sound] da-da-da-da-da-da-da-da . And I can never forget this noise the plotter made because it really had to work hard to follow the contours of the atoms that the tip was following-- da-da-da-da-da-da-da-da . A beautiful noise. At this moment I knew these da's were all atoms, every da was one atom. The plotter drew a picture and you could see it was an atomic structure. And I knew immediately that's it, that's the breakthrough. It was a new world now.
How did you get it from this stage to a working instrument that other scientists could use?
That took a long time. At first, we made a few design mistakes that didn't allow us to scan very far. We didn't really have an image. We just had a few lines that showed steps on the surface due to individual atoms. What does this mean? Some people will say it is probably an artifact. And it was slow, so nobody really got interested in it.
We were more or less ignored. I gave quite a few presentations in the United States and went to famous universities like Harvard and MIT and so on. The students loved it. But the professors were not really interested.
Only later, when we could show a better image of the atomic structure did we convince people. Nevertheless, from there on it still took two years to do the convincing, even though we always shared all the new information we had. We were very kind to everyone and showed them our lab, all the little details of how the microscope worked. Still, it took a long time from the first experiment to having an instrument accepted by the community.
When did you know you had broken into the scientific mainstream?
It was 1984 at an American Physics Society meeting, and I gave an invited talk. And directly after me a guy from Bell Labs presented a beautiful result using our design, much more beautiful than the results I had presented. Much more data, much bigger images. I was completely impressed. The room was filled with almost 1000 people. His results were the breakthrough because then it was not just one group that could produce results. Another group could as well, and its results were even better than ours.
What was the next step after the STM?
From the very beginning, we planned to do spectroscopy on the atoms, to see the color of the atoms we were imaging with the STM. That's what spectroscopy is about; it gives you chemical information.
But I didn't continue this work because I went to the States for a year. And then I started playing golf and was thinking more than doing. That was when I invented the AFM, by just lying for a while on a couch.
There's a popular notion of the inventor who has the "eureka" moment in the lab and goes, "Ha, I see it!"
The atomic force microscope was an extreme case of eureka because I was not even thinking about it. And suddenly the solution was there. My subconscious mind produced it. The problem was: how could you possibly get atomic resolution with insulators? We could work with conductors--and maybe also with biological material. Suddenly the solution was there, out of the blue.
But you prepare for such a moment by sorting things out and trying many different approaches. Although they may not be successful, they're all gathered somewhere in the back of your mind. Because it's so complex, you can't solve the problem with your conscious mind. Your subconscious shuffles around all the possibilities and suddenly presents you with a solution. So something like [the eureka moment] exists, but you prepare for it over months and sometimes years.