TR: Where are we in terms of actually realizing some of these things?
WHITESIDES: At the stage of laboratory prototypes. People have made little CDs, but they are not something that you can use outside the laboratory. It’s going to be very hard to extend the fabrication methods that people now use for making these small structures to anything that’s really manufacturable, but it will happen.
TR: How big a challenge is this?
WHITESIDES: We have a demonstration in principle from microelectronics that if you can make things smaller, people will find lots of exciting things to do with them. Right at the moment, we can make small things in laboratories, but we don’t know how to make really small things en masse in a manufacturing environment. And we don’t know how to use them once we make them. Until that manufacturing problem is solved, we won’t know what things can be made, and we will not know what the technology is going to be like.
TR: Photolithography that uses ultraviolet light to etch out patterns on silicon chips is the dominant technology in making microelectronics on the micrometer scale. But, I take it, you don’t see it having much of a future in terms of nanotechnology?
WHITESIDES: Photolithography has been very successful. We’ve had a wonderful run with this technology, and there’s every reason to think this will continue for a while. But now you begin to step back a little bit and say, well, it’s hard to go below 100 nanometers, and you can’t build 3-D things. It really doesn’t work for too many materials other than silicon and stuff like that. We would like to make things small so they can be fast and cheap and portable and not power consuming. How do we do that?
TR: What are some of the alternatives?
WHITESIDES: One is electron beams, an embodiment of which is Scalpel. [Scalpel is a system developed at Lucent Technologies’ Bell Labs that uses electron beams to pattern silicon wafers]. Another contender is X-ray lithography [this process uses X-rays to pattern wafers]. Both of them have a lot of very difficult technical issues, which we presume will be worked out more or less, but whether they’re really cheap enough is another question. And then there are newer technologies coming along which are, I think, legitimately long shots, such as lithography using neutral atoms or ion beams. It is, at the moment, a real horse race as to which technologies will be used in nanotechnology. But this is just the beginning.
TR: Are the limitations in photolithography fundamental enough to drive a whole new area of technology for making microelectronics?
WHITESIDES: They could be. Photolithography is getting very complicated and very expensive. For the new generation fabs [fabrication facilities for making semiconductor chips] that are being planned now for the years past 2000, the capital cost per fab is estimated to be $3 billion to $10 billion. If you want 20 percent return on investment, and you put in $10 billion, how many microwidgets do you have to sell every year for the few years that that fab is the state of the art? The answer is, a lot. And people who have to put up the money don’t like that.
TR: So it still remains a question how very small things will be made. What are some of the other unknowns about the future of nanotechnology?
WHITESIDES: There’s the problem that the devices, when you get down to true nanoscale size, no longer work as expected based on extrapolations of existing devices. You get somewhat different opinions as to how far existing technology can be extrapolated. My guess is that one can take existing systems and extrapolate them to somewhere in the 50 to 100 nanometers region. As you start getting wires, transistors and other components closer together, they start to talk to one another, and this crosstalk becomes a very serious problem. The properties of the basic materials used-doped silicon-also become hard to control.