The Art Of Building Small

Copyright 2001 Scientific American, Inc.

NANOFABRICATION

art Building
The
of

Small

BY GEORGE M. WHITESIDES AND J. CHRISTOPHER LOVE RESEARCHERS ARE DISCOVERING CHEAP, EFFICIENT WAYS TO MAKE STRUCTURES ONLY A FEW BILLIONTHS OF A METER ACROSS
INTRICATE DIFFRACTION PATTERNS are created by nanoscale-width rings (too small to see) on the surface of one-centimeter-wide hemispheres madeof clear polymer. Kateri E. Paul, a graduate student in George M. Whitesides’s group at Harvard University, fashioned the rings in a thin layer of gold on the hemispheres using a nanofabrication technique called soft lithography. www.sciam.com SCIENTIFIC AMERICAN

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Copyright 2001 Scientific American, Inc.

Overview/Nanofabrication
The development of nanotechnology will depend on theability of researchers to efficiently manufacture structures smaller than 100 nanometers (100 billionths of a meter) across. I Photolithography, the technology now used to fabricate circuits on microchips, can be modified to produce nanometer-scale structures, but the modifications would be technically difficult and hugely expensive. I Nanofabrication methods can be divided into two categories:top-down methods, which carve out or add aggregates of molecules to a surface, and bottom-up methods, which assemble atoms or molecules into nanostructures. I Two examples of promising top-down methods are soft lithography and dip-pen lithography. Researchers are using bottom-up methods to produce quantum dots that can serve as biological dyes.
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SCIENTIFIC AMERICAN

SEPTEMBER 2001Copyright 2001 Scientific American, Inc.

IMAGE BY FELICE FRANKEL, WITH TECHNICAL HELP FROM KATERI E. PAUL; COURTESY OF GEORGE M. WHITESIDES Harvard University ( page 38)

is a technological edict that has changed the world. The development of microelectronics— first the transistor and then the aggregation of transistors into microprocessors, memory chips and controllers— has brought forth acornucopia of machines that manipulate information by streaming electrons through silicon. Microelectronics rests on techniques that routinely fabricate structures almost as small as 100 nanometers across (that is, 100 billionths of a meter). This size is tiny by the standards of everyday experience— about one thousandth the width of a human hair— but it is large on the scale of atoms and molecules. Thediameter of a 100-nanometer-wide wire would span about 500 atoms of silicon. The idea of making “nanostructures” that comprise just one or a few atoms has great appeal, both as a scientific challenge and for practical reasons. A structure the size of an atom represents a fundamental limit: to make anything smaller would require manipulating atomic nuclei—essentially, transmuting one chemical elementinto another. In recent years, scientists have learned various techniques for building nanostructures, but they have only just begun to

“Make it small!”

investigate their properties and potential applications. The age of nanofabrication is here, and the age of nanoscience has dawned, but the age of nanotechnology— finding practical uses for nanostructures— has not really started yet.

TheConventional Approach
RESEARCHERS

may well develop nanostructures as electronic components, but the most important applications could be quite different: for example, biologists might use nanometer-scale particles as minuscule sensors to investigate cells. Because scientists do not know what kinds of nanostructures they will ultimately want to build, they have not yet determined the best waysto construct them. Photolithography, the technology used to manufacture computer chips and virtually all other microelectronic systems, can be refined to make structures smaller than 100 nanometers, but doing so is very difficult, expensive and inconvenient. In a search to find better alternatives, nanofabrication researchers have adopted the philosophy “Let a thousand flowers bloom.” First,...