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The Diamond Age

Natural diamond is expensive, we can’t make it in the shapes we want, and it shatters. Nanotechnology will let us inexpensively make shatterproof diamond (with a structure that might resemble diamond fibers) in exactly the shapes we want. This would let us make a Boeing 747 that would weigh one fiftieth of today’s versions without any sacrifice in strength. The benefit to space travel would also be dramatic. The strength-to-weight ratio and the cost of components are critical to the performance and economy of space ships: nanotechnology could improve both of these parameters by about two orders of magnitude.

Nanotechnology could also radically alter the economics of energy production. The sun could provide orders of magnitude more power than people now use-and do so more cleanly and less expensively than fossil fuels and nuclear reactors-if only we could make low-cost solar cells and batteries. We already know how to make efficient solar cells: nanotechnology could cut their costs, finally making solar power economical. In this application we need not make new or technically superior devices; just by making inexpensively what we already know how to make expensively we would move solar power into the mainstream.

The manufacture of computer chips could undergo a profound change. There seem to be fundamental limits in how much further we can improve lithography, the process by which chips are now made. In lithography (literally, “stone writing”), we draw fine lines on a silicon wafer using methods borrowed from photography. A light-sensitive film-called a “resist”-is spread over the silicon wafer. The resist is exposed to a complex pattern of light and dark, like a negative in a camera, and developed. By repeating this process, an intricate set of interlocking patterns can be made that defines the complex logic elements of a computer chip.

But arranging atoms by throwing photons (or other particles) at a surface from a distance doesn’t seem like the best approach, especially if we want to use three dimensions instead of just two; imagine building a car by throwing tools at it from more than a mile away. Thus if improvements to computer hardware are to continue at the current pace, in a decade or so we’ll have to move beyond lithography to some new manufacturing technology. Designs for computer logic elements composed of fewer than 1,000 atoms have already been suggested-but each atom in such a small device has to be in exactly the right place. And spraying chemicals around simply can’t arrange atoms with the needed precision.

Fortunately, diamond is an excellent electronic material. It outperforms silicon in several key respects. For one thing, electrons move faster in diamond than in silicon. Diamond can also work better than silicon at high temperatures. This is important because as chips get faster and faster, their performance is limited by the need to dissipate the heat that builds up in the circuitry.

Diamond has this advantage for two reasons. First, diamond has greater thermal conductivity than silicon, which lets heat move out of a diamond transistor more quickly. Second, diamond has a larger “bandgap” than silicon-5.5 electron volts, as opposed to 1.1 electron volts in silicon. The bandgap is the minimum amount of energy required to boost an electron from its relatively immobile state into the semiconductor’s conduction band, where the electron moves freely under the influence of a voltage. As the temperature increases, more electrons gain the energy needed to jump into the conduction band. When too many electrons do this, the device changes from a semiconductor into a conductor; the transistor shorts out and stops working. Diamond’s higher bandgap means it shorts out at a higher temperature.

With nanotechnology, we should be able to build mass storage devices that can store more than 100 billion billion bytes in a volume the size of a sugar cube, and massively parallel computers of the same size that can deliver a billion billion instructions per second-a billion times more than today’s desktop computers.

The availability of nanoscale devices could radically redefine surgery, too. There is today a fundamental mismatch between what’s needed to treat injuries and the capabilities of our tools. The cellular and molecular machinery in our tissue is small and precise, yet today’s scalpels are, as seen by a cell, crude scythes that rip through tissue, leaving dead and maimed cells in their wake. The only reason that modern surgery works is the remarkable ability of cells to regroup, bury their dead, and heal over the wound.

Surgical tools that are molecular in both size and precision should let us directly heal, at the molecular and cellular level, the injuries that cause disease. A molecular robotic arm less than 100 nanometers long, for example, would easily fit into the circulatory system (a single red blood cell is about 8,000 nanometers in diameter) and would even be able to squeeze inside individual cells.

One application would be in cancer therapy. We could design a small device able to identify and kill cancer cells. The device, which would incorporate a nanoscale computer and several binding sites that are shaped to fit specific molecules, would circulate freely throughout the body, periodically sampling its environment by determining whether its binding sites were occupied. The more frequently a site was occupied, the higher the concentration of the molecule for which that site was designed. A nanodevice with a dozen different types of binding sites could in this way monitor the concentrations of a dozen different types of molecules that occur normally in the body but whose concentrations relative to one another change when cancer is present. The computer could determine if the profile of concentrations fit a preprogrammed profile and would, when a cancerous profile was encountered, release a poison that selectively kills the cancer cells.

Each device could incorporate a nanoscale pressure sensor that would allow the cancer killer to receive instructions through ultrasonic signals in the megahertz range. By “listening” to several macroscopic acoustic signal sources, the device could determine its location within the body much as a radio receiver on earth can use the transmissions from several satellites to determine its position. Awareness of its own location within the body would help the device decide whether it was near the cancer. In the absence of location information, it might sometimes mistakenly release poison in a cell that seemed to be a cancer cell. If the objective was to kill a colon cancer, for example, a cancer killer in the big toe would not release its poison no matter what its cancer sensors told it.

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Tagged: Communications

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