Dotty ideas that prove spot on

The Quantum Dot
September 1, 1995

Popular physics books have been around for a good many years; the majority are philosophical, capturing the reader's imagination about whether physics can prove or disprove God, or determine the origin of the universe. The armchair scientist can also discover the secret of chaos or the exotic world of particle physics.

Richard Turton breaks new ground by presenting popular physics with the motivation for application: his book can be even classed as popular microtechnology. He explores the future of the semiconductor microchip industry.

Major advances in technology in the past couple of decades have resulted in the components of microchips becoming increasingly small. With these developments a playground for fundamental physicists has been built: as the structures approach atomic size, a new physics takes over; "classical" physics breaks down and quantum concepts become important. Physics literally takes on new dimensions in this quantum world, their numbers being two, one and zero. The quantum dot that gives the book its name is a structure completely ruled by quantum mechanics, so it is thought to be zero dimensional, as the electrons are confined to a point with no freedom. Mark Reed, who made the first lithographically defined quantum dots, coined the phrase "designer atoms" because the size and shape of the atom plus the number of electrons in it can be as the experimenter desires. George Bernard Shaw wrote: "The unreasonable man persists in trying to adapt the world to himself. Therefore all progress depends on the unreasonable man." Although the concept of artificial atoms may be nonsensical, atomic physics not found in nature may be studied using these peculiar dots. Not only interesting for physicists, these quantum devices can be exploited in industry, for example to make faster and smaller computers. This is not just science fantasy: already many homes have a two-dimensional quantum mechanical semiconductor device, namely the laser in a compact-disc player.

Turton is highly ambitious and enthusiastic in his book, covering a great deal of mesoscopic physics (the fundamental study of structures approaching atomic size). He begins with the basics of semiconductor structure and then goes on to describe the working of semiconductor devices such as transistors. The book is aimed at "those with little or no previous knowledge of physics or electronics", but I wonder how many readers will be prepared to wade through pages of grim details of how electrons behave in these non-quantum devices. The story becomes more interesting when quantum mechanics is introduced in a fairly standard way. Finally in the ninth chapter the quest for the "holy grail" of microelectronics is ended and the quantum dot is described. The climax is reached in the last chapter: a description is given of how electronics could be replaced with components using light instead of electrons, the ultimately fast method of processing.

It is questionable whether all the devices described in the book will ever be employed in the microchip industry. Turton glosses over some problems, such as the very low temperature often needed to work quantum devices. As the Chinese saying goes: "If a melon seed is sown, beans are reaped." That is, although the incentive of mesoscopic physicists a few years ago was to revolutionise the microchip industry, perhaps the insight thus gained into the physics of atoms and molecules will be of most use in other applications such as in chemistry or in medicine.

Geraldine Houston is at the Delft University of Technology.

The Quantum Dot: A Journey into the Future of Microelectronics

Author - Richard Turton
ISBN - 0 7167 4517 8
Publisher - W. H. Freeman
Price - £11.99
Pages - 256

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