Bite-sized vacuum tubes.

Paying homage to the early days of broadcasting, when oak-paneled radios blared out swing tunes, physicists Griff L. Bilbro and Christopher W. Hatfield of North Carolina State University in Raleigh and their colleagues are fashioning tiny vacuum tubes out of diamonds.

'We're revisiting vacuum tubes from the 1940s,' says Bilbro. 'But now we're taking advantage of new materials and computer design tools to predict their performance at very high frequencies, for use in radar and cellular phones.'

Vacuum tubes offer some advantages over semiconductors and computer chips, Bilbro says. They're more durable than other microelectronics materials, outperforming semiconductors at high temperatures, voltages, and radiation levels.

The researchers made arrays of vacuum tubes by encasing electrodes in diamond, then evacuating the air from the interiors. These arrays resemble 'furrowed fields, with rows of ridges and troughs,' Bilbro says. 'Each array looks like a glass bead, about the size of a match head.'

A big difference between the new diamond vacuum tubes and the large glass bulbs of 50 years ago is heat. The old tubes had to glow red-hot to emit streams of electrons. The new tubes produce current at room temperature.

'There's an interesting irony here,' says Hatfield. 'Vacuum tubes paved the way for solid-state transistors. Now we're seeing that, for certain applications, the new vacuum tubes offer advantages over solid-state components.'