A microchip the size of a fingernail gives off as much heat as a small light bulb. Getting rid of that heat is like trying to cool a cup of hot tea with a teaspoon: the insulating material around transistors is usually a poor heat conductor. Diamond conducts heat a hundred times better, but growing it on a finished chip has been thwarted by high temperatures — silicon can't take the heat.
Researchers found a way around this: they grew a diamond film directly on silicon at temperatures below 400°C, like baking a pie in the oven without going above the point where the filling is done but the crust is still raw. Films 760 and 1000 nanometers thick (a thousand times thinner than a human hair) were tested three ways: laser probing, electron microscopy, and thermal response measurements.
The films' thermal conductivity came out to 73 and 86 watts per meter-kelvin — about a hundred times higher than that of common insulators like silicon dioxide. That means heat from a transistor flows away like water down a wide trough, not seeping through sand. Such diamond layers can be applied to already-finished microchips without destroying them, and they become a heat sink inside the chip, where heat used to get stuck.
Diamond is the best natural heat conductor among solids: it dissipates heat five times faster than copper, even though it doesn't conduct electricity.
In Arthur C. Clarke's novel The Fountains of Paradise, diamond filaments are used to build a space elevator: there, strength is key; here, it's diamond's ability to spread heat.