Carbon or Silicon there is one -on - onomasticon tougher than diamond.

The possibility of life based on silicon fascinated writers and scientists as far back as 1894, H.G. Wells wrote,
“ One is startled towards fantastic imaginings by such a suggestion: visions of silicon-aluminium organisms - why not silicon-aluminium men at once? - wandering through an atmosphere of gaseous sulphur, let us say, by the shores of a sea of liquid iron some thousand degrees or so above the temperature of a blast furnace. “

Silicon is abundant in the universe and is also an element of group IV, lying directly below carbon in the periodic table of elements, so that much of its basic chemistry is similar. Yet for life building purposes it was also noted, that when oxidized silicon forms crystals in contrary to our common CO2. Such as it is not conceivable how would respiratory functions be preserved in organisms based on silicon chemistry. You need very high temperatures of 2000 degrees Celsius and higher to turn SiO2 into gaseous form.

Starting from 1950-ties we've learned to build integrated circuits on silicon wafers. Constantly improving technological processes today we are able to pack as much as 2bln transistors on a single die chip. But these circuits have an unfortunate property, if just a single transistor fails, the entire circuit also fails. To remedy this problem researchers at Caltech have proposed "self-healing" circuits.

Such circuits are "inspired by biological systems that constantly heal themselves in the presence of random and intentional failures," says Ali Hajimiri, a professor of electrical engineering at the California Institute of Technology (Caltech).

Thus we see at least two flaws for basing life upon silicon: one when approaching from the grounds of our physiology, the other - not robust enough in massive scaling.
Another approach to use silicon is to build a system on chip which will recreate the circuitry of human brain, mimicking electric signals with such as received by synapses. Personally, I'm highly dubious that we hold enough data and understanding of how synapses work from In-vivo brain to build something functional.

The latest discoveries in nanotechnology from MIT open doors for a graphene based microchips. If successful such chips could operate at frequencies 500-1000 gigahertz. This in turn would facilitate raw processing computational power in a given volume 100 folds. Once again back to carbon, though once twisted, after flattened, unnatural kind of carbon. Such compounds do not exist in the wild cosmos outside our artificially created conditions. Essentially graphene is tougher than diamond and has very unique electron spin properties due to his specially crafted crystall lattices.






The picture above depicts our current model for silicon atom - nothing biological in it, lifeless static mechanical model with electrons on the outside shell. Yet under our current paradigm this model does require complicated quanto-mechanical rules, partially statistically based, to explain how those electrons are bundled together.
Pure silicon crystals have the diamond lattice structure where each atom forms four identical covalent bonds with its neighbours, resulting in a tetrahedral arrangement.








One recurrent theme is diamond, of course it is not a physical diamond which is important but the symbolism of what diamond represents

We don't know yet what is the crucial part for building life, but we do making steady progress in this direction. Sometimes by exhilarating fantasy as H.G. Wells, sometimes this drive unfolds unconsciously, disguised by the need to justify so called Moore's Law. Our early observations for what is needed for life, like the ability to breath - thus enabling exchange of energy and matter, has changed to more subtle requirements - to be self-sustainable.
It may be not that important on which chemical element we want to imitate life, but the principle desire to do so. There is a much deeper question: why we want to make another life ?