Still only half the thermal conductivity of diamond. But pretty awesome nonetheless! I hope it's easy to make.
Can we make heat sink out of synthetic diamonds?
As another poster has said, heatsinks made of synthetic diamonds have been used for a long time in the most demanding applications.
However, until now their use has been limited by very high cost and by small maximum sizes.
Thus you will not see them in consumer applications, for now.
Yes, that is a thing.
Also fabricating integrated circuits on a diamond substrate.
Yeah, that's the main reason why copper is used, it's relatively cheap, safe, and very easy to work with. There are far better heat conductors out there but they're either extremely expensive or extremely toxic, e.g. beryllium. So this new stuff would have to be both very cheap and easy to make and easy to work with in order to succeed in the market, otherwise it'd be confined to niche applications like the military with beryllium.