A composition of matter comprising: a graphitic substrate optionally carried on a support; a seed layer having a thickness of no more than 50 nm deposited directly on top of said substrate, opposite any support; and an oxide or nitride masking layer directly on top of said seed layer; wherein a plurality of holes are present through said seed layer and through said masking layer to said graphitic substrate; and wherein a plurality of nanowires or nanopyramids are grown from said substrate in said holes, said nanowires or nanopyramids comprising at least one semiconducting group III-V compound.