New features of the nanoscale structure of amorphous (a)‐Si produced by ion‐implantation‐induced amorphization of crystalline (c)‐Si have been determined by the technique of small‐angle x‐ray scattering (SAXS). Si ion energies up to 17 MeV were used to generate a thick amorphous layer (8 &mgr;m) on ac‐Si wafer to enable the SAXS measurements. As‐implanted and thermally annealed (up to 540 °C)a‐Si were studied. No nanovoids were detected within a sensitivity of 0.1 vol %, but the atomic‐scale structure produced a measurable diffuse scattering signal that decreased with increasing anneal temperatures. These measurements show that the known density deficit of 1.8% ina‐Si relative toc‐Si cannot be due to voids and thata‐Si is homogeneous on nm length scale. ©1995 American Institute of Physics.