Thin layers of amorphous silicon (a‐Si) were produced by noble gas ion implantation of (100) substrates held at 77 K. Rutherford backscattering and channeling, and differential scanning calorimetry were used to measure the heat of crystallization, &Dgr;Hac, to be 11.9±0.7 kJ/mol, substantially less than the value predicted by scaling &Dgr;Hacofa‐Ge. The crystal growth velocity is found to have the formv=v0 exp(−2.24 eV/kT). We obtain a new estimate, 1420 K, for the melting temperature ofa‐Si.