Interface compound formation at Cu-In films is studied with the perturbed $\gamma -\gamma$ angular correlation method using radioactive ${}_{}{}^{111}{}_{}{}^{}\mathrm{In}$ probe atoms. The growth of a Cu${\mathrm{In}}_2$ intermetallic interface phase is observed with a sensitivity on the scale of atomic distances in the temperature range between 220 and 340 K. This new phase is characterized by an electric field gradient (at $T=77\mathrm{}$ K) with $V_{\mathrm{zz}}=4.50\mathrm{}\left(5\right)\mathrm{}\times {10}^{17}$ V/${\mathrm{cm}}^2$ and $\eta =0.57\mathrm{}\left(1\right)\mathrm{}$. The activation energy of phase formation for Cu${\mathrm{In}}_2$ was determined to be 0.42(2) eV.

• Received 28 January 1985

DOI:https://doi.org/10.1103/PhysRevLett.54.2371