Latent ion tracks in amorphous silicon

We present experimental evidence for the formation of ion tracks in amorphous Si induced by swift heavy-ion irradiation. An underlying core-shell structure consistent with remnants of a high-density liquid structure was revealed by small-angle x-ray scattering and molecular dynamics simulations. Ion track dimensions differ for as-implanted and relaxed Si as attributed to different microstructures and melting temperatures. The identification and characterization of ion tracks in amorphous Si yields new insight into mechanisms of damage formation due to swift heavy-ion irradiation in amorphous semiconductors.

Figure 1

Scattering images for ion tracks in as-implanted a-Si (a) aligned and (b) tilted with respect to the incoming x-ray beam.

Figure 2

SAXS spectra (background subtracted) of ion tracks in as-implanted a-Si irradiated with 185-MeV Au ions. Solid lines are fits using a cylindrical core-shell model [Eq. (1)].

Figure 3

Comparison of simple [dashed line, Eq. (2)] and core-shell [solid line, Eq. (1)] cylinder models in the case of as-implanted a-Si irradiated with 185-MeV Au ions ($1\times {10}^{11}\mathrm{ions}/{\mathrm{cm}}^2$). The inset shows the magnitude of the model radial density distribution function $\left|\rho \right|$, scaled to the fit parameters for both models. $\left|\rho \right|=1$ represents the density of the surrounding a-Si matrix.

Figure 4

Comparison of SAXS spectra of as-implanted a-Si irradiated at 185 and $89\mathrm{MeV}$ (both $1\times {10}^{11}\mathrm{ions}/{\mathrm{cm}}^2$) and relaxed a-Si irradiated at $185\mathrm{MeV}$ ($3\times {10}^{11}\mathrm{ions}/{\mathrm{cm}}^2$). Solid lines are fits using a core-shell model. Spectra are offset for clarity.

Figure 5

Ion track density profiles of MD simulation (five-point average, $200\mathrm{ps}$ after energy deposition) and SAXS measurements (as-implanted a-Si, 185-MeV Au). The inset shows the time evolution of the radial MD temperature profile (kinetic energy in units of K). The dotted lines indicate the melting temperature of as-implanted and relaxed a-Si[19, 20] and the corresponding radius of the temperature profile.