In-situ Measurement of Self-Atom Diffusion in Solids Using Amorphous Germanium as a Model System

Area of Science:

• Materials Science
• Solid-State Physics
• Neutron Scattering

Background:

• Classical ex-situ diffusion measurements are time-consuming and have limitations.
• Understanding self-diffusion in amorphous materials is crucial for their technological applications.

Purpose of the Study:

• To introduce and validate an in-situ self-diffusion measurement technique using Focussing Neutron Reflectometry.
• To investigate the time and temperature dependence of self-diffusion in amorphous germanium.
• To determine the activation energy for self-diffusion in amorphous germanium.

Main Methods:

• In-situ self-diffusion experiments on isotope multilayers.
• Focussing Neutron Reflectometry (FNR).
• Isothermal annealing at various temperatures.

Main Results:

• Identified time-dependent diffusivities with reduced error limits and experimental time.
• Measured unknown self-diffusivities in amorphous germanium quasi-continuously.
• Observed a one-order-of-magnitude decrease in diffusivity due to structural relaxation and defect annihilation.
• Determined Arrhenius behavior between 375–412°C with an activation energy of (2.11 ± 0.12) eV.
• Found diffusivities five orders of magnitude higher than in germanium single crystals.

Conclusions:

• In-situ FNR is a powerful technique for studying time-dependent diffusion in solids.
• Structural relaxation significantly impacts self-diffusion in amorphous germanium.
• Amorphous germanium exhibits much higher self-diffusivity than crystalline germanium due to lower activation energy.