Three-dimensional scanning transmission electron microscopy of dislocation loops in tungsten

Area of Science:

• Materials Science
• Nuclear Engineering
• Condensed Matter Physics

Background:

• Scanning transmission electron microscopy (STEM) is crucial for analyzing crystal defects.
• Tungsten irradiation forms nanometric dislocation loops, potentially creating 3-D rafts.
• Understanding defect behavior is vital for materials under irradiation.

Purpose of the Study:

• To quantitatively assess the spatial distribution and characteristics of radiation-induced defects in tungsten.
• To investigate the impact of temperature on defect formation and arrangement.
• To evaluate STEM's capability for 3-D defect analysis.

Main Methods:

• In situ irradiation of tungsten samples with 1.2 MeV W ions to 0.017 dpa at room temperature and 700°C.
• Quantitative characterization using stereo imaging in STEM mode for Burgers vector analysis, number density, size, and spatial arrangement.
• Comparison with conventional transmission electron microscopy (TEM).

Main Results:

• Dislocation loops with Burgers vectors ½ a₀〈111〉 and a₀〈100〉 were observed.
• Loops exhibited significant diffusion, even at room temperature, extending beyond the simulated damage profile.
• At 700°C, loops formed elongated rafts on {111} planes, aligned along 〈110〉 directions.

Conclusions:

• STEM provides powerful 3-D quantitative analysis of defects in tungsten.
• Tungsten defects exhibit high mobility, even at room temperature.
• The formation of rafts and defect behavior are temperature-dependent.