Shape-dependent local internal stress of α-Cr 2O 3 nanocrystal fabricated by pulsed laser ablation

Abstract

The α-Cr 2O 3 single-crystal nanocondensates were fabricated by pulsed laser ablation in air and characterized by analytical electron microscopy regarding shape-dependent local internal stress of the anisotropic crystal. The nanocondensates formed predominantly as rhombohedra with well-developed { 0 1 1 ¯ 2 } surfaces and occasionally hexagonal plate with thin { 1 1 2 ¯ 0 } edges and blunt corners. Such nanocondensates showed Raman shift for the CrO 6 polyhedra, indicating a local compressive stress up to ca. 4 GPa on the average. Careful analysis of the lattice fringes revealed a local compressive stress (0.5% strain) at the thin edge of the hexagonal plates and a local tensile stress (0.3–1.0% strain) near the relaxed { 1 ¯ 0 1 2 } , { 1 0 1 ¯ 1 } , and (0 0 0 1) surfaces of truncated rhombohedra. The combined effects of nanosize, capillarity force at sharp edge, and specific surface relaxation account for the retention of a local internal compressive stress built up in an anisotropic crystal during a very rapid heating–cooling process.