Crystalline: The materials atoms are arranged in a periodic fashion Single crystal: in the form of one crystal grains y Polycrystalline grain boundaries Amorphous: The material's atoms do not have a long-range order (0.1~1nm)➢ Crystalline: The materials atoms are arranged in a periodic fashion. ➢ Amorphous: The material’s atoms do not have a long-range order (0.1～1nm). ✓ Single crystal: in the form of one crystal grains ✓ Polycrystalline: grain boundaries