Cover Picture: Crystal Research and Technology 7'2018

Single‐Crystal Diamonds Single crystal diamonds grown by chemical vapor deposition (CVD) often exhibit strain‐induced birefringence arising from bundles of dislocation. The CVD layer exhibits high‐order anomalous birefringence under crossed polarizers. It is found that the dislocation density is higher as the higher‐order anomalous birefringence becomes more obvious. The higher the dislocation density of the sample, the greater the stress and strain, and the higher‐order anomalous birefringence of the sample is more pronounced (appeared red, green, yellow, etc.). This phenomenon is related to the growth of sample. The photograph of a sample with a thickness of 1.4 mm is shown on the cover. When the epitaxial CVD layer grows out of polycrystalline diamond on the shielding ring, the thickness of the polycrystalline edge of the sample becomes greater than the thickness of its surface. The surface becomes uneven and shows an edge‐to‐center growth morphology. Dislocations of the CVD layer grown from the edge to the center are bent, and the dislocations converge toward the central area. A small low‐stress zone is formed in the central region. The birefringence photograph in the left half of the sample picture shows that the stress in the middle region of the CVD layer is lower than the stress around it. This is reported by Yun Zhao, Chengming Li and co‐workers in article number 1800055 .