Magneto-Optical Evaluation of Q-Carbon Thin Films

We report the facile rowth of Q-carbon films over a large area, and propose a detailed mechanism to describe the formation of Q-carbon via the low-energy ion bombardment in the PECVD process. The energy of these ions is just adequate to generate a Frenkel pair, which facilitates the conversion of twofold coordinated sp² carbon units in the as-deposited carbon layer to fourfold sp³-bonded tetrahedral carbon units in Q-carbon but does not induce damage to the formed structure. This enhances the sp³ content and the atomic number density due to the random packing of tetrahedral units in the Q-carbon structure. The cluster of four tetrahedra leads to the formation of the diamond unit cell, which provides a nucleus for diamond growth. Thus, large-area diamond films can be grown by seeding with Q-carbon layers. Attributing to its unique structure, we show that Q-carbon is ferromagnetism at room temperature, while the untreated amorphous carbon is diamagnetic. As a wide-bandgap material, wafer-scale deposition of Q-carbon may facilitate the development of diamond-based heterostructures. Its optical properties are also studied in detail.