Triggering One-Dimensional Phase Transition with Defects at the Graphene Zigzag Edge.

One well-known argument about a one-dimensional (1D) system is that 1D phase transition at finite temperature cannot exist even though this concept depends on conditions such as range of interaction, external fields, and periodicity. Therefore, 1D systems usually have random fluctuations with intrinsic domain walls arising that naturally bring disorder during transition. Herein, we introduce a real 1D system in which artificially created defects can induce a well-defined 1D phase transition. The dynamics of structural reconstructions at graphene zigzag edges are examined by in situ aberration-corrected transmission electron microscopy. Combined with an in-depth analysis by ab initio simulations and quantum chemical molecular dynamics, the complete defect induced 1D phase transition dynamics at graphene zigzag edge is clearly demonstrated and understood on the atomic scale. Further, following this phase transition scheme, graphene nanoribbons (GNR) with different edge symmetries can be fabricated and, according to our electronic structure and quantum transport calculations, a metal-insulator-semiconductor transition for ultrathin GNRs is proposed.