AML, Department of Engineering Mechanics, Tsinghua University, Beijing 100084, China.
Nanoscale. 2012 Aug 7;4(15):4555-61. doi: 10.1039/c2nr30648d. Epub 2012 Jun 15.
Though the all-semiconducting nature of ultrathin graphene nanoribbons (GNRs) has been demonstrated in field-effect transistors operated at room temperature with ∼10(5) on-off current ratios, the borderline for the potential of GNRs is still untouched. There remains a great challenge in fabricating even thinner GNRs with precise width, known edge configurations and specified crystallographic orientations. Unparalleled to other methods, low-voltage electron irradiation leads to a continuous reduction in width to a sub-nanometer range until the occurrence of structural instability. The underlying mechanisms have been investigated by the molecular dynamics method herein, combined with in situ aberration-corrected transmission electron microscopy and density functional theory calculations. The structural evolution reveals that the zigzag edges are dynamically more stable than the chiral ones. Preferential bond breaking induces atomic rings and dangling bonds as the initial defects. The defects grow, combine and reconstruct to complex edge structures. Dynamic recovery is enhanced by thermal activation, especially in cooperation with electron irradiation. Roughness develops under irradiation and reaches a plateau less than 1 nm for all edge configurations after longtime exposure. These features render low-voltage electron irradiation an attractive technique in the fabrication of ultrathin GNRs for exploring the ultimate electronic properties.
虽然在室温下操作的场效应晶体管中已经证明了超窄石墨烯纳米带（GNR）的全半导体性质，具有约 10(5)的开/关电流比，但 GNR 的潜力边界仍未触及。制造具有精确宽度、已知边缘构型和指定晶体学取向的甚至更薄的 GNR 仍然具有很大的挑战性。与其他方法相比，低电压电子辐照导致宽度连续减小到亚纳米范围，直到发生结构不稳定。本文通过分子动力学方法，结合原位像差校正透射电子显微镜和密度泛函理论计算，研究了这种方法的潜在机制。结构演化表明，锯齿形边缘比手性边缘在动力学上更稳定。优先的键断裂导致原子环和悬空键作为初始缺陷。缺陷生长、结合和重构为复杂的边缘结构。热激活，特别是与电子辐照协同作用，增强了动态恢复。在辐照下会产生粗糙度，并且对于所有边缘构型，在长时间暴露后，粗糙度会达到小于 1nm 的平台。这些特征使得低电压电子辐照成为探索最终电子性质的超窄 GNR 制造的一种有吸引力的技术。
