外延石墨烯应力弛豫的原位观察
In situ observation of stress relaxation in epitaxial graphene
摘要：
在冷却时，在Pt（111）和Ir（111）上在高温下生长的外延石墨烯中产生分支线缺陷。使用原子分辨扫描隧道显微镜，我们证明，这些缺陷是在石墨烯层中的皱纹，即部分分层的石墨烯的条纹。用低能电子显微镜（LEEM），我们研究了在原位的闪烁现象。在温度循环时，我们观察到皱纹的出现和消失的滞后。与皱纹形成同时，发生相邻区域的明场成像强度的变化和这些区域的微衍射的莫尔斑位置的移位。通过褶皱形成而释放的应力是由于石墨烯和衬底的热膨胀系数不匹配。一个简单的一维模型，考虑到能量相关的应变，分层和弯曲的石墨烯是在定性与我们的观察。
英文摘要：
Upon cooling, branched line defects develop in epitaxial graphene grown at high temperature on Pt(111) and Ir(111). Using atomically resolved scanning tunneling microscopy we demonstrate that these defects are wrinkles in the graphene layer, i.e. stripes of partially delaminated graphene. With low energy electron microscopy (LEEM) we investigate the wrinkling phenomenon in situ. Upon temperature cycling we observe hysteresis in the appearance and disappearance of the wrinkles. Simultaneously with wrinkle formation a change in bright field imaging intensity of adjacent areas and a shift in the moire spot positions for micro diffraction of such areas takes place. The stress relieved by wrinkle formation results from the mismatch in thermal expansion coefficients of graphene and the substrate. A simple one-dimensional model taking into account the energies related to strain, delamination and bending of graphene is in qualitative agreement with our observations.
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