Self-Optimizing Effect of a Few-Layer Graphene's Top-Edge Structure during Field Electron Emission Observed by In Situ TEM
Self-Optimizing Effect of a Few-Layer Graphene's Top-Edge Structure during Field Electron Emission Observed by In Situ TEM
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原位TEM观察场电子发射过程中少层石墨烯顶边结构的自优化效应
DOI：
10.1021/acsami.0c01731
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发表时间：
2020
影响因子：
9.5
通讯作者：
Zhang Yu
中科院分区：
文献类型：
--
作者：
Tang Shuai;Deng Shaozhi;Zhao Peng;Zhan Runze;Chen Jun;Zhang Yu
利用原位透射电子显微镜（TEM）观察到了场致电子发射过程中，几层石墨烯（FLG）的顶部转变为单层石墨烯（SLG），表面形成了双层/三层的片状结构。在高发射电流场致电子发射过程中，FLG的前五层发生分裂，最终转变为SLG，其表面有一些结晶度较好的双层/三层结构。这是由于焦耳热引起的高温下的热剥离和原子复合。热诱导的结构自转变优化了石墨烯顶部边缘的场电子发射。在高场区（>307 V/μm），相变后的发射电流增加了一个数量级。用改进的石墨烯场发射理论分析了这一现象，得到了高场和低场下的ln（I/E3/2）ε 1/E2和ln（I/E3）ε 1/E2曲线。石墨烯二维结构的线电流密度及其在Dirac点K态的特殊能量色散关系使ln（I/E3/2）λ 1/E2和ln（I/E3）λ 1/E2曲线呈现上弯特征，导致场致电子发射隧穿效率随外加电场的增加而提高。这些结果表明，石墨烯的本征场发射特性可以实现后，FLG的结构自优化转换在强流场电子发射。这为石墨烯场发射体的高性能化提供了一种有效的后处理方法。
A phenomenon that a few-layer graphene’s (FLG) top transformed to single-layer graphene (SLG) with some bilayer/triple-layer patches on its surface during field electron emission was observed using in situ transmission electron microscopy (TEM). During field electron emission with high emission current, the FLG’s top five layers split and finally transformed to SLG with some bilayer/triple-layer patches on its surface with a better crystallinity. It was due to thermal exfoliation and atom recombination at high temperatures induced by joule heat. The heat-induced structural self-transformation optimizes the field electron emission from the graphene’s top edge. After transformation, the emission current increased with an order of magnitude at high field region (>307 V/μm). A modified field emission theory of graphene with curves of ln (I/E3/2)∼1/Eand ln (I/E3)∼1/E2in high and low field regimes, respectively, has been used to analyze the phenomenon. The graphene’s line current density of two-dimensional (2D) structure and its special energy-dispersion relation atKstate of Dirac point makes the curves of ln (I/E3/2)∼1/Eand ln (I/E3)∼1/E2to show up-bending features, which leads to the improvement of the field electron emission tunneling efficiency as the applied electric field increases. These results revealed that the intrinsic field emission characteristics of graphene can be achieved after a structural self-optimizing transformation of FLG during high current field electron emission. It offers an efficient post-treatment method to achieve high performance of graphene field emitter.