School of Materials Science, Japan Advanced Institute of Science and Technology, 1-1 Asahidai, Nomi, Ishikawa 923-1292, Japan.
Nanoscale. 2017 Jan 26;9(4):1662-1669. doi: 10.1039/c6nr08117g.
The transformation of systematic vacuum and hydrogen annealing effects in graphene devices on the SiO surface is reported based on experimental and van der Waals interaction corrected density functional theory (DFT) simulation results. Vacuum annealing removes p-type dopants and reduces charged impurity scattering in graphene. Moreover, it induces n-type doping into graphene, leading to the improvement of the electron mobility and conductivity in the electron transport regime, which are reversed by exposing to atmospheric environment. On the other hand, annealing in hydrogen/argon gas results in smaller n-type doping along with a decrease in the overall conductivity and carrier mobility. This degradation of the conductivity is irreversible even the graphene devices are exposed to ambience. This was clarified by DFT simulations: initially, silicon dangling bonds were partially terminated by hydrogen, subsequently, the remaining dangling bonds became active and the distance between the graphene and SiO surface decreased. Moreover, both annealing methods affect the graphene channel including the vicinity of the metal contacts, which plays an important role in asymmetric carrier transport.
基于实验和范德华相互作用修正的密度泛函理论（DFT）模拟结果，报道了 SiO2 表面上石墨烯器件中系统真空和氢退火效应的转变。真空退火去除了 p 型掺杂剂，并减少了石墨烯中的带电杂质散射。此外，它诱导石墨烯发生 n 型掺杂，从而提高了电子输运模式下的电子迁移率和电导率，但在暴露于大气环境时会发生逆转。另一方面，在氢气/氩气中退火会导致 n 型掺杂减少，整体电导率和载流子迁移率下降。即使石墨烯器件暴露在环境中，这种电导率的降低也是不可逆的。DFT 模拟澄清了这一点：最初，硅悬挂键部分被氢终止，随后，剩余的悬挂键变得活跃，石墨烯和 SiO2 表面之间的距离减小。此外，这两种退火方法都会影响石墨烯沟道，包括金属接触附近的区域，这在非对称载流子输运中起着重要作用。
