We, for the first time, report the nanoscopic imaging study of anomalous infrared (IR) phonon enhancement of bilayer graphene, originated from the charge imbalance between the top and bottom layers, resulting in the enhancement of E_1u mode of bilayer graphene near 0.2 eV. We modified the multifrequency atomic force microscope platform to combine photo-induced force microscope with electrostatic/Kelvin probe force microscope constituting a novel hybrid nanoscale optical-electrical force imaging system. This enables to observe a correlation between the IR response, doping level, and topographic information of the graphene layers. Through the nanoscale spectroscopic image measurements, we demonstrate that the charge imbalance at the graphene interface can be controlled by chemical (doping effect via Redox mechanism) and mechanical (triboelectric effect by the doped cantilever) approaches. Moreover, we can also diagnosis the subsurface cracks on the stacked few-layer graphene at nanoscale, by monitoring the strain-induced IR phonon shift. Our approach provides new insights into the development of graphene-based electronic and photonic devices and their potential applications.

我们首次报道了双层石墨烯异常红外（IR）声子增强的纳米成像研究，源于顶层和底层之间的电荷不平衡，导致双层石墨烯的E 1u 模式增强到_0.2 eV附近。我们改进了多频原子力显微镜平台，将光致力显微镜与静电/开尔文探针力显微镜相结合，构成了一种新型混合纳米级光电力成像系统。这使得能够观察石墨烯层的红外响应、掺杂水平和形貌信息之间的相关性。通过纳米级光谱图像测量，我们证明石墨烯界面的电荷不平衡可以通过化学（通过氧化还原机制的掺杂效应）和机械（通过掺杂悬臂梁的摩擦电效应）方法来控制。此外，我们还可以通过监测应变引起的红外声子位移来诊断纳米级堆叠的几层石墨烯上的地下裂纹。我们的方法为基于石墨烯的电子和光子器件的开发及其潜在应用提供了新的见解。