Detection of local strain at the nanometer scale with high sensitivity remains challenging. Here we report near-field infrared nano-imaging of local strains in bilayer graphene by probing strain-induced shifts of phonon frequency. As a non-polar crystal, intrinsic bilayer graphene possesses little infrared response at its transverse optical phonon frequency. The reported optical detection of local strain is enabled by applying a vertical electrical field that breaks the symmetry of the two graphene layers and introduces finite electrical dipole moment to graphene phonon. The activated phonon further interacts with continuum electronic transitions, and generates a strong Fano resonance. The resulted Fano resonance features a very sharp near-field infrared scattering peak, which leads to an extraordinary sensitivity of ∼ 0.002% for the strain detection. Our results demonstrate the first nano-scale near-field Fano resonance, provide a new way to probe local strains with high sensitivity in non-polar crystals, and open exciting possibilities for studying strain-induced rich phenomena.

以高灵敏度检测纳米尺度的局部应变仍然具有挑战性。在这里，我们通过探测应变引起的声子频率变化来报告双层石墨烯中局部应变的近场红外纳米成像。作为一种非极性晶体，本征双层石墨烯在其横向光学声子频率下几乎没有红外响应。所报道的局部应变的光学检测是通过施加垂直电场来实现的，该电场打破了两个石墨烯层的对称性并将有限的电偶极矩引入石墨烯声子。激活的声子进一步与连续电子跃迁相互作用，并产生强烈的 Fano 共振。由此产生的 Fano 共振具有非常尖锐的近场红外散射峰，这导致了 ∼ 0 的非凡灵敏度。002% 用于应变检测。我们的结果证明了第一个纳米级近场 Fano 共振，为探测非极性晶体中的高灵敏度局部应变提供了一种新方法，并为研究应变诱导的丰富现象开辟了令人兴奋的可能性。