Imaging strain fields at the nanoscale is crucial for understanding the physical properties as well as the performance of oxide heterostructures and electronic devices. Based on scanning transmission electron microscopy (STEM) techniques, we successfully imaged the random strain field at the interface of core-shell ZnO nanowires. Combining experimental observations and image simulations, we find that the strain contrast originates from dechanneling of electrons and increased diffuse scattering induced by static atomic displacements. For a thin sample with a random strain field, a positive strain contrast appears in the low-angle annular dark-field (LAADF) image and a negative contrast in the high-angle annular dark-field (HAADF) image, but for a thick sample (> 120 nm), the positive contrast always occurs in both the LAADF and HAADF images. Through the analysis of the relationship between strain contrast and various parameters, we also discuss the optimum experimental condition for imaging random strain fields.

在纳米尺度上成像应变场对于理解物理性质以及氧化物异质结构和电子设备的性能至关重要。基于扫描透射电子显微镜（STEM）技术，我们成功地在核壳ZnO纳米线的界面处成像了随机应变场。结合实验观察和图像模拟，我们发现应变对比源自电子的去通道化和静态原子位移引起的扩散散射的增加。对于具有随机应变场的薄样品，低角度环形暗场（LAADF）图像中出现正应变对比度，而高角度环形暗场（HAADF）图像中出现负对比度，但对于较厚的样品样品（> 120 nm）时，在LAADF和HAADF图像中总是出现正对比度。