Understanding the role of interfacial topography and defects in controlling reactivity remains incomplete because of the difficulty in imaging interfacial topography with nanometric spatial resolution. Here we demonstrate the feasibility of imaging, in three dimensions, the surface topography of calcite ($\mathrm{CaC}{\mathrm{O}}_3$) using coherent x-ray reflectivity (CXR). While these images have a vertical resolution of $\sim 30$ nm, we show that the phase of the interfacial density provides sub-nm sensitivity to the interfacial topography, a $\sim 100$-fold enhancement with respect to resolution limits. This is achieved by extending the concepts of Bragg coherent diffraction imaging (BCDI) to CXR, revealing surfaces with nearly atomically flat and micron-scale topographies. It is demonstrated for surfaces of individual µm-sized particles and extended crystals, including free surfaces and buried interfaces.

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• Interfaces
• Surfaces
• Coherent X-ray scattering
• X-ray imaging
• X-ray reflectivity