Nano- and meso- scale materials properties are crucial to the macroscopic performance of a wide range of functional and photovoltaic devices. In 2-dimensions, photoconductivity, ferroelectricity, and even domain dynamics have thus been investigated for decades now especially using variations of Atomic Force Microscopy. Our work and others reveals how these properties are frequently mediated by strain, orientation, grain boundaries, and other microstructural defects or heterogeneities. However, practical devices are often sensitive to, or even controlled by, sub-surface effects or thickness dependencies related to microstructure and concentration, polarization, and/or field gradients. Therefore, we are advancing Tomographic AFM for volumetric materials property mapping, with voxels of properties on the order of ~10 nm3. With polycrystalline photovoltaics such as MAPbI3 and CdTe, TAFM literally uncovers new pathways to improve carrier separation via inter- and intra- granular defects (Luria, Nature Energy, 2017; Song, Nature Communications, 2020). For BiFeO3, Tomographic AFM confirms Kay-Dunn thickness scaling, LGD behavior with a minimum switchable thickness of <5 nm, and even co-located domain and current maps which together directly reveal sub-surface topological defects (Steffes, PNAS, 2018). Such volumetric insight is increasingly important for engineering optimal performance and reliability of real-world, 3-Dimensional materials devices.