  From ripples to defects, edges and grain boundaries, the 3D atomic structure
of 2D materials is critical to their properties. However the damage inflicted
by conventional 3D analysis precludes its use with fragile 2D materials,
particularly for the analysis of local defects. Here we dramatically increase
the potential for precise local 3D atomic structure analysis of 2D materials,
with both greatly improved dose efficiency and sensitivity to light elements.
We demonstrate light atoms can now be located in complex 2D materials with
picometer precision at doses 30 times lower than previously possible. Moreover
we demonstrate this using a material, WS$_2$, in which the light S atoms are in
fact practically invisible to conventional methods. The key advance is
combining the concept of few tilt tomography with highly dose efficient
ptychography in scanning transmission electron microscopy. We further
demonstrate the method experimentally with the even more challenging and newly
discovered 2D CuI, leveraging a new extremely high temporal resolution camera.
