a, Illustration of the SVSEM reconstruction method. In step 1, low-energy incident electrons (1 KeV) are used to image the near-surface region of a bulk sample. In step 2, a Ga+ beam is used to slice a roughly 3-nm-thick section from the sample surface. In step 3, electrons are again used to image the ion-beam-milled sample surface. The process is repeated. With a large enough number of images (more than 200), the 3D morphology can be constructed via alignment of the stack of slices. b, Different sample stage positions are used for undistorted imaging during slice-and-view. i, For ion milling during slicing, the sample observing surface is parallel to the ion beam. ii, For electron imaging, the sample observing surface is perpendicular to the electron beam.