Extended Data Fig. 1: Atomic-scale multilayer structure.

a, Schematic of the HfO₂–ZrO₂ multilayer structure on SiO₂-buffered Si. b, Synchrotron X-ray reflectivity (XRR) of thicker HZH heterostructures (left) repeated with the same periodicity as the thinner trilayer structure; XRR fitting (right) demonstrates the presence of well separated HfO₂–ZrO₂ layers, that is, not a solid solution, for three different multilayer repeats of fixed periodicity, all approximately following the expected 4 Å–12 Å–4 Å HZH structure. c, Layer-resolved electron energy loss spectroscopy (EELS) of the 2-nm HZH trilayer, demonstrating clear separation of HfO₂ and ZrO₂ layers. The exact layer thicknesses are extracted from XRR, which spans a wider sample footprint, rather than the local EELS measurement in which the apparent width increase can be due to beam spreading and local thickness variation. d, Angle-resolved X-ray photoelectric spectroscopy (XPS) of the 2-nm HZH trilayer (left) and the extracted atomic composition (right). The presence of increasing Zr content as the grazing angle increases is expected from the multilayer structure in which Zr content increases after the surface Hf-rich layer. Therefore XRR, EELS and XPS data all indicate the presence of a multilayer structure in which the HfO₂ layer is directly on the SiO₂ layer.