The control of three-dimensional (3D) geometrical shapes is one of important approaches that contribute the development of new functionalities in material science. We produced 3D Si pyramids with atomically flat and reconstructed {111} facet surfaces supporting atomically resolved material growth in 3D space for the first time. The complex 4-fold clean 7×7 and 2×2-Fe low-energy electron diffraction (LEED) patterns reflecting the pyramidal geometry showed the realization of atomically reconstructed facet surfaces on the 3D patterned Si. Cross-sectional transmission electron microscopy (TEM) revealed the epitaxial heterointerfaces between Fe nanofilm and Si facet surfaces. The LEED and TEM results indicate the applicability of the Si pyramid as a supporting substrate for arbitrarily oriented 3D functional structures. The pyramidal Fe nanofilm displayed magnetic properties depending on the geometric shape, owing to the facet surfaces and the sharp facet edges. The unique anisotropic magnetization behavior of the 3D pyramid shape indicates that the epitaxial growth of an arbitrary geometry by virtue of the atomically ordered substrate surfaces in 3D space can contribute to the modification of the functionality.

The creation of three-dimensional (3D) geometrical shapes with atomically ordered surfaces and the investigation of their physical properties are major steps contributing to the development of a new paradigm in surface science. We produced a 3Dpatterned Si sample with atomically flat and reconstructed {111} facet surfaces, and investigated its structural and physical properties. To apply the conventional techniques in surface science to 3D samples with various oriented surfaces, instead of two-dimensional planar samples, an appropriate relationship between the crystallographic surface ordering on the 3D-architected surfaces and the angle-resolved photoelectron spectroscopy (ARPES) setup considering the configuration in 3D space is indispensable. The distinctive and complex low-energy electron diffraction (LEED) patterns reflecting the 3D-arranged facet surfaces showed the realization of atomically reconstructed facet surfaces on 3D-patterned Si. Surface states of the 3D-patterned Si{111} surfaces are mapped by ARPES by considering the 3D geometrical relationship. The selection of the appropriate alignment of the incident electron beam (light) for the target surfaces allows the clear observation of the band dispersion from the produced {111}7×7 facet surfaces in 3D space. Our demonstration of accessibility of ARPES technique could provide useful guidelines for new methodologies, giving a fundamental understanding of 3D-shape-induced novel functionalities.