“…Since Richard Feynman proposed the possibility of direct manipulation of individual atoms as a powerful way for materials synthesis and discovery more than 70 years ago, precise control of lattice structures and compositions of materials has been a focus of nanoscience and nanotechnology toward achieving engineered properties and functionalities. Such control is especially relevant and viable in two-dimensional (2D) materials build via van der Waals (vdW) assembly of a number of vertically stacked multilayers with designable properties. − Of particular interest is the vdW gap, defined as an angstrom-scale emptiness between adjacent layers in the multilayers, which has been exploited to favorably host a diverse range of foreign species via intercalation. − Successful intercalants include commonly used metal atoms ranging from alkali to noble metals and a series of organic molecules. − In addition to introducing inherent properties to systems, the intercalants offer charge transfers to 2D materials, which may significantly modify interlayer interactions, thereby opening unprecedented opportunities of potential applications in a variety of domains, such as electronics, , thermoelectrics, , catalysis, − and energy storage. − Among reported intercalated materials, layered self-intercalated materials, where intercalated metal atoms are native to host 2D materials, have been intensively studied. − In contrast to intercalation of foreign atoms that usually requires postgrowth treatment and is difficult to yield long-range crystalline phase, self-intercalation can be directly achieved with controlled stoichiometry by growing 2D materials under conditions involving high chemical potential of metals. ,− Moreover, self-intercalation avoids uncontrollable chemical doping issues that are often encountered when foreign atoms react with the hosting materials. A recent experiment reported synthesis of a class of ultrathin, covalently bonded 2D materials with well-defined stoichiometries and composition-tunable properties by self-intercalation of native atoms into bilayer transition metal dichalcogenides, MX 2 (M = transition metal and X = S, Se, Te, etc.)…”