• • Single-phosphorus-atom bridges link neighboring blueP islands on Ag(111), a structural feature that dictates island coalescence and must be controlled for uniform nanostructure growth.
• • Introducing a tellurium interlayer forms an interfacial AgTe buffer that decouples blueP islands from the Ag(111) substrate, enabling the synthesis of magic-number clusters with uniform size and geometry.
• • Substrate temperature tuning achieves magic-number blueP clusters with uniform size and geometry, which are essential for realizing higher-order topological corner states in triangular geometries.
• • The isolated blueP nanostructures exhibit higher-order topological corner states, positioning them as building blocks for topological quantum devices.