Electronic Structure and Spin Transport Properties of a New Class of Semiconductor Surface-Confined One-Dimensional Half-Metallic [Eu-(CnHn-2)](N) (n=7-9) Sandwich Compounds and Molecular Wires: First Principle Studies

Transition-metal atom/pi-conjugated ring sandwich compounds are promising candidates for application in molecular spintronics. However, a great challenge that has significantly restrained the practical application of these sandwich compounds is their fabrication on a well-characterized solid-state substrate in a controllable manner. In this work, we suggested a two-step self-assemble way to fabricate the Eu-CnHn-2 compounds on the hydrogen-terminated Si(100) surface and theoretically studied the geometric structure and electronic and magnetic properties. Theoretical results indicate that the silicon surface is an ideal substrate to support such kind of metal atom-encapsulated sandwich compounds as the lattice distance of silicon (100) surface is close to the inter-ring distances of freestanding gas-phase sandwich compounds. On the basis of the spin-polarized density functional theory calculations and ab initio molecular dynamics simulations, we find that the silicon surface-supported Si-[EuCh](N), Si-[EuCOT](N), and Si-[EuCnt](N) sandwich compounds all process a ferromagnetic ground state. Moreover, the cycloheptatrienyl (Ch) and cyclononatetraenyl (Cnt) Eu sandwich compounds show half-metallic properties. The calculation of electron/spin transport properties using the nonequilibrium Green's-function method confirms that the Ch Eu sandwich compounds are excellent spin filters, and the spin filter efficiency (SFE) is independent of the cluster size (N), whereas the SFE of Si-[EuCOT](N) decreases rapidly with the increase of cluster size. The perfect half-metallic properties of these surface-supported sandwich compounds are promising for future application in spin devices. The present work suggests a way to fabricate the half-metallic sandwich compounds on a semiconductor silicon surface.