Crystal of Semiconducting Quantum Dots Built on Covalently Bonded T5 [In₂₈Cd₆S₅₄]⁻¹²:  The Largest Supertetrahedral Cluster in Solid State

Periodic array of nanoparticles is essential for practical applications in optical devices. Periodic dot arrays often exhibit very interesting collective phenomenon. We report a periodic crystal of InCdS pseudo-T5 nanocluster, the largest supertetrahedral cluster found thus far in solid state. Each InCdS cluster behaves like a nanoparticle with the same size. Unlike the array of colloidal dots in which the dot-dot separation is large ( approximately 5 nm), the neighboring T5 clusters in [In28Cd6S54].[(CH3)4N]12[(HSCH2COOH)2]3.5 crystal form a natural point contact by sharing covalently bonded S atoms. Both experimental and theoretical studies show that this crystal is a semiconductor with a band gap of 3.0 eV.