Fluorescent Asymmetrically Cobalt-Tipped CdSe@CdS Core@Shell Nanorod Heterostructures Exhibiting Room-Temperature Ferromagnetic Behavior

Abstract

A colloidal two-step seeded-growth approach has been devised to selectively synthesize three-component magnetic/semiconductor hybrid nanocrystals (HNCs) with a matchstick-like profile and tunable geometric parameters. The newly developed heterostructures individually comprise a single metallic Co head connected to either apexes of one rod-shaped section made of a CdSe core eccentrically embedded in a CdS shell. The specific topological arrangement realized arises from the peculiar anisotropic reactivity of the noncentrosymmetric CdSe@CdS core@shell nanorods that have been used as substrates to seed heterogeneous nucleation of Co in a surfactant-free environment from an organometallic precursor. The HNCs retain appreciable fluorescent emission in spite of photoexcited charge transfer from the semiconductor to the metal domain and exhibit unusual ferromagnetic-like behavior at room temperature.

Colloidal Magnetic Heterostructured Nanocrystals with Asymmetric Topologies: Seeded-Growth Synthetic Routes and Formation Mechanisms

“…Similarly, the apexes and the longitudinal sidewalls of the arms sections of branched NCs (Li et al, 2013) can be expected to exhibit distinct reactivity behavior ( Figure 7B). Furthermore, depending on the specific case, shaped NCs, which have formed with a lattice deviating from the ideal bulk crystallographic structure, or, which have been configured with an inner core@shell architecture, can hold an intrinsic dipole moment or accommodate defective or strained near sub-surface regions, which may influence their seeding capabilities (Menagen et al, 2008;Deka et al, 2009;Costi et al, 2010;Li et al, 2013;Banin et al, 2014).…”

“…At the relevant bonding heterointerfaces, the mismatched lattice arrangement can break the crystal periodicity to a varying extent, giving rise to noticleable interfacial strain, which may, in turn, affect their electronic-band structure (Costi et al, 2010;Sitt et al, 2013;Banin et al, 2014;Xu et al, 2015) as well as the type and extent of exchange coupling between different magnetic phases or between the optical and magnetic functionalities (Casavola et al, , 2009Wetz et al, 2007;Deka et al, 2009;Maynadiè et al, 2009;Liakakos et al, 2014). Interfacial misfit strain may be alleviated by different pathways.…”

“…In the extreme cases of exceedingly large misfit, plastic relaxation may induce formation of interfacial defects, such as dislocations and stacking faults (Dunstan, 1997;Markov, 2003;Carbone and Cozzoli, 2010;Li et al, 2014). Experimental results (Casavola et al, , 2009Koo and Korgel, 2008;Deka et al, 2009;Yuhas et al, 2009;Liakakos et al, 2014) and thermodynamic modeling (Sadowski and Ramprasad, 2010;Xu et al, 2015) have indicated that the temperature and the particular chemical pathways underlying MHNC formation are decisive in determining whether either uniformly alloyed, graded, or abrupt interfaces may be attained.…”

“…Interestingly, the overall magnetic behavior may also result in being remarkably affected, even when magnetic modules are connected to non-magnetic materials (Casavola et al, , 2009Wetz et al, 2007;Deka et al, 2009;Maynadiè et al, 2009;Liakakos et al, 2014). Such hybrid nanoarchitectures hold promise as new functional elements for the realization of optoelectronic devices and efficient magnetically recoverable photo(electro)catalytic platforms (Costi et al, 2010;de Mello Donegà, 2011;Sitt et al, 2013;Banin et al, 2014), spintronic devices, and magnetic recording systems (Casavola et al, , 2009Wetz et al, 2007;Deka et al, 2009;Maynadiè et al, 2009;Liakakos et al, 2014).…”

“…To achieve Co deposition on eccentric CdSe@CdS core@shell nanorods and γ-Fe 2 O 3 tetrapods upon Co 2 (CO) 8 decomposition, non-coordinating ODE was selected as the reaction medium, without any extra surfactants or ligands added in (Casavola et al, 2009;Deka et al, 2009). The seeds became activated toward heterogeneous nucleation due to partial displacement of their original capping molecules A technique that involved controllably slow Co 2 (CO) 8 addition and delayed delivery of excess OLAC to a stage at which Co growth had almost reached completion, guaranteed the high-yield formation of heterostructures with high colloidal stability (Figures 8B,C).…”