Engineered inorganic core/shell nanoparticles

Abstract

It has been for a long time recognized that nanoparticles are of great scientific interest as they are effectively a bridge between bulk materials and atomic structures. At first, size effects occurring in single elements have been studied. More recently, progress in chemical and physical synthesis routes permitted the preparation of more complex structures. Such structures take advantages of new adjustable parameters including stoichiometry, chemical ordering, shape and segregation opening new fields with tailored materials for biology, mechanics, optics magnetism, chemistry catalysis, solar cells and microelectronics. Among them, core/shell structures are a particular class of nanoparticles made with an inorganic core and one or several inorganic shell layer(s). In earlier work, the shell was merely used as a protective coating for the core. More recently, it has been shown that it is possible to tune the physical properties in a larger range than that of each material taken separately. The goal of the present review is to discuss the basic properties of the different types of core/shell nanoparticles including a large variety of heterostructures. We restrict ourselves on all inorganic (on inorganic/inorganic) core/shell structures. In the light of recent developments, the applications of inorganic core/shell particles are found in many fields including biology, chemistry, physics and engineering. In addition to a representative overview 2 of the properties, general concepts based on solid state physics are considered for material selection and for identifying criteria linking the core/shell structure and its resulting properties. Chemical and physical routes for the synthesis and specific methods for the study of core/shell nanoparticle are briefly discussed.

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

“…In such systems an inner NC "core" is evenly enwrapped within a "shell" made of one or more layers of other materials, which ultimately governs or mediates MHNC interactions with the external environment. Semiconductors, metals, and oxides arranged in centrosymmetric onionlike or eccentric core@shell configurations share large connecting heterointerfaces, across which direct electronic communication and hybridization may lead not only to chemical-physical properties distinct from those inherent to the individual components (e.g., increased photoluminescence, emission over spectral ranges prohibited to the individual material components alone, enhanced or modified LSPR absorption, increased magnetic anisotropy, enhanced ionintercalation capabilities, and unexpected catalytic activity), but also to exchange interactions of non-homologous properties (e.g., exciton-LSPR coupling, exchange coupling between different magnetic phases), depending on the specific material association (Casavola et al, 2008;Carbone and Cozzoli, 2010;Talapin et al, 2010;Ghosh Chaudhuri and Paria, 2011;Lee and Cho, 2011;Liu et al, 2011;Su et al, 2011;Chatterjee et al, 2014;Melinon et al, 2014;Oszajca et al, 2014;Purbia and Paria, 2015).…”

“…HNCs incorporate a countable number of discrete nanometer-scale modules (with the largest dimension smaller than~100-150 nm) made of chemically and/or structurally different materials, which are welded together via direct solid-state chemically bonded heterointerfaces to form individually distinguishable, solution freestanding multifunctional hybrid nanoplatforms. In general, HNCs may group inorganic Buonsanti et al, 2007;Jun et al, 2007;Casavola et al, 2008;Carbone and Cozzoli, 2010;Talapin et al, 2010;de Mello Donegà, 2011;Liu et al, 2011;Buck and Schaak, 2013;Sitt et al, 2013;Banin et al, 2014;Melinon et al, 2014;Purbia and Paria, 2015;Qi et al, 2015) and/or organic materials, such as polymers (Lattuada and Hatton, 2011;Liu et al, 2011;Zhang et al, 2012;He et al, 2013;Kaewsaneha et al, 2013;Pang et al, 2014;Purbia and Paria, 2015) or some carbon allotropes Liu et al, 2011;Purbia and Paria, 2015;Yan et al, 2015b). As far as the attached domains grow crystalline, the relevant heterojunctions can develop epitaxially, allowing the concerned lattices to hold precise, yet synthetically adjustable, crystallographic, and spatial relationships relative to one other (Carbone and Cozzoli, 2010;Shim and McDaniel, 2010).…”

“…The most easily controllable prototypes of HNCs delivered so far can be roughly classified into two main categories: (i) core@shell architectures, in which the component domains are arranged in concentric or eccentric onionlike topologies, where only the outer shell material, which protects the inner core, is exposed to the external environment Buonsanti et al, 2007;Jun et al, 2007;Casavola et al, 2008;Carbone and Cozzoli, 2010;de Mello Donegà, 2011;Liu et al, 2011;Zhang et al, 2012;Kaewsaneha et al, 2013;Sitt et al, 2013;Banin et al, 2014;Melinon et al, 2014;Purbia and Paria, 2015;Qi et al, 2015) [in the yolk/shell variant, a core-or shellconformal void space may also intervene in the interior (Casavola et al, 2008;Carbone and Cozzoli, 2010;Liu et al, 2011;Purbia and Paria, 2015)]; (ii) non-core@shell segregated heteroclusters, in which the constituent sections are asymmetrically arranged in space through small heterojunctions, such that a substantial fraction of the surface of each material module remains accessible Buonsanti et al, 2007;Jun et al, 2007;Casavola et al, 2008;Peng et al, 2009;Carbone and Cozzoli, 2010;de Mello Donegà, 2011;Lattuada and Hatton, 2011;Buck and Schaak, 2013;Kaewsaneha et al, 2013;Sitt et al, 2013;Banin et al, 2014;Melinon et al, 2014;Pang et al, 2014;Yan et al, 2015b). The latter cluster-type heterostructures, which encompass two-component Janus-type HNCs Casavola et al, 2008;C...…”

“…Second, MHNCs represent appealing multifunctional nanoplatforms on which new processes and applications can be founded and governed. These encompass, for example, the feasibility to assemble nanoparticle-based "superstructures, " to carry out cooperative chemical conversions over magnetically recoverable catalytic grounds, to perform remote manipulations for assembly or delivery purposes, to install an anisotropic surface distribution of functional molecules, and to elaborate multimodal techniques for biomedical diagnostics and therapeutics Buonsanti et al, 2007;Jun et al, 2007;Casavola et al, 2008;Wang et al, 2009c;Carbone and Cozzoli, 2010;Feyen et al, 2010;Talapin et al, 2010;de Mello Donegà, 2011;Lattuada and Hatton, 2011;Liu et al, 2011;He et al, 2013;Kaewsaneha et al, 2013;Sitt et al, 2013;Banin et al, 2014;Melinon et al, 2014;Pang et al, 2014;Purbia and Paria, 2015;Qi et al, 2015;Yan et al, 2015b). Additionally, the direct electronic communication that is established in MHNCs across their interconnected material domains may underlie exchangecoupling interactions between non-homologous moieties, leading to modulated, synergistically reinforced, or even entirely unprecedented properties and functionalities, otherwise unreachable to their isolated material components and their physical-mixture counterparts.…”

“…Additionally, the direct electronic communication that is established in MHNCs across their interconnected material domains may underlie exchangecoupling interactions between non-homologous moieties, leading to modulated, synergistically reinforced, or even entirely unprecedented properties and functionalities, otherwise unreachable to their isolated material components and their physical-mixture counterparts. For example, MHNCs based on optically active semiconductors and/or noble metals supporting localized surface plasmon resonances (LSPRs) may exhibit anomalous absorption/emission and/or conductivity behavior due to modifications in electronic structure, degree of carrier confinement, recombination, separation and relocation dynamics of photostimulated charges carriers, and/or LSPR-to-exciton coupling (de Mello Donegà, 2011;He et al, 2013;Sitt et al, 2013;Banin et al, 2014;Melinon et al, 2014). In the case of MHNCs embodying magnetic phases and plasmonic metals, abnormally modified or mutually switchable magnetic, optical, and magneto-optical responses may reflect the synergistic interplay of magnetism, magneto-optical activity, and LSPR oscillations through various exchange-coupling mechanisms Jun et al, 2007;Casavola et al, 2008;Carbone and Cozzoli, 2010;Armelles et al, 2013;Pineider et al, 2013;López-Ortega et al, 2015).…”