Self-Assembly of Quantum Dot-Gold Heterodimer Nanocrystals with Orientational Order

Type-I CdS/ZnS Core/Shell Quantum Dot-Gold Heterostructural Nanocrystals for Enhanced Photocatalytic Hydrogen Generation

Developing Type-I core/shell quantum dots is of great importance toward fabricating stable and sustainable photocatalysts. However, the application of Type-I systems has been limited due to the strongly confined photogenerated charges by the energy barrier originating from the wide-bandgap shell material. In this project, we found that through the decoration of Au satellite-type domains on the surface of Type-I CdS/ZnS core/shell quantum dots, such an energy barrier can be effectively overcome and an over 400-fold enhancement of photocatalytic H2 evolution rate was achieved compared to bare CdS/ZnS quantum dots. Transient absorption spectroscopic studies indicated that the charges can be effectively extracted and subsequently transferred to surrounding molecular substrates in a subpicosecond time scale in such hybrid nanocrystals. Based on density functional theory calculations, the ultrafast charge separation rates were ascribed to the formation of intermediate Au2S layer at the semiconductor-metal interface, which can successfully offset the energy confinement introduced by the ZnS shell. Our findings not only provide insightful understandings on charge carrier dynamics in semiconductor-metal heterostructural materials but also pave the way for the future design of quantum dot-based hybrid photocatalytic systems.

Chemical and Physical Properties of Photonic Noble-Metal Nanomaterials

Colloidal noble metal nanoparticles (NPs) are composed of metal cores and organic or inorganic ligand shells. These NPs support size- and shape-dependent plasmonic resonances. They can be assembled from dispersions into artificial metamolecules which have collective plasmonic resonances originating from coupled bright and dark optical electric and magnetic modes that form depending on the size and shape of the constituent NPs and their number, arrangement, and interparticle distance. NPs can also be assembled into extended 2D and 3D metamaterials that are glassy thin films or ordered thin films or crystals, also known as superlattices and supercrystals. The metamaterials have tunable optical properties that depend on the size, shape, and composition of the NPs, and on the number of NP layers and their interparticle distance. Interestingly, strong light-matter interactions in superlattices form plasmon polaritons. Tunable interparticle distances allow designer materials with dielectric functions tailorable from that characteristic of an insulator to that of a metal, and serve as strong optical absorbers or scatterers, respectively. In combination with lithography techniques, these extended assemblies can be patterned to create subwavelength NP superstructures and form large-area 2D and 3D metamaterials that manipulate the amplitude, phase, and polarization of transmitted or reflected light.

Self-Assembly of Atomically Aligned Nanoparticle Superlattices from Pt-Fe3O4 Heterodimer Nanoparticles

Multicomponent nanoparticle superlattices (SLs) promise the integration of nanoparticles (NPs) with remarkable electronic, magnetic, and optical properties into a single structure. Here, we demonstrate that heterodimers consisting of two conjoined NPs can self-assemble into novel multicomponent SLs with a high degree of alignment between the atomic lattices of individual NPs, which has been theorized to lead to a wide variety of remarkable properties. Specifically, by using simulations and experiments, we show that heterodimers composed of larger Fe₃O₄ domains decorated with a Pt domain at one vertex can self-assemble into an SL with long-range atomic alignment between the Fe₃O₄ domains of different NPs across the SL. The SLs show an unanticipated decreased coercivity relative to nonassembled NPs. In situ scattering of the self-assembly reveals a two-stage mechanism of self-assembly: translational ordering between NPs develops before atomic alignment. Our experiments and simulation indicate that atomic alignment requires selective epitaxial growth of the smaller domain during heterodimer synthesis and specific size ratios of the heterodimer domains as opposed to specific chemical composition. This composition independence makes the self-assembly principles elucidated here applicable to the future preparation of multicomponent materials with fine structural control.

Dual Atomic Coherence in the Self-Assembly of Patchy Heterostructural Nanocrystals

Advances in the synthesis and self-assembly of nanocrystals have enabled researchers to create a plethora of different nanoparticle superlattices. But while many superlattices with complex types of translational order have been realized, rotational order of nanoparticle building blocks within the lattice is more difficult to achieve. Self-assembled superstructures with atomically coherent nanocrystal lattices, which are desirable due to their exceptional electronic and optical properties, have been fabricated only for a few selected systems. Here, we combine experiments with molecular dynamics (MD) simulations to study the self-assembly of heterostructural nanocrystals (HNCs), consisting of a near-spherical quantum dot (QD) host decorated with a small number of epitaxially grown gold nanocrystal (Au NC) "patches". Self-assembly of these HNCs results in face-centered-cubic (fcc) superlattices with well-defined orientational relationships between the atomic lattices of both QD hosts and Au patches. MD simulations indicate that the observed dual atomic coherence is linked to the number, size, and relative positions of gold patches. This study provides a strategy for the design and fabrication of NC superlattices with large structural complexity and delicate orientational order.

Synthesis of Patchy Nanoparticles with Symmetry Resembling Polar Small Molecules

Patchy nanoparticles (NPs) show many important applications, especially for constructing structurally complex colloidal materials, but existing synthetic strategies generate patchy NPs with limited types of symmetry. This article describes a versatile copolymer ligand-based strategy for the scalable synthesis of uniform Au-(SiO₂ )_x patchy NPs (x is the patch number and 1 ≤ x ≤ 5) with unusual symmetry at high yield. The hydrolysis and condensation of tetraethyl orthosilicate on block-random copolymer ligands induces the segregation of copolymers on gold NPs (AuNPs) and hence governs the structure and distribution of silica patches formed on the AuNPs. The resulting patchy NPs possess unique configurations where the silica patches are symmetrically arranged at one side of the core NP, resembling the geometry of polar small molecules. The number, size, and morphology of silica patches, as well as the spacing between the patches and the AuNP can be precisely tuned by tailoring copolymer architectures, grafting density of copolymers, and the size of AuNPs. Furthermore, it is demonstrated that the Au-(SiO₂ )_x patchy NPs can assemble into more complex superstructures through directional interaction between the exposed Au surfaces. This work offers new opportunities of designing next-generation complex patchy NPs for applications in such as biomedicines, self-assembly, and catalysis.

Crystallographically Textured Electrodes for Rechargeable Batteries: Symmetry, Fabrication, and Characterization

The vast of majority of battery electrode materials of contemporary interest are of a crystalline nature. Crystals are, by definition, anisotropic from an atomic-structure perspective. The inherent structural anisotropy may give rise to favored mesoscale orientations and anisotropic properties whether the material is in a rest state or subjected to an external stimulus. The overall perspective of this review is that intentional manipulation of crystallographic anisotropy of electrochemically active materials constitute an untapped parameter space in energy storage systems and thus provide new opportunities for materials innovations and design. To that end, we contend that crystallographically textured electrodes, as opposed to their textureless poly crystalline or single-crystalline analogs, are promising candidates for next-generation storage of electrical energy in rechargeable batteries relevant to commercial practice. This perspective is underpinned first by the fundamental─to a first approximation─uniaxial, rotation-invariant symmetry of electrochemical cells. On this basis, we show that a crystallographically textured electrode with the preferred orientation aligned out-of-plane toward the counter electrode represents an optimal strategy for utilization of the crystals' anisotropic properties. Detailed analyses of anisotropy of different types lead to a simple, but potentially useful general principle that "P_ec//P_c" textures are optimal for metal anodes, and "P_ec//S_c" textures are optimal for insertion-type electrodes.

Diversified applications of self-assembled nanocluster delivery systems- A state-of-the- art review

BACKGROUND

Self-assembled nanoclusters arrange the components into an organized structure for the nanoparticulate system and also in the transportation of cellular elements for the fabrication of microelectronic devices. Nanoclusters reduce transcytosis and increase endocytosis in intestinal mucin to strengthen the retrograde pathway that helped in the delivery of actives to the Golgi apparatus.

OBJECTIVES

This review article focuses on the self-assembled nanoclusters for cellular transportation, applications of self-assembled structures in the delivery of essential elements like the use of a peptide in targeted and stimuli-responsive drug delivery systems, self-assembly of tocopherol nanoclusters that promotes vitamin E delivery across the endothelial barrier. Methods Current innovation in the self-assembly of peptides includes the formation of nanostructures like vesicles, fibers, and rod-coil in the applications of wound healing, tissue engineering, treatment of atherosclerosis, in sensing heavy metals from biological and environmental samples and advanced drug delivery.

RESULTS

Self-assembled biodegradable nanoclusters are used as biomimetic structures for synergistic effect. Improvement in the methods of preparation like the addition of a copolymer is used for temperature-triggered drug release nanoclusters.

CONCLUSION

Green synthesis of nanoclusters, nanocluster-based biosensor and artificial intelligence are the future concept in the manufacturing and the prevention of toxicity in humans.

Double-helical assembly of heterodimeric nanoclusters into supercrystals

DNA has long been used as a template for the construction of helical assemblies of inorganic nanoparticles^1-5. For example, gold nanoparticles decorated with DNA (or with peptides) can create helical assemblies^6-9. But without such biological ligands, helices are difficult to achieve and their mechanism of formation is challenging to understand^10,11. Atomically precise nanoclusters that are protected by ligands such as thiolate^12,13 have demonstrated hierarchical structural complexity in their assembly at the interparticle and intraparticle levels, similar to biomolecules and their assemblies¹⁴. Furthermore, carrier dynamics can be controlled by engineering the structure of the nanoclusters¹⁵. But these nanoclusters usually have isotropic structures^16,17 and often assemble into commonly found supercrystals¹⁸. Here we report the synthesis of homodimeric and heterodimeric gold nanoclusters and their self-assembly into superstructures. While the homodimeric nanoclusters form layer-by-layer superstructures, the heterodimeric nanoclusters self-assemble into double- and quadruple-helical superstructures. These complex arrangements are the result of two different motif pairs, one pair per monomer, where each motif bonds with its paired motif on a neighbouring heterodimer. This motif pairing is reminiscent of the paired interactions of nucleobases in DNA helices. Meanwhile, the surrounding ligands on the clusters show doubly or triply paired steric interactions. The helical assembly is driven by van der Waals interactions through particle rotation and conformational matching. Furthermore, the heterodimeric clusters have a carrier lifetime that is roughly 65 times longer than that of the homodimeric clusters. Our findings suggest new approaches for increasing complexity in the structural design and engineering of precision in supercrystals.

Recent Advances in Ligand Design and Engineering in Lead Halide Perovskite Nanocrystals

Lead halide perovskite (LHP) nanocrystals (NCs) have recently garnered enhanced development efforts from research disciplines owing to their superior optical and optoelectronic properties. These materials, however, are unlike conventional quantum dots, because they possess strong ionic character, labile ligand coverage, and overall stability issues. As a result, the system as a whole is highly dynamic and can be affected by slight changes of particle surface environment. Specifically, the surface ligand shell of LHP NCs has proven to play imperative roles throughout the lifetime of a LHP NC. Recent advances in engineering and understanding the roles of surface ligand shells from initial synthesis, through postsynthetic processing and device integration, finally to application performances of colloidal LHP NCs are covered here.

Unconventional-Phase Crystalline Materials Constructed from Multiscale Building Blocks

Crystal phase, an intrinsic characteristic of crystalline materials, is one of the key parameters to determine their physicochemical properties. Recently, great progress has been made in the synthesis of nanomaterials with unconventional phases that are different from their thermodynamically stable bulk counterparts via various synthetic methods. A nanocrystalline material can also be viewed as an assembly of atoms with long-range order. When larger entities, such as nanoclusters, nanoparticles, and microparticles, are used as building blocks, supercrystalline materials with rich phases are obtained, some of which even have no analogues in the atomic and molecular crystals. The unconventional phases of nanocrystalline and supercrystalline materials endow them with distinctive properties as compared to their conventional counterparts. This Review highlights the state-of-the-art progress of nanocrystalline and supercrystalline materials with unconventional phases constructed from multiscale building blocks, including atoms, nanoclusters, spherical and anisotropic nanoparticles, and microparticles. Emerging strategies for engineering their crystal phases are introduced, with highlights on the governing parameters that are essential for the formation of unconventional phases. Phase-dependent properties and applications of nanocrystalline and supercrystalline materials are summarized. Finally, major challenges and opportunities in future research directions are proposed.

Self-assembly of anisotropic nanoparticles into functional superstructures

Self-assembly of colloidal nanoparticles (NPs) into superstructures offers a flexible and promising pathway to manipulate the nanometer-sized particles and thus make full use of their unique properties. This bottom-up strategy builds a bridge between the NP regime and a new class of transformative materials across multiple length scales for technological applications. In this field, anisotropic NPs with size- and shape-dependent physical properties as self-assembly building blocks have long fascinated scientists. Self-assembly of anisotropic NPs not only opens up exciting opportunities to engineer a variety of intriguing and complex superlattice architectures, but also provides access to discover emergent collective properties that stem from their ordered arrangement. Thus, this has stimulated enormous research interests in both fundamental science and technological applications. This present review comprehensively summarizes the latest advances in this area, and highlights their rich packing behaviors from the viewpoint of NP shape. We provide the basics of the experimental techniques to produce NP superstructures and structural characterization tools, and detail the delicate assembled structures. Then the current understanding of the assembly dynamics is discussed with the assistance of in situ studies, followed by emergent collective properties from these NP assemblies. Finally, we end this article with the remaining challenges and outlook, hoping to encourage further research in this field.

Shape-directed self-assembly of nanodumbbells into superstructure polymorphs

Self-assembly of colloidal nanoparticles into ordered superstructures provides a promising route to create novel/enhanced functional materials. Much progress has been made in self-assembly of anisotropic nanoparticles, but the complexity and tunability of superstructures remain restricted by their available geometries. Here we report the controlled packing of nanodumbbells (NDs) with two spherical lobes connected by one rod-like middle bar into varied superstructure polymorphs. When assembled into two-dimensional (2D) monolayer assemblies, such NDs with specific shape parameters could form orientationally ordered degenerate crystals with a 6-fold symmetry, in which these NDs possess no translational order but three allowed orientations with a rotational symmetry of 120 degrees. Detailed analyses identify the distinct roles of subunits in the ND assembly: the spherical lobes direct NDs to closely assemble together into a hexagonal pattern, and the rod-like connection between the lobes endows NDs with this specific orientational order. Such intralayer assembly features are well maintained in the two-layer superstructures of NDs; however, the interlayer stackings could be adjusted to produce stable bilayer superstructures and a series of metastable moiré patterns. Moreover, in addition to horizontal alignment, these NDs could gradually stand up to form tilted or even vertical packing based on the delicate control over the liquid-liquid interface and ND dimensions. This study provides novel insights into creating superstructures by controlling geometric features of nanoscale building blocks and may spur their novel applications.

Multicomponent Plasmonic Nanoparticles: From Heterostructured Nanoparticles to Colloidal Composite Nanostructures

Plasmonic nanostructures possessing unique and versatile optoelectronic properties have been vastly investigated over the past decade. However, the full potential of plasmonic nanostructure has not yet been fully exploited, particularly with single-component homogeneous structures with monotonic properties, and the addition of new components for making multicomponent nanoparticles may lead to new-yet-unexpected or improved properties. Here we define the term "multi-component nanoparticles" as hybrid structures composed of two or more condensed nanoscale domains with distinctive material compositions, shapes, or sizes. We reviewed and discussed the designing principles and synthetic strategies to efficiently combine multiple components to form hybrid nanoparticles with a new or improved plasmonic functionality. In particular, it has been quite challenging to precisely synthesize widely diverse multicomponent plasmonic structures, limiting realization of the full potential of plasmonic heterostructures. To address this challenge, several synthetic approaches have been reported to form a variety of different multicomponent plasmonic nanoparticles, mainly based on heterogeneous nucleation, atomic replacements, adsorption on supports, and biomolecule-mediated assemblies. In addition, the unique and synergistic features of multicomponent plasmonic nanoparticles, such as combination of pristine material properties, finely tuned plasmon resonance and coupling, enhanced light-matter interactions, geometry-induced polarization, and plasmon-induced energy and charge transfer across the heterointerface, were reported. In this review, we comprehensively summarize the latest advances on state-of-art synthetic strategies, unique properties, and promising applications of multicomponent plasmonic nanoparticles. These plasmonic nanoparticles including heterostructured nanoparticles and composite nanostructures are prepared by direct synthesis and physical force- or biomolecule-mediated assembly, which hold tremendous potential for plasmon-mediated energy transfer, magnetic plasmonics, metamolecules, and nanobiotechnology.

2D Freestanding Janus Gold Nanocrystal Superlattices

2D freestanding nanocrystal superlattices represent a new class of advanced metamaterials in that they can integrate mechanical flexibility with novel optical, electrical, plasmonic, and magnetic properties into one multifunctional system. The freestanding 2D superlattices reported to date are typically constructed from symmetrical constituent building blocks, which have identical structural and functional properties on both sides. Here, a general ligand symmetry-breaking strategy is reported to grow 2D Janus gold nanocrystal superlattice sheets with nanocube morphology on one side yet with nanostar on the opposite side. Such asymmetric metallic structures lead to distinct wetting and optical properties as well as surface-enhanced Raman scattering (SERS) effects. In particular, the SERS enhancement of the nanocube side is about 20-fold of that of the nanostar side, likely due to the combined "hot spot + lightening-rod" effects. This is nearly 700-fold of SERS enhancement as compared with the symmetric nanocube superlattices without Janus structures.

Controlling Nanoparticle Orientations in the Self-Assembly of Patchy Quantum Dot-Gold Heterostructural Nanocrystals

Self-assembly of nanocrystals is a promising route for creating macroscale materials that derive function from the properties of their nanoscale building blocks. While much progress has been made assembling nanocrystals into different superlattices, controlling the relative orientations of nanocrystals in those lattices remains a challenge. Here, we combine experiments with computer simulations to study the self-assembly of patchy heterostructural nanocrystals (HNCs), consisting of near-spherical quantum dots decorated with regular arrangements of small gold satellites, into close-packed superlattices with pronounced orientational alignment of HNCs. Our simulations indicate that the orientational alignment is caused by van der Waals interactions between gold patches and is sensitive to the interparticle distance in the superlattice. We demonstrate experimentally that the degree and type of orientational alignment can be controlled by changing ligand populations on HNCs. This study provides guidance for the design and fabrication of nanocrystal superlattices with enhanced structural control.