skip to main content

Attention:

The NSF Public Access Repository (PAR) system and access will be unavailable from 11:00 PM ET on Friday, December 13 until 2:00 AM ET on Saturday, December 14 due to maintenance. We apologize for the inconvenience.


Title: Colloidal Metal Nanocrystals with Metastable Crystal Structures
Abstract

In addition to the conventional knobs such as composition, size, shape, and defect structure, the crystal structure (or phase) of metal nanocrystals offers a new avenue for engineering their properties. Various strategies have recently been developed for the fabrication of colloidal metal nanocrystals in metastable phases different from their bulk counterparts. With a focus on noble metals, we begin with a brief introduction to their atomic packing, followed by a discussion about five major synthetic approaches to their colloidal nanocrystals in unconventional phases. We then highlight the success of synthesis in terms of mechanistic insights and experimental controls, as well as the enhanced catalytic properties. We end this Minireview with perspectives on the remaining issues and future opportunities.

 
more » « less
Award ID(s):
1804970
PAR ID:
10229571
Author(s) / Creator(s):
 ;  ;  
Publisher / Repository:
Wiley Blackwell (John Wiley & Sons)
Date Published:
Journal Name:
Angewandte Chemie International Edition
Volume:
60
Issue:
22
ISSN:
1433-7851
Page Range / eLocation ID:
p. 12192-12203
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. Abstract

    In addition to the conventional knobs such as composition, size, shape, and defect structure, the crystal structure (or phase) of metal nanocrystals offers a new avenue for engineering their properties. Various strategies have recently been developed for the fabrication of colloidal metal nanocrystals in metastable phases different from their bulk counterparts. With a focus on noble metals, we begin with a brief introduction to their atomic packing, followed by a discussion about five major synthetic approaches to their colloidal nanocrystals in unconventional phases. We then highlight the success of synthesis in terms of mechanistic insights and experimental controls, as well as the enhanced catalytic properties. We end this Minireview with perspectives on the remaining issues and future opportunities.

     
    more » « less
  2. null (Ed.)
    The past decade has witnessed tremendous advances in synthesis of metal halide perovskites and their use for a rich variety of optoelectronics applications. Metal halide perovskite has the general formula ABX 3 , where A is a monovalent cation (which can be either organic ( e.g. , CH 3 NH 3 + (MA), CH(NH 2 ) 2 + (FA)) or inorganic ( e.g. , Cs + )), B is a divalent metal cation (usually Pb 2+ ), and X is a halogen anion (Cl − , Br − , I − ). Particularly, the photoluminescence (PL) properties of metal halide perovskites have garnered much attention due to the recent rapid development of perovskite nanocrystals. The introduction of capping ligands enables the synthesis of colloidal perovskite nanocrystals which offer new insight into dimension-dependent physical properties compared to their bulk counterparts. It is notable that doping and ion substitution represent effective strategies for tailoring the optoelectronic properties ( e.g. , absorption band gap, PL emission, and quantum yield (QY)) and stabilities of perovskite nanocrystals. The doping and ion substitution processes can be performed during or after the synthesis of colloidal nanocrystals by incorporating new A′, B′, or X′ site ions into the A, B, or X sites of ABX 3 perovskites. Interestingly, both isovalent and heterovalent doping and ion substitution can be conducted on colloidal perovskite nanocrystals. In this review, the general background of perovskite nanocrystals synthesis is first introduced. The effects of A-site, B-site, and X-site ionic doping and substitution on the optoelectronic properties and stabilities of colloidal metal halide perovskite nanocrystals are then detailed. Finally, possible applications and future research directions of doped and ion-substituted colloidal perovskite nanocrystals are also discussed. 
    more » « less
  3. Abstract

    Ternary metal‐chalcogenide semiconductor nanocrystals are an attractive class of materials due to their tunable optoelectronic properties that result from a wide range of compositional flexibility and structural diversity. Here, the phase‐controlled synthesis of colloidal silver iron sulfide (AgFeS2) nanocrystals is reported and their resonant light–matter interactions are investigated. The product composition can be shifted selectively from tetragonal to orthorhombic by simply adjusting the coordinating ligand concentration, while keeping the other reaction parameters unchanged. The results show that excess ligands impact precursor reactivity, and consequently the nanocrystal growth rate, thus deterministically dictating the resulting crystal structure. Moreover, it is demonstrated that the strong ultraviolet‐visible extinction peak exhibited by AgFeS2nanocrystals is a consequence of a quasi‐static dielectric resonance (DR), analogous to the optical response observed in CuFeS2nanocrystals. Spectroscopic studies and computational calculations confirm that a negative permittivity at ultraviolet/visible frequencies arises due to the electronic structure of these intermediate‐band (IB) semiconductor nanocrystals, resulting in a DR consisting of resonant valence‐band‐to‐intermediate‐band excitations, as opposed to the well‐known localized surface plasmon resonance response typically observed in metallic nanostructures. Overall, these results expand the current library of an underexplored class of IB semiconductors with unique optical properties, and also enrich the understanding of DRs in ternary metal‐iron‐sulfide nanomaterials.

     
    more » « less
  4. Abstract

    Decahedral nanocrystals have received great attention owing to their unique symmetry and strain‐energy distribution. In contrast to other noble metals, it has been difficult to synthesize decahedral Rh nanocrystals. We report a robust, one‐pot method based on polyol reduction for the facile synthesis of Rh decahedral nanocrystals in high purity, with sub‐20 nm sizes. The success of the synthesis relied on our ability to manipulate reduction kinetics by systematically tuning experimental parameters. We found that the yield of Rh decahedral nanocrystals could be maximized by optimizing:i) the concentration of Rh(acac)3(metal precursor);ii) the molecular weight and amount of poly(vinyl pyrrolidone) (colloidal stabilizer/capping agent); andiii) the chain length of the polyol (solvent/reducing agent), with tetraethylene glycol being the best. We believe the mechanisms elucidated herein can be extended to other syntheses to produce metal nanocrystals with multiply twinned structures.

     
    more » « less
  5. Abstract

    Surface capping agents have been extensively used to control the evolution of seeds into nanocrystals with diverse but well‐controlled shapes. Here we offer a comprehensive review of these agents, with a focus on the mechanistic understanding of their roles in guiding the shape evolution of metal nanocrystals. We begin with a brief introduction to the early history of capping agents in electroplating and bulk crystal growth, followed by discussion of how they affect the thermodynamics and kinetics involved in a synthesis of metal nanocrystals. We then present representative examples to highlight the various capping agents, including their binding selectivity, molecular‐level interaction with a metal surface, and impacts on the growth of metal nanocrystals. We also showcase progress in leveraging capping agents to generate nanocrystals with complex structures and/or enhance their catalytic properties. Finally, we discuss various strategies for the exchange or removal of capping agents, together with perspectives on future directions.

     
    more » « less