Browsing by Author "Cheng, Zhihua"

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    Assembly of planar chiral superlattices from achiral building blocks
    (Springer Nature, 2022) Cheng, Zhihua; Jones, Matthew R.
    The spontaneous assembly of chiral structures from building blocks that lack chirality is fundamentally important for colloidal chemistry and has implications for the formation of advanced optical materials. Here, we find that purified achiral gold tetrahedron-shaped nanoparticles assemble into two-dimensional superlattices that exhibit planar chirality under a balance of repulsive electrostatic and attractive van der Waals and depletion forces. A model accounting for these interactions shows that the growth of planar structures is kinetically preferred over similar three-dimensional products, explaining their selective formation. Exploration and mapping of different packing symmetries demonstrates that the hexagonal chiral phase forms exclusively because of geometric constraints imposed by the presence of constituent tetrahedra with sharp tips. A formation mechanism is proposed in which the chiral phase nucleates from within a related 2D achiral phase by clockwise or counterclockwise rotation of tetrahedra about their central axis. These results lay the scientific foundation for the high-throughput assembly of planar chiral metamaterials.
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    Assembly of planar chiral superlattices from achiral building blocks
    (2024-08-27) Jones, Matthew R.; Cheng, Zhihua; Xing, Yuchen; Rice University; United States Patent and Trademark Office
    The spontaneous assembly of chiral structures from building blocks that lack chirality is fundamentally important for colloidal chemistry and has implications for the formation of advanced optical materials. Here, we find that purified achiral gold tetrahedron-shaped nanoparticles assemble into two-dimensional superlattices that exhibit planar chirality under a balance of repulsive electrostatic and attractive van der Waals and depletion forces. A model accounting for these interactions shows that the growth of planar structures is kinetically preferred over similar three-dimensional products, explaining their selective formation.
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    Preserving surface strain in nanocatalysts via morphology control
    (AAAS, 2024) Shi, Chuqiao; Cheng, Zhihua; Leonardi, Alberto; Yang, Yao; Engel, Michael; Jones, Matthew R.; Han, Yimo
    Engineering strain critically affects the properties of materials and has extensive applications in semiconductors and quantum systems. However, the deployment of strain-engineered nanocatalysts faces challenges, in particular in maintaining highly strained nanocrystals under reaction conditions. Here, we introduce a morphology-dependent effect that stabilizes surface strain even under harsh reaction conditions. Using four-dimensional scanning transmission electron microscopy (4D-STEM), we found that cube-shaped core-shell Au@Pd nanoparticles with sharp-edged morphologies sustain coherent heteroepitaxial interfaces with larger critical thicknesses than morphologies with rounded edges. This configuration inhibits dislocation nucleation due to reduced shear stress at corners, as indicated by molecular dynamics simulations. A Suzuki-type cross-coupling reaction shows that our approach achieves a fourfold increase in activity over conventional nanocatalysts, owing to the enhanced stability of surface strain. These findings contribute to advancing the development of advanced nanocatalysts and indicate broader applications for strain engineering in various fields.
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    Symmetry Reduction in the Self-Assembly of Anisotropic Nanoparticles
    (2022-12-01) Cheng, Zhihua; Jones, Matthew R.
    Self-assembly, as a spontaneously process to organize building blocks, has been heralded as a tunable, low-cost, scalable method to generate advanced optical materials for energetic, optical, and biological applications. A major challenge in this field has been the development of synthetic strategies that allow for the assembly of low-symmetry configurations of particles, as these have generally been the structures predicted to have the most appealing optical properties. Although there are many efforts have been made in the self-assembly, however, due to the vast majority of colloidal particle building blocks are highly symmetric and they tent to spontaneously form high symmetric superstructures, which show weakly shape and packing symmetry dependent properties and thus becoming unsuitable for optical metamaterial applications. To this end, the use of low symmetric anisotropic building blocks then is believed to be a possible route to the formation of low symmetric superlattices because these building blocks can give rise to more complex, directional interactions and restrained attachments and orientations between them. This intrinsic advantage of anisotropic building blocks makes them become the most promising candidates and thus receiving intensive attentions in the previous simulations and experiments as discussed in Chapter 1. According to those studies, the achievement of the low symmetric configuration with anisotropic building blocks requires the design and balances of the shape anisotropy, surface chemistry, particle interaction and self-assembly conditions, which are all in this infant. Therefore, although many efforts have been made, however, the achievement of the low symmetric structures is only limited to few cases due to the limited anisotropic building blocks and the poor understanding of symmetry reduction in the self-assembly system. To this end, a more general study about controlling the symmetry reduction behaviors during the self-assembly of anisotropic building blocks is necessary for the achievement of low symmetric superstructures. To address these problems, I have been devoting myself to the manipulation of self-assembly process to break the symmetry of the superstructures by using low symmetric anisotropic building blocks. To better control the self-assembly process, the prerequisite is to have high quality and uniform anisotropic building blocks, which is challenging because most syntheses for such particles, particularly those composed of Au or Ag, are “seeded” with spherical particles possessing a range of internal defect structures and proceed through poorly understood reaction pathways. Therefore, a better control over the quality of seeds is necessary. In Chapter 2, we developed an Ag overgrowth method to exaggerate the differences among the different types of seeds and then achieved the separation of single-crystalline and penta-twinned seeds with high purity and uniformity. With these purified seeds, a library of anisotropic nanoparticles has been obtained, in which some of the particles were first time to achieve with new growth pathways. This method set the basis for the future works that demand for highly uniform and pure anisotropic building blocks to better control the symmetry breaking behaviors. With the similar methods, in Chapter 3, low symmetric tetrahedral shaped Au nanoparticles were also obtained with high quality. And more importantly, with these large Au tetrahedral nanoparticles, a spontaneous formation of symmetry broken planar chiral superlattices with only one-unit-cell thickness was achieved with the presence of substrate, which is regarded as a strong candidate for the emergent metamaterials with negative refractive index. And by comparing the growth kinetics, we realized that the kinetically driven side attachment is the key pathway for the formation of the 2D lattices and thus a domain size of more than 1 µm was achieved. In addition to that, with our calculation of interparticle potential, we realized the balances of attractive and repulsive interactions is the driven force to achieve the spontaneous rotational symmetry breaking. And by further extending these understanding of rotation phase transition, in Chapter 4, we tailored a more complex 3D rotation phase transition process through manipulating the flexibility of the interparticle interaction during the self-assembly of tetrahedra in solution, which further broke the symmetry of the system to get 3D chiral base centered monoclinic superlattices. Moreover, because of the shear strain during the phase transition, screw dislocations on the superlattices were also formed and eventually drove the formation of dual spiral superstructures as a higher level of symmetry breaking event. Apart from that, we were able to tune the interparticle interactions to be more rigid by using short surfactant and micelle during the self-assembly, and with this type of interaction, an ordered but aperiodic dodecagonal quasicrystal can be also obtained. The dodecagonal quasicrystal has lowest symmetry among all tetrahedra superstructures, and which relied on the formation of localized tetrahedra clusters and ongoing hierarchical cluster packing behaviors. These works demonstrate the usage of low symmetric tetrahedral building blocks in the formation of low symmetric superstructures and the importance of tailoring interparticle interactions. To apply our understanding of rotation phase transition, in Chapter 4, we pushed our limits to test the possibility of symmetry breaking behaviors in high symmetry self-assembly systems—the space filled tetrahedral and octahedral honeycomb. Our calculations based on interparticle potential shows that the symmetry of the honeycomb superlattices can be reduced if a specific range of mismatch in both size ratio and number ratio present in the self-assembly system. By controlling the size and the molar ratios of the building blocks, we got at least 9 different superlattices with unique packing behaviors including 2D and 3D chiral superlattices as well as a well-defined heterostructures. By extending our understanding of tetrahedral and octahedral co-crystallization, a phase diagram for the controlling the formation of co-assembled superstructures was obtained as a guideline for the future exploration and applications.