A word cloud based on all my publication abstracts (January 2022)

Complex Nanoparticle Libraries

To make nanomaterials practically useful, it is usually necessary to integrate multiple elements and/or structures, making them “complex nanoparticles,” to enhance properties or achieve multi-functionality. Conventional approaches for studying multi-component nanoparticles require serial, batch-by-batch colloidal synthesis and characterization. However, such a slow process cannot address the need for combinatorial identification of new nanoparticle types with desired properties. In this regard, we have been developing library-synthesis and characterization methods to discover nanoparticles with na variety of composition, size, and crystal structures. Specifically, I used scanning probe lithography to deposit precursor-containing nanoreactors on substrates. The precursors crystallize within the nanoscale confinement to yield individual nanocrystals that are location encoded. This method creates a particle library that integrates complex nanoparticles with different compositions, sizes, and crystal structures on a chip, each individually addressable. Several new particle structures obtained from these massive particle libraries have shown promising optoelectronic, light-emission, catalysis, and plasmonic properties.

Representative publications:

  • “Halide Perovskite Nanocrystal Arrays: Multiplexed Synthesis and Size-dependent Emission.” Science Advances 2020, 6 (39), eabc4959. DOI:10.1126/sciadv.abc4959
  • “Interface and Heterostructure Design in Polyelemental Nanoparticles.” Science 2019, 363 (6430), 959–964. DOI:10.1126/science.aav4302
  • “The Structural Fate of Individual Multicomponent Metal-Oxide Nanoparticles in Polymer Nanoreactors.” Angewandte Chemie International Edition 2017, 56 (26), 7625–7629. DOI:10.1002/anie.201703296

Colloidal Crystals by Design

Colloidal crystals are a type of strategically important, emerging materials for advanced photonic devices. In particular, they can be used to fabricate optical/quantum computing chips and are also proven useful to make microwave/millimeter antennae for communication. Similar to how atoms make crystals in nature, colloidal crystals consist of nano- or micro-particles that organize periodically. We chose DNA as a versatile surface modifier for metal nanoparticles to induce crystallization. The length, strength, and interaction between these oligonucleotide strands can be programmed and customized. When two groups of nanoparticles (A and B) were coated with complementary DNA strands, these nanoparticles assemble into A-B “ionic” supra-crystals similar to salts in nature. This analogy has been well accepted for colloidal crystals and in general chemistry in the past decade. Our study discovered a group of “metallic” colloidal crystals. One type of DNA-functionalized Au nanoparticles forms a crystalline lattice, similar to the atom cores in a metal. Though they are repulsive to each other, the classical electron-equivalent particles carry complementary DNA strands and bind the crystal together due to the attractive DNA interaction. Higher-order colloidal systems, including colloidal “alloys” and covalent compound-like structures with complicated crystals tructures are further accessed. These discoveries significantly expanded the scope of materials that are possible with colloidal crystals.

Representative publications:

  • “The Emergence of Valency in Colloidal Crystals Through Electron Equivalents.” Nature Materials 2022, 21 (5), 580–587. DOI:10.1038/s41563-021-01170-5
  • “Colloidal Crystal ‘Alloys.’” Journal of the American Chemical Society 2019, 141 (51), 20443–20450. DOI:10.1021/jacs.9b11109
  • “Particle Analogs of Electrons in Colloidal Crystals.” Science 2019, 364 (6446), 1174–1178. DOI:10.1126/science.aaw8237

Nanoscale Particle Dynamics and Evolution

Nanoparticles are not static. Nanoparticles have shown great promise in catalysis, environmental protection, therapeutics, and diagnosis. In these applications, most scenarios require nanoparticles to be used in a highly corrosive environment (in electrolytes, biofluids, etc.). However, how nanoparticles transform and degrade in these environments has been historically overlooked, and the loss of stability and functionality is one of the main barriers to their practical, commercial use. We developed new technologies to monitor how multicomponent nanoparticles, as small as a few nanometers, dynamically interact and transform in environments. In particular, real-time monitoring of particle dynamics with a spatial resolution down to the sub-nanometer resolution was achieved. These studies revealed important mechanistic pathways during particle formation, transformation, and degradation.

Representative publications:

  • “Galvanic Transformation Dynamics in Heterostructured Nanoparticles.” Advanced Functional Materials 2021, 31 (46), 2105866. DOI:10.1002/adfm.202105866
  • “Twin Pathways: Discerning the Origins of Multiply Twinned Colloidal Nanoparticles.” Angewandte Chemie International Edition 2021, 60 (13), 6858−6863. DOI:10.1002/anie.202015166
  • “Windowless Observation of Evaporation-Induced Coarsening of Au-Pt Nanoparticles in Polymer Nanoreactors.” Journal of the American Chemical Society 2018, 140 (23), 7213–7221. DOI:10.1021/jacs.8b03105
  • “Multi-Stage Transformation and Lattice Fluctuation at AgCl-Ag Interface.” The Journal of Physical Chemistry Letters 2017, 8 (23), 5853–5860. DOI:10.1021/acs.jpclett.7b02875
  • “The Structural Evolution of Three-component Nanoparticles in Polymer Nanoreactors” Journal of the American Chemical Society 2017, 139 (29), 9876–9884. DOI:10.1021/jacs.7b03163

Wet Chemical Synthesis of Functional Nanomaterials with Complex Geometries

Noble metals, transition metal oxides, and their hybrids are promising catalysts and sensor materials. In these applications, complex geometries are often required to provide specific dielectric environments or surface chemistry. However, large-scale synthesis of such nanostructures through wet chemical approaches is typically challenging and requires delicate design and control over the synthetic system. In these studies, we design new nanostructures and geometries that tackle s a specific need, for example, high-temperature catalysis or multifunctional sensing, and implement them by controlling the thermodynamics and kinetics in crystal growth or deploy new nanomodification techniques.

Representative publications:

  • “Bidirectional Nanomodification Enables Hierarchically Structured Mixed Oxide Electrodes for Oxygen Evolution.” Small 2021, 17 (17), 2007287. DOI:10.1002/smll.202007287
  • “Embedding Ultrafine Pt Nanoparticles at Ceria Surface for Enhanced Thermal Stability.” Advanced Science 2017, 4 (9), 1700056. DOI:10.1002/advs.201700056
  • “Intermetallic Nanocrystals: Syntheses and Catalytic Applications.” Advanced Materials 2017, 29 (14), 1605997. DOI:10.1002/adma.201605997
  • “Developing an Aqueous Approach for Synthesizing Au and [email protected] (M = Pd, CuPt) Hybrid Nanostars with Plasmonic Properties.” Physical Chemistry Chemical Physics 2015, 17 (2), 1265–1272. DOI:10.1039/C4CP04757E