Abstract word cloud
A word cloud based on publication abstracts (February 2024).

Molecular-Scale Structure and Dynamics of Weakly Bonded Crystals

Weakly-bonded crystals, such as ice, are ubiquitous in nature and have important applications in various fields, including atmospheric science, biophysics, and nanotechnology. However, the structure and dynamics of these crystals are often complex and challenging to characterize, especially under extreme conditions of temperature and pressure. In my research, I develop novel correlative cryogenic/in-situ microscopy and combine in silico simulations with theories to investigate the molecular-scale structures of weakly bonded crystals and their interfaces with other materials. Importantly, I aim to reveal the mechanisms of ice nucleation, phase transformation, and defect formation, as well as the interactions of ice with minerals and biomolecules. My work provides new insights into the fundamental physics and chemistry of weakly bonded crystals and their potential applications.

Representative publications:

Complex Nanoparticle Libraries

Nanomaterials often need to combine different elements and structures to achieve better performance or multiple functions, leading to “complex nanoparticles.” 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. To solve this problem, we have developed new methods to create and characterize large collections of nanoparticles with a variety of compositions, sizes, and crystal structures. I used scanning probe lithography to deposit tiny droplets of precursor materials on a surface. These droplets act as nanoscale reactors that produce individual nanocrystals with specific locations. This technique allows us to create a library of complex nanoparticles with various compositions, sizes, and crystal structures on a single chip. Each nanoparticle can be easily identified and accessed. We have discovered several new nanoparticle structures from these libraries that have promising applications in optoelectronics, light-emission, catalysis, and plasmonics.

Representative publications:

  • Discovering Polyelemental Nanostructures with Redistributed Plasmonic Modes Through Combinatorial Synthesis.
    Science Advances 2023, 9 (51), eadj6129. DOI:10.1126/sciadv.adj6129
  • Intermetallic Nanocrystal Discovery Through Modulation of Atom Stacking Hierarchy.
    ACS Nano 2022, 16 (12), 20796–20804. DOI:10.1021/acsnano.2c08038
  • 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 materials made of tiny particles that arrange in regular patterns. They have potential applications in advanced photonic devices, such as optical/quantum computing chips and microwave/millimeter antennae. We use DNA to modify the surface of metal nanoparticles and make them form colloidal crystals. DNA is a flexible and programmable molecule that can bind different nanoparticles together. For example, we can make “ionic” colloidal crystals that resemble natural salts by coating two types of nanoparticles with matching DNA strands. This idea has been widely accepted in the field of colloidal crystals and chemistry. We also discovered a new type of “metallic” colloidal crystals that are made of atom-equivalent and much smaller classical electron-equivalent DNA-coated nanoparticles. We can also create more complex colloidal systems, such as colloidal “alloys” and covalent compound-like structures. These discoveries open up new possibilities for designing colloidal crystals with different properties.

Representative publications:

Materials Dynamics and Evolution on the Nanoscale

Nanomaterials are dynamic. They can change their shape, size, and composition in response to their environment. In particular, nanoparticles have many potential applications in catalysis, environmental protection, therapeutics, and diagnosis. However, these applications often expose nanoparticles to harsh conditions (such as electrolytes, biofluids, etc.) that can affect their stability and performance. This is a major challenge for their practical use. We developed new methods to track how multicomponent nanoparticles interact and transform in different environments. We observe the dynamics of nanomaterials in real-time with a very high resolution, often down to the sub-nanometer level. These observations reveal how materials form, change, and degrade under various conditions.

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

Functional Nanomaterials with Complex Geometries and Surface Configurations

Noble metals, transition metal oxides, and their hybrids are promising catalysts and sensor materials. For these purposes, they often need to have complex shapes that provide specific optical and chemical properties. However, it is not easy to make such nanostructures in large quantities using wet chemical methods. They require careful design and control of the synthesis process. In these studies, we create new nanostructures and shapes that meet a specific need, such as high-temperature catalysis or multifunctional sensing. We do this by manipulating the factors that influence crystal growth or developing new techniques to modify the surface structures.

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 M@Au (M = Pd, CuPt) Hybrid Nanostars with Plasmonic Properties.
    Physical Chemistry Chemical Physics 2015, 17 (2), 1265–1272. DOI:10.1039/C4CP04757E

Impact of Emerging Technologies on Research and Society

The landscape of research is changing rapidly with the emergence of new technologies and concepts, such as AI and open access. These developments have profound implications for how research is conducted, communicated, and evaluated. How well are research communities adapting to these changes and preparing for the future? In my work, I explore and assess the impact of these new technologies on various stakeholders in the research ecosystem, such as researchers, funders, and publishers. I share my insights and perspectives through a series of opinion and commentary articles that aim to inform and stimulate discussion among the research community.

Representative publications: