Mechanism of Shape Symmetry Breaking in Surfactant Mediated Crystal Growth
We present a dynamical model of crystal growth, in which it is possible to reliably achieve asymmetric products, beginning from symmetric initial conditions and growing within an isotropic environment. The asymmetric growth is the result of a positive feedback mechanism that amplifies the effect of thermal fluctuations in the coverage of surfactants on the growing crystalline facets. Within our simple model, we are able to understand the kinetic and thermodynamic factors involved in both the onset of symmetry breaking and the persistence of anisotropic growth. We demonstrate that the mechanism is general by studying models with increasing complexity. We argue that this mechanism of symmetry breaking underpins observations of colloidal, seed-mediated syntheses of single crystalline metal nanorods capped with strongly interacting surfactants. The parameters within our model are related to experimental observables such as the concentration, hydrophobicity, and binding strength of the surfactants, which suggests a potential route to optimize the yield of asymmetric products in colloidal nanoparticle syntheses.
Sam Oaks-Leaf is a 4th year Ph.D. candidate in Prof. David Limmer's group. Sam's research focuses on the theory and computational simulation of processes of nucleation and growth within nanomaterials. He received a B.S. in Chemical Physics from Brown University.
From Spectral Clues to Catalytic Control: Unraveling CO₂ Electroreduction with In Situ Raman Spectroscopy
Copper-based catalysts are among the few materials capable of converting CO₂ into multicarbon products through electrochemical reduction. A rigorous understanding of local mechanistic pathways towards enabling selective electrochemical CO2 reduction begins with the ability to detect active species within the catalytic environment; without which we accept a paucity of meaningful progress. In situ Surface-Enhanced Raman Spectroscopy (SERS) has emerged as a powerful means of tracking catalyst evolution, reactive intermediates and local electrolyte environments under operating conditions. In this work, we apply in situ Raman spectroscopy to study Cu nanocatalysts during CO₂ reduction, with emphasis on how substrate design, excitation wavelength (resonant vs. off-resonant), isotopic labeling, and electrolyte composition impact spectral interpretation. Our findings underscore the importance of tailoring spectroscopic setups to specific catalytic questions. Particular attention is given to the ongoing challenges in detecting elusive, transient species and the challenges of interpreting overlapping spectral features, where resolution is limiting. By evaluating these methodological considerations, opportunities and pitfalls in extracting mechanistic insight from Raman spectroscopy are identified. Correlating surface-level observations with catalytic behavior, this work supports a transition from observation to control, codifies crucial steps in active site formation, and ultimately guides the development of fine-tuned selectivity in electrochemical CO₂ reduction
Maria Fonseca Guzman is a 4th year Ph.D. candidate in Prof. Peidong Yang’s group. Maria’s work integrates nanomaterial synthesis with in situ spectroscopic tools to uncover often-obscured reaction mechanisms at the molecular level.