Single-Nanocrystal Reaction Trajectories Reveal Sharp Cooperative Transitions

Abstract

Whereas pathways of chemical reactions involving small molecules are well-understood, the dynamics of reactions in extended solids remain difficult to elucidate. Frequently, kinetic studies on bulk materials provide a picture averaged over multiple domains or grains, smearing out interesting dynamics such as critical nucleation phenomena or sharp phase transitions occurring within individual, often nanoscale, grains, or domains. By optically monitoring a solid-state reaction with single nanocrystal resolution, we directly identified a unique, previously unknown, reaction pathway. Reaction trajectories of single cadmium selenide nanocrystals undergoing ion exchange with silver reveal that each individual nanocrystal waits a unique amount of time before making an abrupt switch to the silver selenide phase on a few hundred millisecond time scale. The gradual reaction progress of ensemble-scale cation exchange is actually comprised of these sharp single-nanocrystal switching events. Statistical distributions of waiting times suggest that the reaction is a cooperative transition rather than a diffusion-limited cation-by-cation exchange, which is confirmed by a stochastic reaction model. Such insight, achievable from single nanocrystal reaction studies, furthers mechanistic understanding of heterogeneous reactions, solid-state catalysis, bottom-up nanostructure growth, and materials' transformations and degradation in reactive environments.

In situ detection of hydrogen-induced phase transitions in individual palladium nanocrystals

“…The observed size-dependence therefore further supports the coherent model for the ↵-to-phase transition. mechanism could be used to interpret a wide range of solid state reactions in which a reservoir of intercalants is in equilibrium with a coherent host lattice, such as Li-ion insertion in nanostructured electrodes 5,7 and ion exchange reactions in quantum dots 11,17 . More generally, our in-situ detection scheme offers new avenues to study phase-transitions of single nanoparticles in a wide-range of reactive environments, with as-of-yet unknown thermodynamic properties.…”

“…Single particle measurements would resolve this ambiguity, but observing phase transitions in individual nanoparticles is extremely challenging 10,16,17 , particularly in reactive gaseous or liquid environments. One elegant approach to sense hydrogenation in an individual Pd nanoparticle relies on shifts in the surface plasmon resonance of a nearby gold nano-antenna [18][19][20] .…”

Selective Cation Exchange in the Core Region of Cu2–xSe/Cu2–xS Core/Shell Nanocrystals

“…This was also proven in a recent work by optically monitoring the same reaction with single NC resolution. 5 Therefore, while in CE reactions in NCs there could be multiple entry points for ions (virtually the whole NC surface), the actual exchange, initiated by ions that have already diffused in the particles, can start from a region inside the NC that does not necessarily coincide with the entry point(s). This should be especially true when the guest ions are fast diffusing in the host lattice, so that they can quickly probe the whole NC in the quest for regions where it would be energetically more favorable for them to engage in CE reactions.…”

Catalytic Kinetics of Different Types of Surface Atoms on Shaped Pd Nanocrystals

“…[1] However,s tudy is often hampered by the difficulty of identifying the properties or roles of different types of surface atoms,s uch as the plane,e dge,o rc orner atoms on as ingle nanoparticle surface. [11][12][13][14][15][16][17][18][19] Furthermore,t he activity of different parts of an individual nanocatalyst (from af ew hundred nanometers to microns in size) was visualized approximately using super-resolution fluorescence microscopy. [11][12][13][14][15][16][17][18][19] Furthermore,t he activity of different parts of an individual nanocatalyst (from af ew hundred nanometers to microns in size) was visualized approximately using super-resolution fluorescence microscopy.…”

“…[2][3][4] To elucidate this problem, various experiments and computations have been conducted, [2,[4][5][6][7][8][9][10] but it is still difficult to clarify the quantitative contribution of different types of surface atoms to the total catalytic reactivity of as ingle nanoparticle.I nr ecent years,s inglemolecule fluorescence microscopy (SMFM) has been used to investigate the kinetic and dynamic behaviors of the whole single nanoparticles in real time with single-turnover resolution. [11][12][13][14][15][16][17][18][19] Furthermore,t he activity of different parts of an individual nanocatalyst (from af ew hundred nanometers to microns in size) was visualized approximately using super-resolution fluorescence microscopy. [20][21][22] However,o wing to the limitation of spatial resolution and the vague partition of corner,e dge,o rp lane on individual nanocatalysts,t he catalytic kinetic and dynamic study of different types of surface atoms cannot be studied quantitatively with SMFM.In this work, based on well-defined palladium (Pd) nanocubes and rational physical models,b yastatistical quantitative deconvolution of observables obtained from traditional single-molecule nanocatalysis of Pd nanocrystals, the catalytic kinetics and dynamics of the different types of surface atoms (plane and edge) were studied quantitatively for the first time.T his work pushes traditional SMFM as tep forward to sub-particle level.…”