Predicting the formation dynamics of nanomaterials is a long-standing challenge. Generic models are lacking, and existing ones fail to account for chemical or structural properties of particles at the nanoscale. The groundbreaking discoveries of novel nanomaterials are currently achieved via laborious Edisonian trial-error protocols. Bridging this gap between theory and experiment requires tools, techniques and strategies with high spatial, temporal and chemical resolutions. For a successful implementation of predictive tools, it is also essential to probe the real-time dynamics of nanoparticle formation. Synchrotron X-ray absorption spectroscopy is a technique with chemical sensitivity, and have already achieved X-ray probe sizes in the order of microns and temporal resolution in the order of sub-seconds using Quick XAS mode in which photon energies are scanned rapidly and repetitively. Applying x-ray microprobes in a continuous flow mode renders possible detection of milliseconds time scales by way of trading distance with time. In this talk, two examples implementing this trading time-space strategy using the microprobe at the Advanced Light Source will be discussed. The first is the in-situ monitoring of reduction, nucleation and growth dynamics of ultra-small bimetallic CoPt nanoparticles. In this case, the time transients in the order of milliseconds are recorded by adjusting liquid flow rates and reactor volume. Mixtures of salt precursors in dioctylamine are flowed through a thermally regulated capillary bed while changing the capillary position along its long axis relative to the X-rays. Both near edge and extended edge XAS spectra are obtained at the Pt L3 and Co K absorption edges. The second example is the real-time monitoring of the laser-induced formation and self-assembly of Ag nanoparticle gratings in mesostructured titania substrate. A 35-micron spot 532-nm cw laser is lightly focused on a titania substrate impregnated with Ag salt precursor, and a 5-micron X-ray probe is overlapped on the laser spot. Then, the substrate is rastered at a constant speed allowing for laser writing, leading to nucleation and growth of the Ag nanoparticles with subsequent organization along the direction of the laser polarization. By scanning the X-ray microprobe along the laser beam profile, time transients with 50 msec resolution are obtained at the Ag L3 and Ti K edges affording a window into the dynamics of self-organization in such laser matter interaction.

Monitoring real-time dynamics of nanoparticle formation via trading space with time strategy and synchrotron x-ray absorption spectroscopy technique

253rd National Meeting (2017)

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