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  1. Abstract

    Under-oil open microfluidic system, utilizing liquid-liquid boundaries for confinements, offers inherent advantages including clogging-free flow channels, flexible access to samples, and adjustable gas permeation, making it well-suited for studying multi-phase chemical reactions that are challenging for closed microfluidics. However, reports on the novel system have primarily focused on device fabrication and functionality demonstrations within biology, leaving their application in broader chemical analysis underexplored. Here, we present a visualization-enhanced under-oil open microfluidic system for in situ characterization of multi-phase chemical reactions with Raman spectroscopy. The enhanced system utilizes a semi-transparent silicon (Si) nanolayer over the substrate to enhance visualization in both inverted and upright microscope setups while reducing Raman noise from the substrate. We validated the system’s chemical stability and capability to monitor gas evolution and gas-liquid reactions in situ. The enhanced under-oil open microfluidic system, integrating Raman spectroscopy, offers a robust open-microfluidic platform for label-free molecular sensing and real-time chemical/biochemical process monitoring in multi-phase systems.

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    Free, publicly-accessible full text available December 1, 2025
  2. Abstract

    Charge ordering (CO), characterized by a periodic modulation of electron density and lattice distortion, has been a fundamental topic in condensed matter physics, serving as a potential platform for inducing novel functional properties. The charge-ordered phase is known to occur in a doped system with highd-electron occupancy, rather than low occupancy. Here, we report the realization of the charge-ordered phase in electron-doped (100) SrTiO3epitaxial thin films that have the lowestd-electron occupancy i.e.,d1-d0. Theoretical calculation predicts the presence of a metastable CO state in the bulk state of electron-doped SrTiO3. Atomic scale analysis reveals that (100) surface distortion favors electron-lattice coupling for the charge-ordered state, and triggering the stabilization of the CO phase from a correlated metal state. This stabilization extends up to six unit cells from the top surface to the interior. Our approach offers an insight into the means of stabilizing a new phase of matter, extending CO phase to the lowest electron occupancy and encompassing a wide range of 3dtransition metal oxides.

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    Free, publicly-accessible full text available December 1, 2025
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  5. The surface diffusion kinetics on a Pd77.5Cu6Si16.5 metallic glass is measured using a scratch smoothing method in the range of 107–57 K below the glass transition temperature. Within this temperature range, the surface diffusion coefficients are determined to vary between (8.66 ± 0.80) × 10−19 and (5.90 ± 0.60) × 10−18 m2 s−1. The corresponding activation energy is 0.93 ± 0.18 eV, which is about half the value for bulk diffusion. These measurements also corroborate the correlation between enhanced surface diffusion and liquid fragility in glasses.

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    Free, publicly-accessible full text available February 26, 2025
  6. Parallel algorithms exploit structure to compute the Euler characteristic (a powerful topological descriptor that is used to quantify shape of data) at significantly less computational expense than traditional software tools.

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    Free, publicly-accessible full text available February 14, 2025
  7. In this work, we propose a linear machine learning force matching approach that can directly extract pair atomic interactions from ab initio calculations in amorphous structures. The local feature representation is specifically chosen to make the linear weights a force field as a force/potential function of the atom pair distance. Consequently, this set of functions is the closest representation of the ab initio forces, given the two-body approximation and finite scanning in the configurational space. We validate this approach in amorphous silica. Potentials in the new force field (consisting of tabulated Si–Si, Si–O, and O–O potentials) are significantly different than existing potentials that are commonly used for silica, even though all of them produce the tetrahedral network structure and roughly similar glass properties. This suggests that the commonly used classical force fields do not offer fundamentally accurate representations of the atomic interaction in silica. The new force field furthermore produces a lower glass transition temperature (Tg ∼ 1800 K) and a positive liquid thermal expansion coefficient, suggesting the extraordinarily high Tg and negative liquid thermal expansion of simulated silica could be artifacts of previously developed classical potentials. Overall, the proposed approach provides a fundamental yet intuitive way to evaluate two-body potentials against ab initio calculations, thereby offering an efficient way to guide the development of classical force fields.

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    Free, publicly-accessible full text available February 7, 2025
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