Label-Free Characterization of Organic Nanocarriers Reveals Persistent Single Molecule Cores For Hydrocarbon Sequestration

Self-assembled molecular nanostructures embody an enormous potential for new technologies, therapeutics, and understanding of molecular biofunctions. Their structure and function are dependent on local environments, necessitating in-situ/operando investigations for the biggest leaps in discovery and design. However, the most advanced of such investigations involve laborious labeling methods that can disrupt behavior or are not fast enough to capture stimuli-responsive phenomena. We utilize X-rays resonant with molecular bonds to demonstrate an in-situ nanoprobe that eliminates the need for labels and enables data collection times within seconds. Our analytical spectral model quantifies the structure, molecular composition, and dynamics of a copolymer micelle drug delivery platform using resonant soft X-rays. We additionally apply this technique to a hydrocarbon sequestrating polysoap micelle and discover that the critical organic-capturing domain does not coalesce upon aggregation but retains distinct single-molecule cores. This characteristic promotes its efficiency of hydrocarbon sequestration for applications like oil spill remediation and drug delivery. Such a technique enables operando, chemically sensitive investigations of any aqueous molecular nanostructure, label-free

Combining theory and experiment for X-ray absorption spectroscopy and resonant X-ray scattering characterization of polymers

An improved understanding of fundamental chemistry, electronic structure, morphology, and dynamics in polymers and soft materials requires advanced characterization techniques that are amenable to in situ and operando studies. Soft X-ray methods are especially useful in their ability to non-destructively provide information on specific materials or chemical moieties. Analysis of these experiments, which can be very dependent on X-ray energy and polarization, can quickly become complex. Complementary modeling and predictive capabilities are required to properly probe these critical features. Here, we present relevant background on this emerging suite of techniques. We focus on how the combination of theory and experiment has been applied and can be further developed to drive our understanding of how these methods probe relevant chemistry, structure, and dynamics in soft materials

Picometer sensitivity metrology for EUV absorber phase

With growing interest in EUV attenuated phase-shift masks due to their superior image quality for applications such as dense contact and pillar arrays, it is becoming critical to model, measure, and monitor the intensity and relative phase of multilayer and absorber reflections. We present a solution based on physical modeling of reflectometry data, which can achieve single picometer phase precision and sensitivity to changes in average film thickness below one atomic monolayer. We measure absorber and multilayer reflectivity to determine thin-film parameters with a multidimensional optimization and then acquire a new measurement of either multilayer or absorber to determine perturbations in surface contamination thickness. While it is difficult to assess the accuracy of the first step, the simplicity of the second step allows us to characterize our sensitivity to changes in contamination thickness. We apply this analysis using an initial set of measurements and repeated measurements after a period of storage. For the multilayer, the total contamination growth was 1068 pm, which occurred almost exclusively during storage (1085 pm) and decreased very slightly during repeated measurements (-17 pm). For the absorber, the behavior was quite different, with a total growth of 126 pm, which occurred much less during storage (28 pm) and primarily during repeated measurements (98 pm). Ultimately, the change in relative phase (absorber minus multilayer) was -0.86 deg for the multilayer and -1.12 deg for the absorber. We estimate the precision of the surface contamination measurement to be 3σ < 6 pm for measuring thickness and 3σ < 0.2 deg for measuring phase

Reprint of: Combining theory and experiment for X-ray absorption spectroscopy and resonant X-ray scattering characterization of polymers

An improved understanding of fundamental chemistry, electronic structure, morphology, and dynamics in polymers and soft materials requires advanced characterization techniques that are amenable to in situ and operando studies. Soft X-ray methods are especially useful in their ability to non-destructively provide information on specific materials or chemical moieties. Analysis of these experiments, which can be very dependent on X-ray energy and polarization, can quickly become complex. Complementary modeling and predictive capabilities are required to properly probe these critical features. Here, we present relevant background on this emerging suite of techniques. We focus on how the combination of theory and experiment has been applied and can be further developed to drive our understanding of how these methods probe relevant chemistry, structure, and dynamics in soft materials

Chemical and Morphological Origins of Improved Transport in Perfluoro Ionene Chain Extended Ionomers

The performance of proton-conducting ionomer membranes used in electrochemical applications such as fuel cells is complicated by an intricate interplay between chemistry and morphology that is challenging to characterize and control. Here, we report on a class of perfluoro ionene chain extended (PFICE) ionomers that contain either one (PFICE-2) or two (PFICE-3) bis(sulfonyl)imide groups on the side-chain in addition to a terminal sulfonic acid group. PFICE ionomers are promising materials, exhibiting greater water uptake and conductivity over a range of relative humidity values compared to prototypical perfluorinated sulfonic acid (PFSA) ionomers. Advanced in situ synchrotron characterization combined with simulations reveals insights into the connections between molecular structure and morphology that dictate performance. Energy-tunable X-rays with sensitivity to sulfur can decipher the unique bonding environment of different protogenic groups on the polymer side-chain. Guided by simulations, X-ray absorption spectroscopy can be sensitive to hydration level and configuration that dictates proton dissociation. In situ resonant X-ray scattering reveals that PFICE ionomers have a phase-separated morphology with enhanced short-range order that persists in both dry and hydrated state, allowing for improved transport pathways across hydration levels. Furthermore, side-chain chemistry and length can be used as a molecular design parameter to predict phase-separated domain spacing. The enhanced conductivity of PFICE ionomers is attributed to a unique side-chain chemistry and structure promoting hydrogen bonding configurations that facilitate proton dissociation at low water content in combination with a well-ordered phase-separated morphology that forms transport pathways. Overall, these results provide guidelines to design new ionomers with improved transport properties and demonstrate the value of in situ characterization methods such as resonant X-ray scattering and spectroscopy for unraveling the structural features in chemically-heterogeneous materials used in electrochemical systems

Chemical and Morphological Origins of Improved Ion Conductivity in Perfluoro Ionene Chain Extended Ionomers.

The performance of ion-conducting polymer membranes is complicated by an intricate interplay between chemistry and morphology that is challenging to understand. Here, we report on perfuoro ionene chain extended (PFICE) ionomers that contain either one or two bis(sulfonyl)imide groups on the side-chain in addition to a terminal sulfonic acid group. PFICE ionomers exhibit greater water uptake and conductivity compared to prototypical perfluorinated sulfonic acid ionomers. Advanced in situ synchrotron characterization reveals insights into the connections between molecular structure and morphology that dictate performance. Guided by first-principles calculations, X-ray absorption spectroscopy at the sulfur K-edge can discern distinct protogenic groups and be sensitive to hydration level and configurations that dictate proton dissociation. In situ resonant X-ray scattering at the sulfur K-edge reveals that PFICE ionomers have a phase-separated morphology with enhanced short-range order that persists in both dry and hydrated states. The enhanced conductivity of PFICE ionomers is attributed to a unique multi-acid side-chain chemistry and structure that facilitates proton dissociation at low water content in combination with a well-ordered phase-separated morphology with nanoscale transport pathways. Overall, these results provide insights for the design of new ionomers with tunable phase separation and improved transport properties as well as demonstrating the efficacy of X-rays with elemental sensitivity for unraveling structural features in chemically heterogeneous functional materials for electrochemical energy applications

LixNiO/Ni Heterostructure with Strong Basic Lattice Oxygen Enables Electrocatalytic Hydrogen Evolution with Pt-like Activity.

The low-cost hydrogen production from water electrolysis is crucial to the deployment of sustainable hydrogen economy but is currently constrained by the lack of active and robust electrocatalysts from earth-abundant materials. We describe here an unconventional heterostructure composed of strongly coupled Ni-deficient LixNiO nanoclusters and polycrystalline Ni nanocrystals and its exceptional activities toward the hydrogen evolution reaction (HER) in aqueous electrolytes. The presence of lattice oxygen species with strong Brønsted basicity is a significant feature in such heterostructure, which spontaneously split water molecules for accelerated Volmer H-OH dissociation in neutral and alkaline HER. In combination with the intimate LixNiO and Ni interfacial junctions that generate localized hotspots for promoted hydride coupling and hydrogen desorption, the catalysts produce hydrogen at a current density of 10 mA cm-2 under overpotentials of only 20, 50, and 36 mV in acidic, neutral, and alkaline electrolytes, respectively, making them among the most active Pt-free catalysts developed thus far. In addition, such heterostructures also exhibited superior activity toward the hydrogen oxidation reaction in alkaline electrolytes

LixNiO/Ni Heterostructure with Strong Basic Lattice Oxygen Enables Electrocatalytic Hydrogen Evolution with Pt-like Activity.

The low-cost hydrogen production from water electrolysis is crucial to the deployment of sustainable hydrogen economy but is currently constrained by the lack of active and robust electrocatalysts from earth-abundant materials. We describe here an unconventional heterostructure composed of strongly coupled Ni-deficient LixNiO nanoclusters and polycrystalline Ni nanocrystals and its exceptional activities toward the hydrogen evolution reaction (HER) in aqueous electrolytes. The presence of lattice oxygen species with strong Brønsted basicity is a significant feature in such heterostructure, which spontaneously split water molecules for accelerated Volmer H-OH dissociation in neutral and alkaline HER. In combination with the intimate LixNiO and Ni interfacial junctions that generate localized hotspots for promoted hydride coupling and hydrogen desorption, the catalysts produce hydrogen at a current density of 10 mA cm-2 under overpotentials of only 20, 50, and 36 mV in acidic, neutral, and alkaline electrolytes, respectively, making them among the most active Pt-free catalysts developed thus far. In addition, such heterostructures also exhibited superior activity toward the hydrogen oxidation reaction in alkaline electrolytes

Additive Lithography-Organic Monolayer Patterning Coupled with an Area-Selective Deposition.

The combination of area-selective deposition (ASD) with a patternable organic monolayer provides a versatile additive lithography platform, enabling the generation of a variety of nanoscale feature geometries. Stearate hydroxamic acid self-assembled monolayers (SAMs) were patterned with extreme ultraviolet (λ = 13.5 nm) or electron beam irradiation and developed with ASD to achieve line space patterns as small as 50 nm. Density functional theory was employed to aid in the synthesis of hydroxamic acid derivatives with optimized packing density to enhance the imaging contrast and improve dose sensitivity. Near-edge X-ray absorption fine structure spectroscopy and infrared spectroscopy reveal that the imaging mechanism is based on improved deposition inhibition provided by the cross-linking of the SAM to produce a more effective barrier during a subsequent deposition step. With patterned substrates composed of coplanar copper lines and silicon spacers, hydroxamic acids selectively formed monolayers on the metal portions and could undergo a pattern-wise exposure followed by ASD in the first combination of a patternable monolayer with ASD. This material system presents an additional capability compared to traditional ASD approaches that generally reflect a starting patterned surface. Furthermore, this bottoms-up additive approach to lithography may be a viable alternative to subtractive nanoscale feature generation