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Many functional properties of molecular systems sensitively depend the local chemical environment seen by each molecule. In that regard, intermolecular coupling plays a pivotal role in controlling energy and charge transfer on molecular length scales. However, determining molecular structure and disorder and with nanometer resolution has notoriously been difficult. Conventional crystallography techniques based on the diffraction of high energy photons and electrons are not sensitive to this low-frequency intermolecular energy landscape.

STROBE teams have recently demonstrated that coupling between molecular vibrations and the resulting collective vibrational states have spectral features that allows one to derive not only the local molecular disorder and nano-scale domain formation, but also enables spectroscopic access to the low-frequency intermolecular energy landscape itself. The spatio-spectral nano-imaging of these collective vibrations in IR nano-spectroscopy has provided a new crystallography technique of vibrational coupling nano-crystallography (VCNC), which offers information on molecular order, disorder, and defects with nano-scale resolution.

In the new work, a STROBE team from CU Boulder collaborating with scientists from the University of Oklahoma now provides a solid theoretical foundation and benchmark measurements to make VCNC quantitative and predictive. This work advances VCNC from a qualitative tool capable of measuring changes in local molecular order to a quantitative technique able to measure and image precise vibrational wavefunction delocalization lengths and intermolecular interaction distances. The technique can now be applied to a wide range of functional molecular systems to image molecular order and disorder on their fundamental length scales.

Biological structures are often characterized by patterns that are self-similar, fractal, or periodic, over a hierarchy of length scales serving specific metabolic, skeletal, or locomotory functions. Many of these motifs have inspired human engineering designs including photonic devices based on butterfly wings, aerospace materials based on avian bone structures, or reduced hydrodynamic drag by emulating shark skin. Further, biological motives can serve as inspiration to address societal challenges including carbon sequestration, bone implants, and dental remineralization. However, understanding biomineralization relies on imaging chemically heterogeneous organic-inorganic interfaces across a hierarchy of spatial scales from atomic structure to nano- and micrometer crystallite dimensions, up to decimeter-size mollusk shells.

Here, a STROBE team from CU Boulder and PNNL collaborating with scientists in oceanography from the University of Washington combine nanoscale secondary ion mass spectroscopy (NanoSIMS) with spectroscopic nano-IR imaging (IR s-SNOM) for simultaneous chemical, molecular, and elemental nanoimaging. At the example of the black-lip pearl oyster mollusk shells they identified for the first time from the morphology of ~50 nm interlamellar protein sheets to aragonite subdomains encapsulated in the prism-covering organic membrane. The results help explain how mollusk shells as complex organic-inorganic composites gain their remarkable combination of stiffness, strength, and toughness unmatched by most manmade materials.

Uterine cervical remodeling is a fundamental feature of pregnancy, facilitating the delivery of the fetus through the cervical canal. Yet, we still know very little about this process due to the lack of methodologies that can quantitatively and unequivocally pinpoint the changes the cervix undergoes during pregnancy. We utilize polarization-resolved second harmonic generation to visualize the alterations the cervix extracellular matrix, specifically collagen, undergoes during pregnancy with exquisite resolution. This technique provides images of the collagen orientation at the pixel level (0.4 μm) over the entire murine cervical section. They show tight and ordered packing of collagen fibers around the os at the early stage of pregnancy and their disruption at the later stages. Furthermore, we utilize a straightforward statistical analysis to demonstrate the loss of order in the tissue, consistent with the loss of mechanical properties associated with this process. This work provides a deeper understanding of the parturition process and could support research into the cause of pathological or premature birth.

Polymeric organic mixed ionic–electronic conductors (OMIECs) underpin several technologies where their electrochemical properties are desirable. These properties however depend on the microstructure that develops in their aqueous operational environment. In relevant experimental conditions, electrolyte-induced swelling amounts to up 20% in volume. We investigated the structure of a model OMIEC across multiple length-scales using cryogenic four-dimensional scanning transmission electron microscopy (cryo-4D-STEM) in both dry and hydrated states. 4D STEM allows us to identify the prevalent defects in the polymer crystalline regions and to analyze the liquid-crystalline nature of the polymer. The orientation maps of the dry and hydrated polymer show that swelling-induced disorder is mostly localized within discrete regions, thus largely preserving liquid crystalline order. Therefore, the liquid crystalline mesostructure makes electronic transport robust to electrolyte ingress. This study demonstrates that cryo-4D-STEM provides multiscale structural insights into complex, hierarchical structures such as polymeric OMIECs, even in their hydrated operating state.

Aluminum nanocrystals created by catalyst-driven colloidal synthesis support excellent plasmonic properties, due to their high level of elemental purity, monocrystallinity, and controlled size and shape. Reduction in the rate of nanocrystal growth enables the synthesis of highly anisotropic Al nanowires, nanobars, and singly twinned “nanomoustaches”. Electron energy loss spectroscopy was used to study the plasmonic properties of these nanocrystals, spanning the broad energy range needed to map their plasmonic modes. The coupling between these nanocrystals and other plasmonic metal nanostructures, specifically Ag nanocubes and Au films of controlled nanoscale thickness, was investigated. Al nanocrystals show excellent long-term stability under atmospheric conditions, providing a practical alternative to coinage metal-based nanowires in assembled nanoscale devices.