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High fidelity soft X-ray imaging using both tabletop and facility-scale light sources is very powerful, enabling static and dynamic imaging with ~10 nm spatial resolution. However, it can suffer from several challenges. First, phase-matched soft x-ray high harmonic generation (SXR HHG) produces a bright supercontinuum that is spatially and temporally coherent. However, reconstructing objects from broadband illumination poses a severe challenge to widely used phase retrieval techniques. The performance is further degraded by photon shot noise, detector noise, and parasitic scattering from optics. For example, stray scattered light can be a challenge for tomographic imaging – since at high tilt angles, this stray light can appear close to the scattered light from the sample (see image).

To address this challenge, STROBE developed the first ptychography algorithms that simultaneously model broadband illumination, shot/detector noise, and parasitic scattering. The first algorithm, PaCMAN, corrects bandwidth using numerical monochromatization, enabling ~4x faster data acquisition relative to ePIE when both are speed-optimized, and 1.5-2x lower dose when dose-optimized. Thus, PaCMAN can advance low-dose imaging of delicate materials (cells, polymers, catalysts). A variant, Ms. PaCMAN, replaces monochromatization with multiple wavelength-dependent modes, providing superior reconstructions to multi-wavelength ePIE, and should provide state-of-the-art reconstructions from broadband illumination across elemental absorption edges. Figure shows experimental data on soft x-ray ptychography of skyrmion samples from the COSMIC beamline at the ALS that was used to test the base ADMM algorithm in the monochromatic limit, demonstrating a substantial improvement relative to ePIE in the presence of shot noise and parasitic scattering.

This advance required the combination of x-ray imaging (Thrust II), new models and algorithms to optimize the image extraction (Thrust IV), and data from a COSMIC beam time.

In many areas of non-invasive optical imaging, particularly in biology and materials science, the use of conventional fluorescence-based microscopy techniques is constrained by a number of factors, including the need for molecular labels and the occurrence of photobleaching. Optical scattering methods provide a powerful alternative that can overcome these limitations by detecting the inherent light-scattering properties of a sample. One such technique, interferometric scattering (iSCAT) microscopy, is a highly sensitive, label-free method that enables the detection of subwavelength entities, such as nanoparticles and single molecules, by using optical interference to translate a weak scattering signal into a strong, detectable intensity change. Because it is a label-free technique, it avoids issues like photobleaching and allows for the precise determination of a nanoparticle’s properties, such as size and mass. It is also highly effective for 3D tracking and quantifying ultrafast diffusion in solids.

STROBE contributed to an important review article in Nature Reviews Methods Primers that provides a comprehensive overview of iSCAT microscopy, its theoretical underpinning, practical implementation, and applications. In particular, STROBE’s contribution focuses on the Center’s development of stroboSCAT, an advanced, time-resolved variant of iSCAT. This innovative technique was created to address a critical challenge in materials science: the difficulty of quantitatively separating different physical phenomena, such as the generation of electronic charge carriers (excitons) and unwanted heat, which have overlapping optical signatures.

stroboSCAT employs a unique pump-probe and multi-wavelength strategy to quantitatively separate and map these contributions with exceptional spatiotemporal precision. This enables accurate observation and characterization of electronic, thermal, and mass transport in a wide range of materials at the nanoscale both separately and also in combination. This methodological advancement represents a significant step forward for fundamental research in optoelectronics and materials science, given the complexities of energy transport and conversion in next-generation functional materials.

For example, stroboSCAT is specifically applied to simultaneously map heat and exciton populations in materials like few-layer molybdenum disulfide (MoS₂). By enabling the quantitative separation of these signals, stroboSCAT transforms iSCAT from a general imaging platform into a powerful analytical instrument for resolving ultrafast energy transport and transduction at the nanoscale.

A new approach for high-resolution, three-dimensional elemental imaging has been demonstrated using soft X-ray ptychographic tomography. This technique leverages both optical density and phase contrast reconstructions to identify elements from a single-energy tilt series, reducing acquisition time by more than half compared to traditional multi-energy tomography. The method was validated on nickel-alumina catalyst particles, where nickel nanoparticles were distinguished from the porous alumina matrix with nanometer-scale resolution. By combining high optical density and low phase contrast signals near an absorption edge, nickel precipitates were identified robustly within the reconstructed volumes, providing critical insights into how metallic particles exsolve and redistribute under catalytic conditions.

This advance opens the door for efficient, element-specific 3D characterization of complex materials, with particular relevance for catalytic systems where nanoscale compositional changes drive performance. The approach not only streamlines experiments at synchrotron facilities, where acquisition time is highly limited, but also establishes a scalable framework for future studies involving multiple transition metals. Such capabilities are essential for unraveling the nanoscale dynamics of catalytic processes, and ultimately for guiding the design of more efficient and durable catalysts for environmentally important applications such as methane reforming.

Semiconductor nanowires offer unique opportunities for next-generation electronic and photonic devices due to their high surface-to-volume ratio, ability to suppress dislocations, accommodate large lattice mismatches, and support both axial and radial heterostructure growth. In particular, the non-polar planes of GaN nanowires provide a promising platform for high-performance optoelectronics by mitigating quantum-confined Stark effects and reducing Auger recombination losses.

STROBE scientists, together with collaborators in Cambridge, Lund, and Denmark, report the discovery of unexpected electrostatic potential wells across the non-polar m-plane and at the core/shell interface in n-type GaN nanowires. Using off-axis electron holography (OAEH), quantum-well-like potential drops were mapped at both the core/shell interface and the nanowire center. Valance electron energy loss spectroscopy (VEELS) revealed localized bandgap narrowing of 30–40 meV in the same regions, while cathodoluminescence spectroscopy linked the reduced potential in the core to C_N defects, and suggested V_GaO_N defect complexes as the most likely origin of the non-radiative wells at the core/shell interface.

These findings demonstrate that point defects can play a dominant role in shaping electrostatic potential landscapes and optical properties of GaN nanowires. Since such defects act as non-radiative recombination centers, they have critical implications for the efficiency and design of nanowire-based LEDs, lasers, and quantum devices. The study highlights the need for careful defect management in epitaxial growth and provides a roadmap for understanding defect-driven electronic behavior in other III-V core/shell heterostructures.