Katherine Harmon

All Publications

• pH-Driven Restructuring of Hydration Layers and Cation Adsorption at the Alumina-Water Interface JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Neumann, J., Kim, Y., Wang, X., Harmon, K. J., Carr, A. J., Lutzenkirchen, J., Fenter, P., Lee, S. 2026

  Abstract

  Oxide-water interfaces underpin ion separations, catalysis, and electrochemical energy technologies, where the electrical double layer (EDL) controls adsorption, transport, and reactivity. However, the molecular-scale links between pH-dependent surface protonation, hydration-layer structure, and counterion adsorption remain poorly defined. Here, we combine in situ crystal truncation rod (CTR) and resonant anomalous X-ray reflectivity (RAXR) with streaming potential measurements and ab initio molecular dynamics (AIMD) simulations to resolve the chemical and structural evolution of the EDL at the single-crystal alumina (012)-water interface in 10 mM Rb+ over pH 3-12. CTR measurements reveal two distinct adsorbed water layers at ∼2.2 and ∼3.5 Å above the surface. Each water layer shifts toward the substrate at transition pHs near 6.5 and 10.6, respectively, reflecting changes in primary hydration layer structure in response to the deprotonation of bridging and terminal aluminol groups. RAXR shows a 10-fold increase in Rb+ coverage and a decrease in mean adsorption height from ∼3.5 to ∼2.7 Å with increasing pH, indicating enhanced counterion binding accompanied by Stern layer contraction. Streaming potential measurements demonstrate that the zeta potential, i.e., the potential at the hydrodynamic shear plane, is positive at pH 3 and becomes negative at pH ≥ 3.5. The negative charge magnitude increases with increasing pH, consistent with progressive surface deprotonation at higher pH. AIMD identifies inner- and outer-sphere Rb+ complexes whose adsorption heights and coordination geometries depend sensitively on the protonation state of surface oxygens, providing atomistic support for the experimentally inferred trends. These measurements establish two discrete, site-specific pH transitions in hydration-layer structure that track aluminol (de)protonation and quantitatively link them to a pH-driven contraction of the Stern layer (increasing Rb+ coverage and decreasing adsorption height). This provides a direct structural basis for connecting surface acid-base chemistry to ion binding distances at an oxide-water interface.

  View details for DOI 10.1021/jacs.5c21453

  View details for Web of Science ID 001765570700001

  View details for PubMedID 42119997

• Concurrent multi-peak Bragg coherent x-ray diffraction imaging of 3D nanocrystal lattice displacement via global optimization NPJ COMPUTATIONAL MATERIALS Maddali, S., Frazer, T. D., Delegan, N., Harmon, K. J., Sullivan, S. E., Allain, M., Cha, W., Dibos, A., Poudyal, I., Kandel, S., Nashed, Y. S. G., Heremans, F., You, H., Cao, Y., Hruszkewycz, S. O. 2023; 9 (1)

  View details for DOI 10.1038/s41524-023-01022-7

  View details for Web of Science ID 000993832300001

• Designing silicon carbide heterostructures for quantum information science: challenges and opportunities MATERIALS FOR QUANTUM TECHNOLOGY Harmon, K. J., Delegan, N., Highland, M. J., He, H., Zapol, P., Heremans, F. J., Hruszkewycz, S. O. 2022; 2 (2)

  View details for DOI 10.1088/2633-4356/ac6b76

  View details for Web of Science ID 001084798700001

• Nonreciprocal interactions induced by water in confinement PHYSICAL REVIEW RESEARCH Jimenez-Angeles, F., Harmon, K. J., Trung Dac Nguyen, Fenter, P., de la Cruz, M. 2020; 2 (4)

  View details for DOI 10.1103/PhysRevResearch.2.043244

  View details for Web of Science ID 000605411800002

• Validating first-principles molecular dynamics calculations of oxide/water interfaces with x-ray reflectivity data PHYSICAL REVIEW MATERIALS Harmon, K. J., Letchworth-Weaver, K., Gaiduk, A. P., Giberti, F., Gygi, F., Chan, M. K. Y., Fenter, P., Galli, G. 2020; 4 (11)

  View details for DOI 10.1103/PhysRevMaterials.4.113805

  View details for Web of Science ID 000591531700008

• Insights on the Alumina Water Interface Structure by Direct Comparison of Density Functional Simulations with X-ray Reflectivity JOURNAL OF PHYSICAL CHEMISTRY C Harmon, K. J., Chen, Y., Bylaska, E. J., Catalano, J. G., Bedzyk, M. J., Weare, J. H., Fenter, P. 2018; 122 (47): 26934-26944

  View details for DOI 10.1021/acs.jpcc.8b08522

  View details for Web of Science ID 000451933400018

• Enhancing Tabletop X-Ray Phase Contrast Imaging with Nano-Fabrication. Scientific reports Miao, H., Gomella, A. A., Harmon, K. J., Bennett, E. E., Chedid, N., Znati, S., Panna, A., Foster, B. A., Bhandarkar, P., Wen, H. 2015; 5: 13581

  Abstract

  X-ray phase-contrast imaging is a promising approach for improving soft-tissue contrast and lowering radiation dose in biomedical applications. While current tabletop imaging systems adapt to common x-ray tubes and large-area detectors by employing absorptive elements such as absorption gratings or monolithic crystals to filter the beam, we developed nanometric phase gratings which enable tabletop x-ray far-field interferometry with only phase-shifting elements, leading to a substantial enhancement in the performance of phase contrast imaging. In a general sense the method transfers the demands on the spatial coherence of the x-ray source and the detector resolution to the feature size of x-ray phase masks. We demonstrate its capabilities in hard x-ray imaging experiments at a fraction of clinical dose levels and present comparisons with the existing Talbot-Lau interferometer and with conventional digital radiography.

  View details for DOI 10.1038/srep13581

  View details for PubMedID 26315891

  View details for PubMedCentralID PMC4551996

• Motionless electromagnetic phase stepping versus mechanical phase stepping in x-ray phase-contrast imaging with a compact source. Physics in medicine and biology Harmon, K. J., Miao, H., Gomella, A. A., Bennett, E. E., Foster, B. A., Bhandarkar, P., Wen, H. 2015; 60 (8): 3031-43

  Abstract

  X-ray phase contrast imaging based on grating interferometers detects the refractive index distribution of an object without relying on radiation attenuation, thereby having the potential for reduced radiation absorption. These techniques belong to the broader category of optical wavefront measurement, which requires stepping the phase of the interference pattern to obtain a pixel-wise map of the phase distortion of the wavefront. While phase stepping traditionally involves mechanical scanning of a grating or mirror, we developed electromagnetic phase stepping (EPS) for imaging with compact sources to obviate the need for mechanical movement. In EPS a solenoid coil is placed outside the x-ray tube to shift its focal spot with a magnetic field, causing a relative movement between the projection of the sample and the interference pattern in the image. Here we present two embodiments of this method. We verified experimentally that electromagnetic and mechanical phase stepping give the same results and attain the same signal-to-noise ratios under the same radiation dose. We found that the relative changes of interference fringe visibility were within 3.0% when the x-ray focal spot was shifted by up to 1.0 mm in either direction. We conclude that when using x-ray tube sources, EPS is an effective means of phase stepping without the need for mechanical movement.

  View details for DOI 10.1088/0031-9155/60/8/3031

  View details for PubMedID 25803511

  View details for PubMedCentralID PMC6933752

• Efficient decoding of 2D structured illumination with linear phase stepping in X-ray phase contrast and dark-field imaging. PloS one Harmon, K. J., Bennett, E. E., Gomella, A. A., Wen, H. 2014; 9 (1): e87127

  Abstract

  The ability to map the phase distribution and lateral coherence of an x-ray wavefront offers the potential for imaging the human body through phase contrast, without the need to deposit significant radiation energy. The classic means to achieve this goal is structured illumination, in which a periodic intensity modulation is introduced into the image, and changes in the phase distribution of the wavefront are detected as distortions of the modulation pattern. Two-dimensional periodic patterns are needed to fully characterize a transverse wavefront. Traditionally, the information in a 2D pattern is retrieved at high resolution by acquiring multiple images while shifting the pattern over a 2D matrix of positions. Here we describe a method to decode 2D periodic patterns with single-axis phase stepping, without either a loss of information or increasing the number of sampling steps. The method is created to reduce the instrumentation complexity of high-resolution 2D wavefront sensing in general. It is demonstrated with motionless electromagnetic phase stepping and a flexible processing algorithm in x-ray dark-field and phase contrast imaging.

  View details for DOI 10.1371/journal.pone.0087127

  View details for PubMedID 24489853

  View details for PubMedCentralID PMC3904978