Publications

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Acid gases (e.g., NOx and SOx), commonly found in complex chemical and petrochemical streams, require material development for their selective adsorption and removal. Here, we report the NOx adsorption properties in a family of rare earth (RE) metal-organic frameworks (MOFs) materials. Fundamental understanding of the structure-property relationship of NOx adsorption in the RE-DOBDC materials platform was sought via a combined experimental and molecular modeling study. No structural change was noted following humid NOx exposure. Density functional theory (DFT) simulations indicated that H2O has a stronger affinity to bind with the metal center than NO2, while NO2 preferentially binds with the DOBDC ligands. Further modeling results indicate no change in binding energy across the RE elements investigated. Also, stabilization of the NO2 and H2O molecules following adsorption was noted, predicted to be due to hydrogen bonding between the framework ligands and the molecules and nanoconfinement within the MOF structure. This interaction also caused distinct changes in emission spectra, identified experimentally. Calculations indicated that this is due to the adsorption of NO2 molecules onto the DOBDC ligand altering the electronic transitions and the resulting photoluminescent properties, a feature that has potential applications in future sensing technologies.

Abstract not provided.

Abstract not provided.

Recent years have seen an explosion in research efforts discovering and understanding novel electronic and optical properties of topological quantum materials (TQMs). In this LDRD, a synergistic effort of materials growth, characterization, electrical-magneto-optical measurements, combined with density functional theory and modeling has been established to address the unique properties of TQMs. Particularly, we have carried out extensive studies in search for Majorana fermions (MFs) in TQMs for topological quantum computation. Moreover, we have focused on three important science questions. 1) How can we controllably tune the properties of TQMs to make them suitable for quantum information applications? 2) What materials parameters are most important for successfully observing MFs in TQMs? 3) Can the physical properties of TQMs be tailored by topological band engineering? Results obtained in this LDRD not only deepen our current knowledge in fundamental quantum physics but also hold great promise for advanced electronic/photonic applications in information technologies. ACKNOWLEDGEMENTS The work at Sandia National Labs was supported by a Laboratory Directed Research and Development project. Device fabrication was performed at the Center for Integrated Nanotechnologies, an Office of Science User Facility operated for the U.S. Department of Energy (DOE) Office of Science. We are grateful to many people inside and outside Sandia for their support and fruitful collaborations. This report describes objective technical results and analysis. Any subjective views or opinions that might be expressed in the paper do not necessarily represent the views of the U.S. Department of Energy or the United States Government. Sandia National Laboratories is a multimission laboratory managed and operated by National Technology & Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International Inc., for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-NA0003525.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Iodine detection is crucial for nuclear waste clean-up and first responder activities. For ease of use and durability of response, robust active materials that enable the direct electrical detection of I2 are needed. Herein, a large reversible electrical response is demonstrated as I2 is controllably and repeatedly adsorbed and desorbed from a series of metal-organic frameworks (MOFs) MFM-300(X), each possessing a different metal center (X = Al, Fe, In, or Sc) bridged by biphenyl-3,3′,5,5′-tetracarboxylate linkers. Impedance spectroscopy is used to evaluate how the different metal centers influence the electrical response upon cycling of I2 gas, ranging from 10× to 106× decrease in resistance upon I2 adsorption in air. This large variation in electrical response is attributed not only to the differing structural characteristics of the MOFs but also to the differing MOF morphologies and how this influences the degree of reversibility of I2 adsorption. Interestingly, MFM-300(Al) and MFM-300(In) displayed the largest changes in resistance (up to 106×) yet lost much of their adsorption capacity after five I2 adsorption cycles in air. On the other hand, MFM-300(Fe) and MFM-300(Sc) revealed more moderate changes in resistance (10-100×), maintaining most of their original adsorption capacity after five cycles. This work demonstrates how changes in MOFs can profoundly affect the magnitude and reversibility of the electrical response of sensor materials. Tuning both the intrinsic (resistivity and adsorption capacity) and extrinsic (surface area and particle morphology) properties is necessary to develop highly reversible, large signal-generating MOF materials for direct electrical readout for I2 sensing.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Detection of radiological iodine gas after nuclear accidents or in nuclear fuel reprocessing is necessary for the safety of human life and the environment. The development of sensors for the detection of iodine benefits from the incorporation of nanoporous materials with high selectivity for I2 from common competing gases in air. Silver mordenite zeolite (Ag-MOR) is widely-used material for capture of gaseous iodine (I2). Herein, thin film zeolite coatings were applied to Pt interdigitated electrodes (IEDs) to fabricate iodine gas sensors with direct electrical readout responses. Correlations between occluded ion, exposure to iodine gas, resultant AgI nanoparticle polymorphs and location in zeolite with resultant impedance spectroscopy (IS) properties are described. Furthermore, IS is leveraged to elucidate the changes in charge conduction pathways as determined by the cation-zeolite film incorporated in the sensor. Silver mordenite reveals a significant change in impedance upon exposure to gaseous I2 at 70 °C, and the magnitude and direction of the response is dependent on whether the Ag+-mordenite is reduced (Ag0) before I2 exposure. An equivalent circuit model is developed to describe the movement of charge along the surface and through the pores of the mordenite grains. Relative changes in the impedance of these conduction pathways are related to the chemical changes from Ag+ or Ag0 to resultant AgI polymorph phase. Together, these results inform design of a compact Ag-mordenite sensor for direct electrical detection of gaseous I2.