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335 results on '"Neilson, James R."'

102. Erratum: “A high precision gas flow cell for performing in situ neutron studies of local atomic structure in catalytic materials” [Rev. Sci. Instrum. 88, 034101 (2017)]

Author

Olds, Daniel, primary, Page, Katharine, additional, Paecklar, Arnold, additional, Peterson, Peter F., additional, Liu, Jue, additional, Rucker, Gerald, additional, Ruiz-Rodriguez, Mariano, additional, Olsen, Michael, additional, Pawel, Michelle, additional, Overbury, Steven H., additional, and Neilson, James R., additional

Published
2017
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105. Amide-Assisted Synthesis of Iron Germanium Sulfide (Fe2GeS4) Nanostars: The Effect of LiN(SiMe3)2on Precursor Reactivity for Favoring Nanoparticle Nucleation or Growth

Author

Miller, Rebecca C., Neilson, James R., and Prieto, Amy L.

Abstract

Olivine Fe2GeS4has been identified as a promising photovoltaic absorber material introduced as an alternate candidate to iron pyrite, FeS2. The compounds share similar benefits in terms of elemental abundance and relative nontoxicity, but Fe2GeS4was predicted to have higher stability with respect to decomposition to alternate phases and, therefore, more optimal device performance. Our initial report of the nanoparticle (NP) synthesis for Fe2GeS4was not well understood and required an inefficient 24 h growth to dissolve an iron sulfide impurity. Here, we report an amide-assisted Fe2GeS4NP synthesis that directly forms the phase-pure product in minutes. This significant advance was achieved by the replacement of the poorly understood hexamethyldisilazane (HMDS) additive and TMS2S by the conjugate base, lithium bis(trimethylsilyl)amide (LiN(SiMe3)2), and elemental S, respectively. We hypothesized that fragments of both TMS2S and HMDS had carried out the roles that Brønsted bases play in amide-assisted NP syntheses and were necessary for Ge incorporation. Convolution of this role with the supply of S in TMS2S caused the iron sulfide impurities. Separating these effects in the use of LiN(SiMe3)2and elemental S resulted in synthetic control over the ternary phase. Herein we explore the Fe–Ge–S reaction landscape and the role of the base. Its concentration was found to increase the reactivities of the Fe, Ge, and S precursors, and we discuss possible metal-amide intermediates. This affords tunability in two areas: favorability of NP nucleation versus growth and phase formation. The phase-purity of Fe2GeS4depends on the molar ratios of the cations, base, and amine as well as the Fe:Ge:S molar ratios. The resultant Fe2GeS4NPs exhibit an interesting star anise-like morphology with stacks of nanoplates that intersect along a 6-fold rotation axis. The optical properties of the Fe2GeS4NPs are consistent with previously published measurements showing a measured band gap of 1.48 eV.

Published
2020
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111. Synthetic control over orientational degeneracy of spacer cations enhances solar cell efficiency in two-dimensional perovskites.

Author

Jun Hu, Oswald, Iain W. H., Stuard, Samuel J., Nahid, Masrur Morshed, Ninghao Zhou, Williams, Olivia F., Zhenkun Guo, Liang Yan, Huamin Hu, Zheng Chen, Xun Xiao, Yun Lin, Zhibin Yang, Jinsong Huang, Moran, Andrew M., Ade, Harald, Neilson, James R., and Wei You

Abstract

Two-dimensional perovskites have emerged as more intrinsically stable materials for solar cells. Chemical tuning of spacer organic cations has attracted great interest due to their additional functionalities. However, how the chemical nature of the organic cations affects the properties of two-dimensional perovskites and devices is rarely reported. Here we demonstrate that the selection of spacer cations (i.e., selective fluorination of phenethylammonium) affects the film properties of two-dimensional perovskites, leading to different device performance of two-dimensional perovskite solar cells (average n = 4). Structural analysis reveals that different packing arrangements and orientational disorder of the spacer cations result in orientational degeneracy and different formation energies, largely explaining the difference in film properties. This work provides key missing information on how spacer cations exert influence on desirable electronic properties and device performance of twodimensional perovskites via the weak and cooperative interactions of these cations in the crystal lattice. [ABSTRACT FROM AUTHOR]

Published
2019
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124. A high precision gas flow cell for performing in situ neutron studies of local atomic structure in catalytic materials.

Author

Olds, Daniel, Page, Katharine, Paecklar, Arnold, Peterson, Peter F., Jue Liu, Rucker, Gerald, Ruiz-Rodriguez, Mariano, Olsen, Michael, Pawe, Michelle, Overbury, Steven H., and Neilson, James R.

Subjects
ATOMIC structure, CATALYSIS, GAS-solid interfaces, HETEROGENEOUS catalysis, GAS flow
Abstract

Gas-solid interfaces enable a multitude of industrial processes, including heterogeneous catalysis; however, there are few methods available for studying the structure of this interface under operating conditions. Here, we present a new sample environment for interrogating materials under gas-flow conditions using time-of-flight neutron scattering under both constant and pulse probe gas flow. Outlined are descriptions of the gas flow cell and a commissioning example using the adsorption of N2 by Ca-exchanged zeolite-X (Na78-2xCaxAl78Si144O384, x ≈ 38). We demonstrate sensitivities to lattice contraction and N2 adsorption sites in the structure, with both static gas loading and gas flow. A steady-state isotope transient kinetic analysis of N2 adsorption measured simultaneously with mass spectrometry is also demonstrated. In the experiment, the gas flow through a plugged-flow gas-solid contactor is switched between 15N2 and 14N2 isotopes at a temperature of 300 K and a constant pressure of 1 atm; the gas flow and mass spectrum are correlated with the structure factor determined from event-based neutron total scattering. Available flow conditions, sample considerations, and future applications are discussed. [ABSTRACT FROM AUTHOR]

Published
2017
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148. Combinatorial Synthesis of Cation-Disordered Manganese Tin Nitride MnSnN2Thin Films with Magnetic and Semiconducting Properties

Author

Rom, Christopher L., Smaha, Rebecca W., Melamed, Celeste L., Schnepf, Rekha R., Heinselman, Karen N., Mangum, John S., Lee, Sang-Jun, Lany, Stephan, Schelhas, Laura T., Greenaway, Ann L., Neilson, James R., Bauers, Sage R., Tamboli, Adele C., and Andrew, Jennifer S.

Abstract

Magnetic semiconductors may soon improve the energy efficiency of microelectronics, but materials exhibiting these dual properties remain underexplored. Here, we report the computational prediction and realization of a new magnetic and semiconducting material, MnSnN2, via combinatorial sputtering of thin films. Grazing incidence wide-angle X-ray scattering and laboratory X-ray diffraction studies show MnSnN2exhibits a wurtzite-like crystal structure with cation disorder. This new material has a wide composition tolerance, with a single-phase region ranging from 20% < Mn/(Mn + Sn) < 65%. Spectroscopic ellipsometry identifies an optical absorption onset of 1 eV, consistent with the computationally predicted 1.2 eV bandgap. Resistivity measurements as a function of temperature support the semiconducting nature of MnSnN2. Hall effect measurements show carrier density has a weak inverse correlation with temperature, indicating that the charge transport mechanisms are more complex than in a pristine semiconductor. Magnetic susceptibility measurements reveal a low-temperature magnetic ordering transition (≈10 K) for MnSnN2and strong antiferromagnetic correlations. This finding contrasts with bulk, cation-ordered MnSiN2and MnGeN2, which exhibited antiferromagnetic ordering above 400 K in previous studies. To probe the origin of this difference, we perform Monte Carlo simulations of cation-ordered and cation-disordered MnSnN2. They reveal that cation disorder lowers the magnetic transition temperature relative to the ordered phase. In addition to discovering a new compound, this work shows that future efforts could use cation (dis)order to tune magnetic transitions in semiconducting materials for precise control of properties in microelectronics.

Published
2023
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150. Assessing Thermodynamic Selectivity of Solid-State Reactions for the Predictive Synthesis of Inorganic Materials

Author

McDermott, Matthew J., McBride, Brennan C., Regier, Corlyn E., Tran, Gia Thinh, Chen, Yu, Corrao, Adam A., Gallant, Max C., Kamm, Gabrielle E., Bartel, Christopher J., Chapman, Karena W., Khalifah, Peter G., Ceder, Gerbrand, Neilson, James R., and Persson, Kristin A.

Abstract

Synthesis is a major challenge in the discovery of new inorganic materials. Currently, there is limited theoretical guidance for identifying optimal solid-state synthesis procedures. We introduce two selectivity metrics, primary and secondary competition, to assess the favorability of target/impurity phase formation in solid-state reactions. We used these metrics to analyze 3520 solid-state reactions in the literature, ranking existing approaches to popular target materials. Additionally, we implemented these metrics in a data-driven synthesis planning workflow and demonstrated its application in the synthesis of barium titanate (BaTiO3). Using an 18-element chemical reaction network with first-principles thermodynamic data from the Materials Project, we identified 82985 possible BaTiO3synthesis reactions and selected 9 for experimental testing. Characterization of reaction pathways via synchrotron powder X-ray diffraction reveals that our selectivity metrics correlate with observed target/impurity formation. We discovered two efficient reactions using unconventional precursors (BaS/BaCl2and Na2TiO3) that produce BaTiO3faster and with fewer impurities than conventional methods, highlighting the importance of considering complex chemistries with additional elements during precursor selection. Our framework provides a foundation for predictive inorganic synthesis, facilitating the optimization of existing recipes and the discovery of new materials, including those not easily attainable with conventional precursors.

Published
2023
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