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2. Site-Specific Structure at Multiple Length Scales in Kagome Quantum Spin Liquid Candidates

Author

Smaha, Rebecca W., Boukahil, Idris, Titus, Charles J., Jiang, Jack Mingde, Sheckelton, John P., He, Wei, Wen, Jiajia, Vinson, John, Wang, Suyin Grass, Chen, Yu-Sheng, Teat, Simon J., Devereaux, Thomas P., Pemmaraju, C. Das, and Lee, Young S.

Subjects
Condensed Matter - Strongly Correlated Electrons, Condensed Matter - Materials Science
Abstract

Realizing a quantum spin liquid (QSL) ground state in a real material is a leading issue in condensed matter physics research. In this pursuit, it is crucial to fully characterize the structure and influence of defects, as these can significantly affect the fragile QSL physics. Here, we perform a variety of cutting-edge synchrotron X-ray scattering and spectroscopy techniques, and we advance new methodologies for site-specific diffraction and L-edge Zn absorption spectroscopy. The experimental results along with our first-principles calculations address outstanding questions about the local and long-range structures of the two leading kagome QSL candidates, Zn-substituted barlowite Cu$_3$Zn$_{x}$Cu$_{1-x}$(OH)$_6$FBr and herbertsmithite Cu$_3$Zn(OH)$_6$Cl$_2$. On all length scales probed, there is no evidence that Zn substitutes onto the kagome layers, thereby preserving the QSL physics of the kagome lattice. Our calculations show that antisite disorder is not energetically favorable and is even less favorable in Zn-barlowite compared to herbertsmithite. Site-specific X-ray diffraction measurements of Zn-barlowite reveal that Cu$^{2+}$ and Zn$^{2+}$ selectively occupy distinct interlayer sites, in contrast to herbertsmithite. Using the first measured Zn L-edge inelastic X-ray absorption spectra combined with calculations, we discover a systematic correlation between the loss of inversion symmetry from pseudo-octahedral (herbertsmithite) to trigonal prismatic coordination (Zn-barlowite) with the emergence of a new peak. Overall, our measurements suggest that Zn-barlowite has structural advantages over herbertsmithite that make its magnetic properties closer to an ideal QSL candidate: its kagome layers are highly resistant to nonmagnetic defects while the interlayers can accommodate a higher amount of Zn substitution., Comment: 13 pages, 6 figures

Published
2020
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3. Tuning Excited State Electron Transfer in Fe Tetracyano-Polypyridyl Complexes

Author

Kunnus, Kristjan, Li, Lin, Titus, Charles J., Lee, Sang Jun, Reinhard, Marco E., Koroidov, Sergey, Kjær, Kasper S., Hong, Kiryong, Ledbetter, Kathryn, Doriese, William B., O'Neil, Galen C., Swetz, Daniel S., Ullom, Joel N., Li, Dale, Irwin, Kent, Nordlund, Dennis, Cordones, Amy A., and Gaffney, Kelly J.

Subjects
Physics - Chemical Physics
Abstract

We have investigated photoinduced intramolecular electron transfer dynamics following metal-to-ligand charge-transfer (MLCT) excitation of [Fe(CN)$_4$(2,2'-bipyridine)]$^{2-}$ (1), [Fe(CN)$_4$(2,3-bis(2-pyridyl)pyrazine)]$^{2-}$ (2) and [Fe(CN)$_4$(2,2'-bipyrimidine)]$^{2-}$ (3) complexes in various solvents with static and time-resolved UV-visible absorption spectroscopy and Fe 2p3d resonant inelastic X-ray scattering. We observe $^3$MLCT lifetimes from 180 fs to 67 ps over a wide range of MLCT energies in different solvents by utilizing the strong solvatochromism of the complexes. Intramolecular electron transfer lifetimes governing $^3$MLCT relaxation increase monotonically and (super)exponentially as the $^3$MLCT energy is decreased in 1 and 2 by changing the solvent. This behavior can be described with non-adiabatic classical Marcus electron transfer dynamics along the indirect $^3$MLCT->$^3$MC pathway, where the $^3$MC is the lowest energy metal-centered (MC) excited state. In contrast, the $^3$MLCT lifetime in 3 changes non-monotonically and exhibits a maximum. This qualitatively different behaviour results from direct electron transfer from the $^3$MLCT to the electronic ground state (GS). This pathway involves nuclear tunnelling for the high-frequency polypyridyl skeleton mode ($\hbar\omega$ = 1530 cm$^{-1}$), which is more displaced for 3 than for either 1 or 2, therefore making the direct pathway significantly more efficient in 3. To our knowledge, this is the first observation of an efficient $^3$MLCT->GS relaxation pathway in an Fe polypyridyl complex. Our study suggests that further extending the MLCT state lifetime requires (1) lowering the $^3$MLCT state energy with respect to the $^3$MC state and (2) suppressing the intramolecular distortion of the electron-accepting ligand in the $^3$MLCT excited state to suppress the rate of direct $^3$MLCT->GS electron transfer.

Published
2019

4. Materializing Rival Ground States in the Barlowite Family of Kagome Magnets: Quantum Spin Liquid, Spin Ordered, and Valence Bond Crystal States

Author

Smaha, Rebecca W., He, Wei, Jiang, Jack Mingde, Titus, Charles J., Wen, Jiajia, Jiang, Yi-Fan, Sheckelton, John P., Wang, Suyin Grass, Chen, Yu-Sheng, Teat, Simon J., Aczel, Adam A., Zhao, Yang, Xu, Guangyong, Lynn, Jeffrey W., Jiang, Hong-Chen, and Lee, Young S.

Subjects
Condensed Matter - Strongly Correlated Electrons
Abstract

The spin-$\frac{1}{2}$ kagome antiferromagnet is considered an ideal host for a quantum spin liquid ground state. We find that when the bonds of the kagome lattice are modulated with a periodic pattern, new quantum ground states emerge. Newly synthesized crystalline barlowite (Cu$_4$(OH)$_6$FBr) and Zn-substituted barlowite demonstrate the delicate interplay between singlet states and spin order on the spin-$\frac{1}{2}$ kagome lattice. Comprehensive structural measurements demonstrate that our new variant of barlowite maintains hexagonal symmetry at low temperatures with an arrangement of distorted and undistorted kagome triangles, for which numerical simulations predict a pinwheel valence bond crystal (VBC) state instead of a quantum spin liquid (QSL). The presence of interlayer spins eventually leads to an interesting pinwheel $q=0$ magnetic order. Partially Zn-substituted barlowite (Cu$_{3.44}$Zn$_{0.56}$(OH)$_6$FBr) has an ideal kagome lattice and shows QSL behavior, indicating a surprising robustness of the QSL against interlayer impurities. The magnetic susceptibility is similar to that of herbertsmithite, even though the Cu$^{2+}$ impurities are above the percolation threshold for the interlayer lattice and they couple more strongly to the nearest kagome moment. This system is a unique playground displaying QSL, VBC, and spin order, furthering our understanding of these highly competitive quantum states., Comment: 31 pages, 7 figures

Published
2019
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6. Site-specific structure at multiple length scales in kagome quantum spin liquid candidates

Author

Smaha, Rebecca W, Boukahil, Idris, Titus, Charles J, Jiang, Jack Mingde, Sheckelton, John P, He, Wei, Wen, Jiajia, Vinson, John, Wang, Suyin Grass, Chen, Yu-Sheng, Teat, Simon J, Devereaux, Thomas P, Pemmaraju, C Das, and Lee, Young S

Subjects
Physical Sciences, Condensed Matter Physics, cond-mat.str-el, cond-mat.mtrl-sci, Macromolecular and materials chemistry, Materials engineering, Condensed matter physics
Abstract

Realizing a quantum spin liquid (QSL) ground state in a real material is a leading issue in condensed matter physics research. In this pursuit, it is crucial to fully characterize the structure and influence of defects, as these can significantly affect the fragile QSL physics. Here, we perform a variety of cutting-edge synchrotron X-ray scattering and spectroscopy techniques, and we advance new methodologies for site-specific diffraction and L-edge Zn absorption spectroscopy. The experimental results along with our first-principles calculations address outstanding questions about the local and long-range structures of the two leading kagome QSL candidates, Zn-substituted barlowite (Cu3Zn x Cu1-x (OH)6FBr) and herbertsmithite (Cu3Zn(OH)6Cl2). On all length scales probed, there is no evidence that Zn substitutes onto the kagome layers, thereby preserving the QSL physics of the kagome lattice. Our calculations show that antisite disorder is not energetically favorable and is even less favorable in Zn-barlowite compared to herbertsmithite. Site-specific X-ray diffraction measurements of Zn-barlowite reveal that Cu2+ and Zn2+ selectively occupy distinct interlayer sites, in contrast to herbertsmithite. Using the first measured Zn L-edge inelastic X-ray absorption spectra combined with calculations, we discover a systematic correlation between the loss of inversion symmetry from pseudo-octahedral (herbertsmithite) to trigonal prismatic coordination (Zn-barlowite) with the emergence of a new peak. Overall, our measurements suggest that Zn-barlowite has structural advantages over herbertsmithite that make its magnetic properties closer to an ideal QSL candidate: its kagome layers are highly resistant to nonmagnetic defects while the interlayers can accommodate a higher amount of Zn substitution.

Published
2020

7. Surface-to-Bulk Redox Coupling through Thermally Driven Li Redistribution in Li- and Mn-Rich Layered Cathode Materials

Author

Li, Shaofeng, Lee, Sang-Jun, Wang, Xuelong, Yang, Wanli, Huang, Hai, Swetz, Daniel S, Doriese, William B, O’Neil, Galen C, Ullom, Joel N, Titus, Charles J, Irwin, Kent D, Lee, Han-Koo, Nordlund, Dennis, Pianetta, Piero, Yu, Chang, Qiu, Jieshan, Yu, Xiqian, Yang, Xiao-Qing, Hu, Enyuan, Lee, Jun-Sik, and Liu, Yijin

Subjects
Engineering, Materials Engineering, Chemical Sciences, Physical Chemistry, General Chemistry, Chemical sciences
Abstract

Li- and Mn-rich (LMR) layered cathode materials have demonstrated impressive capacity and specific energy density thanks to their intertwined redox centers including transition metal cations and oxygen anions. Although tremendous efforts have been devoted to the investigation of the electrochemically driven redox evolution in LMR cathode at ambient temperature, their behavior under a mildly elevated temperature (up to ∼100 °C), with or without electrochemical driving force, remains largely unexplored. Here we show a systematic study of the thermally driven surface-to-bulk redox coupling effect in charged Li1.2Ni0.15Co0.1Mn0.55O2. We for the first time observed a charge transfer between the bulk oxygen anions and the surface transition metal cations under ∼100 °C, which is attributed to the thermally driven redistribution of Li ions. This finding highlights the nonequilibrium state and dynamic nature of the LMR material at deeply delithiated state upon a mild temperature perturbation.

Published
2019

8. L-Edge Spectroscopy of Dilute, Radiation-Sensitive Systems Using a Transition-Edge-Sensor Array

Author

Titus, Charles J., Baker, Michael L., Lee, Sang Jun, Cho, Hsiao-mei, Doriese, William B., Fowler, Joseph W., Gaffney, Kelly, Gard, Johnathon D., Hilton, Gene C., Kenney, Chris, Knight, Jason, Li, Dale, Marks, Ron, Minitti, Michael P., Morgan, Kelsey M., O'Neil, Galen C., Reintsema, Carl D., Schmidt, Daniel R., Sokaras, Dimosthenis, Swetz, Daniel S., Ullom, Joel N., Weng, Tsu-Chien, Williams, Christopher, Young, Betty A., Irwin, Kent D., Solomon, Edward I., and Nordlund, Dennis

Subjects
Physics - Instrumentation and Detectors
Abstract

We present X-ray absorption spectroscopy and resonant inelastic X-ray scattering (RIXS) measurements on the iron L-edge of 0.5 mM aqueous ferricyanide. These measurements demonstrate the ability of high-throughput transition-edge-sensor (TES) spectrometers to access the rich soft X-ray (100-2000eV) spectroscopy regime for dilute and radiation-sensitive samples. Our low-concentration data are in agreement with high-concentration measurements recorded by conventional grating-based spectrometers. These results show that soft X-ray RIXS spectroscopy acquired by high-throughput TES spectrometers can be used to study the local electronic structure of dilute metal-centered complexes relevant to biology, chemistry and catalysis. In particular, TES spectrometers have a unique ability to characterize frozen solutions of radiation- and temperature-sensitive samples., Comment: 19 pages, 4 figures

Published
2017
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13. Correction to “Quantifying the Steric Effect on Metal–Ligand Bonding in Fe Carbene Photosensitizers with Fe 2p3d Resonant Inelastic X-ray Scattering”

Author

Kunnus, Kristjan, primary, Guo, Meiyuan, additional, Biasin, Elisa, additional, Larsen, Christopher B., additional, Titus, Charles J., additional, Lee, Sang Jun, additional, Liu, Yizhu, additional, Wärnmark, Kenneth, additional, Nordlund, Dennis, additional, Cordones, Amy A., additional, Uhlig, Jens, additional, and Gaffney, Kelly J., additional

Published
2023
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14. Scrutinizing formally NiIV centers through the lenses of core spectroscopy, molecular orbital theory, and valence bond theory

Author

DiMucci, Ida M., primary, Titus, Charles J., additional, Nordlund, Dennis, additional, Bour, James R., additional, Chong, Eugene, additional, Grigas, Dylan P., additional, Hu, Chi-Herng, additional, Kosobokov, Mikhail D., additional, Martin, Caleb D., additional, Mirica, Liviu M., additional, Nebra, Noel, additional, Vicic, David A., additional, Yorks, Lydia L., additional, Yruegas, Sam, additional, MacMillan, Samantha N., additional, Shearer, Jason, additional, and Lancaster, Kyle M., additional

Published
2023
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20. Trends in Carbon, Oxygen, and Nitrogen Core in the X-ray Absorption Spectroscopy of Carbon Nanomaterials : A Guide for the Perplexed

Author

Sainio, Sami, Wester, Niklas, Aarva, Anja, Titus, Charles J., Nordlund, Dennis, Kauppinen, Esko I., Leppänen, Elli, Palomäki, Tommi, Koehne, Jessica E., Pitkänen, Olli, Kordas, Krisztian, Kim, Maria, Lipsanen, Harri, Mozetič, Miran, Caro, Miguel A., Meyyappan, M., Koskinen, Jari, Laurila, Tomi, Stanford University, Department of Chemistry and Materials Science, Department of Electrical Engineering and Automation, Department of Applied Physics, NASA Ames Research Center, University of Oulu, Department of Electronics and Nanoengineering, J. Stefan Institute, Aalto-yliopisto, and Aalto University

Abstract

openaire: EC/H2020/824070/EU//CONNECT Successful deployment of carbon nanomaterials in many applications, such as sensing, energy storage, and catalysis, relies on the selection, synthesis, and tailoring of the surface properties. Predictive analysis of the behavior is difficult without detailed knowledge of the differences between various carbon nanomaterials and their surface functionalization, thus leaving the selection process to traditional trial-and-error work. The present characterization fills this knowledge gap for carbon nanomaterial surface properties with respect to chemical states and functionalization. We present an overview of the chemical trends that can be extracted from soft X-ray absorption spectroscopy (XAS) spectra on an extended set of nonideal carbon nanomaterials as a function of sp2 bonded carbon and bond ordering. In particular, the surface chemical state, the presence of long-range order in the carbon matrix, and a qualitative estimation of the amount of oxygen and nitrogen and their respective functional group formation on the material surface, together with the detailed material fabrication parameters, are reported. The results expand our understanding of carbon nanomaterial functionalization, which can support material selection in practice, provided that the specifications of the application are known.

Published
2021

21. Trends in Carbon, Oxygen, and Nitrogen Core in the X-ray Absorption Spectroscopy of Carbon Nanomaterials: A Guide for the Perplexed

Author

Sainio, Sami, primary, Wester, Niklas, additional, Aarva, Anja, additional, Titus, Charles J., additional, Nordlund, Dennis, additional, Kauppinen, Esko I., additional, Leppänen, Elli, additional, Palomäki, Tommi, additional, Koehne, Jessica E., additional, Pitkänen, Olli, additional, Kordas, Krisztian, additional, Kim, Maria, additional, Lipsanen, Harri, additional, Mozetič, Miran, additional, Caro, Miguel A., additional, Meyyappan, M., additional, Koskinen, Jari, additional, and Laurila, Tomi, additional

Published
2020
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24. Materializing rival ground states in the barlowite family of kagome magnets: quantum spin liquid, spin ordered, and valence bond crystal states

Author

Smaha, Rebecca W., primary, He, Wei, additional, Jiang, Jack Mingde, additional, Wen, Jiajia, additional, Jiang, Yi-Fan, additional, Sheckelton, John P., additional, Titus, Charles J., additional, Wang, Suyin Grass, additional, Chen, Yu-Sheng, additional, Teat, Simon J., additional, Aczel, Adam A., additional, Zhao, Yang, additional, Xu, Guangyong, additional, Lynn, Jeffrey W., additional, Jiang, Hong-Chen, additional, and Lee, Young S., additional

Published
2020
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25. Saturation and self-absorption effects in the angle-dependent 2 p3d resonant inelastic X-ray scattering spectra of Co3+

Author

Wang, Ru Pan, Elnaggar, Hebatalla, Titus, Charles J., Tomiyasu, Keisuke, Geessinck, Jaap, Koster, Gertjan, Frati, Federica, Okamoto, Jun, Huang, Di Jing, De Groot, Frank M.F., Wang, Ru Pan, Elnaggar, Hebatalla, Titus, Charles J., Tomiyasu, Keisuke, Geessinck, Jaap, Koster, Gertjan, Frati, Federica, Okamoto, Jun, Huang, Di Jing, and De Groot, Frank M.F.

Abstract

Angle-dependent 2p3d resonant inelastic X-ray scattering spectra of a LaCoO3 single crystal and a 55 nm LaCoO3 film on a SrTiO3 substrate are presented. Theoretical calculation shows that, with ∼20 meV resolved Co 2p3d resonant inelastic X-ray scattering (RIXS), the excited states of the isotropic 1A1g (O h) ground state are split by 3d spin-orbit coupling, which can be distinguished via their angular dependence. However, strong self-absorption and saturation effects distort the spectra of the LaCoO3 single crystal and limit the observation of small angular dependence. In contrast, the RIXS on 55 nm LaCoO3 shows less self-absorption effects and preserves the angular dependence of the excited states.

Published
2020

26. Chemical control of competing electron transfer pathways in iron tetracyano-polypyridyl photosensitizers

Author

Kunnus, Kristjan, primary, Li, Lin, additional, Titus, Charles J., additional, Lee, Sang Jun, additional, Reinhard, Marco E., additional, Koroidov, Sergey, additional, Kjær, Kasper S., additional, Hong, Kiryong, additional, Ledbetter, Kathryn, additional, Doriese, William B., additional, O'Neil, Galen C., additional, Swetz, Daniel S., additional, Ullom, Joel N., additional, Li, Dale, additional, Irwin, Kent, additional, Nordlund, Dennis, additional, Cordones, Amy A., additional, and Gaffney, Kelly J., additional

Published
2020
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27. X-ray absorption spectroscopy of organic sulfoxides

Author

Vogt, Linda I., primary, Cotelesage, Julien J. H., additional, Dolgova, Natalia V., additional, Titus, Charles J., additional, Sharifi, Samin, additional, George, Simon J., additional, Pickering, Ingrid J., additional, and George, Graham N., additional

Published
2020
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28. Single-ion magnetism in the extended solid-state: insights from X-ray absorption and emission spectroscopy

Author

Huzan, Myron S., primary, Fix, Manuel, additional, Aramini, Matteo, additional, Bencok, Peter, additional, Mosselmans, J. Frederick W., additional, Hayama, Shusaku, additional, Breitner, Franziska A., additional, Gee, Leland B., additional, Titus, Charles J., additional, Arrio, Marie-Anne, additional, Jesche, Anton, additional, and Baker, Michael L., additional

Published
2020
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29. The Myth of d8 Copper(III)

Author

DiMucci, Ida M., primary, Lukens, James T., additional, Chatterjee, Sudipta, additional, Carsch, Kurtis M., additional, Titus, Charles J., additional, Lee, Sang Jun, additional, Nordlund, Dennis, additional, Betley, Theodore A., additional, MacMillan, Samantha N., additional, and Lancaster, Kyle M., additional

Published
2019
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30. Soft X-ray spectroscopy with transition-edge sensors at Stanford Synchrotron Radiation Lightsource beamline 10-1

Author

Lee, Sang-Jun, primary, Titus, Charles J., additional, Alonso Mori, Roberto, additional, Baker, Michael L., additional, Bennett, Douglas A., additional, Cho, Hsiao-Mei, additional, Doriese, William B., additional, Fowler, Joseph W., additional, Gaffney, Kelly J., additional, Gallo, Alessandro, additional, Gard, Johnathon D., additional, Hilton, Gene C., additional, Jang, Hoyoung, additional, Joe, Young Il, additional, Kenney, Christopher J., additional, Knight, Jason, additional, Kroll, Thomas, additional, Lee, Jun-Sik, additional, Li, Dale, additional, Lu, Donghui, additional, Marks, Ronald, additional, Minitti, Michael P., additional, Morgan, Kelsey M., additional, Ogasawara, Hirohito, additional, O’Neil, Galen C., additional, Reintsema, Carl D., additional, Schmidt, Daniel R., additional, Sokaras, Dimosthenis, additional, Ullom, Joel N., additional, Weng, Tsu-Chien, additional, Williams, Christopher, additional, Young, Betty A., additional, Swetz, Daniel S., additional, Irwin, Kent D., additional, and Nordlund, Dennis, additional

Published
2019
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32. Two-Level Switches for Advanced Time-Division Multiplexing

Author

Dawson, Carl S., primary, Chaudhuri, Saptarshi, additional, Titus, Charles J., additional, Cho, Hsiao-Mei, additional, Denison, Edward V., additional, Doriese, W. Bertrand, additional, Durkin, Malcolm, additional, FitzGerald, Connor T., additional, Hilton, Gene C., additional, Irwin, Kent D., additional, Li, Dale, additional, O'Neil, Galen C., additional, Reintsema, Carl D., additional, Steffen, Zach, additional, Stevens, Robert W., additional, Swetz, Daniel S., additional, Ullom, Joel N., additional, Vale, Leila R., additional, Weber, Joel C., additional, and Young, Betty A., additional

Published
2019
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34. Use of Transition Models to Design High Performance TESs for the LCLS-II Soft X-Ray Spectrometer

Author

Morgan, Kelsey M., primary, Becker, Dan T., additional, Bennett, Douglas Alan, additional, Doriese, William B., additional, Gard, Johnathon D., additional, Irwin, Kent D., additional, Lee, Sang Jun, additional, Li, Dale, additional, Mates, John A. B., additional, Pappas, Christine G., additional, Schmidt, Dan R., additional, Titus, Charles J., additional, Van Winkle, Dan D., additional, Ullom, Joel N., additional, Wessels, Abigail, additional, and Swetz, Daniel S., additional

Published
2019
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35. High-Throughput, DC-Parametric Evaluation of Flux-Activated-Switch-Based TDM and CDM SQUID Multiplexers

Author

Reintsema, Carl D., primary, Bennett, Doug A., additional, Denison, Edward V., additional, Durkin, Malcolm, additional, Doriese, Willaim B., additional, Fowler, Joseph W., additional, Gard, Johnathon D., additional, Grigorian, Arpi, additional, Hilton, Gene C., additional, Hubmayr, Johannes, additional, O'Neil, Galen C., additional, Mates, John A. B., additional, Morgan, Kelsey M., additional, Schmidt, Dan R., additional, Stevens, Robert W., additional, Swetz, Daniel S., additional, Vale, Leila R., additional, Ullom, Joel N., additional, Irwin, Kent D., additional, Chaudhuri, Saptarshi, additional, Titus, Charles J., additional, and Dawson, Carl S., additional

Published
2019
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36. Hybrid X-ray Spectroscopy-Based Approach To Acquire Chemical and Structural Information of Single-Walled Carbon Nanotubes with Superior Sensitivity

Author

Sainio, Sami, primary, Wester, Niklas, additional, Titus, Charles J., additional, Liao, Yongping, additional, Zhang, Qiang, additional, Nordlund, Dennis, additional, Sokaras, Dimosthenis, additional, Lee, Sang-jun, additional, Irwin, Kent D., additional, Doriese, William B., additional, O’Neil, Galen C., additional, Swetz, Daniel S., additional, Ullom, Joel N., additional, Kauppinen, Esko I., additional, Laurila, Tomi, additional, and Koskinen, Jari, additional

Published
2019
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38. Saturation and self‐absorption effects in the angle‐dependent 2p3d resonant inelastic X‐ray scattering spectra of Co3+.

Author

Wang, Ru-Pan, Elnaggar, Hebatalla, Titus, Charles J., Tomiyasu, Keisuke, Geessinck, Jaap, Koster, Gertjan, Frati, Federica, Okamoto, Jun, Huang, Di-Jing, and de Groot, Frank M. F.

Abstract

Angle‐dependent 2p3d resonant inelastic X‐ray scattering spectra of a LaCoO3 single crystal and a 55 nm LaCoO3 film on a SrTiO3 substrate are presented. Theoretical calculation shows that, with ∼20 meV resolved Co 2p3d resonant inelastic X‐ray scattering (RIXS), the excited states of the isotropic 1A1g(Oh) ground state are split by 3d spin–orbit coupling, which can be distinguished via their angular dependence. However, strong self‐absorption and saturation effects distort the spectra of the LaCoO3 single crystal and limit the observation of small angular dependence. In contrast, the RIXS on 55 nm LaCoO3 shows less self‐absorption effects and preserves the angular dependence of the excited states. [ABSTRACT FROM AUTHOR]

Published
2020
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40. L-edge spectroscopy of dilute, radiation-sensitive systems using a transition-edge-sensor array

Author

Titus, Charles J., primary, Baker, Michael L., additional, Lee, Sang Jun, additional, Cho, Hsiao-Mei, additional, Doriese, William B., additional, Fowler, Joseph W., additional, Gaffney, Kelly, additional, Gard, Johnathon D., additional, Hilton, Gene C., additional, Kenney, Chris, additional, Knight, Jason, additional, Li, Dale, additional, Marks, Ronald, additional, Minitti, Michael P., additional, Morgan, Kelsey M., additional, O’Neil, Galen C., additional, Reintsema, Carl D., additional, Schmidt, Daniel R., additional, Sokaras, Dimosthenis, additional, Swetz, Daniel S., additional, Ullom, Joel N., additional, Weng, Tsu-Chien, additional, Williams, Christopher, additional, Young, Betty A., additional, Irwin, Kent D., additional, Solomon, Edward I., additional, and Nordlund, Dennis, additional

Published
2017
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41. [(MeCN)Ni(CF3)3]−and [Ni(CF3)4]2–: Foundations toward the Development of Trifluoromethylations at Unsupported Nickel

Author

Shreiber, Scott T., DiMucci, Ida M., Khrizanforov, Mikhail N., Titus, Charles J., Nordlund, Dennis, Dudkina, Yulia, Cramer, Roger E., Budnikova, Yulia, Lancaster, Kyle M., and Vicic, David A.

Abstract

Nickel anions [(MeCN)Ni(CF3)3]−and [Ni(CF3)4]2–were prepared by the formal addition of 3 and 4 equiv, respectively, of AgCF3to [(dme)NiBr2] in the presence of the [PPh4]+counterion. Detailed insights into the electronic properties of these new compounds were obtained through the use of density functional theory (DFT) calculations, spectroscopy-oriented configuration interaction (SORCI) calculations, X-ray absorption spectroscopy, and cyclic voltammetry. The data collectively show that trifluoromethyl complexes of nickel, even in the most common oxidation state of nickel(II), are highly covalent systems whereby a hole is distributed on the trifluoromethyl ligands, surprisingly rendering the metal to a physically more reduced state. In the cases of [(MeCN)Ni(CF3)3]−and [Ni(CF3)4]2–, these complexes are better physically described as d9metal complexes. [(MeCN)Ni(CF3)3]−is electrophilic and reacts with other nucleophiles such as phenoxide to yield the unsupported [(PhO)Ni(CF3)3]2–salt, revealing the broader potential of [(MeCN)Ni(CF3)3]−in the development of “ligandless” trifluoromethylations at nickel. Proof-in-principle experiments show that the reaction of [(MeCN)Ni(CF3)3]−with an aryl iodonium salt yields trifluoromethylated arene, presumably via a high-valent, unsupported, and formal organonickel(IV) intermediate. Evidence of the feasibility of such intermediates is provided with the structurally characterized [PPh4]2[Ni(CF3)4(SO4)], which was derived through the two-electron oxidation of [Ni(CF3)4]2–.

Published
2020
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42. The Myth of d8 Copper(III).

Author

DiMucci, Ida M., Lukens, James T., Chatterjee, Sudipta, Carsch, Kurtis M., Titus, Charles J., Lee, Sang Jun, Nordlund, Dennis, Betley, Theodore A., MacMillan, Samantha N., and Lancaster, Kyle M.

Published
2019
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46. Characterization of optima in smooth Pareto economic systems

Author

University of Michigan, Ann Arbor, Mich. 48103, USA, Simon, Carl P., Titus, Charles J., University of Michigan, Ann Arbor, Mich. 48103, USA, Simon, Carl P., and Titus, Charles J.

Abstract

Simple techniques of calculus and geometry are used to study and characterize the optima of pure exchange economies in which the utility functions are smooth but not necessarily convex. It is also shown how one can reduce the problem of optimizing p functions on the manifold of states to that of maximizing a single function on a submanifold of this space. Two models are described: one in which a person cannot trade to an optimum unless he starts at one; and one in which a person cannot even get near a local Pareto optimum along continuous `trade curves' from most initial distributions. Finally, the set of optima is described for a generic set of utility mappings.

Published
2006

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