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202 results on '"Kikkawa, James M."'

1. Electrically Tunable Magnetoconductance of Close-Packed CVD Bilayer Graphene Layer Stacking Walls

Author

Zhang, Qicheng, Wang, Sheng, Gao, Zhaoli, Hurtado-Parra, Sebastian, Berry, Joel, Addison, Zachariah, Das, Paul Masih, Parkin, William M., Drndic, Marija, Kikkawa, James M., Wang, Feng, Mele, Eugene J., Johnson, A. T. Charlie, and Luo, Zhengtang

Subjects
Condensed Matter - Mesoscale and Nanoscale Physics, Condensed Matter - Materials Science
Abstract

Quantum valley Hall (QVH) domain wall states are a new class of one-dimensional (1D) one-way conductors that are topologically protected in the absence of valley mixing. Development beyond a single QVH channel raises important new questions as to how QVH channels in close spatial proximity interact with each other, and how that interaction may be controlled. Scalable epitaxial bilayer graphene synthesis produces layer stacking wall (LSW) bundles, where QVH channels are bound, providing an excellent platform to study QVH channel interactions. Here we show that distinct strain sources lead to the formation of both well-separated LSWs and close packed LSW bundles. Comparative studies of electronic transport in these two regimes reveal that close-packed LSW bundles support electrically tunable magnetoconductance. The coexistence of different strain sources offers a potential pathway to realize scalable quantum transport platform based on LSWs where electrically tunability enables programmable functionality.

Published
2024

2. High Purity Orbital Angular Momentum of Light

Author

Sontag, Andrew, Noyan, Mehmet A., and Kikkawa, James M.

Subjects
Physics - Optics
Abstract

We present a novel technique for generating beams of light carrying orbital angular momentum (OAM) that increases mode purity and decreases singularity splitting by orders of magnitude. This technique also works to control and mitigate beam divergence within propagation distances less than the Rayleigh length. Additionally, we analyze a tunable parameter of this technique that can change the ratio of beam purity to power to fit desired specifications. Beam generation via this technique is achievable using only phase-modulating optical elements, which reduces experimental complexity and beam energy loss., Comment: 9 pages, 7 figures, submitted to Optics Express 18 August 2022

Published
2022
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3. Anomalous Hall and Nernst effects in epitaxial films of topological kagome magnet Fe3Sn2

Author

Khadka, Durga, Thapaliya, T. R., Parra, Sebastian Hurtado, Wen, Jiajia, Need, Ryan, Kikkawa, James M., and Huang, S. X.

Subjects
Condensed Matter - Materials Science, Condensed Matter - Mesoscale and Nanoscale Physics, Condensed Matter - Strongly Correlated Electrons
Abstract

The topological kagome magnet (TKM) Fe3Sn2 exhibits unusual topological properties, flat electronic bands, and chiral spin textures, making it an exquisite materials platform to explore the interplay between topological band structure, strong electron correlations, and magnetism. Here we report the first synthesis of high-quality epitaxial (0001) Fe3Sn2 films with large intrinsic anomalous Hall effect close to that measured in bulk single crystals. In addition, we measured a large, anisotropic anomalous Nernst coefficient Syx of 1.26 {\mu}V/K, roughly 2-5x greater than that of common ferromagnets, suggesting the presence of Berry curvature sources near the Fermi level in this system. Crucially, the realization of high-quality Fe3Sn2 films opens the door to explore emergent interfacial physics and create novel spintronic devices based on TKMs by interfacing Fe3Sn2 with other quantum materials and by nanostructure patterning., Comment: accepted by Physical Review Materials

Published
2020
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4. Kondo physics in antiferromagnetic Weyl semimetal Mn3+xSn1-x films

Author

Khadka, Durga, Thapaliya, T. R., Parra, Sebastian Hurtado, Han, Xingyue, Wen, Jiajia, Need, Ryan F., Khanal, Pravin, Wang, Weigang, Zang, Jiadong, Kikkawa, James M., Wu, Liang, and Huang, S. X.

Subjects
Condensed Matter - Materials Science, Condensed Matter - Mesoscale and Nanoscale Physics, Condensed Matter - Strongly Correlated Electrons
Abstract

Topology and strong electron correlations are crucial ingredients in emerging quantum materials, yet their intersection in experimental systems has been relatively limited to date. Strongly correlated Weyl semimetals, particularly when magnetism is incorporated, offer a unique and fertile platform to explore emergent phenomena in novel topological matter and topological spintronics. The antiferromagnetic Weyl semimetal Mn3Sn exhibits many exotic physical properties such as a large spontaneous Hall effect and has recently attracted intense interest. In this work, we report synthesis of epitaxial Mn3+xSn1-x films with greatly extended compositional range in comparison with that of bulk samples. As Sn atoms are replaced by magnetic Mn atoms, the Kondo effect, which is a celebrated example of strong correlations, emerges, develops coherence, and induces a hybridization energy gap. The magnetic doping and gap opening lead to rich extraordinary properties as exemplified by the prominent DC Hall effects and resonance-enhanced terahertz Faraday rotation.

Published
2020
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5. Tailoring Hot Exciton Dynamics in 2D Hybrid Perovskites through Cation Modification

Author

Straus, Daniel B., Hurtado-Parra, Sebastian, Iotov, Natasha, Zhao, Qinghua, Gau, Michael R., Carroll, Patrick J., Kikkawa, James M., and Kagan, Cherie R.

Subjects
Physics - Applied Physics, Condensed Matter - Materials Science, Physics - Chemical Physics
Abstract

We report a family of two-dimensional hybrid perovskites (2DHPs) based on phenethylammonium lead iodide ((PEA)$_2$PbI$_4$) that show complex structure in their low-temperature excitonic absorption and photoluminescence (PL) spectra as well as hot exciton PL. We replace the 2-position (ortho) H on the phenyl group of the PEA cation with F, Cl, or Br to systematically increase the cation's cross-sectional area and mass and study changes in the excitonic structure. These single atom substitutions substantially change the observable number of and spacing between discrete resonances in the excitonic absorption and PL spectra and drastically increase the amount of hot exciton PL that violates Kasha's rule by over an order of magnitude. To fit the progressively larger cations, the inorganic framework distorts and is strained, reducing the Pb-I-Pb bond angles and increasing the 2DHP band gap. Correlation between the 2DHP structure and steady-state and time-resolved spectra suggests the complex structure of resonances arises from one or two manifolds of states, depending on the 2DHP Pb-I-Pb bond angle (as)symmetry, and the resonances within a manifold are regularly spaced with an energy separation that decreases as the mass of the cation increases. The uniform separation between resonances and the dynamics that show excitons can only relax to the next-lowest state are consistent with a vibronic progression caused by a vibrational mode on the cation. These results demonstrate that simple changes to the structure of the cation can be used to tailor the properties and dynamics of the confined excitons without directly modifying the inorganic framework., Comment: 39 pages

Published
2020
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6. Large-area epitaxial growth of curvature-stabilized ABC trilayer graphene.

Author

Gao, Zhaoli, Wang, Sheng, Berry, Joel, Zhang, Qicheng, Gebhardt, Julian, Parkin, William M, Avila, Jose, Yi, Hemian, Chen, Chaoyu, Hurtado-Parra, Sebastian, Drndić, Marija, Rappe, Andrew M, Srolovitz, David J, Kikkawa, James M, Luo, Zhengtang, Asensio, Maria C, Wang, Feng, and Johnson, AT Charlie

Abstract

The properties of van der Waals (vdW) materials often vary dramatically with the atomic stacking order between layers, but this order can be difficult to control. Trilayer graphene (TLG) stacks in either a semimetallic ABA or a semiconducting ABC configuration with a gate-tunable band gap, but the latter has only been produced by exfoliation. Here we present a chemical vapor deposition approach to TLG growth that yields greatly enhanced fraction and size of ABC domains. The key insight is that substrate curvature can stabilize ABC domains. Controllable ABC yields ~59% were achieved by tailoring substrate curvature levels. ABC fractions remained high after transfer to device substrates, as confirmed by transport measurements revealing the expected tunable ABC band gap. Substrate topography engineering provides a path to large-scale synthesis of epitaxial ABC-TLG and other vdW materials.

Published
2020

14. Binary nanocrystal superlattice membranes self-assembled at the liquid-air interface

Author

Dong, Angang, Chen, Jun, Vora, Patrick M., Kikkawa, James M., and Murray, Christopher B.

Subjects
Properties, Nanocrystals -- Properties, Superlattices -- Properties, Superlattices as materials -- Properties
Abstract

In comparison with the growth of single-component superlattices (11), the assembly process for BNSLs is more complicated, with a number of distinct pairwise interactions (van der Waals, dipolar, Coulombic and [...], The spontaneous organization of multicomponent micrometresized colloids (1) or nanocrystals (2) into superlattices is of scientific importance for understanding the assembly process on the nanometre scale and is of great interest for bottom-up fabrication of functional devices. In particular, co-assembly of two types of nanocrystal into binary nanocrystal superlattices (BNSLs) has recently attracted significant attention (2-8), as this provides a low-cost, programmable way to design metamaterials (4) with precisely controlled properties that arise from the organization and interactions of the constituent nanocrystal components (9). Although challenging, the ability to grow and manipulate large-scale BNSLs is critical for extensive exploration of this new class of material. Here we report a general method of growing centimetre-scale, uniform membranes of BNSLs that can readily be transferred to arbitrary substrates. Our method is based on the liquid-air interfacial assembly of multicomponent nanocrystals and circumvents the limitations associated with the current assembly strategies, allowing integration of BNSLs on any substrate for the fabrication of nanocrystal-based devices (10). We demonstrate the construction of magnetoresistive devices by incorporating large-area (1.5 mm x 2.5 mm) BNSL membranes; their magnetotransport measurements clearly show that device magnetoresistance is dependent on the structure (stoichiometry) of the BNSLs. The ability to transfer BNSLs also allows the construction of free-standing membranes and other complex architectures that have not been accessible previously.

Published
2010
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15. Robotic Microcapsule Assemblies with Adaptive Mobility for Targeted Treatment of Rugged Biological Microenvironments

Author

Tran, Hong Huy, Xiang, Zhenting, Oh, Min Jun, Liu, Yuan, Ren, Zhi, Chen, Chider, Jaruchotiratanasakul, Nadasinee, Kikkawa, James M., Lee, Daeyeon, Koo, Hyun, and Steager, Edward

Abstract

Microrobots are poised to transform biomedicine by enabling precise, noninvasive procedures. However, current magnetic microrobots, composed of solid monolithic particles, present fundamental challenges in engineering intersubunit interactions, limiting their collective effectiveness in navigating irregular biological terrains and confined spaces. To address this, we design hierarchically assembled microrobots with multiaxis mobility and collective adaptability by engineering the potential magnetic interaction energy between subunits to create stable, self-reconfigurable structures capable of carrying and protecting cargo internally. Using double emulsion templates and magnetic control techniques, we confine 10 nm iron oxide and 15 nm silica nanoparticles within the shell of 100 μm microcapsules that form multiunit robotic collectives. Unexpectedly, we find that asymmetric localization of iron oxide nanoparticles in the microcapsules enhances the intercapsule potential energy, creating stable connections under rotating magnetic fields without altering the magnetic susceptibility. These robotic microcapsule collectives exhibit emergent behaviors, self-reconfiguring into kinematic chain-like structures to traverse complex obstacles, arched confinements, and adhesive, rugged biological tissues that typically impede microscale systems. By harnessing these functions, we demonstrate targeted antifungal delivery using a localized biofilm model on mucosal tissues, showing effective killing ofCandidawithout binding or causing physical damage to host cells. Our findings show how hierarchical assembly can produce cargo-carrying microrobots with collective, self-adaptive mobility for traversing complex biological environments, advancing targeted delivery for biomedical applications.

Published
2025
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16. Paramagnetic Organocobalt Capsule Reveals Xe Host-Guest Chemistry

Author

Du, Kang, Zemerov, Serge D., Parra, Sebastian Hurtado, Kikkawa, James M., and Dmochowski, Ivan J.

Subjects
Article
Abstract

We investigated Xe binding in a previously reported paramagnetic metal-organic tetrahedral capsule, [Co(4)L(6)](4−), where L(2−) = 4,4'-bis[(2-pyridinylmethylene)amino]-[1,1'-biphenyl]-2,2'-disulfonate. The Xe-inclusion complex, [XeCo(4)L(6)](4−), was confirmed by (1)H NMR spectroscopy to be the dominant species in aqueous solution saturated with Xe gas. The measured Xe dissociation rate in [XeCo(4)L(6)](4−) (4.4(5) × 10(2) s(−1)) was at least forty times greater than in the analogous [XeFe(4)L(6)](4−) complex, highlighting the capability of metal-ligand interactions to tune capsule size and guest permeability. The rapid exchange of (129)Xe nuclei in [XeCo(4)L(6)](4−) produced significant hyperpolarized (129)Xe chemical exchange saturation transfer (hyper-CEST) NMR signal at 298 K, detected at a concentration of [XeCo(4)L(6)](4−) as low as 100 pM, with presaturation at −89 ppm, which was referenced to solvated (129)Xe in H(2)O. The saturation offset was highly temperature-dependent with a slope of −0.41(3) ppm/K, which is attributed to hyperfine interactions between the encapsulated (129)Xe nucleus and electron spins on the four Co(II) centers. As such, [XeCo(4)L(6)](4−) represents the first example of a paramagnetic hyper-CEST (paraHYPERCEST) sensor. Remarkably, the hyper-CEST (129)Xe NMR resonance for [XeCo(4)L(6)](4−) (δ = −89 ppm) was shifted 105 ppm upfield from the diamagnetic analog [XeFe(4)L(6)](4−) (δ = +16 ppm). The Xe inclusion complex was further characterized in the crystal structure of (C(NH(2))(3))(4)[Xe(0.7)Co(4)L(6)]·75 H(2)O (1). Hydrogen bonding between capsule-linker sulfonate groups and exogenous guanidinium cations, (C(NH(2))(3))(+), stabilized capsule-capsule interactions in the solid-state, and also assisted in trapping a Xe atom (~42 Å(3)) in the large (135 Å(3)) cavity of 1. Magnetic susceptibility measurements confirmed the presence of four non-interacting, magnetically anisotropic high-spin Co(II) centers in 1. Furthermore, [Co(4)L(6)](4−) was found to be stable towards aggregation and oxidation, and the CEST performance of [XeCo(4)L(6)](4−) was unaffected by biological macromolecules in H(2)O. These results recommend metal-organic capsules for fundamental investigations of Xe host-guest chemistry as well as applications with highly sensitive (129)Xe-based sensors.

Published
2020

17. Kondo physics in antiferromagnetic Weyl semimetal Mn3+ xSn1− xfilms

Author

Khadka, Durga, primary, Thapaliya, T. R., additional, Hurtado Parra, Sebastian, additional, Han, Xingyue, additional, Wen, Jiajia, additional, Need, Ryan F., additional, Khanal, Pravin, additional, Wang, Weigang, additional, Zang, Jiadong, additional, Kikkawa, James M., additional, Wu, Liang, additional, and Huang, S. X., additional

Published
2020
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21. Electron spin and optical coherence in semiconductors

Author

Awschalom, David D. and Kikkawa, James M.

Subjects
Semiconductors -- Research, Coherence (Optics) -- Research, Coherent states -- Research, Electron transport -- Research, Physics
Abstract

Electron-hole pairs in semiconductors may be altered through ultrafast laser pulses and magnetic fields. These two methods may also be used in preserving electron spin states over long times and distances.

Published
1999

22. Alternate current magnetic property characterization of nonstoichiometric zinc ferrite nanocrystals for inductor fabrication via a solution based process.

Author

Hongseok Yun, Jungkwun Kim, Taejong Paik, Lingyao Meng, Pil Sung Jo, Kikkawa, James M., Kagan, Cherie R., Allen, Mark G., and Murray, Christopher B.

Subjects
NANOCRYSTALS, ZINC ferrites, FERRITES, MAGNETIC materials, SOLENOIDS
Abstract

We investigate the ac magnetic behavior of solution processable, non-stoichiometric zinc ferrite nanocrystals with a series of sizes and zinc concentrations. Nearly monodisperse ZnxFe3-xO4 nanocrystals (x = 0-0.25) with an average size ranging from 7.4 nm to 13.8 nm are synthesized by using a solvothermal method. All the nanocrystals are in a superparamagnetic state at 300 K, which is confirmed by Superconductive Quantum Interference Device magnetometry. Due to the doping of non-magnetic Zn2+ into A site of ferrite, the saturation magnetization of nanocrystals increases as the size and Zn concentration increases. The ac magnetic permeability measurements at radio frequencies reveal that the real part of the magnetic permeability of similarly sized ferrite nanocrystals can be enhanced by almost twofold as the Zn2+ doping level increases from 0 to 0.25. The integration of 12.3 nm Zn0.25Fe2.75O4 nanocrystals into a toroidal inductor and a solenoid inductor prepared via a simple solution cast process yields a higher quality factors than air core inductors with the same geometries up to 5MHz and 9MHz, respectively, which is in the regime of the switching frequencies for the advanced integrated power converters. [ABSTRACT FROM AUTHOR]

Published
2016
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23. Large-area epitaxial growth of curvature-stabilized ABC trilayer graphene

Author

Centre National de la Recherche Scientifique (France), Commissariat à l'Ènergie Atomique et aux Ènergies Alternatives (France), Department of Energy (US), Guangdong Science and Technology Department, German Research Foundation, National Science Foundation (US), Gao, Zhaoli, Wang, Sheng, Berry, Joel, Zhang, Qicheng, Gebhardt, Julian, Parkin, William M., Ávila, José, Yi, Hemian, Chen, Chaoyu, Hurtado-Parra, Sebastián, Drndić, Marija, Rappe, Andrew M., Srolovitz, David J., Kikkawa, James M., Luo, Zhengtang, Asensio, María C., Wang, Feng, Johnson, A. T. Charlie, Centre National de la Recherche Scientifique (France), Commissariat à l'Ènergie Atomique et aux Ènergies Alternatives (France), Department of Energy (US), Guangdong Science and Technology Department, German Research Foundation, National Science Foundation (US), Gao, Zhaoli, Wang, Sheng, Berry, Joel, Zhang, Qicheng, Gebhardt, Julian, Parkin, William M., Ávila, José, Yi, Hemian, Chen, Chaoyu, Hurtado-Parra, Sebastián, Drndić, Marija, Rappe, Andrew M., Srolovitz, David J., Kikkawa, James M., Luo, Zhengtang, Asensio, María C., Wang, Feng, and Johnson, A. T. Charlie

Abstract

The properties of van der Waals (vdW) materials often vary dramatically with the atomic stacking order between layers, but this order can be difficult to control. Trilayer graphene (TLG) stacks in either a semimetallic ABA or a semiconducting ABC configuration with a gate-tunable band gap, but the latter has only been produced by exfoliation. Here we present a chemical vapor deposition approach to TLG growth that yields greatly enhanced fraction and size of ABC domains. The key insight is that substrate curvature can stabilize ABC domains. Controllable ABC yields ~59% were achieved by tailoring substrate curvature levels. ABC fractions remained high after transfer to device substrates, as confirmed by transport measurements revealing the expected tunable ABC band gap. Substrate topography engineering provides a path to large-scale synthesis of epitaxial ABC-TLG and other vdW materials.

Published
2020

24. Assembly of submicrometre ferromagnets in gallium arsenide semiconductors

Author

Shi, Jing, Kikkawa, James M., Proksch, Roger, Schaffer, Tilman, Awschalom, David D., Medeiros-Ribeiro, Gilberto, and Petroff, Pierre M.

Subjects
Gallium arsenide semiconductors -- Research, Ferromagnetism -- Observations, Magneto-optical devices, Environmental issues, Science and technology, Zoology and wildlife conservation
Abstract

The incorporation of submicrometre ferromagnetic structures into a semiconductor such as III-V gallium arsenide forms thin layers of two-dimensional magnetic films. The method described involves implantation of the semiconductor with manganese ions followed by annealing to create a phase separation, after which submicroscopic crystals of GaMn nucleate and develop from the implanted layer. The production of ferromagnetic particles introduces a new material with spin-dependent magnetoelectronic properties.

Published
1995

27. Measurement of chiral-dependent magnetic anisotropy in carbon nanotubes

Author

Torrens, Omar N., Milke, Daniel E., Han Y. Ban, Ming Zheng, Onoa, G. Bibiana, Gierke, Timothy D., and Kikkawa, James M.

Subjects
Nanotubes -- Magnetic properties, Nanotubes -- Optical properties, Photoluminescence -- Research, Chirality -- Research, Chemistry
Abstract

A species-resolved polarized photoluminescence (PL) measurement of single-walled carbon nanotubes (SWNT) magnetic anisotropies is presented. The results have shown differences in magnetism among SWNT chiralities that, in conjunction with theory, has helped in constructing a fan-out diagram for predicting magnetic anisotropies of arbitrary semiconducting SWNTs.

Published
2007

29. Large-area Synthesis of High-quality Monolayer 1T'-WTe2 Flakes

Author

Naylor, Carl H., Parkin, William. M, Gao, Zhaoli, Kang, Hojin, Noyan, Mehmet, Wexler, Robert. B, Tan, Liang. Z, Kim, Youngkuk, Kehayias, Christopher. E, Streller, Frank, Zhou, Yu Ren, Carpick, Robert, Luo, Zhengtang, Park, Yung Woo, Rappe, Andrew. M, DrndiĆ, Marija, Kikkawa, James. M, Johnson, AT Charlie, Naylor, Carl H., Parkin, William. M, Gao, Zhaoli, Kang, Hojin, Noyan, Mehmet, Wexler, Robert. B, Tan, Liang. Z, Kim, Youngkuk, Kehayias, Christopher. E, Streller, Frank, Zhou, Yu Ren, Carpick, Robert, Luo, Zhengtang, Park, Yung Woo, Rappe, Andrew. M, DrndiĆ, Marija, Kikkawa, James. M, and Johnson, AT Charlie

Abstract

Large-area growth of monolayer films of the transition metal dichalcogenides is of the utmost importance in this rapidly advancing research area. The mechanical exfoliation method offers high quality monolayer material but it is a problematic approach when applied to materials that are not air stable. One important example is 1T’-WTe2, which in multilayer form is reported to possess a large non saturating magnetoresistance, pressure induced superconductivity, and a weak antilocalization effect, but electrical data for the monolayer is yet to be reported due to its rapid degradation in air. Here we report a reliable and reproducible large-area growth process for obtaining many monolayer 1T’-WTe2 flakes. We confirmed the composition and structure of monolayer 1T’-WTe2 flakes using x-ray photoelectron spectroscopy, energy-dispersive x-ray spectroscopy, atomic force microscopy, Raman spectroscopy and aberration corrected transmission electron microscopy. We studied the time dependent degradation of monolayer 1T’-WTe2 under ambient conditions, and we used first-principles calculations to identify reaction with oxygen as the degradation mechanism. Finally we investigated the electrical properties of monolayer 1T’-WTe2 and found metallic conduction at low temperature along with a weak antilocalization effect that is evidence for strong spin–orbit coupling. © 2017 IOP Publishing Ltd.

Published
2017

31. Large-area synthesis of high-quality monolayer 1T’-WTe 2 flakes

Author

Naylor, Carl H, primary, Parkin, William M, additional, Gao, Zhaoli, additional, Kang, Hojin, additional, Noyan, Mehmet, additional, Wexler, Robert B, additional, Tan, Liang Z, additional, Kim, Youngkuk, additional, Kehayias, Christopher E, additional, Streller, Frank, additional, Zhou, Yu Ren, additional, Carpick, Robert, additional, Luo, Zhengtang, additional, Park, Yung Woo, additional, Rappe, Andrew M, additional, Drndić, Marija, additional, Kikkawa, James M, additional, and Johnson, A T Charlie, additional

Published
2017
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33. High-strength magnetically switchable plasmonic nanorods assembled from a binary nanocrystal mixture

Author

Zhang, Mingliang, primary, Magagnosc, Daniel J., additional, Liberal, Iñigo, additional, Yu, Yao, additional, Yun, Hongseok, additional, Yang, Haoran, additional, Wu, Yaoting, additional, Guo, Jiacen, additional, Chen, Wenxiang, additional, Shin, Young Jae, additional, Stein, Aaron, additional, Kikkawa, James M., additional, Engheta, Nader, additional, Gianola, Daniel S., additional, Murray, Christopher B., additional, and Kagan, Cherie R., additional

Published
2016
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35. Monolayer Single-Crystal 1T′-MoTe2 Grown by Chemical Vapor Deposition Exhibits Weak Antilocalization Effect

Author

Naylor, Carl H., primary, Parkin, William M., additional, Ping, Jinglei, additional, Gao, Zhaoli, additional, Zhou, Yu Ren, additional, Kim, Youngkuk, additional, Streller, Frank, additional, Carpick, Robert W., additional, Rappe, Andrew M., additional, Drndić, Marija, additional, Kikkawa, James M., additional, and Johnson, A. T. Charlie, additional

Published
2016
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43. Size- and Composition-Dependent Radio Frequency Magnetic Permeability of Iron Oxide Nanocrystals

Author

Yun, Hongseok, primary, Liu, Xiyu, additional, Paik, Taejong, additional, Palanisamy, Duraivelan, additional, Kim, Jungkwun, additional, Vogel, William D., additional, Viescas, Arthur J., additional, Chen, Jun, additional, Papaefthymiou, Georgia C., additional, Kikkawa, James M., additional, Allen, Mark G., additional, and Murray, Christopher B., additional

Published
2014
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46. Electron-Hole Polarization Dynamics in Graphene Oxide

Author

Exarhos, Annemarie L., Turk, Michael E., Luo, Zhengtang, Johnson, Alan T.C., Kikkawa, James M., Exarhos, Annemarie L., Turk, Michael E., Luo, Zhengtang, Johnson, Alan T.C., and Kikkawa, James M.

Abstract

Graphene oxide (GO) has been shown to emit broadband visible and near infrared photoluminescence (PL). Here we use polarization sensitive optical spectroscopy to study spectral diffusion and temporal dynamics of electron-hole polarization in this material. Steady state polarization memory measurements show strong polarization memory close to the excitation energy, which weakens gradually in moving toward lower emission energies. To understand the dynamics underlying this behavior, we also perform time-resolved PL studies using an optical Kerr gate with sub-picosecond temporal resolution. Polarization memories show ultrafast dynamics within the PL lifetime in solid GO preparations where the incident light lies fully in the plane of the GO flakes. Using additional knowledge gained from optical anisotropy measurements, we discuss the relevance of our polarization memory data to the origins of PL in these systems.

Published
2012

47. Photoluminescence and band gap modulation in graphene oxide

Author

Luo, Zhengtang, Vora, Patrick M., Mele, Eugene J., Johnson, A. T. Charlie, Kikkawa, James M., Luo, Zhengtang, Vora, Patrick M., Mele, Eugene J., Johnson, A. T. Charlie, and Kikkawa, James M.

Abstract

We report broadband visible photoluminescence from solid graphene oxide, and modifications of the emission spectrum by progressive chemical reduction. The data suggest a gapping of the two-dimensional electronic system by removal of pi-electrons. We discuss possible gapping mechanisms, and propose that a Kekule pattern of bond distortions may account for the observed behavior.

Published
2009

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