Chabal, Yves J.

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Dr. Chabal holds the Texas Instruments Distinguished University Chair in Nanoelectronics. He serves as professor of Materials Science & Engineering and Physics and department head of Materials Science & Engineering Texas Instruments Distinguished University Chair in Nanoelectronics. His current interests are centered on surface chemical functionalization of semiconductor and oxide surfaces, atomic layer deposition, organic electronics, biosensors and H2 storage materials. For more information about Dr. Chabel visit his home page and his Research Explorer page.

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Recent Submissions

Now showing 1 - 20 of 36
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    Biphenyl-Bridged Wrinkled Mesoporous Silica Nanoparticles for Radioactive Iodine Capture
    (Cambridge Univ Press, 2019-02-11) Brown, Alexander T.; Lin, Jason; Thomas, Milana C.; Chabal, Yves J.; Balkus, Kenneth J.; 0000-0003-0291-2081 (Brown, AT); Brown, Alexander T.; Lin, Jason; Thomas, Milana C.; Chabal, Yves J.; Balkus, Kenneth J.
    The capture of volatile radioactive iodine-129 is an important process for nuclear fission. Biphenyl-bridged wrinkled mesoporous silica shows similar performance for iodine sequestration to commercial Ag-mordenite and avoids the use of expensive silver The biphenyl-wrinkled mesoporous silica nanoparticles function as a scaffold for biphenyl groups and also as a fluorescent indicator for the loading of iodine. The nanoparticles have a surface area of 973 m²/g and the biphenyl molecules form an electron charge-transfer complex with iodine. Iodine was loaded into the biphenyl-bridged wrinkled mesoporous silica (BUMS) at 19 ± 0.2 % loading by mass.
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    Superior Low-Temperature NO Catalytic Performance of PrMn₂O₅ over SmMn₂O₅ Mullite-Type Catalysts
    (Royal Society of Chemistry, 2019) Thampy, Sampreetha; Ashburn, Nickolas; Liu, C.; Xiong, K.; Dillon, Sean; Zheng, Yongping; Chabal, Yves J.; Cho, Kyeongjae; Hsu, Julia W. P.; 0000-0002-7821-3001 (Hsu, JWP); 0000-0002-6435-0347 (Chabal, YJ); 0000-0003-2698-7774 (Cho, K); 369148996084659752200 (Cho, K); Thampy, Sampreetha; Ashburn, Nickolas; Dillon, Sean; Zheng, Yongping; Chabal, Yves J.; Cho, Kyeongjae; Hsu, Julia W. P.
    By studying their surface chemistry, metal-oxygen bond strength, and critical energy barrier heights, we elucidate the differences in the NO oxidation catalytic performance of PrMn₂O₅ and SmMn₂O₅ mullite-type oxides. The 50% conversion temperature is lower (230 °C vs. 275 °C) and the maximum conversion efficiency is higher (81% at 282 °C vs. 68% at 314 °C) for PrMn₂O₅ compared to SmMn₂O₅, despite having a ∼15% lower specific surface area. Furthermore, PrMn₂O₅ exhibits higher maximum efficiency compared to Pt/Al₂O₃. Combined experimental and theoretical findings indicate that the superior catalytic performance of PrMn₂O₅ at low temperatures arises from the presence of more labile and reactive surface lattice oxygen due to weaker Mn-O bond strength and lower thermal stability of surface NOₓ ad-species. ©2019 The Royal Society of Chemistry.
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    Mechanistic Study of the Atomic Layer Deposition of Scandium Oxide Films Using Sc(MeCp)₂(Me₂pz) and Ozone
    (A V S Amer Inst Physics, 2019-01-02) Rahman, Rezwanur; Klesko, Joseph P.; Dangerfield, Aaron; Fang, Ming; Lehn, Jean-Sebastien M.; Dezelah, Charles L.; Kanjolia, Ravindra K.; Chabal, Yves J.; 0000-0002-6435-0347 (Chabal, YJ); 0000-0003-3989-8009 (Klesko, JP); Rahman, Rezwanur; Klesko, Joseph P.; Dangerfield, Aaron; Chabal, Yves J.
    The atomic layer deposition (ALD) of scandium oxide (Sc₂O₃) thin films is investigated using Sc(MeCp)₂(Me₂pz) (1, MeCp = methylcyclopentadienyl, Me₂pz = 3,5-dimethylpyrazolate) and ozone on hydroxyl-terminated oxidized Si(111) substrates at 225 and 275 °C. In situ Fourier transform infrared spectroscopy reveals that 1 not only reacts with surface hydroxyl groups at 275 °C, as expected but also with the SiO₂ layer, as evidenced by losses in the SiO₂ longitudinal optical and transverse optical phonon modes, resulting in the partial transformation of near-surface SiO₂ to an ScSixOy interface layer. Ozone then combusts the MeCp groups of the O-Sc(MeCp)₂ chemisorbed species, yielding surface carbonates, and oxidizes some of the underlying silicon, evidenced by gains in the SiO₂ phonon modes. The Me₂pz group from the next pulse of 1 reacts with these surface carbonates, leading to Sc-O-Sc bond formation (Sc₂O₃ deposition) and the restoration of an O-Sc(MeCp)₂ surface. The reaction of the SiO₂ substrate with 1 and the oxidation of silicon by ozone are temperature-dependent processes that occur during the initial cycles of film growth and directly impact the changes in the intensities of the SiO₂ phonon modes. For instance, the intensity of the net gains in the phonon modes following ozone exposure is greater at 275 °C than at 225 °C. As the ALD cycle is repeated, the formation of an ScSiₓOᵧ interface layer and deposition of an Sc₂O₃ film result in the gradual attenuation of the reaction of the SiO₂ substrate with 1 and the oxidation of the underlying silicon by ozone. In addition to the ALD process, characterized by ligand exchange and self-limiting reactions, there are gas-phase reactions between 1 and residual water vapor near the substrate surface that lead to deposition of additional Sc₂O₃ and surface carbonates, the extent of which are also dependent on the temperature of the substrate. After 20 cycles of 1/ozone, the film thicknesses derived from ex situ X-ray photoelectron spectroscopy measurements are 2.18 nm (225 °C) and 3.88 nm (275 °C). This work constitutes the first mechanistic study of an Sc₂O₃ ALD process using ozone as the oxidant and emphasizes the significance of atypical reactions between the substrate and the reactants that influence the growth rate and near-surface stoichiometry during the initial cycles of film deposition. Published by the AVS.
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    Nanocast Carbon Microsphere Flowers from a Lanthanum-Based Template
    (Elsevier Science B.V., 2018-09-11) Brown, Alexander T.; Thomas, Milana C.; Chabal, Yves J.; Balkus, Kenneth J.; 0000-0001-5926-0200 (Fischetti, MV); 0000-0003-1142-3837 (Balkus, KJ); Brown, Alexander T.; Thomas, Milana C.; Chabal, Yves J.; Balkus, Kenneth J.
    Hollow carbon microsphere flowers were nanocast from glucose, acrylamide, and acetylene sources. Carbon growth was catalyzed by a lanthanum graft copolymer template using wet acetylene. The resulting spherical shape is beneficial for 3-D porosity, and has a highly graphitic content as indicated by raman spectroscopy (I_{D} :I_{G} = 0.99). The carbon has a high surface area of 1000 m²/g, as well as strong π-π stacking of aromatic carbons.
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    Non-Dispersive Infrared (NDIR) Sensor for Real-Time Nitrate Monitoring in Wastewater Treatment
    (SPIE, 2019-02-27) Roodenko, K.; Hinojos, D.; Hodges, Kimari L.; Veyan, Jean-Francois; Chabal, Yves J.; Clark, K. P.; Katzir, A.; Robbins, D.; Hodges, Kimari L.; Veyan, Jean-Francois; Chabal, Yves J.
    Nitrate is a frequent water pollutant that results from human activities such as fertilizer over-Application and agricultural runoff and improper disposal of human and animals waste. Excess levels of nitrate in watersheds can trigger harmful algal blooms (HABs) and biodiversity loss with consequences that affect the economy and pose a threat to human health. Municipal drinking water and wastewater treatment plants are therefore required to control nitrogen levels to ensure the safety of drinking water and the proper discharge of effluent. Nitrate exhibits distinct absorption bands in the infrared spectral range. While infrared radiation is strongly attenuated in water, implementation of fiber optic evanescent wave spectroscopy (FEWS) enables monitoring of water contaminants in real-Time with high sensitivity. This work outlines the development of a non-dispersive infrared (NDIR) detector for the real-Time monitoring of nitrate, nitrite and ammonia concentrations targeting implementation at municipal wastewater treatment plants (WWTPs) and onsite wastewater treatment systems (OWTS). ©2019 SPIE. Downloading of the abstract is permitted for personal use only.
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    Reactivity of Atomic Layer Deposition Precursors with OH/H₂O-Containing Metal Organic Framework Materials
    (American Chemical Society) Tan, Kui; Jensen, S.; Feng, L.; Wang, H.; Yuan, S.; Ferreri, M.; Klesko, Joseph P.; Rahman, Rezwanur; Cure, Jeremy; Li, J.; Zhou, H. -C; Thonhauser, T.; Chabal, Yves J.; 0000-0002-5167-7295 Tan, K); 0000-0003-3989-8009 (Klesko, JP); 0000-0002-8109-4787 (Rahman, R); 0000-0002-6080-6909 (Cure, J); 0000-0002-6435-0347 (Chabal, YJ); Tan, Kui; Klesko, Joseph P.; Rahman, Rezwanur; Cure, Jeremy; Chabal, Yves J.
    Metal organic frameworks (MOFs) are a class of three-dimensional porous architectures that can be chemically functionalized. The ability of atomic layer deposition (ALD) to incorporate metal atoms or functional groups into MOFs offers an interesting alternative to chemically modify MOFs for applications such as catalysis and gas separation, for which transport, adsorption, and the reaction of gases are critical. Optimization of these deposition processes requires an understanding of the underlying reaction mechanisms that is best derived from in situ characterization. We have therefore combined in situ infrared spectroscopy, X-ray photoelectron spectroscopy with in situ sputtering, and ab initio calculations to elucidate the reaction mechanisms of the common ALD precursors trimethylaluminium (TMA), diethylzinc (DEZ), and TiCl 4 with several Zr-MOFs containing hydroxyl (OH) and water (H₂O) groups. Focusing on the OH and H₂O groups is particularly revealing because it makes it possible to explore the reactivity dependence on the chemical and structural (i.e., sterics) environments. We find that the reactivity of the OH groups in the Zr₆(μ₃ -OH)₄ (μ₃ -O)₄ (OH)ₓ (OH₂) y cluster node is highly dependent on their location, accessibility, and chemical environment. For instance, the activation temperature for the reaction of the OH groups of Zr₆ clusters with TMA decreases with the node connectivity: 200, 150, and 24 °C for UiO-66-NH₂ , Zr-abtc, and MOF-808, respectively. Interestingly, the hydroxyl groups in unfunctionalized UiO-66 do not react with TMA molecules. Ab initio calculations reveal that the NH₂ group is directly responsible for catalyzing this reaction by anchoring the TMA molecule in close proximity to the target OH group. Finally, we show that TMA easily reacts with water adsorbed on the external surfaces of wet MOF crystals at room temperature, forming a thick Al₂O₃ blocking layer on the periphery of the MOF crystals. These findings provide a basis for the design and modification of MOFs by ALD processes. © 2019 American Chemical Society.
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    Thermal Atomic Layer Etching of Silica and Alumina Thin Films Using Trimethylaluminum with Hydrogen Fluoride or Fluoroform
    (American Chemical Society) Rahman, Razwanur; Mattson, Eric C.; Klesko, Joseph P.; Dangerfield, Aaron; Rivillon-Amy, S.; Smith, D. C.; Hausmann, D.; Chabal, Yves J.; 0000 0000 4239 3958 (Chabal, YJ); 0000-0002-8109-4787 (Rahman, R); 0000-0002-0755-2583 (Mattson, EC); 0000-0003-3989-8009 (Klesko, JP); 0000-0002-6435-0347 (Chabal, YJ); Rahman, Razwanur; Mattson, Eric C.; Klesko, Joseph P.; Dangerfield, Aaron; Chabal, Yves J.
    Thermal atomic layer etching (ALE) is an emerging technique that involves the sequential removal of monolayers of a film by alternating self-limiting reactions, some of which generate volatile products. Although traditional ALE processes rely on the use of plasma, several thermal ALE processes have recently been developed using hydrogen fluoride (HF) with precursors such as trimethylaluminum (TMA) or tin acetylacetonate. While HF is currently the most effective reagent for ALE, its potential hazards and corrosive nature have motivated searches for alternative chemicals. Herein, we investigate the feasibility of using fluoroform (CHF₃) with TMA for the thermal ALE of SiO₂ and Al₂O₃ surfaces and compare it to the established TMA/HF process. A fundamental mechanistic understanding is derived by combining in situ Fourier transform infrared spectroscopy, ex situ X-ray photoemission spectroscopy, ex situ low-energy ion scattering, and ex situ spectroscopic ellipsometry. Specifically, we determine the role of TMA, the dependence of the etch rate on precursor gas pressure, and the formation of a residual fluoride layer. Although CHF₃ reacts with TMA-treated oxide surfaces, etching is hindered by the concurrent deposition of a fluorine-containing layer, which makes it unfavorable for etching. Moreover, since fluorine contamination can be deleterious to device performance and its presence in thin films is an inherent problem for established ALE processes using HF, we present a novel method to remove the residual fluorine accumulated during the ALE process by exposure to water vapor. XPS analysis herein reveals that an Al₂O₃ film etched using TMA/HF at 325 °C contains 25.4 at. % fluorine in the surface region. In situ exposure of this film to water vapor at 325 °C results in 90% removal of the fluorine. This simple approach for fluorine removal can easily be applied to ALE-treated films to mitigate contamination and retain surface stoichiometry. ©2018 American Chemical Society.
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    Chemical Modification Mechanisms in Hybrid Hafnium Oxo-Methacrylate Nanocluster Photoresists for Extreme Ultraviolet Patterning
    (American Chemical Society) Mattson, Eric C.; Cabrera, Yasiel; Rupich, Sara M.; Wang, Yuxuan; Oyekan, Kolade A.; Mustard, T. J.; Halls, M. D.; Bechtel, H. A.; Martin, M. C.; Chabal, Yves J.; Mattson, Eric C.; Cabrera, Yasiel; Rupich, Sara M.; Wang, Yuxuan; Oyekan, Kolade A.; Chabal, Yves J.
    The potential implementation of extreme ultraviolet (EUV) lithography into next generation device processing is bringing urgency to identify resist materials that optimize EUV lithographic performance. Inorganic/organic hybrid nanoparticles or clusters constitute a promising new class of materials, with high EUV sensitivity from the core and tunable chemistry through the coordinating ligands. Development of a thorough mechanistic understanding of the solubility switching reactions in these materials is an essential first step toward their implementation in patterning applications but remains challenging due to the complexity of their structures, limitations in EUV sources, and lack of rigorous in situ characterization. Here, we report a mechanistic investigation of the solubility switching reactions in hybrid clusters comprising a small HfOx core capped with a methacrylic acid ligand shell (HfMAA). We show that EUV-induced reactions can be studied by performing in situ infrared (IR) spectroscopy of electron-irradiated films using a variable energy electron gun. Combining additional ex situ metrology, we track the chemical evolution of the material at each stage of a typical resist processing sequence. For instance, we find that a cross-linking reaction initiated by decarboxylation of the methacrylate ligands under electron irradiation constitutes the main solubility switching mechanism, although there are also chemical changes imparted by a typical post application bake (PAB) step alone. Lastly, synchrotron-based IR microspectroscopy measurements of EUV-irradiated HfMAA films enable a comparison of reactions induced by EUV vs electron beam irradiation of the same resist material, yielding important insight into the use of electron beam irradiation as an experimental model for EUV exposure.
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    Role of Excess Ligand and Effect of Thermal Treatment in Hybrid Inorganic-Organic EUV Resists
    (SPIE) Mattson, Eric C.; Rupich, S. M.; Cabrera, Y.; Chabal, Yves J.; Mattson, Eric C.; Chabal, Yves J.
    The chemical structure and thermal reactivity of recently discovered inorganic-organic hybrid resist materials are characterized using a combination of in situ and ex situ infrared (IR) spectroscopy and X-ray photoemission spectroscopy (XPS). The materials are comprised of a small HfOx core capped with methacrylic acid ligands that form a combined hybrid cluster, HfMAA. The observed IR modes are consistent with the calculated modes predicted from the previously determined X-ray crystal structure of the HfMAA-12 cluster, but also contain extrinsic hydroxyl groups. We find that the water content of the films is dependent on the concentration of excess ligand added to the solution. The effect of environment used during post-application baking (PAB) is studied and correlated to changes in solubility of the films. In doing so, we find that hydroxylation of the clusters results in formation of additional Hf-O-Hf linkages upon heating, which in turn impacts the solubility of the films.
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    Topologically Guided Tuning of Zr-MOF Pore Structures for Highly Selective Separation of C6 Alkane Isomers
    (Nature Publishing Group) Wang, Hao; Dong, Xinglong; Lin, Junzhong; Teat, Simon J.; Jensen, Stephanie; Cure, Jeremy; Alexandrov, Eugeny V.; Xia, Qibin; Tan, Kui; Wang, Qining; Olson, David H.; Proserpio, Davide M.; Chabal, Yves J.; Thonhauser, Timo; Sun, Junliang; Han, Yu; Li, Jing; 0000-0002-6435-0347 (Chabal, YJ); Cure, Jeremy; Tan, Kui; Chabal, Yves J.
    As an alternative technology to energy intensive distillations, adsorptive separation by porous solids offers lower energy cost and higher efficiency. Herein we report a topology-directed design and synthesis of a series of Zr-based metal-organic frameworks with optimized pore structure for efficient separation of C6 alkane isomers, a critical step in the petroleum refining process to produce gasoline with high octane rating. Zr₆O₄(OH)₄(bptc)₃ adsorbs a large amount of n-hexane but excluding branched isomers. The n-hexane uptake is similar to 70% higher than that of a benchmark adsorbent, zeolite-5A. A derivative structure, Zr₆O₄(OH)₈(-H₂O)₄(abtc)₂, is capable of discriminating all three C6 isomers and yielding a high separation factor for 3-methylpentane over 2,3-dimethylbutane. This property is critical for producing gasoline with further improved quality. Multicomponent breakthrough experiments provide a quantitative measure of the capability of these materials for separation of C6 alkane isomers. A detailed structural analysis reveals the unique topology, connectivity and relationship of these compounds.
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    Nucleation and Growth of WSe₂: Enabling Large Grain Transition Metal Dichalcogenides
    (IOP Publishing Ltd, 2017-09-22) Yue, Ruoyu; Nie, Yifan; Walsh, Lee A.; Addou, Rafik; Liang, Chaoping; Lu, Ning; Barton, Adam T.; Zhu, Hui; Che, Zifan; Barrera, Diego; Cheng, Lanxia; Cha, Pil-Ryung; Chabal, Yves J.; Hsu, Julia W. P.; Kim, Jiyoung; Kim, Moon J.; Colombo, Luigi; Wallace, Robert M.; Cho, Kyeongjae; Hinkle, Christopher L.; 0000-0002-2910-2938 (Liang, C); Yue, Ruoyu; Nie, Yifan; Walsh, Lee A.; Addou, Rafik; Liang, Chaoping; Lu, Ning; Barton, Adam T.; Zhu, Hui; Che, Zifan; Barrera, Diego; Cheng, Lanxia; Chabal, Yves J.; Hsu, Julia W. P.; Kim, Jiyoung; Kim, Moon J.; Wallace, Robert M.; Cho, Kyeongjae; Hinkle, Christopher L.
    The limited grain size (< 200 nm) for transition metal dichalcogenides (TMDs) grown by molecular beam epitaxy (MBE) reported in the literature thus far is unsuitable for high-performance device applications. In this work, the fundamental nucleation and growth behavior of WSe₂ is investigated through a detailed experimental design combined with on-lattice, diffusion-based first principles kinetic modeling to enable large area TMD growth. A three-stage adsorption-diffusion-attachment mechanism is identified and the adatom stage is revealed to play a significant role in the nucleation behavior. To limit the nucleation density and promote 2D layered growth, it is necessary to have a low metal flux in conjunction with an elevated substrate temperature. At the same time, providing a Se-rich environment further limits the formation of W-rich nuclei which suppresses vertical growth and promotes 2D growth. The fundamental understanding gained through this investigation has enabled an increase of over one order of magnitude in grain size for WSe₂ thus far, and provides valuable insight into improving the growth of other TMD compounds by MBE and other growth techniques such as chemical vapor deposition (CVD).
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    Interaction of Acid Gases SO₂ and NO₂ with Coordinatively Unsaturated Metal Organic Frameworks: M-MOF-74 (M = Zn, Mg, Ni, Co)
    (Amer Chemical Soc, 2017-05-01) Tan, Kui; Zuluaga, Sebastian; Wang, Hao; Canepa, Pieremanuele; Soliman, Karim; Cure, Jeremy; Li, Jing; Thonhauser, Timo; Chabal, Yves J.; 0000-0002-5167-7295 (Tan, K); 0000-0002-6435-0347 (Chabal, YJ); Tan, Kui; Cure, Jeremy; Chabal, Yves J.
    In situ infrared spectroscopy and ab initio density functional theory (DFT) calculations are combined to study the interaction of the corrosive gases SO₂ and NO₂ with metal organic frameworks M-MOF-74 (M = Zn, Mg, Ni, Co). We find that NO₂ dissociatively adsorbs into MOF-74 compounds, forming NO and NO₃̅. The mechanism is unraveled by considering the Zn-MOF-74 system, for which DFT calculations show that a strong NO₂-Zn bonding interaction induces a significant weakening of the N-O bond, facilitating the decomposition of the NO₂ molecules. In contrast, SO₂ is only molecularly adsorbed into MOF-74 with high binding energy (>90 kJ/mol for Mg-MOF-74 and >70 for Zn-MOF-74). This work gives insight into poisoning issues by minor components of flue gases in metal organic frameworks materials.
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    Capture of Organic Iodides from Nuclear Waste by Metal-Organic Framework-Based Molecular Traps
    (Nature Publishing Group) Li, Baiyan; Dong, Xinglong; Wang, Hao; Ma, Dingxuan; Tan, Kui; Jensen, Stephanie; Deibert, Benjamin J.; Butler, Joseph; Cure, Jeremy; Shi, Zhan; Thonhauser, Timo; Chabal, Yves J.; Han, Yu; Li, Jing; Tan, Kui; Butler, Joseph; Cure, Jeremy; Chabal, Yves J.
    Effective capture of radioactive organic iodides from nuclear waste remains a significant challenge due to the drawbacks of current adsorbents such as low uptake capacity, high cost, and non-recyclability. We report here a general approach to overcome this challenge by creating radioactive organic iodide molecular traps through functionalization of metal-organic framework materials with tertiary amine-binding sites. The molecular trap exhibits a high CH₃I saturation uptake capacity of 71 wt% at 150 ⁰C, which is more than 340% higher than the industrial adsorbent Ag⁰@MOR under identical conditions. These functionalized metal-organic frameworks also serve as good adsorbents at low temperatures. Furthermore, the resulting adsorbent can be recycled multiple times without loss of capacity, making recyclability a reality. In combination with its chemical and thermal stability, high capture efficiency and low cost, the adsorbent demonstrates promise for industrial radioactive organic iodides capture from nuclear waste. The capture mechanism was investigated by experimental and theoretical methods.
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    Cobalt and Iron Segregation and Nitride Formation from Nitrogen Plasma Treatment of CoFeB Surfaces
    (American Institute of Physics Inc) Mattson, Eric C.; Michalak, D. J.; Veyan, Jean Francois; Chabal, Yves J.; 0000-0002-3743-5521 (Veyan, JF); 0000-0002-6435-0347 (Chabal, YJ); Mattson, Eric C.; Veyan, Jean Francois; Chabal, Yves J.
    Cobalt-iron-boron (CoFeB) thin films are the industry standard for ferromagnetic layers in magnetic tunnel junction devices and are closely related to the relevant surfaces of CoFe-based catalysts. Identifying and understanding the composition of their surfaces under relevant processing conditions is therefore critical. Here we report fundamental studies on the interaction of nitrogen plasma with CoFeB surfaces using infrared spectroscopy, x-ray photoemission spectroscopy, and low energy ion scattering. We find that, upon exposure to nitrogen plasma, clean CoFeB surfaces spontaneously reorganize to form an overlayer comprised of Fe2N3 and BN, with the Co atoms moved well below the surface through a chemically driven process. Subsequent annealing to 400 °C removes nitrogen, resulting in a Fe-rich termination of the surface region. © 2016 Author(s).
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    Substrate Selectivity in the Low Temperature Atomic Layer Deposition of Cobalt Metal Films from Bis(1,4-Di- Tert -Butyl-1,3-Diazadienyl)Cobalt and Formic Acid
    (American Institute of Physics Inc, 2018-08-20) Kerrigan, M. M.; Klesko, Joseph P.; Rupich, Sara M.; Dezelah, C. L.; Kanjolia, R. K.; Chabal, Yves. J.; Winter, C. H.; Klesko, Joseph P.; Rupich, Sara M.; Chabal, Yves. J.
    The initial stages of cobalt metal growth by atomic layer deposition are described using the precursors bis(1,4-di-tert-butyl-1,3-diazadienyl)cobalt and formic acid. Ruthenium, platinum, copper, Si(100), Si-H, SiO₂, and carbon-doped oxide substrates were used with a growth temperature of 180 °C. On platinum and copper, plots of thickness versus number of growth cycles were linear between 25 and 250 cycles, with growth rates of 0.98 Å/cycle. By contrast, growth on ruthenium showed a delay of up to 250 cycles before a normal growth rate was obtained. No films were observed after 25 and 50 cycles. Between 100 and 150 cycles, a rapid growth rate of ∼1.6 Å/cycle was observed, which suggests that a chemical vapor deposition-like growth occurs until the ruthenium surface is covered with ∼10 nm of cobalt metal. Atomic force microscopy showed smooth, continuous cobalt metal films on platinum after 150 cycles, with an rms surface roughness of 0.6 nm. Films grown on copper gave rms surface roughnesses of 1.1-2.4 nm after 150 cycles. Films grown on ruthenium, platinum, and copper showed resistivities of < 20 μΩ cm after 250 cycles and had values close to those of the uncoated substrates at ≤150 cycles. X-ray photoelectron spectroscopy of films grown with 150 cycles on a platinum substrate showed surface oxidation of the cobalt, with cobalt metal underneath. Analogous analysis of a film grown with 150 cycles on a copper substrate showed cobalt oxide throughout the film. No film growth was observed after 1000 cycles on Si(100), Si-H, and carbon-doped oxide substrates. Growth on thermal SiO₂ substrates gave ∼35 nm thick layers of cobalt(II) formate after ≥500 cycles. Inherently selective deposition of cobalt on metallic substrates over Si(100), Si-H, and carbon-doped oxide was observed from 160 °C to 200 °C. Particle deposition occurred on carbon-doped oxide substrates at 220 °C.
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    Novel Binder-Free Electrode Materials for Supercapacitors Utilizing High Surface Area Carbon Nanofibers Derived from Immiscible Polymer Blends of PBI/6FDA-DAM:DABA
    (Royal Society of Chemistry, 2018-06-01) Abeykoon, Nimali C.; Garcia, Velia; Jayawickramage, Rangana A.; Perera, Wijayantha; Cure, Jeremy; Chabal, Yves J.; Balkus, Kenneth J.; Ferraris, John P.; 0000 0000 4239 3958 (Chabal, YJ); 0000-0002-3225-0093 (Ferraris, JP); Abeykoon, Nimali C.; Garcia, Velia; Jayawickramage, Rangana A.; Perera, Wijayantha; Cure, Jeremy; Chabal, Yves J.; Balkus, Kenneth J.; Ferraris, John P.
    Carbon nanofibers with high surface area have become promising electrode materials for supercapacitors because of their importance in increasing energy density. In this study, a high free volume polymer, 6FDA-DAM:DABA (6FDD) was blended with polybenzimidazole (PBI) in different ratios to obtain different compositions of PBI/6FDD immiscible polymer blends. Freestanding nanofiber mats were obtained via electrospinning using blend precursors dissolved in N,N-dimethylacetamide (DMAc). Subsequently, carbonization, followed by CO₂ activation at 1000 °C was applied to convert the fiber mats into porous carbon nanofibers (CNFs). The addition of 6FDD shows significant effects on the microstructure and enhancement of the surface area of the CNFs. The obtained CNFs show specific surface area as high as 3010 m² g⁻¹ with pore sizes comparable to those of the electrolyte ions (PYR₁₄TFSI). This provides good electrolyte accessibility to the pore of the carbon materials resulting in enhanced energy density compared to the CNFs obtained from pure PBI. Electrodes derived from PBI:6FDD (70 : 30) exhibited outstanding supercapacitor performance in coin cells with a specific capacitance of 142 F g⁻¹ at the scan rate of 10 mV s⁻¹ and energy density of 67.5 W h kg⁻¹ at 1 A g⁻¹ (58 W h kg⁻¹ at 10 A g⁻¹) thus demonstrating promising electrochemical performance for high performance energy storage system.
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    Energy Transfer from Colloidal Nanocrystals to Strongly Absorbing Perovskites
    (Royal Society of Chemistry, 2018-06-01) Cabrera, Yasiel; Rupich, Sara M.; Shaw, Ryan; Anand, Benoy; Villa, Manuel de Anda; Rahman, Rezwanur; Dangerfield, Aaron; Gartstein, Yuri N.; Malko, Anton V.; Chabal, Yves J.; 0000-0002-6435-0347 (Chabal, YJ); Cabrera, Yasiel; Rupich, Sara M.; Shaw, Ryan; Anand, Benoy; Villa, Manuel de Anda; Rahman, Rezwanur; Dangerfield, Aaron; Gartstein, Yuri N.; Malko, Anton V.; Chabal, Yves J.
    Integration of colloidal nanocrystal quantum dots (NQDs) with strongly absorbing semiconductors offers the possibility of developing optoelectronic and photonic devices with new functionalities. We examine the process of energy transfer (ET) from photoactive CdSe/ZnS core/shell NQDs into lead-halide perovskite polycrystalline films as a function of distance from the perovskite surface using time-resolved photoluminescence (TRPL) spectroscopy. We demonstrate near-field electromagnetic coupling between vastly dissimilar excitation in two materials that can reach an efficiency of 99% at room temperature. Our experimental results, combined with electrodynamics modeling, reveal the leading role of non-radiative ET at close distances, augmented by the waveguide emission coupling and light reabsorption at separations >10 nm. These results open the way to combining materials with different dimensionalities to achieve novel nanoscale architectures with improved photovoltaic and light emitting functionalities.
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    Understanding and Controlling Water Stability of MOF-74
    (Royal Society of Chemistry, 2018-06-01) Zuluaga, S.; Fuentes-Fernandez, Erika M. A.; Tan, Kui; Xu, F.; Li, J.; Chabal, Yves J.; Thonhauser, T.; 0000 0000 4239 3958 (Chabal, YJ); Fuentes-Fernandez, Erika M. A.; Tan, Kui; Chabal, Yves J.
    Metal organic framework (MOF) materials in general, and MOF-74 in particular, have promising properties for many technologically important processes. However, their instability under humid conditions severely restricts practical use. We show that this instability and the accompanying reduction of the CO2 uptake capacity of MOF-74 under humid conditions originate in the water dissociation reaction H2O → OH + H at the metal centers. After this dissociation, the OH groups coordinate to the metal centers, explaining the reduction in the MOF's CO2 uptake capacity. This reduction thus strongly depends on the catalytic activity of MOF-74 towards the water dissociation reaction. We further show that - while the water molecules themselves only have a negligible effect on the crystal structure of MOF-74 - the OH and H products of the dissociation reaction significantly weaken the MOF framework and lead to the observed crystal structure breakdown. With this knowledge, we propose a way to suppress this particular reaction by modifying the MOF-74 structure to increase the water dissociation energy barrier and thus control the stability of the system under humid conditions.
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    HIF-1α-PDK1 Axis-Induced Active Glycolysis Plays an Essential Role in Macrophage Migratory Capacity
    (American Physical Society) Anand, Benoy; Sampat, Siddharth; Danilov, E. O.; Peng, Weina; Rupich, Sara M.; Chabal, Yves J.; Gartstein, Yuri N.; Malko, Anton V.; 0000 0001 1969 6683 (Gartstein, YN); 0000 0001 2678 9765 (Malko, AV); 170647442 (Gartstein, YN); Anand, Benoy; Sampat, Siddharth; Peng, Weina; Rupich, Sara M.; Chabal, Yves J.; Gartstein, Yuri N.; Malko, Anton V.
    Ultrafast transient pump-probe measurements of thin CH₃NH₃PbI₃ perovskite films over a wide spectral range from 350 to 800 nm reveal a family of photoinduced bleach (PB) and absorption (PA) features unequivocally pointing to the fundamentally multiband character of the underlying electronic structure. Excitation pump-energy dependent kinetics of three long-lived PB peaks at 1.65, 2.55, and 3.15 eV along with a broad PA band shows the involvement of band-edge thermalized carriers in all transitions and at least four, possibly more, electronic bands. The evolution of the transient signatures is described in terms of the redistribution of the conserved oscillator strength of the whole system. The multiband perspective opens up different directions for understanding and controlling photoexcitations in hybrid perovskites.
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    Static and Dynamic Electronic Characterization of Organic Monolayers Grafted on a Silicon Surface
    (Royal Society of Chemistry) Pluchery, O.; Zhang, Y.; Benbalagh, R.; Caillard, Louis; Gallet, J. J.; Bournel, F.; Lamic-Humblot, A.; Salmeron, M.; Chabal, Yves J.; Rochet, F.; Caillard, Louis; Chabal, Yves J.
    Organic layers chemically grafted on silicon offer excellent interfaces that may open up the way for new organic-inorganic hybrid nanoelectronic devices. However, technological achievements rely on the precise electronic characterization of such organic layers. We have prepared ordered grafted organic monolayers (GOMs) on Si(111), sometimes termed self-assembled monolayers (SAMs), by a hydrosilylation reaction with either a 7-carbon or an 11-carbon alkyl chain, with further modification to obtain amine-terminated surfaces. X-ray photoelectron spectroscopy (XPS) is used to determine the band bending (~0.3 eV), and ultraviolet photoelectron spectroscopy (UPS) to measure the work function (~3.4 eV) and the HOMO edge. Scanning tunneling microscopy (STM) confirms that the GOM surface is clean and smooth. Finally, conductive AFM is used to measure electron transport through the monolayer and to identify transition between the tunneling and the field emission regimes. These organic monolayers offer a promising alternative to silicon dioxide thin films for fabricating metal-insulator-semiconductor (MIS) junctions. We show that gold nanoparticles can be covalently attached to mimic metallic nano-electrodes and that the electrical quality of the GOMs is completely preserved in the process.;

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