Chabal, Yves J.
Permanent URI for this collectionhttps://hdl.handle.net/10735.1/2471
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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Item Wet chemical surface functionalization of oxide-free silicon(Elsevier Limited, 2012-09-13) Thissen, Peter; Seitz, Oliver; Chabal, Yves J.; 0000 0000 4239 3958 (Chabal, YJ); 89624105 (Chabal, YJ)Silicon is by far the most important semiconductor material in the microelectronic industry mostly due to the high quality of the Si/SiO2 interface. Consequently, applications requiring chemical functionalization of Si substrates have focused on molecular grafting of SiO2 surfaces. Unfortunately, there are practical problems affecting homogeneity and stability of many organic layers grafted on silicon oxide (SiO2), such as silanes and phosphonates, related to polymerization and hydrolysis of Si-O-Si and Si-O-P bonds. These issues have stimulated efforts in grafting functional molecules on oxide-free Si surfaces, mostly with wet chemical processes. This review focuses therefore directly on wet-chemical surface functionalization of oxide-free Si surfaces, starting from H-terminated Si surfaces. The main preparation methods of oxide-free H-terminated Si and their stability are first summarized. Functionalization is then classified into indirect substitution of H-termination by functional organic molecules, such as hydrosilylation, and direct substitution by other atoms (e.g. halogens) or small functional groups (e.g. OH, NH2) that can be used for further reaction. An emphasis is placed on a recently discovered method to produce a nanopattern of functional groups on otherwise oxide-free, H-terminated and atomically flat Si(111) surfaces. Such model surfaces are particularly interesting because they make it possible to derive fundamental knowledge of surface chemical reactions.Item Energy Transfer from Colloidal Nanocrystals into Si Substrates Studied via Photoluminescence Photon Counts and Decay Kinetics(2013-08-16) Nguyen, H. M.; Seitz, Oliver; Gartstein, Yuri N.; Chabal, Yves J.; Malko, Anton V.; 0000 0001 2678 9765 (Malko, AV); Nguyen, H. M.; Seitz, Oliver; Gartstein, Yuri N.; Chabal, Yves J.; Malko, Anton V.We use time-resolved photoluminescence (PL) kinetics and PL intensity measurements to study the decay of photoexcitations in colloidal CdSe/ZnS nanocrystals grafted on SiO₂ - Si substrates with a wide range of the SiO₂ spacer layer thicknesses. The salient features of experimental observations are found to be in good agreement with theoretical expectations within the framework of modification of spontaneous decay of electric-dipole excitons by their environment. Analysis of the experimental data reveals that energy transfer (ET) from nanocrystals into Si is a major enabler of substantial variations in decay rates, where we quantitatively distinguish contributions from nonradiative and radiative ET channels. We demonstrate that time-resolved PL kinetics provides a more direct assessment of ET, while PL intensity measurements are also affected by the specifics of the generation and emission processes.Item Selectivity of Metal Oxide Atomic Layer Deposition on Hydrogen Terminated and Oxidized Si(001)-(2x1) Surface(A V S Amer Inst Physics, 2014-02-10) Longo, Roberto C.; McDonnell, Stephen; Dick, D.; Wallace, Robert M.; Chabal, Yves J.; Owen, James H. G.; Ballard, Josh B.; Randall, John N.; Cho, Kyeongjae; 0000 0000 4239 3958 (Chabal, YJ); 89624105 (Chabal, YJ)In this work, the authors used density-functional theory methods and x-ray photoelectron spectroscopy to study the chemical composition and growth rate of HfO₂, Al₂O₃, and TiO₂ thin films grown by in-situ atomic layer deposition on both oxidized and hydrogen-terminated Si(001) surfaces. The growth rate of all films is found to be lower on hydrogen-terminated Si with respect to the oxidized Si surface. However, the degree of selectivity is found to be dependent of the deposition material. TiO₂ is found to be highly selective with depositions on the hydrogen terminated silicon having growth rates up to 180 times lower than those on oxidized Si, while similar depositions of HfO₂ and Al₂O₃ resulted in growth rates more than half that on oxidized silicon. By means of density-functional theory methods, the authors elucidate the origin of the different growth rates obtained for the three different precursors, from both energetic and kinetic points of view.Item Influence of Growth Temperature on Bulk and Surface Defects in Hybrid Lead Halide Perovskite Films(Royal Society of Chemistry, 2015-12-14) Peng, Weina; Anand, Benoy; Liu, Lihong; Sampat, Siddharth; Bearden, Brandon E.; Malko, Anton V.; Chabal, Yves J.The rapid development of perovskite solar cells has focused its attention on defects in perovskites, which are gradually realized to strongly control the device performance. A fundamental understanding is therefore needed for further improvement in this field. Recent efforts have mainly focused on minimizing the surface defects and grain boundaries in thin films. Using time-resolved photoluminescence spectroscopy, we show that bulk defects in perovskite samples prepared using vapor assisted solution process (VASP) play a key role in addition to surface and grain boundary defects. The defect state density of samples prepared at 150 °C (~10¹⁷ cm⁻³) increases by 5 fold at 175 °C even though the average grains size increases slightly, ruling out grain boundary defects as the main mechanism for the observed differences in PL properties upon annealing. Upon surface passivation using water molecules, the PL intensity and lifetime of samples prepared at 200 °C are only partially improved, remaining significantly lower than those prepared at 150 °C. Thus, the present study indicates that the majority of these defect states observed at elevated growth temperatures originates from bulk defects and underscores the importance to control the formation of bulk defects together with grain boundary and surface defects to further improve the optoelectronic properties of perovskites.Item 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.Item 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).Item 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.Item 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.Item 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.Item 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.Item 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.Item 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.Item 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.Item 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.Item 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.Item Water Interactions In Metal Organic Frameworks(Royal Society of Chemistry) Tan, Kui; Nijem, Nour; Gao, Yuzhi; Zuluaga, S.; Li, J.; Thonhauser, T.; Chabal, Yves J.; 0000 0000 4239 3958 (Chabal, YJ); 89624105 (Chabal, YJ); A-5998-2011 (Chabal, YJ)Metal organic frameworks (MOFs) have a strong potential for gas adsorption and separation such as H2 and CH4 storage, and CO2 capture. However, their instability in the presence of water vapor (many MOFs are hygroscopic) is one of the key issues that limit their large-scale application. Previous studies of water adsorption in MOFs have mainly relied on isotherm measurements that provide useful parameters such as adsorption uptake and isosteric heat of adsorption. The structural stability of MOFs in water vapor was also evaluated by powder X-ray diffraction measurements (PXRD). However, more studies are required to unravel the water interaction or reaction mechanisms within MOFs, which would be beneficial for the development of more robust frameworks. This review highlight focuses on water adsorption in two representative MOFs: M(bdc)(ted)0.5 [M = Cu2+, Zn2+, Ni2+, Co2+; bdc = 1,4-benzenedicarboxylate; ted = triethylenediamine] with saturated metal centers and MOF-74 [M2(dobdc), M = Mg2+, Zn2+, Ni2+, Co2+ and dobdc = 2,5-dihydroxybenzenedicarboxylic acid] with unsaturated metal centers. It shows how vibrational spectroscopy combined with van der Waals density functional (vdW-DF) calculations makes it possible to elucidate the details of water reaction in MOFs. The results presented in this highlight suggest that the reactivity and initial decomposition pathway of MOFs in water vapor critically depend on their structure and the specific metal cation in the building units. Water interaction with a hydrophobic MOF, in this case FMOF-1, is also reviewed. This information provides a framework for understanding water interactions or reactions within different types of MOFs.Item Colored Porous Silicon as Support for Plasmonic NanoparticlesLublow, M.; Kubala, S.; Veyan, Jean-Francois; Chabal, Yves J.; 0000 0000 4239 3958 (Chabal, YJ); 89624105 (Chabal, YJ)Colored nanoporous silicon thin films were employed as dielectric spacing layers for the enhancement of localized surface plasmon (LSP) polaritons. Upon formation of Au nanoparticles (Au-NPs) on these layers, a visible color change is observed due to multiple LSP resonance excitations. Far-field effects were assessed by angle-resolved reflectometry. Resonance enhancements, particularly for s-polarized light, account for the observed color change and are discussed in terms of effective medium and Mie scattering theory. Enhancements of the electric field strengths in the near-field and of the absorption in the substrate were deduced from finite difference time domain calculations and exceed considerably those of the non-porous Au-NP/Si interface. First results of improved photoelectrocatalytic hydrogen evolution at these interfaces are discussed. Samples were prepared by varied procedures of metal assisted etching and dry etching with XeF2. Structural and chemical properties were investigated by scanning electron and atomic force microscopy as well as energy dispersive x-ray analysis.Item 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.Item 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.Item Effective Sensing of RDX via Instant and Selective Detection of Ketone VaporsHu, Zhichao; Tan, Kui; Lustig, William P.; Wang, Hao; Zhao, Yonggang; Zheng, Chong; Banerjee, Debasis; Emge, Thomas J.; Chabal, Yves J.; Li, Jing; 0000 0000 4239 3958 (Chabal, YJ); 89624105 (Chabal, YJ)Two new luminescent metal-organic frameworks (LMOFs) were synthesized and examined for use as sensory materials. Very fast and effective sensing of RDX was achieved by vapor detection of a cyclic ketone used as a solvent in the production of plastic explosives. The effects of porosity and electronic structure of the LMOFs on their sensing performance were evaluated. We demonstrate that the optimization of these two factors of an LMOF can significantly improve its sensitivity and selectivity. We also elucidate the importance of both electron and energy transfer processes on the fluorescence response of a sensory material.