299 research outputs found
Role of excess ligand and effect of thermal treatment in hybrid inorganic-organic EUV resists
No full textFull text access from Treasures at UT Dallas is restricted to current UTD affiliates.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.Erik Jonsson School of Engineering and Computer Scienc
Cobalt and iron segregation and nitride formation from nitrogen plasma treatment of CoFeB surfaces
No full textCobalt-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).National Science Foundation (Grant No. CHE1300180)Erik Jonsson School of Engineering and Computer Scienc
Static and Dynamic Electronic Characterization of Organic Monolayers Grafted on a Silicon Surface
No full textIncludes supplementary material.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.
Understanding and Controlling Water Stability of MOF-74
No full textMetal 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."This work was entirely supported by Department of Energy Grant No. DE–FG02–08ER46491. It further used resources of the Oak Ridge Leadership Computing Facility at Oak Ridge National Laboratory, which is supported by the Office of Science of the Department of Energy under Contract DE–AC05– 00OR22725.
Wet chemical surface functionalization of oxide-free silicon
No full textSilicon 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.Accepted author's manuscrip
Colored porous silicon as support for plasmonic nanoparticles
No full textColored porous silicon as support for plasmonic nanoparticles M. Lublow,1,2,a S. Kubala,1,2 J. F. Veyan,3 and Y. J. Chabal3 1Helmholtz Centre Berlin for Materials and Energy, Institute for Heterogeneous Materials Systems, Berlin, Germany 2Department of Physical Chemistry, Fritz Haber Institute, Berlin, Germany 3Department of Materials Science and Engineering, University of Texas at Dallas, Texas, USA Received 15 November 2011; accepted 9 March 2012; published online 16 April 2012 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. VC 2012 American Institute of Physics. [http dx.doi.org 10.1063 1.370346
Non-Dispersive Infrared (NDIR) Sensor for Real-Time Nitrate Monitoring in Wastewater Treatment
No full textDue to copyright restrictions and/or publisher's policy full text access from Treasures at UT Dallas is limited to current UTD affiliates (use the provided Link to Article).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.National Science Foundation STTR program (contract# 1745730)Erik Jonsson School of Engineering and Computer Scienc
Interaction of Acid Gases SO<sub>2</sub> and NO<sub>2</sub> with Coordinatively Unsaturated Metal Organic Frameworks: M-MOF-74 (M = Zn, Mg, Ni, Co)
No full textFull text access from Treasures at UT Dallas is available only to current UTD affiliates.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.Department of Energy Grant No. DE-FG02-08ER46491; Simons Foundation Grant No. 391888.Erik Jonsson School of Engineering and Computer Scienc
Biphenyl-Bridged Wrinkled Mesoporous Silica Nanoparticles for Radioactive Iodine Capture
No full textDue to copyright restrictions and/or publisher's policy full text access from Treasures at UT Dallas is not available. UTD affiliates may be able to acquire a copy through Interlibrary Loan by using the link to UTD ILL.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.School of Natural Sciences and MathematicsErik Jonsson School of Engineering and Computer Scienc
Diffusion of Small Molecules in Metal Organic Framework Materials
No full textAb initio simulations are combined with in situ infrared spectroscopy to unveil the molecular transport of H-2, CO2, and H2O in the metal organic framework MOF-74-Mg. Our study uncovers-at the atomistic level-the major factors governing the transport mechanism of these small molecules. In particular, we identify four key diffusion mechanisms and calculate the corresponding diffusion barriers, which are nicely confirmed by time-resolved infrared experiments. We also answer a long-standing question about the existence of secondary adsorption sites for the guest molecules, and we show how those sites affect the macroscopic diffusion properties. Our findings are important to gain a fundamental understanding of the diffusion processes in these nanoporous materials, with direct implications for the usability of MOFs in gas sequestration and storage applications. DOI: 10.1103/PhysRevLett.110.02610
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