1,721,086 research outputs found
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.
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
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
Energy Transfer from Colloidal Nanocrystals into Si Substrates Studied via Photoluminescence Photon Counts and Decay Kinetics
No full textWe 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.NSF (DMR-1207123), NSF (CHE-091197) and the Texas Higher Education Coordinating Board NHARP programs
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
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.
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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
Nanocast Carbon Microsphere Flowers from a Lanthanum-Based Template
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).Supplementary material is available on publisher's website. Use the DOI link below.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.Robert A. Welch Foundation (AT-1153)School of Natural Sciences and MathematicsErik Jonsson School of Engineering and Computer Scienc
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