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Results for “Surface functionalization”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 1,081 records · Page 60
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Simulating groundwater uptake and hydraulic redistribution by phreatophytes in a high-resolution, coupled subsurface-land surface model

Several new functions representing groundwater dependent vegetation were incorporated into a coupled subsurface-land surface model, ParFlow.CLM, in order to adequately describe groundwater water uptake, hydraulic redistribution, and plant water stress. The modified model was used to conduct three-dimensional, stand-scale simulations of a Mediterranean oak savanna in California. It performed well and captured daily, hourly and spatial water and energy dynamics, as well as groundwater evapotranspiration rates. The new model was then compared to various approaches, the original ParFlow.CLM and a version using a root water uptake compensation equation. During the dry season, the modified model closely predicted the measured transpiration rate while the original model predicted that it would become zero and the compensation approach overestimated it by nearly double. The modified model also allowed for analysis of several key ecohydrological processes, namely the hydraulic redistribution when plants were both active and dormant, the leaf water potential, and xylem cavitation.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2016

Growth and characterization of Al{sub 2}O{sub 3} films on fluorine functionalized epitaxial graphene

Intelligent engineering of graphene-based electronic devices on SiC(0001) requires a better understanding of processes used to deposit gate-dielectric materials on graphene. Recently, Al{sub 2}O{sub 3} dielectrics have been shown to form conformal, pinhole-free thin films by functionalizing the top surface of the graphene with fluorine prior to atomic layer deposition (ALD) of the Al{sub 2}O{sub 3} using a trimethylaluminum (TMA) precursor. In this work, the functionalization and ALD-precursor adsorption processes have been studied with angle-resolved photoelectron spectroscopy, low energy electron diffraction, and X-ray photoelectron spectroscopy. It has been found that the functionalization process has a negligible effect on the electronic structure of the graphene, and that it results in a twofold increase in the adsorption of the ALD-precursor. In situ TMA-dosing and XPS studies were also performed on three different Si(100) substrates that were terminated with H, OH, or dangling Si-bonds. This dosing experiment revealed that OH is required for TMA adsorption. Based on those data along with supportive in situ measurements that showed F-functionalization increases the amount of oxygen (in the form of adsorbed H{sub 2}O) on the surface of the graphene, a model for TMA-adsorption on graphene is proposed that is based on a reaction of a TMA molecule with OH.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Transport Measurements of Surface Electrons in 200-nm-Deep Helium-Filled Microchannels Above Amorphous Metallic Electrodes

We report transport measurements of electrons on helium in a microchannel device where the channels are 200 nm deep and 3μm wide. The channels are fabricated above amorphous metallic Ta 40 W 40 Si 20 , which has surface roughness below 1 nm and minimal variations in work function across the surface due to the absence of polycrystalline grains. We are able to set the electron density in the channels using a ground plane. We estimate a mobility of 300cm 2 /Vs and electron densities as high as 2.56×10 9 cm -2 . We demonstrate control of the transport using a barrier which enables pinch-off at a central microchannel connecting two reservoirs. The conductance through the central microchannel is measured to be 10 nS for an electron density of 1.58×10 9 cm -2 . Lastly, our work extends transport measurements of surface electrons to thin helium films in microchannel devices above metallic substrates.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2020

First-principles study of the surface properties of uranium carbides

Uranium carbides have attracted renewed interest as advanced nuclear fuels for Generation IV reactors. As an important property required for gas bubble modeling in nuclear fuels, the surface energy of uranium carbides is scarce in literature. In this work, we study the surface properties of uranium carbides by first-principles density functional theory calculations. Surface orientations with maximum Miller index up to 3, 2 and 2 are investigated for UC, U 2 C 3 and α-UC 2 , respectively. By studying the effects of surface termination and chemical potential on surface energy, we identify the factors that determines the surface stability. From the calculated surface energies, the surface properties of uranium carbide single crystals are obtained from Wulff construction, including equilibrium morphology, dominant surface orientation and area weighted surface energy.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Methyl Formate Formation during Methanol Conversion over the (111) Ceria Surface

We study methyl formate formation during methanol conversion on the fully oxidized and partially reduced ceria (111) surface using density functional theory. Starting from methanol and formaldehyde adsorbed on the surface, we consider two pathways of methyl formate production. Pathway 1 consists of formaldehyde dehydrogenation followed by oxygen–carbon bond formation. Along pathway 2, the oxygen–carbon bond is established prior to intermediate dehydrogenation. Formaldehyde production is observed at elevated temperature at which we expect both pathways to be energetically attainable on the fully oxidized surface. However, the probability of both reactants being adsorbed next to each other is low. This probability can be increased by the reduction of the surface. The partially reduced ceria surface is modeled by the introduction of an oxygen vacancy in the surface. If formaldehyde adsorbs over a vacancy, both pathways potentially contribute to methyl formate formation. In contrast, if methoxide that is obtained by dissociative adsorption of methanol is placed in the vacancy, methyl formate production becomes energetically highly demanding. Still, dehydrogenation of methoxide or methoxide exchange with coadsorbates converts methoxide in a vacancy to an active species for methyl formate formation while increasing the residence time of methoxide on the surface. Importantly, the preference of pathway 1 is due to the promotion of surface-bound formaldehyde dehydrogenation by methoxide.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1973

Geometry program for aerodynamic lifting surface theory

A computer program that provides the geometry and boundary conditions appropriate for an analysis of a lifting, thin wing with control surfaces in linearized, subsonic, steady flow is presented. The kernel function method lifting surface theory is applied. The data which is generated by the program is stored on disk files or tapes for later use by programs which calculate an influence matrix, plot the wing planform, and evaluate the loads on the wing. In addition to processing data for subsequent use in a lifting surface analysis, the program is useful for computing area and mean geometric chords of the wing and control surfaces.

Medan, R. T.↗
DOE OSTI2022

UAS remote sensing (DJI Phantom 4 RTK platform): RGB orthomosaic, digital surface and canopy height models, plant functional type map, Seward Peninsula, Alaska, 2019

Airborne remote sensing data collected using a DJI Phantom 4 RTK unoccupied aerial system (UAS) ? operated by the University of Maine Wheatland Geospatial Lab (https://wheatlandlab.org/). This package includes data from 17 flights flown over the NGEE-Arctic Council, Kougarok, Kougarok Mile80, Teller, and Teller Mile32 sites in July 2019. The Phantom 4 RTK is a drone platform that collects very high spatial resolution optical red/green/blue (RGB) imagery. Derived image products include point cloud, ortho-mosaiced RGB, a digital surface model (DSM) using the structure from motion (SfM) technique, and a canopy height model (CHM). Unprocessed and processed data products (1,000+ files) are included in this package (processing levels 0-3). Data and metadata are provided as text (*.txt, *.json, *hdr,), ENVI image file (*.dat), point cloud (*.laz) and image (*.jpg, *.tif, *png) formats. The Next-Generation Ecosystem Experiments: Arctic (NGEE Arctic), was a research effort to reduce uncertainty in Earth System Models by developing a predictive understanding of carbon-rich Arctic ecosystems and feedbacks to climate. NGEE Arctic was supported by the Department of Energy's Office of Biological and Environmental Research. The NGEE Arctic project had two field research sites: 1) located within the Arctic polygonal tundra coastal region on the Barrow Environmental Observatory (BEO) and the North Slope near Utqiagvik (Barrow), Alaska and 2) multiple areas on the discontinuous permafrost region of the Seward Peninsula north of Nome, Alaska. Through observations, experiments, and synthesis with existing datasets, NGEE Arctic provided an enhanced knowledge base for multi-scale modeling and contributed to improved process representation at global pan-Arctic scales within the Department of Energy's Earth system Model (the Energy Exascale Earth System Model, or E3SM), and specifically within the E3SM Land Model component (ELM).

54 ENVIRONMENTAL SCIENCES↗
NASA NTRS1997

Functional specializations in human cerebral cortex analyzed using the Visible Man surface-based atlas

We used surface-based representations to analyze functional specializations in the human cerebral cortex. A computerized reconstruction of the cortical surface of the Visible Man digital atlas was generated and transformed to the Talairach coordinate system. This surface was also flattened and used to establish a surface-based coordinate system that respects the topology of the cortical sheet. The linkage between two-dimensional and three-dimensional representations allows the locations of published neuroimaging activation foci to be stereotaxically projected onto the Visible Man cortical flat map. An analysis of two activation studies related to the hearing and reading of music and of words illustrates how this approach permits the systematic estimation of the degree of functional segregation and of potential functional overlap for different aspects of sensory processing.

Non-NASA Center↗
DOE OSTI2020

Incorporating Electronic Information into Machine Learning Potential Energy Surfaces via Approaching the Ground-State Electronic Energy as a Function of Atom-Based Electronic Populations

Machine learning (ML) approximations to density functional theory (DFT) potential energy surfaces (PESs) are showing great promise for reducing the computational cost of accurate molecular simulations, but at present, they are not applicable to varying electronic states, and in particular, they are not well suited for molecular systems in which the local electronic structure is sensitive to the medium to long-range electronic environment. With this issue as the focal point, we present a new machine learning approach called "BpopNN" for obtaining efficient approximations to DFT PESs. Conceptually, the methodology is based on approaching the true DFT energy as a function of electron populations on atoms; in practice, this is realized with available density functionals and constrained DFT (CDFT). Additionally, the new approach creates approximations to this function with neural networks. These approximations thereby incorporate electronic information naturally into a ML approach, and optimizing the model energy with respect to populations allows the electronic terms to self-consistently adapt to the environment, as in DFT. We confirm the effectiveness of this approach with a variety of calculations on LinHn clusters.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

The Effect of Surface Terminations on the Initial Stages of TiO 2 Deposition on Functionalized Silicon

As atomic layer deposition (ALD) emerges as a method to fabricate architectures with atomic precision, emphasis is placed on understanding surface reactions and nucleation mechanisms. ALD of titanium dioxide with TiCl 4 and water has been used to investigate deposition processes in general, but the effect of surface termination on the initial TiO 2 nucleation lacks needed mechanistic insights. Here, this work examines the adsorption of TiCl 4 on Cl–, H–, and HO– terminated Si(100) and Si(111) surfaces to elucidate the general role of different surface structures and defect types in manipulating surface reactivity of growth and non-growth substrates. The surface sites and their role in the initial stages of deposition are examined by X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). Density functional theory (DFT) computations of the local functionalized silicon surfaces suggest oxygen-containing defects are primary drivers of selectivity loss on these surfaces.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

Structure and stability of CaH 2 surfaces: on the possibility of electron-rich surfaces in metal hydrides for catalysis

Structure, thermodynamic stability, and electronic properties of CaH 2 surfaces in (001),(110), and (111) crystallographic orientations are investigated using ab initio modeling. We show that stoichiometric surfaces terminated with a hydrogen atomic plane are the most energetically favorable and discuss properties of hydrogen vacancies (VH) at these surfaces. The average calculated work function of the most stable pristine surfaces (~5.2 eV) is in agree-ment with experimental data for powder samples. Neutral hydrogen vacancies host localized electrons and induce defect states in the band gap, thereby shifting the effective work function to much lower values of ~2.7 eV. Surface VH are predicted to aggregate into dimers and form electron-rich centers (e - )Ca 2+ (e - ) stable to over 800 K. These results suggest that hydrogen-deficient surfaces of CaH 2 can host a large concentration of localized electrons and, thus, give rise to new catalytic functionalities involving electron transfer between the surface, catalysts supported on it, and reacting species.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Selective acetylene hydrogenation over single metal atoms supported on Fe 3 O 4 (001): A first-principle study

Supported single-atom catalysts (SACs) have gained increasing attention for improved catalytic activity and selectivity for industrially-relevant reactions. In this study, we explore the hydrogenation of acetylene over single Pt, Ru, Rh, Pd, and Ir atoms supported on the Fe 3 O 4 (001) surface using density functional theory (DFT) calculations. The thermodynamic profile of H diffusion is significantly changed with the type of single metal atoms used and suggests that H spillover from the single atom dopant to the Fe 3 O 4 (001) surface is favored and will likely lead to high H coverages in the functioning catalyst. Correspondingly, as the surface H coverage increases, the important desorption step of ethylene becomes energetically competitive against the detrimental hydrogenation steps of ethylene to ethane. Overall, we show herein that the selectivity of SACs towards ethylene production can be tuned by considering the proper type of metal and controlling the redox state of the support.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Mapping VIS-terahertz (=17 THz) surface plasmons sustained on native and chemically functionalized percolated gold thin films using EELS

Heterogeneous assemblies of molecules (Rhodamine B) adsorbed onto a nano-corrugated metallic surface (a percolated Au network) are investigated using electron energy loss spectroscopy in the scanning transmission electron microscope (STEM-EELS). Our first measurements target the native metallic substrate, which consists of a commercial Au thin film atop an ultrathin carbon membrane. The Au film displays a percolated morphology with nanostructures of estimated thickness = 10nm approximately. We observe a rich plasmonic response from the metallic substrate; one which varies nanometrically and spans the VISterahertz region. Multiple localized plasmons are detected at individual nanometric integrated areas, while the spatial distribution of the fields reveal that LSPRs within the same integrated energy window (of 50meV) are supported at different locations simultaneously. We record subsequent EEL spectrum images of the hybrid molecular-metallic construct after deposition of Rhodamine B molecules onto the substrate, where plasmons, molecular vibrations and electronic excitations might all be simultaneously detected. A comparison of average signals for both systems is performed and spectral variations within the three spectral regions where molecular signatures may be observed are discussed. Our measurements and their analysis if applied to the same location before and after molecular deposit, may be used to rationalize optical microscopic and spectroscopic measurements that take advantage of the interplay between molecules and plasmons.

Abellan, Patricia↗
DOE OSTI2016

Novel Structure and Unexpected RNA-Binding Ability of the C-Terminal Domain of Herpes Simplex Virus 1 Tegument Protein UL21

Proteins forming the tegument layers of herpesviral virions mediate many essential processes in the viral replication cycle, yet few have been characterized in detail. UL21 is one such multifunctional tegument protein and is conserved among alphaherpesviruses. While UL21 has been implicated in many processes in viral replication, ranging from nuclear egress to virion morphogenesis to cell-cell spread, its precise roles remain unclear. Here we report the 2.7-Å crystal structure of the C-terminal domain of herpes simplex virus 1 (HSV-1) UL21 (UL21C), which has a unique α-helical fold resembling a dragonfly. Analysis of evolutionary conservation patterns and surface electrostatics pinpointed four regions of potential functional importance on the surface of UL21C to be pursued by mutagenesis. In combination with the previously determined structure of the N-terminal domain of UL21, the structure of UL21C provides a 3-dimensional framework for targeted exploration of the multiple roles of UL21 in the replication and pathogenesis of alphaherpesviruses. Additionally, we describe an unanticipated ability of UL21 to bind RNA, which may hint at a yet unexplored function. IMPORTANCE Due to the limited genomic coding capacity of viruses, viral proteins are often multifunctional, which makes them attractive antiviral targets. Such multifunctionality, however, complicates their study, which often involves constructing and characterizing null mutant viruses. Systematic exploration of these multifunctional proteins requires detailed road maps in the form of 3-dimensional structures. In this work, we determined the crystal structure of the C-terminal domain of UL21, a multifunctional tegument protein that is conserved among alphaherpesviruses. Structural analysis pinpointed surface areas of potential functional importance that provide a starting point for mutagenesis. In addition, the unexpected RNA-binding ability of UL21 may expand its functional repertoire. The structure of UL21C and the observation of its RNA-binding ability are the latest additions to the navigational chart that can guide the exploration of the multiple functions of UL21.

Metrick, Claire M.↗
DOE OSTI2025

Tuning Molecular Interactions between Peptoids and Substrates to Achieve Surface-Agnostic Coating

Achieving programmable and robust coatings that maintain functionality while adhering to various surface types with molecular-level tunability and programmable features remains challenging. In this study, we develop adaptable and stable surface-agnostic coatings (SACs) based on crystalline peptoid membranes by tuning interpeptoid and peptoid-substrate interactions. We utilize two complementary methods: (1) surfaceinduced assembly, where peptoid membranes form directly on substrates, and (2) depositing preformed peptoid crystalline membranes via an aqueous layer-by-layer (LbL) assembly technique. These strategies are applied to substrates with diverse surface chemistries and topographies, including mica, highly ordered pyrolytic graphite (HOPG), MoS 2 , sapphire, and porous membranes like porous alumina and polysulfide. Atomic force microscopy confirms the formation of peptoid coatings and reveals differences in assembly behavior across surfaces. Moisture vapor transport measurements serve as a proof-of-concept test for membrane continuity and tunable permeance. Together, these findings demonstrate the adaptability and programmability of peptoid-based SACs, enabling rational coating design on surfaces with diverse chemical and topographical features. Furthermore, this work opens pathways for using peptoid membranes as programmable surface modifiers in functional interfaces, protective coatings, and membrane platforms.

biomimetic polymers↗
DOE OSTI2020

Stronger field-emission science via coupling novel nanoscale imaging techniques

We implemented a vacuum field emission electron microscope (FEM) using the electron optics of a low-energy /photoemission electron microscope (LEEM/PEEM). Historically, there have been other FEM hardware platforms, and the distinctive feature of our method is that it integrates with the LEEM/PEEM and associated techniques, enabling a powerful multi-capability toolset for studying fundamental materials properties underpinning field emission (FE) and vacuum arc initiation. Typically, LEEM is used to image surface structure, which influences both work function and electric field distribution near a surface, while PEEM is used to map photoelectric work function across a surface. Our FEM adds the capability for spatially-correlated coincident-site measurements of FE currents to go-along with structure and work function. LEEM, PEEM, and our FEM implementation achieve nanoscale spatial resolution relevant for materials studies in nanoscience/engineering. Our approach requires a straightforward calibration of the electron optics to enable focused FEM imaging under intentional electric field variation. We demonstrate the FEM approach by imaging field emitter arrays relevant for vacuum nanoelectronics. We demonstrate submicron spatial resolution and dynamic measurement of FE versus applied electric field. We anticipate this capability will enable fundamental structure-function studies of FE and arc initiation.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2022

Surface and Optoelectronic Properties of Ultrathin Trigonal Selenium: A Density Functional Theory Study with van der Waals Correction

Selenium is a crucial earth-abundant and non-toxic semiconductor with a wide range of applications across the semiconductor industries. Selenium has drawn attention from scientific communities for its wide range of applicability: from photovoltaics to imaging devices. Its usage as a photosensitive material largely involves the synthesis of the amorphous phase (a-Se) via various experimental techniques. However, the ground state crystalline phase of this material, known as the trigonal selenium (\textit{t}-Se), is not extensively studied for its optimum electronic and optical properties. In this work, we present density functional theory (DFT) based systematic studies on the ultra-thin $(10\overline{1}0)$ surface slabs of \textit{t}-Se. We report the surface energies, work function, electronic and optical properties as a function of number of layers for $(10\overline{1}0)$ surface slabs to access its suitability for applications as a photosensitive material.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
NASA NTRS2007

Seeking to Improve Low Energy Neutral Atom Detection in Space

The detection of energetic neutral atoms allows for the remote examination of the interactions between plasmas and neutral populations in space. Before these neutral atoms can be measured, they must first be converted to ions. For the low energy end of this spectrum, interaction with a conversion surface is often the most efficient method to convert neutrals into ions. It is generally thought that the most efficient surfaces are low work functions materials. However, by their very nature, these surfaces are highly reactive and unstable, and therefore are not suitable for space missions where conditions cannot be controlled as they are in a laboratory. We therefore are looking to optimize a stable surface for conversion efficiency. Conversion efficiency can be increased either by changing the incident angle of the neutral particles to be grazing incidence and using stable surfaces with high conversion efficiencies. We have examined how to increase the angle of incidence from -80 degrees to -89 degrees, while maintaining or improving the total active conversion surface area without increasing the overall volume of the instrument. We are developing a method to micro-machine silicon, which will reduce the volume to surface area ratio by a factor of 60. We have also examined the material properties that affect the conversion efficiency of the surface for stable surfaces. Some of the parameters we have examined are work function, smoothness, and bond structure. We find that for stable surfaces, the most important property is the smoothness of the surface.

Shappirio, M.↗