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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 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Controlling the Schottky Barrier at the Pt/TiO 2 Interface by Intercalation of a Self-Assembled Monolayer with Oriented Dipole Moments

Interfacial Schottky barriers can impact the catalytic function of Pt on TiO 2 . Since the electronic structure is characteristic of each material, it may be advantageous to tailor the interfacial Schottky barrier by the addition of adsorbed layers. Here, we show that the Schottky barrier in Pt/TiO 2 can be mitigated by the insertion of self-assembled monolayers (SAM) of carboranethiols that possess an oriented dipole moment. A Pt substrate with the SAM on which TiO 2 nanoparticles are deposited is used to that effect. Kelvin Probe Force Microscopy shows thatm-9-carboranethiolate SAM with perpendicular dipole moments decreases the potential difference between TiO 2 and Pt by ~0.3 eV due to the interfacial electric field of the SAM. Furthermore, our findings open new opportunities for tailoring interfacial electronic structures not only in the metal-semiconductor junction, but also the semiconductor heterojunctions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Synchrotron micro-computed tomography analysis of neutron-irradiated U-Mo fuel

The three-dimensional (3D) microstructure of neutron-irradiated uranium-10 wt.% molybdenum (U-10Mo) fuel with a burn-up of 9.8 × 10 21 fissions/cm 3 was characterized using a novel, multi-modal synchrotron micro-computed tomography approach combining propagation-based phase-contrast enhanced and absorption contrast techniques. The porosity development, porosity interconnectedness, swelling, composition, local thickness of the zirconium (Zr) diffusion barrier, and the influence of the fuel–cladding interaction on the local composition and pore morphology, were uniquely determined in 3D. Two cuboids were produced using a focused ion beam-scanning electron microscope at the Zr diffusion barrier–fuel interface and in the bulk fuel. The bulk fuel sample swelled by 53.3 [+9.7/−3.1]%, while the fuel near the Zr–fuel interface swelled by 63.3 [+14.7/−7.2]%. The average local thickness of the Zr diffusion barrier decreased by 53 %, compared to the expected pre-irradiated thickness. Four pore morphology regions were identified initiating parallel to the fuel–Zr interaction region: (1) an interaction layer of suppressed porosity, (2) a layer of elongated and interconnected porosity, (3) a transition zone of low porosity, and (4) a layer of unoriented porosity representative of the bulk fuel behavior. The increase in porosity near the diffusion barrier corresponded to a higher U concentration compared to that in the bulk fuel. The interconnected porosity in the fuel near the diffusion barrier was extensive and oriented parallel to the diffusion barrier, while the bulk fuel had more compact and isolated pore networks. The interaction layer, despite having suppressed porosity, was nearly 100 wt.% U. Porosity suppression at the diffusion barrier corresponds to the expected reduction in radiation-driven diffusion of Xe at the interface despite the anticipated increase in fission product nucleation originating from a higher U concentration. In conclusion, the novel 3D insights of the porosity, swelling, and compositional variations characterized herein can improve the fidelity of fuel performance codes for proliferation-resistant fuels for research and test reactors.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2016

Prospects of zero Schottky barrier height in a graphene-inserted MoS{sub 2}-metal interface

A low Schottky barrier height (SBH) at source/drain contact is essential for achieving high drive current in atomic layer MoS{sub 2}-channel-based field effect transistors. Approaches such as choosing metals with appropriate work functions and chemical doping are employed previously to improve the carrier injection from the contact electrodes to the channel and to mitigate the SBH between the MoS{sub 2} and metal. Recent experiments demonstrate significant SBH reduction when graphene layer is inserted between metal slab (Ti and Ni) and MoS{sub 2}. However, the physical or chemical origin of this phenomenon is not yet clearly understood. In this work, density functional theory simulations are performed, employing pseudopotentials with very high basis sets to get insights of the charge transfer between metal and monolayer MoS{sub 2} through the inserted graphene layer. Our atomistic simulations on 16 different interfaces involving five different metals (Ti, Ag, Ru, Au, and Pt) reveal that (i) such a decrease in SBH is not consistent among various metals, rather an increase in SBH is observed in case of Au and Pt; (ii) unlike MoS{sub 2}-metal interface, the projected dispersion of MoS{sub 2} remains preserved in any MoS{sub 2}-graphene-metal system with shift in the bands on the energy axis. (iii) A proper choice of metal (e.g., Ru) may exhibit ohmic nature in a graphene-inserted MoS{sub 2}-metal contact. These understandings would provide a direction in developing high-performance transistors involving heteroatomic layers as contact electrodes.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Paving the way to nanoionics: Atomic origin of barriers for ionic transport through interfaces

The blocking of ion transport at interfaces strongly limits the performance of electrochemical nanodevices for energy applications. The barrier is believed to arise from space-charge regions generated by mobile ions by analogy to semiconductor junctions. Here we show that something different is at play by studying ion transport in a bicrystal of yttria (9% mol) stabilized zirconia (YSZ), an emblematic oxide ion conductor. Aberration-corrected scanning transmission electron microscopy (STEM) provides structure and composition at atomic resolution, with the sensitivity to directly reveal the oxygen ion profile. We find that Y segregates to the grain boundary at Zr sites, together with a depletion of oxygen that is confined to a small length scale of around 0.5 nm. Contrary to the main thesis of the space-charge model, there exists no evidence of a long-range O vacancy depletion layer. Combining ion transport measurements across a single grain boundary by nanoscale electrochemical strain microscopy (ESM), broadband dielectric spectroscopy measurements, and density functional calculations, we show that grain-boundary-induced electronic states act as acceptors, resulting in a negatively charged core. In conclusion, besides the possible effect of the modified chemical bonding, this negative charge gives rise to an additional barrier for ion transport at the grain boundary.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Impact of interface materials on side permeation in indirect encapsulation of organic electronics

This work demonstrates the impact of the contact interface between barrier films and adhesives on the side permeation of moisture into packaged devices. When barrier films are brought into contact with the adhesive layer during indirect encapsulation, permeation along defects at this interface can occur due to the imperfect nature of contact, resulting in the formation of pores. The connected network of pores can act as capillaries and be an alternative pathway for water permeation as opposed to the bulk of the adhesive or edge seal materials used for barrier attachment to the package. The rate of water permeation through the capillaries is governed by surface energies of the materials at the interfaces. Experimental results demonstrate that the rate of water permeation is significantly lowered by using materials with higher contact angles at the interface.

36 MATERIALS SCIENCE↗
NASA NTRS1995

Finding the forest in the trees: The challenge of combining diverse environmental data

It has become increasingly important to conduct interdisciplinary environmental research assessments, both nationally and internationally. For this reason, the Committee for a Pilot Study on Database Interfaces was charged to review and advise on data interfacing activities. The committee used six case studies (1) to identify and understand the most important problems associated with collecting, integrating, and analyzing environmental data from local to global spatial scales and over a very wide range of temporal scales; and (2) to elaborate the common barriers to interfacing data of disparate sources and types. Consistent with the committee's charge, the primary focus was the interfacing of geophysical and ecological data. The case studies used by the committee were: The Impact Assessment Project for Drought Early Warning in the Sahel, The National Acid Precipitation Assessment Program, The H.J. Andrew Experimental Forest Long-Term Ecological Research Site, The Carbon Dioxide Information Analysis Center, The First International Satellite Land Surface Climatology Project (ISLSCP) Field Experiment, and The California Cooperative Oceanic Fisheries Investigation. The committee derived a number of lessons from the case studies, and these lessons are summarized at the end of each case study and analyzed in the last chapter. Some are generic in nature; others are more specific to a discipline or project. The conclusions and recommendations are based on the committee's analysis of the case studies and additional research. They are organized according to four major areas of barriers or challenges to the effective interfacing of diverse environmental data. In the final section the committee offers a set of broadly applicable principles (Ten Keys to Success) that can be used by scientists and data managers in planning and conducting interfacing activities.

Source record↗
DOE OSTI2022

Monocrystalline 1.7-eV MgCdTe solar cells

Monocrystalline 1.7-eV Mg 0.13 Cd 0.87 Te/Mg x Cd 1-x Te (x > 0.13) double-heterostructure (DH) solar cells with varying Mg composition in the barrier layers are grown by molecular beam epitaxy. Furthermore, a Mg 0.13 Cd 0.87 Te/Mg 0.37 Cd 0.63 Te DH solar cell featuring abrupt interfaces between barriers and absorber and the addition of a SiO 2 anti-reflective coating demonstrates open-circuit voltage (V OC ), short-circuit current density (J SC ), fill factor (FF), and device active-area efficiencies up to 1.129 V, 17.3 mA/cm 2 , 77.7% and 15.2%, respectively. The V OC and FF vary oppositely with the Mg x Cd 1-x Te barrier height indicating an optimal design of the MgCdTe DHs as a tradeoff between carrier confinement and carrier transport. Temperature-dependent V OC measurements reveal the majority of carrier recombination in the devices occurs outside the DHs, in the a-Si:H hole-contact layer and at the interface between the a-Si:H layer and the Mg x Cd 1-x Te top barrier at room temperature. Simulation results for the device with the highest efficiency show that the p-type a-Si:H layer and Mg 0.37 Cd 0.63 Te top barrier contribute 1.3 mA/cm 2 and 2.4 mA/cm 2 J SC loss, respectively.

14 SOLAR ENERGY↗
DOE OSTI2018

TiN diffusion barrier for stable W/SiC(0001) interfaces in inert ambient at high temperature

The effect of high-temperature annealing on tungsten (W) films deposited on silicon carbide (SiC) with and without a titanium nitride (TiN) diffusion barrier was examined as a function of time. Evolutions in phase composition, surface morphology, and roughness from annealing at 1273 K were investigated for up to 24 h. Without a TiN diffusion barrier, solid state reactions between the W film and SiC substrate led to the formation of W 5 Si 3 , W 2 C, and WC species and the rise of an inhomogeneous surface structure that was initially web-like and later discontinuous. Severe roughening on the order of the initial film thickness was observed. Incorporation of a 100 nm TiN diffusion barrier suppressed the formation of W 5 Si 3 and W 2 C and only trace WC could be detected due to species diffusion through TiN grain boundaries. Changes in the surface structure and roughness were minimal. Our results warrant consideration of TiN as an effective diffusion barrier for W on SiC systems where structural stability at high temperatures is highly desired.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Understanding and Design of Polymer Device Interfaces

The research performed under grant DE-FG02-04ER46165 between May 2008 and April 2011 focused on the understanding and control of interfaces of organic semiconductors in general, and polymer interfaces more specifically. This work was a joined effort by three experimentalists and a theoretician. Emphasis was placed on the determination of the electronic structure of these interfaces, i.e. the relative energy position of molecular levels across these interfaces. From these electronic structures depend the injection, extraction and transport of charge carriers into, from and across, respectively, all (opto)electronic devices made of these semiconductors. A significant fraction of our work focused on ways to modify and optimize interfaces, for example via chemical doping of the semiconductors to reduce interface energy barriers or via deposition of ultra-thin work function-reducing polymer or self-assembled monolayers of dipolar molecules. Another significant fraction of our work was devoted to exploring alternate and unconventional interface formation methods, in particular the soft-contact lamination of both metal contacts and polymer overlayers on top of polymer films. These methods allowed us to better understand the impact of hot metal atom evaporation on a soft organic surface, as well as the key mechanisms that control the energetics of polymer/polymer heterojunctions. Finally, a significant fraction of the research was directed to understanding the electronic structure of buried polymer heterojunctions, in particular within donor/acceptor blends of interest in organic photovoltaic applications. The work supported by this grant resulted in 17 publications in some of the best peer-reviewed journals of the field, as well as numerous presentations at US and international conferences.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Analytic model of electron transport through and over non-linear barriers

Tunneling barriers are an essential component of electron sources, sensors, detectors, and vacuum nanoelectronics, and a pivotal factor in their performance, but the barriers themselves routinely depart from the analytic models used to model their behavior. Here, a new formalism is developed to analytically and accurately model emission through and over barriers associated with depletion layers, nanotip barriers, and MIM structures. The transmission probability for depletion layer and metal-insulator-metal (MIM) and metaloxide-semiconductor (MOS) barriers is accurately modeled as the electron energy exceeds the barrier height using approaches designed for rapid implementation demanded by simulation codes, and extensible to general barriers. The models supersede conventional thermal and field models in depletion and MIM/MOS barrier studies. Thermal-field methods are used to treat the transmission probability, and shape factor methods to treat the tunneling factor. Analytic formulae for current density are obtained. The methods ease device simulation and characterization of current-voltage relations for emerging technologically interesting barriers with better accuracy.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2021

Solid-state batteries and the critical role of interfaces

The Grand Challenge for the next generation of energy storage technologies is no longer the identification of electroactive cathode or anode materials thanks to extensive worldwide synthesis efforts along with theory and modeling like the Materials Project.1 Instead, the critical challenges revolve around assembling materials in the right architecture to achieve maximum performance and cell life at reasonable temperatures and pressures. Nowhere is this more critical than on the next generation of energy storage technologies revolving around all solid-state batteries. These batteries are the ultimate challenge for materials science requiring new ways to assemble multiple dissimilar materials such that: (1) interfaces are optimized to facilitate ion motion across the different compounds while (2) maintaining chemical stability and (3) simultaneously preserving the crystal structures of each phase during (4) large volume changes due to shuttling of lithium, at (5) room temperature and under (6) atmospheric pressure. To address these requirements will require insights and expertise from research fields outside the traditional lithium-ion battery community such as solid oxide fuel cells, synthesis science, barrier layers, interface formers, sintering, and mechanical properties.

25 ENERGY STORAGE↗
NASA NTRS1990

Surface Cracking and Interface Reaction Associated Delamination Failure of Thermal and Environmental Barrier

In this paper, surface cracking and interface reactions of a ZrO2-8wt%Y2O3 and mullite/BSAS/Si thermal and environmental barrier coating system on SiC/SiC ceramic matrix composites were characterized after long-term combined laser thermal gradient and furnace cyclic tests in a water vapor containing environment. The surface cracking was analyzed based on the coating thermal gradient sintering behavior and thermal expansion mismatch stress characteristics under the thermal cyclic conditions. The interface reactions that were largely enhanced by the coating surface cracking in the water vapor environment were investigated in detail, and the reaction phases were identified for the coating system after the long-term exposure. The accelerated coating delamination failure was attributed to the increased delamination driving force under the thermal gradient cyclic loading and the reduced interface adhesion due to the detrimental interface reactions. The coating design issues will also be discussed based on the observed failure mechanisms under the high-heat-flux test conditions.

Zhu, Dongming↗
DOE OSTI2019

Influences of buffer material and fabrication atmosphere on the electrical properties of CdTe solar cells

Abstract The electrical properties such as interface energy barriers, defect energy levels, and densities dictate the performance of thin film solar cells. Here, we show that these properties can be quantified in cadmium telluride (CdTe) thin‐film solar cells using admittance spectroscopy‐based techniques. Our results reveal that the electrical properties in CdTe thin‐film solar cells depend on both buffer material and the fabrication atmosphere. We find that only a negligible front contact barrier exists at the CdS/CdTe front junction regardless of the fabrication atmospheres, while an obvious front barriers are observed at the ZnMgO (ZMO)/CdTe junctions. Both CdS/CdTe and ZMO/CdTe solar cells exhibit back contact barrier. The energy level of defects is shallower in CdS/CdTe cells than in ZMO/CdTe cells. The fabrication atmosphere influences the electrical properties, i.e., an oxygen‐free atmosphere reduces the front and back barrier heights and lowers the energy level of defects. The results provide critical insights for understanding and optimizing the performance of CdTe thin‐film solar cells.

Awni, Rasha A.↗
DOE OSTI2017

Spin-polarized confined states in Ag films on Fe(110)

Spin- and angle-resolved photoemission spectroscopy of thin Ag(111) films on ferromagnetic Fe(110) shows a series of spin-polarized peaks. These features derive from Ag sp -bands, which form quantum well states and resonances due to confinement by a spin-dependent interface potential barrier. The spin-up states are broader and located at higher binding energy than the corresponding spin-down states at Gamma, although the differences attenuate near the Fermi level. The spin-down states display multiple gap openings, which interrupt their parabolic-like dispersion. As a result, first-principles calculations attribute these findings to the symmetry- and spin-selective hybridization of the Ag states with the exchange-split bands of the substrate.

36 MATERIALS SCIENCE↗
NASA NTRS1976

Metal interfaces - Adhesive energies and electronic barriers

We report a fully self-consistent calculation of the electron number density, barrier height and adhesive energy as a function of separation in an aluminum-aluminum (100) contact. The local density approximation is used for exchange and correlation. The electron number density and barrier heights are strong functions of the separation. The range of strong chemical bonding is about 0.2 nm.

Ferrante, J.↗
NASA NTRS1995

Finding the forest in the trees. The challenge of combining diverse environmental data

Development of analytical and functional guidelines to help researchers and technicians engaged in interdisciplinary research to better plan and implement their supporting data management activities is addressed. An emphasis is on the projects that involve both geophysical and ecological issues. Six case studies were used to identify and to understand problems associated with collecting, integrating, and analyzing environmental data from local to global spatial scales and over a range of temporal scales. These case studies were also used to elaborate the common barriers to interfacing data of disparate sources and types. A number of lessons derived from the case studies are summarized and analyzed.

Source record↗
DOE OSTI2015

Tuning band alignment using interface dipoles at the Pt/anatase TiO 2 interface

The Schottky barrier heights at the Pt/TiO 2 (001) junctions are modulated over 0.8 eV by inserting <1 nm of LaAlO 3 . The large electric field in the LaAlO 3 is stabilized by preserving the continuity of in-plane lattice symmetry at the oxide interface. Lastly, these results greatly expand the application of dipole engineering to versatile polycrystalline metal/binary oxide functional interfaces.

36 MATERIALS SCIENCE↗