Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “material defects”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,387 records · Page 77
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Recovery of Acid-Gas-Degraded Zeolitic Imidazolate Frameworks by Solvent-Assisted Crystal Redemption (SACRed)

The acid stability of zeolitic imidazolate frameworks (ZIFs) is an important issue hindering their application. Acid-gas damage of ZIFs has been considered irreversible. However, we demonstrate here a methodology called solvent-assisted crystal redemption (SACRed) to reverse acid-gas damage to ZIFs with a high degree of structural and functional recovery. For example, post-SACRed ZIF-8 is shown to be structurally and chemically near-identical with the original pristine ZIF-8 that suffered a large loss of surface area, porosity, and crystallinity during acid-gas exposure. We also provide mechanistic insight into the recovery process using deuterium-labeled linkers and 2 H NMR spectroscopy. SACRed treatments could allow large extensions in the lifetime of ZIF-based membranes and adsorbents that degrade over time.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Tunability of multichannel optical filter based on magnetized one-dimensional plasma photonic crystal

A one dimensional plasma photonic crystal (1DPPC) structure was proposed to design a tunable compressing/broadening multi-channel optical filter with external controllability. The 1DPPC with arrangement of (AP){sup n}D(PA){sup n}, where A and D are the dielectric materials, P is a magnetized plasma layer and n is the number of the periodicity, was proposed. The well-known transfer matrix method was employed for analysis. In linear transmittance spectrum, n − 1 defect modes were appeared inside the photonic band gap. The results were shown that by increasing the applied magnetic field intensity and its direction, a red-shift and blue-shift were, respectively, observed in defect mode frequencies. On the other hand, the modes were compressed and broadened with increasing the intensity and the direction of the applied magnetic field, respectively. Externally controllable defect modes can be useful in designing a multichannel tunable optical filter.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2025

Controllable oxygen vacancy defect engineering of BiVO 4 porous structures for room temperature NH 3 detection

Controlling structural features of sensing material while judiciously introducing vacancy defect states for revamping the electronic properties of the sample to obtain its superior gas sensing performance, is quite rare. Herein, we report for the first time, the room temperature (RT) ammonia (NH 3 ) detection of peanut-like porous bismuth vanadate (BiVO 4 ) with a stable monoclinic phase. The developed BiVO 4 possess abundant oxygen vacancies and porosity by virtue of calcinations (400–800 ℃). BiVO 4 calcined at 400 ℃ exhibits high selectivity towards NH 3 with a maximum response of 1421 @ 270 ppm at RT, which is 2.5 fold enhanced compared to without calcined BiVO 4 (response of 547 @ 270 ppm NH 3 ). The oxygen defective BiVO 4 appeared highly durable and stable even under high humid conditions (∼60 %). Besides, the porosity of BiVO 4 not only enhances the specific surface area (19.8 m 2 /g) but also results in fast diffusion of NH 3 molecules, leading to a reduction in the decay time (34 s for 90 ppm NH 3 ). The density functional theory (DFT) uncovers that the oxygen vacancy formation in BiVO 4 augments the NH 3 sensing capabilities by enhancing the adsorption energy of NH 3 . This work provides insight into the sensing mechanism of increased response caused by defect engineering and porosity, which will be favourable for fabricating high-performance NH 3 sensors at RT.

DFT analysis↗
DOE OSTI2015

Point defect states in Sb-doped germanium

Defect states in n-type Sb-doped germanium were investigated by deep-level transient spectroscopy. Cobalt-60 gamma rays were used to generate isolated vacancies and interstitials which diffuse and react with impurities in the material to form four defect states (E{sub 37}, E{sub 30}, E{sub 22}, and E{sub 21}) in the upper half of the bandgap. Irradiations at 77 K and 300 K as well as isothermal anneals were performed to characterize the relationships between the four observable defects. E{sub 37} is assigned to the Sb donor-vacancy associate (E-center) and is the only vacancy containing defect giving an estimate of 2 × 10{sup 11 }cm{sup −3} Mrad{sup −1} for the uncorrelated vacancy-interstitial pair introduction rate. The remaining three defect states are interstitial associates and transform among one another. Conversion ratios between E{sub 22}, E{sub 21}, and E{sub 30} indicate that E{sub 22} likely contains two interstitials.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2010

Observation and Destruction of an Elusive Adsorbate with STM: O{sub 2}/TiO{sub 2}(110)

When a slightly defective rutile TiO{sub 2}(110) surface is exposed to O{sub 2} at elevated temperatures, the molecule dissociates at defects, filling O vacancies (V{sub O}) and creating O adatoms (O{sub ad}) on Ti{sub 5c} rows. The adsorption of molecular O{sub 2} at low temperatures has remained controversial. Low-temperature scanning tunneling microscopy of O{sub 2}, dosed on TiO{sub 2}(110) at a sample temperature of {approx_equal}100 K and imaged at 17 K, shows a molecular precursor at V{sub O} as a faint change in contrast. The adsorbed O{sub 2} easily dissociates during the STM measurements, and the formation of O{sub ad}'s at both sides of the original V{sub O} is observed.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2018

Probing Plasticity and Strain-Rate Effects of Indium Submicron Pillars Using Synchrotron Laue X-ray Microdiffraction

We present that mechanical behaviors and especially the strain-rate responses at the nanoscales of low melting temperature metals, such as indium have not been much studied. Indium is one of the key materials or alloy-components in advanced microelectronics and nanotechnology industry, and understanding their mechanical behaviors at nanoscales becomes increasingly important to ensure lifetime reliability of their applications in novel nanoscale devices or advanced systems (for packaging at the nanoscales, for instance). Synchrotron X-ray microdiffraction has been utilized to examine defect structures of nanoscale materials as well as their strain-rate responses. Nanoscale or advanced microelectronics packaging, for instance, require acceptable levels of drop test results. For these low melting temperature materials especially, this technique offers a unique advantage as conventional methods such as TEM and EBSD will expose the structure to high energy electron beams that may significantly alter the microstructure and defect structure during analysis. Using this approach, we found interesting differences in term of X-ray peak broadening after deformation with different strain rates, which could indicate differences in plasticity mechanisms in the submicron pillars of indium, which could be important for its applications in nanodevices. Finally, understanding these differences could lead to better control of mechanical properties of low melting temperature metals at the nanoscales and thus have important implications for nanodevice reliability.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Enhanced defect annihilation capability of the graphene/copper interface: An in situ study

It is well known that energetic heavy ion irradiations can often induce defects and ultimately lead to material degradations. Interfaces, such as high-angle grain boundaries (HAGBs), are generally used as defect sinks for alleviating the irradiation damage. However, HAGBs are often unstable during radiation. Here we investigate the interfacial irradiation responses of the graphene (Gr)/Cu composites by using in situ Kr ++ ions irradiation under transmission electron microscopy. The results revealed that the Gr/Cu interface exhibits higher defect annihilation capability compared to the HAGBs in Cu. Moreover, the atomistic simulations suggested a slightly higher and larger range of stress field for the Gr/Cu interface, which contributes to the enhanced defects absorption capability. The present findings are essential to understand and design a new class of carbon/metal composites with superior irradiation tolerance.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Computational investigation of hydrogen-induced phonon changes in carbon fiber

Optical vibrational spectroscopy has shown promise as a noninvasive means of monitoring the mechanical properties of carbon fiber (CF), which is increasingly used for industrial and consumer purposes. However, interpretation of optical vibrational spectra for solid materials is inferential, particularly when defects are present. Because inelastic neutron scattering (INS) spectroscopy is not subject to selection rules, the full vibrational spectra can be measured. And, identifying correlations between INS features and tensile properties can assist in the interpretation of spectra from more commonly used optical vibrational spectroscopic techniques, such as Raman and infrared (IR) spectroscopy. Recent INS experiments on high-performance commercial carbon fibers showed features near 900 and 1100 cm –1 in addition to a broad feature near 3000 cm –1 that increased in intensity with decreasing tensile strength. These features were assigned to hydrogen defects. Here, we use density functional theory to simulate the INS spectra of several hydrogen defect geometries in graphite as a model for carbon fiber structure units, confirming the experimental assignment of these peaks to hydrogen modes and providing insights into the structure and lattice dynamics of the defects.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Unraveling small-scale defects in irradiated ThO 2 using kinetic Monte Carlo simulations

Point defects and their clusters generated through irradiation can have significant impact on the physical and mechanical properties of materials. However, direct experimental visualization of these small-scale defects using high-resolution scanning transmission electron microscopy remains a challenging task. In this study, using thorium dioxide (ThO 2 ) with the fluorite structure as a model system, we demonstrate the use of ab initio basin-hopping simulations in synergy with object kinetic Monte Carlo simulations as a powerful tool for identifying small defect complexes in irradiated materials. In addition to providing quantitative insights into defect evolution in ThO 2 under irradiation, our study reveals an unexpected role of bound anti-Schottky defect clusters in mediating defect transport. Remarkably, despite their poor thermal stability against dissociation at high temperatures, the transient formation of bound anti-Schottky defects under irradiation and their subsequent migration provide the dominant mechanism for the growth of large interstitial loops that have been experimentally observed in ThO 2 .

36 MATERIALS SCIENCE↗
DOE OSTI2021

Deep Learning Segmentation of Complex Features in Atomic-Resolution Phase-Contrast Transmission Electron Microscopy Images

Phase-contrast transmission electron microscopy (TEM) is a powerful tool for imaging the local atomic structure of materials. TEM has been used heavily in studies of defect structures of two-dimensional materials such as monolayer graphene due to its high dose efficiency. However, phase-contrast imaging can produce complex nonlinear contrast, even for weakly scattering samples. It is, therefore, difficult to develop fully automated analysis routines for phase-contrast TEM studies using conventional image processing tools. For automated analysis of large sample regions of graphene, one of the key problems is segmentation between the structure of interest and unwanted structures such as surface contaminant layers. In this study, we compare the performance of a conventional Bragg filtering method with a deep learning routine based on the U-Net architecture. We show that the deep learning method is more general, simpler to apply in practice, and produces more accurate and robust results than the conventional algorithm. We provide easily adaptable source code for all results in this paper and discuss potential applications for deep learning in fully automated TEM image analysis.

47 OTHER INSTRUMENTATION↗
DOE OSTI2019

Impact of irradiation induced dislocation loops on thermal conductivity in ceramics

Experimental work aimed at understanding the role of dislocation loops in limiting phonon mediated thermal transport in ceramics is presented. Faulted dislocation loops, having diameters of a few nanometers, were introduced by irradiating a polycrystalline cerium dioxide sample with 1.6 MeV protons at 700°C. XRD analysis indicated that irradiated samples retained their crystalline structure and exhibit very little lattice expansion suggesting a low concentration of point defects. Additionally, further microstructure characterization using transmission electron microscopy revealed that interstitial type faulted dislocation loops were primarily created as expected for these irradiation conditions. Thermal conductivity of the damaged layer was measured using a modulated thermoreflectance approach. Analysis of the experimental data using the classical Klemens-Callaway approach reveals that the conductivity reduction is primarily due to dislocation loops, while point defects and voids play only a minor role. These results provide experimental confirmation that faulted loops offer a unique arrangement for displaced atoms that leads to an unusually large reduction of thermal conductivity.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Process-Structure-Property Relationships for 316L Stainless Steel Fabricated by Additive Manufacturing and Its Implication for Component Engineering

We investigate the process-structure-property relationships for 316L stainless steel prototyping utilizing 3-D laser engineered net shaping (LENS), a commercial direct energy deposition additive manufacturing process. Our study concluded that the resultant physical metallurgy of 3-D LENS 316L prototypes is dictated by the interactive metallurgical reactions, during instantaneous powder feeding/melting, molten metal flow and liquid metal solidification. This study also showed 3-D LENS manufacturing is capable of building high strength and ductile 316L prototypes due to its fine cellular spacing from fast solidification cooling, and the well-fused epitaxial interfaces at metal flow trails and interpass boundaries. However, without further LENS process control and optimization, the deposits are vulnerable to localized hardness variation attributed to heterogeneous microstructure, i.e., the interpass heat-affected zone (HAZ) from repetitive thermal heating during successive layer depositions. Most significantly, the current deposits exhibit anisotropic tensile behavior, i.e., lower strain and/or premature interpass delamination parallel to build direction (axial). This anisotropic behavior is attributed to the presence of interpass HAZ, which coexists with flying feedstock inclusions and porosity from incomplete molten metal fusion. Our current observations and findings contribute to the scientific basis for future process control and optimization necessary for material property control and defect mitigation.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Native point defects in GaSb

We have applied positron annihilation spectroscopy to study native point defects in Te-doped n-type and nominally undoped p-type GaSb single crystals. The results show that the dominant vacancy defect trapping positrons in bulk GaSb is the gallium monovacancy. The temperature dependence of the average positron lifetime in both p- and n-type GaSb indicates that negative ion type defects with no associated open volume compete with the Ga vacancies. Based on comparison with theoretical predictions, these negative ions are identified as Ga antisites. The concentrations of these negatively charged defects exceed the Ga vacancy concentrations nearly by an order of magnitude. We conclude that the Ga antisite is the native defect responsible for p-type conductivity in GaSb single crystals.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Carbon trimer as a 2 eV single-photon emitter candidate in hexagonal boron nitride: A first-principles study

The generation of single-photon emitters in hexagonal boron nitride around 2 eV emission is experimentally well recognized; however, the atomic nature of these emitters is unknown. In this Letter, we use first-principles calculations to demonstrate that carbon trimer substitutional defect (C 2 C N ) is a possible source of 2 eV single-photon emitter in hBN. Here, we showcase the calculations of a complete set of static and dynamical properties related to quantum defects, including exciton-defect couplings and electron-phonon interactions, from both density functional theory and many-body perturbation theory. In particular, we show that it is critical to consider both radiative and nonradiative processes when comparing with experimental lifetime for known 2 eV emitters. We find that C 2 C N has several key physical properties matching the ones of experimentally observed single-photon emitters. These include the zero-phonon line (2.13 eV), Huang-Rhys factor (1.35), photoluminescence lifetime (2.19 ns), phonon-sideband energy (180 meV), and photoluminescence spectrum. The identification of defect candidates for 2 eV emission paves the way for controllable single-photon emission generation.

36 MATERIALS SCIENCE↗