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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
NASA NTRS1970

A Study of the Electrotransport in Thin Films: An Advanced Method for the Study of Electrotransport in Thin Films Using Electrical Resistance Measurements

To date, very little is understood about electrotransport in thin films. One reason for this is the lack of methods in which electromigration can be adequately monitored dynamically. In this thesis, a new nondestructive method for the study of the electrotransport phenomenon in thin aluminum films is presented. This method makes use of electrical resistance measurements of various regions along the test sample to monitor changes in resistance resulting from electromigration. The advantage of this method is that resistance changes can be observed long before void formation can be seen using standard microscopy methods. In order to achieve the best efficiency using this method, special consideration must be given to the design of the sample. Design problems and their respective solutions are given. The results of the electrical resistance measurements are interpreted by means of photographs taken with an scanning electron microscope. The increase in resistance of the aluminum samples is interpreted to be due to void formation. The expected decrease in resistance near the anode was never observed. It is shown that mass accumulation takes on the form of hillocks and whiskers on the surface of the aluminum film, which does not contribute appreciably to conductivity.

Hummel, R. E.↗
DOE OSTI2019

Highly Selective Current-Induced Accumulation of Trace Ions at Micro-/NanoPorous Interfaces

During application of an electrical current through a composite micro-/nano-porous membrane, trace-ion accumulation in the microporous layer should vary greatly with the ion diffusion coefficient to allow selective accumulation of specific ions. In this study, we examine the theoretical enrichment factors in the microporous region as a function of current density and trace-ion diffusion coefficient to demonstrate the promise of such micro-/nano-porous interfaces for ion separations. Trace-ion accumulation relies on charged nanopores that exclude coions (ions with the same charge as the nanopore walls)and give rise (under current) to depletion of the dominant (high-concentration) salt in the region next to the nanopores. This depletion gives rise to high local electric fields. Trace ions accumulate in this region because convection carries them toward the nanoporous interface, whereas electromigration in the opposite direction is strongest next to the interface. For ions whose diffusion coefficients are half of the corresponding value for the dominant salt, calculated enrichment factors reach 150. In contrast depletion occurs for ions with the same diffusion coefficient as the dominant salt. Even higher enrichment factors appear for divalent ions due to their relatively low diffusion coefficients. Lastly, with monovalent coions whose diffusion coefficients differ by only 2%, calculated selectivity factors reach values >1.2 (>1.8 for divalent coions), depending on the magnitudes of the diffusion coefficients. Such selectivities may prove useful in separating very similar species such as isotopes or equally charged peptides.

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

Analysis of current-driven oscillatory dynamics of single-layer homoepitaxial islands on crystalline conducting substrates

Here we report results of a systematic study on the complex oscillatory current-driven dynamics of single-layer homoepitaxial islands on crystalline substrate surfaces and the dependence of this driven dynamical behavior on important physical parameters, including island size, substrate surface orientation, and direction of externally applied electric field. The analysis is based on a nonlinear model of driven island edge morphological evolution that accounts for curvature-driven edge diffusion, edge electromigration, and edge diffusional anisotropy. Using a linear theory of island edge morphological stability, we calculate a critical island size at which the island’s equilibrium edge shape becomes unstable, which sets a lower bound for the onset of time-periodic oscillatory dynamical response. Using direct dynamical simulations, we study the edge morphological dynamics of current-driven single-layer islands at larger-than-critical size, and determine the actual island size at which the migrating islands undergo a transition from steady to time-periodic asymptotic states through a subcritical Hopf bifurcation. At the highest symmetry of diffusional anisotropy examined, on {111} surfaces of face-centered cubic crystalline substrates, we find that more complex stable oscillatory states can be reached through period-doubling bifurcation at island sizes larger than those at the Hopf points. We characterize in detail the island morphology and dynamical response at the stable time-periodic asymptotic states, determine the range of stability of these oscillatory states terminated by island breakup, and explain the morphological features of the stable oscillating islands on the basis of linear stability theory.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Assessment of Blocking Contacts in Suppressing Polarization Effects in CsPbBr 3 Perovskite Detectors

The CsPbBr 3 perovskite has garnered significant attention as a room-temperature semiconductor for hard radiation detection due to straightforward synthesis, scalable crystal growth, low cost, and excellent energy resolution. However, despite these advantages, at ambient temperature, CsPbBr 3 devices may experience performance deterioration and irreversible failure due to “polarization” induced by electromigration of ions to electrical connections on the device. In this study, we tested several contact materials and their optimization deposition techniques to assess the stability of high-performance CsPbBr 3 γ-ray detectors. Metals, with low work functions (Ti, In, Sn, Sb, Pb, Bi, Al, Au, and TiC) and high-work-function (Au or Pt) contacts, were used to form different Schottky junctions using vacuum thermal evaporation, electron-beam evaporation, and sputtering methods. These detectors were tested in intermittent and continuous modes to assess their stability. Among the tested detectors, the Bi/CLB/Pt electrode configuration demonstrated superior stability, operating effectively for 11 months under periodic testing and 16 days under continuous testing. In contrast, other configurations functioned only for a few months under intermittent conditions. Upon incorporating a ~40-nm-thick TiC passivation layer on the anode side (Bi/TiC/CLB/Pt), the CLB device operated continuously for 36 days without degradation. In many cases, the failure mode of the devices was due to the degradation of the anode. Here, the chemical changes in the fresh and deteriorated anodes were characterized using scanning electron microscopy and energydispersive X-ray spectroscopy

CsPbBr3 perovskite↗
DOE OSTI2018

Microstructure Evolution and Implications for Cu Nanointerconnects and Beyond

The continued scaling of Cu low k technology is facing serious challenges imposed by basic limits from materials, processing and reliability. This has generated great interests recently to further develop Cu nanointerconnects and alternates, particularly Co and Ru nanointerconnects beyond the 10nm node. The performance and reliability are important considerations for the development of nanointerconnects in addition to challenges from processing complexity and manufacturing cost. In this paper, we investigate the microstructure evolution in Cu, Co and Ru nanointerconnects and the effects on resistivity and electromigration (EM), two key factors contributing to the RC delay and reliability of the nanointerconnects.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Direct Observation of Halide Migration and its Effect on the Photoluminescence of Methylammonium Lead Bromide Perovskite Single Crystals

Optoelectronic devices based on hybrid perovskites have demonstrated outstanding performance within a few years of intense study. However, commercialization of these devices requires barriers to their development to be overcome, such as their chemical instability under operating conditions. In order to investigate this instability and its consequences, the electric field applied to single crystals of methylammonium lead bromide (CH 3 NH 3 PbBr 3 ) is varied, and changes are mapped in both their elemental composition and photo-luminescence. Synchrotron-based nanoprobe X-ray fluorescence (nano-XRF) with 250 nm resolution reveals quasi-reversible field-assisted halide migration, with corresponding changes in photoluminescence. It is observed that higher local bromide concentration is correlated to superior optoelectronic performance in CH 3 NH 3 PbBr 3 . A lower limit on the electromigration rate is calculated from these experiments and the motion is interpreted as vacancy-mediated migration based on nudged elastic band density functional theory (DFT) simulations. The XRF mapping data provide direct evidence of field-assisted ionic migration in a model hybrid-perovskite thin single crystal, while the link with photoluminescence proves that the halide stoichiometry plays a key role in the optoelectronic properties of the perovskite.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Bipolar Membranes Inhibit Product Crossover in CO 2 Electrolysis Cells

Abstract As electrocatalysts and electrolyzer designs for CO 2 reduction continue to improve in terms of current density and product selectivity, product crossover from the cathode to the anode is a loss mechanism that is relatively unexplored. The crossover rates of formate, methanol, and ethanol, which are desirable CO 2 reduction products, are compared in electrolyzers containing anion‐exchange membranes and bipolar membranes. The crossover of formate, an anionic CO 2 reduction product, occurs by electromigration through anion‐exchange membranes, and its rate increases linearly with current density. Crossover of electroneutral methanol or ethanol through anion‐exchange membranes occurs to a lesser extent through both diffusion and electroosmotic drag, the latter increasing with current density in anion‐exchange membranes. In contrast, the outward fluxes of protons and hydroxide ions generated in bipolar membranes inhibit the crossover of both anionic and neutral products, even with membranes that contain high surface area junctions. Calculated electroosmotic drag coefficients for each of the neutral products confirm the better performance of bipolar membranes in terms of product losses.

Li, Yuguang C.↗
DOE OSTI2019

Electrically Driven Dynamics of Few‐Chain NbSe 3

An in situ transmission electron microscopy study of few‐chain NbSe 3 encapsulated within the hollow core of carbon nanotubes is presented, where the tube/chain system is subjected to applied axial electrical currents. Electromigration and thermal excitation forces result in collective and individual chain dynamics, with concomitant radial deformations of the encapsulating tubes.

Pham, Thang↗
DOE OSTI2021

Evolution of glass structure during femtosecond laser assisted crystallization of LaBGeO 5 in glass

Single crystal LaBGeO 5 architecture formed in La 2 O 3 -B 2 O 3 -2GeO 2 glass serves as a model system for understanding of the transformation from glass to single crystal under fs laser irradiation. This transformation is highly sensitive to glass composition, raising the need to understand how the glass structure and composition evolve during crystallization. In this work, micro X-ray absorption spectroscopy and X-ray fluorescence mapping were used to study the glass structure and composition preceding LaBGeO5 crystallization in the region surrounding the single crystal growth front. The results show precipitation of germanium nanoparticles, as well as anisotropic segregation of Ge and La prior to LaBGeO5 crystallization, which are explained assuming electromigration in high fields within the plasma formed by the fs laser irradiation. However, these nanoparticles do not serve as sites for heterogeneous nucleation. Furthermore, the similarity of local structure around Ge in the starting glass and the ultimate crystal appears to enhance the crystallization process.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Layer-by-layer modification of aliphatic polyamide anion-exchange membranes to increase Cl - /SO 4 2- selectivity

Development of anion-exchange membranes (AEMs) with selectivities among anions may expand the applications of these membranes in salt separations. This work shows that layer-by-layer coating of aliphatic polyamide AEMs with poly(4-styrenesulfonate) (PSS)/protonated poly(allylamine) (PAH) films enhances Cl - /SO 4 2- dialysis selectivities, and the extent of this enhancement depends on the source-phase salt concentrations. For a source phase containing 0.01 M NaCl and 0.01 M Na 2 SO 4 and a receiving phase of 0.01 M Na 2 CO 3 , a (PSS/PAH) 5 PSS coating (5 PSS/PAH “bilayers” capped with a layer of PSS) increases the Cl - /SO 4 2- selectivity from 1.7 to 5.3 in diffusion dialysis and from 1.3 to 7.4 in electrodialysis. Remarkably, the diffusion dialysis selectivity of a coated membrane increases to 140 when the salt concentrations in the source phase are 0.1 M. Even with bare membranes, selectivity increases to 13 with 0.1 M source-phase salt concentrations. Moreover, AEMs coated only on the receiving side show much higher selectivities but lower fluxes than those coated only on the source side. In conclusion, partitioning experiments and modelling suggest that the increased Cl - /SO 4 2- selectivities at high source-phase salt concentrations stem from enhanced Cl - partitioning and electromigration that disproportionately decreases SO 4 2- flux in the AEM.

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

Electro-osmo-dialysis through nanoporous layers physically conjugated to micro-perforated ion-exchange membranes: Highly selective accumulation of trace coions

This study explores theoretically and numerically the phenomenon of counter-flow accumulation of trace coions during electro-osmo-dialysis through composite membranes containing nanoporous and perforated ion-exchange layers. The combination of charged nanopores and perforations allows electroosmosis, and ion concentration polarization appears near the ion-exchange layer. Accumulation of trace coions occurs because their advective and electromigration flow velocity components have opposite signs and are locally compensating in depletion regions where electric fields are high. This local compensation of flow components can give rise to high accumulation factors (>1000 in some cases) for trace coions at some distance from the interface between the nanoporous and ion-exchange layers. Moreover, the extent of this accumulation depends on the trace-coion diffusion coefficient. The resulting selectivity between different coions might serve as a basis for environmentally friendly separation of ionic species such as synthetic peptides or rare-earth elements. For example, a periodic process might include accumulation followed by species release into smaller volumes of solution. For both rare-earth ions and peptide-like species, the accumulation selectivity between ions with small differences in mobilities depends on system parameters such as nanoporous-layer thickness, distance between the perforations, and the zeta potential of the nanopore surface. Here, the use of optimal values of these membrane parameters may enable tuning of the electro-osmo-dialysis system for separation of specific ions. Modelling reveals that despite inhomogeneous patterns of fluid and ion flows close to the nanoporous/perforated ion-exchange interface, at relatively short distances from this interface (less than half the distance between the perforations) all the flows become practically one-dimensional (1D). Similarly, the concentration profiles of trace coions also become 1D. The flow one-dimensionality at short distances from the current-polarized interface enables a simple 1D approximation that is useful for an approximate analysis of trends in this multi-parameter system.

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

Exchange of Ions across the TiN/TaO x Interface during Electroformation of TaO x -Based Resistive Switching Devices

The valence change model describes the resistive switching in metal oxide-based devices as due to electroreduction of the oxide and subsequent electromigration of oxygen vacancies. Here, we present cross-sectional X-ray energy-dispersive spectroscopy elemental maps of Ta, O, N, and Ti in electroformed TiN/TaO 2.0 /TiN structures. O, N, and Ti were exchanged between the anode and the functional oxide in devices formed at high power (~1 mW), but the exchange was below the detection limit at low power (<0.5 mW). All structures exhibit a similar Ta-enriched and O-depleted filament formed by the elemental segregation in the functional oxide by the temperature gradient. The elemental interchange is interpreted as due to Fick’s diffusion caused by high temperatures in the gap of the filament and is not an essential part of electroformation.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Direct-Liquid-Evaporation Chemical Vapor Deposition of Nanocrystalline Cobalt Metal for Nanoscale Copper Interconnect Encapsulation

In advanced microelectronics, precise design of liner and capping layers become critical, especially when it comes to the fabrication of Cu interconnects with dimensions lower than its mean free path. Here in this paper, we demonstrate that direct-liquid-evaporation chemical vapor deposition (DLE-CVD) of Co is a promising method to make liner and capping layers for nanoscale Cu interconnects. DLE-CVD makes pure, smooth, nanocrystalline, and highly conformal Co films with highly controllable growth characteristics. This process allows full Co encapsulation of nanoscale Cu interconnects, thus stabilizing Cu against diffusion and electromigration. Electrical measurements and high-resolution elemental imaging studies show that the DLE-CVD Co encapsulation layer can improve the reliability and thermal stability of Cu interconnects. Also, with the high conductivity of Co, the DLE-CVD Co encapsulation layer have the potential to further decrease the power consumption of nanoscale Cu interconnects, paving the way for Cu interconnects with higher efficiency in future high-end microelectronics.

36 MATERIALS SCIENCE↗
DOE OSTI2018

High Selectivities among Monovalent Cations in Dialysis through Cation-Exchange Membranes Coated with Polyelectrolyte Multilayers

Cation-exchange membranes allow preferential passage of cations over anions, but they show minimal selectivity among cations, which limits their use in ion separations. Recent studies show that modification of cation-exchange membranes with polyelectrolyte multilayers leads to exceptional monovalent/divalent cation electrodialysis selectivities, but no studies report high selectivity among monovalent ions. Here, this work demonstrates that adsorption of protonated poly(allylamine) (PAH)/poly(4-styrenesulfonate) (PSS) multilayers on Nafion membranes leads to high K + /Li + selectivities in Donnan dialysis, where K + and Li + ions in a source phase pass through the membrane and exchange with Na + ions in a receiving phase. Addition of 0.01 M HNO 3 to a source phase containing 0.01 M KNO 3 and 0.01 M LiNO 3 increases the K + /Li + selectivity from 8 to ~60 through (PAH/PSS) 5 PAH-coated Nafion membranes, primarily because of a ≥fivefold increase in K + flux. These selectivities are much larger than the ratio of 1.9 for the aqueous diffusion coefficients of K + and Li + , and uncoated Nafion membranes give a K + /Li + selectivity <3. Bi-ionic transmembrane potential measurements at neutral pH confirm that the membrane is more permeable to K + than Li + , but this selectivity is less than in Donnan dialysis with acidic solutions. In situ ellipsometry data indicate that PAH/PSS multilayers (assembled at pH 2.3, 7.5, or 9.3) swell at pH 2.0, and this swelling may open cation-exchange sites that preferentially bind K + to enable highly selective transport. The coated membranes also exhibit modest selectivity for K + over H + , suggesting selective transport based on preferential partitioning of K + into the coatings. Selectivity declines when increasing the source-phase KNO 3 concentration to 0.1 M, perhaps because the discriminating transport pathway saturates. Finally, selectivities are lower in electrodialysis than in Donnan dialysis, presumably because electrodialysis engages other transport mechanisms, such as electroosmosis and strong electromigration.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Membrane-Induced Vanadium Crossover-Blocking Polybenzimidazole Copolymer with Exceptional Proton Selectivity

Broad deployment of redox flow batteries is hindered, in part, due to the lack of highly selective ion-exchange membranes with high proton conductivity. We report a post-functionalization strategy for polybenzimidazole copolymer (PBI-co) membranes by a reacting mixture of concentrated sulfuric and phosphoric acids that led to improved membrane selectivity while retaining high proton conductivity. Fourier-transform infrared spectroscopy confirmed successful sulfonation and protonation of benzimidazole functionalities. PBI-co exhibits a very high room-temperature proton conductivity of 0.138 S cm -1 , as measured by electrochemical impedance spectroscopy. PBI-co also demonstrates electromigration crossover mitigation under applied current densities up to 500 mA cm -2 , and voltage pulses up to 1.4 V, while also inhibiting diffusion-driven vanadium crossover for over 20 days. Single-cell vanadium flow battery testing on post-functionalized PBI-co further confirms state-of-the-art battery performance with an ~99.5% Coulombic efficiency at 100 mA cm -2 and an area-specific resistance of ~20 mO cm 2 lower than Nafion-212 membrane.

25 ENERGY STORAGE↗
DOE OSTI2026

Coupled Roles of Surface Chemistry and Hydrogen-Assisted Cycling in Ruthenium Atomic Layer Deposition on Silicon Oxides

Ruthenium (Ru) is a promising interconnect material for advanced semiconductor technologies due to its favorable scaling characteristics, including a short electron mean free path and strong electromigration resistance. In semiconductor integration, silicon oxide-based dielectrics serve as dominant insulating materials and constitute ubiquitous interfaces for metallization; however, their formation-dependent surface chemistry and its impact on Ru growth remain insufficiently explored. Here, we investigate Ru ALD on native oxide SiO x (N-SiO x ) and thermally grown SiO 2 (T-SiO 2 ) as model substrates using bis(ethylcyclopentadienyl)ruthenium(II) [Ru(EtCp) 2 ] under two distinct reactant-sequence environments: AB-type (Ru(EtCp) 2 /O 2 ) and hydrogenassisted ABC-type (Ru(EtCp) 2 /O 2 /H 2 ). Under the AB-type process, both N-SiO x and T-SiO 2 exhibit pronounced nucleation delay. N-SiO x shows earlier nucleation and higher nucleation density than T-SiO 2 , plausibly attributed to differences in surface hydroxyl populations. Similar temperature-dependent phase evolution is observed on both substrates, with mixed Ru and RuO 2 phases at 250 °C and predominantly metallic Ru at 300 °C accompanied by increased morphological roughening. In contrast, incorporating an H 2 subpulse (ABC-type) mitigates nucleation delay, particularly on hydroxyl-deficient T-SiO 2 , thereby reducing the substratedependent disparity observed under AB cycling. Moreover, RuO 2 formation is suppressed even at 250 °C on both substrates, shifting growth toward more metallic Ru with reduced resistivity (∼20 μΩ·cm at ∼ 20 nm on N-SiO x ). These trends suggest that H 2 influences the surface reaction pathway, contributing to enhanced metallic stabilization and altered early stage growth kinetics. Overall, this work clarifies the coupled roles of substrate chemistry and reactant-sequence design in governing Ru nucleation and early stage film evolution, providing insight relevant to next-generation interconnect integration and future area-selective deposition strategies.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Suppression of atom motion and metal deposition in mixed ionic electronic conductors

Many superionic mixed ionic–electronic conductors with a liquid-like sublattice have been identified as high efficiency thermoelectric materials, but their applications are limited due to the possibility of decomposition when subjected to high electronic currents and large temperature gradients. Here, through systematically investigating electromigration in copper sulfide/selenide thermoelectric materials, we reveal the mechanism for atom migration and deposition based on a critical chemical potential difference. Then, a strategy for stable use is proposed: constructing a series of electronically conducting, but ion-blocking barriers to reset the chemical potential of such conductors to keep it below the threshold for decomposition, even if it is used with high electric currents and/or large temperature differences. This strategy not only opens the possibility of using such conductors in thermoelectric applications, but may also provide approaches to engineer perovskite photovoltaic materials and the experimental methods may be applicable to understanding dendrite growth in lithium ion batteries.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗