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At least 775 records · Page 43
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Daylight-Mediated, Passive, and Sustained Release of the Glaucoma Drug Timolol from a Contact Lens

Timolol, a potent inhibitor of β-adrenergic receptors (βARs), is a first-line drug for decreasing the intraocular pressure (IOP) of patients with glaucoma. Timolol is administered using 0.5% eye-drop solutions at >3 × 10 7 times the inhibitory concentration ( k i ) for βARs. This high dose is wasteful and triggers off-target effects that increase medication noncompliance. Here, we introduce contact lenses that release timolol to the eye throughout the day during passive exposures to natural daylight at a more therapeutically relevant concentration (>3000 k i ). Timolol is coupled to the polymer of the contact lens via a photocleavable caged cross-linker and is released exclusively to the surrounding fluid after the 400-430 nm mediated cleavage of the cross-linking group. Studies conducted in a preclinical mouse model of glaucoma show photoreleased timolol is effective as authentic timolol in reducing IOP. Our studies highlight several advantages of daylight-mediated release of timolol from lenses compared to eye-drops. First, fitted contact lenses exposed to natural daylight release sufficient timolol to sustain the inhibition of βARs over a 10 h period. Second, the contact lenses inhibit βARs in the eye using only 5.7% of the timolol within a single eye-drop. Third, the lenses allow the patient to passively control the amount of timolol released from the lens-for example, early morning exposure to outdoor sunlight would release enough timolol to maximally reduce the IOP, whereas subsequent periodic exposures to indoor daylight would release sufficient timolol to overcome the effects of its spontaneous dissociation from βARs. Fourth, our lenses are disposable, designed for single day use, and manufactured at a low cost.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2022

Dual Passivation of Cathode and Anode through Electrode–Electrolyte Interface Engineering Enables Long-Lifespan Li Metal–SPAN Batteries

The reliability and durability of lithium metal (Li 0 )–sulfur batteries are largely limited by the undesired Li 0 plating-stripping irreversibility and the detrimental polysulfide dissolution, yet approaches that can simultaneously address the above anodic and cathodic problems are scarce. In this study, we report the stable operation of a Li 0 -SPAN (sulfurized polyacrylonitrile) battery via an anode–cathode dual-passivation approach. By combination of a fluorinated localized high concentration electrolyte (LHCE) and a Li 3 N-forming additive (TMS-N 3 ), robust and highly conductive electrode passivation layers are formed in situ on the surface of both the Li 0 anode and the SPAN cathode. The resulting highly reversible, dendrite-free, and high-density Li 0 plating morphology enables a high Coulombic efficiency of 99.4%. Advanced tender energy X-ray spectroscopy also reveals the eliminated Li 2 S formation and minimized polysulfide dissolution in SPAN cathodes, leading to a high capacity of 580 mAh/g SPAN and stable cycling with negligible capacity decay (0.7%) for 800 cycles. This electrode–electrolyte interphase engineering strategy has tackled the major limitations of Li–S batteries in both ether- and carbonate-based electrolyte systems and under a wide temperature range from –10 to +50 °C, thus providing insightful guidelines for the rational design of highly durable and high-energy-density Li 0 -S batteries.

25 ENERGY STORAGE↗
DOE OSTI2026

Quantification of Shallow Defect Suppression in Aminosilane-Passivated Lead Halide Perovskites via Optical and Electrochemical Methods

We combine fluence-dependent photoluminescence (PL) and electrochemical characterization to estimate defect-dependent trapping rates, energetic distributions, and densities of defects, in lead halide perovskite films Cs 0.1 FA 0.9 PbI 3 and Cs 0.17 FA 0.83 Pb­(I 0.75 Br 0.25 ) 3 , before and after trap passivation with vapor-deposited (3-aminopropyl)­trimethoxysilane (APTMS). For both compositions, the PL studies show that energetically shallow subgap near-valence defect densities lead to bimolecular nonradiative recombination which is reduced by 92% after APTMS treatment. Electrochemical characterization of these same active layers shows for the first time that APTMS passivation impacts mainly on near-valence (mobile anionic) defects that decrease in density by 4 orders of magnitude, from 10 18 cm –3 to 10 14 cm –3 , as a result of silane modification. Here, the combination of PL and electrochemical characterization promises a unique approach to speciation and quantification of a broader distribution of trap states in perovskites and provides straightforward assessments of the efficacy of defect mitigation strategies.

Defects↗
DOE OSTI2023

The Effect of the SEI Layer Mechanical Deformation on the Passivity of a Si Anode in Organic Carbonate Electrolytes

The solid electrolyte interphase (SEI) on a Si negative electrode in carbonate-based organic electrolytes shows intrinsically poor passivating behavior, giving rise to unsatisfactory calendar life of Li-ion batteries. Moreover, mechanical strains induced in the SEI due to large volume changes of Si during charge-discharge cycling could contribute to its mechanical instability and poor passivating behavior. This study elucidates the influence that static mechanical deformation of the SEI has on the rate of unwanted parasitic reactions at the Si/electrolyte interface as a function of electrode potential. Further, the experimental approach involves the utilization of Si thin-film electrodes on substrates with disparate elastic moduli, which either permit or suppress the SEI deformation in response to Si volume changes upon charging-discharging. We find that static mechanical stretching and deformation of the SEI results in an increased parasitic electrolyte reduction current on Si. Furthermore, attenuated total reflection and near-field Fourier-transform infrared nanospectroscopy reveal that the static mechanical stretching and deformation of the SEI fosters a selective transport of linear carbonate solvent through, and nanoconfinement within, the SEI. These, in turn, promote selective solvent reduction and continuous electrolyte decomposition on Si electrodes, reducing the calendar life of Si anode-based Li-ion batteries. Finally, possible correlations between the structure and chemical composition of the SEI layer and its mechanical and chemical resilience under prolonged mechanical deformation are discussed in detail.

25 ENERGY STORAGE↗
DOE OSTI2016

Elasticity-induced force reversal between active spinning particles in dense passive media

The self-organization of active particles is governed by their dynamic effective interactions. Such interactions are controlled by the medium in which such active agents reside. Here we study the interactions between active agents in a dense non-active medium. Our system consists of actuated, spinning, active particles embedded in a dense monolayer of passive, or non-active, particles. We demonstrate that the presence of the passive monolayer alters markedly the properties of the system and results in a reversal of the forces between active spinning particles from repulsive to attractive. The origin of such reversal is due to the coupling between the active stresses and elasticity of the system. This discovery provides a mechanism for the interaction between active agents in complex and structured media, opening up opportunities to tune the interaction range and directionality via the mechanical properties of the medium.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Origin and elimination of photocurrent hysteresis by fullerene passivation in CH 3 NH 3 PbI 3 planar heterojunction solar cells

The large photocurrent hysteresis observed in many organometal trihalide perovskite solar cells has become a major hindrance impairing the ultimate performance and stability of these devices, while its origin was unknown. Here we demonstrate the trap states on the surface and grain boundaries of the perovskite materials to be the origin of photocurrent hysteresis and that the fullerene layers deposited on perovskites can effectively passivate these charge trap states and eliminate the notorious photocurrent hysteresis. Fullerenes deposited on the top of the perovskites reduce the trap density by two orders of magnitude and double the power conversion efficiency of CH 3 NH 3 PbI 3 solar cells. As a result, the elucidation of the origin of photocurrent hysteresis and its elimination by trap passivation in perovskite solar cells provides important directions for future enhancements to device efficiency.

14 SOLAR ENERGY↗
DOE OSTI2018

Impact of alkali on the passivation of silicate glass

Amorphous silica-rich surface layers, also called gels, can passivate silicate glass and minerals depending on environmental conditions. However, several uncertainties remain on the mechanisms controlling the formation of these layers. In this paper, the influence of exogenous ions supplied by solutions is studied, both on the formation and on the properties of the gel formed on international simple glass (ISG). ISG was altered at 90 °C, pH 90 °C 7, in silica-saturated solutions containing various alkaline cations separately (Li + , Na + , K + , and Cs + ). The alteration kinetics observed with Li and Na in the solution is similar to that observed with no ions, while K and Cs in the solution tend to decrease glass alteration. Furthermore, for K or Cs ions, the kinetics decreases as the ionic strength of the solution increases. The passivation layer formed in these solutions shows a selectivity toward cations following the series K > Cs > Na >> Li. These alkalis replace Ca from pristine glass in the altered structures, leading to differences in [AlO4] - units charge compensation. Importantly, exchange between Ca and alkali also affects the total quantity of water inside each gel and this effect is well correlated with the observed drop in glass alteration.

36 MATERIALS SCIENCE↗
DOE OSTI2021

The passivity of lithium electrodes in liquid electrolytes for secondary batteries

Rechargeable Li metal batteries are currently limited by electrolyte decomposition and rapid Li consumption. Li plating and stripping greatly depend on the solid electrolyte interphase formed at the Li metal-liquid electrolyte interface. This Review discusses the reactions occurring at this interface from a corrosion science perspective, highlighting the requirements for an ideal passivation layer. Rechargeable Li metal batteries are currently limited by safety concerns, continuous electrolyte decomposition and rapid consumption of Li. These issues are mainly related to reactions occurring at the Li metal-liquid electrolyte interface. Additionally, the formation of a passivation film (that is, a solid electrolyte interphase) determines ionic diffusion and the structural and morphological evolution of the Li metal electrode upon cycling. In this Review, we discuss spontaneous and operation-induced reactions at the Li metal-electrolyte interface from a corrosion science perspective. We highlight that the instantaneous formation of a thin protective film of corrosion products at the Li surface, which acts as a barrier to further chemical reactions with the electrolyte, precedes film reformation, which occurs during subsequent electrochemical stripping and plating of Li during battery operation. Finally, we discuss solutions to overcoming remaining challenges of Li metal batteries related to Li surface science, electrolyte chemistry, cell engineering and the intrinsic instability of the Li metal-electrolyte interface.

25 ENERGY STORAGE↗
DOE OSTI2016

Stability and self-passivation of copper vanadate photoanodes under chemical, electrochemical, and photoelectrochemical operation

We discuss how deployment of solar fuels technology requires photoanodes and that long term stability, can be accomplished using light absorbers that self-passivate under operational conditions. We recently reported that several copper vanadates are promising photoanode materials, and their stability and self-passivation is demonstrated through a combination of Pourbaix calculations and combinatorial experimentation.

14 SOLAR ENERGY↗
DOE OSTI2021

Passivation-driven speciation, dealloying and purification

Thin passivating surface oxide layers on metal alloys form a dissipation horizon between dissimilar phases, hence harbour an inherent free energy and composition gradient. We exploit this gradient to drive order and selective surface separation (speciation), enabling redox-driven enrichment of the core by selective conversion of low standard reduction potential (E°) components into oxides. Additionally, coupling this oxide growth to volumetric changes during solidification allows us to create oxide crystallites trapped in a metal (‘ship-in-a-bottle’) or extrusion of metal fingerlings on the heavily oxidized particle. We confirm the underlying mechanism through high temperature X-ray diffraction and characterization of solidification-trapped particle states. We demonstrate that engineering the passivating surface oxide can lead to purification via selective dealloying with concomitant enrichment of the core, leading to disparate particle morphologies.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Ultrathin alumina passivation for improved photoelectrochemical water oxidation catalysis of tin oxide sensitized by a phosphonate-functionalized perylene diimide first without, and then with, CoOy

Previously, a photoanode composed of nanostructured SnO 2 coated with the perylene diimide dye N,N'-bis(phosphonomethyl)-3,4,9,10-perylenediimide (PMPDI) plus photoelectrochemically deposited cobalt oxide (CoO y ) was shown to photoelectrochemically oxidize water at 31 ± 7% faradaic efficiency. A non-ideal part of that prior system is that the addition of the known CoO y water oxidation catalyst (WOC) resulted in a reduction of the total photocurrent rather than the anticipated increase, due to an increase in charge-carrier recombination. Herein, we show deposition of an ultrathin alumina overlayer applied by atomic layer deposition (ALD) on the SnO 2 /PMPDI photoanode can improve the photoactivity and catalytic activity of the system; the addition a ca. 1 nm-thick AlO x layer deposited on a 4000 nm (i.e., 4 micron) thick mesoporous anode system can and does have a positive, 2.5-fold improvement in the steady-state photocurrent with 29 ± 9% faradaic efficiency vs. the control anode without alumina passivation by reducing charge-carrier recombination. Moreover, ALD-deposited AlO x layer does help support the understanding of the “anti-catalysis” of co-depositing a CoO y WOC on the SnO 2 /PMPDI DS-PECs—specifically the picture of direct CoO y –SnO 2 contact-mediated recombination—but that AlO x layer was unable to improve the photocurrent in a net SnO 2 /PMPDI/AlO x (/CoO y ) system. We attribute the lack of a performance enhancement by CoOy WOC to incomplete coverage of each SnO 2 nanoparticle by the AlO x . Overall, we find the addition of an optimized ultrathin AlOx layer (0.6 nm thick; deposited at 85 °C) improves the SnO 2 /PMPDI/AlO x system's photoactivity by a factor of up to ca. 3-fold with reduced recombination. These results document that metal-oxide passivation by low-temperature ALD can be an effective strategy for improving the water oxidation performance of even nanostructured dye sensitized-photoelectrochemical cell.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Electrochemical quantification of phosphonic acid passivated surface sites of NiO x for perovskite solar cells

Nickel oxide (NiO x ) is among the few p-type metal oxide semiconductors considered a strong candidate for hole transport layers in halide perovskite solar cells (PSCs). However, its reactivity with perovskite ions poses significant challenges to achieving high efficiency and long-term stability. Here, we investigate passivation of detrimental reactive surface sites on NiO x by carbazole phosphonic acids. We leverage electrochemical cyclic voltammetry (CV) of NiO x electrodes as a proxy measure for the redox activity that afflicts PSCs. From the CVs, we derive a metric, N (units cm −2 ), that relates to the number of redox active sites on NiO x surfaces. We observe a statistically significant negative correlation between PSC efficiency and N-value that indicates PSCs are more efficient on NiO x with lower electrochemical reactivity. The new mechanistic insight into NiO x passivation demonstrates it requires a reducing agent and Brønsted acid combination, providing a broadly applicable approach for evaluating and enhancing the stability and performance of NiO x -based interfaces in photovoltaics.

14 SOLAR ENERGY↗
DOE OSTI2026

Photovoltage behaviour of p-Sb 2 S 3 photocathodes for hydrogen evolution: effect of n-In 2 S 3 passivation layers

The 1.76 eV band gap of antimony(iii) sulphide (Sb 2 S 3 ) makes this semiconductor material a promising light absorber for photoelectrochemical water splitting, but scalable fabrication approaches to efficient devices are still lacking. Here we show that compact Sb 2 S 3 films on FTO can be obtained by electrochemical growth from aqueous colloidal sulphur and antimony trichloride solutions, followed by mild annealing. These films can be converted into hydrogen evolution photocathodes after coating with In 2 S 3 passivation layers and the addition of Pt proton reduction co-catalysts. For the first time, vibrating Kelvin probe surface photovoltage (VKP-SPV) spectroscopy is used to observe the carrier dynamics in such photoelectrodes. While the bare Sb 2 S 3 films suffer from high surface recombination rates and poor electron extraction, the In 2 S 3 overlayer is found to raise the photovoltage and cathodic photocurrent density, due to passivation of surface defects and formation of a p–n heterojunction. In thick In 2 S 3 films, these benefits are offset by shading and slow electron transfer. Also, we find that O 2 strongly affects the band bending in the Sb 2 S 3 –air and In 2 S 3 –air junctions and their photovoltage. The optimised devices evolve H 2 at 77.5% Faradaic efficiency and with 0.084% applied bias photon-to-current efficiency (ABPE) at 0.12 V vs. RHE. The low ABPE value is attributed to Sb 2 S 3 sub-bandgap defects visible in SPV spectra, the random orientation of Sb 2 S 3 crystallites in the films, which inhibits charge transport, the absence of crystal facets of Sb 2 S 3 , and a detrimental Schottky junction at the FTO|Sb 2 S 3 interface.

de Araújo, Moisés A. [University of California, Da↗
DOE OSTI2021

Evaluation of the Passive Cooling Potential of Thermal Mass Inherent in Medium to Large Commercial Buildings

Typical commercial construction inherently contains large surface areas of relatively thin mass located in the floor slabs. This research asks how effective this mass could be for passive cooling, relative to other mass depths, if it were to be exposed and used as thermal mass. Although much of the rich literature on thermal mass has been conducted with far greater mass depths, a more limited amount of research suggests that because the surface heat transfer rate is limited, the focus should be on the surface area of exposed mass, not its depth. This presents an opportunity for more buildings to behave more thermally massively, if the mass inherent in typical floor slabs contains utility, particularly over diurnal cycles. In all climates analyzed, it was found that there is a pronounced shoulder where energy savings from passive cooling of increasing mass depths was steep until roughly 7.5–10 cm, and beyond this point the achieved energy savings diminished rapidly. When considering the embodied energy of concrete, the incremental benefit of added mass beyond a typical topping slab of 10 cm does not justify the incremental embodied energy cost from a total energy standpoint alone.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
DOE OSTI2013

Improved Stability Of Amorphous Zinc Tin Oxide Thin Film Transistors Using Molecular Passivation

The role of back channel surface chemistry on amorphous zinc tin oxide (ZTO) bottom gate thin film transistors (TFT) have been characterized by positive bias-stress measurements and x-ray photoelectron spectroscopy. Positive bias-stress turn-on voltage shifts for ZTO-TFTs were significantly reduced by passivation of back channel surfaces with self-assembled monolayers of n-hexylphosphonic acid (n-HPA) when compared to ZTO-TFTs with no passivation. These results indicate that adsorption of molecular species on exposed back channel of ZTO-TFTs strongly influence observed turn-on voltage shifts, as opposed to charge injection into the dielectric or trapping due to oxygen vacancies.

Environmental Molecular Sciences Laboratory↗
DOE OSTI2013

Effect of sidewall surface recombination on the quantum efficiency in a Y{sub 2}O{sub 3} passivated gated type-II InAs/GaSb long-infrared photodetector array

Y{sub 2}O{sub 3} was applied to passivate a long-wavelength infrared type-II superlattice gated photodetector array with 50% cut-off wavelength at 11 μm, resulting in a saturated gate bias that was 3 times lower than in a SiO{sub 2} passivated array. Besides effectively suppressing surface leakage, gating technique exhibited its ability to enhance the quantum efficiency of 100 × 100 μm size mesa from 51% to 57% by suppressing sidewall surface recombination. At 77 K, the gated photodetector showed dark current density and resistance-area product at −300 mV of 2.5 × 10{sup −5} A/cm{sup 2} and 1.3 × 10{sup 4} Ω cm{sup 2}, respectively, and a specific detectivity of 1.4 × 10{sup 12} Jones.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Passively Q-switching induced by the smallest single-walled carbon nanotubes

We report a passively Q-switched erbium-doped fiber laser (EDFL) by using the smallest single-walled carbon nanotubes (SWNTs) with a diameter of 0.3 nm as the saturable absorber. These small SWNTs are fabricated in the nanochannels of a ZnAPO-11 (AEL) single crystal. By inserting one of the AEL crystal into an EDFL cavity pumped by a 980 nm laser diode, stable passive Q-switching is achieved for a threshold pump power of 206.2 mW, and 4.73 μs pulses with a repetition rate of 41.78 kHz and an average output power of 3.75 mW are obtained for a pump power of 406 mW.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Dense nanoimprinted silicon nanowire arrays with passivated axial p-i-n junctions for photovoltaic applications

We report on the fabrication and photovoltaic characteristics of vertical arrays of silicon axial p-i-n junction nanowire (NW) solar cells grown by vapor-liquid-solid (VLS) epitaxy. NW surface passivation with silicon dioxide shell is shown to enhance carrier recombination time, open-circuit voltage (V{sub OC}), short-circuit current density (J{sub SC}), and fill factor (FF). The photovoltaic performance of passivated individual NW and NW arrays was compared under 532 nm laser illumination with power density of ∼10 W/cm{sup 2}. Higher values of V{sub OC} and FF in the NW arrays are explained by enhanced light trapping. In order to verify the effect of NW density on light absorption and hence on the photovoltaic performance of NW arrays, dense Si NW arrays were fabricated using nanoimprint lithography to periodically arrange the gold seed particles prior to epitaxial growth. Compared to sparse NW arrays fabricated using VLS growth from randomly distributed gold seeds, the nanoimprinted NW array solar cells show a greatly increased peak external quantum efficiency of ∼8% and internal quantum efficiency of ∼90% in the visible spectral range. Three-dimensional finite-difference time-domain simulations of Si NW periodic arrays with varying pitch (P) confirm the importance of high NW density. Specifically, due to diffractive scattering and light trapping, absorption efficiency close to 100% in the 400–650 nm spectral range is calculated for a Si NW array with P = 250 nm, significantly outperforming a blanket Si film of the same thickness.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗