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All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

A Novel Experimental Approach to Understand the Transport of Nanodrugs

Nanoparticle-based drugs offer attractive advantages like targeted delivery to the diseased site and size and shape-controlled properties. Therefore, understanding the particulate flow of the nanodrugs is important for effective delivery, accurate prediction of required dosage, and developing efficient drug delivery platforms for nanodrugs. In this study, the transport of nanodrugs including flow velocity and deposition is investigated using three model metal oxide nanodrugs of different sizes including iron oxide, zinc oxide, and combined Cu-Zn-Fe oxide synthesized via a modified polyol approach. The hydrodynamic size, size, morphology, chemical composition, crystal phase, and surface functional groups of the water-soluble nanodrugs were characterized via dynamic light scattering, transmission electron microscopy, scanning electron microscopy-energy dispersive X-ray, X-ray diffraction, and fourier transform infrared spectroscopy, respectively. Two different biomimetic flow channels with customized surfaces are developed via 3D printing to experimentally monitor the velocity and deposition of the different nanodrugs. A diffusion dominated mechanism of flow is seen in size ranges 92 nm to 110 nm of the nanodrugs, from the experimental velocity and mass loss profiles. The flow velocity analysis also shows that the transport of nanodrugs is controlled by sedimentation processes in the larger size ranges of 110–302 nm. However, the combined overview from experimental mass loss and velocity trends indicates presence of both diffusive and sedimentation forces in the 110–302 nm size ranges. It is also discovered that the nanodrugs with higher positive surface charges are transported faster through the two test channels, which also leads to lower deposition of these nanodrugs on the walls of the flow channels. The results from this study will be valuable in realizing reliable and cost-effective in vitro experimental approaches that can support in vivo methods to predict the flow of new nanodrugs.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Reproducible emission from nonlinear random lasers

Multiple scattering of light serves as a mechanism for feedback in random lasers. Consequently, internal spatial mode patterns, lasing wavelengths, and output directionality can all be random. Strong mode interaction can occur in such devices due to spatially overlapping modes resulting in nonlinearity with respect to the pump input power. Nevertheless, temporal coherence and lasing mode amplitude can be fixed at a constant pumping rate. This is a property desirable for applications where unique randomness is exploited but expected to be reliable over time, such as physical unclonable functions. Random lasers can also be cheaply and easily fabricated, exhibit relatively low lasing thresholds and high emission intensity. However, the precise scattering properties of such structures and fluctuations in the pump field can make device emission irreproducible, thereby limiting random laser applications. Here, in this work, we directly compare the random lasing spectra from zinc oxide samples fabricated in four distinct ways: spin-coating, sputtering, solgel deposition, and atomic layer deposition. The particular method of fabrication has a strong impact. Samples made through atomic layer deposition here exhibit both reproducibility and strong nonlinearity desirable for applications. Randomness in emission spectra persists across hundreds of repeated and averaged measurements irrespective of spatial location and is demonstrably nonlinear with respect to input signal intensity.

47 OTHER INSTRUMENTATION↗
DOE OSTI2021

Reactive phosphine combinatorial co-sputtering of cation disordered ZnGeP2 films

The discovery of new materials by coupling high-throughput synthesis with computational screening is being increasingly adopted. However, thus far, phosphides have been largely overlooked for both computational screening and high-throughput synthesis. In this paper, we report on the use of a high-throughput synthesis technique, reactive combinatorial co-sputtering with PH 3 , to deposit ZnGeP 2 thin films. We grew amorphous films over a wide range of compositions and found an upper limit in growth temperature determined by Zn and P volatility. We found that depositing in a Ge-limited regime could be utilized to slow the growth rate to compensate for the desorption of the Zn and P. Crystalline films were achieved by depositing films at higher temperatures in this Ge-limited regime with a reduced deposition rate. X-ray diffraction revealed that the films had crystallized in the zinc blende, cation-disordered structure. The crystalline films exhibited optical absorption energy threshold values ranging from 0.8 to 1.3 eV. Increased Ge content was found in films that exhibited a decreased absorption onset energy. Native defect calculations were used to gain an understanding of the off-stoichiometry seen in these films. This work provides the first high-throughput investigation of ZnGeP 2 , demonstrating the ability to grow amorphous and cation disordered ZnGeP 2 over a wide range of compositions with varying optical properties.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Silver nanowire-indium zinc oxide composite flexible transparent conducting electrodes made by spin-coating and photonic curing

Flexible transparent conducting electrodes (TCE) play a critical role in modern technologies. Eliminating the high-temperature annealing of vacuum- or solution-deposited films will increase production throughput and lower the cost of the final products. Photonic curing uses intense pulses of broadband light to induce material transformations instead of heat. In this work, we combine solution deposition and photonic curing, replacing thermal annealing, to fabricate flexible composite TCE films on plastic polyethylene terephthalate (PET) substrates. The composite TCE films are composed of spin-coated silver nanowire-indium zinc oxide layers. Further, the TCE films’ electrical, optical, and morphological properties are investigated and compared to those of commercially available PET/TCE. A sheet resistance of 15 Ω/sq and an average transmittance from 400 – 700 nm of 77% are achieved with the spin-coated and photonic-cured composite flexible TCE films.

14 SOLAR ENERGY↗
DOE OSTI2024

Self-Sacrificial Template Synthesis of Fe-N-C Catalysts with Dense Active Sites Deposited on A Porous Carbon Network for High Performance in PEMFC

In this study, iron-nitrogen-carbon (Fe-N-C) single-atom catalysts are promising sustainable alternatives to the costly and scarce platinum (Pt) to catalyze the oxygen reduction reactions (ORR) at the cathode of proton exchange membrane fuel cells (PEMFCs). However, Fe-N-C cathodes for PEMFC are made thicker than Pt/C ones, in order to compensate for the lower intrinsic ORR activity and site density of Fe-N-C materials. The thick electrodes are bound with mass transport issues that limit their performance at high current densities, especially in H 2 /air PEMFCs. Practical Fe-N-C electrodes must combine high intrinsic ORR activity, high site density, and fast mass transport. Herein, it has achieved an improved combination of these properties with a Fe-N-C catalyst prepared via a two-step synthesis approach, constructing first a porous zinc-nitrogen-carbon (Zn-N-C) substrate, followed by transmetallating Zn by Fe via chemical vapor deposition. A cathode comprising this Fe-N-C catalyst has exhibited a maximum power density of 0.53 W cm -2 in H 2 /air PEMFC at 80 °C. The improved power density is associated with the hierarchical porosity of the Zn-N-C substrate of this work, which is achieved by epitaxial growth of ZIF-8 onto g-C 3 N 4 , leading to a micro-mesoporous substrate.

25 ENERGY STORAGE↗
DOE OSTI2022

Techno-economic analysis of the use of atomic layer deposited transition metal oxides in silicon heterojunction solar cells

The industry for producing silicon solar cells and modules has grown remarkably over the past decades, with more than a 100-fold reduction in price over the past 45?years. The main solar cell fabrication technology has shifted over that time and is currently dominated by the passivated emitter and rear cell (PERC). Other technologies are expected to increase in market share, including tunnel-oxide passivated contact (TOPCon) and heterojunction technology (HJT). In this paper, we examine the cost potential for using atomic layer deposition (ALD) to form transition metal oxide (TMO) layers (MoO x , TiO x and aluminium-doped zinc oxide [AZO]) to use as lower cost alternatives of the p-doped, n-doped and indium tin oxide (ITO) layers, respectively, the layers normally used in HJT solar cells. Using a bottom-up cost and uncertainty model with equipment cost data and process experience in the lab, we find that the production cost of these variations will likely be lower per wafer than standard HJT, with the main cost drivers being the cost of the ALD precursors at high-volume production. We then considered what efficiency is required for these sequences to be cost effective in $/W and discuss whether these targets are technically feasible. This work motivates further work in developing these ALD TMO processes to increase their efficiency towards their theoretical limits to take advantage of the processing cost advantage.

14 SOLAR ENERGY↗
DOE OSTI2025

Monocrystalline CdSeTe/MgCdTe Double‐Heterostructure Solar Cells

This article reports monocrystalline CdSeTe/MgCdTe double‐heterostructure (DH) solar cells with varying Se compositions in the absorber layers that are grown on InSb substrates by using molecular beam epitaxy. The Se composition in the samples studied is determined to be 4%–11% through high‐resolution X‐ray diffraction (XRD) and photoluminescence measurements. Increased Se incorporation induces higher defect density attributed to increased lattice mismatch, and mixed‐phase formation due to the small difference in formation energies between the wurtzite and zinc blende phases of CdSe, which causes stacking faults and grain boundaries. Devices are fabricated by directly depositing an n‐type indium tin oxide (ITO) layer on the CdSeTe/MgCdTe DHs followed by Ag metal contacts. Reduced bandgap is observed in solar cells with increased Se composition. The devices with an absorber containing 4% Se exhibit an average open‐circuit voltage ( V OC ) of 0.925 V, a short‐circuit current density ( J SC ) of 23.4 mA/cm 2 , a fill factor ( FF ) of 0.650 and an efficiency of 14.1% without anti‐reflection coating. Absorbers with higher Se compositions result in poor device performance, mainly attributed to high defect density in the materials.

Ju, Zheng [Center for Photonics Innovation Arizona↗
DOE OSTI2026

Particle Tracking Methods for Battery Precipitation Reactions

Precipitation and deposition reactions at solid–liquid interfaces play a key role in a number of battery chemistries, including Li-ion, so-called “anode free” batteries, zinc-based battery chemistries, and lithium–sulfur, among others. Although models with heterogeneous nucleation and growth phenomena are present in the literature, papers have not to date provided much detail on the numerical algorithms used to track the temporal evolution of the particle size distribution of deposits on electrode surfaces. In this paper we examine several approaches to discretize and track the particle size distribution, demonstrating that common approaches lead to anomalous flattening of the particle size distribution. We conclude by presenting an algorithm that preserves the appropriate particle size distribution during particle growth.

Algorithms↗
DOE OSTI2024

Dynamical Janus Interface Design for Reversible and Fast-Charging Zinc–Iodine Battery under Extreme Operating Conditions

Aqueous zinc (Zn) iodine (I 2 ) batteries have emerged as viable alternatives to conventional metal-ion batteries. However, undesirable Zn deposition and irreversible iodine conversion during cycling have impeded their progress. Here, to overcome these concerns, we report a dynamical interface design by cation chemistry that improves the reversibility of Zn deposition and four-electron iodine conversion. Due to this design, we demonstrate an excellent Zn-plating/-stripping behavior in Zn||Cu asymmetric cells over 1000 cycles with an average Coulombic efficiency (CE) of 99.95%. Moreover, the Zn||I 2 full cells achieve a high-rate capability (217.1 mA h g –1 at 40 A g –1 ; C rate of 189.5C) at room temperature and enable stable cycling with a CE of more than 99% at -50 °C at a current density of 0.05 A g –1 . In situ spectroscopic investigations and simulations reveal that introducing tetraethylammonium cations as ion sieves can dynamically modulate the electrode–electrolyte interface environment, forming the unique water-deficient and chloride ion (Cl – )-rich interface. Such Janus interface accounts for the suppression of side reactions, the prevention of ICl decomposition, and the enrichment of reactants, enhancing the reversibility of Zn-stripping/-plating and four-electron iodine chemistry. This fundamental understanding of the intrinsic interplay between the electrode–electrolyte interface and cations offers a rational standpoint for tuning the reversibility of iodine conversion.

25 ENERGY STORAGE↗
DOE OSTI2025

In Situ Studies of Copper-Zirconia-Zinc Oxide Model Catalysts for CO 2 Hydrogenation

A combination of in situ X-ray photoelectron spectroscopy (XPS) and infrared reflection absorption spectroscopy (IRAS) was used to investigate the formation of surface intermediates from CO 2 hydrogenation on copper-zirconia-zinc oxide model catalysts under reaction conditions. Copper clusters with different numbers of atoms (n = 1, 4, 13) were deposited onto bare and ZrO 2 -modified ZnO powder supports to systematically examine the effects of Cu cluster size and the synergy between metal and metal-oxide components. Under low pressure CO 2 hydrogenation conditions (CO 2 :H 2 = 1:9, 0.4 mbar, 300–600 K), XPS and IRAS identify the most prominent intermediates as carbonate (CO 3 *), formate (HCOO*) and methoxy (CH 3 O*), which is the final surface-bound intermediate leading to methanol. The temperature profiles are consistent with a mechanism in which CO 2 is adsorbed as carbonate species (HCO 3 *, CO 3 *) followed by hydrogenation reactions to formate (HCOO*) and methoxy (CH 3 O*), but the relative yields strongly depend on surface composition. Specifically, the presence of ZrO 2 promotes CO 2 adsorption and activation and improves the thermal stability of the Cu clusters against loss of surface area. Moreover, the ternary Cu 4 /ZrO 2 /ZnO surface is significantly more active than Cu 4 /ZnO and ZrO 2 /ZnO surfaces for the formation of methoxy (CH 3 O*), indicating that Cu–ZrO 2 interfaces promote the formation of key intermediates leading to methanol. Finally, the yields of intermediates are similar for all Cu cluster sizes (Cu 1 , Cu 4 and Cu 13 ), indicating that the primary role of Cu is to provide H atoms via H 2 dissociation and spillover. In conclusion, these molecular-level insights provide a fundamental understanding of the enhanced efficiency of ternary Cu–ZrO 2 –ZnO catalysts and establish design principles for developing improved catalysts for CO 2 conversion.

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

Measurement of spin-polarized photoemission from wurtzite and zinc blende gallium nitride photocathodes

Spin-polarized photoemission from wurtzite and zinc blende gallium nitride (GaN) photocathodes has been observed and measured. The p-doped GaN photocathodes were epitaxially grown and activated to negative electron affinity with a cesium monolayer deposited on their surfaces. A field-retarding Mott polarimeter was used to measure the spin polarization of electrons photoemitted from the top of the valence band. A spectral scan with a tunable optical parametric amplifier constructed to provide low-bandwidth light revealed peak spin polarizations of 17% and 29% in the wurtzite and zinc blende photocathodes, respectively. Zinc blende GaN results are analyzed with a spin polarization model accounting for experimental parameters used in the measurements, while possible mechanisms influencing the obtained spin polarization values of wurtzite GaN are discussed.

Physics↗
DOE OSTI2026

Bias-Modulated ALD of ZnO: Insights into Precursor-Surface Interactions for ZnO Films

Atomic layer deposition (ALD) is widely used to deposit conformal thin films but is often limited in the tunability of the resulting material’s properties. Substrate bias and electric fields alter precursor-surface interactions and provide means to tune material properties. To explore this, we performed zinc oxide (ZnO) ALD using diethylzinc (DEZ) and water on silicon native oxide substrates at 150 °C in a sample holder designed to create a static electrical field by biasing one plate of a parallel plate capacitor-style sample holder during deposition. ZnO films prepared in an electric field/on a biased sample holder were thinner, changed relative crystalline composition, and contained more carbon compared to samples grown in identical sample holders without bias. The thickness was independent of the magnitude of the eletric field between plates, indicating that the primary driver for the change was substrate biasing not the electric field between plates of the parallel plate capacitor-style sample holder. Density functional theory calculations showed enhanced electron migration between dissociatively adsorbed DEZ molecules and the ZnO (002) facet with increasing force from an electric field at the substrate surface, which strengthens the electronic interactions between the surface and the adsorbate. These models offer a compelling explanation for the inhibited growth, changes in the crystallinity, and increase in carbon content of films grown in an electric field/on biased plates.

Jones, Jessica C. (ORCID:0000000174754620)↗
DOE OSTI2020

Stabilizing Zinc Anode Reactions by Polyethylene Oxide Polymer in Mild Aqueous Electrolytes

Abstract Zn dendrites growth and poor cycling stability are significant challenges for rechargeable aqueous Zn batteries. Zn metal deposition‐dissolution in aqueous electrolytes is typically determined by Zn anode–electrolyte interfaces. In this work, the role of a long‐chain polyethylene oxide (PEO) polymer as a multifunctional electrolyte additive in stabilizing Zn metal anodes is reported. PEO molecules suppress Zn 2+ ion transfer kinetics and regulate Zn 2+ ion concentration in the vicinity of Zn anodes through interactions between ether groups of PEO and Zn 2+ ions. The suppressed Zn 2+ ion transfer kinetics and homogeneous Zn 2+ ion distribution at the interface promotes dendrite‐free homogeneous Zn deposition. In addition, electrochemically inert PEO molecules adsorbed onto Zn anodes can protect the anode surfaces from H 2 generation and, thereby, enhance their electrochemical stability. Stable cycling over 3000 h and high reversibility (Coulombic efficiency > 99.5%) of Zn anodes is demonstrated in 1 m ZnSO 4 electrolyte with 0.5 wt% PEO. This finding provides helpful insights into the mechanism of Zn metal anodes stabilization by low‐cost multifunctional polymer electrolyte additives that stabilize interfacial reactions.

Jin, Yan↗
DOE OSTI2022

Effect of proton irradiation temperature on persistent photoconductivity in zinc oxide metal-semiconductor-metal ultraviolet photodetectors

The electrical and structural characteristics of 50-nm-thick zinc oxide (ZnO) metal-semiconductor-metal ultraviolet (UV) photodetectors subjected to proton irradiation at different temperatures are reported and compared. The devices were irradiated with 200 keV protons to a fluence of 1016 cm−2. Examination of the x-ray diffraction (XRD) rocking curves indicates a preferred (100) orientation prior to irradiation, with decrease in crystal quality afterward. Additionally, peak shifts in XRD and Raman spectra of the control sample relative to well-known theoretical positions are indicative of tensile strain in the as-deposited ZnO films. Shifts toward theoretical unstrained positions are observed in the irradiated films, which indicates partial relaxation. Raman spectra also indicate increase in oxygen vacancies (VO) and zinc interstitial defects (Zni) compared to the control sample. Additionally, transient photocurrent measurements performed on each sample at different temperatures showed up to 2× increase in photocurrent decay time constants for irradiated samples vs the control. This persistent photoconductive behavior is linked to the activation of electron and hole traps near the surface, and to the desorption and reabsorption of O2 molecules on the ZnO surface under the influence of UV light. Using an Arrhenius model, trap activation energies were extracted and, by comparing with known energies from the literature, the dominant defects contributing to persistent photoconductivity for each irradiation condition were identified. The persistence of differences in photocurrent transients between different samples months after irradiation indicates that the defects introduced by the suppression of thermally activated dynamic annealing processes have a long-term deleterious effect on device performance.

Heuser, Thomas A. (ORCID:0000000225642400)↗
DOE OSTI2021

Hydrophobic Molecule Monolayer Brush-Tethered Zinc Anodes for Aqueous Zinc Batteries

Aqueous zinc batteries are of great interest as a rechargeable energy storage system, particularly owing to the low cost and high safety of aqueous electrolytes, as well as the high capacity of zinc anodes. Unfortunately, the wide commercialization of aqueous zinc batteries is impeded by the irreversible water reduction and irregular zinc evolution issues on the anode side. Hereby, a hydrophobic and ultrathin polystyrene molecule brush layer is tethered onto the surface of zinc metal anodes to tackle the above limitations. Here, experimental investigations reveal that the waterproof artificial layer can sustain fast interfacial ionic transportation, minimize hydrogen evolution, and smoothen Zn deposition, thus conferring enhanced electrochemical performance to the as-protected Zn anode in both symmetric Zn//Zn cells and Zn//LiV 3 O 8 full cells.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2024

Physics-Based Continuum Modeling for an Aqueous Rechargeable Zn/MnO 2 Battery

This study introduces a framework for modeling the aqueous Zn/MnO 2 rechargeable battery. A reaction system and a physics-based continuum model are proposed based on two reaction types, one involving insertion and the second related to dissolution and deposition of a solid reaction product. The model, fitted to empirical data, predicts voltage behavior and capacity limitations during cycling, identifying electrolytic zinc depletion as a limiting mechanism, depending on the original cell construction. The research suggests the need for further material characterization and reaction analysis, which will advance our understanding and facilitate the development of grid-scale energy storage solutions.

Electrochemistry↗