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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 199 records · Page 11
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

A spectroscopic study of uranyl speciation in chloride-bearing solutions at temperatures up to 250 °C

The speciation of U in NaCl-bearing solutions at temperatures up to 250 °C and concentrations of NaCl up to 1.5 m has been investigated using an in situ spectroscopic technique. The recorded spectra permit us to identify the species present in the solutions as UO 2 2+ , UO 2 Cl + , and UO 2 Cl 2 °. UO 2 Cl 3 - is also likely present at high temperatures and NaCl concentrations, but concentrations of this species are insufficient for derivation of the formation constants. No evidence was found for species of higher ligand (Cl-) number. Thermodynamic stability constants derived for these species show fair agreement with published data for 25 °C, but differ significantly from those predicted by an earlier high-temperature study (Dargent et al., 2013), which suggested that UO 2 Cl 4 2- and UO 2 Cl 5 3- contribute significantly to the mass balance of uranyl chloride complexes, especially at high temperature. In contrast, our data suggest that the main uranyl-chloride complex present in aqueous solutions at T >150 °C and concentrations of NaCl relevant to natural hydrothermal systems is UO 2 Cl 2 °. The values of the logarithms of thermodynamic formation constants (β) for the reaction UO 2 2+ + Cl - = UO 2 Cl + are 0.02, 0.25, 0.55, 1.09, 1.59, and 2.28 derived at 25, 50, 100, 150, 200, and 250 °C, respectively. For the reaction UO 2 2+ + 2Cl - = UO 2 Cl 2 ° the values of log β derived at these temperatures are 0.4, 0.58, 0.74, 1.44, 2.18, and 3.42. Values of the formation constant estimated for uranyl-chloride species predict the high concentrations of U observed by Richard et al. (2011) in fluid inclusions of the giant McArthur River unconformity-type uranium deposit.

58 GEOSCIENCES↗
DOE OSTI2018

Synthesis, Characterization, and Oxidation Catalysis Studies of a Monofunctionalized Copper Pyridine-Aza Macrocycle

For this study, a copper-containing pyridine-aza macrocycle (PyMACs) with a propionic acid functionality was synthesized and characterized using X-ray crystallography and various spectroscopic techniques. The complex was then screened for peroxidase , olefin epoxidation, and phenol oxidation properties, using an ABTS assay, GC-MS, and UV-Vis spectrophotometry, respectively. The control copper (II) perchlorate salts were superior oxidation catalysts to the pentadentate carboxylic acid complex, CuLCOOH, and the unfunctionalized amine PyMAC, CuCRH. This might indicate that free copper ions facilitate the one-electron oxidations necessary for the reactions better than complexed copper. It also indicates that the copper PyMACs are far less effective than the analogous nickel and iron systems. We did, however, obtain valuable insights on the chemistry governing this family of PyMACs by probing the CuLCOOH’s solution and solid-phase protonation equilibria, which will be useful for isolating and studying the analogous iron complex, FeLCOOH.

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

Plasmonic hybrid core-shell (HyCoS) AgPt NP template hybridized with GQDs for SERS enhancement of 4-MBA and BT

Surface-enhanced Raman spectroscopy (SERS) is an attractive vibrational spectroscopic technique that can enable a non-destructive and ultra-sensitive detection down to the single-molecule level. Herein, a novel hybrid SERS platform is developed based on hybrid core-shell (HyCoS) AgPt nanoparticles (NPs) and graphene quantum dots (GQDs) for the enhancement of Raman vibration of 4-mercaptobenzoic acid (4-MBA) and benzenethiol (BT). The unique design of HyCoS AgPt NPs induces strong electromagnetic mechanism (EM) enhancement through the amplification of electromagnetic fields by the excitation of high-density surface plasmons and hot spots. Superior localized surface plasmon resonance (LSPR) is generated by the AgPt core-shell and background Ag NP coupling, which is systematically investigated by the optical properties and FDTD simulations. The background Ag NPs can further increase the coverage of metallic NPs, leading to higher-density hot spots and enhanced SERS response. At the same time, GQDs can provide plentiful accessible edges for the charge transfer to the HOMO and LUMO of 4-MBA and BT based on the chemical mechanism (CM) enhancement. The mixing approach of GQDs and target molecules on the HyCoS AgPt NPs can significantly amplify the Raman signals via the strong adsorption of probe molecules by the π – π interaction. The enhancement factors of proposed SERS platform can reach ~107 and ~105 for the 4-MBA and BT respectively.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Quantification of active sites in yttrium containing dealuminated Beta zeolites during conversion of ethanol and acetaldehyde to butadiene

Here, in this work, yttrium containing dealuminated Beta zeolites (Y/deAlBeta) were synthesized and characterized by various spectroscopic techniques to improve understanding of ethanol upgrading over these materials. Characterization results indicate yttrium atoms partially condense with framework silanol nests formed during dealumination of parent Al-Beta supports. Active sites for conversion of ethanol and acetaldehyde to butadiene were quantified on a series of Y/deAlBeta catalysts (0.1–10 wt% yttrium) via ex situ chemisorption and transmission Fourier transformed infrared (FTIR) spectroscopy measurements by first measuring the integrated molar extinction coefficient (IMEC) for pyridine bound to Lewis acidic yttrium sites. In situ titrations with pyridine demonstrate that the number of sites quantified by ex situ chemisorption IR is quantitatively similar to the number of sites that catalyze butadiene formation, which varies (from 0.05 to 0.35) across the series of catalysts. In situ pyridine titrations impact butadiene site time yields (STY), but not crotonaldehyde STY, indicating that a distribution of yttrium sites is present, and that discrete yttrium site types participate in distinct steps in the pathway from ethanol to butadiene. Apparent kinetic parameters including activation energies and reaction orders were measured, these suggest differences in reactant (or reactant-derived intermediate) surface coverages result in higher STYs (per mol Y or per Lewis acidic Y site) for samples with low Y loadings relative to those with higher Y loadings. Isotopic labeling experiments evince the existence of other kinetically relevant steps in addition to the crotonaldehyde transformation to crotyl alcohol. Together, these findings provide further guidance into the heterogeneities in site structures in yttrium-containing zeolites and their relevance for the various steps in the pathway from ethanol to C 4 products useful for production of sustainable aviation fuel and renewable butadiene.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

Adsorption of hydroxamic acid ligands for improved extraction of rare earth elements from monazite ores

Efficient separation of rare earth element (REE) ores via froth flotation requires the development of novel ligands with enhanced adsorption capacity and selectivity. To realize these advances, understanding the mechanisms underlying interactions between the ligand and mineral surfaces is essential. This study systematically evaluates the adsorption behavior of alkyl- and aromatic alkyl-substituted hydroxamic acid ligands on monazite surfaces using complementary spectroscopic techniques, including UV–visible (UV–vis) spectroscopy, Raman spectroscopy, infrared spectroscopy, and vibrational sum frequency generation (SFG) spectroscopy, together with the ab initio molecular dynamics (AIMD) simulations. Among the studied ligands, octanohydroxamic acid (OHA) and 4-ethoxy-N,2-dihydroxybenzamide (EDHBA) exhibit high adsorption capacity under basic pH (8–10) by forming multilayers on the surface. OHA has a higher equilibrium adsorption capacity compared to EDHBA, but it forms a less stable multilayer susceptible to disruption in the presence of interfering ions. AIMD results show that OHA adopts a single stable chelating geometry, while EDHBA exhibits multiple binding modes involving distinct interactions with La surface atoms and phosphate-bound oxygens, resulting in more complex adsorption kinetics. The variations in surface binding and intermolecular interactions observed between alkyl and aromatic molecules influence the differences in adsorption kinetics, equilibrium adsorption capacities on the mineral surface, and their flotation performance. This work provides valuable insight into the adsorption mechanism of ligands at mineral interfaces, which is crucial for guiding the design of new ligands with enhanced separation performance.

Zhou, Muchu [ORNL] (ORCID:0000000182650215)↗
DOE OSTI2018

1 H NMR-based metabolomics of antimalarial plant species traditionally used by Vha-Venda people in Limpopo Province, South Africa and isolation of antiplasmodial compounds

The Vha-Venda people living in rural areas of Limpopo Province of South Africa regularly use traditional plant-based medicines to treat malaria. In our earlier publication, twenty indigenous plant species used to treat malaria or its symptoms by Vha-Venda people were evaluated for antiplasmodial activity. The main objective of the current paper was to assess the robustness of NMR-based metabolomics in discriminating classes of secondary compounds that are responsible for the observed antimalarial activity and the isolation of antiplasmodial compounds. Twenty dichloromethane extracts were reconstituted in CDCl 3 , subjected to 1 H NMR-based metabolomic analysis on a Varian 600 MHz spectrometer and the acquired 1 H NMR spectra were then evaluated collectively using multivariate data analysis (MDA). Principal Component Analysis (PCA) and Orthogonal Projections to Latent Structures–Discriminant Analysis (OPLS-DA) were used to ‘globally’ discern antiplasmodial profiles. A contribution plot was then generated from the OPLS-DA scoring plot in an attempt to determine the classes of compounds that are responsible for the observed grouping. Further phytochemical analyses were conducted on the lipophilic extracts of Tabernaemontana elegans and Vangueria infausta subsp. infausta. These best candidates were fractionated, purified and their isolated compounds identified based on conventional chromatographic and spectroscopic techniques. The PCA did not separate the acquired profiles according to the detected antiplasmodial bioactivity. Application of a supervised OPLS-DA on the 1 H NMR profiles resulted in a discrimination pattern that could be correlated to the observed antimalarial bioactivity. A contribution plot generated from the OPLS-DA scoring plot illustrated the classes of compounds responsible for the observed grouping. Prominent peaks were observed in the aromatic, sugar-based/N-containing and aliphatic spectral regions of the contribution plot. Two known indole alkaloids were isolated from T. elegans, and identified as tabernaemontanine (IC 50 = 12.0±0.8 µM) and dregamine (IC 50 = 62.0±2.4 µM). Friedelin (IC 50 = 7.20±0.5 µM) and morindolide (IC 50 = 107.1±0.6 µM) were isolated from V. infausta subsp. infausta. This is the first report of the rare iridoid lactone, morindolide's antimalarial activity. While these two compounds have been previously identified, this is the first account of their occurrence in the genus Vangueria. The study illustrated the potential of NMR-based metabolomics in discriminating classes of compounds that may be attributed to antiplasmodial activity. Finally and additionally, the study demonstrated the potential of discovering novel antiplasmodial scaffolds from medicinal plants and the rationale for the bioprospecting antimalarial plant species used by Vha-Venda people.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2017

Iron phosphate glasses: Bulk properties and atomic scale structure

Bulk properties such as glass transition temperature, density and thermal expansion of iron phosphate glass compositions, with replacement of Cs by Ba, are investigated as a surrogate for the transmutation of 137Cs to 137Ba, relevant to the immobilisation of Cs in glass. These studies are required to establish the appropriate incorporation rate of 137Cs in iron phosphate glass. Density and glass transition temperature increases with the addition of BaO indicating the shrinkage and reticulation of the iron phosphate glass network. The average thermal expansion coefficient reduces from 19.8 × 10-6 K-1 to 13.4 × 10-6 K-1, when 25 wt. % of Cs2O was replaced by 25 wt. % of BaO in caesium loaded iron phosphate glass. In addition to the above bulk properties, the role of Ba as a network modifier in the structure of iron phosphate glass is examined using various spectroscopic techniques. The FeII content and average coordination number of iron in the glass network was estimated using Mössbauer spectroscopy. The FeII content in the un-doped iron phosphate glass and barium doped iron phosphate glasses was 20, 21 and 22 ± 1% respectively and the average Fe coordination varied from 5.3 ± 0.2 to 5.7 ± 0.2 with increasing Ba content. The atomic scale structure was further probed by Fe K-edge X-ray absorption spectroscopy. The average coordination number provided by extended X-ray absorption fine structure spectroscopy and X-ray absorption near edge structure was in good agreement with that given by the Mössbauer data.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Insights into the thermal decomposition of plutonium(IV) oxalate – a DFT study of the intermediate structures

The thermal decomposition of plutonium oxalate to oxide is one of the most studied reactions in actinide chemistry but the intermediates have been the subject of debate for decades. Recent experimental data suggest that the decomposition of Pu(IV) oxalate in air undergoes dehydration first, then reduction to Pu(III) oxalate. The precise structural modifications that take place are unknown as experiments have not been able to fully characterize the intermediates at the microscopic level. To rectify this, we employed solid state density functional theory calculations at the PBE-D3 level with a Hubbard U correction to model the structures and energetics of potential dehydrated Pu(IV) and Pu(III) oxalate intermediate compounds. Based on the theoretical study presented here, the anhydrous analogues of the known hydrated Pu(IV) and Pu(III) oxalates are the preferred crystal structures formed through an overall exothermic reaction process. However, decomposition could proceed through the formation of a higher energy, more complicated 3D lattice structure with frustrated oxalate binding. It is expected that the intermediates presented here could be identified using spectroscopic techniques to enable further insight into the reaction mechanism.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2021

Transient absorption spectroscopy to explore cellular pathways to photobiomodulation

Photobiomodulation (PBM) describes the use of low irradiance light in the red to near-infrared wavelength range to stimulate biological effects in tissue, and many biological and spectroscopic techniques are used to study PBM. However, these techniques focus on the products or downstream effects rather than the electronic transitions that initiate the PBM processes. This study presents a novel approach to studying low irradiance light exposures on individual proteins and/or protein complexes by combining a continuous wave (CW) laser diode with femtosecond transient absorption spectroscopy (TAS), coined here as CW-TAS, and tests the system on reduced cytochrome c (Cyt c) for proof of principle. TAS was conducted using a 532-nm excitation pump beam and a 350-600 nm supercontinuum probe. In this work, CW laser diodes with wavelengths of 450 nm, 635 nm, and 808 nm were interchangeably fiber coupled into the HELIOS Fire. Samples of Cyt c were tested by TAS using a pump power of 15 µW, both with and without CW exposure. CW exposures were carried out with irradiances of 1.60 and 3.20 mW/cm 2 , except for 808 nm, which was only tested at 1.60 mW/cm 2 . Both kinetic and global analyses were performed on the TAS data and the time constants for sets with and without CW exposures were compared. The TAS data for Cyt c with the full dosage of CW exposures did not alter the TAS data distinguishably from the control data. No new electronic transient signals were observed beyond the background when testing Cyt c with the CW exposures. Kinetic analysis confirmed that existing transients did not deviate beyond uncertainty. Global time constants for Cyt c were calculated to be 0.25 ± 0.03 ps and 5.1 ± 0.3 ps for the control study, and the time constants for the CW exposed Cyt c were not significantly different. This study concludes that CW irradiation, at doses delivered, does not alter the transient absorption data of Cyt c. The CW-TAS method provides a new tool for studying PBM effects in other proteins and protein complexes, such as Complex IV, in future studies.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2017

Synthesis and characterization of heterometallic uranyl pyridinedicarboxylate compounds

The incorporation of transition metals into hybrid uranyl materials can result in more diverse structural topologies and variations in physical and chemical properties. To explore the impact of transition metals on the uranyl cation, five uranium containing bimetallic chain compounds, [(UO{sub 2})M(PDC){sub 2}(H{sub 2}O){sub 4}]·4(H{sub 2}O) (PDC = 2,6 pyridinedicarboxylate; M = Ni{sup 2+}, Co{sup 2+}, Fe{sup 2+}, Zn{sup 2+,} and Cu{sup 2+}) were synthesized by evaporation of aqueous solutions at room temperature. The uranyl cation is complex by two PDC ligands and the transition metal cations bond to the complex to form a one-dimensional chain topology. The presence of the transition metal leads to the presence of a stronger uranyl oxo bonds as shown by the single-crystal X-ray diffraction data and the Raman spectra. Solid state diffuse reflectance UV/Visible spectra confirmed the presence of the transition metals in the structure by the broad bands that appeared at relevant wavelengths. - Graphical abstract: Synthesis and characterization of [(UO{sub 2})M(2,6 pyridinedicarboxylate)(H{sub 2}O){sub 4}]·4(H{sub 2}O) [M = Ni{sup 2+}, Co{sup 2+}, Fe{sup 2+}, Zn{sup 2+}, and Cu{sup 2+}] compounds reveals impact of transition metals in uranyl hybrid systems. Display Omitted - Highlights: • 5 heterometallic uranyl PDC compounds were synthesized and characterized by X-ray diffraction and spectroscopic techniques. • Uranyl PDC 1-D chain complexes that were linked via transition metal cations were further linked through π- πinteractions. • Structural data denotes shorter uranyl bonds in the presence of the transition metals and this is confirmed by Raman shifts. • Solid-state UV/Vis spectroscopy confirms the presence of transition metals in this system.

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

Choline Fluoride-Ethylene glycol deep eutectic solvent mixture – Synthesis and physicochemical properties

A critical factor in achieving tunability in DESs is varying the type of hydrogen bond acceptors (HBAs) and donors (HBDs). Choline halides (ChX), such as ChCl and ChBr, have been studied to investigate the effect of the choline anion on DESs. However, ChF-based DESs have been underrepresented in scientific research. ChF has excellent potential, such as high electron affinity, ionization potential, and strong hydrogen bond interactions. Moreover, ChF-based DES can lead to a deeper understanding of DESs due to the NMR-active 19F nuclear spin nature. We report the first synthesis and characterization of choline fluoride-EG (1:2, ChF:EG) DES, which we named “EthalineF.” We studied this mixture using various spectroscopic techniques, including NMR, FT-IR, Raman, and UV–vis spectroscopies. Polarity, density, viscosity, and conductivity measurements were collected as well. Transient absorption spectroscopy (TAS) was used to study the solvation dynamics of EthalineF. 19F NMR indicated that some fluoride anions (~15%) are coordinated to the choline cation. In EthalineF, the new type of observed fluoride anions is proposed to be a tight-binding choline-fluoride ion pair. Further, EthalineF has a larger solvodynamic radius than Ethaline. This can explain the lower conductivity for EthalineF compared to Ethaline despite the higher fluidity and solvation dynamics for EthalineF.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Template-free cyclic hexavanadate: Synthesis, characterization, solid-state structure, and solution-state dynamics

A novel hexavanadate–organic hybrid material of the formula [NH 4 ] 2 [V 6 (µ 2 -O) 6 (O) 4 (PDC) 6 ] (PDC = 2,6-pyridinedicarboxylate) has been prepared in dilute nitric acid under hydrothermal reaction conditions. The product was characterized by single crystal and powder X-ray diffraction, FTIR, UV–Vis, Raman, and thermogravimetric analyses in the solid state, and small angle X-ray scattering, ESI-MS, NMR ( 1 H, 13 C, 51 V), and Raman spectroscopic techniques in aqueous solution. The crystal structure revealed a rare structure type in vanadium chemistry which crystallizes in the monoclinic space group P2 1/n and consists of a cyclic polyoxovanadate core with edge-capped tetrahedral and octahedral vanadium centers. The “hollow” polyoxovanadate is stabilized by a PDC ligand on each metal center, and ammonium ions charge balance the anionic core and form hydrogen bonding interactions with the hexavanadate units. Solution-state studies showed that the structural unit observed in the solid state hydrolyzes upon dissolution in water, resulting in a symmetric dimer bearing similar ligand sets. Finally, catalytic experiments on the photodecomposition of crystal violet, rhodamine B, methylene blue, and rhodamine 6G showed ≥93% degradation of the dyes under UV light irradiation upon addition of the vanadium complex.

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

Polybenzimidazole based random copolymers containing hexafluoroisopropylidene functional groups for gas separations at elevated temperatures

Polybenzimidazoles (PBIs) are attractive membrane materials for H 2 /CO 2 separation at hydrocarbon fuel derived synthesis gas operating conditions due to their exceptional physicochemical stability and promising permselectivity character. PBI molecular structure modification is a viable approach to disrupt chain packing altering the free-volume architecture which results in improved gas transport characteristics. This work is focused on the synthesis and characterization of novel PBI random copolymers for application as elevated temperature H 2 /CO 2 membranes. The co-polymerization route is expected to result in tailorable permeability and selectivity by combining the high H 2 permeability aspect of the highly disrupted loosely packed hexafluoroisopropylidene diphenyl group containing PBI segments (6F-PBI) with the highly selective tightly packed phenylene group containing PBI segments (m-PBI). 6F/m-PBI copolymers with varying 6F-PBI and m-PBI ratios having high inherent viscosity were synthesized. The structure and ratio of the 6F- and m-PBI fractions were confirmed using FTIR and NMR spectroscopic techniques. The measured gas transport properties of copolymer thin films cast in controlled environment were measured as a function of the operating conditions. Lastly, the H 2 permeability increased while H 2 /CO 2 selectivity decreased as the 6F-PBI copolymer fraction was increased.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Water at surfaces and interfaces: From molecules to ice and bulk liquid

The structure and growth of water films on surfaces is reviewed, starting from single molecules to two-dimensional wetting layers, and liquid interfaces. This progression follows the increase in temperature and vapor pressure from a few degrees Kelvin in ultra-high vacuum, where Scanning Tunneling and Atomic Force Microscopies (STM and AFM) provide crystallographic information at the molecular level, to ambient conditions where surface sensitive spectroscopic techniques provide electronic structure information. We show how single molecules bind to metal and non-metal surfaces, their diffusion and aggregation. We examine how water molecules can be manipulated by the STM tip via excitation of vibrational and electronic modes, which trigger molecular diffusion and dissociation. We review also the adsorption and structure of water on non-metal substrates including mica, alkali halides, and others under ambient humid conditions. Finally, we discuss recent progress in the exploration of the molecular level structure of solid-liquid interfaces, which impact our fundamental understanding of corrosion and electrochemical processes.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2023

Structure design enables stable anionic and cationic redox chemistry in a T2-type Li-excess layered oxide cathode

Coupled with anionic and cationic redox chemistry, Li-rich/excess cathode materials are prospective high-energy-density candidates for the next-generation Li-ion batteries. However, irreversible lattice oxygen loss would exacerbate irreversible transition metal migration, resulting in a drastic voltage decay and capacity degeneration. Herein, a metastable layered Li-excess cathode material, T2-type Li 0.72 [Li 0.12 Ni 0.36 Mn 0.52 ]O 2 , was developed, in which both oxygen stacking arrangement and Li coordination environment fundamentally differ from that in conventional O3-type layered structures. By means of the reversible Li migration processes and structural evolutions, not only can voltage decay be effectively restrained, but also excellent capacity retention can be achieved upon long-term cycling. Moreover, irreversible/reversible anionic/cationic redox activities have been well assigned and quantified by various in/ex-situ spectroscopic techniques, further clarifying the charge compensation mechanism associated with (de)lithiation. These findings of the novel T2 structure with the enhanced anionic redox stability will provide a new scope for the development of high-energy-density Li-rich cathode materials.

25 ENERGY STORAGE↗
DOE OSTI2018

Effect of temperature on light induced degradation in methylammonium lead iodide perovskite thin films and solar cells

Here in this study we investigate the light and heat-induced degradation of methylammonium lead iodide (MAPbI 3 ) perovskite films in an inert atmosphere to exclude the effect of oxygen and humidity. Films aged under solar intensities started to degrade above 75 °C, while films in the dark degraded at 95 °C. To investigate the temperature-induced degradation mechanism, spectroscopic techniques such as Ultraviolet-Visible (UV–Vis) absorption spectroscopy, X-Ray Diffraction (XRD), Extended X-ray Absorption Fine Structure (EXAFS), and Fourier Transform Infrared (FT-IR) were used. Results show that the films aged under light at 75 °C degraded to a mixture of PbI 2 and metallic Pb. In contrast, films aged thermally in the dark, or with light and oxygen, degraded to PbI 2 only. MAPbI 3 solar cells were aged to show the effect of the metallic lead on the charge transfer mechanism

14 SOLAR ENERGY↗
DOE OSTI2023

Interfacial bond characterization of epoxy adhesives to aluminum alloy and carbon fiber-reinforced polyamide by vibrational spectroscopy

Vibrational spectroscopic technique has been utilized to investigate interfacial bonding chemistry of two epoxy adhesive products, XP0012 and XP5005F, on plasma-treated AA6061 and carbon fiber-reinforced polyamide 66 (CFRP-PA66) surfaces. The change in vibrational peak ratios was measured by attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy to deduce bonding mechanisms. Both adhesives showed strong crosslinking polymerization of hydroxyl- and amine-initiated epoxy ring opening on AA6061 surface, but on CFRP surface XP0012 formed a simple amide linkage by the reaction of surface hydroxyl groups and nitrile groups of curing agent, and XP5005F formed a crosslinked network by hydroxyl-initiated epoxy ring opening polymerization. The different interfacial bonding formation of two adhesives on CFRP-PA66 surface is attributed to additive effect. Addition of additives to epoxy adhesives (XP5005F) changed the interfacial bonding mechanism on CFRP-PA66 surface, rather forming hydroxyl-initiated epoxy opening crosslinking polymerization than a simple amide bond formation (XP0012). The interfacial bonding chemistry was also proved by addition of bisphenol A (BA) to a simplified model diglycidyl ether of bisphenol A/dicyandiamide (DGEBA/DICY) epoxy system. When BA was added to the model DGEBA/DICY system, epoxy ring gradually decreased on CFRP-PA66 surface, while without BA, DGEBA/DICY showed only decrease in a nitrile peak intensity in ATR-FTIR. In conclusion, the foregoing different types of interfacial chemical bonds at the adhesive/CFRP-PA66 interfaces can affect the lap shear behavior of the joint.

36 MATERIALS SCIENCE↗
DOE OSTI2024

The effects of thickness, polarization, and strain on vibrational modes of 2D Fe 3 GeTe 2

In this study, we investigated the effects of thickness, light polarization, and strain on the Raman spectra of two-dimensional (2D) Fe 3 GeTe 2 (FGT) crystals synthesized via chemical vapor transport. The crystals are thoroughly characterized using a combination of microscopic, diffraction, and spectroscopic techniques. Particularly, a systematic angle-resolved polarized Raman spectroscopy study reveals a clear polarization dependence of the Raman intensity in both parallel and crossed polarization directions, with the $A$$^{1}_{g}$ mode completely disappearing in the crossed polarization direction. The angle-dependent intensity of both the $A$$^{1}_{g}$ and $E$$^{2}_{2g}$ modes in parallel polarization and the intensity of the $E$$^{2}_{2g}$ mode in the crossed polarization remain constant at all angles. These findings align with predictions from Raman tensor analysis, providing compelling evidence for the unambiguous assignment of the $A$$^{1}_{g}$ and $E$$^{2}_{2g}$ modes to specific peaks observed in the Raman spectrum of FGT, resolving existing confusion in the literature regarding their assignment. Furthermore, we examine the effect of strain on the Raman spectrum of 2D FGT in-situ using a bending device. Our study, conducted on a monolayer to few-layer 2D FGT deposited onto polyethylene terephthalate and subjected to outward (inward), i.e., tensile (compressive) bending, demonstrates appreciable downshifting (upshifting) of the Raman peak position of both $A$$^{1}_{g}$ and $E$$^{2}_{2g}$ modes. Furthermore, these findings are particularly significant given that strain engineering represents an effective approach to modulate the magnetic properties of FGT and other 2D magnetic materials.

2D materials↗