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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 595 records · Page 33
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

HIV-1 stimulates nuclear entry of amyloid beta via dynamin dependent EEA1 and TGF-β/Smad signaling

Clinical evidence indicates increased amyloid deposition in HIV-1-infected brains, which contributes to neurocognitive dysfunction in infected patients. Here we show that HIV-1 exposure stimulates amyloid beta (Aβ) nuclear entry in human brain endothelial cells (HBMEC), the main component of the blood–brain barrier (BBB). Treatment with HIV-1 and/or Aβ resulted in concurrent increase in early endosomal antigen-1 (EEA1), Smad, and phosphorylated Smad (pSmad) in nuclear fraction of HBMEC. A series of inhibition and silencing studies indicated that Smad and EEA1 closely interact by influencing their own nuclear entry; the effect that was attenuated by dynasore, a blocker of GTP-ase activity of dynamin. Importantly, inhibition of dynamin, EEA1, or TGF-β/Smad effectively attenuated HIV-1-induced Aβ accumulation in the nuclei of HBMEC. The present study indicates that nuclear uptake of Aβ involves the dynamin-dependent EEA1 and TGF-β/Smad signaling pathways. These results identify potential novel targets to protect against HIV-1-associated dysregulation of amyloid processes at the BBB level. - Highlights: • HIV-1 induces nuclear accumulation of amyloid beta (Aβ) in brain endothelial cells. • EEA-1 and TGF-Β/Smad act in concert to regulate nuclear entry of Aβ. • Dynamin appropriates the EEA-1 and TGF-Β/Smad signaling. • Dynamin serves as a master regulator of HIV-1-induced nuclear accumulation of Aβ.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2014

JMJD2A attenuation affects cell cycle and tumourigenic inflammatory gene regulation in lipopolysaccharide stimulated neuroectodermal stem cells

JMJD2A is a lysine trimethyl-specific histone demethylase that is highly expressed in a variety of tumours. The role of JMJD2A in tumour progression remains unclear. The objectives of this study were to identify JMJD2A-regulated genes and understand the function of JMJD2A in p53-null neuroectodermal stem cells (p53{sup −/−} NE-4Cs). We determined the effect of LPS as a model of inflammation in p53{sup −/−} NE-4Cs and investigated whether the epigenetic modifier JMJD2A alter the expression of tumourigenic inflammatory genes. Global gene expression was measured in JMJD2A knockdown (kd) p53{sup −/−} NE-4Cs and in LPS-stimulated JMJD2A-kd p53{sup −/−} NE-4C cells. JMJD2A attenuation significantly down-regulated genes were Cdca2, Ccnd2, Ccnd1, Crebbp, IL6rα, and Stat3 related with cell cycle, proliferation, and inflammatory-disease responses. Importantly, some tumour-suppressor genes including Dapk3, Timp2 and TFPI were significantly up-regulated but were not affected by silencing of the JMJD2B. Furthermore, we confirmed the attenuation of JMJD2A also down-regulated Cdca2, Ccnd2, Crebbp, and Rest in primary NSCs isolated from the forebrains of E15 embryos of C57/BL6J mice with effective p53 inhibitor pifithrin-α (PFT-α). Transcription factor (TF) motif analysis revealed known binding patterns for CDC5, MYC, and CREB, as well as three novel motifs in JMJD2A-regulated genes. IPA established molecular networks. The molecular network signatures and functional gene-expression profiling data from this study warrants further investigation as an effective therapeutic target, and studies to elucidate the molecular mechanism of JMJD2A-kd-dependent effects in neuroectodermal stem cells should be performed. - Highlights: • Significant up-regulation of epigenetic modifier JMJD2A mRNA upon LPS treatment. • Inhibition of JMJD2A attenuated key inflammatory and tumourigenic genes. • Establishing IPA based functional genomics in JMJD2A-attenuated p53{sup −/−} NE4C cells. • Finding JMJD2A-based molecular targets and crucial pathways in p53{sup −/−} NE4C cells.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2017

Lin28b stimulates the reprogramming of rat Müller glia to retinal progenitors

In lower-order vertebrates, Müller glia exhibit characteristics of retinal progenitor cells, while in higher vertebrates, such as mammals, the regenerative capacity of Müller glia is limited. Recently, we reported that Lin28b promoted the trans-differentiation of Müller cells to rod photoreceptor and bipolar cells in the retina of retinitis pigmentosa rat model, whereas it is unclear whether Lin28b can stimulate the reprogramming of Müller glia in vitro for transplantation into a damaged retina. In the present study, Long-Evens rat Müller glia were infected with Adeno-Lin28b or Adeno-GFP. Over-expression of Lin28b in isolated rat Müller glia resulted in the suppression of GFAP expression, enhancement of cell proliferation and a significant increase of the expression of retinal progenitor markers 5 days after infection. Moreover, Lin28b caused a significant reduction of the Let-7 family of microRNAs. Following sub-retinal space transplantation, Müller glia-derived retinal progenitors improved b-wave amplification of 30d Royal College of Surgeons retinitis pigmentosa model (RCS-P+) rats, as detected by electroretinography (ERG) recordings. Taken together, these data suggest that the up-regulation of Lin28b expression facilitated the reprogramming of Müller cells toward characteristics of retinal progenitors. - Highlights: • Lin28b reprograms Müller glia to retinal progenitors. • Let-7 micrRNAs are suppressed by Lin28b. • Transplantation of reprogrammed Müller glia restores retinal function.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2017

Vasodilator-Stimulated Phosphoprotein (VASP) depletion from breast cancer MDA-MB-231 cells inhibits tumor spheroid invasion through downregulation of Migfilin, β-catenin and urokinase-plasminogen activator (uPA)

A hallmark of cancer cells is their ability to invade surrounding tissues and form metastases. Cell-extracellular matrix (ECM)-adhesion proteins are crucial in metastasis, connecting tumor ECM with actin cytoskeleton thus enabling cells to respond to mechanical cues. Vasodilator-stimulated phosphoprotein (VASP) is an actin-polymerization regulator which interacts with cell-ECM adhesion protein Migfilin, and regulates cell migration. We compared VASP expression in MCF-7 and MDA-MB-231 breast cancer (BC) cells and found that more invasive MDA-MB-231 cells overexpress VASP. We then utilized a 3-dimensional (3D) approach to study metastasis in MDA-MB-231 cells using a system that considers mechanical forces exerted by the ECM. We prepared 3D collagen I gels of increasing concentration, imaged them by atomic force microscopy, and used them to either embed cells or tumor spheroids, in the presence or absence of VASP. We show, for the first time, that VASP silencing downregulated Migfilin, β-catenin and urokinase plasminogen activator both in 2D and 3D, suggesting a matrix-independent mechanism. Tumor spheroids lacking VASP demonstrated impaired invasion, indicating VASP’s involvement in metastasis, which was corroborated by Kaplan-Meier plotter showing high VASP expression to be associated with poor remission-free survival in lymph node-positive BC patients. Hence, VASP may be a novel BC metastasis biomarker. - Highlights: • More invasive MDA-MB-231 overexpress VASP compared to MCF-7 breast cancer cells. • We prepared 3D collagen I gels of increasing concentration and characterized them. • VASP silencing downregulated Migfilin, β-catenin and uPA both in 2D and 3D culture. • Tumor spheroids lacking VASP demonstrated impaired invasion. • Kaplan-Meier plotter shows association of high VASP expression with poor survival.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2018

ADAMTS-1 disrupts HGF/c-MET signaling and HGF-stimulated cellular processes in fibrosarcoma

Extracellular matrix (ECM) serves as a reservoir for biologically active factors, such as growth factors and proteases that influence the tumor cell behavior. ADAMTS-1 (a disintegrin and metalloprotease with thrombospondin motifs) is a secreted protease that has the ability to modify the ECM during physiological and pathological processes. Here, we analyzed the role played by ADAMTS-1 regulating HGF and TGF-β1 activities in the high-grade fibrosarcoma cell line (HT1080). We generated HT1080 and HEK293T cells overexpressing ADAMTS-1. HT1080 cells overexpressing ADAMTS-1 (HT1080-MPA) exhibited a significant decrease in cell proliferation and migration velocity, both in presence of HGF. We obtained similar results with ADAMTS-1-enriched conditioned medium from other cell type. However, ADAMTS-1 overexpression failed to affect TGF-β1 activity associated with HT1080 cell proliferation and migration velocity. Immunoblotting showed that ADAMTS-1 overexpression disturbs c-Met activation upon HGF stimulation. Downstream ERK1/2 and FAK signaling pathways are also influenced by this protease. Additionally, ADAMTS-1 decreased the size of the fibrosarcospheres, both under normal conditions and in the presence of HGF. Likewise, in presence of HGF, ADAMTS-1 overexpression in HT1080 disrupted microtumors formation in vivo. These microtumors, including individual cells, presented characteristics of non-invasive lesions (rounded morphology). Our results suggest that ADAMTS-1 is involved in regulating HGF-related functions on fibrosarcoma cells. This protease may then represent an endogenous mechanism in controlling the bioavailability of different growth factors that have a direct influence on tumor cell behavior.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2018

Streptococcus salivarius-mediated CD8+ T cell stimulation required antigen presentation by macrophages in oral squamous cell carcinoma

It has been shown that the peripheral blood mononuclear cells (PBMCs) from oral squamous cell carcinoma (OSCC) patients presented cytotoxic CD8 T cell response against Streptococcus salivarius (S. salivarius), of which the frequency was positively associated with recurrence-free survival in OSCC patients. To identify the conditions required for regulating S. salivarius-specific CD8 T cell-mediated cytotoxicity, we selectively depleted individual components of the PBMCs, and observed that the depletion of monocytes/macrophages, but not other immune cell subsets, significantly downregulated the S. salivarius-specific CD8 T cell cytotoxicity. Monocyte/macrophage alone was sufficient to reconstitute optimal granzyme B expression from S. salivarius-specific CD8 T cells. Also, both the memory and the naive CD8 T cells reacted to S. salivarius-stimulation, with the memory CD8 T cells presenting significantly higher S. salivarius-reactivity. Using M1- and M2-polarized macrophages from circulating monocytes, we found that M1-polarized macrophages, with significantly higher IL-12 expression and significantly lower IL-10 and MHC class II molecule expression, was more effective at promoting granzyme B responses in CD8 T cells, and required CD80/CD86 costimulating molecules for optimal responses. Interestingly, the tumor-associated macrophages (TAMs) from resected tumors presented characteristics of M2-polarized macrophages with high MHC class II expression and low IL-12 secretion. The frequency of tumor-infiltrating S. salivarius-specific cytotoxic CD8 T cell was inversely correlated with the level of IL-10 secretion and the MHC class II molecule expression in autologous TAMs. Together, we demonstrated that monocyte/macrophages presented essential antigen-presentation and costimulatory roles in CD8 T cell-mediated S. salivarius-specific granzyme B responses, and the polarization of macrophages could influence the potency of CD8 T cell responses.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2018

The functional potency of natural killer cells in response to IL-2/IL-15/IL-21 stimulation is limited by a concurrent upregulation of Tim-3 in bladder cancer

Highlights: • NK cells from bladder cancer patients presented significant Tim-3 upregulation. • NK cells from bladder cancer patients presented significantly reduced cytotoxicity. • Cytokine-mediated stimulatory effects were less potent in bladder cancer patients. • Treatment with cytokines increased the expression of Tim-3 by NK cells. • Tim-3 blockade allowed the NK cells to present higher cytotoxicity in patients. For reasons not completely clear, natural killer (NK) cells from tumor patients displayed multiple exhaustion features and could not be completely restored even when the inhibitory signals from the intratumoral environment had ceased to exist. Here, we found that the circulating NK cells from bladder cancer patients presented significantly reduced cytotoxicity than the circulating NK cells from healthy volunteers. This impairment in cytotoxicity resulted in part from an overrepresentation of Tim-3{sup +} NK cells in bladder cancer patients. Interestingly, patients with higher frequency of Tim-3{sup +} NK cells tended to present higher frequency of Gal-9{sup +} cells in tumor. Exogenous Gal-9 significantly reduced the cytotoxicity of Tim-3{sup +}, but not Tim-3{sup -}, NK cells. Patients with better prognosis presented lower levels of Tim-3{sup +} NK cells and Gal-9{sup +} tumor cells. We then attempted to improve the cytotoxicity of NK cells using a combination of exogenous cytokines. IL-2 + IL-15 and IL-2 + IL-21 significantly enhanced, but could not completely restore, the cytotoxicity of NK cells in bladder cancer patients. Notably, when the cytokine concentration increased from intermediate levels to high levels, the cytotoxicity of NK cells from healthy volunteers significantly increased with a strong upward trend, whereas the cytotoxicity of NK cells from bladder cancer patients plateaued at intermediate levels. Further examination revealed that high cytokine concentration significantly increased the Tim-3 expression in NK cells from bladder cancer patients. Blocking Tim-3 not only improved the cytotoxicity of NK cells from bladder cancer patients, but also eliminated the plateauing effect when the NK cells were stimulated with high concentrations of cytokines. Together, these data suggested that proinflammatory cytokines could moderately improve NK cell cytotoxicity in bladder cancer patients. However, the effect was limited due to a concurrent upregulation of Tim-3.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2022

Impact of Acid–Base Stimulation Sequence on Mineral Stability for Tight/Impermeable Unconventional Carbonate-Rich Rocks: A Delaware Basin Case Study

We report mineral precipitation due to reactions with injected fluids during unconventional fracture stimulation is a well-recognized problem. The goal of this study is to evaluate secondary mineral precipitation and permeability attenuation under chemical injection scenarios specific to the Delaware basin. Whole cylindrical cores (2.54 cm diameter and 2.54 cm height) and ground shale (150–250 μm) from the carbonate-rich Bone Spring Formation, Delaware Basin TX (Leonardian), were reacted at 80 °C and 85 bar using a hydraulic fracturing fluid (HFF) recipe and an injection sequence typical of the Delaware Basin. The reacted shales and solutions were analyzed using a variety of laboratory- and synchrotron-based techniques to characterize both the chemical and spatial distributions of secondary mineral precipitation and identify changes in permeability and mineralogy. This carbonate-rich shale (>84% calcite) rapidly neutralized the acidic HFF. Synchrotron-based X-ray fluorescence mapping coupled with X-ray absorption spectroscopy (both bulk and micro) showed that most of the iron was in an oxidized form prior to exposure to HFF and that almost all iron(II) became fully oxidized after the reaction. Scanning electron microscopy images of the ground shale samples primarily identified iron(oxyhydr)oxide microcrystals on grain surfaces. A few small isolated iron-rich areas also contained sulfur, suggesting that some pyrite was preserved when isolated within a calcite crystal but that most was oxidized. The rapid neutralization of the acid spearhead in these carbonate-rich samples demonstrates that the acid spearhead is useful for initiating fractures in extremely calcite-rich rocks but does little to enhance rock permeability. This suggests that the impact of the acid spearhead is significantly smaller for carbonate-rich shales compared to clay-rich shales, which has broad implications for acidizing in carbonate-rich shale formations and iron transformations within these shales.

58 GEOSCIENCES↗
DOE OSTI2018

Monitoring Ultrafast Spin Crossover Intermediates in an Iron(II) Complex by Broad Band Stimulated X-ray Raman Spectroscopy

Here, the photoinduced spin crossover dynamics of transition metal complexes is of fundamental scientific importance and is used for sensor device applications and solar energy harvesting. Current X-ray and optical spectroscopy experiments for [Fe II (bpy) 3 ], an archetypal earth-abundant metal complex, show conflicting spin dynamics. We have simulated the broad band transient X-ray absorption and hybrid (broad + narrow band) X-ray stimulated Raman signals at the N and Fe K-edges of the key excited state intermediates involved in the spin crossover process of this complex. We find that these signals are much more sensitive to electron and spin populations than transition absorption and may be useful in the design of photovoltaic and artificial photosynthetic systems.

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

Facile Background Discrimination in Femtosecond Stimulated Raman Spectroscopy Using a Dual-Frequency Raman Pump Technique

Femtosecond stimulated Raman spectroscopy (FSRS) is a useful technique for uncovering chemical reaction dynamics by acquiring high-resolution Raman spectra with ultrafast time resolution. However, in FSRS, it can be challenging to discern Raman features from signals arising from transient absorption and other four-wave mixing pathways. To overcome this difficulty, we combine the principles of shifted excitation Raman difference spectroscopy with a simple fixed frequency comb to perform dual-frequency Raman pump FSRS. Through the addition of only two mirrors and a slit to the standard FSRS setup, this method provides Raman spectra at two different excitation wavelengths that can be processed by an automated algorithm to reconstruct the Raman spectrum. In this study, we demonstrate the utility of dual-frequency Raman pump FSRS to easily identify Raman signatures by visual inspection for excited-state and ground-state spectra, both on- and off-resonance. We show that previously assigned short-lived vibrations of photoexcited β-carotene are actually not vibrational in nature. We also use crystalline betaine-30 as a challenging test case for this method, as the FSRS spectra contain a number of narrow transient vibronic and non-SRS features. By reliably reducing interference from background signals, the interpretation is substantially more quantitative and enables the future study of new systems, particularly those with small Raman cross-sections or solid-state samples with narrow vibronic features.

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

Diffusion and photon-stimulated desorption of CO on TiO2(110)

Thermal diffusion of CO adsorbed on rutile TiO2(110) was studied in the 20 - 110 K range using photon-stimulated desorption (PSD), temperature programmed desorption (TPD) and scanning tunneling microscopy. During UV irradiation, CO desorbs from certain photoactive sites (e.g. oxygen vacancies). This phenomenon was exploited to study CO thermal diffusion in three steps: first empty these sites during a first irradiation cycle, then replenish them with CO during annealing, and finally probe the active site occupancy in the second PSD cycle. The PSD and TPD experiments show that the CO diffusion rate correlates with the CO adsorption energy – stronger binding corresponds to slower diffusion. Increasing the CO coverage or hydroxylation of the surface decreases the CO binding and increases the CO diffusion rate. Relative to the reduced surface, the CO adsorption energy increases and the diffusion decreases on the oxidized surface. The CO diffusion kinetics can be modeled satisfactorily as an Arrhenius process with a “normal” prefactor (i.e. = 1012 s 1) and a Gaussian distribution of activation energies where the peak of the distribution is ~0.28 eV and the full width at half maximum (FWHM) is 0.1 eV at the lowest coverages. The observations are consistent with a significant electrostatic component of the CO binding energy on the TiO2(110) surface which is affected by changes in the surface dipole and dipole-dipole interactions.

Petrik, Nikolay G.↗
DOE OSTI2019

Electron- and Thermal-Stimulated Synthesis of Water on Boehmite (y-AlOOH) Nanoplates

Utilizing a combination of electron stimulated desorption, infrared spectroscopy and temperature program desorption measurements, we show that molecular water is synthesized during electron irradiation on boehmite nanoplates and postulate that the reaction proceeds first through decomposition of the hydroxyl to produce trapped hydrogen atoms. Once released, these hydrogen atoms can react with a neighboring hydroxyl resulting in adsorbed water. In addition, molecular water is readily formed on the surface of the boehmite nanosheets through thermal induced recombinative desorption. Peak water production via recombinative desorption occurs at 750 K in agreement with previous studies. We have also identified a weak desorption feature near 400 K which is likely strongly adsorbed water. The derived experimental desorption activation energy of water assuming full coverage is 98.6 kJ mol-1.

Jones, Brant M.↗
DOE OSTI2021

Resonant Stimulated X-ray Raman Spectroscopy of Mixed-Valence Manganese Complexes

Resonant stimulated X-ray Raman spectroscopy of the bimetallic [Mn III Mn IV (μ-O) 2 (μ-OAC)(tacn) 2 ] 2+ manganese complex is investigated in a simulation study. A pump–probe sequence of resonant X-ray Raman excitations is employed to generate and monitor valence-electron wave packets at selected regions in the molecule, by exploiting element specific core-excited states. A two-color protocol is presented, with pump and probe pulses tuned to the Mn and N K-edges. A natural orbital decomposition allows the visualization of the electron dynamics underlying the signal.

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

Conical Intersection Passages of Molecules Probed by X-ray Diffraction and Stimulated Raman Spectroscopy

Conical intersections (CoIns) play an important role in ultrafast relaxation channels. Their monitoring remains a formidable experimental challenge. We theoretically compare the probing of the S 2 → S 1 CoIn passage in 4-thiouracil by monitoring its vibronic coherences, using off-resonant X-ray-stimulated Raman spectroscopy (TRUECARS) and time resolved X-ray diffraction (TRXD). The quantum nuclear wavepacket (WP) dynamics provides an accurate picture of the photoinduced dynamics. Upon photoexcitation, the WP oscillates among the Franck–Condon point, the S2 minimum, and the CoIn with a 70 fs period. A vibronic coherence first emerges at 20 fs and can be observed until the S 2 state is fully depopulated. The distribution of the vibronic frequencies involved in the coherence is recorded by the TRUECARS spectrogram. Here, the TRXD signal provides spatial images of electron densities associated with the CoIn. In combination, the two signals provide a complementary picture of the nonadiabatic passage, which helps in the study of the underlying photophysics in thiobases.

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

Stimulated X-ray Raman and Absorption Spectroscopy of Iron–Sulfur Dimers

Iron–sulfur complexes play an important role in biological processes such as metabolic electron transport. A detailed understanding of the mechanism of long-range electron transfer requires knowledge of the electronic structure of the complexes, which has traditionally been challenging to obtain, either by theory or by experiment, but the situation has begun to change with advances in quantum chemical methods and intense free electron laser light sources. We compute the spectra for stimulated X-ray Raman spectroscopy (SXRS) and absorption spectroscopy of homovalent and mixed-valence [2Fe–2S] complexes, using the ab initio density matrix renormalization group algorithm. The simulated spectra show clear signatures of the theoretically predicted dense low-lying excited states within the d–d manifold. Finally, the difference in spectral intensity between the absorption-active and Raman-active states provides a potential mechanism to selectively excite states by a proper tuning of the excitation pump, to access the electronic dynamics within this manifold.

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

Curvature Memory in Electrically Stimulated Lipid Membranes

Here, we demonstrate, using non-equilibrium molecular dynamics simulations, that lipid membrane capacitance varies with surface charge accumulation linked to membrane shape and curvature changes. Specifically, we show that lipid membranes exhibit a hysteretic response when exposed to oscillatory electric fields. The electromechanical coupling in these membranes leads to hysteretic buckling, in which the membrane can spontaneously buckle in one of two distinct directions along the electric field, even for the same ionic charge accumulation at the water–membrane interface. In this regard, these binary buckled membrane states suggest potential applications in neuromorphic computing. Their bistable nature, characterized by two distinct and stable configurations, could serve as a foundation for implementing memory storage systems and logic operations. Furthermore, we introduce a circuit model that captures these dynamic effects, offering insights into emergent memory effects in electrically stimulated lipid membranes. Finally, this work presents lipid bilayers as dynamic, adaptable elements and suggests a new platform for exploring energy storage, information processing, and memory encoding at the lipid membrane level.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2021

Direct Observation of Plasma-Stimulated Activation of Surface Species Using Multimodal In Situ/Operando Spectroscopy Combining Polarization-Modulation Infrared Reflection-Absorption Spectroscopy, Optical Emission Spectroscopy, and Mass Spectrometry

Nonthermal plasmas (NTPs) produce reactive chemical environments, including electrons, ions, radicals, and vibrationally excited molecules, that can drive chemistry at temperatures at which such species are thermally inaccessible. There has been growing interest in the integration of conventional catalysis with reactive NTPs to promote novel chemical transformations. Unveiling the full potential of plasma-catalytic processes requires a comprehensive understanding of plasma-catalytic synergies, including characterization of plasma-catalytic surface interactions. In this work, we report on a newly designed multimodal spectroscopic instrument combining polarization-modulation infrared reflection-absorption spectroscopy (PM-IRAS), mass spectrometry, and optical emission spectroscopy (OES) for the investigation of plasma–surface interactions such as those found in plasma catalysis. In particular, this tool has been utilized to correlate plasma-phase chemistry with both surface chemistry and gas-phase products in situ (1) during the deposition of carbonaceous surface species via NTP-promoted nonoxidative coupling of methane and (2) during subsequent activation of surface deposits with an atmospheric pressure and temperature argon plasma jet on both nickel (Ni) and silicon dioxide (SiO 2 ) surfaces. For the first time, the activation of carbonaceous surface species by a NTP on Ni and SiO 2 surfaces to form hydrogen gas and C 2 hydrocarbons was directly observed, where both PM-IRAS and OES measurements suggest that they may form through different pathways. Furthermore, this unique tool for studying plasma–surface interactions could enable more rational design of plasma-stimulated catalytic processes.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Visualizing Electric and Magnetic Field Coupling in Au-Nanorod Trimer Structures via Stimulated Electron Energy Gain and Cathodoluminescence Spectroscopy: Implications for Meta-Atom Imaging

In this work, trimer meta-atoms composed of three gold rods in an equilateral triangular geometry were fabricated, and their near-field plasmonic responses were characterized via electron energy loss (EEL), cathodoluminescence (CL), and stimulated electron energy loss/gain (sEEL/sEEG) spectroscopy. The trimer structure hybridizes into a low-energy mode with all three rods coupling in-phase, which produces a circulating current and thus a magnetic field. The next highest-energy mode consists of two rods coupling out-of-phase and produces a net electric dipole. We investigate the near fields of hybridized magnetic and electric modes via EEL and CL and correlate their spectral characteristics and intensity maps. Then, by changing the length of the trimer rods, we tune the magnetic and electric modes to our laser energy and characterize the excited state via sEEL/sEEG spectroscopy. Exploration of the tilt dependence, relative to the optical source, of the two modes reveals that the electric mode sEEG intensity increases more than the expected sin 2 (θ) dependence of the optical electric field coupling (see the Supporting Information for a detailed description). After correcting for the tail of the close-proximity electric mode, we demonstrate sEEG via coupling of the magnetic component of the optical field to the magnetic meta-atoms, which has the expected cos 2 (θ) tilt dependence. This realization opens the possibility to explore the nanoscale excited-state near-field imaging of other magnetic meta-atom structures.

36 MATERIALS SCIENCE↗