Pulsed Technique Research Articles

Engineering Controls for Scaling CO2 Electrolyzers

The electrochemical CO2 reduction (CO2R) to ethylene on copper-based catalysts has garnered significant attention for its potential in sustainable industrial practices. While substantial progress has been achieved in the development of small-scale electrolyzers with geometric areas ranging from 1 to 5 cm2, the imperative to address larger scales for industrial decarbonization necessitates a shift in focus. There are inherent critical risks when scaling a nascent technology like CO2 electrolysis. There can be emergent phenomena observed only at larger scales, that can prevent it from reaching commercialization, such as change in local CO2 concentration, defects in the porous transport layer, and temperature gradients The optimized conditions for operating a 5 cm2 electrolyzer may not work well with a 25 cm2 electrolyzer leading to failures. Therefore, there is a need to develop a systematic way to test for these phenomena to address these challenges to successfully operate a CO2R electrolyzer at an industrially relevant scale. In this work, we highlight the performance of a Cu-based catalyst designed for the selective reduction of CO2 to ethylene across varying scales, ranging from 5 to 100 cm2. This investigation shows the changes in the electrolyzer performance at different scales. Our findings highlight the critical importance of implementing engineering controls to overcome challenges associated with the scaling of electrolyzers. Specifically, we explore the impact of anolyte flow rate, gasket compression, and electrochemical pulsing techniques on maintaining the desired selectivity of the electrocatalyst across different scales. By systematically adjusting these parameters, we demonstrate the ability to mitigate non-linear effects and uphold the efficiency of CO2 reduction to ethylene, even on larger electrode surfaces.This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

Pitting behavior of austenitic stainless-steel welded joints with dense inclusions and methods to enhance pitting resistance

PurposeThis study aims to assess the pitting resistance of austenitic stainless steel welded joints fusion zone (FZ) with high density of inclusions before and after surface treatment, including potentiostatic pulse technique (PPT) and pickling.Design/methodology/approachThe potentiodynamic polarization tests and critical pitting temperature tests were carried out for estimating pitting resistance. The PPT and pickling were performed as surface treatment. Scanning electron microscope (SEM) and energy dispersive spectrometer were used for characterize the microstructure and elemental distribution. Electron back-scattered diffraction (EBSD) was used to assess the portion of phases and morphology of grains.FindingsThe weld metal exhibits a higher degree of alloying compared to the base metal, and it contains d-phase and sulfur-containing inclusions. Sulfur-containing inclusions serve as initiation sites for pitting, and they diminish the pitting resistance of weld metal. Both PPT and pickling can remove sulfur-containing inclusions, but PPT causes localized dissolution of the weld metal matrix around the inclusions, while pickling does not. Because of the high density of inclusions, certain pits initiated by PPT are significantly deeper, which makes the formation of stable pitting easier. Because of the high density of inclusions, certain pits initiated by the PPT are deeper. This characteristic facilitates the progression of these initial defects into fully developed, stable pits.Originality/valueAnalysis of pitting initiation in shielded metal arc welding FZ with PPT and ex situ SEM tracking observation. Explanation of why the PPT surface treatment is not able to enhance the pitting resistance of stainless steel with a high inclusion density.

Progress and challenges in the design of ITER's polarimetric Thomson scattering diagnostic system.

Polarimetric Thomson scattering (PTS) is a technique that allows for accurate measurements of electron temperature (Te) in very hot plasmas (Te > 10 keV, a condition expected to be regularly achieved in ITER). Under such conditions, the spectral region spanned by the TS spectrum is large and extends to low wavelengths, where the transmission of the collection optics decreases, available detectors are less efficient, and the high level of plasma background light perturbs the measurements. This work presents the recent developments in the design of a PTS system for ITER, along with the challenges posed by the complex machine design. The system performance is assessed for an updated geometry (with respect to previous publication), showing that, with a scattering angle θscat = 167°, the expected signal is strongly reduced. Potential alternatives are analyzed: (1) a system employing a different laser injection position, allowing for a more favorable scattering angle and (2) a recently proposed dual-polarization laser pulse technique. The latter is evaluated for the possible ITER geometry, again showing that a more favorable scattering angle is needed for a robust performance.

An Air-Stable Carbon-Centered Triradical with a Well-Addressable Quartet Ground State.

Organic polyradicals with a high-spin ground state and quantum magnetic properties suitable for spin manipulation are valuable materials for diverse innovative technologies, including quantum devices. However, the typically high reactivity and low stability of conventional polyradicals present a major obstacle to such applications. In this study, a highly stable carbon-centered triradical TR with a quartet ground state and excellent stability (τ1/2 of ∼90 days in air-saturated toluene at room temperature) is achieved, which shows apposite magnetic anisotropy and Zeeman splitting partition with favorable addressability. By virtue of the optimal stability, thorough structural and magnetic characterizations are realized. With X-ray crystallography unambiguously proving the molecular structure, the quartet ground state (ΔED-Q = 0.78 kcal/mol) is confirmed by the SQUID measurements, while the cw- and pulsed EPR techniques offer additional supportive evidence for the high-spin nature. Remarkably, owing to the easily attained magnetic anisotropy, selective excitations between different Zeeman splitting levels are successfully demonstrated with TR in its frozen toluene solution without the requirement for special alignment, which is unprecedented for organic polyradicals. Along with the millisecond spin-lattice relaxation and microsecond coherence time manifested by TR, this triradical is promising for potential coherent spin manipulation applications as a multienergy-level quantum information carrier.

Dynamic Cation Enrichment during Pulsed CO2 Electrolysis and the Cation-Promoted Multicarbon Formation.

Recently, pulsed electrolysis has been demonstrated as an emerging electrochemical technique that significantly promotes the performance of various electrocatalysis applications. The ionic nature of aqueous electrolytes implies a likely change in ionic distribution under these alternating potential conditions. However, despite the well-known importance of cations, the impact of pulsed electrolysis on the cation distribution remains unexplored as well as its influences on the performance. Herein, we explore the cation effects on the pulsed electrochemical CO2 reduction (p-CO2RR) using the most widely utilized alkali metal cations, including Li+, Na+, K+, and Cs+. It is discovered that the nature of cations can significantly influence the product ratio of C2+ over C1 (mostly CH4) during p-CO2RR in an order of Li+< Na+< K+< Cs+, much more profoundly than those of static cases. We report direct experimental evidence for the cation enrichment caused by pulsed electrolysis, depending on the radius of the hydrated ions. With further quasi-in situ analysis of the catalyst surface, the cation-promoted Cu dissolution-and-redeposition process was identified; this is found to alter the surface CuxO/Cu ratio during the pulsed process. We demonstrate that both the cation enrichment and the cation-adjusted surface CuxO/Cu composition impact the C2+/C1 ratio through the control of the surface-adsorbed CO population. These results reveal the presence of pulse-induced cation redistribution in emerging pulsed electrolysis techniques and provide a comprehensive understanding of alkali metal cation effects for improving the selectivity of p-CO2RR.

Enhanced Nondestructive Testing Using Pulsed Eddy Current and Electromagnetic Ultrasonic Techniques

Enhanced Nondestructive Testing Using Pulsed Eddy Current and Electromagnetic Ultrasonic Techniques

Synthesized of gallium Nitride/PSi nano thin films using 532 nm wavelength by pulsed laser deposition technique

Synthesized of gallium Nitride/PSi nano thin films using 532 nm wavelength by pulsed laser deposition technique

Tunable charge transport properties in non-stoichiometric SrIrO3 thin films

Delving into the intricate interplay between spin-orbit coupling and Coulomb correlations in strongly correlated oxides, particularly perovskite compounds, has unveiled a rich landscape of exotic phenomena ranging from unconventional superconductivity to the emergence of topological phases. In this study, we have employed pulsed laser deposition technique to grow SrIrO3 (SIO) thin films on SrTiO3 substrates, systematically varying the oxygen content during the post-deposition annealing. X-ray photoelectron spectroscopy (XPS) provided insights into the stoichiometry and spin-orbit splitting energy of Iridium within the SIO film, while high-resolution x-ray studies meticulously examined the structural integrity of the thin films. Remarkably, our findings indicate a decrease in the metallicity of SIO thin films with reduced annealing O2 partial pressure. Furthermore, we carried out magneto-transport studies on the SIO thin films, the results revealed intriguing insights into spin transport as a function of oxygen content. The tunability of the electronic band structure of SIO films with varying oxygen vacancy is correlated with the density functional theory calculations. Our findings elucidate the intricate mechanisms dictating spin transport properties in SIO thin films, offering invaluable guidance for the design and optimization of spintronic devices based on complex oxide materials. Notably, the ability to tune bandwidth by varying post-annealing oxygen partial pressure in iridate-based spintronic materials holds significant promise for advancing technological applications in the spintronics domain.

Surface pre-treatment of aluminum alloy for mechanical improvement of adhesive bonding by maple-assisted pulsed laser evaporation technique.

Adhesive joints are widely used for structural bonding in various industrial sectors. The performance of bonded joints is commonly attributed to the cleanliness of the substrate and the pre-treatment of the surfaces to be bonded. In this study, the Matrix Assisted Pulsed Laser Evaporation (MAPLE) deposition technique was used for surface modification of aluminum (Al) plates by the deposition of poly(propylene glycol) bis(2-aminopropyl ether) (PPG-NH2) of different number average molecular weights (Mn) of 400 g mol-1, 2000 g mol-1, and 4000 g mol-1, respectively. Fourier-transformed infrared spectroscopy (FT-IR) analysis indicated the characteristic peaks for the deposited layers of PPG-NH2 of different molecular weights in all cases while scanning electron microscopy (SEM) revealed continuous layers on the surface of Al plates. In order to demonstrate alterations in the wettability of Al substrates, a crucial aspect in surface treatment and adhesive bonding, measurements of contact angles, surface free energies (SFE), and adhesion work (W a) were conducted. The tensile strength measurements were performed using the lap-joint test after applying the commercial silyl-based polymer adhesive Bison Max Repair Extreme Adhesive®. It was evidenced that at higher values of the SFE and W a, the tensile strength was almost 3 times higher for PPG-NH2 with Mn = 4000 g mol-1 compared with the untreated Al sample. This study provides valuable insights into the successful application of the MAPLE technique as a pre-treatment method for reinforcing adhesive bonding of Al plates, which can lead to improved mechanical performance in various industrial applications.

Magnetic resonance imaging of the cerebellopontine angle: comparison between constructive interference steady-state and small field-of-view technique turbo spin echo sequences.

The aim of this work was to optimize athree-dimensional (3D) turbo-spin-echo (TSE) sequence using asmall field-of-view (FOV) technique for the study of the cerebellopontine angle and to compare it with aconstructive interference steady-state (CISS) sequence. A total of 30consecutive patients underwent magnetic resonance imaging with a3Tesla (T) scanner, including 3D CISS and the optimized 3D small FOV technique turbo spin echo (3D SFT-TSE) T2-weightedsequences for the study of the cerebellopontine angle. The 3D SFT-TSE sequence was optimized after three different steps, and aquantitative evaluation of the signal-to-noise ratio (SNR) was obtained according to the National Electrical Manufacturers Association (NEMA) method. Three neuroradiologists made ablind comparative qualitative evaluation of the images between the 3D CISS and the 3D SFT-TSE obtained after the third optimization step, based on spatial resolution, contrast resolution, and presence of artifacts and noise. The calculation of SNR using the NEMA method confirmed the superiority of the third optimization step over the others. For both spatial and contrast resolution, the optimized SFT-TSE was considered better (p < 0.001) than the CISS, while image artifacts and noise were considered worse in the CISS sequence (p < 0.001). Intraobserver analysis showed that all neuroradiologists preferred the 3D SFT-TSE sequence in terms of both spatial resolution and contrast resolution and found more noise and artifact disruption in the CISS sequence. The use of the 2D radiofrequency pulse technique with a3D SFT-TSE T2 sequence was significantly more efficient than the 3D CISS sequence for the study of the cerebellopontine angle and inner ear structures.

Impact of oxygen vacancy on luminescence properties of dysprosium-doped zinc oxide thin films

Pristine and dysprosium-doped ZnO thin films, highly c-axis oriented, were grown on a c-Al2O3 substrate using the pulsed laser deposition technique. During the deposition process, the growth was impacted by changes in the oxygen partial pressure. The structural, optical, and compositional properties of the pristine and dysprosium-doped ZnO thin films were systematically characterized using various state-of-the-art experimental techniques. The crystallinity associated with these films was observed to be highly dependent on the oxygen partial pressure maintained during the growth process. An average optical transparency of more than ∼90% in the visible spectral range (i.e., 400–800 nm) was observed for all specimens. For doped specimens, expected intra-4fn emissions of (dysprosium) Dy3+ ions that emanated from the 4F9/2 energy state were observed in room-temperature photoluminescence spectra under direct excitation. The Jacobian-transformed wavelength-to-energy plot for Dy-doped ZnO thin films in the UV-Visible region revealed intriguing findings. Specifically, it depicted a prominent peak at 2.82 eV, indicative of the energy state of Dy3+ ions, alongside intense band-edge emission and various defect-related emissions. The intensity of these transitions was observed to depend on the oxygen partial pressure kept during deposition. An x-ray photoelectron spectroscopy analysis of the doped specimen confirmed the +3 oxidation state of dysprosium into the ZnO matrix. These results provide a promising approach for controlling the doping and growth strategy of Dy-doped ZnO thin films, thereby opening up a wide range of applications and enhancement for next-generation optoelectronic devices.

Frequency tunable mid-infrared split ring resonators on a phase change material

Meta-surfaces arrays are 2D meta-materials with a periodicity below the diffraction limit that permits to obtain homogeneous layers of resonant effective refractive index. In this work we present an analytical model that describes the electromagnetic behavior of meta-surfaces constituted by split-ring resonators (SRR). SRR resonance frequency can be adjusted by choosing their geometric parameters and the materials they are made of. Their deposition on a phase change material enables an optical modulation of resonance peak during the phase transition. We demonstrate a mid-infrared tunable SRR meta-surface using Vanadium dioxide (VO2) as phase change material deposited on III-V semiconductors by low temperature pulsed laser ablation technique. The presented measurements exhibit a maximum of 100 cm−1 resonance shift. This result is very promising for the conception of monolithic, robust, compact, frequency tunable III-V based devices in the mid-infrared.

Biological and Physicochemical Analysis of Sr-Doped Hydroxyapatite/Chitosan Composite Layers.

In this work results are presented on the evaluation of HAp, HApSr, HAp_CS, and HApSr_CS layers deposited on Ti substrates regarding L929 cell viability and cytotoxicity as well as antimicrobial activity against Staphylococcus aureus, in connection with their physicochemical properties. The HAp and HApSr layers generated by radio-frequency magnetron sputtering technique were further covered with chitosan by a matrix-assisted pulsed laser evaporation technique. During the plasma depositions, the Ti substrates were heated externally by a home-made oven above 100 °C. The HApSr_CS layers generated on the unpolished Ti substrates at 100 °C and 400 °C showed the highest biocompatibility properties and antimicrobial activity against Staphylococcus aureus. The morphology of the layer surfaces, revealed by scanning electron microscopy, is dependent on substrate temperature and substrate surface roughness. The optically polished surfaces of Ti substrates revealed grain-like and microchannel structure morphologies of the layers deposited at 25 °C substrate temperature and 400 °C, respectively. Chitosan has no major influence on HAp and HApSr layer surface morphologies. X-ray photoelectron spectroscopy indicated the presence of Ca 2p3/2 peak characteristic of the HAp structure even in the case of the HApSr_CS samples generated at a 400 °C substrate temperature. Fourier transform infrared spectroscopy investigations showed shifts in the wavenumber positions of the P-O absorption bands as a function of Sr or chitosan presence in the HAp layers generated at 25, 100, and 400 °C substrate temperatures.

Nonlinear Multimodal Interference as Ultrafast Photonic Device for Dual-Wavelength Domain-Wall Dark Pulse Generation

Abstract In comparison to bright pulses, better stability that is not susceptible to loss makes dark pulses accessible for applications in such fields as signal processing, optics sensing, and quantum communication. Here we investigate the dual-wavelength domain-wall dark pulse generation in a graded-index multimode fiber (GIMF) based anomalous dispersion single-mode fiber (SMF) laser. By optimizing intra-cavity nonlinearity and pulse polarization, the mode-locked states can evolve each other between bright pulses, dark pulses, and bright-dark pulse pairs. The evolution mechanism among them may be relevant to the coherent mode superposition, spectral filtering, and mode selection in SMF-GIMF-SMF hybrid-fiber modulation devices that affect the pulse formation and evolution in temporal, frequency, and space domains. These results provide a valuable reference for promoting further development of nonlinear optics and ultrafast optics, in which ultrafast photonic devices, with low cost, simple manufacture as well as wide adaptability, as novel pulsed generation technique, play a vital role.

The influence of surfactant type on the formation of zinc oxide nanoparticles via liquid phase pulsed laser ablation technique

The influence of surfactant type on the formation of zinc oxide nanoparticles via liquid phase pulsed laser ablation technique

Room-temperature tuning of mid-infrared optical phonons and plasmons in W-doped VO2 thin films

The development of mid-infrared nanophotonics relies on the availability of new materials combining metal- and insulator-like optical features. We systematically studied the phase transition of thermochromic vanadium dioxide (VO2) using substitutional tungsten doping at room temperature. Our results reveal that vanadium dioxide thin films, doped with tungsten and grown via pulsed laser deposition techniques on sapphire substrates, can be precisely engineered to exhibit tailored infrared phonon and plasmon polaritonic responses. By controlling the extent of tungsten concentration, starting from VO2-WO3 cold-pressed powder targets, we demonstrate the ability to continuously adjust both the amplitude and frequency of optical phonon resonances. Furthermore, we observe tunable free-electron response due to varying tungsten concentrations. The adopted fabrication technique makes it possible to create multilayer structures by alternating layers with different concentrations of tungsten. Our results pave the way for the development of tunable mid-infrared metamaterial devices operating at room-temperature.

Deep Ultraviolet Optical Anisotropy of β-Gallium Oxide Thin Films.

β-Crystalline phase gallium oxide (β-Ga2O3) is an ultrawide bandgap material with prospective applications in electronics and deep ultraviolet (DUV) optoelectronics and optics. The monoclinic crystal structure of β-Ga2O3 results in optical anisotropy to incident light with different polarization states. This attribute can lead to different optical applications in the DUV. In this article, we investigated the optical properties of β-Ga2O3 thin films grown by pulsed laser deposition technique on sapphire substrates with different crystallographic orientations. Marked in-plane polarization anisotropy, determined by reflectance and Raman spectroscopy, was observed for β-Ga2O3 films deposited on an r-cut sapphire substrate. In contrast, isotropic optical properties were observed in β-Ga2O3 films deposited on a c-cut sapphire substrate.

Long-term evolution of Ti-Cu amorphous film: Agglomeration and crystallization behaviors of Cu

Sometimes the films deposited by magnetron sputtering are in a metastable state. The films tend to transition to the equilibrium phase, which is crucial for the stability of the microstructure and properties of the films in practical applications. In this study, Ti-Cu films were deposited using a high-power pulsed magnetron sputtering technique, and the evolution of the microstructure of the film under natural aging and thermal aging conditions was systematically investigated. The results showed that the as-deposited Ti-Cu film was amorphous, and as the aging time increased, particles comprising Cu agglomerates and crystalline phases were gradually formed in the film. During aging treatments, Cu agglomerates at the Ti-Cu film led to strong scattering and absorption of the incident light, resulting in reflectance losses. Cu agglomerates at the film was more intense under thermal aging conditions than under natural aging conditions, which was attributed to the fact that the provision of additional temperature could accelerate the diffusion of the smaller Cu atoms in the Ti-Cu amorphous film. Exploring the long-term evolution of the Ti-Cu film structure will provide theoretical guidance for the stability of films in practical applications.

Laser-induced growth of metal oxide films on quartz tubes for photocatalytic water treatments

A solid-state pulsed laser technique was developed to in situ grow arbitrary immobilized catalysts (Fe3O4, CeO2, WO3 etc.) on the inner surface of quartz tube with robust adhering strength. In a case study, anatase/rutile hetero-phase TiO2 film was deposited to serve as immobilized photocatalysts for the effective removal of antibiotics from aqueous environment. The X-ray absorption spectroscopy, low temperature electron paramagnetic resonance and the density functional theory simulation directly confirm a defect-assisted type-II band alignment was established to facilitate the charge transfer at the hereto-interphase. In addition, the oxygen vacancy enriched anatase phase with greater binding energy towards the dissolved oxygen facilitated the O2– generation. Meanwhile, the rutile phase enriched with Ti3+ could effectively activate the antibiotics to promote the direct h+ mediated oxidation. Such integration of unique atomic vacancies prevent defects from becoming electron-hole recombination centers and consequently extend the lifetime of the photoexcited charge carrier. The degradation mechanism of oxytetracycline was thoroughly examined by ultra-high resolution electrospray time-of-flight mass spectrometry and Fukui function, while the ecological structure–activity relationships program assessed the toxicity of contaminant to the environment. Milewhile, a continuous water treatment apparatus employing the catalytic tubes as reactors was established and demonstrated a ∼ 95 % OTC degradation under the natural sunlight adopting river water as the background. The experimental studies also claimed that ∼ 90 % of the initial activity could be retained after 100 cycles reuse, which permits their great potential for the applicational scenarios.

Physical Investigations of GaN/Porous Silicon at Different Laser Wavelengths

In this study, we prepared PSi using the laser-assisted electrochemical etching method and deposited Gallium nitride (GaN) on the PSi substrate using the pulsed laser technique at different pulsed laser wavelengths (1064, 532, and 355 nm). We investigated the optical, structural, topographical, and morphological properties of Gallium Nitride on the substrate PSi by various pulsed laser wavelengths. The X-Ray Diffraction (XRD) analysis revealed that gallium nitride on PSi was polycrystalline and hexagonal, cubic structural at 532 nm, with a high peak intensity and crystallite size at 2θ=36.96°and 57.80 related to (101) and (110) planes, respectively, while the c-GaN phase is observed at 2θ = 25.43 degrees and is reflected from the (200) plane. PL shows two emission peaks were observed for the GaN film (430,345,413 nm) and the PSi substrate (867,891,876 nm), and the energy gap increased as the wavelength decreased. The field emission scanning electron microscopy (FESEM) pictures revealed that the synthetic sample had an average size of 24.45, 23.91, and 21.30 nm, and the nanoparticles appeared spherical and similar to cauliflower. The atomic force microscopy (AFM) results showed that the average roughness was 7.62, 10.64, and 13.62 nm, respectively, and it was observed the root mean square increased as a result of the uniform distribution of high-quality crystals and the excellent quality of the crystal structure. The UV-Visible (UV) results showed that the transmission decreased with a decrease in wavelength, and the absorption was inversely proportional to the transmission.