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Results for “Raman process”

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 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Imprinting a Three-Dimensional Skyrmion in a Bose–Einstein Condensate Via a Raman Process

We describe an experimental protocol for the creation of a three-dimensional topological defect, a skyrmion, in a pseudo-spin-1/2 Bose–Einstein condensate (BEC) confined in a spin-independent harmonic trap. We show that one can imprint the skyrmion on the BEC within a few tens of microseconds using a Raman process with the structured laser fields. We numerically solved the mean-field Gross– Pitaevskii equation to examine our imprinting scheme and found that all parameters we use are experimentally feasible.

3D Skyrmion↗
DOE OSTI2021

Detection of photon statistics and multimode field correlations by Raman processes

Glauber’s g (2) -function provides a common measure of quantum field statistics through two-photon coincidence counting in Hanbury Brown–Twiss measurements. Here, we propose to use nonlinear optical signals as a tool for the characterization of quantum light. In particular, we show that Raman measurements provide an alternative direct probe for a different component of the four-point correlation function underlying the g (2) -function. We illustrate this capacity for a specific quantum state obtained from a frequency conversion process. Our work points out how the analysis of controlled optical nonlinear processes can provide an alternative window toward the analysis of quantum light sources.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Enabling Microscale Processing: Combined Raman and Absorbance Spectroscopy for Microfluidic On-Line Monitoring

Microfluidics have many potential applications including characterization of chemical processes on a reduced scale, spanning the study of reaction kinetics using on-chip liquid–liquid extractions, sample pretreatment to simplify off-chip analysis, and for portable spectroscopic analyses. The use of in situ characterization of process streams from laboratory-scale and microscale experiments on the same chemical system can provide comprehensive understanding and in-depth analysis of any similarities or differences between process conditions at different scales. A well-characterized extraction of Nd(NO 3 ) 3 from an aqueous phase of varying NO 3– (aq) concentration with tributyl phosphate (TBP) in dodecane was the focus of this microscale study and was compared to an earlier laboratory-scale study utilizing counter current extraction equipment. Here, we verify that this same extraction process can be followed on the microscale using spectroscopic methods adapted for microfluidic measurement. Concentration of Nd (based on UV–vis) and nitrate (based on Raman) was chemometrically measured during the flow experiment, and resulting data were used to determine the distribution ratio for Nd. Extraction distributions measured on the microscale were compared favorably with those determined on the laboratory scale in the earlier study. Both micro-Raman and micro-UV–vis spectroscopy can be used to determine fundamental parameters with significantly reduced sample size as compared to traditional laboratory-scale approaches. This leads naturally to time, cost, and waste reductions.

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

Reconsidering spin-phonon relaxation in magnetic molecules

Because of the larger intra-molecular distortion, optical phonons usually have stronger spin-phonon coupling than acoustic phonons in molecular magnets. This property may pose problems to the theory of spin relaxation in ordinary paramagnetic materials, which have served as the basis for the understanding of spin dynamics in molecular magnets for decades. In this review, we explain why the Raman processes driven by optical phonons can play a dominant role at low temperature and provide unconventional dependence between relaxation time and temperature. Especially, we emphasize that the sub-barrier relaxation and anomalously low Raman exponents are two common signatures of the dominance. Here, we also present the algorithm and implementation for calculating spin-phonon relaxation in molecular solids with density functional theory codes.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Real-Time Automated pH Control within Batch Processes Relying on Raman pH Measurement

Nuclear fission is an energy source that can provide consistent power with very low associated carbon emissions. However, management of the used nuclear fuel is an important aspect of the application of nuclear power. Recycling of useful components from used fuel is an attractive option, but this involves chemical processing of the fuel. Possible chemical separation technologies that might be used in this regard are sensitive to solution pH. Raman spectroscopy is a promising technique for monitoring the pH of solutions in real time. Classical pH probes are too fragile to be used in the harsh environments encountered in nuclear fuel processing. Raman probes are robust and can withstand these harsh environments to track pH. Coupled with chemometric analysis, the demonstration of the use of Raman spectroscopy to track and predict the pH in carboxylate-buffered systems is made possible. Utilizing this spectroscopy in conjunction with Programmable Logic Controllers mimics industrial control systems used in many modern industrial settings. This showcases a pragmatic approach toward leveraging Raman spectroscopy and chemometric model outputs as inputs for a real-time control system. The model to predict pH created by chemometrics proved to be successful in tracking pH. The optimal pH for TALSPEAK extraction of lanthanides and actinides from aqueous solution is known to proceed in a narrow pH range of around pH = 2.8 ± 0.1. This study uses Raman optical monitoring and automated control to return and maintain solution pH within this range after acid or base perturbations move the solution pH well outside this region. Root-mean-square errors show that pH changes measured using Raman spectroscopy on the batch process solution are reliably measured and used to automatically correct and maintain solution pH. Measurement of solution pH tracks favorably with electrochemical pH probe comparison measurements. As a result, the ability to showcase Raman spectroscopy paired with chemometrics analysis acts as a durable, better alternative data source compared to traditional pH probes to optimize the separation efficiency in the used nuclear fuel processing.

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

Gate-tunable modulation of the optical properties of multilayer graphene by the reversible intercalation of ionic liquid anions

We demonstrate a substantial modulation of the optical properties of multilayer graphene (~100 layers) using a simple device consisting of a multilayer graphene/polymer electrolyte membrane/gold film stack. Applying a voltage of 3–4 V drives the intercalation of anion [TFSI] - [ion liquid diethylmethyl(2-methoxyethyl)ammonium bis(trifluoromethylsulfonyl)imide [DEME][TFSI]] resulting in the reversible modulation of the properties of this optically dense material. Upon intercalation, we observe an abrupt shift of 35 cm -1 in the G band Raman mode, an abrupt increase in FTIR reflectance over the wavelength range from 1.67 to 5 $μ$m (2000–6000 cm -1 ), and an abrupt increase in luminescent background observed in the Raman spectra of graphene. Furthermore, all of these abrupt changes in the optical properties of this material arise from the intercalation of the TFSI - ion and the associated change in the free carrier density (Δ$n$ = 10 20 cm -3 ). Suppression of the 2D band Raman mode observed around 3 V corresponds to Pauli blocking of the double resonance Raman process and indicates a modulation of the Fermi energy of Δ$E$ F = 1.1 eV.

42 ENGINEERING↗
DOE OSTI2021

Stress- and Time-Dependent Formation of Self-Lubricating In Situ Carbon (SLIC) Films on Catalytically-Active Noble Alloys

Abstract Low shear strength (30 MPa) organic films were grown in situ on Pt 0.9 Au 0.1 surfaces via cyclic sliding contact in dry N 2 with trace concentrations of ambient hydrocarbons. We present a systematic investigation of the stress- and time-dependent film formation. Steady-state friction coefficients were found to be as low as µ ~ 0.015 and inversely proportional to contact pressure, revealing non-Amontonian behavior. Above a Hertzian contact pressure of ~500 MPa, shear strength dropped, indicating an activated process. Raman spectroscopy identified non-uniformity in areal coverage and relative order with contact pressure. Regions of steady-state low-friction behavior exhibited spectra similar to DLC coatings. Atomic force microscopy was used to study the formation and growth of films at the nanoscale. Stress- and time-dependent measurements suggested a sublinear increase of film volume with time, and a transition from growth to wear at a Hertzian contact pressure of ~1.2 GPa.

Jones, Morgan R.↗
DOE OSTI2021

Few-layer tin sulfide (SnS): Controlled synthesis, thickness dependent vibrational properties, and ferroelectricity

Group IV monochalcogenides, anisotropic van der Waals crystals (and black phosphorus analogues), are attracting increasing interest due to a number of exceptional properties including anisotropic optoelectronics and multiferroicity predicted and in part realized in the ultrathin limit. Due to their enhanced chemical reactivity, both exfoliation and synthesis of monolayer and few-layer crystals pose challenges not found in other 2D/layered materials, such as the transition metal dichalcogenides. In this work, we show that SnS synthesis on SnS 2 van der Waals substrates can address these challenges and consistently produces few-layer flakes, a capability that is explained via analysis of real-time microscopy of the growth process. Raman spectroscopy combined with efficient computations of the Raman-active modes across an extended thickness range enables a comprehensive understanding of the evolution of the vibrational properties of SnS with number of layers. Lateral piezoresponse force microscopy provides unprecedented insight into the stacking-dependent polarization and ferroelectric domain structures in large few-layer SnS flakes. The combined results establish a basis for further fundamental studies and applications of SnS and other group IV monochalcogenides in the few-layer regime.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Strong Electronic and Magnetic Coupling in M 4 (M = Ni, Cu) Clusters via Direct Orbital Interactions between Low-Coordinate Metal Centers

In this report we present an extensive study of tetranuclear transition-metal cluster compounds M 4 (NP t Bu 3 ) 4 and [M 4 (NP t Bu 3 ) 4 ][B(C 6 F 5 ) 4 ] (M = Ni, Cu; t Bu = tert -butyl), which feature low-coordinate metal centers and direct metal-metal orbital overlap. X-ray diffraction, electrochemical, magnetic, spectroscopic, and computational analysis elucidate the nature of the bonding interactions in these clusters and the impact of these interactions on the electronic and magnetic properties. Direct orbital overlap results in strongly coupled, large-spin ground states in the [Ni 4 (NP t Bu 3 ) 4 ] +/0 clusters and fully delocalized, spin-correlated electrons. Correlated electronic structure calculations confirm the presence of ferromagnetic ground states that arise from direct exchange between magnetic orbitals, and, in the case of the neutral cluster, itinerant electron magnetism similar to that in metallic ferromagnets. The cationic nickel cluster also possesses large magnetic anisotropy exemplified by a large, positive axial zero-field splitting parameter of D = +7.95 or +9.2 cm -1 , as determined by magnetometry or electron paramagnetic resonance spectroscopy, respectively. The [Ni 4 (NP t Bu 3 ) 4 ] + cluster is also the first molecule with easy-plane magnetic anisotropy to exhibit zero-field slow magnetic relaxation, and under a small applied field, it exhibits relaxation exclusively through an Orbach mechanism with a spin relaxation barrier of 16 cm -1 . The S = 1 / 2 complex [Cu 4 (NP t Bu 3 ) 4 ] + exhibits slow magnetic relaxation via a Raman process on the millisecond time scale, supporting the presence of slow relaxation via an Orbach process in the nickel analogue. Overall, this work highlights the unique electronic and magnetic properties that can be realized in metal clusters featuring direct metal-metal orbital interactions between low-coordinate metal centers.

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

Data-driven design of molecular nanomagnets

Three decades of research in molecular nanomagnets have raised their magnetic memories from liquid helium to liquid nitrogen temperature thanks to a wise choice of the magnetic ion and coordination environment. Still, serendipity and chemical intuition played a main role. In order to establish a powerful framework for statistically driven chemical design, here we collected chemical and physical data for lanthanide-based nanomagnets, catalogued over 1400 published experiments, developed an interactive dashboard (SIMDAVIS) to visualise the dataset, and applied inferential statistical analysis. Our analysis shows that the Arrhenius energy barrier correlates unexpectedly well with the magnetic memory. Furthermore, as both Orbach and Raman processes can be affected by vibronic coupling, chemical design of the coordination scheme may be used to reduce the relaxation rates. Indeed, only bis-phthalocyaninato sandwiches and metallocenes, with rigid ligands, consistently present magnetic memory up to high temperature. Analysing magnetostructural correlations, we offer promising strategies for improvement, in particular for the preparation of pentagonal bipyramids, where even softer complexes are protected against molecular vibrations.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2022

Static and dynamic magnetic properties of the spiin-$\frac{5}{2}$triangle lattice antiferromagnet Na 3 Fe(PO 4 ) 2 studied by 31 P NMR

We report 31 P nuclear magnetic resonance (NMR) measurements have been carried out to investigate the magnetic properties and spin dynamics of Fe 3+ (S = 5/2) spins in the two-dimensional triangular lattice (TL) compound Na 3 Fe(PO 4 ) 2 . The temperature (T) dependence of nuclear spin-lattice relaxation rates (1/T 1 ) shows a clear peak around Néel temperature, T N = 10.9 K, corresponding to an antiferromagnetic (AFM) transition. From the temperature dependence of NMR shift (K) above T N , an exchange coupling between Fe 3+ spins was estimated to be J/k B ≃ 1.9 K using the spin-5/2 Heisenberg isotropic-TL model. The temperature dependence of 1/T 1 T divided by the magnetic susceptibility (χ), 1/T 1 T χ , above T N proves the AFM nature of spin fluctuations below ~50 K in the paramagnetic state. In the magnetically ordered state below T N , the characteristic rectangular shape of the NMR spectra is observed, indicative of a commensurate AFM state in its ground state. The strong temperature dependence of 1/T 1 in the AFM state is well explained by the two-magnon (Raman) process of the spin waves in a 3D antiferromagnet with a spin-anisotropy energy gap of 5.7 K. The temperature dependence of sublattice magnetization is also well reproduced by the spin waves. Those results indicate that the magnetically ordered state of Na 3 Fe(PO 4 ) 2 is a conventional 3D AFM state, and no obvious spin frustration effects were detected in its ground state

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Anomalous phonon-mode dependence in polarized Raman spectroscopy of the topological Weyl semimetal TaP

Topological Weyl semimetals (WSMs) have attracted widespread interest due to the chiral Weyl fermions and surface Fermi arcs that enable unique optical and transport phenomena. In this work, we present angle-resolved Raman spectroscopy of TaP, a prototypical noncentrosymmetric WSM, for five excitation wavelengths ranging from 364 to 785 nm. The Raman-active modes, $A_1$, $B^1_1$, and $B^2_1$ modes, exhibit two main unique features beyond the conventional Raman theory. First, the relative intensities of Raman-active modes change as a function of the excitation wavelength. Second, angle-resolved polarized Raman spectra show systematic deviation from the Raman tensor theory. In particular, the $B^1_1$ mode is absent for 633-nm excitation, whereas the $B^2_1$ mode shows an unusual twofold symmetry instead of a fourfold symmetry for 488-, 532-, and 633-nm excitations. Finally, these unconventional phenomena are attributed to the interference effect in the Raman process owing to the existence of multiple carrier pockets with almost the same energy but different symmetries.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

Multidimensional coherent spectroscopy of light-driven states and their collective modes in multiband superconductors

We present a comprehensive theory of light-controlled multiband superconductivity, and apply it to predict distinctive signatures of light-driven superconducting (SC) states in terahertz multidimensional coherent spectroscopy (THz-MDCS) experiments. We first derive gauge-invariant Maxwell-Bloch equations for multiband BCS superconductors with spatial fluctuations. We consider driving electromagnetic fields determined self-consistently by Maxwell's equations. By calculating the THz-MDCS spectra measured experimentally in the clean SC limit, we identify unique signatures of finite-momentum Cooper-pairing states that live longer than the laser pulse. They are controlled by a pair of THz laser pulses with well-defined relative phase (pulse pair). The pseudospin oscillators that describe the properties of these SC states are parametrically driven by both finite-momentum Cooper pairing and by time oscillations of the order-parameter relative phase. We show that such strong parametric driving leads to drastic changes in the THz-MDCS spectral shape from the predictions of third-order nonlinear susceptibility calculations. These spectral changes strongly depend on the interband-to-intraband interaction ratio and on the collective modes of the light-driven state. For negligible interband interaction, the spectra show a transition with increasing field, from traditional pump-probe, four-wave-mixing, and third-harmonic generation peaks determined by the laser frequency to sidebands determined by the excitations of the driven system. These sidebands emerge from difference-frequency Raman processes in the nonequilibrium SC state. For interband couplings weaker than the intraband pairing, we show that the Leggett phase collective mode leads to harmonic sidebands around the traditional pump-probe peaks. Additional Higgs collective mode peaks result from light-induced inversion-symmetry breaking in a thin-film geometry. For strong interband coupling, we find a transition from a nonequilibrium finite Cooper-pair momentum state characterized by hybrid-Higgs amplitude mode peaks in THz-MDCS spectra to a driven state identified experimentally by the emergence of Floquet-type sidebands at bi-Higgs frequencies. Those dominant bi-Higgs-frequency satellites are manifestations of a new order parameter relative phase collective mode that characterizes the nonequilibrium SC state. The predicted interaction- and field-dependent transitions in the spectral profile allow us to propose THz-MDCS experiments for quantum tomography of light-driven superconductivity.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2024

Magnetic properties of the double trillium lattice antiferromagnet KBaCr 2 ⁢(PO 4 ) 3

Trillium lattices formed by corner-shared triangular units are the platform for magnetic frustration in three dimensions. Herein, we report structural and magnetic properties of the Cr-based (S = 3/2) double trillium lattice material KBaCr 2 ⁢(PO 4 ) 3 studied by x-ray diffraction, dc and ac magnetization, heat capacity, thermal conductivity, and 31 P nuclear magnetic resonance (NMR) measurements complemented by density-functional band-structure calculations. Magnetization, heat capacity, and 31 P NMR measurements reveal the magnetic transition at T N⁢1 ≃ 12.5 K in zero field followed by another transition (T N⁢2 ) at low temperatures in weak applied fields. The 31 P spin-lattice relaxation rate in the ordered state follows the T 3 behavior indicative of the two-magnon Raman process. Finally, the spin lattice of KBaCr 2 ⁢(PO 4 ) 3 comprises two crystallographically nonequivalent ferromagnetic sublattices that are coupled antiferromagnetically, thus eliminating frustration in this trillium network and leading to weak ferromagnetism in the vicinity of T N⁢1 .

36 MATERIALS SCIENCE↗
DOE OSTI2023

Enhancement of chiral edge currents in ($d$+1)-dimensional atomic Mott-band hybrid insulators

We consider the effect of a local interatomic repulsion on synthetic heterostructures where a discrete synthetic dimension is created by Raman processes on top of SU(N) S U ( N ) -symmetric two-dimensional lattice systems. At a filling of one fermion per site, increasing the interaction strength, the system is driven towards a Mott state which is adiabatically connected to a band insulator. The chiral currents associated with the synthetic magnetic field increase all the way to the Mott transition, where they reach the maximum value, and they remain finite in the whole insulating state. The transition towards the Mott-band insulator is associated with the opening of a gap within the low-energy quasiparticle peak, while a mean-field picture is recovered deep in the insulating state.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2023

On-line Measurement of Hydrogen Gas using Raman Spectroscopy for Process Gas Systems

Advanced reprocessing schemes such as the Zircex process are important for continued development of the nuclear fuel cycle. The hydrochlorination reaction of the Zircex process flow sheet for metallic fuels has a known off-gas stream of H 2 (g) and HCl. The flow sheet can be simplified through HCl recycling, which requires detection and quantification of any residual H 2 (g) for safety and purity. In this work, commercially available Raman spectroscopy was applied for low-level, on-line detection of H 2 (g) in process gas streams, and parameters were adjusted to optimize the H 2 (g) Raman signal. Increasing the number of scans and exposure time in the spectrometer increased the signal-to-noise ratio of the H 2 (g) Raman signal, while the gas flow rate was optimized at 2.3 L/min. The limit of detection for H 2 (g) was estimated to be 2,100 ppm H 2 (g) in an N 2 (g) background. This scoping study for the application of Raman spectroscopy for on-line measurements of H 2 (g) shows that H 2 (g) can be detected at low levels (approximately 5% of the lower explosive limit (LEL)) in flowing gas streams.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2022

Leveraging Multiple Raman Excitation Wavelength Systems for Process Monitoring of Nuclear Waste Streams

Processing nuclear waste from sites such as Hanford is a significant environmental cleanup need while being a significant logistical challenge. Integration of process monitoring tools, that can provide in situ and real-time feedback about the process, can significantly alleviate needs to collect grab samples for process control and product characterization. Raman spectroscopy paired with chemometric analysis is one process monitoring tool that can provide chemical composition information on a large number of chemical targets in nuclear waste streams. However, methods to improve limits of detection as well as drop uncertainty in quantification are needed. Optimizing instrument specifications can achieve this, here this is demonstrated by comparing limits of detection for key analytes when using Raman systems with 671 nm, 532 nm, and 405 nm excitation wavelengths. Generally, limits of detection decease (allowing the measurement of lower salt concentrations) with decreasing wavelength. Similarly, data collection times and averaging were optimized. Finally, multiple chemometric modeling approaches were leveraged, including multiblock methods that combined data from all three Raman systems to simultaneously quantify targets with improved sensitivity.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2021

Quantification of Raman-Interfering Polyoxoanions for Process Analysis: Comparison of Different Chemometric Models and a Demonstration on Real Hanford Waste

The Hanford site represents a complicated environmental remediation challenge, remaining from the production of nuclear weapons. Over 100 million gallons of liquid radioactive waste of unknown composition will be chemically processed and vitrified, but the varying chemical composition and highly radioactive nature of the waste preclude the implementation of more developed, offline technologies to determine the composition. The only practical approach to waste treatment will require the significant utilization of real-time, chemometric modeling approaches. Although chemometric approaches have been applied to the analysis of Hanford waste, the models developed were highly tank-specialized, and limited discussion was provided on how models fared with interfering signals. As the tank waste is largely composed of oxoanions, which tend to have interfering Raman spectra, the general question was posed as to what chemometric approach is best suited to accurately quantify analytes in the presence of interfering signals. This was carried out by examining the ability of classical least square (CLS), principal component regression (PCR), partial least square (PLS), and locally weighted regression (LWR) to quantify NO 3 – and CO 3 2– using their bands around 1050 cm –1 . Finally, for all samples, the PLS-based model was found to be the most efficient approach from a model building and application perspective.

54 ENVIRONMENTAL SCIENCES↗