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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 811 records · Page 45
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Phonon-assisted nonlinear optical processes in ultrashort-pulse pumped optical parametric amplifiers

Optically active phonon modes in ferroelectrics such as potassium titanyl phosphate (KTP) and potassium titanyl arsenate (KTA) in the ~7–20 THz range play an important role in applications of these materials in Raman lasing and terahertz wave generation. Previous studies with picosecond pulse excitation demonstrated that the interaction of pump pulses with phonons can lead to efficient stimulated Raman scattering (SRS) accompanying optical parametric oscillation or amplification processes (OPO/OPA), and to efficient polariton-phonon scattering. In this work, we investigate the behavior of infrared OPAs employing KTP or KTA crystals when pumped with ~800-nm ultrashort pulses of duration comparable to the oscillation period of the optical phonons. We demonstrate that under conditions of coherent impulsive Raman excitation of the phonons, when the effective χ (2) nonlinearity cannot be considered instantaneous, the parametrically amplified waves (most notably, signal) undergo significant spectral modulations leading to an overall redshift of the OPA output. Furthermore, the pump intensity dependence of the redshifted OPA output, the temporal evolution of the parametric gain, as well as the pump spectral modulations suggest the presence of coupling between the nonlinear optical polarizations P NL of the impulsively excited phonons and those of parametrically amplified waves.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Two-photon-absorption line strengths for nitric oxide: Comparison of theory and sub-Doppler, laser-induced fluorescence measurements

In this paper, we discuss the results of high-resolution, sub-Doppler two-photon-absorption laser-induced fluorescence (TPALIF) spectroscopy of nitric oxide at low pressure and room temperature. The measurements were performed using the single-longitudinal mode output of a diode-laser-seeded optical parametric generator (OPG) system with a measured frequency bandwidth of 220 MHz. The measurements were performed using a counter-propagating pump beam geometry, resulting in sub-Doppler TPALIF spectra of NO for various rotational transitions in the (0,0) vibrational band of the A 2 Σ + - X 2 Π electronic transition. The experimental results are compared with the results of a perturbative treatment of the rotational line strengths for the 20 different rotational branches of the X 2 Π(v" = 0) → A 2 Σ + (v' = 0) two-photon absorption band. In the derivation of the expressions for the two-photon transition absorption strength, the closure relation is used for rotational states in the intermediate levels of the two-photon transition in analogy with the Placzek treatment of Raman transitions. The theoretical treatment of the effect of angular momentum coupling on the two-photon rotational line strengths features the use of irreducible spherical tensors and 3j symbols. The final results are expressed in terms of the Hund’s case (a) coupling coefficients aJ and bJ for the X 2 Π(v" = 0) rotational level wavefunctions, which are intermediate between Hund’s case (a) and case (b). Considerable physical insight is provided by this final form of the equations for the rotational line strengths. Corrections to the two-photon absorption rotational line strength for higher order effects such as centrifugal stretching can be included in a straightforward fashion in the analysis by incorporating higher order terms in these coupling coefficients a J and b J , although these corrections are essentially negligible for J < 50. The theoretical calculations of relative line intensities are in good agreement both with our experiment and with published experimental results. Furthermore, the calculated line shapes and relative intensities for closely spaced main branch and satellite transitions are in excellent agreement with our experimental measurements

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

A magnetic phase diagram for nanoscale epitaxial BiFeO 3 films

BiFeO 3 thin films have attracted considerable attention by virtue of their potential application in low-energy spintronic and magnonic devices. BiFeO 3 possesses an intricate magnetic structure, characterized by a spin cycloid with period ~62 nm that governs the functional magnonic response, and which can be modulated or even destroyed by strain, magnetic and electric fields, or chemical doping. The literature on (110)-oriented BiFeO 3 films is not explicit in defining the conditions under which this cycloid persists, as its presence depends on synthesis method and thin-film boundary conditions, especially in the sub-100 nm thickness regime. This report aims to end “trial and error” approaches in determining the conditions under which this cycloid and its associated functional magnonic response exist. We show that in specific crystallographic orientations of epitaxial BiFeO 3 , an unexplored strain parameter—the distortion in the ab plane of the monoclinic unit cell—significantly influences the spin structure. Combining Mössbauer spectroscopy and low-energy Raman spectroscopy with first-principles-based effective Hamiltonian calculations, we show that both average strain and this distortion destroy the cycloid. For films grown on (110)-oriented SrTiO 3 substrates, if the BiFeO 3 lattice parameters a and b differ by more than about 1.2%, the cycloid is destabilized, resulting in a pseudocollinear magnetic order ground state. We are thereby able to construct a phase diagram of the spin structure for nanoscale epitaxial BiFeO 3 films, which aims to resolve long-standing literature inconsistencies and provide powerful guidelines for the design of future magnonic and spintronic devices.

36 MATERIALS SCIENCE↗
DOE OSTI2014

The Ba 4d-4f giant dipole resonance in complex Ba/Si compounds

The shape of the Ba 4d–4f giant dipole resonance is studied for Ba atoms embedded inside complex Si networks covering structures consisting of Si nanocages and nanotubes, i.e. the clathrate Ba 8 Si 46 , the complex compound BaSi 6 , and the semiconducting BaSi 2 . Here, non-resonant x-ray Raman scattering is used to investigate confinement effects on the shape of the giant resonance in the vicinity of the Ba NIV, V-edge. The distinct momentum transfer dependence of the spectra is analyzed and discussed. The measurements are compared to calculations of the giant resonance within time-dependent local density approximation in the dipole limit. No modulation of the giant resonance's shape for Ba atoms confined in different local environments was observed, in contrast to the calculations. The absence of such shape modulation for complex Ba/Si compounds is discussed providing important implications for further studies of giant resonance phenomena utilizing both theory and experiment.

Sahle, Ch. J.↗
DOE OSTI2014

Characterization of the cleaning process on a transferred graphene

Intrinsic graphene possesses many outstanding physical and chemical properties, but their full explorations are often hindered by the effects of substrate and/or contamination. The authors employ the ultrahigh vacuum transmission electron microscopy equipped with a residual gas analyzer to in-situ characterize an effective decontamination process on a suspended graphene. Raman spectroscopic spectra further verify the cleanness of the resultant graphene membrane. The authors also present two contrasting growth morphologies of copper nanoparticles obtained on both clean and unclean graphene surfaces and show that the intrinsic growth dynamics can only manifest on the surface without contaminations.

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

Photoluminescence and Raman spectroscopy of wide bandgap semiconductors damaged by deep-UV laser irradiation

The effects of a pulsed, focused, deep-UV (4.66 eV) laser on wide and ultra-wide bandgap semiconductors were investigated with photoluminescence (PL) and Raman spectroscopy. Three semiconductor single crystals were studied: silicon carbide (6H-SiC), gallium nitride (GaN), and gallium oxide (β-Ga 2 O 3 ). Atomic emission lines from neutral Ga or Si were observed during the laser-damage process. For all three semiconductors, PL mapping (3.49 eV laser excitation) of the damaged material revealed visible emission bands in the 2.6–2.8 eV range, attributed to point defects. Raman spectra (2.33 eV excitation) showed a reduction in the Raman peak intensities in the damaged region, along with weak PL bands around 1.9–2.1 eV.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Spin transitions in La{sub 0.7} Ba{sub 0.3}CoO{sub 3} thin films revealed by combining Raman spectroscopy and X-ray diffraction

In cobaltite, the spin states transitions of Co{sup 3+/4+} ions govern the magnetic and electronic conduction properties. These transitions are strain-sensitive and can be varied using external parameters, including temperature, hydrostatic pressure, or chemical stresses through ionic substitutions. In this work, using temperature dependent Raman spectroscopy and X-ray diffraction, the epitaxial strain effects on both structural and vibrational properties of La{sub 0.7} Ba{sub 0.3} CoO{sub 3} (LBCO) cobaltite thin films are investigated. All Raman active phonon modes as well as the structure are found to be strongly affected. Both Raman modes and lattice parameter evolutions show temperature changes correlated with magnetic and electronic transitions properties. Combining Raman spectroscopy and X-ray diffraction appears as a powerful approach to probe the spin transition in thin film cobaltite. Our results provide insight into strong spin-charge-phonon coupling in LBCO thin film. This coupling manifests as vibrational transition with temperature in the Raman spectra near the ferromagnetic spin ordered transition at 220 K.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Preparation of graphene/WO3/TiO2 composite and its photocathodic protection performance for 304 stainless steel

Highlights: • TiO{sub 2} nanoparticles and WO{sub 3} nanorods were immobilized onto graphene by the hydrothermal method. • The composite can provide an effective protection for 304 stainless steel under visible light. • The composite can offer a sufficient cathodic protection even in the dark. • Possible photocathodic protection mechanism of graphene/WO{sub 3}/TiO{sub 2} composite was proposed. - Abstract: Graphene/WO{sub 3}/TiO{sub 2} composite (RGO/WO{sub 3}/TiO{sub 2}) was successfully fabricated via a two-step hydrothermal method. The structure, morphology and optical property of the as-prepared composite were characterized by X-ray powder diffraction, fourier transform infrared spectra, Raman spectra, transmission electron microscope, scanning electron microscope and ultraviolet-visible diffuse reflectance spectra, respectively. Results showed that the composite was incorporated by graphene nanosheets, WO{sub 3} nanorods and TiO{sub 2} nanoparticles. It exhibited favorable absorption ability in both UV and visible light region. The photocathodic protection performance for 304 stainless steel (304SS) was proven by photocurrent density, open circuit potential, Tafel polarization curves and electrochemical impedance spectroscopy. It was found that the composite could provide an efficient protection for 304SS under visible light irradiation and even in the dark compared to the pure TiO{sub 2}. The electrode potentials negatively shifted to −760 mV under visible light. The possible photocathodic protection mechanism of the composite was also proposed.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2016

Estimation of electron–phonon coupling and Urbach energy in group-I elements doped ZnO nanoparticles and thin films by sol–gel method

Highlights: • Comparison of group-I elements doped ZnO nanoparticles and thin films. • Calculation of electron–phonon coupling and phonon lifetime from Raman spectroscopy. • Estimation of interband states from Urbach energy. - Abstract: Group-I (Li, Na, K & Cs) elements doped ZnO nanoparticles (NPs) and thin films were prepared using sol–gel method. XRD data and TEM images confirm the absence of any other secondary phase different from wurtzite type ZnO. Spherical shapes of grains are observed from the surfaces of doped ZnO films by atomic force microscope images (AFM) and presences of dopants are confirmed from energy dispersive X-ray spectra. The Raman active E{sub 2} (high), E{sub 2} (low), E{sub 1} and A{sub 1} (LO) modes are observed from both ZnO NPs and thin films. First-order longitudinal optical (LO) phonon is found to have contributions from direct band transition and localized excitons. Electron–phonon coupling, phonon lifetime and deformation energy of ZnO are calculated based on the effect of dopants with respect to the multiple Raman LO phonon scattering. Presence of localized interbands states in doped ZnO NPs and thin films are found from the Urbach energy calculations.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Excitation intensity dependent photoluminescence of annealed two-dimensional MoS{sub 2} grown by chemical vapor deposition

Here, we present detailed results of Raman and photoluminescence (PL) characterization of monolayers of MoS{sub 2} grown by chemical vapor deposition (CVD) on SiO{sub 2}/Si substrates after thermal annealing at 150 °C, 200 °C, and 250 °C in an argon atmosphere. In comparison to the as-grown monolayers, annealing in the temperature range of 150–250 °C brings about significant changes in the band edge luminescence. It is observed that annealing at 150 °C gives rise to a 100-fold increase in the PL intensity and produces a strong band at 1.852 eV attributed to a free-to-bound transition that dominates over the band edge excitonic luminescence. This band disappears for the higher annealing temperatures. The improvement in PL after the 200 °C anneal is reduced in comparison to that obtained after the 150 °C anneal; this is suggested to arise from a decrease in the non-radiative lifetime caused by the creation of sulfur di-vacancies. Annealing at 250 °C degrades the PL in comparison to the as-grown sample because of the onset of disorder/decomposition of the sample. It is clear that the PL features of the CVD-grown MoS{sub 2} monolayer are profoundly affected by thermal annealing in Ar atmosphere. However, further detailed studies are needed to identify, unambiguously, the role of native defects and/or adsorbed species in defining the radiative channels in annealed samples so that the beneficial effect of improvement in the optical efficiency of the MoS{sub 2} monolayers can be leveraged for various device applications.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Effect of nanographene platelets on adsorption and sonophotocatalytic performances of TiO2/CuO composite for removal of organic pollutants

Highlights: • TiO{sub 2}/CuO composite incorporated with nanographene platelets (NGP). • Catalytic ability of TiO{sub 2}/CuO/NGP composite for removal of MB investigated. • Better adsorption ability for MB compared to TiO{sub 2}/CuO composite without NGP. • Adsorption ability increases with increasing NGP content up to optimal level. • TiO{sub 2}/CuO/NGP with 10 wt% NGP exhibits best photo- and sonophoto-catalysis. - Abstract: TiO{sub 2}/CuO composites incorporated with different amounts of nanographene platelets (NGP) were synthesized by hydrothermal processing. The TiO{sub 2}/CuO/NGP composite was characterized by X-ray diffraction, transmission electron microscopy, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, dynamical light scattering, Raman spectroscopy, Fourier–transform infrared spectroscopy, ultraviolet (UV)-visible diffuse reflectance spectroscopy, Brunauer—Emmett—Teller (BET) surface area analysis, and electron spin resonance. The catalytic ability of the composite for the removal of methylene blue from an aqueous solution was examined by adsorption, photocatalytic, and sonophotocatalytic experiments. The composite was found to exhibit better adsorption ability for methylene blue compared to the TiO{sub 2}/CuO composite without NGP. The photocatalytic activity of the composite was examined by UV and visible (Vis) light irradiation, while the sonophotocatalytic activity was examined by a combination of UV and Ultrasound (UV + US) and Vis + US. Both examinations showed that the light and ultrasonic responses were enhanced by compositing with NGP.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2015

Semiconductor-to-metallic flipping in a ZnFe{sub 2}O{sub 4}–graphene based smart nano-system: Temperature/microwave magneto-dielectric spectroscopy

Zn-(FeO{sub 2}){sub 2}–graphene smart nano-composites were synthesized using a novel modified solvothermal synthesis with different percentages of graphene. The structure of the nanocomposite was confirmed through X-ray diffraction, micro-Raman scattering spectroscopy, Ultraviolet–Visible spectroscopy, and Fourier transform infrared spectroscopy. The structural growth and morphological aspects were analyzed using scanning/transmission electron microscopy, revealing marvelous micro-structural features of the assembled nano-system resembling a maple leaf. To determine the composition, energy dispersive spectroscopy and X-ray photoelectron spectroscopy were used. Microwave magneto-dielectric spectroscopy revealed the improved dielectric properties of the nano-composite compared to those of the parent functional nanocrystals. Temperature gradient dielectric spectroscopy was used over the spectral range from 100 Hz to 5 MHz to reveal the phenomenological effect that the nanosystem flips from its usual semiconductor nature to a metallic nature with sensing temperature. Electrical conductivity and dielectric analysis indicated that the dielectric loss and the dielectric permittivity increased at room temperature. This extraordinary switching capability of the functionalized graphene nanosystem opens up a new dimension for engineering advanced and efficient smart composite materials. - Graphical abstract: Display Omitted - Highlights: • Zn-(FeO{sub 2}){sub 2}–graphene smart nano-composites were synthesized using a novel modified solvothermal synthesis. • The synthesized nano-system exhibits marvelous leaf like microstructure. • These nano-composites show improved magneto dielectric response. • This engineered smart nano-system shows phenomenological flipping from semiconductor like nature to metallic behavior.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2012

High-power SRS lasers - coherent summators (the way it was)

The history of the research works performed under the guidance of H.G. Basov and aimed at developing high-energy lasers - coherent summators (CSs) - based on stimulated Raman scattering (SRS) in liquid nitrogen and liquid oxygen is reported. The work was performed jointly by researchers of FIAN [the Laboratory of Quantum Radiophysics (LQRP)] and VNIIEF. Many problems were solved as a result of these studies. Liquid nitrogen and oxygen were found to be optimal active media for high-power SRS lasers with high energy per pulse. A method for purifying these cryogenic liquids from micro- and nanoimpurities was developed, which made it possible to eliminate nonlinear loss of pump radiation and converted radiation in the active medium and ensure effective operation of SRS lasers - coherent summators (SRSL CSs) with high output energy. Cryogenic cells providing high optical homogeneity of liquid nitrogen and oxygen were developed, which ensured low (at a level of 0.1 mrad) divergence of converted radiation with high energy density. Raster focusing systems providing optimal concentration of pump radiation in the active medium were designed. These studies resulted in the development of high-power highenergy SRSL CSs with a low beam divergence, based on liquid nitrogen ({lambda}{sub S} = 1.89 {mu}m) and liquid oxygen ({lambda}{sub S} = 1.65 {mu}m), with pumping by explosively pumped iodine lasers (EPILs) ({lambda}{sub p} = 1.315 {mu}m). The characteristics of the SRSL CSs developed were record for that time (the end of 1960s and the beginning of 1970s): energy up to 2.5 kJ per 10-{mu}s pulse, beam divergence {approx}10{sup -4} rad, and beam energy density of several hundreds of J cm{sup -2}. (special issue devoted to the 90th anniversary of n.g. basov)

36 MATERIALS SCIENCE↗
DOE OSTI2025

Solvent Dynamics in Gel Polymer Electrolytes for Lithium–Sulfur Batteries

Li−sulfur (Li−S) batteries are promising as the next-generation energy storage technology but face challenges due to sluggish sulfur redox reaction (SRR) kinetics and a sulfur shuttling effect. While many studies have explored polycaprolactone (PCL)-based gel polymer electrolytes (GPEs) to address these issues, the influence of solvent properties, including dielectric constant (ϵ) and donor and acceptor numbers (DN and AN), remain unexplored despite their critical impact on performance and full-scale implementation. This study systematically compares three distinct electrolytes, dimethoxyethane (DME), dimethyl sulfoxide (DMSO), and tetraethylene glycol dimethyl ether (TEGDME)-paired with PCL, to correlate the varied solvent properties and their effects on the physical properties of the GPE, in terms of Li + transport and solvation, and polysulfide’s confinement. Among them, the DME-based GPE, with an intermediate DN, exhibited the lowest crystallinity (2.31%), highest ionic conductivity (7.49 mS/cm), and high Li + transference number (0.77). As a result, it achieved a specific capacity of 795 mAh/g sulfur and an average Coulombic efficiency of 97.5% after 120 cycles at C/5, outperforming its competitors. Operando Raman and UV−vis spectroscopy confirmed that PCL effectively confines long-chain polysulfides within its network, mitigating the shuttle effect and facilitating reversible polysulfide conversion. These findings demonstrate that GPEs with moderate DN values and balanced ϵ significantly enhance stability, extend cycle life, and improve rate performance for Li−S batteries. This work provides valuable insights into the design of advanced electrolyte systems for practical energy storage applications.

25 ENERGY STORAGE↗
DOE OSTI2014

Photoluminescence properties and crystallization of silicon quantum dots in hydrogenated amorphous Si-rich silicon carbide films

Silicon quantum dots (QDs) embedded in hydrogenated amorphous Si-rich silicon carbide (α-SiC:H) thin films were realized by plasma-enhanced chemical vapor deposition process and post-annealing. Fluorescence spectroscopy was used to characterize the room-temperature photoluminescence properties. X-ray photoelectron spectroscopy was used to analyze the element compositions and bonding configurations. Ultraviolet visible spectroscopy, Raman scattering, and high-resolution transmission electron microscopy were used to display the microstructural properties. Photoluminescence measurements reveal that there are six emission sub-bands, which behave in different ways. The peak wavelengths of sub-bands P1, P2, P3, and P6 are pinned at about 425.0, 437.3, 465.0, and 591.0 nm, respectively. Other two sub-bands, P4 is red-shifted from 494.6 to 512.4 nm and P5 from 570.2 to 587.8 nm with temperature increasing from 600 to 900 °C. But then are both blue-shifted, P4 to 500.2 nm and P5 to 573.8 nm from 900 to 1200 °C. The X-ray photoelectron spectroscopy analysis shows that the samples are in Si-rich nature, Si-O and Si-N bonds consumed some silicon atoms. The structure characterization displays that a separation between silicon phase and SiC phase happened; amorphous and crystalline silicon QDs synthesized with increasing the annealing temperature. P1, P2, P3, and P6 sub-bands are explained in terms of defect-related emission, while P4 and P5 sub-bands are explained in terms of quantum confinement effect. A correlation between the peak wavelength shift, as well as the integral intensity of the spectrum and crystallization of silicon QDs is supposed. These results help clarify the probable luminescence mechanisms and provide the possibility to optimize the optical properties of silicon QDs in Si-rich α-SiC: H materials.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2011

Structural Changes of (KGd)2Ta2O7 Pyrochlore at High Pressure

The structure of K-bearing tantalate pyrochlore (K{sub 2-x}Gd{sub x})Ta{sub 2}O{sub 6+x}(x {approx} 0.4) was studied at high pressures using in situ X-ray diffraction and Raman scattering methods. Experimental results indicated that (K{sub 2-x}Gd{sub x})Ta{sub 2}O{sub 6+x}(x {approx} 0.4) retains the pyrochlore structure up to 40 GPa, but partial amorphization occurred at pressures above 23 GPa. The amorphous phase was also confirmed in the quenched sample by means of transmission electron microscopy. The tantalate pyrochlore lattice is more stable than pyrochlore compounds in other systems, such as rare earth titanates, zirconates and stannates. The structural stability of pyrochlore tantalate may be mainly related to the size ratio of cations on the 16d and 16c sites in the lattice.

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

Raman Laser-Induced Structural Modification in CVD-Grown Monolayer MoS 2 for Multi-Purposed Nanofabrication

Molybdenum disulfide (MoS 2 ) has been extensively explored to be utilized as an electronic material in a variety of device applications. In particular, the tunability of MoS 2 enhances its electrical properties making it an intriguing candidate for field-effect transistors (FETs), while also extending beyond electrical properties to structural phase engineering. Laser-induced modifications, particularly with Raman lasers, offer a straightforward method to modulate materials via thermal processes with precise patterning control and energy-level flexibility. However, most studies on the modification of MoS 2 have focused on multilayered structures or have been conducted under low-power laser conditions, leaving the feasibility of structural modifications in monolayer MoS 2 elusive. In this study, we fundamentally elucidated the effects of high-power Raman laser irradiation on the surface of chemical vapor deposition (CVD)-grown monolayer MoS 2 under ambient conditions and uncovered the underlying mechanisms of laser-induced modifications by applying intense photon energy with highly interactive reactions. Our results revealed both etching and deposition phenomena in two discernible regions, and it can be demonstrated by intensity regimes based on the spatial distribution of laser irradiance within the laser-irradiated spot. Furthermore, phase transition was found to be inhibited due to the promoted oxidation and the deposition of hydrogenated amorphous carbon (a-C:H), and p-type doping was observed, likely occurring in the region beneath the a-C:H deposition as substitutional doping on the 2H phase of MoS 2 . To compare the thermal effects, MoS 2 modifications were further analyzed using simplified heat transfer estimations. In conclusion, these findings deepen our understanding of how Raman laser irradiation modifies MoS 2 under ambient conditions, providing guidelines for optimizing its modification processes.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Deuterium isotope effects in polymerization of benzene under pressure

The enormous versatility in the properties of carbon materials depends on the content of the sp 2 and sp 3 covalent bonds. Under compression, if intermolecular distances cross a critical threshold, then unsaturated hydrocarbons gradually transform to saturated carbon polymers. However, the mechanism of polymerization, even for benzene, the simplest aromatic hydrocarbon, is still not understood. We used high-pressure synchrotron X-ray, neutron diffraction, and micro-Raman spectroscopy together with density functional calculations to investigate the isotope effects in benzene isotopologues C 6 H 6 and C 6 D 6 up to 46.0 GPa. Raman spectra of polymeric products recovered from comparable pressures show the progression of polymerization exhibiting a pronounced kinetic isotope effect. Kinetically retarded reactions in C 6 D 6 shed light on the mechanism of polymerization of benzene. Lastly, we find that C 6 D 6 -derived products recovered from P < 35 GPa actively react with moisture, forming polymers with higher sp 3 hydrogen contents. Significant isotopic shift (≥7 GPa) in persistence of Bragg reflections of C 6 D 6 is observed.

36 MATERIALS SCIENCE↗