Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “RAMAN EFFECT”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,315 records · Page 73
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

Atmospheric pressure route to epitaxial nitrogen-doped trilayer graphene on 4H-SiC (0001) substrate

Large-area graphene film doped with nitrogen is of great interest for a wide spectrum of nanoelectronics applications, such as field effect devices, super capacitors, and fuel cells among many others. Here, we report on the structural and electronic properties of nitrogen doped trilayer graphene on 4H-SiC (0001) grown under atmospheric pressure. The trilayer nature of the growth is evidenced by scanning transmission electron microscopy. X-ray photoelectron spectroscopy shows the incorporation of 1.2% of nitrogen distributed in pyrrolic-N, and pyridinic-N configurations as well as a graphitic-N contribution. This incorporation causes an increase in the D band on the Raman signature indicating that the nitrogen is creating defects. Ultraviolet photoelectron spectroscopy shows a decrease of the work function of 0.3 eV due to the N-type doping of the nitrogen atoms in the carbon lattice and the edge defects. A top gate field effect transistor device has been fabricated and exhibits carrier mobilities up to 1300 cm{sup 2}/V s for holes and 850 cm{sup 2}/V s for electrons at room temperature.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS2006

Remote Pulsed Laser Raman Spectroscopy System for Detecting Qater, Ice, and Hydrous Minerals

For exploration of planetary surfaces, detection of water and ice is of great interest in supporting existence of life on other planets. Therefore, a remote Raman spectroscopy system was demonstrated at NASA Langley Research Center in collaboration with University of Hawaii for detecting ice-water and hydrous minerals on planetary surfaces. In this study, a 532 nm pulsed laser is utilized as an excitation source to allow detection in high background radiation conditions. The Raman scattered signal is collected by a 4-inch telescope positioned in front of a spectrograph. The Raman spectrum is analyzed using a spectrograph equipped with a holographic super notch filter to eliminate Rayleigh scattering, and a holographic transmission grating that simultaneously disperses two spectral tracks onto the detector for higher spectral range. To view the spectrum, the spectrograph is coupled to an intensified charge-coupled device (ICCD), which allows detection of very weak Stokes line. The ICCD is operated in gated mode to further suppress effects from background radiation and long-lived fluorescence. The sample is placed at 5.6 m from the telescope, and the laser is mounted on the telescope in a coaxial geometry to achieve maximum performance. The system was calibrated using the spectral lines of a Neon lamp source. To evaluate the system, Raman standard samples such as calcite, naphthalene, acetone, and isopropyl alcohol were analyzed. The Raman evaluation technique was used to analyze water, ice and other hydrous minerals and results from these species are presented.

Garcia, Christopher S.↗
DOE OSTI2022

An Investigation of the Ice Cloud Detection Sensitivity of Cloud Radars Using the Raman Lidar at the ARM SGP Site

The ice cloud detection sensitivity of the millimeter cloud radar (MMCR) and the Ka-band Zenith radar (KAZR) is investigated using a collocated Raman lidar (RL) at the Atmospheric Radiation Measurement Program Southern Great Plains site. Only profiles that are transparent to the RL with ice clouds only are considered in this study. The MMCR underestimates the RL ice cloud optical depth (COD) by 20%. The MMCR detects no ice clouds in 37% of the profiles. These profiles where ice cloud goes undetected by the MMCR typically contain very optically thin clouds, with a mean RL ice COD of 0.03. Higher ice cloud detection sensitivity is found for the KAZR, which underestimates the RL ice COD by 15%. The decrease in the ice COD bias for the KAZR compared to the MMCR is largely due to a decrease in the ice COD bias for the situation where the transparent profiles with ice clouds are detected by both the RL and cloud radar. The climatic net ice cloud radiative effects (CREs) from the RL at the top of the atmosphere (TOA) and the surface are 3.2 W m−2 and −0.6 W m−2, respectively. The ice CREs at the TOA and surface are underestimated for the MMCR by 0.7 W m−2 and 0.16 W m−2 (21% and 29%) and underestimated for the KAZR by 0.6 W m−2 and 0.14 W m−2 (17% and 24%). The ice clouds undetected by the cloud radars led to underestimating the climatic net cloud heating rates below 150 hPa by about 0–0.04 K day−1.

54 ENVIRONMENTAL SCIENCES↗
NASA NTRS2014

Two Dimensional Symmetric Correlation Functions of the S Operator and Two Dimensional Fourier Transforms: Considering the Line Coupling for P and R Lines of Linear Molecules

The refinement of the Robert-Bonamy (RB) formalism by considering the line coupling for isotropic Raman Q lines of linear molecules developed in our previous study [Q. Ma, C. Boulet, and R. H. Tipping, J. Chem. Phys. 139, 034305 (2013)] has been extended to infrared P and R lines. In these calculations, the main task is to derive diagonal and off-diagonal matrix elements of the Liouville operator iS1 − S2 introduced in the formalism. When one considers the line coupling for isotropic Raman Q lines where their initial and final rotational quantum numbers are identical, the derivations of off-diagonal elements do not require extra correlation functions of the ^S operator and their Fourier transforms except for those used in deriving diagonal elements. In contrast, the derivations for infrared P and R lines become more difficult because they require a lot of new correlation functions and their Fourier transforms. By introducing two dimensional correlation functions labeled by two tensor ranks and making variable changes to become even functions, the derivations only require the latters' two dimensional Fourier transforms evaluated at two modulation frequencies characterizing the averaged energy gap and the frequency detuning between the two coupled transitions. With the coordinate representation, it is easy to accurately derive these two dimensional correlation functions. Meanwhile, by using the sampling theory one is able to effectively evaluate their two dimensional Fourier transforms. Thus, the obstacles in considering the line coupling for P and R lines have been overcome. Numerical calculations have been carried out for the half-widths of both the isotropic Raman Q lines and the infrared P and R lines of C2H2 broadened by N2. In comparison with values derived from the RB formalism, new calculated values are significantly reduced and become closer to measurements.

infrared radiation↗
DOE OSTI2021

The adsorption of As(V) on poorly crystalline Fe oxyhydroxides, revisited: Effect of the reaction media and the drying treatment

Arsenic (As) adsorbed on Fe oxyhydroxides (adsorbent) is widely occurring in many environmental settings such as in acid mine drainage systems or in the hydrometallurgical operations to form Fe-As coprecipitates. However, the influence of the reaction media and the drying treatment on the microstructure of the directly formed adsorbents at various pHs was still not fully understood. In this work, As adsorption behaviors on various forms of Fe oxyhydroxides were systematically investigated by using XRD, FTIR, Raman, XANES, and HRTEM. Overall, the results revealed that at weak acidic pH, more As could adsorbed on the suspension adsorbent formed in sulfate and chloride media than that in nitrate media, possibly due to the microstructure alteration of the adsorbent in the presence of sulfate and chloride. Besides, the increasing crystallinity of the Fe oxyhydroxides and the aggregation effect after drying were the major reasons why less As could be hold by the dried adsorbents than that of the corresponding suspension adsorbents. These findings could shed more light on the nature of the Fe oxyhydroxides which may be helpful for more precisely predicting the fate of some toxic metal(loid)s in the environment.

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

Ultrasensitive and selective non-enzymatic electrochemical glucose sensor based on hybrid material of graphene nanosheets/graphene nanoribbons/nickel nanoparticle

Highlights: • Nickel nanoparticles incorporated graphene nanosheets/graphene nanoribbons (GS/GNR/Ni) composite was synthesized by in-situ chemical reduction route and the as prepared GS/GNR/Ni modified glassy carbon electrode (GCE) was applied to detect glucose. • The fabricated GS/GNR/Ni/GCE modified electrode exhibits outstanding performance for non-enzymatic glucose sensing with sensitivity (2.3 mA/mM cm{sup 2}), linear range (5 nM - 5 mM) and detection limit (2.5 nM). • GS/GNR/Ni/GCE modified electrode exhibited a high selectivity towards glucose against the interferents, such as ascorbic acid (AA), uric acid (UA), dopamine and sucrose. - Abstract: A fast, highly sensitive and selective non-enzymatic electrochemical glucose sensor based on graphene sheet/graphene nanoribbon/nickel nanoparticles (GS/GNR/Ni) hybrid material modified electrode was fabricated. The hybrid material was synthesized via facile in-situ chemical reduction and characterized by X-ray diffraction, transmission electron microscopy, Raman spectroscopy, cyclic voltammetry and electrochemical impedance spectroscopy. The GS/GNR/Ni/GCE showed high electrochemical activity towards the oxidation of glucose in a 0.1 M NaOH solution. At an applied potential of +0.5 V, it displayed wide linear amperometric response towards glucose from the range of 5 nM–5 mM, with a detection limit of 2.5 nM and sensitivity of 2.3 mA/mM cm{sup 2}. Moreover, the modified electrode was relatively insensitive to commonly interfering species such as dopamine, ascorbic acid, sucrose, uric acid and Cl{sup −} ions. The fabricated sensor with better reproducibility, good long term stability, makes it a promising electrode for the development of effective glucose sensor.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2020

Melting of charge order in the low-temperature state of an electronic ferroelectric-like system

Strong electronic interactions can drive a system into a state with a symmetry breaking. Lattice frustration or competing interactions tend to prevent symmetry breaking, leading to quantum disordered phases. In spin systems frustration can produce a spin liquid state. Frustration of a charge degree of freedom also can result in various exotic states, however, experimental data on these effects is scarce. In this work we demonstrate how in a Mott insulator on a weakly anisotropic triangular lattice a charge ordered state melts on cooling down to low temperatures. Raman scattering spectroscopy finds that κ -(BEDT-TTF) 2 Hg(SCN) 2 Cl enters an insulating “dipole solid” state at T =30K, but below T =15K the order melts, while preserving the insulating energy gap. Based on these observations, we suggest a phase diagram relevant to other quantum paraelectric materials.

36 MATERIALS SCIENCE↗
DOE OSTI2019

In situ , operando studies on the size and structure of supported Pt catalysts under supercritical conditions by simultaneous synchrotron-based X-ray techniques

To control the size and structure of supported Pt catalysts, the influence of additional metal particles and the effect of supports were elucidated during the cracking reaction of n-dodecane under supercritical reaction conditions. The dynamical changes in nanocatalysts and catalytic activity are studied under realistic reaction conditions by using a combination of simultaneous temperature-programmed heating, in situ Small Angle X-ray Scattering (SAXS) and X-ray Absorption Near Edge Structure (XANES). In situ SAXS results indicate that the stability of the catalysts increases with Sn concentration. In situ XANES analysis reveals that the degree of oxidation and the electronic states of catalysts are dependent on the amount of Sn. Carbonaceous deposits over spent catalysts were characterized by Raman spectroscopy, suggesting that the highest Sn loading inhibits the formation of disordered graphitic lattices, which leads to an increased catalytic activity. SiO 2 , γ-Al 2 O 3 and Mg(Al)Ox were employed as supports to investigate the support effect on the stability of Pt catalysts. In situ SAXS and XANES findings clearly reflect the improved stability of catalysts on γ-Al 2 O 3 and Mg(Al)Ox supports compared to Pt catalysts on SiO 2 and the electronic states of catalysts are strongly influenced by support materials.

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

Exploring Cs 2 AgIn x Bi 1− x Cl 6 double perovskites for optoelectronics: insights from theoretical and photophysical approaches

Lead-free halide double perovskites (HDPs) have become attractive materials for optoelectronic applications owing to their nontoxicity, structural stability, and germane photoelectric properties. In this work, we report the synthesis of high-quality In-alloyed Cs 2 AgIn x Bi (1−x) Cl 6 nanocrystals (NCs) using the antisolvent recrystallization method and comprehensively investigate the effects of In alloying on the structural, morphological, optoelectronic, and temperature-dependent photoluminescence (TDPL) properties using the state-of-the-art experimental and computational tools. Both XRD and Raman spectroscopy analyses confirmed the synthesis of highly crystalline Cs 2 AgIn x Bi (1−x) Cl 6 materials, which exhibited cubic morphology, as confirmed by TEM analysis. Room-temperature photoluminescence (PL) measurements revealed a drastic increase in the intensity above 75% In concentration with dual emission, whereas the time-resolved PL (TR-PL) results show an increase in the average lifetime values with an increase in In content, suggesting that the materials have excellent optical properties and hence are suitable candidates for optoelectronics. The TDPL measurements revealed the smallest Huang–Rhys factor (18.6) for the Cs 2 AgIn x Bi (1−x) Cl 6 (x = 0.9) sample, indicating weak exciton–phonon coupling in this composition. When deployed in the fabrication of a photodetector device, the Cs 2 AgIn x Bi (1−x) Cl 6 (x = 0.9) sample exhibited significantly enhanced photoresponsivity and a faster response time, confirming its potential for photodetector applications. Complementary DFT calculations showed that In alloying modifies the band structure of Cs 2 AgIn x Bi (1−x) Cl 6 . Our results provide valuable insights for designing multifunctional Cs 2 AgIn x Bi (1−x) Cl 6 -based materials for next-generation energy and optoelectronic devices.

14 SOLAR ENERGY↗
DOE OSTI2019

Physics of picosecond pulse laser ablation

This study investigates the physical processes involved in picosecond pulse (20-28 ps FWHM) laser ablation of Al 6061, 316L stainless steel, and undoped crystalline Si ($\langle$100$\rangle$) over a range of laser wavelength (355 nm and 1064 nm) and fluence (0.1-40 J/cm 2 ). Experimental measurements of material ablation rate show enhanced removal at the 355 nm wavelength, primarily due to laser-plasma interaction (LPI) within the ablative plume that approaches an order of magnitude increase over the measured removal at 1064 nm. A transition in the ablation rate at 355 nm is identified around ~10 J/cm 2 above which the removal efficiency increases by a factor of two to three. Multi-physics radiation hydrodynamic simulations, considering LPI effects and utilizing a novel mixed-phase equation of state model, show that the transition in ablation efficiency is due to the onset of melt ejection through cavitation, where laser-driven shock heating sets the depth of melt penetration and the ensuing release wave from the ablation surface drives cavitation through the imposition of tensile strain within the melt. High-speed pump-probe imaging of the ejecta and ejecta collection studies, as well as scanning electron microscopy of the ablation craters, support the proposed cavitation mechanism in the higher fluence range. The ablation process is vitally influenced by LPI effects and the thermophysical properties of the material.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Laser-plasma instabilities in long scale-length plasmas relevant to shock-ignition

We present 2D particle-in-cell simulations of laser-plasma instabilities (LPI) performed using conditions relevant to experiments on the OMEGA and NIF laser facilities. The laser intensity used is 2×10 15 W cm -2 , which allows comparison with previous experiments and simulations investigating shock ignition, though this is a relatively low intensity for the scheme. We find that the large convective gain of the instabilities leads to dynamics that are largely controlled by pump depletion and to scattering or absorption by LPIs predominantly occurring away from the quarter-critical density. The two-plasmon decay (TPD) instability is dominant for OMEGA-type conditions and remains important at the NIF-scale. In both cases, most absorption from TPD occurs near its Landau cutoff density, and we examine its nonlinear dynamics in this region, focusing on the ion-acoustic waves responsible for saturation. For NIF-type conditions, stimulated Raman scattering (SRS) and stimulated Brillouin scattering divert significant fractions of laser energy, and we find that SRS backscatter can occur with high gain at low densities due to kinetic effects. An in-depth analysis of hot-electron production is performed to identify the main sources and their characteristic electron temperature. For both simulations presented, the overall hot-electron temperature lies between 30 and 35 keV. This is relatively low and will likely increase shock pressure; however, the distributions also contain a significant number of high-energy (E k >100 keV) electrons that would likely cause unacceptable preheat. We, therefore, suggest some strategies that may be utilized to minimize this high-energy component. I. INTROD

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1989

Subharmonic and fundamental high amplitude excitation of an axisymmetric jet

A circular jet was excited simultaneously by two different harmonically related tones. Data for three pairs of Strouhal numbers (St(D) = f*D/U (sub j) = 0.2 and 0.4, 0.3 and 0.6, 0.4 and 0.8). For each case the initial phase difference between the two waves was varied in steps of 45 deg, for one full cycle and the level of the fundamental and subharmonic forcing were varied independently over the range of 0.1 to 7 percent of the jet exit velocity. Our initial findings concurred with published findings, such as a critical level of the fundamental is required for subharmonic augmentation, the initial phase difference is critical in determining whether the subharmonic is augmented or suppressed. The detailed documentation of several aspects of this phenomenon all measured in one and the same experimental facility in a controlled manner, bring out several important points that eluded previous researchers: (1) At high amplitudes of the fundamental and subharmonic forcing levels the subharmonic augmentation is independent of the initial phase difference. (2) Contrary to the earlier belief that stable pairing could be produced only with an initial laminar boundary layer, the present work shows that by the two-frequency excitation method this phenomenon can be induced over a range of conditions for a jet with an initially turbulent boundary layer. (3) It is seen that two-frequency excitation is indeed more effective than single frequency excitation in jet mixing enhancement. Higher spreading rates seem to go along with higher subharmonic levels.

Raman, Ganesh↗
DOE OSTI2014

Two dimensional symmetric correlation functions of the S-circumflex operator and two dimensional Fourier transforms: Considering the line coupling for P and R lines of linear molecules

The refinement of the Robert-Bonamy (RB) formalism by considering the line coupling for isotropic Raman Q lines of linear molecules developed in our previous study [Q. Ma, C. Boulet, and R. H. Tipping, J. Chem. Phys. 139, 034305 (2013)] has been extended to infrared P and R lines. In these calculations, the main task is to derive diagonal and off-diagonal matrix elements of the Liouville operator iS{sub 1} − S{sub 2} introduced in the formalism. When one considers the line coupling for isotropic Raman Q lines where their initial and final rotational quantum numbers are identical, the derivations of off-diagonal elements do not require extra correlation functions of the S-circumflex operator and their Fourier transforms except for those used in deriving diagonal elements. In contrast, the derivations for infrared P and R lines become more difficult because they require a lot of new correlation functions and their Fourier transforms. By introducing two dimensional correlation functions labeled by two tensor ranks and making variable changes to become even functions, the derivations only require the latters’ two dimensional Fourier transforms evaluated at two modulation frequencies characterizing the averaged energy gap and the frequency detuning between the two coupled transitions. With the coordinate representation, it is easy to accurately derive these two dimensional correlation functions. Meanwhile, by using the sampling theory one is able to effectively evaluate their two dimensional Fourier transforms. Thus, the obstacles in considering the line coupling for P and R lines have been overcome. Numerical calculations have been carried out for the half-widths of both the isotropic Raman Q lines and the infrared P and R lines of C{sub 2}H{sub 2} broadened by N{sub 2}. In comparison with values derived from the RB formalism, new calculated values are significantly reduced and become closer to measurements.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Detailed investigation of optoelectronic and microstructural properties of plasma polymerized cyclohexane thin films: Dependence on the radiofrequency power

Optical properties of polymerized cyclohexane films deposited by radiofrequency plasma enhanced chemical vapor deposition technique at different radiofrequency powers onto glass and silicon substrates, are studied and correlated with the microstructure of the films, using a combination of atomic force microscopy, Raman and Fourier Transformer Infrared spectroscopy and optical measurements. The optical constants such as refractive index n, dielectric permittivity ε and extinction k and absorption α coefficients, are extracted from transmission and reflection spectra through the commercial software CODE. These constants lead, by using common theoretical models as Cauchy, Lorentz, Tauc and single effective oscillator, to the determination of the static refractive index n{sub s} and permittivity ε{sub s}, the plasma frequency ω{sub p}, the carrier density to effective mass ratio N/m{sub e}{sup *}, the optical conductivity σ{sub oc}, the optical band gap E{sub g} and the oscillation and dispersion energies E{sub 0} and E{sub d}, respectively. We find that n, ε{sub s}, ω{sub p}, N/m{sub e}{sup *}, E{sub d}, increase with radiofrequency power, while E{sub g} and E{sub 0} decrease in the same range of power. These results are well correlated with those obtained from atomic force microscopy, Raman and infrared measurements. They also indicate that the increase of the radiofrequency power promotes the fragmentation of the precursor and increases the carbon C-sp{sup 2} hybridization proportion, which results in an improvement of the optoelectronic properties of the films.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Magnetic Behavior of Ni/NiO Core–Shell Nanoparticles under Electromagnetic Waves for Oil–Water Interfacial Tension Reduction

The increasing demand for oil and gas has led to a hope of developing more efficient recovery methods. It is well known that nanoparticles adsorbed at the oil–water interface, but there is no consensus that has been reached on whether magnetic nanoparticles under electromagnetic waves affect the interfacial tension. In this paper, nickel/nickel oxide nanoparticles have been synthesized using sol–gel auto combustion method. The product was characterized using x-ray diffraction, Raman spectroscopy, field emission scanning electron microscopy, Fourier transforms infrared spectroscopy and vibrating sample magnetometer. The results show the Ni/NiO phases and the ferromagnetic nature of the sample. The Ni/NiO nanofluids were prepared to investigate the effect on oil–water interfacial tension in enhanced oil recovery under electromagnetic waves using an inverted pendant drop method. The results show a significant decrease in interfacial tension under electromagnetic waves of frequency 2.2 kHz at low wt.% of Ni/NiO and at room temperature. The decrease in the interfacial tension has been observed by increasing the temperature to 90 °C using temperature controller. The decrease in the interfacial tension could be due to the interaction of oscillating B-field of waves and magnetic domains of adsorbing nanoparticles at the oil–water interface which disturbed the oil–water interface.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Strong magnetoelectric and spin phonon coupling in SmFeO{sub 3}/PMN-PT composite

We have investigated spin phonon coupling in the strain coupled magnetoelectric SmFeO{sub 3}/0.65Pb(Mg{sub 1/3}Nb{sub 2/3})O{sub 3}–0.35PbTiO{sub 3} (PMN-PT) composite in the temperature range of 300–650 K by Raman spectroscopy and magnetic measurements. The SmFeO{sub 3}/PMN-PT composite shows sharp rise in magnetic moment across ferroelectric transition temperature (T{sub c}) of PMN-PT. Around this transition temperature (T{sub c} of PMN-PT), the temperature evolution of Raman spectra of the composite also shows anomalies in the phonon frequencies and line width corresponding to the SmFeO{sub 3} phase which indicate structural modifications in the SmFeO{sub 3} phase around T{sub c} of PMN-PT. The observed structural, magnetic, and phonon anomalies of SmFeO{sub 3} around T{sub c} of PMN-PT in SmFeO{sub 3}/PMN-PT are attributed to spin-phonon coupling providing evidence of strong strain mediated magnetoelectric effects.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2026

In Situ Insights into Enhanced Cooperative Ligand Exchange Kinetics via Solvent-Induced Restacking in a 2D Metal–Organic Framework

Understanding the reaction kinetics at catalytically active sites is crucial for integrating catalytic two-dimensional (2D) materials into industrial processes. This study focuses on in situ observation of ligand exchange kinetics and solvent-assisted structural restacking transition in the 2D paddle wheel-based MOF [Cu 2 (dttc) 2 ] n (DUT-134(Cu), dttc = dithieno[3,2-b:2′,3′- d]thiophene-2,6-dicarboxylate). The ligand exchange process, involving the replacement of dimethylformamide (DMF) with nitriles such as acetonitrile (ACN), pentanenitrile, and heptanenitrile, was investigated using advanced in situ characterization techniques with high temporal resolution, including powder X-ray diffraction and Raman spectroscopy. The larger analytes exhibited reduced exchange rates, consistent with enhanced steric hindrance and greater diffusion constraints. Interestingly, the study revealed that the exchange of DMF with ACN induces a structural transition to higher symmetry within few seconds, a transition from AB to AA stacking mode of the layers, and a widening of the interlayer distance. Crucially, this structural transition dramatically accelerates the solvent exchange process through cooperative effects, offering critical advantages for catalytic applications. Notably, the reverse exchange from ACN to DMF proceeds more slowly and does not reverse the structural changes, but a new phase is formed with preserved AA stacking. By isotope labeling of linker molecules in combination with two complementary theoretical vibrational simulation methods, the precise assignment of Raman bands and the vibrational modes associated with the ligand exchange process could be achieved. These pioneering insights into the dynamic behavior of 2D MOFs, coupled with ligand exchange, establish a highly promising and transformative approach to achieving enhanced tunability and responsiveness in future catalytic applications.

Layers↗
DOE OSTI2014

A hydrogen peroxide electrochemical sensor based on silver nanoparticles decorated three-dimensional graphene

A facile strategy has been developed to synthesize sliver nanoparticles (Ag NPs) decorated three-dimensional graphene (3DG) through hydrothermal process. The AgNPs-3DG composites are directly fabricated into a free standing sensing electrode for electrochemical detection of hydrogen peroxide (H{sub 2}O{sub 2}) in phosphate buffered solutions. Various techniques equipments including scanning electron microscopy, X-ray diffraction, and Raman spectroscopy are used to characterize the morphology and structure of the as-prepared composite. The electrochemical experiments reveal the AgNPs-3DG based biosensor exhibits fast amperometric sensing, low detection limitation, wide linear responding range, and perfect selectivity for non-enzyme H{sub 2}O{sub 2} detection, indicating the well synergistic effect of Ag NPs high electrocatalytic activity and 3DG high conductivity and large surface area.

77 NANOSCIENCE AND NANOTECHNOLOGY↗