Cherno Jaye

National Institute of Standards and Technology, GAI, Maryland, United States

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Publications (112)440.73 Total impact

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    ABSTRACT: A range of different activated carbons was characterized and evaluated for promotion of the oxidative desulfurization (ODS) of JP-8 fuel using H2O2 oxidant and acetic acid. Wood-based carbons activated by acid treatment showed much higher effectiveness than all other carbon types, regardless of source or activation method. Under identical test conditions designed to differentiate material performance, the most effective carbon material yielded 69% oxidation of 2,3-dimethylbenzothiophene (2,3-DMBT) whereas the ineffective materials scarcely out-performed the control (10% oxidation). To understand the characteristics most associated with reaction promotion, the textural, chemical, and defect features of the carbon materials were examined using a battery of techniques. The effective promoters all shared in common high surface areas and high pore volumes; however, surface area and pore volume alone could not explain the observed trends in performance. Investigating surface chemistry, presence of strong acid sites was strongly related to ODS performance. Overall, long-range order was not required for high activity, yet neither were edge defect sites. These results suggest that carbon promotes ODS by formation of percarboxylic acid species at defect sites within the carbon basal planes. Post-reaction analysis of the carbon materials provided evidence to support this explanation.
    No preview · Article · Jan 2016
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    ABSTRACT: During slithering locomotion the ventral scales at a snake's belly are in direct mechanical interaction with the environment, while the dorsal scales provide optical camouflage and thermoregulation. Recent work has demonstrated that compared to dorsal scales, ventral scales provide improved lubrication and wear protection. While biomechanic adaption of snake motion is of growing interest in the fields of material science and robotics, the mechanism for how ventral scales influence the friction between the snake and substrate, at the molecular level, is unknown. In this study, we characterize the outermost surface of snake scales using sum frequency generation (SFG) spectra and near-edge X-ray absorption fine structure (NEXAFS) images collected from recently shed California kingsnake (Lampropeltis californiae) epidermis. SFG's nonlinear optical selection rules provide information about the outermost surface of materials; NEXAFS takes advantage of the shallow escape depth of the electrons to probe the molecular structure of surfaces. Our analysis of the data revealed the existence of a previously unknown lipid coating on both the ventral and dorsal scales. Additionally, the molecular structure of this lipid coating closely aligns to the biological function: lipids on ventral scales form a highly ordered layer which provides both lubrication and wear protection at the snake's ventral surface.
    Preview · Article · Dec 2015 · Journal of The Royal Society Interface
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    ABSTRACT: As a model system for understanding charge transfer in novel architectural designs for solar cells, double-walled carbon nanotube (DWNT)-CdSe quantum dot (QD) (QDs with average diameters of 2.3, 3.0, and 4.1 nm) heterostructures have been fabricated. The individual nanoscale building blocks were successfully attached and combined using a hole-trapping thiol linker molecule, i.e., 4-mercaptophenol (MTH), through a facile, noncovalent stacking attachment strategy. Transmission electron microscopy confirmed the attachment of QDs onto the external surfaces of the DWNTs. We herein demonstrate a meaningful and unique combination of near-edge X-ray absorption fine structure (NEXAFS) and Raman spectroscopies bolstered by complementary electrical transport measurements in order to elucidate the synergistic interactions between CdSe QDs and DWNTs, which are facilitated by the bridging MTH molecules that can scavenge photoinduced holes and potentially mediate electron redistribution between the conduction bands in CdSe QDs and the C 2p-derived states of the DWNTs. Specifically, we correlated evidence of charge transfer as manifested by (i) changes in the NEXAFS intensities of resonance in the C K-edge and Cd M3-edge spectra, (ii) a perceptible outer tube G-band downshift in frequency in Raman spectra, as well as (iii) alterations in the threshold characteristics present in transport data as a function of CdSe QD deposition onto the DWNT surface. In particular, the separate effects of (i) varying QD sizes and (ii) QD coverage densities on the electron transfer were independently studied.
    Full-text · Article · Nov 2015 · The Journal of Physical Chemistry C
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    ABSTRACT: Detailed analysis of the C K near-edge X-ray absorption fine structure (NEXAFS) spectra of a series of saccharides (fructose, xylose, glucose, galactose, maltose monohydrate, α-lactose monohydrate, anhydrous β-lactose, cellulose) indicates that the precise determination of IPs and σ* shape resonance energies is sensitive enough to distinguish different crystalline saccharides through the variations in their average C-OH bond lengths. Experimental data as well as FEFF8 calculations confirm that bond length variations in the organic solid state of 10─2 Å can be experimentally detected, opening up the possibility to use NEXAFS for obtaining incisive structural information for molecular materials, including non-crystalline systems without long-range order such as dissolved species in solutions, colloids, melts and similar amorphous phases. The observed bond length sensitivity is as good as that originally reported for gas phase and adsorbed molecular species. NEXAFS-derived molecular structure data for the condensed phase may therefore be used to guide molecular modelling as well as to validate computationally derived structure models for such systems. Some results indicate further analytical value, in that the σ* shape resonance analysis may distinguish hemiketals from hemiacetals (i.e. derived from ketoses and aldoses), as well as α from β forms of otherwise identical saccharides.
    Full-text · Article · Oct 2015 · The Journal of Physical Chemistry B
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    ABSTRACT: In this paper, we examine the effects of excessive sonication during surfactant-assisted multiwall carbon nanotubes (MWCNT) dispersion in ethylene vinyl acetate (EVA) by way of monitoring molecular arrangements upon progressive straining. Aberration-corrected transmission electron microscopy confirms the structural damage on the graphitic layers upon prolonged sonication. The resulting lack on MWCNT alignment is shown by atomic force microscopy. Further, molecular interface dynamics in progressively strained EVA|MWCNT composites have been studied through Raman and NEXAFS spectroscopies. NEXAFS spectra have identified graphitic amorphization and further C-vacancy rehybridization by way of hydrogen passivation as the damage mechanism to the graphitic structure upon sonication. In this scheme, MWCNTs did not align despite the range of composite strains discussed due to stick and slip dynamics of surrounding EVA. Ultimately, damaged MWCNTs rendered the necessary dispersant π–π interactions suboptimal and insufficient for nanomechanically interlocked polymer–filler interactions. Remarkably, upon large strains, polymer chains are seen to unlatch from the MWCNT and undergo mechanically induced backbone twisting. The possibility of mechanically induced backbone twisting might offer alternative processing routes in photovoltaic systems, where chemically induced conjugated backbone twisting yields increased power conversion efficiency.
    No preview · Article · Aug 2015 · The Journal of Physical Chemistry C
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    ABSTRACT: Interfacing graphene with metal oxides is of considerable technological importance for modulating carrier density through electrostatic gating as well as for the design of earth-abundant electrocatalysts. Herein, we probe the early stages of the atomic layer deposition (ALD) of HfO2 on graphene oxide using a combination of C and O K-edge near-edge X-ray absorption fine structure spectroscopies and X-ray photoelectron spectroscopy. Dosing with water is observed to promote defunctionalization of graphene oxide as a result of the reaction between water and hydroxyl/epoxide species, which yields carbonyl groups that further react with migratory epoxide species to release CO2 . The carboxylates formed by the reaction of carbonyl and epoxide species facilitate binding of Hf precursors to graphene oxide surfaces. The ALD process is accompanied by recovery of the π-conjugated framework of graphene. The delineation of binding modes provides a means to rationally assemble 2D heterostructures. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    No preview · Article · Jul 2015 · ChemPhysChem

  • No preview · Chapter · Jul 2015
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    Full-text · Dataset · Jun 2015
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    ABSTRACT: Graphene (Gr)–polystyrene (PS) and graphene (Gr)–ultra-high molecular weight polyethylene (UHMW PE) laminates were fabricated using a transfer print approach that relies on differential adhesion to remove graphene from Cu foil without chemical etching. The polymer surfaces were prepared using plasma functionalization followed by N-ethylamino-4-azidotetrafluorobenzoate (TFPA) deposition. Then, the graphene on Cu foil and the TFPA coated polymers were pressed at elevated temperature and mild pressure. Finally, they were separated by mechanical peeling. No additional processing was applied. Detailed chemical, structural, and morphological characterization of PS and UHMW PE before and after graphene transfer print was performed using a suite of complementary surface analysis techniques including X-ray Photoelectron Spectroscopy (XPS), Near Edge X-ray Absorption Fine Structure Spectroscopy (NEXAFS), Raman Spectroscopy, and Atomic Force Microscopy (AFM). The charge carrier density and charge carrier mobility of the transferred graphene were determined using Hall effect measurements. We found that graphene’s electrical properties were preserved and comparable to those of graphene on SiO2/Si. Furthermore, modulation of TFPA attachment to PS and UHMW PE led to different TFPA-layer microstructure and therefore to a different amount of functional azide groups available to form carbene bonds with graphene causing changes in graphene’s compressive strain, doping and mobility.
    No preview · Article · May 2015 · Carbon
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    ABSTRACT: X-ray emission spectroscopy (XES) is a powerful element-selective tool to analyze the oxidation states of atoms in complex compounds, determine their electronic configuration, and identify unknown compounds in challenging environments. Until now the low efficiency of wavelength-dispersive X-ray spectrometer technology has limited the use of XES, especially in combination with weaker laboratory X-ray sources. More efficient energy-dispersive detectors have either insufficient energy resolution because of the statistical limits described by Fano or too low counting rates to be of practical use. This paper updates an approach to high-resolution X-ray emission spectroscopy that uses a microcalorimeter detector array of superconducting transition-edge sensors (TESs). TES arrays are discussed and compared with conventional methods, and shown under which circumstances they are superior. It is also shown that a TES array can be integrated into a table-top time-resolved X-ray source and a soft X-ray synchrotron beamline to perform emission spectroscopy with good chemical sensitivity over a very wide range of energies.
    Full-text · Article · May 2015 · Journal of Synchrotron Radiation
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    ABSTRACT: A two-step method consisting of solid-state microwave irradiation and heat treatment under NH3 gas was used to prepare nitrogen-doped reduced graphene oxide (N-RGO) with a high specific surface area (1007 m(2) g(-1) ), high electrical conductivity (1532 S m(-1) ), and low oxygen content (1.5 wt %) for electrical double-layer capacitor applications. The specific capacitance of N-RGO was 291 F g(-1) at a current density of 1 A g(-1) , and a capacitance of 261 F g(-1) was retained at 50 A g(-1) , which indicated a very good rate capability. N-RGO also showed excellent cycling stability and preserved 96 % of the initial specific capacitance after 100 000 cycles. Near-edge X-ray absorption fine-structure spectroscopy results provided evidenced for the recovery of π conjugation in the carbon networks with the removal of oxygenated groups and revealed chemical bonding of the nitrogen atoms in N-RGO. The good electrochemical performance of N-RGO is attributed to its high surface area, high electrical conductivity, and low oxygen content. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    Full-text · Article · Apr 2015 · ChemSusChem
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    ABSTRACT: The sensitivity of near-edge X-ray absorption fine structure (NEXAFS) spectroscopy to Brønsted donation and the protonation state of nitrogen in the solid state is investigated through a series of multicomponent bipyridine-acid systems alongside X-ray photoelectron spectroscopy (XPS) data. A large shift to high energy occurs for the 1s → 1π* resonance in the nitrogen K-edge NEXAFS with proton transfer from the acid to the bipyridine base molecule and allows assignment as a salt (C═NH+), with the peak ratio providing the stoichiometry of the types of nitrogen species present. A corresponding binding energy shift for C═NH+ is observed in the nitrogen XPS, clearly identifying protonation and formation of a salt. The similar magnitude shifts observed with both techniques relative to the unprotonated nitrogen of co-crystals (C═N) suggest that the chemical state (initial-state) effects dominate. Results from both techniques reveal the sensitivity to identify proton transfer, hydrogen bond disorder, and even the potential to distinguish variations in hydrogen bond length to nitrogen.
    Full-text · Article · Apr 2015 · Crystal Growth & Design
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    ABSTRACT: Transition edge sensor microcalorimeters can measure x-ray and gamma-ray energies with very high energy resolution and high photon-collection efficiency. For this technology to reach its full potential in future x-ray observatories, each sensor must be able to measure hundreds or even thousands of photon energies per second. Current "optimal filtering" approaches to achieve the best possible energy resolution work only for photons well isolated in time, a requirement in direct conflict with the need for high-rate measurements. We describe a new analysis procedure to allow fitting for the pulse height of all photons even in the presence of heavy pulse pile-up. In the limit of isolated pulses, the technique reduces to the standard optimal filtering with long records. We employ reasonable approximations to the noise covariance function in order to render multi-pulse fitting computationally viable even for very long data records. The technique is employed to analyze x-ray emission spectra at 600 eV and 6 keV at rates up to 250 counts per second in microcalorimeters having exponential signal decay times of approximately 1.2 ms.
    Preview · Article · Mar 2015 · The Astrophysical Journal Supplement Series
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    ABSTRACT: As a first step, we have synthesized and optically characterized a systematic series of one-dimensional (1D) single-crystalline Eu3+-activated alkaline-earth metal tungstate/molybdate solid-solution composite CaW1-xMoxO4 (0 ≤ “x” ≤ 1) nanowires of controllable chemical composition using a modified template-directed methodology under ambient room-temperature conditions. Extensive characterization of the resulting nanowires has been performed using X-ray diffraction, electron microscopy, and optical spectroscopy. The crystallite size and single crystallinity of as-prepared 1D CaW1-xMoxO4:Eu3+ (0 ≤ “x” ≤ 1) solid-solution composite nanowires increase with increasing Mo component (“x”). We note a clear dependence of luminescence output upon nanowire chemical composition with our 1D CaW1-xMoxO4:Eu3+ (0 ≤ “x” ≤ 1) evincing the highest photoluminescence (PL) output at “x” = 0.8, among samples tested. Subsequently, coupled with either zero-dimensional (0D) CdS or CdSe quantum dots (QDs), we successfully synthesized and observed charge transfer processes in 1D CaW1-xMoxO4:Eu3+ (“x” = 0.8)-0D QD composite nanoscale heterostructures. Our results show that CaW1-xMoxO4:Eu3+ (“x” = 0.8) nanowires give rise to PL quenching when CdSe QDs and CdS QDs are anchored onto the surfaces of 1D CaWO4-CaMoO4:Eu3+ nanowires. The observed PL quenching is especially pronounced in CaW1-xMoxO4:Eu3+ (“x” = 0.8)-0D CdSe QD heterostructures. Conversely, the PL output and lifetimes of CdSe and CdS QDs within these heterostructures are not noticeably altered as compared with unbound CdSe and CdS QDs. The differences in optical behavior between 1D Eu3+ activated tungstate and molybdate solid-solution nanowires and the semiconducting 0D QDs within our heterostructures can be correlated with the relative positions of their conduction and valence energy band levels. We propose that the PL quenching can be attributed to a photoinduced electron transfer process from CaW1-xMoxO4:Eu3+ (“x” = 0.8) to both CdSe and CdS QDs, an assertion supported by complementary near edge X-ray absorption fine structure (NEXAFS) spectroscopy measurements.
    Full-text · Article · Feb 2015 · The Journal of Physical Chemistry C
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    ABSTRACT: Two titanium silicalite-1 samples with different crystal sizes were synthesized in the tetrapropylammonium bromide (TPABr) and tetrapropylammonium hydroxide (TPAOH) hydrothermal systems. The small-crystal TS-1 with a size of 600 nm was then treated with different organic bases. These TS-1 samples were evaluated in the epoxidation of propene, and characterized by ultraviolet-visible diffuse reflectance (UV-vis), X-ray absorption near edge structure (XANES) and Raman spectroscopies. The Ti L-edge absorption spectra show that a new Ti species, pentahedrally coordinated Ti, appears in some of the samples. This pentahedrally coordinated Ti species is correlated with the catalytic oxidation activity of TS-1, closely. Tetrahedrally coordinated Ti in TS-1 is the primary active center for selective oxidation reactions, but the existence of a small amount of pentahedrally coordinated Ti can further improve the catalytic activity. A high molar ratio of Si/Ti (n(Si/Ti)) in the synthesis process (n(Si/Ti) = 92.78) was beneficial for the generation of pentahedrally coordinated Ti. The improved catalytic activity of the TPAOH treated TS-1 is mainly due to the increasing amount of pentahedrally coordinated Ti, besides the elimination of diffusion limitation. Slowing down the crystallization rate can also increase the content of pentahedrally coordinated Ti.
    Full-text · Article · Feb 2015 · RSC Advances
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    ABSTRACT: In this report, we synthesize and characterize the structural and optical properties of novel heterostructures composed of (i) semiconducting nanocrystalline CdSe quantum dots (QDs) coupled with (ii) both one- and zero-dimensional (1D and 0D) motifs of self-activated luminescent CaWO4 metal oxides. Specifically, ∼4 nm CdSe QDs have been anchored onto (i) high-aspect ratio 1D nanowires, measuring ∼230 nm in diameter and ∼3 μm in length, as well as onto (ii) crystalline 0D nanoparticles (possessing an average diameter of ∼80 nm) of CaWO4 through the mediation of 3-mercaptopropionic acid (MPA) as a connecting linker. Composite formation was confirmed by complementary electron microscopy and spectroscopy (i.e., IR and Raman) data. In terms of luminescent properties, our results show that our 1D and 0D heterostructures evince photoluminescence (PL) quenching and shortened PL lifetimes of CaWO4 as compared with unbound CaWO4. We propose that a photoinduced electron transfer process occurs from CaWO4 to CdSe QDs, a scenario which has been confirmed by NEXAFS measurements and which highlights a decrease in the number of unoccupied orbitals in the conduction bands of CdSe QDs. By contrast, the PL signature and lifetimes of MPA-capped CdSe QDs within these heterostructures do not exhibit noticeable changes as compared with unbound MPA-capped CdSe QDs. The striking difference in optical behavior between CaWO4 nanostructures and CdSe QDs within our heterostructures can be correlated with the relative positions of their conduction and valence energy band levels. In addition, the PL quenching behaviors for CaWO4 within the heterostructure configuration were examined by systematically varying (i) the quantities and coverage densities of immobilized CdSe QDs as well as (ii) the intrinsic morphology (and by extension, the inherent crystallite size) of CaWO4 itself.
    Full-text · Article · Jan 2015 · Chemistry of Materials
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    ABSTRACT: Using near-edge X-ray absorption fine structure (NEXAFS) spectroscopy, we shed light on the nature of the interaction between CO2 and the amine moieties in a hyperbranched aminosilica (HAS) material, a porous aminosilica composite with great potential for postcombustion carbon capture applications. We show that after dosing a pristine (annealed) HAS sample with CO2, the C K-edge NEXAFS spectrum presents a new π* resonance at 289.9 eV, which can be attributed to the formation of a C═O (carbonyl) bond. Additional analyses of the O K-edge using model samples containing carbamate, carbonate, and bicarbonate functional groups as reference demonstrate a carbamate bonding mechanism for the chemical adsorption of CO2 by the HAS material under the conditions employed. These findings show the capability of the C and O K-edge NEXAFS technique to identify CO2–adsorbate species despite the high concentration of C and O atoms inherently present in the sample (prior to CO2 dosing) and the significant similarities between the possible adsorbates.Keywords: hyperbranched aminosilica; NEXAFS; carbon capture materials; CO2 capture materials; carbon mitigation
    No preview · Article · Jan 2015 · Journal of Physical Chemistry Letters
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    ABSTRACT: In situ temperature-resolved Near-edge X-ray Absorption Fine Structure (NEXAFS) measurements were performed on thermo-active ethylene-vinyl acetate (EVA) - multiwall carbon nanotube (MWCNT) composites 12 months following synthesis, and compared with spectra acquired shortly after synthesis to examine aging effects on non-covalent interactions. Room temperature spectra revealed no difference between unstrained and strained composites, suggesting relaxation. Further, energy shifts in π* C=C resonances indicated a change in π-π interactions between MWCNT walls and chemical dispersant, supported also by AFM phase imaging. Temperature-resolved NEXAFS analysis showed a lack of interaction between nanotubes and polymeric chains, suggesting the chemical dispersant unlatched from MWCNT walls. The extent of this effect is finally quantified through a comparative study of spectral trends.
    No preview · Article · Jan 2015 · MRS Online Proceeding Library
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    ABSTRACT: We adsorbed fluorinated-alkyl (FmSAM) and hydrogenated-alkyl (HmSAM) phosphonic acids with different molecular lengths on anodes of bulk-heterojunction polymer solar cells. We found the fill factors and series resistances of devices having FmSAMs to more steeply depend on molecular length than those having HmSAMs. We attribute this phenomenon to the smaller tunneling decay factor of HmSAM compared to FmSAM, which is consistent with DFT calculations that reveal differences in the extents of electron density localization of the highest occupied molecular orbitals of these species.
    No preview · Article · Nov 2014 · Organic Electronics
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    ABSTRACT: Tracking thermally induced reactions has always been challenging for electrode materials of electrochemical battery systems. Traditionally, a variety of calorimetric techniques and in situ XRD at elevated temperatures has been used to evaluate the thermal stability of electrode materials. These techniques are capable of providing variations in heat capacity, mass and average bulk composition of materials only. Herein, we report investigation of thermal characteristics of Li0.33Ni0.8Co0.15Al0.05O2 by using in situ soft XAS measurements in combination with XRD. Fluorescence yield and partial electron yield measurements are used simultaneously to obtain element selective surface and bulk information. Fluorescence yield measurements reveal no energy change of the absorption peak and thus no valence state change in the bulk. However, electron yield measurements indicate that NiO-type rock salt structure is formed at the surface at temperatures above 200°C while no evidence for a surface reaction near Co sites in investigated temperature range is found. These results clearly show that in situ soft XAS can give a unique understanding of the role of each element in the structural transformation under thermal abuse offering a useful guidance in developing new battery system with improved safety performance.
    Full-text · Article · Oct 2014 · Scientific Reports

Publication Stats

1k Citations
440.73 Total Impact Points

Institutions

  • 2008-2015
    • National Institute of Standards and Technology
      • • Semiconductor and Dimensional Metrology Division
      • • Material Measurement Laboratory (MML)
      • • Materials Science and Engineering Division
      GAI, Maryland, United States
  • 2004-2012
    • North Carolina State University
      • Department of Physics
      Raleigh, North Carolina, United States
  • 2011
    • Princeton University
      • Department of Electrical Engineering
      Princeton, New Jersey, United States
  • 2010
    • University of Houston
      • Department of Electrical & Computer Engineering
      Houston, Texas, United States