Cherno Jaye

National Institute of Standards and Technology, Maryland, United States

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Publications (91)345.45 Total impact

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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.
    Carbon. 05/2015; 86.
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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.
    RSC Advances 02/2015; 5(23). · 3.71 Impact Factor
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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.
    Scientific Reports 10/2014; 4:6827. · 5.08 Impact Factor
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    ABSTRACT: Works of art prepared with acrylic emulsion paints became commercially available in the 1960s. It is increasingly necessary to undertake and optimise cleaning and preventative conservation treatments to ensure their longevity. Model artists' acrylic paint films covered with artificial soiling were thus prepared on a canvas support and exposed to a variety of wet cleaning treatments based on aqueous or hydrocarbon solvent systems. This included some with additives such as chelating agents and/or surfactants, and microemulsion systems made specifically for conservation practice. The impact of cleaning (soiling removal) on the paint film surface was examined visually and correlated with results of attenuated total reflection Fourier transform infrared, XPS and near‐edge X‐ray absorption fine structure analyses – three spectroscopic techniques with increasing surface sensitivity ranging from approximately − 1000, 10 and 5 nm, respectively. Visual analysis established the relative cleaning efficacy of the wet cleaning treatments in line with previous results. X‐ray spectroscopy analysis provided significant additional findings, including evidence for (i) surfactant extraction following aqueous swabbing, (ii) modifications to pigment following cleaning and (iii) cleaning system residues. © 2014 The Authors. Surface and Interface Analysis published by John Wiley & Sons, Ltd.
    Surface and Interface Analysis 10/2014; 46. · 1.39 Impact Factor
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    ABSTRACT: The α-form of crystalline para-aminobenzoic acid (PABA) has been examined as a model system for demonstrating how the core level spectroscopies XPS (X-ray photoelectron spectroscopy) and NEXAFS (near-edge X-ray absorption fine-structure) spectroscopy can be combined with CASTEP DFT (density functional theory) to provide reliable modelling of intermolecular bonding in organic molecular crystals. Through its dependence on unoccupied valence states NEXAFS is an extremely sensitive probe of variations in intermolecular bonding. Prediction of NEXAFS spectra by CASTEP, in combination with core level shifts predicted by WIEN2K, reproduced experimentally observed data very well when all significant intermolecular interactions were correctly taken into account. CASTEP-predicted NEXAFS spectra for the crystalline state were compared with those for an isolated PABA monomer to examine the impact of intermolecular interactions and local environment in the solid state. As expected, the effects of the loss of hydrogen-bonding in carboxylic acid dimers and intermolecular hydrogen bonding between amino and carboxylic acid moieties are evident, with energy shifts and intensity variations of NEXAFS features arising from the associated alterations in electronic structure and bonding.
    The Journal of Physical Chemistry B 09/2014; · 3.38 Impact Factor
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    ABSTRACT: Photo-and thermo-mechanical actuation behaviour in specific polymer-carbon nanotube composites has been observed in recent years and studied at the macroscale. These systems may prove to be suitable components for a wide range of applications, from MOEMs and nanotechnology to neuroscience and tissue engineering. Absence of a unified model for actuation behaviour at a molecular level is hindering development of such smart materials. We observed thermo-mechanical actuation of ethylene-vinyl acetate | carbon nanotube composites through in situ near-edge X-ray absorption fine structure spectroscopy to correlate spectral trends with macroscopic observations. This paper presents spectra of composites and constituents at room temperature to identify resonances in a building block model, followed by spectra acquired during thermo-actuation. Effects of strain-induced filler alignment are also addressed. Spectral resonances associated with C=C and C=O groups underwent synchronised intensity variations during excitation, and were used to propose a conformational model of actuation based on carbon nanotube torsion. Future actuation studies on other active polymer nanocomposites will verify the universality of the proposed model.
    SPIE NanoScience+ Engineering; 09/2014
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    ABSTRACT: Vanadium oxide bronzes, with the general formula MxV2O5, provide a wealth of compositions and frameworks where strong electron correlation can be systematically (albeit thus far only empirically) tuned. In this work, we report the synthesis of single-crystalline δ-Ag0.88V2O5 nanowires and unravel pronounced electronic phase transitions induced in response to temperature and applied electric field. Specifically, a pronounced semiconductor–semiconductor transition is evidenced for these materials at ca. 150 K upon heating, and a distinctive insulator–conductor transition is observed upon application of an in-plane voltage. An orbital-specific picture of the mechanistic basis of the phase transitions is proposed using a combination of density functional theory (DFT) and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. Structural refinements above and below the transition temperature, angle-resolved O K-edge NEXAFS spectra, and DFT calculations suggest that the electronic phase transitions in these 2D frameworks are mediated by a change in the overlap of dxy orbitals.
    The Journal of Physical Chemistry C 08/2014; 118(36):21235. · 4.84 Impact Factor
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    ABSTRACT: Monodispersed strontium titanate nanoparticles were prepared and studied in detail. It is found that ~10 nm as-prepared stoichiometric nanoparticles are in a polar structural state (with possibly ferroelectric properties) over a broad temperature range. A tetragonal structure, with possible reduction of the electronic hybridization is found as the particle size is reduced. In the 10 nm particles, no change in the local Ti-off centering is seen between 20 and 300 K. The results indicate that nanoscale motifs of SrTiO3 may be utilized in data storage as assembled nano-particle arrays in applications where chemical stability, temperature stability and low toxicity are critical issues.
    Applied Physics Letters 08/2014; 105(9). · 3.52 Impact Factor
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    ABSTRACT: Near-edge x-ray absorption fine structure (NEXAFS) spectroscopy provides detailed information about the orientation and alignment of thin films. NEXAFS is a synchrotron based technique - the availability of beam-time per user is typically limited to no more than a few weeks per year. The limited availability is currently a true barrier for using NEXAFS in combinatorial studies of molecular alignment. We have recently demonstrated how large area full field NEXAFS imaging allows users to pursue combinatorial studies of surface chemistry. Now we report an extension of this approach which allows the acquisition of orientation information from a single NEXAFS image. An array with 80 elements (samples) containing eight series of different surface modifications was mounted on a curved substrate allowing the collection of NEXAFS spectra with a range of orientations with respect to the x-ray beam. Images collected from this array show how hyperspectral NEXAFS data collected from curved surfaces can be used for high-throughput molecular orientation analysis.
    ACS Combinatorial Science 07/2014; · 3.40 Impact Factor
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    ABSTRACT: An important and fast-growing technology in the realm of cryogenic detectors has recently been applied to beamline science: the superconducting Transition-Edge Sensor (TES). A TES consists of a thin metal film that is held in the superconducting-to-normal transition by a voltage bias. When a single X-ray photon is absorbed, the temperature and resistance of the film increase, which causes a negative-going current pulse with amplitude proportional to the deposited energy. The thin-film thermometer is typically coupled to a photon absorber composed of a high atomic number element such as bismuth or gold, so efficiencies near unity are possible for X-rays up to 10 keV. TESs are an example of a broader class of sensors called microcalorimeters that measure energetic events through a change in temperature. The energy resolution of a well-designed microcalorimeter is set by thermodynamic power fluctuations between the sensor and the local heat bath as well as by additional noise terms such as the Johnson noise in the sensing element. The energy resolution ΔE of a microcalorimeter is proportional to (kbT2C)1/2 where T is the sensor temperature and C is its specific heat. The temperature dependence of ΔE makes it advantageous to operate TESs at the lowest temperatures that can be conveniently reached, typically 0.1 K. For X-ray measurements between 1–10 keV, the dependence of ΔE on C limits the C of individual sensors to about 10−12 J/K, corresponding to device areas near 0.1 mm2 [1].
    Synchrotron Radiation News 07/2014; 27(4).
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    ABSTRACT: Carbon nanotubes (CNTs) continue to attract significant interests due to their unique combination of extraordinary thermal, electrical, optical, and mechanical properties. The preparation of CNTs coated with magnetically sensitive Fe2O3 nanoparticles has implications to the development of advanced heat transfer nanofluids and high capacity lithium ion batteries. In this paper, various characterization methods confirm that single-walled carbon nanotubes (SWNTs) were uniformly coated with Fe2O3 nanoparticles through solution mixture. Scanning and transmission electron microscopy were used to compare the morphology of pristine SWNTs and as-prepared SWNTs coated with Fe2O3 nanoparticles. Raman spectroscopy and thermo gravimetric analysis presented the extent of defects and the amount of Fe2O3 nanoparticles present in the sample. Near edge X-ray absorption fine structure spectroscopy was used to probe the electronic band structure of as-prepared core-shell structures. Magnetization measurements indicate that the coercive field of SWNTs coated with Fe2O3 nanoparticles was twice that of pristine SWNTs
    ECS Journal of Solid State Science and Technology. 06/2014; 3(8):M39-M44.
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    ABSTRACT: Effects of aging on chemical structure and molecular dynamic behaviour of strained thermally active ethylene-vinyl acetate | multiwall carbon nanotube (EVA|MWCNT) composites were investigated by spectroscopy and microscopy techniques. Aged composites showed spatial inhomogeneity due to system relaxation. Inhomogeneity is attributed to segregation of non-covalently linked cholestryl 1-pyrenecarboxylate, acting as MWCNT dispersant and polymer compatibilizer. Analysis of molecular interplay between filler and matrix upon in situ temperature variation showed a lack of synchronicity, which had been observed in fresh composites. Reduced synchronous interplay allowed quantification of degraded π-π interactions, promoting PyChol unlatching as a result of both sonication and strained-derived π-π degradation.
    APL Materials. 06/2014; 2(6):066105.
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    ABSTRACT: Lithium–sulfur batteries have drawn much attention in advanced energy storage development due to their high theoretical specific capacity; however, several obstacles hinder their applications, including rapid capacity loss due to dissolution of polysulfide into the electrolyte. Nitrogen-doped mesoporous carbon cathode materials were found to effectively immobilize sulfur species and minimize the sulfur loss. In this work, we use X-ray absorption near-edge structure (XANES) spectroscopy to probe the coordination structures of C, O, and N in a carbon cathode before and after the sulfur loading in order to better understand the effects of nitrogen doping. A significant change in oxygen coordination structure is observed, whereas the carbon and nitrogen chemical environments remain unaltered. In addition, the significant change in S K-edge XANES spectra is also observed after sulfur was loaded on nitrogen-doped carbon cathode material. These observations reveal that strong interaction between the nitrogen-doped carbon and sulfur is through oxygen functional groups, and nitrogen doping probably makes oxygen functional groups more reactive toward sulfur.
    The Journal of Physical Chemistry C 04/2014; 118(15):7765–7771. · 4.84 Impact Factor
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    ABSTRACT: NEXAFS spectroscopy was used to investigate the temperature dependence of thermally active ethylene-vinyl acetate | multiwall carbon nanotube (EVA|MWCNT) films. The data shows systematic variations of intensities with increasing temperature. Molecular orbital assignment of interplaying intensities identified the 1s → π*C=C and 1s → π*C=O transitions as the main actors during temperature variation. Furthermore, enhanced near-edge interplay was observed in prestrained composites. Because macroscopic observations confirmed enhanced thermal-mechanical actuation in prestrained composites, our findings suggest that the interplay of C=C and C=O π orbitals may be instrumental to actuation.
    The Journal of Physical Chemistry C 02/2014; 118(7):3733-3741. · 4.84 Impact Factor
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    ABSTRACT: We explore structural changes of the carbon in MnO2/reduced graphene oxide (RGO) hybrid materials prepared by the direct redox reaction between carbon and permanganate ions (MnO4–) to reach better understanding for the effects of carbon corrosion on carbon loss and its bonding nature during the hybrid material synthesis. In particular, we carried out near-edge X-ray absorption fine structure spectroscopy at the C K-edge (284.2 eV) to show the changes in the electronic structure of RGO. Significantly, the redox reaction between carbon and MnO4– causes both quantitative carbon loss and electronic structural changes upon MnO2 deposition. Such disruptions of carbon bonding have a detrimental effect on the initial electrical properties of the RGO and thus lead to a significant decrease in electrical conductivity. Electrochemical measurements of the MnO2/reduced graphene oxide hybrid materials using a cavity microelectrode revealed unfavorable electrochemical properties that were mainly due to the poor electrical conductivity of the hybrid materials. The results of this study should serve as a useful guide to rationally approaching the syntheses of metal/RGO and metal oxide/RGO hybrid materials.
    The Journal of Physical Chemistry C 01/2014; · 4.84 Impact Factor
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    ABSTRACT: Annealing graphene oxide under an ammonia environment provides a facile approach to defunctionalise this material while simultaneously enabling nitrogen incorporation en route to the preparation of chemically derived graphene. Here, we use X-ray photoemission spectroscopy (XPS) in conjunction with near-edge X-ray absorption fine-structure (NEXAFS) spectroscopy to probe both the global recovery of electronic structure in this material as well as to monitor evolution of the local structure of incorporated nitrogen atoms when graphene oxide is reduced under an ammonia gas environment at ambient and low pressures in the temperature range between 250 and 1000 °C. The local structure and extent of recovery of the π-conjugated framework is correlated to electrical conductivity measurements. Angle-resolved C K-edge NEXAFS spectra along with O K-edge NEXAFS and C 1s high-resolution XPS spectra suggest that hydroxyl and epoxide functional groups on the basal plane of graphene oxide are eliminated upon annealing to a temperature of 250 °C, bringing about substantial restoration of the π-conjugated framework of graphene. Furthermore, an increase in the in-plane orientation of constituent graphene oxide flakes is observed up to a temperature of 750 °C for annealing under both sets of conditions and is manifested as a greater spread in the intensity of the C K-edge π* resonance as a function of angle of incidence of the X-ray beam. Angle-resolved N K-edge NEXAFS spectra and high-resolution N 1s XPS spectra supplement the global view of recovery of π-conjugation with a local perspective of the chemical bonding environments of incorporated nitrogen atoms. Three distinct modes of nitrogen incorporation are evidenced: amine or nitrile like (N1), pyridinic (N2), and substitutional/graphitic (N3). The data suggest that nitrogen is initially incorporated as nitrile like functionalities at lower temperatures with these moieties protruding above and below the graphene basal plane; however, the nitrile and amine groups are subsequently transformed at higher temperatures through the elimination of oxygenated functional groups and reconstitution of the sp2-hybridized network to in-plane pyridinic and graphitic moieties. The latter two configurations are seen to substantially enhance the conductivity of reduced graphene oxide.
    RSC Advances 01/2014; 4(2):634. · 3.71 Impact Factor
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    ABSTRACT: This work describes the near conduction band edge structure of electrospun mats of MWCNT-PDMS-PMMA by near edge X-Ray absorption fine structure (NEXAFS) spectroscopy. Effects of adding nanofillers of different sizes were addressed. Despite observed morphological variations and inhomogeneous carbon nanotube distribution, spun mats appeared homogeneous under NEXAFS analysis. Spectra revealed differences in emissions from glancing and normal spectra; which may evidence phase separation within the bulk of the micron-size fibers. Further, dicroic ratios show polymer chains did not align, even in the presence of nanofillers. Addition of nanofillers affected emissions in the C-H, C=O and C-C regimes, suggesting their involvement in interfacial matrix-carbon nanotube bonding. Spectral differences at glancing angles between pristine and composite mats suggest that geometric conformational configurations are taking place between polymeric chains and carbon nanotubes. These differences appear to be carbon nanotube-dimension dependent, and are promoted upon room-temperature mixing and shear flow during electrospinning. CH- π bonding between polymer chains and graphitic walls, as well as H-bonds between impurities in the as-grown CNTs and polymer pendant groups are proposed bonding mechanisms promoting matrix conformation.
    Langmuir 12/2013; 29(51). · 4.38 Impact Factor
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    ABSTRACT: The systematic insertion of thin films of P3HT and PCBM at the electron- and hole-collecting interfaces, respectively, in bulk-heterojunction polymer solar cells results in different extents of reduction in device characteristics, with the insertion of P3HT at the electron-collecting interface being less disruptive to the output currents compared to the insertion of PCBM at the hole-collecting interface. This asymmetry is attributed to differences in the tail state-assisted charge injection and recombination at the active layer-electrode interfaces. P3HT exhibits a higher density of tail states compared to PCBM; holes in these tail states can thus easily recombine with electrons at the electron-collection interface during device operation. This process is subsequently compensated by the injection of holes from the cathode into these tail states, which collectively enables net current flow through the polymer solar cell. The study presented herein thus provides a plausible explanation for why preferential segregation of P3HT to the cathode interface is inconsequential to device characteristics in P3HT:PCBM bulk-heterojunction solar cells.
    Laser Physics Review 12/2013; 3(12). · 14.39 Impact Factor
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    ABSTRACT: We use scanning tunneling microscopy and x-ray spectroscopy to characterize the atomic and electronic structure of boron-doped and nitrogen-doped graphene created by chemical vapor deposition on copper substrates. Microscopic measurements show that boron, like nitrogen, incorporates into the carbon lattice primarily in the graphitic form and contributes ~0.5 carriers into the graphene sheet per dopant. Density functional theory calculations indicate that boron dopants interact strongly with the underlying substrate while nitrogen dopants do not. The local bonding differences between graphitic boron and nitrogen dopants lead to large scale differences in dopant distribution. The distribution of dopants is observed to be completely random in the case of boron, while nitrogen displays strong sublattice clustering. Structurally, nitrogen-doped graphene is relatively defect-free while boron-doped graphene films show a large number of Stone-Wales defects. These defects create local electronic resonances and cause electronic scattering, but do not electronically dope the graphene film.
    Nano Letters 09/2013; · 13.03 Impact Factor
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    ABSTRACT: The oxidative chemistry of graphite has been investigated for over 150 years and has attracted renewed interest given the importance of exfoliated graphene oxide as a precursor to chemically derived graphene. However, the bond connectivities, steric orientations, and spatial distribution of functional groups remain to be unequivocally determined for this highly inhomogeneous nonstoichiometric material. Here, we demonstrate the application of principal component analysis to scanning transmission X-ray microscopy data for the construction of detailed real space chemical maps of graphene oxide. These chemical maps indicate very distinct functionalization motifs at the edges and interiors and, in conjunction with angle-resolved near-edge X-ray absorption fine structure spectroscopy, enable determination of the spatial location and orientations of functional groups. Chemical imaging of graphene oxide provides experimental validation of the modified Lerf–Klinowski structural model. Specifically, we note increased contributions from carboxylic acid moieties at edge sites with epoxide and hydroxyl species dominant within the interior domains.
    Journal of Physical Chemistry Letters 08/2013; 4(18):3144. · 6.69 Impact Factor

Publication Stats

716 Citations
345.45 Total Impact Points


  • 2008–2014
    • National Institute of Standards and Technology
      • • Material Measurement Laboratory (MML)
      • • Semiconductor and Dimensional Metrology Division
      • • Materials Science and Engineering Division
      Maryland, United States
  • 2012
    • New Jersey Institute of Technology
      • Department of Physics
      Newark, NJ, United States
  • 2004–2012
    • North Carolina State University
      • Department of Physics
      Raleigh, North Carolina, United States
  • 2009
    • University at Buffalo, The State University of New York
      • Department of Chemistry
      Buffalo, NY, United States
    • Brookhaven National Laboratory
      New York City, New York, United States