Cherno Jaye

National Institute of Standards and Technology, Maryland, United States

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Publications (85)270.6 Total impact

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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;
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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). · 3.79 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; · 3.64 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: 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.
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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: 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; · 4.38 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. · 6.59 Impact Factor
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    ABSTRACT: Resistivity and Seebeck coefficient measurements on Ca3Co4−xFexO9 (x = 0, 0.05, 0.1, 0.2 and 0.25) reveal enhanced thermoelectric performance with an optimal x value of 0.2. X-ray diffraction measurements show continuous Fe doping into the host lattice, while X-ray absorption experiments reveal that Fe substitutes for Co in the Ca2CoO3 (rock salt) block. The Fe substitution for Co produces electron doping. The local structure around Fe in the Ca2CoO3 block becomes disordered, while the structure in the conducting CoO2 layer becomes more ordered. The structural change in the CoO2 layer plays the key role to enhance the electron transport. The highest ordered structure is achieved at x = 0.2 with the lowest resistivity. Soft X-ray absorption measurements find no Co site spin-state change with Fe doping. Thermoelectric property enhancement associated with doping induced structural change points to a new approach for creating materials with improved ZT in complex oxide systems.
    J. Mater. Chem. C. 06/2013; 1(26):4114-4121.
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    ABSTRACT: Near-edge x-ray absorption fine structure (NEXAFS) spectroscopy, as a technique, offers detailed information about the bonding environment of molecules at a surface. However, because it is a synchrotron based method beam-time is limited and users must typically prioritize and narrow the scopes of experiments. In this study we demonstrate a novel method that opens up the possibility of using large area NEXAFS imaging to pursue combinatorial studies. To explore the capabilities of the NIST full field NEXAFS microscope available at the National Synchrotron Light Source as a high throughput imaging instrument, we collected NEXAFS images from a sample array consisting of 144 different elements with a periodic sequence of different surface modifications. NEXAFS images collected from this model system illustrate how hyperspectral NEXAFS data can be used for parallel analysis of large numbers of samples either directly from the overall image or by extracting spectra from regions of interest.
    Analytical Chemistry 04/2013; · 5.70 Impact Factor
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    ABSTRACT: Single-phase [Ca2CoO3][CoO2]1.61 (Ca3Co4O9) materials doped by transition metals were prepared by solid state reaction followed by annealing under oxygen. The temperature dependent thermoelectric properties, including resistivity (ρ), Seebeck coefficient (S) and thermal conductivity (κ), were measured. In order to understand the origin of the changes in ZT with doping, local (XAS) and long range (XRD) structural measurements as a function of doping were conducted. The electronic properties were probed by x-ray spectroscopic methods. Identification of the locations of the dopant sites and the impact on ZT will be discussed. This work is supported by DOE Grant DE-FG02-07ER46402. The Physical Properties Measurements System was acquired under NSF MRI Grant DMR-0923032 (ARRA award).
    03/2013;
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    ABSTRACT: Bias stress, during which a reduction in source-drain current is observed under continuous application of gate voltage in organic thin-film transistors, originates from trapped mobile charges. Organic semiconductors often exhibit tail states that extend into their band gap; these tail states can act as traps to immobilize charge. Alternatively, defects at the organic semiconductor-dielectric interface can also trap charge. Whether bias stress originates from impurities or defects in the bulk of the organic semiconductor or at the organic semiconductor-dielectric interface, however, remains unclear. By building and testing organic single-carrier diodes having different active layer thicknesses, we can infer the trapping contributions in the bulk of the organic semiconductor relative to those at the organic semiconductor-electrode interface. In conjunction with device characteristics of organic thin-film transistors having different dielectrics, we found that the broad distribution of tail states that is present in poly(3-hexyl thiophene), P3HT, is responsible for bias stress in P3HT-comprising devices. On the other hand, traps at the [6,6]-phenyl-C61-butyric acid methyl ester, PCBM,-dielectric interface are more dominant than those in the bulk in PCBM-containing devices.
    03/2013;
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    ABSTRACT: Self-assembled monolayers (SAMs) of alkyl and fluorinated thiols were investigated after ozonolysis shadow mask treatments with varying areal domains and after exposure to displacing thiols. Imaging near edge X-ray absorption fine structure (NEXAFS) spectroscopy was used as a novel method for investigating the resulting heterogeneous SAM films. Composition and work function were characterized via X-ray and ultraviolet photoelectron spectroscopy, respectively. Imaging NEXAFS characterization of these heterogeneous films clearly shows the displacement of oxidized thiols after ozonolysis patterning. Changes in the SAM after patterning, and after displacement from back-filling thiols, can be inferred from changes in the effective work function. Larger changes in work function were observed for cases where thiols were deposited after ozonolysis suggesting that the displacing SAM was denser and/or more ordered than as-deposited films. These results highlight one of the first demonstrations of imaging NEXAFS and present measurements of effective work function on intentionally heterogeneous SAM films. Copyright © 2013 John Wiley & Sons, Ltd.
    Surface and Interface Analysis 03/2013; · 1.39 Impact Factor
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    ABSTRACT: We have used flip chip lamination (FCL) to form monolayer and bilayer molecular junctions of carboxylic acid-containing molecules with Cu atom incorporation. Carboxylic acid-terminated monolayers are self-assembled onto ultrasmooth Au by using thiol chemistry and grafted onto n-type Si. Prior to junction formation, monolayers are physically characterized by using polarized infrared absorption spectroscopy, X-ray photoelectron spectroscopy, and near-edge X-ray absorption fine structure spectroscopy, confirming the molecular quality and functional group termination. FCL was used to form monolayer junctions onto H-terminated Si or bilayer junctions of carboxylic acid monolayers on Au and Si. From the electrical measurements, we find that the current through the junction is attenuated as the effective molecular length within the junction increases, indicating that molecules are electrically active within the junction. We find that the electronic transport through the bilayer junction saturates at very thick effective distances possibly because of another electron-transport mechanism that is not nonresonant tunneling as a result of trapped defects or sequential tunneling. In addition, bilayer junctions are fabricated with and without Cu atoms, and we find that the electron transport is not distinguishably different when Cu atoms are within the bilayer.
    Langmuir 01/2013; · 4.38 Impact Factor
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    ABSTRACT: A series of well-defined perfluoroalkyl end-functionalized poly(3-hexylthiophenes) (P3HT) were synthesized by Stille coupling of stannylated 2-perfluoralkylthiophene with the bromine end of P3HT. The length of the perfluoroalkyl end group was varied from −C4F13 to −C8F17. These polymers were fully characterized and tested in bulk heterojunction solar cells with phenyl-C61-butyric acid methyl ester (PCBM) as the acceptor. Performance of the solar cells was highest for the unmodified P3HT and decreased as the length of the perfluoroalkyl end increased. The most affected device parameters were the short-circuit current density (Jsc) and series resistance, pointing to lower charge carrier mobility and poor morphology as the cause for the lower performance. While the morphology of blends did not significantly change with perfluoroalkyl end modification, analysis of blended films by energy-filtered transmission electron microscopy (EF-TEM) revealed wider P3HT domains, consistent with the perfluorinated end groups segregating to the edge or exterior of P3HT domains, causing two domains to join. This study demonstrates that the perfluoroalkyl end group can be detrimental to polymer solar cell device performance, and further work toward understanding the interface between the donor and acceptor phases is required to fully understand this effect.
    Macromolecules 01/2013; 46(1):103-112. · 5.93 Impact Factor

Publication Stats

180 Citations
270.60 Total Impact Points

Institutions

  • 2008–2014
    • National Institute of Standards and Technology
      • • Material Measurement Laboratory (MML)
      • • Materials Science and Engineering Division
      Maryland, United States
  • 2012
    • New Jersey Institute of Technology
      • Department of Physics
      Newark, NJ, United States
  • 2009–2011
    • 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
  • 2004–2007
    • North Carolina State University
      Raleigh, North Carolina, United States