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Fu-rong Chen - One of the best experts on this subject based on the ideXlab platform.

  • Atomic and Electronic Structure of Interfaces at Sic Studied by Indirect Super Hrtem and Electron Spectroscopyn Imaging
    MRS Online Proceedings Library, 2011
    Co-Authors: J. Y. Yan, Fu-rong Chen, Hideki Ichinose, J. J. Kai, Eriko Takuma
    Abstract:

    Obtaining electronic and atomic structure of material simultaneously is very important for developing the nano-technology. In this paper, we demonstrate that atomic and electronic structure of an interface can be extracted with combination of Gerchberg-Saxton indirect microscopy and electron spectroscopy imaging (ESI) technique. Basically, Gerchberg-Saxton algorithm includes two projections. Projection in the real space is a maximum entropy (ME) de-convolution process and in reciprocal space is an amplitude substitution process. It has been shown that Gerchberg-Saxton algorithm can extend the structural resolution to near 0.1nm. An application case of Gerchberg-Saxton algorithm to solve the atomic structure for 3C-polytypic SiC boundary is shown. ESI Spectrum processed by FFT interpolation, maximum entropy de-convolution and wavelet transformation allow us to extract 2-dimensional map of the sp^2/sp^3 with a sub-nanometer resolution. Grain boundary and interface at SiC are good candidates for this study, since the bond distance of Si-C is slightly less than 0.1nm which is not routinely resolvable using a FEG TEM and Si-L (99eV) and C-K-edges (283 eV) locate in a reasonable energy range. The resultant electronic structure can be compared with that calculated using WIEN97. An example of quantitative analysis on 2-dimensional sp^3/sp^2 map deduced from the C K-edge of ESI spectra acquired from 6H-SiC is given.

  • Valence state map of iron oxide thin film obtained from electron spectroscopy imaging series.
    Micron (Oxford England : 1993), 2006
    Co-Authors: Ko Feng Chen, Ji Jung Kai, Li Chang, Ray F. Egerton, Juhn-jong Lin, Fu-rong Chen
    Abstract:

    Abstract This paper demonstrates the applicability of electron-spectroscopic imaging (ESI) for valence-state mapping of the iron oxide system. We have previously developed a set of signal-processing methods for an ESI series, to allow mapping of sp 2 /sp 3 ratio, dielectric function and energy bandgap. In this study, these methods are applied to generate a valence-state map of an iron oxide thin film (Fe/α-Fe 2 O 3 ). Two problems, data undersampling and a convolution effect associated with extraction of the image-Spectrum from the core loss image series, were overcome by using cubic-polynomial interpolation and maximum-entropy deconvolution. As a result, the reconstructed image-Spectrum obtained from the ESI series images has a quality as good as that of conventional electron energy-loss spectra. The L 3 / L 2 ratio of the reconstructed ESI Spectrum is determined to be 3.30 ± 0.30 and 5.0 ± 0.30 for Fe and α-Fe 2 O 3 , respectively. Our L 3 / L 2 ratio mapping shows an accurate correspondence across the Cu/Fe/α-Fe 2 O 3 region. The effect of delocalization and chromatic aberration on the ESI resolution is discussed and estimated to be about 2 nm for the case of L 3 / L 2 ratio mapping.

  • Mapping of sp2/sp3in DLC thin film by signal processed ESI series energy-loss image
    Journal of Electron Microscopy, 2002
    Co-Authors: Jing Yi Yan, Fu-rong Chen, Ji Jung Kai
    Abstract:

    A set of signal processing methods comprising fast Fourier transform inter- polation, maximum entropy deconvolution and wavelet transformation has been successfully integrated to improve the equality of the extracted C K-edge spectra from electron spectroscopic imaging (ESI) series. Fast Fou- rier transform interpolation is used to improve the dispersion arising from discrete sampling of ESI series in the energy space. The maximum entropy method is used to dispel the convolution effect resulting from that ESI series acquired with a finite energy window. Wavelet transformation is applied to de-noise the extracted ESI Spectrum. The post-processed ESI Spectrum has quality as good as that of a probe-acquired Spectrum and makes semi-quantitative analysis of the two-dimensional sp2/sp3 ratio map in diamond-like carbon thin film possible. In general, this method is appli- cable for reconstructing good quality core-loss electron energy-loss spectra from a nanometre-sized area, so that it may be possible to quantitatively analyse two-dimensional information about electronic structure in materi- als with near nanometre resolution.

Jens Nielsen - One of the best experts on this subject based on the ideXlab platform.

  • The yeast metabolome addressed by electrospray ionization mass spectrometry: Initiation of a mass spectral library and its applications for metabolic footprinting by direct infusion mass spectrometry
    Metabolomics, 2008
    Co-Authors: Jesper Højer-pedersen, Jørn Smedsgaard, Jens Nielsen
    Abstract:

    Mass spectrometry (MS) has been a major driver for metabolomics, and gas chromatography (GC)-MS has been one of the primary techniques used for microbial metabolomics. The use of liquid chromatography (LC)-MS has however been limited, but electrospray ionization (ESI) is very well suited for ionization of microbial metabolites without any previous derivatization needed. To address the capabilities of ESI-MS in detecting the metabolome of Saccharomyces cerevisiae , the in silico metabolome of this organism was used as a template to present a theoretical metabolome. This showed that in combination with the specificity of MS up to 84% of the metabolites can be identified in a high mass accuracy ESI-Spectrum. A total of 66 metabolites were systematically analyzed by positive and negative ESI-MS/MS with the aim of initiating a spectral library for ESI of microbial metabolites. This systematic analysis gave insight into the ionization and fragmentation characteristics of the different metabolites. With this insight, a small study of metabolic footprinting with ESI-MS demonstrated that biological information can be extracted from footprinting spectra. Statistical analysis of the footprinting data revealed discriminating ions, which could be assigned using the in silico metabolome. By this approach metabolic footprinting can advance from a classification method that is used to derive biological information based on guilt-by-association, to a tool for extraction of metabolic differences, which can guide new targeted biological experiments.

S. Kusum Perera - One of the best experts on this subject based on the ideXlab platform.

  • Identification of unknowns in atmospheric pressure ionization mass spectrometry using a mass to structure search engine.
    Analytical chemistry, 2008
    Co-Authors: Wenta Liao, William M. Draper, S. Kusum Perera
    Abstract:

    This study evaluates a new model for identifying unknown compounds in atmospheric pressure ionization mass spectrometry based on a mass-to-structure (MTS) paradigm. In this method, rudimentary ESI Spectrum interpretation is required to recognize key spectral features such as MH (+), MNa (+), and MNH 4 (+), which lead to the unknown's monoisotopic mass. The unknown's mass is associated directly with known organic compounds using an Access 2003 database containing records of 19,438 substances assembled from common sources such as the Merck Index, pesticide and pharmaceutical compilations, and chemical catalogues. A user-defined mass tolerance (+/-0.001-0.5 Da) is set according to the instrument mass accuracyunit mass resolution data require a wide mass tolerance ( approximately 0.5 Da) while tolerances for accurate mass data can be as narrow as +/-0.001 Da. Candidate structures retrieved with the MTS Search Engine appear in a report window providing formulas, mass error, and Internet links. This paper provides examples of structure elucidation with 15 organic compounds based on ESI mass spectra from both unit mass resolution (e.g., quadrupole ion trap and triple-stage quadrupole) and accurate mass instruments (e.g., TOF and Q-TOF). Orthogonal information (e.g., isotope ratios and fragmentation data) is complementary and useful for ranking candidates and confirming assignments. The MTS Search Engine identifies unknowns quickly and efficiently, and supplements existing interpretation schemes for unknown identification.

Paul A. Price - One of the best experts on this subject based on the ideXlab platform.

  • High-Resolution Spectroscopy of GRB030226: Features of a Massive Star Progenitor or Intervening Absorption Systems?
    arXiv: Astrophysics, 2006
    Co-Authors: Min-su Shin, Edo Berger, Bryan E. Penprase, Derek B. Fox, Paul A. Price, Shri Kulkarni, Alicia M. Soderberg, Michael J. West, Patrick Côté, Andrés Jordán
    Abstract:

    We present a high-resolution Keck/ESI Spectrum of GRB, which exhibits four absorption systems at z=1.04329, 1.95260, 1.96337, and 1.98691. The two highest redshift systems, separated by about 2400 km/s, have been previously suspected as kinematic features arising in the circumstellar wind around the progenitor star. However, the high column densities of low-ionization species (including possibly neutral hydrogen) in the blue-shifted system, are inconsistent with the expected highly ionized state of the circumstellar wind from the massive progenitor star, even prior to the GRB explosion. This conclusion is also supported by the lack of detectable absorption from fine-structure transitions of SiII and FeII. Instead we conclude that the two redshift systems are similar to multiple DLAs found in QSO sight lines with a similar velocity separation and chemical abundance of [Cr/Fe] and [Zn/Fe]. The absorption system at z=1.96337 is likely an intervening low-mass galaxy, possibly related to the GRB host as part of a forming large-scale structure.

  • Time-Dependent Optical Spectroscopy of GRB 010222: Clues to the GRB Environment
    The Astrophysical Journal, 2002
    Co-Authors: Nestor Mirabal, J. P. Halpern, S. R. Kulkarni, Sandra Castro, J. S. Bloom, S. G. Djorgovski, Titus Galama, Fiona A. Harrison, Dale A. Frail, Paul A. Price
    Abstract:

    We present sequential optical spectra of the afterglow of GRB 010222 obtained one day apart using the Low Resolution Imaging Spectrometer (LRIS) and the Echellette Spectrograph and Imager (ESI) on the Keck telescopes. Three low-ionization absorption systems are spectroscopically identified at z1=1.47688, z2=1.15628, and z3=0.92747. The higher resolution ESI Spectrum reveals two distinct components in the highest redshift system at z1a=1.47590 and z1b=1.47688. We interpret the z1b=1.47688 system as an absorption feature of the disk of the host galaxy of GRB 010222. The best fitted power-law optical continuum and [Zn/Cr] ratio imply low dust content or a local gray dust component near the burst site. In addition, we do not detect strong signatures of vibrationally excited states of H_2. If the GRB took place in a superbubble or young stellar cluster, there are no outstanding signatures of an ionized absorber, either. Analysis of the spectral time dependence at low resolution shows no significant evidence for absorption-line variability. This lack of variability is confronted with time-dependent photoionization simulations dESIgned to apply the observed flux from GRB 010222 to a variety of assumed atomic gas densities and cloud radii. The absence of time dependence in the absorption lines implies that high-density environments are disfavored. In particular, if the GRB environment was dust free, its density was unlikely to exceed nH=10^2 cm^-3. If depletion of metals onto dust is similar to Galactic values or less than solar abundances are present, then nH > 2 x 10^4 cm^-3 is probably ruled out in the immediate vicinity of the burst.

Ji Jung Kai - One of the best experts on this subject based on the ideXlab platform.

  • Valence state map of iron oxide thin film obtained from electron spectroscopy imaging series.
    Micron (Oxford England : 1993), 2006
    Co-Authors: Ko Feng Chen, Ji Jung Kai, Li Chang, Ray F. Egerton, Juhn-jong Lin, Fu-rong Chen
    Abstract:

    Abstract This paper demonstrates the applicability of electron-spectroscopic imaging (ESI) for valence-state mapping of the iron oxide system. We have previously developed a set of signal-processing methods for an ESI series, to allow mapping of sp 2 /sp 3 ratio, dielectric function and energy bandgap. In this study, these methods are applied to generate a valence-state map of an iron oxide thin film (Fe/α-Fe 2 O 3 ). Two problems, data undersampling and a convolution effect associated with extraction of the image-Spectrum from the core loss image series, were overcome by using cubic-polynomial interpolation and maximum-entropy deconvolution. As a result, the reconstructed image-Spectrum obtained from the ESI series images has a quality as good as that of conventional electron energy-loss spectra. The L 3 / L 2 ratio of the reconstructed ESI Spectrum is determined to be 3.30 ± 0.30 and 5.0 ± 0.30 for Fe and α-Fe 2 O 3 , respectively. Our L 3 / L 2 ratio mapping shows an accurate correspondence across the Cu/Fe/α-Fe 2 O 3 region. The effect of delocalization and chromatic aberration on the ESI resolution is discussed and estimated to be about 2 nm for the case of L 3 / L 2 ratio mapping.

  • Mapping of sp2/sp3in DLC thin film by signal processed ESI series energy-loss image
    Journal of Electron Microscopy, 2002
    Co-Authors: Jing Yi Yan, Fu-rong Chen, Ji Jung Kai
    Abstract:

    A set of signal processing methods comprising fast Fourier transform inter- polation, maximum entropy deconvolution and wavelet transformation has been successfully integrated to improve the equality of the extracted C K-edge spectra from electron spectroscopic imaging (ESI) series. Fast Fou- rier transform interpolation is used to improve the dispersion arising from discrete sampling of ESI series in the energy space. The maximum entropy method is used to dispel the convolution effect resulting from that ESI series acquired with a finite energy window. Wavelet transformation is applied to de-noise the extracted ESI Spectrum. The post-processed ESI Spectrum has quality as good as that of a probe-acquired Spectrum and makes semi-quantitative analysis of the two-dimensional sp2/sp3 ratio map in diamond-like carbon thin film possible. In general, this method is appli- cable for reconstructing good quality core-loss electron energy-loss spectra from a nanometre-sized area, so that it may be possible to quantitatively analyse two-dimensional information about electronic structure in materi- als with near nanometre resolution.