Inner-shell excitation studies of conducting organic polymers: selenophene, 3-methyl selenophene, and their polymers

1989 ◽  
Vol 67 (11) ◽  
pp. 1819-1827 ◽  
Author(s):  
A. P. Hitchcock ◽  
G. Tourillon ◽  
W. Braun
Keyword(s):  
Electrical Conductivity ◽  
Polymeric Chain ◽  
Core Excitation ◽  
Structural Units ◽  
X Ray ◽  
Methyl Substitution ◽  
Electrically Conducting ◽  
Electron Energy Loss ◽  
X Ray Absorption ◽  
Electron Energy Loss Spectra

Inner-shell electron energy loss spectra (ISEELS) of gaseous selenophene and 3-methylselenophene in the regions of Se 3d, Se 3p, Se 3s, and C 1s are presented and analyzed. The ISEELS spectra are compared to the C 1s near-edge X-ray absorption fine structure (NEXAFS) spectra of the corresponding polymers deposited electrochemically onto Pt, both with and without doping, to form the electrically conducting state. Methyl substitution at the 3-position of the selenophene ring is found to have little effect on the intensity of the C 1s → π* transition, suggesting that the π manifold is relatively unaffected. The C 1s NEXAFS of thin polyselenophene and poly-3-methylselenophene films confirms that (1) the polymeric chain is composed of the same structural units as the monomers and (2) doping enhances electrical conductivity via a narrowing of the π–π* band gap. Keywords: core excitation, ISEELS, NEXAFS, conducting polymers.

Core excitation studies of poly(ethylene terephthalate) and molecular analogues by EELS

1991 ◽  
Vol 49 ◽  
pp. 1044-1045
Author(s):  
E. G. Rightor ◽  
A. P. Hitchcock ◽  
S. G. Urquhart ◽  
A. T. Wen
Keyword(s):  
Ethylene Terephthalate ◽  
Incident Radiation ◽  
Core Excitation ◽  
X Ray ◽  
Poly Ethylene Terephthalate ◽  
Local Bonding ◽  
Poly Ethylene ◽  
Electron Energy Loss ◽  
X Ray Absorption ◽  
Diamond Knife

The near-edge region of core ionization edges can be used as a probe of the local bonding and structure of atoms excited by incident radiation, such as in electron energy loss spectroscopy (EELS) or x-ray absorption techniques. Recent installation of efficient parallel EELS spectrometers in ATEMs promotes study of these transitions in radiation sensitive materials such as polymers. To study relationships between poly(ethylene terephthalate) [PET] structure and EELS transitions, we compared polymer spectra with molecular analogues.The PET examined (from Scientific Polymer Products) was cut using a diamond knife and a Reichert-Jung Ultracut E ultramicrotome with FC4E cryoattachment. A JEOL 2000FX TEM with a LaB6 filament and a Gatan parallel-EELS system was used to examine PET sections on holey carbon. The gas phase EELS of molecules (from Aldrich, Matheson) was performed under inelastic scattering conditions as described previously.

SURFACE STUDIES BY CORE-EXCITATION REFLECTION ELECTRON ENERGY LOSS SPECTROSCOPY

1995 ◽  
Vol 02 (01) ◽  
pp. 43-61 ◽  
Author(s):  
A.P. HITCHCOCK ◽  
T. TYLISZCZAK
Keyword(s):  
Energy Loss ◽  
Electron Energy ◽  
Electron Energy Loss Spectroscopy ◽  
Inelastic Electron ◽  
Core Excitation ◽  
X Ray ◽  
Molecular Adsorbates ◽  
Momentum Transfer Dependence ◽  
Electron Energy Loss ◽  
X Ray Absorption

Inelastic electron scattering in a reflection geometry is a useful alternative to synchrotron radiation X-ray absorption spectroscopy for inner-shell excitation studies of surfaces. This article reviews the current capabilities of reflection electron energy loss spectroscopy for core-excitation studies of the electronic and geometric structure of surfaces. Issues discussed include: momentum transfer dependence, comparison to X-ray techniques, orientational sensitivity, spatial and energy resolution, and technological applications. Examples of applications to clean surfaces, atomic and molecular adsorbates, and thin films are given.

SIGMAL: A Program for Calculating L-Shell lonization Cross-Sections

1981 ◽  
Vol 39 ◽  
pp. 198-199 ◽  
Author(s):  
R.F. Egerton
Keyword(s):  
Cross Sections ◽  
Fortran Program ◽  
Absorption Data ◽  
X Ray ◽  
Atomic Electrons ◽  
Energy Dependent ◽  
Hydrogenic Model ◽  
Electron Energy Loss ◽  
X Ray Absorption ◽  
Shell Ionization

SIGMAL is a short (∼ 100-line) Fortran program designed to rapidly compute cross-sections for L-shell ionization, particularly the partial crosssections required in quantitative electron energy-loss microanalysis. The program is based on a hydrogenic model, the L1 and L23 subshells being represented by scaled Coulombic wave functions, which allows the generalized oscillator strength (GOS) to be expressed analytically. In this basic form, the model predicts too large a cross-section at energies near to the ionization edge (see Fig. 1), due mainly to the fact that the screening effect of the atomic electrons is assumed constant over the L-shell region. This can be remedied by applying an energy-dependent correction to the GOS or to the effective nuclear charge, resulting in much closer agreement with experimental X-ray absorption data and with more sophisticated calculations (see Fig. 1 ).

Analysis of Extended Energy-Loss Fine Structure of Nanometerscale Clusters

1999 ◽  
Vol 5 (S2) ◽  
pp. 708-709
Author(s):  
Y. Ito ◽  
H. Jain ◽  
D.B. Williams
Keyword(s):  
Fine Structure ◽  
Energy Loss ◽  
Atomic Clusters ◽  
Nanometer Scale ◽  
X Ray ◽  
Small Clusters ◽  
Electron Energy Loss ◽  
X Ray Absorption ◽  
Ionization Edge

Small atomic clusters are of great importance for applications such as catalysts whose activity depends on the surface of the cluster. Attempts to determine the atomic short-range order and size of clusters have been made by analyzing the extended X-ray absorption fine structure (EXAFS). However, the analysis was made on an average of many small clusters. Analysis of extended energy-loss fine structure (EXELFS) in an electron energy-loss spectrum (EELS) has developed to the point where in some cases, the quality of the results is comparable to its X-ray analogue, EXAFS. No other technique provides nanometer-scale spatial resolution of the analyzed area for determining the atomic structure. Most EXELFS analysis has been performed on the K-ionization edge of lighter elements. For heavier elements, a more complex ionization edge such as the L-edge has to be used, due to the inefficiency of collecting high quality EEL spectra at higher energy-losses (Z > 18).

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