Photoemission and C 1s near-edge absorption from photopolymerized C60 films

Itchkawitz, B. S.; Long, J. P.; Schedel‐Niedrig, Th.; Kabler, M. N.; Bradshaw, Alexander M.; Schlögl, Robert; Hunter, W. R.

doi:10.1016/0009-2614(95)00788-6

Cited by 35 publications

(20 citation statements)

References 30 publications

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“…Moreover, the shape of the C 1s peak became asymmetric to higher binding energy. Only narrow broadening of the C 1s peak was found for photopolymerized C 60 [16,17]. The calculated chemical shifts of the C 1s binding energy of + 0.3 eV per four-membered ring in C 60 polymers with respect to the isolated C 60 molecule [18] can only partially explain the broadening.…”

Section: Resultsmentioning

confidence: 82%

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X-ray photoelectron spectroscopy and near-edge X-ray-absorption fine structure of C 60 polymer films

Ramm¹,

Ata²,

Groß

et al. 2000

Applied Physics A: Materials Science & Processing

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We report core-level and valence-band X-ray photoelectron spectroscopy (XPS) and carbon K near-edge X-ray-absorption fine structure spectroscopy (NEXAFS) results of plasma-polymerized C 60 . In comparison with evaporated C 60 the C 1s peak is broader and asymmetric for the C 60 polymer and its shake-up satellites diminished. Furthermore, the features of the valence-band as well as the features of the π * antibonding orbitals of the C 60 polymer are broader and reduced in intensity. Changes in the electronic structure are attributed to the polymerization of C 60 , the post-plasma functionalization of the surface by oxygen after exposure to atmosphere, and the occurrence of amorphous carbon. PACS: 73.61.Wp; 68.35.-p; 82.35.+t The fullerene C 60 can be polymerized by different routes including: photo-polymerization [1], hydrostatic pressure [2], charge transfer from alkali-metal dopants to the C 60 molecules [3], plasma [4], and electrochemical process [5].A [2 + 2] cycloaddition via electronically excited triplet states is considered to be the most likely pathway of the polymerization in the photopolymer [1] and subsequent highpressure-high-temperature-(HPHT) induced polymer [6]. The [2 + 2] cycloaddition reaction results in the formation of a cyclobutane ring requiring a sp 2 − sp 3 rehybridization at the 6 − 6 double bonds of C 60 , which form the intermolecular C−C bonds. The formation of the intermolecular bonds leads to a reduced molecular symmetry.In this study, C 60 was polymerized using the plasma deposition technique. The application of radio-frequency (rf) plasma has increased greatly in materials and device processing. However, the physics of the rf plasma and the chemical mechanisms of deposition are not understood in whole, which makes a controlled deposition difficult.Very little is known explicitly about the structure of plasma-polymerized C 60 . In the plasma, various interactions between the vaporized fullerenes and the plasma particles (energetic neutrals, ions, electrons) and photons as well as the already-deposited material occur. The effects of these interactions are dependent on the geometry and the process parameters. Besides the polymerization reaction, undesirable processes such as fullerene fragmentation, substrate heating, re-emission and sputtering of the deposited material, and process gas incorporation have to be considered.Various experimental techniques have been used to characterize the structure of fullerene polymers. In particular, Raman spectroscopy has been widely used [7]. Near-edge X-ray-absorption fine structure spectroscopy (NEXAFS) has proven to be especially useful in examining the electronic structure of carbon materials because it gives a deep insight into the π * and σ * antibonding orbitals and distinguishes between sp 2 and sp 3 bonding with similar sensitivity [8,9].We performed core-level and valence-band X-ray photoelectron spectroscopy (XPS) and C K near-edge X-rayabsorption fine structure spectroscopy to investigate the polymerization and to characterize the chan...

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Section: Resultsmentioning

confidence: 82%

“…In addition to the carbon states, the O 2s peak appears at about 27 eV. Changes in the valenceband upon photopolymerization were observed by UPS [17,21,22] and XPS [16]. These investigations showed that additional features appear and the structures become broadened and reduced in amplitude.…”

Section: Resultsmentioning

confidence: 88%

X-ray photoelectron spectroscopy and near-edge X-ray-absorption fine structure of C 60 polymer films

Ramm¹,

Ata²,

Groß

et al. 2000

Applied Physics A: Materials Science & Processing

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“…Second, the dimerization itself also introduces changes to the electronic structure, observed as spectral broadening and the appearance of two extra structures in between the three highest valence band peaks in photoemission. 5 As compared to C 60 , the gap between occupied and unoccupied states is smaller in ͑C 59 N͒ 2 . 6 This is also confirmed by optical and electron energy loss experiments: ͑C 59 N͒ 2 shows a clear onset at 1.4-1.55 eV and a further strong peak at 1.8 eV which are both optically allowed, whereas in C 60 the onset at 1.55 eV is extremely weak and the nearest optically allowed transition does not occur until 2 eV.…”

Section: Introductionmentioning

confidence: 90%

Resonant processes and Coulomb interactions in (C59N)2

Schulte

Wang

Moriarty

et al. 2007

The Journal of Chemical Physics

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We have determined the on-site molecular Coulomb interaction energy U of a ͑C 59 N͒ 2 bulk film and find values ranging from 1.10± 0.10 eV for the highest occupied molecular orbital to 1.35± 0.10 eV for the deeper lying orbitals, comparable to values found in C 60 . The on-site Coulomb interaction between a carbon core hole and valence electrons, U c , is, however, substantially lower than in C 60 at 1.35± 0.07 eV. Resonant photoemission ͑RESPES͒ results show a weakened participator decay channel, especially around the N 1s threshold, where resonance of the highest occupied molecular orbital shoulder is absent. Near-edge x-ray absorption fine structure and constant initial state measurements, taken in parallel with the RESPES data, indicate, however, that matrix element effects cannot be ruled out.

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“…This is particularly interesting considering that similar effects have not been observed in a chemisorbed monolayer, where C 60 is covalently bound to a metal surface, 32,54 nor in the photopolymer. 62,63 In covalent C 60 monolayers on metals, the C 1s line width is smaller than that in metallic systems (see, e.g., refs 32 and 54), and the full-width-at-halfmaximum of the C 1s line in photopolymerized C 60 is only slightly larger 62,63 (by less than 0.1 eV) that that of pristine C 60 . The difference with the Li 4 C 60 case, where two distinct C 1s lines are observed, could be related to the presence of the light Li counterions, which may occupy an off-centered position in the interstitial sites toward electron-rich regions in the polymer network (see discussion below).…”

Section: Mev)mentioning

confidence: 99%

Low Band Gap and Ionic Bonding with Charge Transfer Threshold in the Polymeric Lithium Fulleride Li₄C₆₀

Macovez¹,

Savage

Schiessling

et al. 2008

J. Phys. Chem. C

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Low band gap and ionic bonding with charge transfer, threshold in the polymeric lithium fulleride Li(4)C(60) Macovez, Roberto; Savage, Rebecca; Schiessling, Joachim; Kamaras, Katalin; Rudolf, Petra; Venema, L.C. Take-down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons the number of authors shown on this cover page is limited to 10 maximum. September 22, 2007; In Final Form: NoVember 19, 2007 We demonstrate the growth of crystalline Li 4 C 60 films. The low-energy electron diffraction pattern of the films indicates the formation of polymer chains in the plane of the surface, consistent with the reported crystal structure. Electron energy loss and photoemission spectra identify the Li 4 C 60 polymer as a low band gap semiconductor, with a relatively strong coupling of electrons to low-frequency stretching modes of the polymer bonds and alkali phonons. No evidence is found for hybridization between the Li-and fullerenederived electronic states. Instead, a partial charge transfer takes place, which is the same for different Li concentrations. This result rationalizes the stability of the polymer phase over a wide range of stoichiometries.

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Photoemission and C 1s near-edge absorption from photopolymerized C60 films

Cited by 35 publications

References 30 publications

X-ray photoelectron spectroscopy and near-edge X-ray-absorption fine structure of C 60 polymer films

X-ray photoelectron spectroscopy and near-edge X-ray-absorption fine structure of C 60 polymer films

Resonant processes and Coulomb interactions in (C59N)2

Low Band Gap and Ionic Bonding with Charge Transfer Threshold in the Polymeric Lithium Fulleride Li₄C₆₀

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Photoemission and C 1s near-edge absorption from photopolymerized C60 films

Cited by 35 publications

References 30 publications

X-ray photoelectron spectroscopy and near-edge X-ray-absorption fine structure of C 60 polymer films

X-ray photoelectron spectroscopy and near-edge X-ray-absorption fine structure of C 60 polymer films

Resonant processes and Coulomb interactions in (C59N)2

Low Band Gap and Ionic Bonding with Charge Transfer Threshold in the Polymeric Lithium Fulleride Li4C60

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Low Band Gap and Ionic Bonding with Charge Transfer Threshold in the Polymeric Lithium Fulleride Li₄C₆₀