Mechanisms of vibrational and electronic excitations of polystyrene films in high resolution electron energy loss spectroscopy

Rego, A.M. Botelho do; Vilar, M. Rei; Silva, J Lopes da

doi:10.1016/s0368-2048(97)00023-6

Cited by 31 publications

(37 citation statements)

References 23 publications

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“…17 For poly(diphenylsiloxane) films, only absorption bands B and C of phenyl pendant group excitations are observed.…”

Section: Resultsmentioning

confidence: 99%

“…32 In HREELS spectra, one can observe that the position of features assignable to triplet and singlet π* r π transitions in both PDPS and PMPS are, within the energy accuracy, in the same energy loss as those found for polystyrene spectra. 17 In fact, HREELS electronic spectra for PDPS show a lower threshold than those found in the UV/vis spectra due to electron ability to excite the triplet π* r π transition, forbidden in optical spectroscopy for spin conservation reasons. In the case of PMPS, this band is situated near the expected σ* r σ excitation.…”

Section: Resultsmentioning

confidence: 99%

“…22 In the case of polymer surfaces, a power law related with E p is also obtained, I exc /I elast ∝ E p R , but the R value varies between -1 and 1 depending on the ratio of dipolar/ impact mechanisms and the thickness of the analyzed layer. 17 Since cross-section variation laws with the incident electron energy are different for each vibration mode, the relative intensity of each excitation is expected to change from spectrum to spectrum as E p varies. This can be observed in Figure 2a,b, where two sets of HREELS vibrational spectra of PMPS and PDPS films are presented for increasing E p .…”

Section: Resultsmentioning

confidence: 99%

“…For electronic losses, differential cross sections usually exhibit a typical behavior of a resonance mechanism. 17 For the films studied here, differential cross sections as a function of E p are displayed for a vibrational loss (the aromatic CH stretching, at 3050 cm -1 ) and an electronic excitation loss (at 4.7 eV) in parts a and b of Figure 5, respectively.…”

Section: Resultsmentioning

confidence: 99%

“…Similarly, in electronic spectra, in addition to optically allowed transitions, forbidden transitions for symmetry or spin conservation rules are also expected to be observed. 17,23 …”

Section: Introductionmentioning

confidence: 99%

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Vibrational and Electronic Excitations in Poly(methylphenylsilane) and Poly(diphenylsiloxane) Films: Surface Aspects

Rego¹,

Pellegrino²,

Vilar

2001

Macromolecules

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High-resolution electron energy loss spectroscopy (HREELS) is applied to study film surfaces of two silicon-based polymers having methyl and/or phenyl rings as pendant groups: poly(diphenylsiloxane) and poly(methylphenylsilane). These spectra are compared with those obtained by infrared absorption, Raman scattering, and UV/vis absorption spectroscopy for the polymer bulk. Both vibrational and electronic spectra of these two polymers exhibit common features corresponding to the phenyl pendant group excitations. Positions of peaks appearing in HREELS vibrational spectra correspond well to infraredand Raman-active modes of the polymer bulk. Electronic losses also correspond to the electronic excited states of phenyl groups cited in the literature. Differences related to secondary emission and accumulation of relaxed electrons are assigned to the electronic structure of the film. The absence of a loss corresponding to the excitation of polysilane chain is related to a trapping mechanism.

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“…17 For poly(diphenylsiloxane) films, only absorption bands B and C of phenyl pendant group excitations are observed.…”

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

“…Similarly, in electronic spectra, in addition to optically allowed transitions, forbidden transitions for symmetry or spin conservation rules are also expected to be observed. 17,23 …”

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Vibrational and Electronic Excitations in Poly(methylphenylsilane) and Poly(diphenylsiloxane) Films: Surface Aspects

Rego¹,

Pellegrino²,

Vilar

2001

Macromolecules

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Surface analysis of oligothiophene films using HREELS: molecular orientation effects

Vilar

Horowitz

Lang

et al. 1999

Adv. Mater. Opt. Electron.

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The surface of evaporated films of α‐oligothiophenes—quaterthiophene (4T), quinquethiophene (5T) and sexithiophene (6T)—was studied by high‐resolution electron energy loss spectroscopy (HREELS), extending the common vibrational domain of energy loss to electronic excitation and secondary emission. Vibrational spectra show that the molecular orientation is not the same on graphite and gold substrates. HREELS results corroborate those obtained by reflection–absorption infrared spectroscopy (RAIRS), confirming that graphite substrates induce films where molecules lie flat on the surface, whereas gold substrates generate a molecular orientation close to perpendicularity. Using these two differently oriented samples, we demonstrate the existence of two relaxation channels for the electron surface interaction: electronic excitation and ionisation. HREELS spectra recorded with incident electron energy between 2 and 7 eV reveal that secondary electron emission originating from ionisations is always more efficient for escape directions perpendicular to the plane of the molecule. This is here associated with the π orbital origin of this emission. Copyright © 2000 John Wiley & Sons, Ltd.

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A hybrid LIBS–Raman system combined with chemometrics: an efficient tool for plastic identification and sorting

et al. 2017

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Classification of plastics is of great importance in the recycling industry as the littering of plastic wastes increases day by day as a result of its extensive use. In this paper, we demonstrate the efficacy of a combined laser-induced breakdown spectroscopy (LIBS)-Raman system for the rapid identification and classification of post-consumer plastics. The atomic information and molecular information of polyethylene terephthalate, polyethylene, polypropylene, and polystyrene were studied using plasma emission spectra and scattered signal obtained in the LIBS and Raman technique, respectively. The collected spectral features of the samples were analyzed using statistical tools (principal component analysis, Mahalanobis distance) to categorize the plastics. The analyses of the data clearly show that elemental information and molecular information obtained from these techniques are efficient for classification of plastics. In addition, the molecular information collected via Raman spectroscopy exhibits clearly distinct features for the transparent plastics (100% discrimination), whereas the LIBS technique shows better spectral feature differences for the colored samples. The study shows that the information obtained from these complementary techniques allows the complete classification of the plastic samples, irrespective of the color or additives. This work further throws some light on the fact that the potential limitations of any of these techniques for sample identification can be overcome by the complementarity of these two techniques. Graphical Abstract ᅟ.

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Mechanisms of vibrational and electronic excitations of polystyrene films in high resolution electron energy loss spectroscopy

Cited by 31 publications

References 23 publications

Vibrational and Electronic Excitations in Poly(methylphenylsilane) and Poly(diphenylsiloxane) Films: Surface Aspects

Vibrational and Electronic Excitations in Poly(methylphenylsilane) and Poly(diphenylsiloxane) Films: Surface Aspects

Surface analysis of oligothiophene films using HREELS: molecular orientation effects

A hybrid LIBS–Raman system combined with chemometrics: an efficient tool for plastic identification and sorting

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