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117 results on '"Siebbeles, L. D."'

1. Efficient photogeneration of charge carriers in silicon nanowires with a radial doping gradient

Author

Murthy, D. H. K., Xu, T., Chen, W. H., A., J. Houtepen, Savenije, T. J., Siebbeles, L. D. A., Nys, J. P., Krzeminski, Christophe, Grandidier, Bruno, Stiévenard, Didier, Pareige, Philippe, Jomard, F., Patriache, Gilles, and Lebedev, O. I.

Subjects
Condensed Matter - Materials Science
Abstract

From electrodeless time-resolved microwave conductivity measurements, the efficiency of charge carrier generation, their mobility, and decay kinetics on photo-excitation were studied in arrays of Si nanowires grown by the vapor-liquid-solid mechanism. A large enhancement in the magnitude of the photoconductance and charge carrier lifetime are found depending on the incorporation of impurities during the growth. They are explained by the internal electric field that builds up, due to a higher doped sidewalls, as revealed by detailed analysis of the nanowire morphology and chemical composition.

Published
2011
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6. Tuning of the excited state properties of phenylenevinylene oligomers: A time-dependent density functional theory study.

Author

Grozema, F. C., Telesca, R., Snijders, J. G., and Siebbeles, L. D. A.

Subjects
DENSITY functionals, MOLECULAR structure, POLARIZATION (Nuclear physics)
Abstract

This paper discusses a time-dependent density functional theory study of the effect of molecular structure on the excited state polarizability of conjugated molecules. A short phenylenevinylene oligomer containing three phenyl rings (PV2, distyryl benzene! is taken as a model system. Introduction of methyl substituents is shown to have only a small influence on the increase in polarizability upon excitation (the excess polarizability, δ&αmacr;). Methoxy groups have a much larger effect but in this case δ&αmacr; depends strongly on the dihedral angle between the side chain and the backbone of the molecule. If the central phenyl ring of PV2 has a meta-configuration rather than para, both the optical absorption spectrum and the excess polarizability change considerably. [ABSTRACT FROM AUTHOR]

Published
2003
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7. Theoretical and experimental studies of the opto-electronic properties of positively charged oligo(phenylene vinylene)s: Effects of chain length and alkoxy substitution.

Author

Grozema, F. C., Candeias, L. P., Swart, M., van Duijnen, P. Th., Wildeman, J., Hadziioanou, G., Siebbeles, L. D. A., and Warman, J. M.

Subjects
POLYMERS, OPTOELECTRONICS
Abstract

In this paper a combined experimental and quantum chemical study of the geometry and opto-electronic properties of unsubstituted and dialkoxy-sustituted phenylene-vinylene oligomers (PV's) is presented. The optical absorption spectra for PV cations with different chain lengths and substitution patterns were measured using pulse radiolysis with time-resolved spectrophotometric detection from 1380 to 500 nm (0.9 to 2.5 eV). The geometries of the PV's studied were optimized using density functional theory (DFT) for both the neutral and singly charged molecule. The spectra for the PV radical cations were then calculated using singly excited configuration interaction with an intermediate neglect of differential overlap reference wave function method together with the DFT geometry. The agreement between experimental and theoretical absorption energies is excellent; most of the calculated radical cation absorption energies are within 0.15 eV of the experimental values. The pattern of dialkoxy-substitution is found to have a large effect on the optical absorption spectrum of the cation. Using the calculated charge distribution it is shown that the degree of delocalization of the charge correlates with the energy of the lowest absorption band. If alkoxy side chains are present on some of the rings the positive charge tends to localize at those sites. [ABSTRACT FROM AUTHOR]

Published
2002
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8. Excited state polarizabilities of conjugated molecules calculated using time dependent density functional theory.

Author

Grozema, F. C., Telesca, R., Jonkman, H. T., Siebbeles, L. D. A., and Snijders, J. G.

Subjects
POLARIZABILITY (Electricity), DENSITY functionals
Abstract

In this paper, time-dependent density functional theory (TDDFT) calculations of excited state polarizabilities of conjugated molecules are presented. The increase in polarizability upon excitation was obtained by evaluating the dependence of the excitation energy on an applied static electric field. The excitation energy was found to vary quadratically with the field strength. The excess polarizabilities obtained for singlet excited states are in reasonable agreement with the experimental results for the shorter oligomers, particularly if the experimental uncertainties are considered. For longer oligomers the excess polarizability is considerably overestimated, similar to DFT calculations of ground state polarizabilities. Excess polarizabilities of triplet states were found to be smaller than those for the corresponding singlet state, which agrees with experimental results that are available for triplet polarizabilities. Negative polarizabilities are obtained for the lowest singlet A[sub g] states of longer oligomers. The polarizability of the lowest B[sub u] and A[sub g] excited states of the conjugated molecules studied here are determined mainly by the interaction between these two states. Upon application of a static electric field a quadratic Stark effect is observed in which the lower B[sub u] state has a positive excess polarizability and the upper A[sub g] state exhibits a decrease in polarizability upon excitation. All results are explained in terms of a sum-over-states description for the polarizability. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Published
2001
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11. Polarization of atomic photofragment fluorescence for excitation along a Fano profile: A quantum-mechanical study.

Author

Siebbeles, L. D. A. and Glass-Maujean, M.

Subjects
*PHOTODISSOCIATION, *POLARIZATION (Nuclear physics), *FLUORESCENCE, *NUCLEAR excitation
Abstract

A quantum-mechanical description of the polarization of the fluorescence from photofragments, obtained by excitation along a Fano profile, is presented. For excitation on a Fano profile, dissociation can occur via two indistinguishable pathways, i.e., dissociation via the resonance and via direct excitation to the continuum. This gives rise to quantum interference effects, which result in an asymmetric profile in the photon absorption spectrum. The effect of the interference on the polarization of the photofragments fluorescence is investigated. The polarization as a function of the excitation energy varies asymmetrically around the resonant excitation energy. However, in contrast to intuition, the polarization changes in a symmetric way around an energy which is shifted from the resonant excitation energy. Simple formulas to calculate the polarization for different rotational and electronic transitions are provided. [ABSTRACT FROM AUTHOR]

Published
1994
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12. Long-range orientation and atomic attachment of nanocrystals in 2D honeycomb superlattices

Author

Condensed Matter and Interfaces, Physical and Colloid Chemistry, Sub Condensed Matter and Interfaces, Sub Physical and Colloid Chemistry, Boneschanscher, M. P., Evers, W. H., Geuchies, J. J., Altantzis, T., Goris, B., Rabouw, F. T., van Rossum, S. A. P., van der Zant, H. S. J., Siebbeles, L. D. A., Van Tendeloo, G., Swart, I., Hilhorst, J., Petukhov, Andrei V., Bals, S., Vanmaekelbergh, D., Condensed Matter and Interfaces, Physical and Colloid Chemistry, Sub Condensed Matter and Interfaces, Sub Physical and Colloid Chemistry, Boneschanscher, M. P., Evers, W. H., Geuchies, J. J., Altantzis, T., Goris, B., Rabouw, F. T., van Rossum, S. A. P., van der Zant, H. S. J., Siebbeles, L. D. A., Van Tendeloo, G., Swart, I., Hilhorst, J., Petukhov, Andrei V., Bals, S., and Vanmaekelbergh, D.

Published
2014

13. Organic Field-Effect Transistors Utilising Oligothiophene Based Swivel Cruciform

Author

Zen, A., Pingel, P., Neher, D., Grenzer, J., Zhuang, W., Rabe, J. P., Bilge, A., Galbrecht, F., Nehls, B., Farrell, T., Scherf, U., Abellons, R. D., Grozema, F. C., and Siebbeles, L. D. A.

Subjects
organic field effect transistors, semiconducting polymers
Abstract

Two types of highly soluble oligothiophene based swivel cruciform are presented as semiconducting materials in OFETs. Transistor made from one of these oligomers exhibited mobilities of more than 0.01 cm^2/Vs and current on/off ratio of >105. This is among the highest values reported to date for wet processed OFETs utilizing oligothiophenes. In fact, the OFET-mobilities are comparable to values extracted from pulse-radiolysis time resolved microwave conductivity (PR-TRMC) experiment, indicating that carrier trapping is insignificant. In depth examination of the morphological, optical characteristics and thermal stability of the materials were carried to obtain information on the packing of the oligomers in the layer. Finally, the correlation between the transistor performance and the crystallinity of the layers is addressed.

Published
2007

14. Organic Field-Effect Transistors Utilising Oligothiophene Based Swivel Cruciform

Author

Zen, A., Pingel, P., Neher, D., Grenzer, J., Zhuang, W., Rabe, J. P., Bilge, A., Galbrecht, F., Nehls, B., Farrell, T., Scherf, U., Abellons, R. D., Grozema, F. C., Siebbeles, L. D. A., Zen, A., Pingel, P., Neher, D., Grenzer, J., Zhuang, W., Rabe, J. P., Bilge, A., Galbrecht, F., Nehls, B., Farrell, T., Scherf, U., Abellons, R. D., Grozema, F. C., and Siebbeles, L. D. A.

Abstract

Two types of highly soluble oligothiophene based swivel cruciform are presented as semiconducting materials in OFETs. Transistor made from one of these oligomers exhibited mobilities of more than 0.01 cm^2/Vs and current on/off ratio of >105. This is among the highest values reported to date for wet processed OFETs utilizing oligothiophenes. In fact, the OFET-mobilities are comparable to values extracted from pulse-radiolysis time resolved microwave conductivity (PR-TRMC) experiment, indicating that carrier trapping is insignificant. In depth examination of the morphological, optical characteristics and thermal stability of the materials were carried to obtain information on the packing of the oligomers in the layer. Finally, the correlation between the transistor performance and the crystallinity of the layers is addressed.

Published
2006

17. Efficient photogeneration of charge carriers in silicon nanowires with a radial doping gradient

Author

Murthy, D H K, primary, Xu, T, additional, Chen, W H, additional, Houtepen, A J, additional, Savenije, T J, additional, Siebbeles, L D A, additional, Nys, J P, additional, Krzeminski, C, additional, Grandidier, B, additional, Stiévenard, D, additional, Pareige, P, additional, Jomard, F, additional, Patriarche, G, additional, and Lebedev, O I, additional

Published
2011
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