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Papers by Emilie Steveler

Research paper thumbnail of Impact of the crystalline order on the exciton diffusion length in organic thin films of donor-acceptor-donor molecules based on triazatruxene units

Organic Electronics and Photonics: Fundamentals and Devices III

Organic semiconductor materials such as planar conjugated small molecules are of great interest t... more Organic semiconductor materials such as planar conjugated small molecules are of great interest to the photovoltaic community. In thin films, the exciton and charge carrier dynamics, which are crucial to photovoltaic device operation, depend in a non-trivial way on the organic molecular structure and on the molecular organization in the solid state. Recently, the exciton diffusion has been found to strongly depend on the crystalline order of the organic thin films. This work presents the study of the exciton lifetime in an innovative class of molecular semiconductors able to present different crystalline order. This family of molecules has a "dumbbell-shaped" structure based on triazatruxene units that act as a π-stacking platform. Such molecules with different side-chains have been found to self-assemble into various crystalline and liquid crystalline phases. We have studied the steady-state photoluminescence and the exciton lifetime for several triazatruxene-based derivatives with different side-chains, in solution and in thin films for different solid state phases. In solution, the fluorescence lifetime corresponds to the reference value that can be obtained without intermolecular interaction. In thin films, we measured the exciton lifetime for different molecular structures in order to correlate the exciton dynamics with the molecular stacking. The results reveal a significant increase in the exciton lifetime with the enhancement of the structural order.

Research paper thumbnail of Study of exciton dynamics in organised organic thin films for photovoltaic applications

Soft Matter Science (SoMaS), 2017

Research paper thumbnail of Etude des mécanismes de photoluminescence dans les nitrures et oxydes de silicium dopés aux terres rares (Er, Nd)

Ce travail de these est dedie a l'etude des transitions radiatives dans les materiaux de nitr... more Ce travail de these est dedie a l'etude des transitions radiatives dans les materiaux de nitrure et d'oxyde de silicium dopes aux ions de terres rares (Er3+, Nd3+). La caracterisation optique des films minces elabores par evaporation thermique est basee sur la spectroscopie de photoluminescence. Les etudes menees s'inscrivent dans la recherche de processus d'excitation indirecte des ions Er3+ et Nd3+ dans des matrices a base de silicium. Dans les nitrures et oxynitrures de silicium, un processus de transfert d'energie permettant l'excitation indirecte des ions Er3+ est mis en evidence. Pour les couches minces amorphes, le couplage est attribue a des etats electroniques localises dans la bande interdite de la matrice. Pour les films recuits a haute temperature, les nanocristaux de silicium (nc-Si) jouent un role majeur dans l'excitation indirecte de l'erbium. Dans les matrices d'oxyde de silicium, l'existence de processus d'excitations dire...

Research paper thumbnail of Efficient 3D charge transport in planar triazatruxene-based dumbbell-shaped molecules forming a bridged columnar phase

Journal of Materials Chemistry A, 2021

Planar conjugated molecular backbones are essential for achieving high charge carrier mobilities ... more Planar conjugated molecular backbones are essential for achieving high charge carrier mobilities along molecular -stacking directions but are often concomitant with poor charge transport in other directions. This is particularly...

Research paper thumbnail of Optical index measurement of InAs/GaSb type-II superlattice for mid-infrared photodetection at cryogenic temperatures

Applied Physics Letters, 2014

ABSTRACT The complex optical index ñ (=n + i κ) of InAs/GaSb type-II superlattice (T2SL) was dete... more ABSTRACT The complex optical index ñ (=n + i κ) of InAs/GaSb type-II superlattice (T2SL) was determined in the 1–6 μm range from reflectivity measurements of resonant structures at 80 K. Several air/superlattice/gold cavities of various thicknesses were fabricated and their reflectivity was measured. As the large variations induced by the cavity resonances in the studied range can be accurately modeled, we were able to determine the complex optical index ñ of InAs/GaSb T2SL with an error of only a few percent. We found that the in-plane refractive index n of the T2SL lies between 3.65 and 3.77 in the mid-infrared wavelength range, and the absorption coefficient κ decreases from 0.23 to 0.001 as the wavelength increases from 1.25 to 5.65 μm. The subtractive Kramers-Kronig relation allowed us to verify our determination of ñ.

Research paper thumbnail of INFRARED LUMINESCENCE AT 1010 nm AND 1500 nm IN LiNbO 3 :Er 3+ EXCITED BY SHORT PULSE RADIATION AT 980 nm

International Journal of Modern Physics: Conference Series, 2012

Luminescence of LiNbO3:Er3+ crystal at a wavelength of 1010 nm and 1500 nm under pulsed excitatio... more Luminescence of LiNbO3:Er3+ crystal at a wavelength of 1010 nm and 1500 nm under pulsed excitation of different power at a wavelength of 980 nm are experimentally and theoretically studied. It is revealed, that the main part of the absorbed energy gives rise to the luminescence at 1500 nm. Considered concentrations of Er3+ impurity ions allow to exclude cooperative processes in the impurity subsystem. The experimental results are interpreted in the framework of a three electronic levels system, assuming that the population of the higher lasing level 4I13/2 in the crystal under study is caused by relaxation processes from the excited level. It is shown that for obtaining of a laser radiation at about 1500 nm one can effectively use a pulse-pumping at 980 nm with a power density in a range of 50 ÷ 60 MW/cm2.

Research paper thumbnail of Enhanced two-photon-absorption using sub-wavelength antennas

Quantum Sensing and Nanophotonic Devices XII, 2015

Degenerate two-photon absorption (TPA) is investigated in a 186 nm thick gallium arsenide (GaAs) ... more Degenerate two-photon absorption (TPA) is investigated in a 186 nm thick gallium arsenide (GaAs) p-in diode embedded in a resonant metallic nanostructure. The full device consists in the GaAs layer, a gold subwavelength grating on the illuminated side, and a gold mirror on the opposite side. For TM-polarized light, the structure exhibits a resonance close to 1.47 μm, with a confined electric field in the intrinsic region, far from the metallic interfaces. A 109 times increase in photocurrent compared to a non-resonant device is obtained experimentally, while numerical simulations suggest that both gain in TPA-photocurrent and angular dependence can be further improved. For optimized grating parameters, a maximum gain of 241 is demonstrated numerically and over incidence angle range of (−30°; +30°). This structure paves the way towards low-noise infrared detection, using non-degenerate TPA, involving two photons of vastly different energies in the same process of absorption in a large bandgap semiconductor material.

Research paper thumbnail of Resonant metallic nanostructure for enhanced two-photon absorption in a thin GaAs p-i-n diode

Applied Physics Letters, 2014

ABSTRACT Degenerate two-photon absorption (TPA) is investigated in a 186 nm thick gallium arsenid... more ABSTRACT Degenerate two-photon absorption (TPA) is investigated in a 186 nm thick gallium arsenide (GaAs) p-i-n diode embedded in a resonant metallic nanostructure. The full device consists in the GaAs layer, a gold subwavelength grating on the illuminated side, and a gold mirror on the opposite side. For TM-polarized light, the structure exhibits a resonance close to 1.47 μm, with a confined electric field in the intrinsic region, far from the metallic interfaces. A 109 times increase in photocurrent compared to a non-resonant device is obtained experimentally, while numerical simulations suggest that both gain in TPA-photocurrent and angular dependence can be further improved. For optimized grating parameters, a maximum gain of 241 is demonstrated numerically and over incidence angle range of (−30°; +30°).

Research paper thumbnail of Photoluminescence properties of Nd-doped silicon oxide thin films containing silicon nanoparticles

Journal of Luminescence, 2014

Research paper thumbnail of Direct and indirect excitation of Nd3+ ions sensitized by Si nanocrystals embedded in a SiO2 thin film

Journal of Applied Physics, 2011

Research paper thumbnail of Experimental demonstration of the optical Helmholtz resonance

Applied Physics Letters, 2018

Optical nanoantennas are studied to manipulate light and enhance light matter interactions. Here,... more Optical nanoantennas are studied to manipulate light and enhance light matter interactions. Here, we experimentally demonstrate the optical Helmholtz resonance in a metallic slit-box structure, which is predicted to be harmonic and to enhance the electric field intensity by several orders of magnitude. It is fabricated thanks to a two step electron beam lithography process, between which the box was filled with benzocyclobutene (BCB). Up to 80% of the light is absorbed at a λ = 2.84 μm wavelength under a beam focused by a Cassegrain objective (NA = 0.4), even if the dimensions of this resonator are deeply subwavelength for both the slit (width λ/55 and height λ/77) and the box (width λ/7 and height λ/37). As expected from the inductance nature of the box, the optical properties of the BCB filling the box have no influence on the resonance behavior.

Research paper thumbnail of Regioisomers of Organic Semiconducting Dumbbell‐Shaped Molecules: Synthesis and Structure‐Properties Relationship

European Journal of Organic Chemistry, 2021

Research paper thumbnail of Exciton dynamics in donor-acceptor-donor molecules: impact of molecular structure and self-assembly on the exciton lifetime

Organic semiconductor materials such as planar conjugated small molecules are of great interest t... more Organic semiconductor materials such as planar conjugated small molecules are of great interest to the photovoltaic community [1, 2]. In thin films, the exciton and charge carrier dynamics, which are crucial to photovoltaic device operation, depend in a non-trivial way on the organic molecular structure and on the molecular organization in the solid state. [3, 4] Several recent studies have established that the exciton diffusion strongly depends on the crystalline order of the organic films. [5, 6] Our work presents the study of the exciton dynamics in an innovative class of molecular semiconductors able to present high crystalline order. This family of molecules has a “dumbbell-shaped” structure based on triazatruxene units that act as a π-stacking platform. [7] Such molecules with different side-chain have been found to self-assemble into various crystalline and liquid crystalline phases. We have studied exciton dynamics of molecular with different side-chain: in solution and in t...

Research paper thumbnail of Impact of the crystalline order on the exciton diffusion length in organic thin films of donor-acceptor-donor molecules based on triazatruxene units

Organic Electronics and Photonics: Fundamentals and Devices III

Organic semiconductor materials such as planar conjugated small molecules are of great interest t... more Organic semiconductor materials such as planar conjugated small molecules are of great interest to the photovoltaic community. In thin films, the exciton and charge carrier dynamics, which are crucial to photovoltaic device operation, depend in a non-trivial way on the organic molecular structure and on the molecular organization in the solid state. Recently, the exciton diffusion has been found to strongly depend on the crystalline order of the organic thin films. This work presents the study of the exciton lifetime in an innovative class of molecular semiconductors able to present different crystalline order. This family of molecules has a "dumbbell-shaped" structure based on triazatruxene units that act as a π-stacking platform. Such molecules with different side-chains have been found to self-assemble into various crystalline and liquid crystalline phases. We have studied the steady-state photoluminescence and the exciton lifetime for several triazatruxene-based derivatives with different side-chains, in solution and in thin films for different solid state phases. In solution, the fluorescence lifetime corresponds to the reference value that can be obtained without intermolecular interaction. In thin films, we measured the exciton lifetime for different molecular structures in order to correlate the exciton dynamics with the molecular stacking. The results reveal a significant increase in the exciton lifetime with the enhancement of the structural order.

Research paper thumbnail of Study of exciton dynamics in organised organic thin films for photovoltaic applications

Soft Matter Science (SoMaS), 2017

Research paper thumbnail of Etude des mécanismes de photoluminescence dans les nitrures et oxydes de silicium dopés aux terres rares (Er, Nd)

Ce travail de these est dedie a l'etude des transitions radiatives dans les materiaux de nitr... more Ce travail de these est dedie a l'etude des transitions radiatives dans les materiaux de nitrure et d'oxyde de silicium dopes aux ions de terres rares (Er3+, Nd3+). La caracterisation optique des films minces elabores par evaporation thermique est basee sur la spectroscopie de photoluminescence. Les etudes menees s'inscrivent dans la recherche de processus d'excitation indirecte des ions Er3+ et Nd3+ dans des matrices a base de silicium. Dans les nitrures et oxynitrures de silicium, un processus de transfert d'energie permettant l'excitation indirecte des ions Er3+ est mis en evidence. Pour les couches minces amorphes, le couplage est attribue a des etats electroniques localises dans la bande interdite de la matrice. Pour les films recuits a haute temperature, les nanocristaux de silicium (nc-Si) jouent un role majeur dans l'excitation indirecte de l'erbium. Dans les matrices d'oxyde de silicium, l'existence de processus d'excitations dire...

Research paper thumbnail of Efficient 3D charge transport in planar triazatruxene-based dumbbell-shaped molecules forming a bridged columnar phase

Journal of Materials Chemistry A, 2021

Planar conjugated molecular backbones are essential for achieving high charge carrier mobilities ... more Planar conjugated molecular backbones are essential for achieving high charge carrier mobilities along molecular -stacking directions but are often concomitant with poor charge transport in other directions. This is particularly...

Research paper thumbnail of Optical index measurement of InAs/GaSb type-II superlattice for mid-infrared photodetection at cryogenic temperatures

Applied Physics Letters, 2014

ABSTRACT The complex optical index ñ (=n + i κ) of InAs/GaSb type-II superlattice (T2SL) was dete... more ABSTRACT The complex optical index ñ (=n + i κ) of InAs/GaSb type-II superlattice (T2SL) was determined in the 1–6 μm range from reflectivity measurements of resonant structures at 80 K. Several air/superlattice/gold cavities of various thicknesses were fabricated and their reflectivity was measured. As the large variations induced by the cavity resonances in the studied range can be accurately modeled, we were able to determine the complex optical index ñ of InAs/GaSb T2SL with an error of only a few percent. We found that the in-plane refractive index n of the T2SL lies between 3.65 and 3.77 in the mid-infrared wavelength range, and the absorption coefficient κ decreases from 0.23 to 0.001 as the wavelength increases from 1.25 to 5.65 μm. The subtractive Kramers-Kronig relation allowed us to verify our determination of ñ.

Research paper thumbnail of INFRARED LUMINESCENCE AT 1010 nm AND 1500 nm IN LiNbO 3 :Er 3+ EXCITED BY SHORT PULSE RADIATION AT 980 nm

International Journal of Modern Physics: Conference Series, 2012

Luminescence of LiNbO3:Er3+ crystal at a wavelength of 1010 nm and 1500 nm under pulsed excitatio... more Luminescence of LiNbO3:Er3+ crystal at a wavelength of 1010 nm and 1500 nm under pulsed excitation of different power at a wavelength of 980 nm are experimentally and theoretically studied. It is revealed, that the main part of the absorbed energy gives rise to the luminescence at 1500 nm. Considered concentrations of Er3+ impurity ions allow to exclude cooperative processes in the impurity subsystem. The experimental results are interpreted in the framework of a three electronic levels system, assuming that the population of the higher lasing level 4I13/2 in the crystal under study is caused by relaxation processes from the excited level. It is shown that for obtaining of a laser radiation at about 1500 nm one can effectively use a pulse-pumping at 980 nm with a power density in a range of 50 ÷ 60 MW/cm2.

Research paper thumbnail of Enhanced two-photon-absorption using sub-wavelength antennas

Quantum Sensing and Nanophotonic Devices XII, 2015

Degenerate two-photon absorption (TPA) is investigated in a 186 nm thick gallium arsenide (GaAs) ... more Degenerate two-photon absorption (TPA) is investigated in a 186 nm thick gallium arsenide (GaAs) p-in diode embedded in a resonant metallic nanostructure. The full device consists in the GaAs layer, a gold subwavelength grating on the illuminated side, and a gold mirror on the opposite side. For TM-polarized light, the structure exhibits a resonance close to 1.47 μm, with a confined electric field in the intrinsic region, far from the metallic interfaces. A 109 times increase in photocurrent compared to a non-resonant device is obtained experimentally, while numerical simulations suggest that both gain in TPA-photocurrent and angular dependence can be further improved. For optimized grating parameters, a maximum gain of 241 is demonstrated numerically and over incidence angle range of (−30°; +30°). This structure paves the way towards low-noise infrared detection, using non-degenerate TPA, involving two photons of vastly different energies in the same process of absorption in a large bandgap semiconductor material.

Research paper thumbnail of Resonant metallic nanostructure for enhanced two-photon absorption in a thin GaAs p-i-n diode

Applied Physics Letters, 2014

ABSTRACT Degenerate two-photon absorption (TPA) is investigated in a 186 nm thick gallium arsenid... more ABSTRACT Degenerate two-photon absorption (TPA) is investigated in a 186 nm thick gallium arsenide (GaAs) p-i-n diode embedded in a resonant metallic nanostructure. The full device consists in the GaAs layer, a gold subwavelength grating on the illuminated side, and a gold mirror on the opposite side. For TM-polarized light, the structure exhibits a resonance close to 1.47 μm, with a confined electric field in the intrinsic region, far from the metallic interfaces. A 109 times increase in photocurrent compared to a non-resonant device is obtained experimentally, while numerical simulations suggest that both gain in TPA-photocurrent and angular dependence can be further improved. For optimized grating parameters, a maximum gain of 241 is demonstrated numerically and over incidence angle range of (−30°; +30°).

Research paper thumbnail of Photoluminescence properties of Nd-doped silicon oxide thin films containing silicon nanoparticles

Journal of Luminescence, 2014

Research paper thumbnail of Direct and indirect excitation of Nd3+ ions sensitized by Si nanocrystals embedded in a SiO2 thin film

Journal of Applied Physics, 2011

Research paper thumbnail of Experimental demonstration of the optical Helmholtz resonance

Applied Physics Letters, 2018

Optical nanoantennas are studied to manipulate light and enhance light matter interactions. Here,... more Optical nanoantennas are studied to manipulate light and enhance light matter interactions. Here, we experimentally demonstrate the optical Helmholtz resonance in a metallic slit-box structure, which is predicted to be harmonic and to enhance the electric field intensity by several orders of magnitude. It is fabricated thanks to a two step electron beam lithography process, between which the box was filled with benzocyclobutene (BCB). Up to 80% of the light is absorbed at a λ = 2.84 μm wavelength under a beam focused by a Cassegrain objective (NA = 0.4), even if the dimensions of this resonator are deeply subwavelength for both the slit (width λ/55 and height λ/77) and the box (width λ/7 and height λ/37). As expected from the inductance nature of the box, the optical properties of the BCB filling the box have no influence on the resonance behavior.

Research paper thumbnail of Regioisomers of Organic Semiconducting Dumbbell‐Shaped Molecules: Synthesis and Structure‐Properties Relationship

European Journal of Organic Chemistry, 2021

Research paper thumbnail of Exciton dynamics in donor-acceptor-donor molecules: impact of molecular structure and self-assembly on the exciton lifetime

Organic semiconductor materials such as planar conjugated small molecules are of great interest t... more Organic semiconductor materials such as planar conjugated small molecules are of great interest to the photovoltaic community [1, 2]. In thin films, the exciton and charge carrier dynamics, which are crucial to photovoltaic device operation, depend in a non-trivial way on the organic molecular structure and on the molecular organization in the solid state. [3, 4] Several recent studies have established that the exciton diffusion strongly depends on the crystalline order of the organic films. [5, 6] Our work presents the study of the exciton dynamics in an innovative class of molecular semiconductors able to present high crystalline order. This family of molecules has a “dumbbell-shaped” structure based on triazatruxene units that act as a π-stacking platform. [7] Such molecules with different side-chain have been found to self-assemble into various crystalline and liquid crystalline phases. We have studied exciton dynamics of molecular with different side-chain: in solution and in t...