Papers by Zohreh Sedaghat
International audienc
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The probe-sample interaction in scattering type Near-field Scanning Optical Microscopy (s-NSOM) i... more The probe-sample interaction in scattering type Near-field Scanning Optical Microscopy (s-NSOM) is investigated theoretically and experimentally. To understand this interaction, a commonly used analytical model is detailed as well as a more rigorous method based on a dyadic Green functions. In the simplest cases, both approaches give similar radiation patterns of the coupled probe-sample and the signal dependence to the probe and sample permittivities is then discussed. The case of tipenhanced resonances is notably highlighted. Experimentally, two s-NSOM setups were considered, one in the mid-IR spectral range and one in the near IR. In the former case, we have imaged several sub-λ gratings for different probe sizes. Interestingly, contrast inversions are obtained when the size is decreased suggesting that tip-induced resonances have been observed for the sharpest probe. Such behavior is in agreement with the probe permittivity value calculated via a model based on an elastic contin...
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Translational Biophotonics: Diagnostics and Therapeutics, 2021
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ACS Omega, 2021
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16th International Conference on Optical MEMS and Nanophotonics, 2011
We report on the fabrication, simulation and use of carbon nano-probes grown on the apex of polym... more We report on the fabrication, simulation and use of carbon nano-probes grown on the apex of polymer-tipped optical fibers. The carbon needles are used as near-field scattering probes to image light propagation in surface waveguides. The scattered light is selectively and efficiently coupled in the supporting optical fiber through the polymeric structure which is used here as a submicronic collection
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physica status solidi (c), 2011
ABSTRACT An approach to calculate the infrared dielectric function of semiconductor nanostructure... more ABSTRACT An approach to calculate the infrared dielectric function of semiconductor nanostructures is presented and applied to silicon (Si) nanowires (NW's). The phonon modes symmetries and frequencies are calculated by means of the elastic continuum medium theory. The modes strengths and damping are calculated from a model for lattice dynamics and perturbation theory. The data are used in anisotropic Lorentz oscillator model to generate the temperature and directional dependences of the infrared dielectric function of free standing Si NW's. Our results showed that in the direction perpendicular to the NW axis, the complex dielectric function is identical to that of bulk Si. However, along the NW axis, the infrared dielectric function is a strong function of the wavelength. (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
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Nanotechnology, 2008
We report a new method of growing Mn-doped CdS (CdS:Mn) nanoparticles in an aqueous solution at b... more We report a new method of growing Mn-doped CdS (CdS:Mn) nanoparticles in an aqueous solution at boiling temperature. The idea is to use precursors that react only at high temperature, in order to gain crystalline luminescent nanoparticles. CdSO(4), Mn(NO(3))(2) and Na(2)S(2)O(3) were used as the precursors, and thioglycerol was employed as the capping agent and also the reaction catalyst. Na(2)S(2)O(3) is thermally sensitive and it releases S(2-) ions upon heating. The CdS:Mn nanoparticles obtained are about 4 nm in size and show both cubic and hexagonal crystalline phases with a ratio of 35% to 65%. The luminescence of nanoparticles contains a peak at 580 nm, which is related to Mn(2+) ions. Prolonged reaction time results in a decrease of the Mn luminescence peak to about 35% of the maximum value. We discuss the possible causes of the Mn peak reduction and attribute it to preferential dissolution of Mn ions into the solution due to shape reconfiguration of the nanoparticles.
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Nanotechnology, 2006
Abstract CdS nanoparticles were grown using CdSO4 and Na2S2O3 as the precursors and thioglycerol ... more Abstract CdS nanoparticles were grown using CdSO4 and Na2S2O3 as the precursors and thioglycerol (TG) as the capping agent. TG was shown to exhibit a catalytic role in the reaction and also acted as a capping agent. It was demonstrated that size growth is linearly related to the temperature of the reaction, ie the sizes can be controllably adjusted by temperature. The crystalline phase of the nanocrystals was also dependent on the temperature of growth: higher temperature favours the cubic phase. The pH also plays an ...
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Applied Physics Letters, 2012
... Zohreh Sedaghat,1 Anna Rumyantseva,1 Aurélien Bruyant,1,a) Sergei Kostcheev,1 Sylvain Blaize,... more ... Zohreh Sedaghat,1 Anna Rumyantseva,1 Aurélien Bruyant,1,a) Sergei Kostcheev,1 Sylvain Blaize,1 Safi Jradi,1 Renaud Bachelot,1 and Antoine Monmayrant2,3 1Laboratoire de Nanotechnologie et d'Instrumentation Optique ... P. Radko, SI Bozhevolnyi, and N. Gregersen, Appl. ...
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Applied Physics Letters, 2012
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Optics express, Jan 8, 2014
A generalized lock-in detection method is proposed to extract amplitude and phase from optical in... more A generalized lock-in detection method is proposed to extract amplitude and phase from optical interferometers when an arbitrary periodic phase or frequency modulation is used. The actual modulation function is used to create the reference signals providing an optimal extraction of the useful information, notably for sinusoidal phase modulation. This simple and efficient approach has been tested and applied to phase sensitive spectroscopy and near-field optical measurements. We analyze the case where the signal amplitude is modulated and we show how to suppress the contribution of unmodulated background field.
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A generalized lock-in detection method is proposed to extract
amplitude and phase from optical i... more A generalized lock-in detection method is proposed to extract
amplitude and phase from optical interferometerswhen an arbitrary periodic
phase or frequency modulation is used. The actual modulation function
is used to create the reference signals providing an optimal extraction
of the useful information, notably for sinusoidal phase modulation. This
simple and efficient approach has been tested and applied to phase sensitive
spectroscopy and near-field optical measurements. We analyze the case
where the signal amplitude is modulated and we show how to suppress the
contribution of unmodulated background field.
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We present a near field optical study of a plasmonic gap waveguide vertically integrated on silic... more We present a near field optical study of a plasmonic gap waveguide vertically integrated on silicon.
The experimental study is based on a near field scanning optical microscope configured in
perturbation mode. This operation mode is described and modeled to give a physical insight into
the measured signal. A high spatial resolution allows for the characteristics of the plasmonic gap
modes, such as near field distributions, effective indices, direction of propagation, and coupling
between perpendicularly polarized modes, to be imaged and analyzed with accuracy. This
experimental work is supported by numerical simulations based on finite element optical mode
solvers and by the application of the strongly coupled-mode theory to the device.
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Pointed carbon nanotips have been deposited on polymer microlensed optical fibers and used as
hi... more Pointed carbon nanotips have been deposited on polymer microlensed optical fibers and used as
highly resolving scattering nanoprobes. Optical characterizations supported by simulations
demonstrate an efficient spatial filtering where the light scattered by the carbon tip is selectively
coupled into the fiber core. As an application, a channel surface waveguide was characterized in
collection mode. A special attention was given to the polarization response, and the s-polarized
field is found to be slightly favored due to the detection direction. The proposed hybrid probe’s
robustness, the symmetric detection and design flexibility it offers, makes it an attractive tool for
nano-optics.
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An approach to calculate the infrared dielectric function
of semiconductor nanostructures is pre... more An approach to calculate the infrared dielectric function
of semiconductor nanostructures is presented and applied
to silicon (Si) nanowires (NW’s). The phonon modes
symmetries and frequencies are calculated by means of
the elastic continuum medium theory. The modes
strengths and damping are calculated from a model for
lattice dynamics and perturbation theory. The data are
used in anisotropic Lorentz oscillator model to generate
the temperature and directional dependences of the infrared
dielectric function of free standing Si NW’s. Our results
showed that in the direction perpendicular to the
NW axis, the complex dielectric function is identical to
that of bulk Si. However, along the NW axis, the infrared
dielectric function is a strong function of the wavelength.
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We have developed a scattering-type microscope operating in the mid-IR range with a polarization ... more We have developed a scattering-type microscope operating in the mid-IR range with a polarization analysis. The experimental development and the operation of the microscope are described. The optical system can provide for each pixel of the image a matrix similar to a Jones matrix. Examples of polarization resolved images obtained on a SiO2/Si surface grating with a tungsten probe are shown and a high optical resolution is clearly demonstrated through the imaging of submicron metallic lines.
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However, in a recent paper we have calculated that the phonon confinement occurring in decananome... more However, in a recent paper we have calculated that the phonon confinement occurring in decananometric scale objects such as near-field probes can lead to a drastic modification of the probe's permittivity. This effect can be very useful as for a range of probe permittivity, much stronger contrast can be expected. To experimentally demonstrate these theoretical expectations, we have built a mid-lR near field microscope and imaged doped Si gratings with a period of 2 μm (fabricated in CEA-LETI) with carefully prepared tungsten tip stuck on a tuning fork. The detection has been done using tips with different radius (30 nm to 100 nm) and a very strong contrast between P doped and P+ doped can be observed for a variety of small-radius probes. An example of highly contrasted profile obtained on the doped silicon grating is shown in the paper.
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We report a new method of growing Mn-doped CdS (CdS:Mn) nanoparticles in an aqueous
solution at ... more We report a new method of growing Mn-doped CdS (CdS:Mn) nanoparticles in an aqueous
solution at boiling temperature. The idea is to use precursors that react only at high
temperature, in order to gain crystalline luminescent nanoparticles. CdSO4, Mn(NO3)2 and
Na2S2O3 were used as the precursors, and thioglycerol was employed as the capping agent and
also the reaction catalyst. Na2S2O3 is thermally sensitive and it releases S2− ions upon heating.
The CdS:Mn nanoparticles obtained are about 4 nm in size and show both cubic and hexagonal
crystalline phases with a ratio of 35% to 65%. The luminescence of nanoparticles contains a
peak at 580 nm, which is related to Mn2+ ions. Prolonged reaction time results in a decrease of
the Mn luminescence peak to about 35% of the maximum value. We discuss the possible causes
of the Mn peak reduction and attribute it to preferential dissolution of Mn ions into the solution
due to shape reconfiguration of the nanoparticles.
Bookmarks Related papers MentionsView impact
CdS nanoparticles were grown using CdSO4 and Na2S2O3 as the precursors and thioglycerol (TG) as t... more CdS nanoparticles were grown using CdSO4 and Na2S2O3 as the precursors and thioglycerol (TG) as the capping agent. TG was shown to exhibit a catalytic role in the reaction and also acted as a capping agent. It was demonstrated that size growth is linearly related to the temperature of the
reaction, i.e. the sizes can be controllably adjusted by temperature. The
crystalline phase of the nanocrystals was also dependent on the temperature
of growth: higher temperature favours the cubic phase. The pH also plays an important role in nanoparticle growth, as lower pH leads to a higher release rate of sulfur species. At pH as high as 10, the growth rate remains slow even
at boiling temperature. This provides a way to controllably grow nanoparticles at high temperatures and/or control the nucleation growth processes.
Bookmarks Related papers MentionsView impact
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Papers by Zohreh Sedaghat
amplitude and phase from optical interferometerswhen an arbitrary periodic
phase or frequency modulation is used. The actual modulation function
is used to create the reference signals providing an optimal extraction
of the useful information, notably for sinusoidal phase modulation. This
simple and efficient approach has been tested and applied to phase sensitive
spectroscopy and near-field optical measurements. We analyze the case
where the signal amplitude is modulated and we show how to suppress the
contribution of unmodulated background field.
The experimental study is based on a near field scanning optical microscope configured in
perturbation mode. This operation mode is described and modeled to give a physical insight into
the measured signal. A high spatial resolution allows for the characteristics of the plasmonic gap
modes, such as near field distributions, effective indices, direction of propagation, and coupling
between perpendicularly polarized modes, to be imaged and analyzed with accuracy. This
experimental work is supported by numerical simulations based on finite element optical mode
solvers and by the application of the strongly coupled-mode theory to the device.
highly resolving scattering nanoprobes. Optical characterizations supported by simulations
demonstrate an efficient spatial filtering where the light scattered by the carbon tip is selectively
coupled into the fiber core. As an application, a channel surface waveguide was characterized in
collection mode. A special attention was given to the polarization response, and the s-polarized
field is found to be slightly favored due to the detection direction. The proposed hybrid probe’s
robustness, the symmetric detection and design flexibility it offers, makes it an attractive tool for
nano-optics.
of semiconductor nanostructures is presented and applied
to silicon (Si) nanowires (NW’s). The phonon modes
symmetries and frequencies are calculated by means of
the elastic continuum medium theory. The modes
strengths and damping are calculated from a model for
lattice dynamics and perturbation theory. The data are
used in anisotropic Lorentz oscillator model to generate
the temperature and directional dependences of the infrared
dielectric function of free standing Si NW’s. Our results
showed that in the direction perpendicular to the
NW axis, the complex dielectric function is identical to
that of bulk Si. However, along the NW axis, the infrared
dielectric function is a strong function of the wavelength.
solution at boiling temperature. The idea is to use precursors that react only at high
temperature, in order to gain crystalline luminescent nanoparticles. CdSO4, Mn(NO3)2 and
Na2S2O3 were used as the precursors, and thioglycerol was employed as the capping agent and
also the reaction catalyst. Na2S2O3 is thermally sensitive and it releases S2− ions upon heating.
The CdS:Mn nanoparticles obtained are about 4 nm in size and show both cubic and hexagonal
crystalline phases with a ratio of 35% to 65%. The luminescence of nanoparticles contains a
peak at 580 nm, which is related to Mn2+ ions. Prolonged reaction time results in a decrease of
the Mn luminescence peak to about 35% of the maximum value. We discuss the possible causes
of the Mn peak reduction and attribute it to preferential dissolution of Mn ions into the solution
due to shape reconfiguration of the nanoparticles.
reaction, i.e. the sizes can be controllably adjusted by temperature. The
crystalline phase of the nanocrystals was also dependent on the temperature
of growth: higher temperature favours the cubic phase. The pH also plays an important role in nanoparticle growth, as lower pH leads to a higher release rate of sulfur species. At pH as high as 10, the growth rate remains slow even
at boiling temperature. This provides a way to controllably grow nanoparticles at high temperatures and/or control the nucleation growth processes.
amplitude and phase from optical interferometerswhen an arbitrary periodic
phase or frequency modulation is used. The actual modulation function
is used to create the reference signals providing an optimal extraction
of the useful information, notably for sinusoidal phase modulation. This
simple and efficient approach has been tested and applied to phase sensitive
spectroscopy and near-field optical measurements. We analyze the case
where the signal amplitude is modulated and we show how to suppress the
contribution of unmodulated background field.
The experimental study is based on a near field scanning optical microscope configured in
perturbation mode. This operation mode is described and modeled to give a physical insight into
the measured signal. A high spatial resolution allows for the characteristics of the plasmonic gap
modes, such as near field distributions, effective indices, direction of propagation, and coupling
between perpendicularly polarized modes, to be imaged and analyzed with accuracy. This
experimental work is supported by numerical simulations based on finite element optical mode
solvers and by the application of the strongly coupled-mode theory to the device.
highly resolving scattering nanoprobes. Optical characterizations supported by simulations
demonstrate an efficient spatial filtering where the light scattered by the carbon tip is selectively
coupled into the fiber core. As an application, a channel surface waveguide was characterized in
collection mode. A special attention was given to the polarization response, and the s-polarized
field is found to be slightly favored due to the detection direction. The proposed hybrid probe’s
robustness, the symmetric detection and design flexibility it offers, makes it an attractive tool for
nano-optics.
of semiconductor nanostructures is presented and applied
to silicon (Si) nanowires (NW’s). The phonon modes
symmetries and frequencies are calculated by means of
the elastic continuum medium theory. The modes
strengths and damping are calculated from a model for
lattice dynamics and perturbation theory. The data are
used in anisotropic Lorentz oscillator model to generate
the temperature and directional dependences of the infrared
dielectric function of free standing Si NW’s. Our results
showed that in the direction perpendicular to the
NW axis, the complex dielectric function is identical to
that of bulk Si. However, along the NW axis, the infrared
dielectric function is a strong function of the wavelength.
solution at boiling temperature. The idea is to use precursors that react only at high
temperature, in order to gain crystalline luminescent nanoparticles. CdSO4, Mn(NO3)2 and
Na2S2O3 were used as the precursors, and thioglycerol was employed as the capping agent and
also the reaction catalyst. Na2S2O3 is thermally sensitive and it releases S2− ions upon heating.
The CdS:Mn nanoparticles obtained are about 4 nm in size and show both cubic and hexagonal
crystalline phases with a ratio of 35% to 65%. The luminescence of nanoparticles contains a
peak at 580 nm, which is related to Mn2+ ions. Prolonged reaction time results in a decrease of
the Mn luminescence peak to about 35% of the maximum value. We discuss the possible causes
of the Mn peak reduction and attribute it to preferential dissolution of Mn ions into the solution
due to shape reconfiguration of the nanoparticles.
reaction, i.e. the sizes can be controllably adjusted by temperature. The
crystalline phase of the nanocrystals was also dependent on the temperature
of growth: higher temperature favours the cubic phase. The pH also plays an important role in nanoparticle growth, as lower pH leads to a higher release rate of sulfur species. At pH as high as 10, the growth rate remains slow even
at boiling temperature. This provides a way to controllably grow nanoparticles at high temperatures and/or control the nucleation growth processes.