Publications

2010

• Optical Properties of Dibenzo[d,d′]thieno[3,2-b;4,5-b′]dithiophene Monocrystals: The Effect of Intermolecular Interactions
  
  • Alessandrini L.
  • Braga D.
  • Jaafari A.
  • Miozzo L.
  • Mora S.
  • Silvestri L.
  • Tavazzi S.
  • Yassar Abderrahim
  Journal of Physical Chemistry A, American Chemical Society, 2010, 115 (3), pp.225-231. The polarized UV−visible absorption spectra of dibenzo[d,d′]thieno[3,2-b;4,5-b′]dithiophene single crystals are reported and interpreted to definitively attribute the observed bands and their polarizations. The results provide information on the intermolecular interactions and on the aggregation in the condensed phase, which can be of either herringbone- or H-type, depending on the electronic transition taken into considerations, with consequences on the order and polarization of the absorption bands. A relatively easy method is also discussed to obtain information on the structural/morphological properties of different types of samples, including thin films, which have been recently proposed for high-performance organic film-effect transistors for their high ionization potential and photostability. (10.1021/jp1052826)
  DOI : 10.1021/jp1052826
• Two-dimensional photonic crystal for absorption enhancement in hydrogenated amorphous silicon thin film solar cells
  
  • Gomard Guillaule
  • Drouard Emmanuel
  • Letartre Xavier
  • Meng Xianqin
  • Kaminski Anne
  • Fave Alain
  • Garcia-Caurel Enric
  • Lemiti Mustapha
  • Seassal Christian
  Journal of Applied Physics, American Institute of Physics, 2010, 108 (12), pp.123102. We propose a photovoltaic solar cell design based on a 100 nm thick absorbing layer made of hydrogenated amorphous silicon and patterned as a two-dimensional planar photonic crystal (PPC). After scanning the parameters of the PPC within the patterned cell, optical simulations performed on the best configuration obtained reveal that a relative increase in the integrated absorption inside the active layer of 28% can be expected between 300 and 720 nm compared to an equivalent but nonpatterned cell under normal incidence. Besides, this integrated absorption is found to be robust toward the angle of incidence. Incident light is efficiently coupled to leaky mode resonances of the PPC provided an appropriated tuning of its parameters. The effects of the reflectance of the back contact coupled to a conductive optical spacer on the absorption are also discussed. (10.1063/1.3506702)
  DOI : 10.1063/1.3506702
• Iron catalyst for the growth of carbon nanofibers: Fe, Fe3C or both?
  
  • He Zhanbing
  • Maurice Jean-Luc
  • Gohier Aurélien
  • Lee Chang Seok
  • Pribat Didier
  • Cojocaru Costel Sorin
  Chemistry of Materials, American Chemical Society, 2010, 23, pp.5379. Iron is a widely used catalyst for the growth of carbon nanotubes (CNTs) or carbon nanofibers (CNFs) by catalytic chemical vapor deposition. However, both Fe and Fe-C compounds (generally, Fe3C) have been found to catalyze the growth of CNTs/CNFs, and a comparison study of their respective catalytic activities is still missing. Furthermore, the control of the crystal structure of iron-based catalysts, that is α-Fe or Fe3C, is still a challenge, which not only obscures our understanding of the growth mechanisms of CNTs/CNFs, but also complicates subsequent procedures, such as the removal of catalysts for better industrial applications. Here, we show a partial control of the phase of iron catalysts (α-Fe or Fe3C), obtained by varying the growth temperatures during the synthesis of carbon-based nanofibers/nanotubes in a plasma-enhanced chemical vapor deposition reactor. We also show that the structure of CNFs originating from Fe3C is bamboo-type, while that of CNFs originating from Fe is not. Moreover, we directly compare the growth rates of carbon-based nanofibers/nanotubes during the same experiments and find that CNFs/CNTs grown by α-Fe nanoparticles are longer than CNFs grown from Fe3C nanoparticles. The influence of the type of catalyst on the growth of CNFs is analyzed and the corresponding possible growth mechanisms, based on the different phases of the catalysts, are discussed. (10.1021/cm202315j)
  DOI : 10.1021/cm202315j
• Thermal effects on the Raman spectra of nanodiamonds
  
  • Chaigneau Marc
  • Girard Hugues
  • Arnault Jean-Charles
  • Ossikovski Razvigor
  , 2011, 1282. (10.1557/opl.2011.309)
  DOI : 10.1557/opl.2011.309
• Experimental demonstration of enhanced slow and fast light by forced coherent population oscillations in a SOA
  
  • Berger Perrine
  • Bourderionnet Jérôme
  • de Valicourt Guilhem
  • Brenot Romain
  • Bretenaker Fabien
  • Alouini Mehdi
  • Dolfi Daniel
  • Bretenaker F
  , 2010. —We experimentally demonstrate enhanced slow and fast light at GHz frequencies by forced coherent population oscillations (CPOs) in a SOA. This opens the possibility to conceive a controllable RF phase shifter based on this setup. Slow and fast light in a semiconductor optical amplifier (SOA) enables to realize RF phase-shifters which are key components in numerous microwave photonics applications [1], [2]. At GHz frequencies, the achievable phase shift experienced by an optically carried RF signal passing through the SOA has been recently increased up to π by optically filtering out the red-shifted modulation sideband before detection [3]. Moreover, a phase shift of 2π at 19 GHz has also been obtained with this method by cascading several SOAs [4]. However, this method involves the use of a very sharp optical notch filter and is consequently efficient mainly for relatively high frequencies (typically above 5 GHz). Furthermore, the insertion of the optical filter leads to a significant noise enhancement [5]. Besides, Anton et al. have recently predicted that modulating the injection current of the SOA at the same frequency of the signal should enhance the phase shift of the signal [6]. The principle of such forced coherent population oscillations has been experimentally validated in an erbium doped fiber amplifier at very low frequency (20 Hz) [7]. In the present paper, we experimentally extend this concept in a SOA at GHz frequencies. We moreover give a comprehensive theoretical description of this phenomena, based on a comparison with optical filtering technique. To experimentally demonstrate forced coherent population oscillations, we used a reflective SOA developed by Alcatel-Thales III-V lab. and specifically designed to be modulated at high frequencies [8]. The experimental setup is shown in Fig. (a). The microwave signal generated by the Vector Network Analyser (VNA) modulates both the injected current of the SOA and the input optical power. An RF attenuator enables to control the modulation depth of the injected current. The gain and the phase shift introduced by the SOA are P. Berger, J. Bourderionnet, M. Alouini and D. Dolfi are with Thales Research&Technology, 1 av. Augustin Fresnel, (10.1109/ISLC.2010.5642729)
  DOI : 10.1109/ISLC.2010.5642729
• Europium(II) Compounds: Simple Synthesis of a Molecular Complex in Water and Coordination Polymers with 2,2'-Bipyrimidine Mediated Ferromagnetic Interactions
  
  • Zucchi Gaël
  • Thuéry Pierre
  • Rivière Eric
  • Ephritikhine M.
  Chemical Communications, Royal Society of Chemistry, 2010, 46, pp.9143. Reaction between EuCl2 and 2,2'-bipyrimidine (bpm) in de-oxygenated water afforded a cationic molecular complex [EuCl(bpm)2(H2O)4][Cl]∙H2O (1). When performed in an organic solvent such as THF or methanol, the same reaction yielded a 3-dimensional coordination polymer of formula [EuCl2(bpm)(MeOH)0.5] (2) in which both bpm and the chloride ions act as linkers between the Eu(II) ions. Upon replacing Cl- by I-, two coordination polymers of formula {[Eu(bpm)2(H2O)3][I]2*0.5bpm}∞ (3) and {[Eu(I)(bpm)(MeOH)]- [I]}∞ (4) were obtained from reaction in water and methanol, respectively. All these compounds were characterized by X-ray crystallography. Investigations of the magnetic properties revealed a weak antiferromagnetic coupling in 2, while 3 and 4 showed a weak ferromagnetic coupling at low temperature. (10.1039/c0cc02539a)
  DOI : 10.1039/c0cc02539a
• Alternative architectures for RF phase shifters and optical delay lines based on slow and fast light in SOAs
  
  • Berger Perrine
  • Bourderionnet Jérôme
  • Dolfi Daniel
  • Alouini Mehdi
  • Bretenaker Fabien
  • de Valicourt Guilhem
  • Brenot Romain
  , 2010. We show that forced coherent population oscillations (CPO) constitute an alternative setup to conceive a controllable RF phase shifter, and that wave-mixing in SOAs opens the possibility to conceive optical tunable delay lines beyond the carrier lifetime limit. (10.1109/MWP.2010.5664183)
  DOI : 10.1109/MWP.2010.5664183
• Process and material challenges in the high rate deposition of microcrystalline silicon thin films and solar cells by Matrix Distributed Electron Cyclotron Resonance plasma
  
  • Kroely Laurent
  , 2010. High deposition rates on large areas are industrial needs for mass production of microcrystalline silicon (μc-Si:H) solar cells. This doctoral work aims at exploring the usefulness of Matrix Distributed Electron Cyclotron Resonance (MDECR) plasmas to process the intrinsic layer of μc-Si:H p-i-n solar cells at high rates. With the high dissociation of silane achieved in MDECR plasmas, deposition rates as high as 6nm/s and 2.8nm/s have been demonstrated in our lab for amorphous and microcrystalline silicon respectively, without hydrogen dilution. This technique is also promising because it can be easily scaled up on large areas, just by extending the matrix of elementary microwave applicators. This subject was a unique opportunity to cover the whole chain of this field of research : A new MDECR reactor has been specially designed and assembled during this project. Its maintenance and its improvement have been important technical challenges : for example, the addition of a load-lock enabled us to lower the oxygen concentration in our films by a factor of 10. The impact of the deposition parameters (e.g. the ion energy, the substrate temperature, different gas mixtures, the microwave power) has been explored in extensive parametric studies in order to optimize the material quality. Great efforts have been invested in the characterization of the films. Our strategy has been to develop a wide range of diagnostics (ellipsometry, Raman spectroscopy, SIMS, FTIR, XRD, electrical characterizations etc.). Finally, p-i-n cells have been processed with the selected interesting materials. The successive successful improvements in the material quality (e.g. diffusion lengths of holes parallel to the substrate as high as 250 nm) did unfortunately not result in high efficiency solar cells. Their limited performance is in particular due to a very poor response in the red part of the spectrum resulting in low current densities. Consequently, the potential sources of limitation of the reactor, the material and the device have been studied : e.g. the presence of “cracks” prone to post-oxidation in the highly crystallized materials and the risk of deterioration of the ZnO substrate or of the p-doped layer by a too high process temperature or by hydrogen diffusing from the plasma.
• Red-emitting fluorescent Organic Light emitting Diodes with low sensitivity to self-quenching
  
  • Forget Sebastien
  • Chenais Sebastien
  • Tondelier Denis
  • Geffroy Bernard
  • Gozhyk Iryna
  • Lebental Mélanie
  • Ishow Eléna
  Journal of Applied Physics, American Institute of Physics, 2010, 108 (6), pp.064509. Concentration quenching is a major impediment to efficient organic light-emitting devices. We herein report on Organic Light-Emitting Diodes (OLEDs) based on a fluorescent amorphous red-emitting starbust triarylamine molecule (4-di(4'-tert-butylbiphenyl-4-yl)amino-4'-dicyanovinylbenzene, named FVIN), exhibiting a very small sensitivity to concentration quenching. OLEDs are fabricated with various doping levels of FVIN into Alq3, and show a remarkably stable external quantum efficiency of 1.5% for doping rates ranging from 5% up to 40%, which strongly relaxes the technological constraints on the doping accuracy. An efficiency of 1% is obtained for a pure undoped active region, along with deep red emission (x=0.6; y=0.35 CIE coordinates). A comparison of FVIN with the archetypal DCM dye is presented in an identical multilayer OLED structure. (10.1063/1.3481460)
  DOI : 10.1063/1.3481460
• Mapping charge transfers between quantum levels using noncontact atomic force microscopy
  
  • Borowik Lukasz
  • Kusiaku Koku
  • Deresmes D.
  • Theron Didier
  • Diesinger Heinrich
  • Melin Thierry
  • Nguyen-Tran Thuat
  • Roca I Cabarrocas Pere
  Physical Review B: Condensed Matter and Materials Physics (1998-2015), American Physical Society, 2010, 82, pp.073302-1-4. We demonstrate the possibility to map nanoscale charge transfers between quantum electronic levels at room temperature, using noncontact atomic force microscopy and Kelvin force microscopy in a regime of weak electromechanical coupling. A two-level system is studied, consisting of degenerately doped silicon nanocrystals on silicon substrates, with size in the 2–50 nm range, in which the energy spacing is tuned by the nanocrystal quantum confinement over a ≈1 eV range. The nanocrystal ionization is found to follow an energy compensation mechanism driven by quantum confinement, in quantitative agreement with parametrized tight-binding calculations of its band structure (10.1103/PhysRevB.82.073302)
  DOI : 10.1103/PhysRevB.82.073302
• Display and lighting applications based on organic light-emitting diode technologies: materials and processes
  
  • Geffroy Bernard
  , 2010.
• Graphene growth directly on functional substrate
  
  • Lee C. S.
  • Baraton L.
  • He Z. B.
  • Maurice Jean-Luc
  • Pribat D.
  • Cojocaru C. S.
  , 2010. Graphene is perhaps the most promising material ever discovered for microelectronics applications, but its preparation includes either high-temperature processing or film transfer, and sometimes both of them, which forbids for the moment its introduction into fabrication lines. In this communication we report a synthesis route involving exposure of nickel thin films deposited on silicon oxide to a mixture of methane and hydrogen activated by DC plasma at 450°C. In addition of the awaited graphene film formed at the surface of catalyst layer, we observed the formation of a second graphene film at the catalyst/silicon oxide interface. To our knowledge, no other team have yet reported graphene synthesis directly on a dielectric substrate at low temperature. With the idea of increasing the graphene structural quality, we studied the effect of additional post growth high temperature annealing. The films synthesized were characterized using Raman spectroscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM).
• Nickel catalyst faceting in plasma-enhanced direct current chemical vapor deposition of carbon nanofibers
  
  • He Z. B.
  • Maurice Jean-Luc
  • Lee C. S.
  • Cojocaru C. S.
  • Pribat D.
  Arabian Journal for Science and Engineering, King Fahd University of Petroleum and Minerals - Springer, 2010, 35 (1C), pp.19. Vertically aligned multi-walled carbon nanofibers (CNFs) were grown by plasma-enhanced chemical vapor deposition with Ni catalysts on the top of nanofibers. Transmission electron microscopy was used to study the morphology and crystallography of Ni catalysts, which are essential for the nucleation and growth of CNFs. A model for the faceted shape of Ni catalytic particles is proposed. It is shown that the exposed polyhedral surfaces of Ni catalytic particles for vertically aligned CNFs are composed of {111}, {110}, and {100}, a faceting that appears to be characteristic of the growth atmosphere.
• Hybrid solar cells based on silicon nanowires impregnated polymeric materials
  
  • Bataille Guillaume
  • Tondelier Denis
  • Yu Linwei
  • Daineka D.
  • Geffroy Bernard
  • Jousselme Bruno
  • Bonnassieux Yvan
  • Palacin Serge
  • Roca I Cabarrocas Pere
  , 2010.
• Absorbing photonic crystals for thin film photovoltaics
  
  • Daif O. El
  • Drouard E.
  • Gomard G.
  • Meng X.
  • Kaminski A.
  • Fave A.
  • Lemiti M.
  • Garcia-Caurel Enric
  • Ahn S.
  • Jeon H.
  • Seassal Christian
  • Roca I Cabarrocas Pere
  , 2010. The absorption of thin hydrogenated amorphous silicon layers can be efficiently enhanced through a controlled periodic patterning. Light is trapped through coupling with photonic Bloch modes of the periodic structures, which act as an absorbing planar photonic crystal. We theoretically demonstrate this absorption enhancement through one or two dimensional patterning, and show the experimental feasibility through large area holographic patterning. Numerical simulations show over 50% absorption enhancement over the part of the solar spectrum comprised between 380 and 750nm. It is experimentally confirmed by optical measurements performed on planar photonic crystals fabricated by laser holography and reactive ion etching.
• Phosphole-based π-conjugated electroluminescent materials for OLEDs
  
  • Joly Damien
  • Tondelier Denis
  • Deborde Valérie
  • Geffroy Bernard
  • Hissler Muriel
  • Réau Régis
  New Journal of Chemistry, Royal Society of Chemistry [1987-....], 2010, 34 (8), pp.1603-1611. Novel mixed phosphole-fluorene π-conjugated systems have been prepared using the Fagan-Nugent route. Their optical (UV-visible absorption, fluorescence spectra) and electrochemical properties have been systematically evaluated. The variation of the substitution pattern of phosphole derivatives and chemical modification of their P atoms afford thermally stable derivatives which are photoluminescent. The use of these derivatives as emitters in OLEDs strongly depends on the substituent linked on the P-atom. The gold complexes are not stable electroluminescent materials since they decompose rapidly when the devices are operating. In contrast, the thiooxophospholes are stable electroluminescent materials, and the OLEDs incorporating these derivatives as emitters display very high performances. (10.1039/C0NJ00122H)
  DOI : 10.1039/C0NJ00122H
• Design and fabrication of photonic crystal thin film photovoltaic cells
  
  • Gomard Guillaume
  • El Daif Ounsi
  • Drouard Emmanuel
  • Meng Xianqin
  • Kaminski Anne
  • Fave Alain
  • Lemiti Mustapha
  • Garcia-Caurel Enric
  • Roca I Cabarrocas Pere
  • Seassal Christian
  , 2010, 7725 (No3), pp./. We present the integration of an absorbing planar photonic crystal within a thin film photovoltaic cell. The devices are based on a stack including a hydrogenated amorphous silicon P-i-N junction surrounded by TCO layers, with a back metallic contact. Optical simulations exhibit a significant increase of the integrated absorption in the 300-720nm wavelength range. The global electro-optical characteristics of such a new solar cell, and the impact of surface passivation, are also discussed. Carrier generation rate maps calculated by optical simulations are introduced as input data in a commercial electrical simulation software. The fabrication of such a device is finally addressed, with a specific focus on the use of low cost nanopatterning processes compatible with large areas. (10.1117/12.854383)
  DOI : 10.1117/12.854383
• Contrast evaluation of the polarimetric images of different targets in turbid medium: possible sources of systematic errors
  
  • Novikova Tatiana
  • Bénière Arnaud
  • Goudail François
  • de Martino Antonello
  , 2010, 7672, pp.76720Q. Subsurface polarimetric (differential polarization, degree of polarization or Mueller matrix) imaging of various targets in turbid media shows image contrast enhancement compared with total intensity measurements. The image contrast depends on the target immersion depth and on both target and background medium optical properties, such as scattering coefficient, absorption coefficient and anisotropy. The differential polarization image contrast is usually not the same for circularly and linearly polarized light. With linearly and circularly polarized light we acquired the orthogonal state contrast (OSC) images of reflecting, scattering and absorbing targets. The targets were positioned at various depths within the container filled with polystyrene particle suspension in water. We also performed numerical Monte Carlo modelling of backscattering Mueller matrix images of the experimental set-up. Quite often the dimensions of container, its shape and optical properties of container walls are not reported for similar experiments and numerical simulations. However, we found, that depending on the photon transport mean free path in the scattering medium, the above mentioned parameters, as well as multiple target design could all be sources of significant systematic errors in the evaluation of polarimetric image contrast. Thus, proper design of experiment geometry is of prime importance in order to remove the sources of possible artefacts in the image contrast evaluation and to make a correct choice between linear and circular polarization of the light for better target detection.
• Tip enhanced Raman spectroscopy evidence for amorphous carbon contamination on gold surfaces
  
  • Chaigneau Marc
  • Picardi Gennaro
  • Ossikovski Razvigor
  Surface Science : A Journal Devoted to the Physics and Chemistry of Interfaces, Elsevier, 2010, 604, pp.701-705. We show that the origin of the spectral fluctuations frequently observed in tip enhanced Raman spectroscopy (TERS) experiments can be mainly related to the presence of surface-contaminating amorphous carbon- based species. We have monitored the spectral fluctuations originating from the sharp metallic tips used as apertureless near field probes, as well as from commonly used noble metal substrates. A correlation between the tip surface roughness and the carbon-based spectral fluctuations has been revealed. An Au-(1 1 1) bare substrate has been mapped with sub-wavelength resolution by TERS, evidencing the localization of the carbon contaminants on the surface steps and grain boundaries. (10.1016/j.susc.2010.01.018)
  DOI : 10.1016/j.susc.2010.01.018
• White electroluminescence of lanthanide complexes resulting from exciplex formation
  
  • Zucchi Gael
  • Jeon Taewoo
  • Tondelier Denis
  • Aldakov Dmitry
  • Thuéry Pierre
  • Ephritikhine M.
  • Geffroy Bernard
  Journal of Materials Chemistry, Royal Society of Chemistry, 2010, 20 (11), pp.2114-2120. Bimetallic complexes of the visible-emitting Eu3+, Tb3+ and Sm3+ ions with 2,2′-bipyrimidine (bpm) and acetylacetonate (acac) ligands have been synthesized and crystallographically characterized. They have been found to be isomorphous with the general formula [{Ln(acac)3}2(μ-bpm)] (Ln = Eu, 1; Ln = Tb, 2; Ln = Sm, 3). Their X-ray crystal structure shows that the aromatic polyamine ligand bridges the two metal ions. These volatile complexes have been thermally evaporated to be introduced in multilayer OLEDs as dopants. In addition to the electroluminescence of the lanthanide ion, a broad emission in the yellow-green region was obtained. This resulted in white electroluminescence of the devices doped with 1 or [{Eu(tta)3}2(μ-bpm)] (4) complexes (tta = 2-thenoyltrifluoromethanesulfonato). This broad emission is shown to be caused by the formation of an exciplex between the dopant and the host matrix within the emitting layer of the devices. (10.1039/B921740A)
  DOI : 10.1039/B921740A
• Top Emission OLED Pixels Driving by Organic Thin Film Transistors
  
  • Bonnassieux Yvan
  • Tondelier Denis
  • Yaghmazadeh Omid
  • Aldakov Dmitry
  • Almutari Bandhar
  • Kim Chang Hyun
  • Geffroy Bernard
  • Horowitz Gilles
  , 2010.
• An electrochemical and structural investigation of silicon nanowires as negative electrode for Li-ion batteries
  
  • Laik Barbara
  • Ung Diane
  • Caillard Amael
  • Cojocaru Costel Sorin
  • Pribat Didier
  • Pereira-Ramos Jean Pierre
  Journal of Solid State Electrochemistry, Springer Verlag, 2010, 14 (10), pp.1835--1839. The electrochemical and structural responses of silicon nanowires deposited by chemical vapor deposition are investigated. Transmission electron microscopy and X-ray diffraction experiments show the electrochemical lithiation of SiNWs is not a quantitative process in good agreement with cycling experiments performed as a function of cycling limits. The SiNWs are not deeply lithiated as revealed by TEM micrographs. Our results suggest the existence of two well-defined lithiation steps, first at ∼0.2 V into amorphous silicon and then into crystalline silicon at ∼0.1 V. Cycling SiNWs above 100 mV avoid the lithiation of c-Si which preserves the silicon 3-D architecture and results in good cycling performances. A stable capacity value of ∼500 mAh g−1 is achieved over at least 50 cycles. (10.1007/s10008-010-1045-5)
  DOI : 10.1007/s10008-010-1045-5
• Plasma emission diagnostics during fast deposition of microcrystalline silicon thin films in matrix distributed electron cyclotron resonance plasma CVD system
  
  • Ram S. K.
  • Kroely Laurent
  • Kasouit Samir
  • Bulkin Pavel
  • Roca I Cabarrocas P.
  Physica Status Solidi C: Current Topics in Solid State Physics, Wiley, 2010, pp.553-556.
• Mueller matrix imaging of human colon tissue for cancer diagnostics: how Monte Carlo modeling can help in the interpretation of experimental data
  
  • Antonelli Maria Rosaria
  • Pierangelo Angelo
  • Novikova Tatiana
  • Validire Pierre
  • Benali Abdelali
  • Gayet Brice
  • de Martino Antonello
  Optics Express, Optical Society of America - OSA Publishing, 2010, 18 (26), pp.10200. Colon samples with both healthy and cancerous regions have been imaged in diffuse light and backscattering geometry by using a Mueller imaging polarimeter. The tumoral parts at the early stage of cancer are found to be less depolarizing than the healthy ones. This trend clearly shows that polarimetric imaging may provide useful contrasts for optical biopsy. Moreover, both types of tissues are less depolarizing when the incident polarization is linear rather than circular. However, to really optimize an optical biopsy technique based on polarimetric imaging a realistic model is needed for polarized light scattering by tissues. Our approach to this goal is based on numerical Monte-Carlo simulations of polarized light propagation in biological tissues modeled as suspensions of monodisperse spherical scatterers representing the cell nuclei. The numerical simulations were validated by comparison with measurements on aqueous polystyrene sphere suspensions, which are commonly used as tissue phantoms. Such systems exhibit lower depolarization for incident linear polarization in the Rayleigh scattering regime, i.e. when the sphere diameters are smaller than the wavelength, which is obviously not the case for cell nuclei. In contrast, our results show that this behaviour can also be seen for "large" scatterers provided the optical index contrast between the spheres and the surrounding medium is small enough, as it is likely to be the case in biological tissues (10.1364/OE.18.010200)
  DOI : 10.1364/OE.18.010200
• Characterization of inclined GaSb nanopillars by Mueller matrix ellipsometry
  
  • Nerbo I. S.
  • Le Roy Séverine
  • Foldyna M.
  • Sondergard E.
  Journal of Applied Physics, American Institute of Physics, 2010, 108 (1), pp.014307. Inclined GaSb nanopillars prepared by low energy ion sputtering with oblique ion beam incidence have been characterized by two different Mueller matrix ellipsometric tools. The optical properties of the nanopillars were found to be well described by a uniaxial anisotropic graded effective medium model. The pillar height and inclination angle were determined by fitting the parameters of the effective medium model to spectroscopic (1.44-2.88 eV) Mueller matrix measurements at multiple azimuth sample orientations. A set of different samples with various average pillar height and inclination angle was studied; results from the optical characterization correspond well with those from scanning electron microscopy analysis. For samples with nanopillars inclined by 45 degrees or less, the height could be determined from a single Mueller matrix measurement at only one azimuth orientation, allowing real-time in situ observation of the formation. The nanopillars were also studied using a single wavelength angle resolved Mueller polarimeter, which also can be used to determine height and inclination of the pillars, in addition to validating the optical model over a wide range of incident and azimuth angles. (10.1063/1.3386460)
  DOI : 10.1063/1.3386460