Nanostructures, Nanoparticles and Nanocrystals

• Spectroscopic ellipsometry and polarimetry for materials and systems analysis at the nanometer scale: state-of-the-art, potential, and perspectives
  Authors: M. Losurdo, M. Bergmair, G. Bruno, D. Cattelan, C. Cobet, A. de Martino, K. Fleischer, Z. Dohcevic-Mitrovic, N. Esser, M. Galliet, R. Gajic, D. Hemzal, K. Hingerl, J. Humlicek, R. Ossikovski, Z.V. Popovic, O. Saxl
  Journal of Nanoparticle Research 11, 1521-1554 (2009)
  Abstract: This paper discusses the fundamentals, applications, potential, limitations, and future perspectives of polarized light reflection techniques for the characterization of materials and related systems and devices at the nanoscale. These techniques include spectroscopic ellipsometry, polarimetry, and reflectance anisotropy. We give an overview of the various ellipsometry strategies for the measurement and analysis of nanometric films, metal nanoparticles and nanowires, semiconductor nanocrystals, and submicron periodic structures. We show that ellipsometry is capable of more than the determination of thickness and optical properties, and it can be exploited to gain information about process control, geometry factors, anisotropy, defects, and quantum confinement effects of nanostructures.
  Email: maria.losurdo@ba.imip.cnr.it, denis.cattelan@horiba.com, melanie.gaillet@horiba.com



• Spectroscopic ellipsometry analysis of silicon nanotips obtained by electron cyclotron resonance plasma etching
  A. Mendoza-Galvan, k. Jarrendahl, H. Arwin, Yi-F. Huang, L.C. Chen, K. H. Chen
  APPLIED OPTICS, 48, Pages: 4996-5004 (2009)
  Abstract: Silicon nanotips fabricated by electron cyclotron resonance plasma etching of silicon wafers are studied by spectroscopic ellipsometry. The structure of the nanotips is composed of columns 100-140 nm wide and spaced by about 200 nm. Ellipsometry data covering a wide spectral range from the midinfrared to the visible are described by modeling the nanotip layer as a graded uniaxial film using the Bruggeman effective medium approximation. The ellipsometry data in the infrared range reveal two absorption bands at 754 and 955 cm(-1), which cannot be resolved with transmittance measurements. These bands indicate that the etching process is accompanied with formation of carbonaceous SiC and CHn species that largely modify the composition of the original crystalline silicon material affecting the optical response of the nanotips.
  Email: amendoza@qro.cinvestav.mx



• On the influence of silicon oxide nanoparticles on the optical and surface properties of hybrid (inorganic-organic) barrier materials
  A. Laskarakis, S. Logothetidis, D. Georgiou, S. Amberg-Schwab, U.Weber
  THIN SOLID FILMS, 517, Pages: 6275-6279 (2009)
  Abstract: One of the major scientific and technological challenges for the production of flexible organic electronic devices is the device protection against atmospheric molecule permeation, which causes corrosion reducing its operation and lifetime. In this work, Spectroscopic Ellipsometry has been implemented to investigate the influence of silicon dioxide nanoparticles on the optical properties of hybrid polymers. The spectra analysis revealed valuable information about the electronic and vibrational response as well as the cross-linking mechanisms of these materials. The correlation of the optical properties with the synthesis parameters and the barrier response will contribute towards their optimization in order to be used as high barrier coatings for flexible organic electronics applications.
  Email: alask@physics.auth.gr



• Combined reflectometry-ellipsometry technique to measure graphite down to monolayer thickness
  W. Wang, M. Balooch, C. Claypool, M. Zawaideh, K. Farnaam
  Abstract: Graphene, the single layer of graphite, has been the focus of many researchers internationally because of its unique electronic properties. The characterization of graphene films deposited on various substrates other than SiO2 has been a challenging task thus far. This article discusses a rapid, sensitive, and non-destructive method for characterization of graphene on various substrates, including silicon, based on combined reflectometry and ellipsometry techniques. The optical properties deduced from the multi-angle, polarized light measurements in the range of 190-1000nm suggest that multi-layer graphite is a birefringent material with thickness-dependent optical properties.
  Email: weie.want@intel.com



• Enhanced absorption in Au nanoparticles/a-Si:H/c-Si heterojunction solar cells exploiting Au surface plasmon resonance
  M. Losurdo, M.M. Giangregorio, G.V. Bianco, A. Sacchetti, P. Capezzuto, G. Bruno
  SOLAR ENERGY MATERIALS AND SOLAR CELLS 93 Pages: 1749-1754 (2009)
  Abstract: Au nanoparticles (NPs)/(n-type)a-Si:H/(p-type)c-Si heterojunctions have been deposited combining plasma-enhanced chemical-vapour deposition (PECVD) with Au sputtering. We demonstrate that a density of similar to 1.3 x 10(11) cm(-2) of Au nanoparticles with an approximately 20 nm diameter deposited onto (n-type)a-Si:H/(p-type)c-Si heterojunctions enhance performance exploiting the improved absorption of light by the surface plasmon resonance of Au NPs. In particular, Au NPs/(n-type)a-Si:H/(p-type)c-Si show an enhancement of 20% in the short-circuit current, J(SC), 25% in the power output, P-max and 3% in the fill factor, FF, compared to heterojunctions without Au NPs. Structures have been characterized by spectroscopic ellipsometry, atomic force microscopy and current-voltage (I-V) measurements to correlate the plasmon resonance-induced enhanced absorption of light with photovoltaic performance.
  Email: giovanni.bruno@ba.imip.cnr.it



• Optical spectroscopy study of nc-Si-based p-i-n solar cells
  J. Sancho-Parramon, D. Gracin, M. Modreanu, A. Gajovic
  SOLAR ENERGY MATERIALS AND SOLAR CELLS: 93 Pages: 1768-1772 (2009)
  Abstract: In the present study we analyzed nanocrystalline silicon (nc-Si)-based p-i-n thin film structures (SiC/nc-Si/n-doped amorphous Si) on glass produced by radio-frequency plasma-enhanced chemical vapor deposition. The crystallinity of the nc-Si layer was modified by varying the deposition conditions ([SiH4]/[H-2] ratio in the plasma and radio-frequency power). Structural properties of the samples (crystalline fraction and crystal size distribution) were inferred by Raman spectroscopy. Different optical spectroscopy methods were combined for the determination of the optical constants in different spectral ranges: spectrophotometry, ellipsometry and photothermal deflection spectroscopy. Characterization results evidence that the optical properties of the nc-Si layers are strongly connected with the layer structural properties. Thus, the correlation between density of defects. Urbach energy, band-gap and line-shape of dielectric function critical points with the crystalline properties of the films is established.
  Email: jsancho@irb.hr



• Optical diagnostics of anisotropic nanoscale films on transparent isotropic materials by integrating reflectivity and ellipsometry
  P. Adamson
  APPLIED OPTICS 48 Pages: 5906-5916 (2009)
  Abstract: The reflection of s-and p-polarized electromagnetic plane waves from an anisotropic ultrathin dielectric film on transparent isotropic substrate is investigated in the long-wavelength limit. The analytical approximate formulas are obtained for the reflection coefficients and ellipsometric angles that agree with the exact computer solution of the reflection problem for anisotropic systems. The possibilities of using the obtained expressions for resolving the inverse problem for ultrathin anisotropic dielectric films upon isotropic dielectric substrates are discussed. It is shown that a promising technique for determining the optical constants of anisotropic dielectric films on transparent substrates is the integration of ellipsometry and differential reflectivity.



• Study on optical constants of ITO:Ag nanocompsite films
  Z. Sun, L. Xiao, C. Cao, Q. Cai, X. Song
  APPLIED OPTICS 48 Pages: 5759-5763 (2009)
  Abstract: Indium tin oxide (ITO) thin films doped with a volume ratio of 0.3% Ag were prepared by sputtering and subsequently annealed in temperatures of 200, 260, 300, 360, and 400 degrees C. The annealed films show increased transmittance in the visible wavelength range. The refractive index n and extinction coefficient k were extracted from simulating the transmittance spectra by using spectroscopic ellipsometry analysis method. The n values apparently increased in the whole wavelength range, but the k values were found to have almost no change in the near ultraviolet region after Ag doping. It is, therefore, proposed that the ITO:Ag combined with an ITO multilayer structure can be applied in special optical devices.
  Email: szq100976@npc.gov.cn



• Influence of nanocrystal size on dielectric functions of Si nanocrystals embedded in SiO2 matrix
  R.J. Zhang, Y.M. Chen, W.J Lu, Q.Y. Cai, Y.X. Zheng, L.Y. Chen
  APPLIED PHYSICS LETTERS 95 161109 (2009)
  Abstract: The complex dielectric functions of Si-nanocrystals (nc-Si) with different sizes embedded in SiO2 matrix synthesized by SiOx/SiO2 superlattice approach is obtained by spectroscopic ellipsometry. The Maxwell-Garnett effective medium approximation and the Lorentz oscillator model are employed in the spectra fitting. The dependence of the dielectric functions on the nc-Si size is observed. A significant suppression in amplitude of the dielectric functions with respect to bulk crystalline silicon, and a large influence of the nc-Si size on the E-1 and E-2 critical points are observed and discussed.
  Email: rjzhang@fudan.edu.cn



• Infrared Spectroscopic Ellipsometry analysis of Nano-structured thin films in polymers and semiconductors
  J.L. Stehle, J.P. Piel
  Abstract: Spectroscopic ellipsometry has long been recognized as a powerful technique to characterize thins films and multilayer structures. It is now routinely used for non-destructive on-line characterization of semiconductor process. SOPRALAB leader in commercial spectroscopic ellipsometry for research and development, has already developed an infrared ellipsometer as an option on visible instrument to provide the largest wavelength range available up to now (from deep UV 190 nm to far infrared up to 28 mm). The instrument is presented here which includes a small spot size to get ride of the problems of back face reflection on silicon wafers, and an improved signal/noise ratio to allow rapid measurements compatible with an industrial environment. Some examples of application concerning thin films in polymer, dopant density, conductivity and sheet resistance in epilayers, composition of low k dielectrics and polymers are presented.
  Email: jeanlouis.stehle@sopra-sa.com



• Optical models for ellipsometric characterization of high temperature annealed nanostructured SiO2 films
  T. Lohner, A. Szekeres, AT. Nikolova, E. Vlaikova, P. Petrik, G. Huhn, K. Havancsak, I. Lisovskyy, S. Zlobin, I.Z. Indutnyy, P.E. Shepeliavyi
  JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS 11 Pages: 1288-1291 (2009)
  Abstract: Silicon oxide films, vacuum evaporated and annealed in Ar atmosphere at temperatures of 1000 and 1100 degrees C have been studied by spectroscopic ellipsometry By the Bruggeman effective-medium approximation, different optical models have been applied for characterization of the nanostructured SO2 films. The results showed that during annealing at 1000 degrees C, Si clusters were formed in the sub-stoichiometric SO1 (61) matrix, which crystallized in nanocrystallites with a volume fraction of similar to 14 % Annealing at 1100 degrees C transformed the oxide structure to stoichiometric SiO2 and created 22% nanocrystalline Si inclusions. A silicon dioxide top layer existed in all films, the thickness of which varied with the technological steps and was well correlated with the surface roughness obtained from the AFM imaging.



• Ellipsometric characterization of SiOx films with embedded Si nanoparticles
  A. Szekeres, E. Vlaikova, T. Lohner, P. Petrik, G. Huhn, K. Havancsak, I. Lisovskyy, S. Zlobin, I.Z. Indutnyy, P.E. Shepehavyi
  VACUUM 84 Pages: 115-118 (2009)
  Abstract: In this work we present results on the ellipsometric study of SiOx films in the spectral range of 280-820 nm. The films were deposited by vacuum thermal evaporation of SiO onto Si substrates heated at 150 degrees C. To stimulate the formation of silicon clusters in the oxide matrix the films were annealed at temperatures 700, 1000 and 1100 degrees C in argon for 5,15 and 30 min. By applying the Bruggeman effective-medium approximation theory and using multiple-layer optical models, from the ellipsometric data analysis the thickness, complex refractive index and composition of the films, as well as the size of the embedded Si nanocrystallites have been determined. Atomic-force microscopy imaging showed a very smooth surface, the roughness value of which correlated well with the top-layer thickness, determined from the ellipsometric data analysis.
  Email: szekeres@issp.bas.bg



• An ellipsometry study of silica nanoparticle layers at the water surface
  D. Zang, A. Stocco, D. Langevin, B. Wei, B.P. Binks
  Abstract: We have studied silica nanoparticle layers spread at the air/water interface. The surface pressure of the layers has been determined in a Langmuir trough via two orthogonal Wilhelmy plates. We observed significant differences in surface pressure according to the preparation protocol: layers spread then compressed or layers obtained after successive spreading steps. We also studied the two types of layers by multiple angle of incidence ellipsometry. We introduce a two-layer model which enables us to evaluate the radius of interfacial aggregates and their contact angle with the air/water interface.



• Optical Characterization of Laser-Synthesized Anatase TiO2 Nanopowders by Spectroscopic Ellipsometry and Photoluminescence Measurements
  M. Scepanovic, M. Grujic-Brojcin, M. Miric, Z. Dohcevic-Mitrovic, Z.V. Popovic
  ACTA PHYSICA POLONICA A 116 Pages: 603-606 (2009)
  Abstract: Nanosized titania (TiO2) is synthesized by laser-induced pyrolysis using TiCl4 as a liquid precursor. X-ray diffraction and Raman scattering confirmed anatase structure of TiO2 nanocrystals. The dielectric function epsilon(omega) of TiO2 nanopowders has been determined by spectroscopic ellipsometry in the energy range from 1.5 to 6 eNT at room temperature. The features observed in epsilon(omega) have been fitted to analytical line shapes by using the second derivatives of experimental spectra. The energies corresponding to different interband electronic transitions have been determined. Photoluminescence measurements have been carried out in vacuum for T = 20 K and T = 300 K. Under laser irradiation with sub-band gap photon energy, anatase nanocrystals have displayed strong visible photoluminescence emission. In this broad photoluminescence band different variations of line shape and position with excitation energy and temperature are observed for nanopowders with different crystallite size, pointing out to the various electronic transitions mediated by defect levels within the band gap.
  Email: maja@phy.bg.ac.rs



• Characterization of ZnSe Nanolayers by Spectroscopic Ellipsometry
  M. Scepanovic, M. Grujic-Brojcin, D. Nesheva, Z. Levi, I. Bineva, Z.V. Popovic
  Abstract: Single layers of ZnSe with thicknesses of 30, 40, 50, 70 and 100 nm are deposited at room substrate temperature by thermal evaporation of ZnSe powder in vacuum. The layers surface morphology has been investigated by atomic force microscopy. Structural characterization by the Raman scattering measurement revealed the existence of randomly oriented crystalline ZnSe particles in all layers, and the presence of amorphous phase in layers thinner than 100 nm. The ellipsometric measurements were performed in the range from 1.5 to 5 eV at room temperature in air. To interpret the experimental results, the Bruggeman effective medium approximation of dielectric function of ZnSe layers has been used, representing the layers as different mixtures of crystalline ZnSe (c-ZnSe), amorphous ZnSe (a-ZnSe), and voids. The assumption of polycrystalline ZnSe layers modeled as mixture of porous c-ZnSe (with volume fraction of voids approximate to 0.17) and a-ZnSe gives the best fit of ellipsometric experimental data. Single layer thicknesses similar to those expected from preparation conditions have been obtained by this fitting procedure. It has been also found that decrease in the layer thickness causes an increase of the volume fraction of a-ZnSe. Thus, c-ZnSe/a-ZnSe ratio, porosity and layer thickness obtained by spectroscopic ellipsometry, provides useful information about crystallinity and micro-/nanostructure of ZnSe nanolayers.
  Email: maja@ipb.ac.rs



• Linear and third-order nonlinear optical responses of multilayered Ag:Si3N4 nanocomposites
  J. Toudert, H. Fernandez, D. Babonneau, S. Camelio, T. Girardeau, J. Solis
  Abstract: The linear and third-order nonlinear responses of tailored Si3N4/Ag/Si3N4 trilayers and (Si3N4/Ag)(n)/Si3N4 multilayers grown by alternating ion-beam sputtering have been studied by combining complementary characterization techniques such as transmission electron microscopy, spectroscopic ellipsometry and degenerate four-wave mixing. The linear optical response dominated by the surface plasmon resonance of Ag nanoparticles has been measured over the whole visible range while the third-order nonlinear susceptibility has been probed at the surface plasmon resonance wavelength. Due to the weak in-plane interaction between Ag nanoparticles, the linear and nonlinear optical responses of the Si3N4/Ag/Si3N4 trilayers are mainly influenced by the size and shape of the nanoparticles. A maximum value of 1.1 x 10(-7) esu has been found at 635 nm for the effective third-order nonlinear susceptibility of the trilayer with the highest amount of silver. The linear optical response of the (Si3N4/Ag)(n)/Si3N4 multilayers is shown to be dominated by the surface plasmon resonance of isolated layers of weakly interacting nanoparticles at wavelengths shorter than 600 nm whereas a contribution due to vertical interactions has been shown for higher wavelengths. Below the vertical percolation threshold, their nonlinear optical response at the surface plasmon resonance wavelength is similar to the one of an isolated assembly of nanoparticles, and the effective third-order nonlinear susceptibility is slightly increased by decreasing the thickness of the Si3N4 spacer.
  Email: johann.toudert@gmail.com



• Combined reflectometry-ellipsometry technique to measure graphite down to monolayer thickness
  Wei-E Wang; M Balooch; C Claypool; M Zawaideh; K Farnaam
  Solid State Technology 52 6 (2009)
  Abstract: The accurate optical properties for graphene and graphite were determined in the 190-1000nm wavelength range using multi-layer graphite flakes on a substrate comprising bulk Si and a 300nm SiO2 film. These optical properties are derived as a function of thickness of graphite for TE and TM polarizations of light. The results suggest the complex index of refraction for TE is independent of thickness down to one monolayer (i.e., graphene).



• Optical and transport properties of ultrathin NbN films and nanostructures
  A. Semenov, B. Guenther, U. Boettger, H.W. Huebers, H. Bartolf, A. Engel, A. Schilling, K. Ilin, K.M Siegel, R. Schneider, D. Gerthsen
  PHYSICAL REVIEW B 80 054510 (2009)
  Abstract: Optical and transport properties of a series of ultrathin NbN films with different thickness grown on sapphire have been evaluated by means of spectral ellipsometry and dc measurements of superconducting critical parameters. The growth process and thus the nitrogen content have been optimized for each film in the series to achieve the highest superconducting transition temperature, which however increases with the film thickness. Optical and transport measurements agree in slowly increasing disorder while the electron density of states at the Fermi level shows a twofold decrease when the film thickness drops from 14 to 3 nm. Near-infrared extinction spectra of nanowire gratings from our films are well described by the scattering matrix method that uses optical parameters of nonstructured films and the grating geometry. The technique provides an attractive tool for analyzing various devices for nanophotonics.



• On the influence of silicon oxide nanoparticles on the optical and surface properties of hybrid (inorganic-organic) barrier materials
  Laskarakis, S. Logothetidis, D. Georgiou, S. Amberg-Schwab, U. Weber
  Abstract: One of the major scientific and technological challenges for the production of flexible organic electronic devices is the device protection against atmospheric molecule permeation, which causes corrosion reducing its operation and lifetime. In this work, Spectroscopic Ellipsometry has been implemented to investigate the influence of silicon dioxide nanoparticles on the optical properties of hybrid polymers. The spectra analysis revealed valuable information about the electronic and vibrational response as well as the cross-linking mechanisms of these materials. The correlation of the optical properties with the synthesis parameters and the barrier response will contribute towards their optimization in order to be used as high barrier coatings for flexible organic electronics applications.
  Email: alask@physics.auth.gr



• Ellipsometric surface plasmon resonance
  W.L. Hsu, S.S. Lee, C.K. Lee
  Society of Photo-Optical Instrumentation Engineers (2009)
  Abstract: We develop a new multifunctional optical biochip system that integrates an ellipsometer with a surface plasmon resonance _SPR_ feature. This newly developed biochip biosensor, which we call ESPR for an ellipsometric SPR, provides us with a system to retrieve detailed information such as the optical properties of immobilized biomolecular monolayers, surface concentration variations of biomedical reactions, and kinetic affinity between biomolecules required for further biotech analysis. Our ESPR can also serve as both a research and development tool and a manufacturing tool for various biomedical applications.
  Email: cklee@ntu.edu.tw



• Using Spectroscopic Ellipsometry to Characterize and Apply the Optical Constants of Hollow Gold Nanoparticles
  D. Wan, H.L. Chen, Y.S. Lin, S.Y. Chuang, J. Shieh, S.H. Chen
  ACS NANO 3 Pages: 960-970 (2009)
  Abstract: In this paper, we report the optical constants (refractive index, extinction coefficient) of self-assembled hollow gold nanoparticle (HGN) monolayers determined through spectroscopic ellipsometry (SE). We prepared a series of HGNs exhibiting various morphologies and surface plasmon resonance (SPR) properties. The extinction coefficient (k) curves of the HGN monolayers exhibited strong SPR peaks located at wavelengths that followed similar trends to those of the SPR positions of the HGNs in solution. The refractive index (n) curves exhibited an abnormal dispersion that was due to the strong SPR extinction. The values of An and k. both correlated linearly with the particle number densities. From a comparison of the optical constant values of HGNs with those of solid Au nanoparticles (NPS), we used SE measurements to demonstrate a highly sensitive Si-based chemical sensor. HGNs display a slightly lower value of k at the SPR peak but a much higher sensitivity to changes in the surrounding medium than do solid Au NPS.
  Email: hsuenlichen@ntu.edu.tw



• Ellipsometric Studies of Optical Properties of Local Surface Plasmon Resonance for Au Nanoparticles on the Substrate
  Y.H. Su, S.H. Chang, L.G. Teoh, S.L. Tu, M.H. Hon
  JOURNAL OF NANOSCIENCE AND NANOTECHNOLOGY 9 Pages: 1181-1184 (2009)
  Abstract: Few ellipsometric studies have been conducted on Au self-assembled monolayers (SAM), with large discrepancies obtained for refractive index values. Because the Au NPs layer is a kind of composite layer, Au NPs and void, the effective media approximate (EMA) model was employed to investigate the optical properties of Au NPs. The reflective coefficient (similar to 1.2) was smaller than the extinction coefficient (similar to 2.5), which is different from the previous reports and corresponds to the Drude model. The absorption peak of surface plasmon resonance for Au NPs on the glass substrate was shifted from 580 nm to 480 nm.



• Plasmonic Gallium Nanoparticles on Polar Semiconductors: Interplay between Nanoparticle Wetting, Localized Surface Plasmon Dynamics, and Interface Charge
  P.C. Wu, M. Losurdo, T.H. Kim, M.M. Giangregorio, G. Bruno, H.O. Everitt, A.S. Brown
  LANGMUIR 25 Pages: 924-930 (2009)
  Abstract: Ga nanoparticles supported on large band gap semiconductors like SiC, GaN, and ZnO are interesting for plasmon-enhanced UV-emitting solid-state devices. We investigate the influence of the polarity of the SiC, GaN, and ZnO wurtzite semiconductors on the wetting of Ga nanoparticles and on the resulting surface plasmon resonance (SPR) by exploiting real time plasmonic ellipsometry. The interface potential between polar semiconductors (SiC, GaN, and ZnO) and plasmonic nanoparticles (gallium) is shown to influence nanoparticle formation dynamics, geometry, and consequently the SPR wavelength. We invoke the Lippman electrowetting framework to elucidate the mechanisms controlling nanoparticle dynamics and experimentally demonstrate that the charge transfer at the Ga nanoparticle/polar semiconductor interface is an intrinsic method for tailoring the nanoparticle plasmon resonance. Therefore, the present data demonstrate that for supported nanoparticles, surface and interface piezoelectric charge of polar semiconductors also affects SPR along with the well-known effect of the media refractive index.
  Email: pae.wu@duke.edu



• Ellipsometry of GeO2 films with Ge nanoclusters: Influence of the quantum-size effect on refractive index
  D. V. Marin, E. B. Gorokhov, A.G. Borisov, V.A. Volodin
  OPTICS AND SPECTROSCOPY 106 Pages: 436-440 (2009)
  Abstract: Using the methods of scanning and spectral laser ellipsometry and Raman scattering spectroscopy, GeO2 films containing Ge nanoclusters with a Ge/GeO2 mole ratio of 1: 1 are studied. A substantial difference is found between the experimental spectral dependence of the complex permittivity of the films and the one calculated for the effective medium in the Bruggeman model. The distinction can be qualitatively explained by the influence of the quantum-size effect. With the use of theoretical models for quantitative analysis, this approach will make it possible to determine the phase composition and dimensions of the nanoclusters of germanium in a contactless way without destructing the film.
  Email: marin@ISP.nsc.ru



• Photoluminescence of nc-Si:Er thin films obtained by physical and chemical vapour deposition techniques: The effects of microstructure and chemical composition
  M.F. Cerqueira, M. Losurdo, M. Stepikhova, P. Alpuim, G. Andres, A. Kozanecki, M. Soares, M. Peres
  THIN SOLID FILMS 517 Pages: 5808-5812 (2009)
  Abstract: Erbium doped nanocrystalline silicon (nc-Si:Er) thin films were produced by reactive magnetron rf sputtering and by Er ion implantation into chemical vapor deposited Si films. The structure and chemical composition of films obtained by the two approaches were studied by micro-Raman scattering, spectroscopic ellipsometry and Rutherford backscattering techniques. Variation of deposition parameters was used to deposit films with different crystalline fraction and crystallite size. Photoluminescence measurements revealed a correlation between film microstructure and the Er3+ photoluminescence efficiency. (C) 2009 Elsevier B.V. All rights reserved.
  Email: fcerqueira@fisica.uminho.pt



• Nanocrystal characterization by ellipsometry in porous silicon using model dielectric function
  P. Petrik, M. Fried, E. Vazsonyi, P. Basa, T. Lohner, P. Kozma, Z. Makkai
  JOURNAL OF APPLIED PHYSICS 105 024908 (2009)
  Abstract: Porous silicon layers were prepared by electrochemical etching of p-type single-crystal Si (c-Si) of varying dopant concentration resulting in gradually changing morphology and nanocrystal (wall) sizes in the range of 2-25 nm. We used the model dielectric function (MDF) of Adachi to characterize these porous silicon thin films of systematically changing nanocrystal size. In the optical model both the surface and interface roughnesses have to be taken into account, and the E-0, E-1, and E-2 critical point (CP) features are all described by a combination of several lineshapes (two-dimensional CP, excitonic, damped harmonic oscillator). This results in using numerous parameters, so the number of fitted parameters were reduced by parameter coupling and neglecting insensitive parameters. Because of the large number of fitted parameters, cross correlations have to be investigated thoroughly. The broadening parameters of the interband transitions in the measured photon energy range correlate with the long-range order in the crystal. The advantage of this method over the robust and simple effective medium approximation (EMA) using a composition of voids and c-Si with a nanocrystalline Si reference [Petrik , Appl. Surf. Sci. 253, 200 (2006)] is that the combined EMA+MDF multilayer method of this work provides a more detailed description of the material and layer structure.
  Email: petrik@mfa.kfki.hu



• Real-time in situ spectroscopic ellipsometry of GaSb nanostructures during sputtering
  I.S. Nerbo, S. Le Roy, M. Kildemo, E. Sondergard
  APPLIED PHYSICS LETTERS 94 213105 (2009)
  Abstract: We demonstrate that real-time in situ spectroscopic ellipsometry can be used to measure the height evolution of nanostructures during low energy ion sputtering of GaSb. A graded anisotropic effective medium approximation is used to extract the height from the optical measurements. Two different growth regimes have been observed, first exponential then followed by a linear regime. The linear regime is not expected from the traditional sputtering theories. The in situ results correspond well to ex situ atomic force microscopy measurements.
  Email: ingar.nerbo@ntnu.no



• Dielectric function of ZnTe nanocrystals by spectroscopic ellipsometry
  F. Ahmed, A.E. Naciri, J.J. Grob, M. Stchakovsky, L. Johann
  NANOTECHNOLOGY 20 305702 (2009)
  Abstract: We have studied the optical properties of ZnTe nanocrystals (ZnTe-nc) by spectroscopic ellipsometry. The ZnTe-nc are embedded in a SiO2 matrix by an ion implantation technique. Two doses of 1 x 10(16) and 5 x 10(15) cm(-2) of tellurium and zinc ions are implanted in a 250 nm thick SiO2 layer thermally grown on silicon with respective implantation energies of 180 and 115 keV. Subsequent thermal treatments at 800 degrees C lead to the formation of ZnTe-nc. Their sizes are characterized by transmission electron microscopy. The ZnTe-nc obtained with the 1 x 10(16) cm(-2) dose are self-organized into two layers parallel to the surface. Their mean radius ranges between 4-17 nm and 7-17 nm. The ZnTe-nc obtained with the 5 x 10(15) cm(-2) dose are self-organized into one layer with a mean radius between 4-17 nm. A critical points (CPs) dispersion model is used to extract the optical responses of the ZnTe-nc. The optical properties such as the dielectric function and the second derivative of the dielectric function are presented and analyzed. The dielectric function spectra reveal distinct structures attributed to band gap and optical transitions at higher energy. The correlation between the optical responses and the size of the nanocrystals is also given.
  Email: ennacir@univ-metz.fr



• Optical, structural, and magnetic properties of cobalt nanostructure thin films
  D. Schmidt, A.C. Kjerstad, T. Hofmann, R. Skomski, E. Schubert, M. Schubert
  JOURNAL OF APPLIED PHYSICS 105 113508 (2009)
  Abstract: We report on optical, structural, and magnetic properties of two substantially different cobalt nanostructure thin films deposited at an oblique angle of incidence of 85 S away from the substrate normal. Comparison is made between an achiral columnar thin film grown without substrate rotation and a chiral nanocoil sculptured thin film by glancing angle deposition with substrate rotation. Generalized spectroscopic ellipsometry is employed to determine geometrical structure properties and the anisotropic optical constants of the films in the spectral range from 400 to 1000 nm. The magnetic properties are analyzed with a superconducting quantum interference device magnetometer. Both nanostructure thin films show highly anisotropic optical properties such as strong form birefringence and large dichroism. In particular, Co slanted columnar thin films are found to possess monoclinic optical properties. Magnetic measurements at room temperature show hysteresis anisotropy with respect to a magnetic field either parallel or perpendicular to the nanostructures' long axis. We find extremely large coercive fields of approximately 3 kOe for our achiral columnar nanostructures.
  Email: schmidt@huskers.unl.edu



• Microstructural, optical and spectroscopic studies of laser ablated nanostructured tantalum oxide thin films
  R.R. Krishnan, K.G. Gopchandran, V.P. MahadevanPillai, V. Ganesan, V. Sathe
  APPLIED SURFACE SCIENCE 255 Pages: 7126-7135 (2009)
  Abstract: Thin films of tantalum oxide (Ta2O5) have been prepared by pulsed laser deposition technique at different substrate temperatures (300-973 K) under vacuum and under oxygen background (pO(2) = 2 x 10 (3) mbar) conditions. The films are annealed at a temperature of 1173 K. The as-deposited films are amorphous irrespective of the substrate temperature. XRD patterns show that on annealing, the films get crystallized in orthorhombic phase of tantalum pentoxide (beta-Ta2O5). The annealed films deposited at substrate temperatures 300 K and 673 K have a preferred orientation along (0 0 1) plane, whereas the films deposited at substrate temperatures above 673 K show a preferred orientation along (2 0 0) crystal plane. The deposited films are characterized using techniques such as grazing incidence Xray diffraction (GIXRD), atomic force microscopy (AFM), micro-Raman spectroscopy, Fourier transform infrared (FTIR) spectroscopy and UV-visible spectroscopy. FTIR and micro-Raman measurements confirm the presence of Ta-O, Ta-O-Ta and O-Ta-O bands in the films. Grain size calculations from Xray diffraction and AFM show a decrease with increase in substrate temperature. The variation of transmittance and band gap with film growth parameters are also discussed.
  Email: vpmpillai9@gmail.com



• Monoclinic optical constants, birefringence, and dichroism of slanted titanium nanocolumns determined by generalized ellipsometry
  D. Schmidt, B. Booso, T. Hofmann, E. Schubert, A. Sarangan, M. Schubert
  APPLIED PHYSICS LETTERS 94 011914 (2009)
  Abstract: Generalized spectroscopic ellipsometry determines the principal monoclinic optical constants of thin films consisting of slanted titanium nanocolumns deposited by glancing angle deposition under 85 degrees incidence and tilted from the surface normal by 47 degrees. Form birefringence measured for wavelengths from 500 to 1000 nm renders the Ti nanocolumns monoclinic absorbing crystals with c-axis along the nanocolumns, b-axis parallel to the film interface, and 67.5 degrees monoclinic angle between the a- and c-axes. The columnar thin film reveals anomalous optical dispersion, extreme birefringence, strong dichroism, and differs completely from bulk titanium. Characteristic bulk interband transitions are absent in the spectral range investigated.
  Email: schmidt@huskers.unl.edu, schubert@engr.unl.edu



• Study of the optical response of hybrid polymers with embedded inorganic nanoparticles for encapsulation of flexible organic electronics
  A.Laskarakis, D. Georgiou, S. Logothetidis, S. Amberg-Scwhab, U. Weber
  MATERIALS CHEMISTRY AND PHYSICS 115 Pages: 269-274 (2009)
  Abstract: Hybrid (inorganic-organic) polymer materials deposited onto flexible polymeric substrates can provide sufficient barrier response against oxygen and water vapor penetration. In the case that they are combined with inorganic oxide layers (e.g. SiOx, AlOx) in multilayered structures onto flexible polymeric substrates, they can achieve barrier values for oxygen and water vapor below 10(-3) cm(3) m(-2) d(-1) bar(-1) and 10(-3) g m(-2) d(-1), respectively. The in depth knowledge of their optical properties can provide significant insights on their structure and it will contribute towards the optimization of their barrier response. In this work, Spectroscopic Ellipsometry from the infrared to the visible-ultraviolet has been implemented for the investigation of the influence of silicon dioxide nanoparticles, which have been added in the hybrid material during its synthesis, in order to strengthen the inorganic-organic network, on the optical properties of hybrid polymers. The performed analysis revealed valuable information about the electronic and vibrational response as well as the crosslinking mechanisms of these materials. The correlation of the optical properties with the synthesis parameters and the barrier response will contribute towards their optimization in order to be widely used as ultra high barrier materials for flexible organic electronics.
  Email: alask@physics.auth.gr



• Spectroscopic ellipsometry of SiO2/CdTe nanocomposite thin films prepared by dc magnetron sputtering
  S.K. Bera, D. Bhattacharyya, R. Ghosh, G.K. Paul
  APPLIED SURFACE SCIENCE 255 6634-6640 (2009)
  Abstract: SiO2/CdTe nanocomposites were prepared in thin film form on quartz substrate using a multi-target dc magnetron sputtering system. The films were deposited at high pressure (similar to 15 Pa) with deposition temperature ranging from 240 to 260 K. The films were characterized by microstructural studies and phase modulated spectroscopic ellipsometry along with optical transmittance measurements. The ellipsometric spectra were recorded in the wavelength range of 300-1200 nm. The spectra were fitted theoretically with an appropriate model assuming a realistic sample structure. Variations of refractive index, extinction coefficient and dielectric constant with wavelength have been derived.
  Email: sujit1974_bera@rediffmail.com



• Flow-Based Multiadsorbate Ellipsometric Porosimetry for the Characterization of Mesoporous Pt-TiO2 and Au-TiO2 Nanocomposites
  Abstract: Au and Pt nanoparticle distributions within hierarchically ordered mesoporous TiO2 were explored using a combination of techniques including ellipsometric porosimetry (EP) and X-ray photoelectron spectroscopy (XPS). EP studies were used to examine adsorbate-TiO2 interactions and the influence of adsorbate polarity upon adsorption isotherms for mesoporous TiO2 films with and without Pt and Au nanoparticles. In particular, methods are described for modeling EP data to estimate the surface area and porosity of mesoporous TiO2 films and for estimating the pore size distribution (PSD) directly from the ellipsometry parameters Psi and Delta when fitting parameters alone are unable to extract reliable optical constants from the ellipsometry data. This approach reveals that mesoporous TiO2 films of similar to 200 nm thickness and similar to 10 nm pore diameter can be loaded with 1.7 nm diameter Pt and 3.9 nm diameter Au nanoparticles up to 26 and 21 wt %, respectively. The BET surface area of a representative mesoporous TiO2 sample using toluene as the adsorbate was found to be 44 m(2)/g with a mean pore diameter of 8.8 nm. EP and XPS depth profiling experiments indicate that 1.7 nm diameter Pt nanoparticles are well dispersed through the mesoporous TiO2 film, while 3.9 nm diameter Au nanoparticles are concentrated at the top of the film, blocking a significant portion of the available TiO2 pore volume. UV irradiation of the TiO2 films indicates that adsorbate-TiO2 interactions and surface wetting effects can play a critical role in the resulting isotherm and in evaluation of PSD.
  Email: stevenson@mail.cm.utexas.edu



• Porous Thin Films of Functionalized Mesoporous Silica Nanoparticles
  Authors: J. Kobler, T. Bein,
  ACS NANO 2 (11) 2324-2330 (2008)
  Abstract: The synthesis of extremely small mesoporous silica nanoparticles via a specific co-condensation process with phenyl groups is demonstrated. The suspensions are ideally suited for the production of nanoscale thin films by spin-coating. Thanks to the small particle size and the resulting low surface roughness, the films show excellent optical qualities and exhibit good diffusion properties and a highly accessible pore system. The availability of such homogeneous porous thin films made it possible to use ellipsometric porosimetry (EP) as a convenient method to determine the effective porosity of the films on their original support without destroying it. It was possible to record sorption isotherms of the thin films with ellipsometry and to correlate the data with nitrogen sorption data of dried powders of the same material. The thin films showed very low refractive indices of around 1.2.
  Email: bein@lmu.de



• Electrostatically self-assembled films containing II-VI semiconductor nanoparticles: Optical and electrical properties
  Authors: Suryajaya, A.V. Nabok, A. Tsargorodskaya, A.K. Hassan, F. Davis,
  THIN SOLID FILMS 516 (24) 8917-8925 (2008)
  Abstract: US and ZnS semiconducting colloid nanoparticles were deposited as thin films using the technique of electrostatic self-assembly. The process of alternative deposition of Poly-allylamine Hydrochloride (PAH) and CdS (or ZnS) layers were monitored with a novel optical method of total internal reflection ellipsometry (TIRE). The fitting of TIRE spectra allowed the evaluation of the parameter (thickness, refractive index and extinction coefficients) of all consecutively deposited layers. 1-V characteristics of the films obtained were studied in sandwich structures on Indium Tin Oxide (ITO) conductive electrodes using the mercury probe technique. The presence of US (or ZnS) nanoparticles in the polyelectrolyte films leads to a switching behaviour, which may be attributed to the resonance electron tunneling via semiconducting nanoparticles.
  Email: s.suryajaya@shu.ac.uk



• Optical properties of carbonaceous nanoparticles produced in sputtering discharges
  Authors: A. Zeinert, C. Amas, C. Dominique, A. Mouberi,
  JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A 26 (6) 1450-1454 (2008)
  Abstract: In this work, the authors report on the optical properties of carbonaceous nanoparticles produced in argon sputtering dc discharges. These particles are the result of a nucleation-condensation mechanism in gas phase and form porous particulates with a mean diameter greater than 20 nm. The resulting powderlike deposit, which can be collected in the chamber, is analyzed in terms of an effective medium approximation that allows the determination of their optical constants. These parameters are then used in a simple application of the Lorenz-Mie theory, in combination with a laser-extinction experiment, to provide the particle density in the plasma.
  Email: andreas.zeinert@u-picardie.fr



• Optical anisotropies of metal clusters supported on a birefringent substrate
  Authors: Flores-Camacho JM, Sun LD, Saucedo-Zeni N, et al.
  NANOTECHNOLOGY 19 (12) 125709 (2008)
  DOI: 10.1088/0957-4484/19/12/125709
  Abstract: The effects of size, shape and organization on the surface plasmon resonances of Ag nanoclusters sandwiched between Si3N4 layers are studied by transmission electron microscopy and anisotropic spectroscopic ellipsometry. We present an easy-to-handle model that quantitatively links the nanostructure and optical response of the films, which are considered as dielectric/metal:dielectric/dielectric trilayers, with the central nanocomposite layer being an effective medium whose optical properties are described by an anisotropic dielectric tensor. The components of this tensor are calculated using a generalization of the Yamaguchi theory taking into account the real organization, size and shape distributions of ellipsoidal nanoclusters, whose electronic properties are assumed to reflect shape-dependent finite size effects. Using this model, it is shown that the optical response of the films in the visible range is dominated by the excitation of the surface plasmon resonance of the clusters along their in-plane long axis, while no surface plasmon resonance resulting from an excitation along their in-plane short axis can be observed due to damping effects. Moreover, the spectral position of this resonance appears to be mainly affected by the average shape of the clusters, and weakly by their size, their shape distribution and the electromagnetic interaction between them.
  Email: johann.toudert@gmail.com



• Enhancement in ellipsometric thin film sensitivity near surface plasmon resonance conditions
  Authors: Arwin H, Poksinski M, Johansen K
  PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE 205 ( 4) 817-820 (2008)
  DOI: 10.1002/pssa.200777899
  Abstract: Ellipsometry used in internal reflection mode exhibits enhanced thin film sensitivity if operated close to surface plasmon resonance conditions. Compared to conventional ellipsometry, the changes in the ellipsometric parameter Delta are several orders of magnitude larger. Here, the origin of this large sensitivity is discussed by analysing thin film approximations of the complex reflectance ratio. It is found that the thickness sensitivity in Delta is proportional to the inverse of the difference between the intrinsic and the radiation-induced damping of the surface plasmons.
  Email: han@ifm.liu.se



• Correlations between microstructure of plasma-modified gold nanoclusters and their optical properties
  Author(s): Fandino J, Garcia-Sanchez MF, Santana G, Crespo A, Alonso JC, Oliver A
  SUPERLATTICES AND MICROSTRUCTURES Volume: 43 Issue: 5-6 Pages: 454-459 (2008)
  DOI: 10.1016/j.spmi.2007.06.015
  Abstract: Gold nanoclusters with diameters up to 50 nm were grown in sandwich structures consisting in 15 nm of plasma deposited silicon nitride, 1 nm of gold grown by sputtering and 15 nm of plasma deposited silicon nitride (SiN/Au/SiN). Previous to the last step, ammonia plasma treatments of the gold surface were carried out with time as the main variable. The resulting structures were analyzed by high resolution transmission electron microscopy and spectroscopic ellipsometry. As a result of plasma treatments, island-like structures of as-grown gold clusters evolve to near spherical-shape features with decreasing diameter as the plasma treatment time rises. Ellipsometric spectra were modeled based on the Bruggeman effective medium approximation and the influence of size and shape of nanoparticles on the optical properties were calculated.



• Active modulation of surface plasmon resonance wavelengths by applying an electric field to gold nanoparticle-embedded ferroelectric films
  Author(s): Hsieh KC, Chen HL, Wan DH, Shieh J
  DOI: 10.1021/jp711828k
  Abstract: In this study, we use organic chemical addition and phase-transfer methods to prepare lead zirconate titanate (PZT) composite films embed with large numbers of gold nanoparticles (Au NPs). The surface plasmon resonance (SPR) wavelength in the nanocomposite materials can be modulated cyclically through the application of an external electric field. The Au NPs are embedded homogeneously in the PZT matrix; the PZT crystal size and the metal particle size both increase upon increasing the annealing temperature. The Au/PZT nanocomposite film displays apparent piezoelectric properties in its ferroelectric hysteresis curve that can be used in the active modulation of the SPR wavelengths. The major factor influencing the shift in the SPR absorption in the Au/PZT nanocomposite films is the change in the refractive index of the host PZT matrix.
  Email: hsuenlichen@ntu.edu.tw



• Assessment of morphological and optical properties of molecularly mediated thin film assembly of gold nanoparticles
  Author(s): Wang LY, Miller D, Fan Q, Luo J, Schadt M, Qiang RD, Wang GR, Wang JG, Kowach GR, Zhong CJ
  JOURNAL OF PHYSICAL CHEMISTRY C 112 (7) 2448-2455 (2008)
  Abstract: This paper reports the results of an investigation of the optical properties of molecularly mediated thin film assemblies of nanoparticles. Thin film assemblies of gold nanoparticles of different sizes that are linked by dithiols and carboxylic acid functionalized thiols of different alkyl chain lengths are studied as a model system. These thin films have been assembled on different substrates for the systematic measurements of the morphological and optical properties. The correlation of the d-spacing values between the experimental and theoretical results has revealed the presence of ordered nanostructures in the thin film assemblies. The wavelength of the surface plasmon resonance band of the nanoparticles in these thin film assemblies is shown to be linearly dependent on the particle size and the interparticle linker chain length. The analyses of the optical properties theoretically using Mie theory and experimentally using reflectometry and spectroscopic ellipsometry have provided important information for the assessment of the optical constants for these nanostructured thin films. Implications of the results to the understanding of the interparticle structural properties are also discussed.
  Email: cjzhong@binghamton.edu



• Birefringence in spin-coated films containing cellulose nanocrystals
  Author(s): Cranston ED, Gray DG
  COLLOIDS AND SURFACES A-PHYSICOCHEMICAL AND ENGINEERING ASPECTS 325(1-2) 44-51 (2008)
  DOI: 10.1016/j.colsurfa.2008.04.042
  Abstract: Layer-by-layer (LbL) self-assembled polyelectrolyte multilayer films containing cellulose nanocrystals and poly(allylamine hydrochloride) were prepared by spin-coating. From 6 to 25 bilayers were deposited on a silicon substrate. The films displayed birefringence as a result of the intrinsic shape and optical anisotropy of rod-like cellulose nanocrystals which were oriented by the spin-coating process. The birefringence varied with thickness and with location relative to the spin axis, ranging from completely isotropic at the spin axis to 0.065 at the film edge. Uniformity and thickness of these composite films were measured by ellipsometry, atomic force microscopy and angle- and wavelength-dependent optical reflectometry. In order to circumvent the difficulties of inferring film thickness and birefringence in anisotropic thin films, a novel approach based on angle-dependent optical reflectometry was used to determine directional refractive indices.



• Optical and AFM study of electrostatically assembled films of CdS and ZnS colloid nanoparticles
  Author(s): Suryajaya, Nabok A, Davis F, Hassan A, Higson SPJ, Evans-Freeman J
  APPLIED SURFACE SCIENCE 254 (15) 4891-4898 (2008)
  DOI: 10.1016/j.apsusc.2008.01.134
  Abstract: CdS and ZnS semiconducting colloid nanoparticles coated with the organic shell, containing either SO3- or NH2+ groups, were prepared using the aqueous phase synthesis. The multilayer films of CdS (or ZnS) were deposited onto glass, quartz and silicon substrates using the technique of electrostatic self-assembly. The films produced were characterized with UV-vis spectroscopy, spectroscopic ellipsometry and atomic force microscopy. A substantial blue shift of the main absorption band with respect to the bulk materials was found for both CdS and ZnS films. The Efros equation in the effective mass approximation (EMA) theoretical model allowed the evaluation of the nanoparticle radius of 1.8 nm, which corresponds well to the ellipsometry results. AFM shows the formation of larger aggregates of nanoparticles on solid surfaces.
  Email: s.suryajaya@shu.ac.uk



• Effect of Si nanoparticles embedded in SiOx on optical properties of the films studied by spectroscopic ellipsometry and photoluminescence spectroscopy
  Author(s): Szekeres A, Nikolova T, Paneva A, Lisovskyy I, Shepeliavyi PE, Rudko GY
  OPTICAL MATERIALS 30 (7) 1115-1120 (2008)
  DOI: 10.1016/j.optmat.2007.05.033
  Abstract: The optical properties of silicon oxide (SiOx) films, vacuum evaporated and thermally annealed in argon atmosphere at 700 degrees C and 1000 degrees C, have been studied by spectral ellipsometry and photoluminescence (PL) measurements. The thickness, complex refractive index values and composition of the films, as well as the size of the formed Si nanocrystallites have been elucidated from the spectral ellipsometric measurements performed in the range of 280-820 nm. The ellipsometric data was analysed by the Bruggeman effective-medium approximation. It has been shown that annealing at 700 degrees C leads to coagulation of Si atoms into amorphous clusters, while at 1000 degrees C the Si clusters start to crystallize and form nanocrystallites with average size of 2.2 nm. The PL emission from the films annealed at 700 degrees C is blue-shifted and 5-10 times more intense in comparison with the films annealed at 1000 degrees C. This behaviour is correlated with the films structure, i.e., amorphous Si nanoclusters formed in the oxide matrix at 700 degrees C yield higher PL intensity than Si nanoclusters crystallized at 1000°C
  Email: szekeres@issp.bas.bg