Materials and Thin Films

Interfacial and structural properties of sputtered HfO2 layers
Authors: G. Aygun, I. Yildiz
JOURNAL OF APPLIED PHYSICS 106 014312 (2009)
Abstract: Magnetron sputtered HfO2 layers formed on a heated Si substrate were studied by spectroscopic ellipsometer (SE), x-ray diffraction (XRD), Fourier transform infrared (FTIR), and x-ray photoelectron spectroscopy (XPS) depth profiling techniques. The results show that the formation of a SiOx suboxide layer at the HfO2/Si interface is unavoidable. The HfO2 thickness and suboxide formation are highly affected by the growth parameters such as sputtering power, O-2/Ar gas ratio during sputtering, sputtering time, and substrate temperature. XRD spectra show that the deposited film has (111) monoclinic phase of HfO2, which is also supported by FTIR spectra. The atomic concentration and chemical environment of Si, Hf, and O have been measured as a function of depth starting from the surface of the sample by XPS technique. It shows that HfO2 layers of a few nanometers are formed at the top surface. Below this thin layer, Si-Si bonds are detected just before the Si suboxide layer, and then the Si substrate is reached during the depth profiling by XPS. It is clearly understood that the highly reactive sputtered Hf atoms consume some of the oxygen atoms from the underlying SiO2 to form HfO2, leaving Si-Si bonds behind.
Email: gulnuraygun@iyte.edu.tr
Optical and electrical characterizations of 4H-SiC-oxide interfaces by spectroscopic ellipsometry and capacitance-voltage measurements
H. Hashimoto, Y. Hijikata, H. Yaguchi, S. Yoshida
APPLIED SURFACE SCIENCE 255 8648-8653 (2009)
Abstract: 4H-SiC-oxide interfaces formed by various oxidation methods on SiC (0 0 0 1) Si-and (0 0 0 (1) over bar) C-face substrates have been characterized by performing spectroscopic ellipsometry in wide spectral region including deep UV spectral range and capacitance-voltage measurements. The results exhibit that the refractive indices of the interface layers well correlate with interface state density in all the cases of oxidation processes. To investigate the difference in interface characteristics between wet and dry oxidation, we compared to the sample fabricated by wet oxidation followed by heating in Ar or O-2 atmosphere, aiming to remove hydrogen related species at the interface. We also tried to make clear the difference in the interface characteristics between Si-and C-faces by lowering the oxidation rate of C-face down to those for Si-face. Putting together with all of the results obtained, we discuss the origins that determine the interface characteristics in terms of both the optical and electrical characterizations.
Spectroscopic ellipsometry study of GaAs1-xBix material grown on GaAs substrate by atmospheric pressure metal-organic vapor-phase epitaxy
Authors: N. Ben Sedrine, I. Moussa, H. Fitouri, A. Rebey, B. El Jani, R. Chtourou
APPLIED PHYSICS LETTERS 95 011910 (2009)
Abstract: The optical properties in terms of complex dielectric function of GaAs1-xBix alloys (0% <= x <= 3.7%), grown by atmospheric pressure metal-organic vapor-phase epitaxy, are determined by using room temperature spectroscopic ellipsometry. The interband transition energies in the energy range of 1.4-5.4 eV are resolved using a line shape fitting on the numerically calculated dielectric function second derivatives. The bismuth effect on the critical point parameters is then determined. We have found that, as for GaAs1-xBix alloys E-0 transition, the bismuth incorporation shifts the E-1, E-1 + Delta(1), E-2, and E-0' transition energies but with a lower magnitude. We also observed a root-square-like increase of the E-1 broadening parameter (Gamma(1)) with respect to the bismuth composition.
Email: bsnebiha@yahoo.fr
Hydrogenation and dehydrogenation processes of palladium thin films measured in situ by spectroscopic ellipsometry
Authors: Y. Yamada, K. Tajima, S. Bao, M. Okada, K. Yoshimura
Abstract: The hydrogenation and dehydrogenation switching processes of Pd thin films were analyzed by measuring in situ in real time the variation in ellipsometric Psi and Delta during hydrogenation and dehydrogenation using spectroscopic ellipsometry. The hydrogenation proceeded from the film surface and a mixture layer of metal and hydride was formed at the surface. With time elapse, the thickness of the mixture layer increased rapidly. After the whole Pd metal layer transformed to the mixture layer, the concentration of hydride in the mixture layer increased. Finally, the concentration reached 1; the whole I'd in the mixture layer was hydrogenated, and the hydrogenation of Pd was complete. On the other hand, the dehydrogenation proceeded in a way completely opposite to the hydrogenation process: the concentration of hydride in the mixture layer decreased, Pd metal layer was formed at the interface between the film and the substrate, and the whole layer returned to Pd metal. The dehydrogenation proceeds much faster than hydrogenation.
Email: yasusei-yamada@aist.go.jp
Electron accumulation at nonpolar and semipolar surfaces of wurtzite InN from generalized infrared ellipsometry
Authors: Darakchieva V, Schubert M, Hofmann T, Monemar B, Hsiao CL, Liu TW, Chen LC, Schaff WJ, Takagi Y, Nanishi Y
Abstract: The free electron properties of nonpolar (1120)-oriented and semipolar (1011)-oriented wurtzite InN films are studied by generalized infrared ellipsometry (GIRSE). We demonstrate the sensitivity of GIRSE to the surface charge accumulation layer and find a distinct surface electron accumulation to occur at all surfaces. The obtained surface electron sheet densities are found to vary from 0.9x10(13) to 2.3x10(14) cm(-2) depending on the surface orientation and bulk electron concentration. The upper limits of the surface electron mobility parameters of 417-644 cm(2)/V s are determined and discussed in the light of electron confinement at the surface.
Email: vanya@ifm.liu.se
Optical Properties of Disulfide-Functionalized Diacetylene Self-Assembled Monolayers on Gold: a Spectroscopic Ellipsometry Study
Authors: M. Prato, M. Alloisio, S.A. Jadhav, A. Chincarini, T. Svaldo-Lanero, F. Bisio, O. Cavalleri, M. Canepa
Abstract: Spectroscopic ellipsometry (SE) has been applied to study the optical properties of thiolate polydiacetylene (PDA) self-assembled monolayers (SAMs) deposited on low-roughness polycrystalline gold. A systematic investigation of methyl-terminated diacetylene (dihexacosa-7,9-diyn disulfide, DS9) SAMs is presented. The results have been compared with experiments on carbazolyl-derivatized diacetylene (14-(9H-9-carbazolyl)tetradeca- 10,12-diyn-1-yl disulfide, CDS9) SAMs and with findings recently obtained on SAMs of alkanethiols. The SE measurements have been complemented with X-ray photoelectron spectroscopy and atomic force microscopy data. The difference between SE spectra measured after and before the monolayer assembly (d?) ?SAM - ?Au and d? ) ?SAM - ?Au) showed specific absorptions of the adsorbed molecules, including narrow features in the 500-700 nm wavelength range which have been interpreted as markers of the SAM polymerization state. To our knowledge, these results represent the first unambiguous optical detection of polymer-induced absorptions in the case of diacetylene SAMs. Polymerization mainly occurred in the socalled red phase (absorption peak around 550 nm) on very flat surface regions obtained by flame-annealing the sample. The polymeric phase was stable against moderate UV irradiance. The detection of the blue phase was questionable as specific absorptions (around 640 nm) overlap with an absorption band related to the formation of the S-Au interface.
Email: canepa@fisica.unige.it
Optical constants of sol-gel derived TiO2 films characterized by spectroscopic ellipsometry
Authors: XD. Wang J. Shen SZ. Wang ZH. Zhang
Abstract: Nanostructured titanium oxide films were deposited on silicon substrate via sol-gel dip coating method with tetrabutyl titanate as precursor. With reflective spectroscopic ellipsometry, the ellipsometric parameters Psi and Delta of TiO2 films were measured. Then, with the Cauchy model, the ellipsometric data were fitted, and both the thickness and the optical constants at 380-800 nm wavelength of the films were obtained. A comparison was made between the reflectance of the films derived with the spectrophotometer and the simulated results. Meanwhile, the thickness of the films was calculated by interference method. Moreover, with the atomic force microscopy the surface microstructures of the films annealed at different temperatures were observed, and the relationship between the surface microstructures and optical constants of films was further discussed. The results showed that Cauchy model works well in describing the dispersion relationship of the TiO2 films, and the variation rules of optical constants (the refractive index, the extinction coefficient) with wavelength were obtained. The optical constants of the films were related with the microstructure. Those simulated reflectance spectrum accorded well with the measured result. And with a deviation of only 2.5%, the calculated value of the thickness was in accordance with which was obtained by spectroscopic ellipsometry.
Email: shenjj@online.sh.cn
Optical Characterization of Graphene and Highly Oriented Pyrolytic Graphite
Authors: R. Kostic, M. Miric, T. Radic, M. Radovic, R. Gajic, Z.V. Popovic
Abstract: We present a symmetry analysis of allowed infrared and Raman modes in graphene and highly oriented pyrolytic graphite. Surface structure for highly oriented pyrolytic graphite is examined using atomic force microscopy. As experimental tools, we used infrared spectroscopic ellipsometry in order to investigate the pseudodielectric function of highly oriented pyrolytic graphite in the mid-infrared range (500-7000 cm(-1)) and Raman spectroscopy to investigate the influence of layers number decrease. As a result, we propose a method for an experimental verification of graphene.
Email: mmiric@ipb.ac.rs
Spectroscopic ellipsometry study of xPbO-(1-x)TiO2 thin films elaborated by mixed reactive thermal co-evaporation
Authors: A. Boulouz, A.E. Nacri, F. Pascal-Delannoy, B. Sorli, L. Koutti
JOURNAL OF PHYSICS D-APPLIED PHYSICS 42 245304 (2009)
Abstract: In this paper, the refractive index, extinction coefficient and optical band gap of xPbO-(1 - x)TiO2 systems are determined by spectroscopic ellipsometry in the spectral range of wavelength 250-850 nm. All films are elaborated by mixed reactive thermal co-evaporation on a SiO2/Si substrate. The Tauc-Lorentz model is used to extract the optical responses and characteristics of the layers. The best values of the fitted parameters are reported. The wavelength-by-wavelength numerical inversion, carried out without considering any fitting parameter, is also represented as another way to derive the optical constants of the layers. The refractive index and the extinction coefficient depend on the PbO content in xPbO-(1 - x)TiO2 systems. The obtained values of the optical band gap are found to change between 2.54 and 3.38 eV. It is demonstrated here that the xPbO-(1 - x)TiO2 systems with the studied compositions have an indirect optical band gap.
Email: ennacir@univ-metz.fr
Spectroscopic ellipsometry of very thin tantalum pentoxide on Si
Authors: I. Karmakov, A. Konova, E. Atanassova, A. Paskaleva
APPLIED SURFACE SCIENCE 255 9211-9216 (2009)
Abstract: Variable angle spectroscopic ellipsometry of very thin T2O5 layers on Si and the previously published appropriate algorithm for data interpretation have been successfully applied in terms of accurate characterization of very thin T2O5/Si systems. The simulation procedure following a simple three and four layered model was used assuming an existence of inhomogeneous interfacial layers. Quantitative determination of the thicknesses and composition identification were achieved, both for the top T2O5 layer and for an interfacial layer. The constituents in the interfacial layer and its depth profiles were recognized.
Email: karma@phys.uni-sofia.bg
Effects of the film thickness on optical constants of transparent CdS thin films deposited by chemical bath deposition
Authors: F. Yakuphanoglu, C. Viswanathan, P. Peranantham, D. Soundarrajan
JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS 11 945-949 (2009)
Abstract: The optical constants and band gaps of the CdS thin films deposited by chemical bath have been calculated in the spectral wavelength range 400-1000 nm from the transmittance and reflectance measurements of normally-incident light. The CdS thin films exhibit good transparent behavior due to high transmittance values. The optical band gaps of the films were respectively found to be 2.34, 2.41 and 2.46 eV for 100, 125 and 152 nm thicknesses. The increase in film thickness leads to an increase in optical band gap of the films. The refractive index values of the thin films changed significantly with film thickness. The dielectric constant of the films was analyzed using Standard Drude model. The optical carrier concentration and mobility values for the CdS thin films were determined and the obtained values changed with film thickness. It is shown that the film thickness modifies the optical constants and band gaps of the CdS films.
Email: fyhanoglu@firat.edu.tr
A combined X-ray, ellipsometry and atomic force microscopy study on thin parylene-C films
Authors: H.G. Flesch, O. Werzer, M. Weis, J. Jakabovic, J. Kovac, D. Hasko, G. Jakopic, H.J. Wondergem, R. Resel, Roland
PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE 206 1727-1730 (2009)
Abstract: Parylene-C thin films in a thickness range from 7 to 35 nm are deposited on silicon oxide and investigated for their structural and morphological properties by different methods. It is shown that spectroscopic ellipsometry (SE) is a powerful too] to obtain spatially resolved information on the homogeneity of thin films revealing relative changes in layer thickness and in the refractive index. However, the results can be considerably improved in combination with X-ray reflectivity (XRR) which provides highly accurate results on layer thickness. The layer thickness from XRR is used as a fixed input value for the evaluation of the ellipsometry data which reveals a layer thickness dependence of the refractive index in the thin film regime. The interface roughness is determined from XRR as well as the surface rms roughness which can be compared to the roughness found by atomic force microscopy (AFM) which varies between 0.5 and 2.0 nm. Both results for the roughness show excellent agreement. Additionally, a correlation of the roughness and the deposition rate is found.
Email: heinz-georg.flesch@tugraz.at
Electrical and optical properties of Sn doped CuInO2 thin films: Conducting atomic force microscopy and spectroscopic ellipsometry studies
Authors: M. Singh, B.R. Mehta, D. Varandani, V.N. Singh
Abstract: Tin doped CuInO2 thin films deposited by rf magnetron sputtering technique show columnar structure with (006) preferred orientation. Conducting atomic force microscopy measurements show the presence of nanoconductivity regions when the current flow direction is along the in-plane InO6 layer and absence of conducting regions when the current direction is along O-Cu-O layers perpendicular to the film surface. The strong anisotropy observed in the electrical properties of tin doped samples is due to the preferred crystallite orientation and highly anisotropic delafossite structure. A large change in the electrical conductivity value and activation energy value in undoped films and tin doped samples has also been explained in terms of change in crystallite orientation on doping. Spectroscopic ellipsometry measurements have been used to determine the optical constant and dielectric function of CuInO2 and CuInO2:Sn films and show a band gap value of 4.5 eV in tin doped samples due to removal of structural defects.
Email: mandeep_s_khalsa@yahoo.co.in, brmehta@physics.iitd.ac.in
Polymer multilayer film formation studied by in situ ellipsometry and electrochemistry
Authors: K. Haberska, T. Ruzgas
BIOELECTROCHEMISTRY 76 153-161 (2009)
Abstract: Polyelectrolyte multilayer films adsorbed on gold surfaces were studied by combined ellipsometric and electrochemical methods. Multilayers were composed of "synthetic" (poly (4-styrenesulfonic acid) ammonium salt (PSS) and poly(allylamine hydrochloride) (PAH) (PSS/PAH)) and "semi-natural" (carboxymethyl cellulose (CIVIC) and chitosan (CHI) (CMC/CHI)) polyelectrolytes. it was found that only PSS/PAH Layer-by-Layer (LbL) assembled structures result in dense surface confined films that limit permeability of small molecules. such as ferri-/ferrocyanide. The PSS/PAH assemblies can be envisaged as films with pinholes, through which small molecules diffuse. During the LbL deposition process of these films a number of pinholes quickly decay. A representative pinhole diameter was found to be approximately 20 mu m, which determines the diffusion of small molecules through LbL films, and yet remains constant when the film consists of a few LbL assembled polyelectrolyte bilayers. CMC/CHI LbL assemblies at gold electrode surfaces give very low density films, which do not limit the diffusion of ferri-/ferrocyanide between the surface of the electrode and the solution
Email: karolina.haberska@mah.se
Spectroscopic ellipsometry study of thin film thermo-optical properties
Authors: H. Xie, F.L. Ng, X.T. Zeng
THIN SOLID FILMS 517 5066-5069 (2009)
Abstract: Spectroscopic ellipsometry (SE) was employed to realize in-situ monitoring and the determination of thermo-optic coefficients (TOC) of thin films by integrating a temperature controlled hot stage to the ellipsometer and applying the empirical relationship of Cauchy between the refractive index and wavelength in the data analysis. Magnetron sputtered titanium oxide thin films of 350 nm thick both as-deposited and post-deposition annealed were prepared on silicon wafers for this investigation. Results of ellipsometric analysis show that as-deposited TiO2 films have a negative TOC of - 1.21 x 10(-4) K-1 at 630 nm over the test temperature range 304-378 K. The post-deposition annealing at 923 K for 2 hours leads an increase in film refractive index to 2.29 from 2.17 foras-deposited TiO2 films. and an enhancement inTOC up to -2.14 x 10(-4) K-1. X-ray diffraction (XRD) and scanning electron microscopy (SEM) cross-sectional analysis were performed for film structure characterization. (c) 2009 Elsevier B.V. All rights reserved.
Email: hxie@SIMTech.a-star.edu.sg
Investigations of the structural, optical, and electrical properties of Pb0.8Sn0.2Te layers grown on Si(100) using BaF2/CaF2 buffer
Authors: D. Ostertak, M. Friedrich, A. Velichko, V. Ilyushin, D.R.T. Zahn
THIN SOLID FILMS 517 4599-4604 (2009)
Abstract: Pb0.8Sn0.2Te thin films were grown on Si(100) substrates using intermediate BaF2/CaF2 buffer layers in a molecular beam epitaxy system. Atomic force microscopy showed that the PbSnTe films become more flat as deposition rate increases, and substrate temperature decreases. The optimal substrate temperature was found to be about 350 degrees C. Fourier-transform infrared spectroscopy and variable angle spectroscopic ellipsometry were used for the optical characterization of the PbSnTe films in the infrared and visible to ultraviolet range of the light, respectively. It was found that the PbSnTe film grown at about 350 degrees C with higher deposition rate has the most pronounced optical characteristics as well as smoothest surface. The charge carrier concentrations and mobilities of the Pb0.8Sn0.2Te films were determined by means of infrared spectroscopy and also using conventional Hall-effect measurements, these results were then compared and analyzed. The different values obtained using these two techniques are explained by the grain structure of the surface and by occurrence of the microcracks in the PbSnTe films. The thicker PbSnTe films have the higher values of carrier mobility.
Email: ostertak@ngs.ru
Effects of air annealing on the optical, electrical, and structural properties of indium-tin oxide thin films
Authors: C. Trejo-Cruz, A. Mendoza-Galvan, A.M. Lopez-Beltran, M. Gracia-Jimenez
THIN SOLID FILMS 517 4615-4620 (2009)
Abstract: The effects of air annealing on the optical, electrical, and structural properties of indium-tin oxide thin films were investigated using spectroscopic ellipsometry in the UV-visible range, reflectance-transmittance spectra at normal incidence in the infrared range, electrical resistivity measurements, and X-ray diffraction. It was found that annealing at 300 degrees C produces an overall shift to lower photon energies of the optical constant spectra, which is related to the increase in electrical resistivity. The electrical measurements performed in the 25-300 K range show a metallic behavior with large residual resistivity, quantity that increases with annealing temperature and is closely related with the change in the relative intensity of the main diffraction peaks. Also it is shown that under certain conditions of film deposition onto indium-tin oxide, some of its properties can change in a similar way as in air-annealing processing.
Email: amendoza@qro.cinvestav.mx
Spectroscopic ellipsometry characterization of amorphous carbon and amorphous, graphitic and fullerene-like carbon nitride thin films
Authors: Berlind, A. Furlan, Zs. Czigany, J. Neidhardt, L. Hultman, H. Arwin
Thin Solid Films 517 6652-6658 (2009)
Abstract: Carbon nitride (CNx) and amorphous carbon (a-C) thin films are deposited by reactive magnetron sputtering onto silicon (001) wafers under controlled conditions to achieve amorphous, graphitic and fullerene-like microstructures. As-deposited films are analyzed by Spectroscopic Ellipsometry in the UV–VIS–NIR and IR spectral ranges in order to get further insight into the bonding structure of the material. Additional characterization is performed by High Resolution Transmission Electron Microscopy, X-ray Photoelectron Spectroscopy, and Atomic Force Microscopy. Between eight and eleven resonances are observed and modeled in the ellipsometrically determined optical spectra of the films. The largest or the second largest resonance for all films is a feature associated with C–N or C–C modes. This feature is generally associated with sp3 C–N or sp3 C–C bonds, which for the nitrogen-containing films instead should be identified as a three-fold or two-fold sp2 hybridization of N, either substituted in a graphite site or in a pyridine-like configuration, respectively. The p?p electronic transition associated with sp2 C bonds in carbon films and with sp2 N bonds (as N bonded in pyridine-like manner) in CNx films is also present, but not as strong. Another feature present in all CNx films is a resonance associated with nitrile often observed in carbon nitrides. Additional resonances are identified and discussed and moreover, several new, unidentified resonances are observed in the ellipsometric spectra.
Ellipsometry investigation of the effects of annealing temperature on the optical properties of indium tin oxide thin films studied by Drude-Lorentz model
Authors: S. D'Elia, N. Scaramuzza, F. Ciuchi, C. Versace, G. Strangi, R. Bartolino
APPLIED SURFACE SCIENCE 255 7203-7211 (2009)
Abstract: Float glass substrates covered by high quality ITO thin films (Balzers) were subjected for an hour to single thermal treatments at different temperature between 100 degrees C and 600 degrees C. In order to study the electric and optical properties of both annealed and not annealed ITO-covered float glasses, ellipsometry, spectrophotometry, impedance analysis, and X-ray measurements were performed. Moreover, variable angle spectroscopic ellipsometry provides relevant information on the electronic and optical properties of the samples. ITO film is modeled as a dense lower layer and a surface roughness layer. The estimated optical density for ITO and the optical density of the surface roughness ITO layer increases with the annealing temperature. In the near-IR range, the extinction coefficient decreases while the maximum of the absorption in the near UV range shift towards low photon energy as the annealing temperature increases. Spectrophotometry was used to estimate the optical band-gap energy of the samples. The thermal annealing changes strongly the structural and optical properties of ITO thin films, because during the thermal processes, the ITO thin film absorbs oxygen from air. This oxygen absorption decreases the oxygen vacancies therefore the defect densities in the crystalline structure of the ITO thin films also decrease, as confirmed both by ellipsometry and X-ray measurements.
Email: scaramuzza@fis.unical.it
Ellipsometric study of the electronic band structure of CrO2 across the ferromagnetic transition
Authors: M.K. Stewart, K.B. Chetry, B. Chapler, M.M. Qazilbash, A.A. Schafgans, A. Gupta, T.E. Tiwald, D.N. Basov
PHYSICAL REVIEW B 79 144414 (2009)
Abstract: The optical properties of half-metallic CrO2 at temperatures below, at, and above the Curie temperature are studied by means of variable angle spectroscopic ellipsometry. The films were epitaxially grown on (100)- and (110)-oriented TiO2 substrates by chemical vapor deposition. Optical conductivity data reveal a pronounced anisotropy of the optical constants for all films which is in good agreement with what is known about their crystal structure. The main features of the conductivity spectra in the ferromagnetic state are consistent with existing band-structure calculations. However, no temperature dependence of these features across the ferromagnetic transition is evident, posing questions about the electronic structure of the material.
Email: mstewart@physics.ucsd.edu
Self-Assembled Monolayers of Alkanethiols on InAs
Authors: D.Y. Petrovykh, J.C. Smith, T.D. Clark, R. Stine, L.A. Baker, L.J. Whitman
Abstract: We describe the deposition and properties of self-assembled monolayers (SAMs) of methyl-terminated alkanethiols on InAs(001) surface. For these model hydrophobic films, we used water contact angle measurements to survey the preparation of alkanethiol monolayers from base-activated ethanolic solutions as a function of the solution and deposition parameters, including chain length of alkanethiols, deposition time, and solution temperature and pH. We then used X-ray photoelectron spectroscopy (XPS), ellipsometry, and electrochemistry to characterize the composition and structure of octadecanethiol (ODT) monolayers deposited on InAs under optimized conditions. When applied to a thoroughly degreased InAs(001) wafer surface, the basic ODT solution removes the native oxide without excessively etching the underlying InAs(001) substrate. The resulting film contains approximately one monolayer of ODT molecules, attached to the InAs surface almost exclusively via thiolate bonds to In atoms, with organic chains extended away from the surface. TheseODTmonolayers are stable against degradation and oxidation in air, organic solvents, and aqueous buffers. The same base-activated ODT treatment can also be used to passivate exposed InAs/AlSb quantum well (QW) devices, preserving the unique electronic properties of InAs surfaces and allowing the operation of such passivated devices as continuous flow pH-sensors.
Email: dmitri.petrovykh@nrl.navy.mil
Passivation of GaAs by octadecanethiol self-assembled monolayers deposited from liquid and vapor phases
Authors: H. A. Budz, M. C. Biesinger, R. R. LaPierre
Abstract: Self-assembled monolayers _SAMs_ of octadecanethiol _ODT_, CH3_CH2_17SH, were deposited on GaAs _100_ substrates from liquid and vapor phases. Liquid-phase-deposited SAMs were prepared by immersing the substrate in a dilute solution of ODT and ethanol, while vapor-phase-deposited monolayers were prepared by exposing the GaAs surface to a stream of ODT vapor in an ultrahigh vacuum environment. The structural and optical properties of the resulting SAMs were examined with contact angle _CA_ analysis, photoluminescence _PL_ spectroscopy, high-resolution x-ray photoelectron spectroscopy _HRXPS_, and spectroscopic ellipsometry. Although well-ordered films were formed from both deposition techniques, PL, CA analysis, and ellipsometry measurements revealed that the overall quality, structure, and long-term durability of the resulting SAMs depended on the preparation method. Specifically, time-dependent PL and CA analysis indicated an enhanced stability for vapor-deposited films stored under ambient conditions. Through HRXPS measurements, the attachment of the thiolate molecules to the GaAs substrates was shown to proceed through the formation of chemical bonds at both Ga and As surface sites, with the percentage of each bonding configuration dictated by the surface termination produced via the cleaning process used prior to the SAM deposition. Collectively, the results suggested that more robust monolayers exhibiting greater surface coverage, and therefore increased passivation and stability characteristics, are assembled from vapor phase.
Email: lapierr@mcmaster.ca
Identification of interfacial defects in high-k gate stack films by spectroscopic ellipsometry
Authors: J. Price, G. Bersuker, P.S. Lysaght
JOURNAL OF VACUUM SCIENCE & TECHNOLOGY B 27 310-312 (2009)
Abstract: The authors present a spectroscopic study of defects in HfO2, Hf0.8Si0.2O2, Al2O3, and SiO2 dielectric gate stacks. The results indicate that all optically observable dielectric-related defects are associated with the interfacial SiO2 layer rather than the bulk high-k film. The identified defects, located at 2.9, 3.5, 3.9, and 4.75 eV within the dielectric film's band gap, are found to be strongly affected by subsequent postdeposition anneal treatments and trend consistently with recent electron spin. resonance results and theoretical calculations of optical transitions associated with negatively charged vacancies in SiO2 media. The close connection between our results and both atomistic calculations and experimental findings motivates the use of spectroscopic ellipsometry as a potential in-line characterization method for identifying process-induced defects during complementary metal oxide semiconductor device fabrication.
Email: jimmy.price@sematech.org
Dielectric response of AlSb from 0.7 to 5.0 eV determined by in situ ellipsometry
Authors: Y.M. Jung, T.H. Ghong, J.S. Byun, Y.D. Kim, H.J. Kim, Y.C. Chang, S.H. Shin, J.D. Song
APPLIED PHYSICS LETTERS 94 231913 (2009)
Abstract: We present pseudodielectric function data <>=<>+i <> from 0.7 to 5.0 eV of oxide-free AlSb that are the closest representation to date of the intrinsic bulk dielectric response epsilon of the material. Measurements were done on a 1.5 mu m thick film grown on (001) GaAs by molecular beam epitaxy. Data were obtained with the film in situ to avoid oxidation artifacts. Overlapping critical-point (CP) structures in the E-2 energy region were identified by means of band-structure calculations done with the linear augmented Slater-type orbital method. Calculated CP energies agree well with those obtained from data, confirming the validity of the calculations.
Email: ydkim@khu.ac.kr
Optical charge transfer absorption in proton injected tungsten oxide thin films analyzed with spectroscopic ellipsometry
Authors: Y. Yamada, K. Tajima, S. Bao, M. Okada, K. Yoshimura
SOLID STATE IONICS 180 659-661 (2009)
Abstract: Tungsten oxide thin films with protons injected during deposition (HxWO3) were prepared using reactive direct-current magnetron sputtering in a mixture of argon, oxygen, and hydrogen gases. The concentration of injected protons, given by the x-values in HxWO3, was evaluated by electrochemically ejecting protons from the films. The complex dielectric functions (epsilon = epsilon(1) + i epsilon(2)) of the films were estimated by analyzing the experimental spectra of Psi and Delta measured with spectroscopic ellipsometry using the model composed of a homogeneous tungsten bronze layer with an additional Surface roughness layer. As a result of this analysis, the imaginary part of the dielectric function epsilon(2), which represents optical absorption, was composed of two Lorentz oscillator terms whose peak positions were about 1.0 eV (L-1) and 1.6 eV (L-2). The two terms with L-1 and L-2 are assumed using the modified site-saturation model to be due to optical charge transition between W6+ and W5+ sites, and between W6+ and W4+ sites, respectively.
Email: yasusei-yamada@aist.go.jp
Electrical levels of defect investigation of ZrO2 thin film by spectroscopic ellipsometry
Authors: Y.R. Chen, P. , J. Li, L.Y. Chen
JOURNAL OF VACUUM SCIENCE & TECHNOLOGY B 27 1030-1034 (2009)
Abstract: The electrical levels of defects of high-k dielectric ZrO2 films deposited with different oxygen fluxes have been investigated using x-ray diffraction, x-ray photoelectron spectroscopy, and spectroscopic ellipsometry. Various defects with the formation of interstitial oxygen and oxygen vacancies existed in monoclinic ZrO2 films. The optical properties of the films are strongly influenced by configuration changes in defects. Parameters were extracted from spectroscopic ellipsometry raw data by Lorentz oscillator model fitting that indicate the probabilities and transition energies for different charged oxygen interstitial and vacancy defects. These correspond to the electron affinity energies calculated by density functional theory and assigned to electrons trapped at different charged defects from the bottom of the conduction band. A nondestructive and noncontact solution is suggested for detecting the defect states and energy level of high-k film.
Email: pengzhou@fudan.edu.cn, lijing@fudan.edu.cn
Optical characterization of BaSm2Ti4O12 thin films by spectroscopic ellipsometry
Authors: J.J. Yoon, S.Y. Hwang, Y.J. Kang, Y.D. Kim, Y.H. Jeong, S. Nahm
THIN SOLID FILMS 517 3923-3926 (2009)
Abstract: We performed spectroscopic ellipsometric measurement to characterize BaSm2Ti4O12 (BST) thin films grown on Pt/Ti/SiO2/c-Si substrate by rf magnetron sputtering. The six BST films were prepared at various deposition temperatures and thermal annealing times. The resulting refractive indices and extinction coefficients of the BST films show only slight change by the deposition temperature but a significant change after thermal annealing, implying the importance of the post annealing process. The increase of the refractive index can be understood by the higher density of the BST films caused by the crystallization after annealing process.
Email: ydkim@khu.ac.kr
Gallium adlayer adsorption and desorption studies with real-time analysis by spectroscopic ellipsometry and RHEED on A-, M-, and C-plane GaN grown by PAMBE
Authors: P. Misra, C. Boney, D. Starikov, A. Bensaoula
JOURNAL OF CRYSTAL GROWTH 311 2033-2038 (2009)
Abstract: The absence of spontaneous and piezoelectric polarization in nonpolar-oriented III nitrides can improve emission efficiency in light-emitting devices due to the absence of electrostatic fields. It is therefore of interest to study the growth processes necessary to achieve smooth morphology for nonpolar-oriented films. In this paper, we compare and contrast gallium adsorption and desorption on C-, M-, and A-plane GaN epilayers by plasma-assisted molecular beam epitaxy (PAMBE) coupled with in-situ spectroscopic ellipsometry (SE). Adsorption/desorption of Ga under vacuum and under active nitrogen flux were investigated. Previous studies on C- and M-plane materials have suggested that optimum growth conditions with respect to surface morphology are those giving rise to a Ga bilayer and trilayer, respectively. Under vacuum, the stable Ga coverage was 0.48-0.50 nm for the C-, M-, and A-planes. While under N plasma, C-plane GaN maintained similar Ga coverage, while a thicker Ga-stable coverage of 0.7 nm was determined for M-plane. This is in contrast to A-plane GaN, which did not have a consistent Ga adlayer under plasma. We observed that Ga-rich growth of A-plane GaN leads to rough surface morphologies and N-rich conditions are necessary for smooth two-dimensional growth.
Email: cboney@uh.edu
Quantifying protein adsorption on combinatorially sputtered Al-, Nb-, Ta- and Ti-containing films with electron microprobe and spectroscopic ellipsometry
Authors: T.M. Byrne, L. Lohstreter, M.J. Filiaggi, Zhijun Ba, J.R. Dahn
Abstract: Although metallic biomaterials are widely used, systematic studies of protein adsorption onto such materials are generally lacking. Combinatorial binary libraries of Al1_xNbx, Al1 _xTax, Al1 _xTix, Nb1 _xTax, Nb1_xTix, and Ta1_xTix (0 6 x 6 1) and a ternary library of Al1_xTixTay (0 6 x 6 1 and 0 6 y 6 0.7), along with their corresponding pure element films were sputtered onto glass substrates using a unique magnetron sputtering technique. Films were characterized with wavelength-dispersive spectroscopy (WDS), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Fibrinogen and albumin adsorption amounts were measured by wavelength-dispersive spectroscopy (WDS) and spectroscopic ellipsometry (SE) equipment, both high throughput techniques with automated motion stage capabilities. Protein adsorption onto these films was found to be closely correlated to the alumina surface fraction, with high alumina content at the surface leading to low amounts of adsorbed fibrinogen and albumin. Protein adsorption amounts obtained with WDS and SE were in good agreement for all films.
Email: jeff.dahn@dal.ca
Generalized ellipsometry for monoclinic absorbing materials: determination of optical constants of Cr columnar thin films
Authors: D. Schmidt, B. Booso, T. Hofmann, E. Schubert, A. Sarangan, M. Schubert
OPTICS LETTERS 34 992-994 (2009)
Abstract: Generalized spectroscopic ellipsometry is used to determine the form-induced birefringence and monoclinic optical constants of chromium columnar thin films. The slanted nanocolumns were deposited by glancing angle deposition under 85 degrees incidence and are tilted from the surface normal. Dichroism measured for wavelengths from 400 to 1000 nm renders the Cr nanocolumns monoclinic absorbing crystals with c axis along the nanocolumns axis, b axis parallel to the film interface, and 74.8 degrees monoclinic angle between a and c axes. The columnar thin film reveals anomalous optical dispersion, extreme birefringence, and strong dichroism and differs entirely from bulk chromium.
Email: schmidt@huskers.unl.edu
Effect of Chemical Treatment on the Optical Properties of a Cadmium Telluride Photovoltaic Device Investigated by Spectroscopic Ellipsometry
Authors: S. Kohli, V. Manivannan, J.N. Hilfiker, P.R. McCurdy, R.A. Enzenroth, K.L. Barth, W.P. Smith, R. Luebs, W.S. Sampath
JOURNAL OF SOLAR ENERGY ENGINEERING-TRANSACTIONS OF THE ASME 131 021009 (2009)
Abstract: Spectroscopic ellipsometry has been successfully used to characterize the CdS/CdTe heterojunction solar cell deposited on TEC15 glass. The effects of copper treatment on the optical properties of a cadmium chloride treated photovoltaic device were investigated using ellipsometry. No changes in either the band gaps or critical points of CdTe layer were noticed as a result of copper treatment. The copper treated CdTe layer exhibited a higher refractive index in the visible and longer wavelengths (<= 3 eV), as compared with the untreated layer. This was attributed to the increased disorder in the case of copper treated layer.
Email: sandeep.kohli@colostate.edu
Electronic and structural properties of molybdenum thin films as determined by real-time spectroscopic ellipsometry
Authors: J.D. Walker, H. Khatri, V. Ranjan, J. Li, R.W. Collins, S. Marsillac
APPLIED PHYSICS LETTERS 94 141908 (2009)
Abstract: Real-time spectroscopic ellipsometry (RTSE) is shown to be an effective contactless probe of radio frequency magnetron sputtered molybdenum thin films used as the back electrode in chalcopyrite [Cu(In,Ga)Se-2] solar cells. A series of Mo thin films was sputtered onto soda-lime glass substrates at Ar pressures ranging from 4 to 20 mTorr. RTSE measurements reveal how Ar pressure affects the nucleation and growth mechanisms that influence the films' ultimate grain structure and properties. Determinations of the free electron relaxation times at optical frequencies reveal that higher pressures lead to a smaller average grain size and increased void volume fraction.
Email: sylvain.marsillac@utoledo.edu
Combinatorial Surface-Enhanced Raman Spectroscopy and Spectroscopic Ellipsometry of Silver Island Films
Authors: T.W.H. Oates, H. Sugirne, S. Noda
JOURNAL OF PHYSICAL CHEMISTRY C 113 4820-4828 (2009)
Abstract: Utilizing a combinatorial method, we used spectroscopic ellipsometry to determine the dielectric functions of silver island films over a large range of sizes and morphologies from the percolation threshold down to average particle size smaller than 5 nm. We measured films on silicon substrates with 2 and 20 nm oxide layers and compared the surface-enhanced Raman scattering properties of the films. As expected, the films on 20-nm-thick oxide substrates showed increased Raman counts due to reduced damping of the plasmon resonance; however, the optical absorption was greater in the films on 2 nm oxide. The maximum Raman scattering was observed for average particle diameters of 13.6 and 25 nm and interparticle spacings of 3.3 and 4.1 nm for the 2 and 20 nm oxide substrates, respectively. The use of a combinatorial method resulted in significantly reduced uncertainties by avoiding multiple sample preparations and allowed unambiguous identification of optimal film parameters for the different substrates.
Email: oates@ifm.liu.se
A spectroscopic ellipsometry study of TiO2 thin films prepared by ion-assisted electron-beam evaporation
Authors: P. Eiamchai, P. Chindaudom, A. Pokaipisit, P. Limsuwan
CURRENT APPLIED PHYSICS 9 707-712 (2009)
Abstract: Film characterization based on variable-angle spectroscopic ellipsometry (VASE) is desirable in order to understand physical and optical characteristics of thin films. A number of TiO2 film samples were prepared by ion-assisted electron-beam evaporation with 200-nm nominal thickness, 2.0 A/s deposition rate and 8 sccm oxygen flow rate. The samples were maintained at 250 C during the deposition, and annealed in air atmosphere afterwards. As-deposited and annealed films were analyzed by VASE, spectrophotoscopy and X-ray diffractometry. From ellipsometry modeling process, the triple-layer physical model and the Cody-Lorentz dispersion model offer the best results. The as-deposited films are inhomogeneous, with luminous transmittance and band gap of 62.37% and 2.95 eV. The 300 degrees C and 500 degrees C are transition temperatures toward anatase and rutile phases, respectively. Increasing temperature results in an increase of refractive index, transmittance percentage and band gap energy. At 500 degrees C, the highest refractive index and band gap energy are obtained at 2.62 and 3.26 eV, respectively. The developed VASE-modeling process should be able to characterize other TiO2 films, using similar physical and optical modeling considerations.
Email: opticslaser@yahoo.com
Characterization of non-uniform diamond-like carbon films by spectroscopic ellipsometry
Authors: I. Ohlidal, D. Necas, D. Franta, V. Bursikova
DIAMOND AND RELATED MATERIALS 18 364-367 (2009)
Abstract: Optical characterization of diamond-like carbon (DLC) films non-uniform in thickness is performed using spectroscopic phase-modulated ellipsometry. This characterization is based on new formulas for the associated ellipsometric parameters of thin films exhibiting a wedge-shaped thickness non-uniformity. These formulas express the associated ellipsometric parameters by means of the density of distribution of local film thickness. The spectral dependences of the optical constants of these non-uniform DLC films are expressed using the dispersion model based on parametrization of density of electronic states. It is shown that this model of the thickness non-uniformity provides a relatively good agreement between the experimental and theoretical data, indicating that the results of the optical characterization of the non-uniform DLC films are close to the correct results. Moreover, it is shown that the model of uniform thin films is unsuitable for the optical characterization of the non-uniform DLC films studied.
Email: Ohlidal@physics.muni.cz
Ellipsometric study of a-Be3N2 thin films prepared by radio frequency magnetron sputtering
Authors: J.M. Khoshman, W.D. Jennings, M.E. Kordesch
APPLIED SURFACE SCIENCE 255 6190-6194 (2009)
Abstract: The ellipsometric characterizations of amorphous beryllium nitride (a-Be3N2) thin films deposited on Si (1 0 0) and quartz at temperature < 50 degrees C using reactive RF sputtering deposition were examined in the wavelength range 280-1600 nm. X-ray diffraction of the films showed no structure, suggesting the Be3N2 films grown on the substrates are amorphous. The composition and chemical structures of the amorphous thin films were determined by using electron spectroscopy for chemical analysis. The surface morphology of a-Be3N2 was characterized by atomic force microscopy. The thicknesses and optical constants of the films were derived from spectroscopic ellipsometry measurements. The variation of the optical constants with thickness of the deposited films has been investigated. From the angle dependence of the polarized reflectivity we deduced a Brewster angle of 64 degrees. At any angle of incidence, the a-Be3N2 shown high transmissivity (80-99%) and low reflectivity (<18%) in the visible and near infrared regions. Hence, the a-Be3N2 could be a good candidate for antireflection optical coatings under conditions of optimized the type of polarization and the angle of incidence.
Email: khoshman@ahu.edu.jo
AlN:Cr thin films synthesized by pulsed laser deposition: Studies by X-ray diffraction and spectroscopic ellipsometry
Authors: A. Szekeres, S. Bakalova, S. Grigorescu, A. Cziraki, G. Socol, C. Ristoscu, I.N. Mihailescu
APPLIED SURFACE SCIENCE 255 5271-5274 (2009)
Abstract: The structure and optical properties of AlN thin films doped with Cr atoms were studied by X-ray diffractometry, Fourier transform infrared spectroscopy and spectroscopic ellipsometry analyses. The films were synthesized by pulsed laser deposition from an AlN: Cr (10% Cr) target onto Si(1 0 0) wafers in vacuum at residual pressure of 10 (-3) Pa or in nitrogen at a dynamic pressure of 0.1 Pa. The study of the XRD patterns revealed that both phases co-existed in the synthesized films and that the amorphous one was prevalent. Two different amorphous matrices, i.e. two types of chemical bond arrangements, were found in films deposited at 0.1 Pa N-2. By difference, deposition in vacuum resulted in the coexistence of hexagonal and cubic crystallites embedded into an amorphous matrix. The introduction of Cr atoms into the AlN lattice causes a broadening of the IR spectrum along with the shift toward higher wavenumbers of the characteristic Al-N bands at 2351 cm (-1) and 665 cm (-1), respectively. This was related to the generation of a compressive stress inside films. In comparison to the optical constants of pure AlN films, the synthesized AlN: Cr films exhibited a smaller refractive index and showed a weak absorption throughout the 300-800 nm spectral region, characteristic to amorphous AlN structure.
Email: ion.mihailescu@inflpr.ro
Optical properties of Mn1.56Co0.96Ni0.48O4 films studied by spectroscopic ellipsometry
Authors: Y.Q. Gao, Z.M. Huang, Y. Hou, J. Wu, Y.J. Ge, J.H. Chu
APPLIED PHYSICS LETTERS 94 011106 (2009)
Abstract: Spectroscopic ellipsometry is used to determine the optical properties of the noncrystalline and crystalline Mn1.56Co0.96Ni0.48O4 (MCN) films prepared by chemical solution deposition method in the range of 250-1100 nm. A pronounced difference in the optical functions is found between 500 and 600 degrees C. Two distinctive peaks, attributed to the critical points of the MCN films, appear in the optical constant spectra for the films annealed at 600 degrees C while they are not obvious for the films annealed at 500 degrees C. The presented results are instructive, further understanding the physical properties of transition metal oxides in theory.
Email: zmhuang8@yahoo.com
Optical study of BST films combining ellipsometry and reflectivity
Authors: V. Zelezny, D. Chvostova, L. Pajasova, M. Jelinek, T. Kocourek, S. Danis, V. Valvoda
APPLIED SURFACE SCIENCE 255 5280-5283 (2009)
Abstract: Optical properties of plasma laser-deposited Ba0.75Sr0.25TiO3 (BST) thin films have been investigated using variable angle spectroscopic ellipsometry (VASE) and near-normal spectroscopic reflectivity (NNSR) within a broad spectral range at room temperature. The samples prepared under various deposition conditions and the Si substrate coated with the structure SiO2/TiOx/Pt were measured. The X-ray diffraction, atomic force microscopy and alpha step measurement were used for characterization of the samples. A special attention was paid to study sample texture. Both sets of experimental data (VASE and NNSR) were fitted simultaneously to obtain the optical constants (e. g. complex refractive index) and thicknesses of the films. For modeling of the experimental data in the range of transparency the Cauchy and Urbach formulas were used. The direct fit procedure and the Cody-Lorentz model were applied around and below absorption edge. In the entire spectral range the reflectivity spectra were analyzed by Kramers-Kronig analysis. The data around the absorption edge were fitted using the single-wavelength method and the absorption edge features were found up about 3.5 eV. The platinum-coated Si substrate data were fitted as a semi-infinite medium using the Drude and Lorentz oscillators model. The structure model for optical characterization of the sample included not only the BST layers and substrate but also the intermix and surface roughness layers to achieve good agreement with experimental data. The substrate structure was modeled by a simple bulk with surface roughness.
Email: zelezny@fzu.cz
Polarization optics of interfaces and thin films
Author: Azzam RMA
PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE 205 (4) 709-714 (2008)
DOI: 10.1002/pssa.200777745
Abstract: The differential reflection of p- and s-polarized light by interfaces and thin films is central to the theory and applications of ellipsometry. It is also the basis of a wide variety of optical devices for the control and analysis of polarized light such as polarizers, polarizing and polarization-preserving beam splitters, and quarter-wave and half-wave retarders. New insight into the correlation between optical properties of film and substrate materials and reflection properties is emphasized.
Superconducting energy gap and c-axis plasma frequency of (Nd, Sm)FeAsO0.82F0.18 superconductors from infrared ellipsometry
Authors: Dubroka A, Kim KW, Rossle M, et al.
PHYSICAL REVIEW LETTERS 101 (9) 097011 (2008)
DOI: 10.1103/PhysRevLett.101.097011
Abstract: We present far-infrared ellipsometric measurements of polycrystalline samples of the pnictide superconductor RFeAsO0.82F0.18 (R = Nd and Sm). We find evidence that the electronic properties are strongly anisotropic such that the optical spectra are dominated by the weakly conducting c-axis response similar to the cuprate high-temperature superconductors. We deduce an upper limit of the c-axis superconducting plasma frequency of omega(SC)(pl,c) <= 260 cm(-1) corresponding to a lower limit of the c-axis magnetic penetration of lambda(c) >= 6 mu m and lambda(c)/lambda(ab) >= 30 as compared to lambda(ab) = 185 nm from muon spin rotation [A. Drew et al., arXiv:0805.1042 [Phys. Rev. Lett. (to be published)]]. We also observe a gaplike suppression of the conductivity in the superconducting state with a shoulderlike feature at omega(SC)* approximate to 300 cm(-1) and spectral shape which is consistent with an unconventional order parameter with 2 Delta approximate to omega(SC)* approximate to 37 meV.
Thermally induced porosity in CSD MgF2-Based optical coatings: An easy method to tune the refractive index
Authors: Bass JD, Boissiere C, Nicole L, Grosso D, Sanchez C
CHEMISTRY OF MATERIALS 20 (17) 5550-5556 (2008)
DOI: 10.1021/cm8010106
Abstract: A very simple and robust method is described to prepare MgF2-based optical thin films exhibiting refractive indices ranging from 1.08 to 1.2. These coatings were deposited on solid substrates through chemical solution deposition from a single and extremely stable (up to few years old) sol-gel solution composed of magnesium acetate and trifluoroacetic acid dissolved in a mixture of ethanol and water. The present work shows that the generation of the porosity responsible for the ultralow refractive indices of these materials is triggered by the thermal decomposition of the metallic precursor ligands. The resulting nanobubbles of gas are then frozen-in by the thermally induced condensation and partial crystallization of the mineral network around them. We demonstrate that such a process is governed, and can be perfectly controlled, by the heating rate and the atmospheric water content applied during calcination, through which nanobubble size, quantity, and the material's chemical makeup are tuned. The resulting vesicle-like porous materials demonstrate a range of tunable compositions with varying refractive indices and combine good mechanical properties with high chemical and thermal resistance. This work is supported by a novel thermal ellipsometry analysis (TEA) method that allows for in situ monitoring of the films' optical constants, structure, and thickness during thermal treatment. This is the first time, to our knowledge, that this technique has been used in the dynamic characterization of evolving unstructured porosity, allowing valuable insight into the thermal decomposition, condensation, crystallization, and sintering processes occurring during calcination.
Anisotropy in the optical response of superconducting MgB2 films
Authors: V. Železný, D. Chvostova, A. Tarasenko, N. Klein and X.X. Xi
DOI:10.1016/j.tsf.2008.03.026
Abstract: The anisotropy of the dielectric function of c-axis oriented MgB2 thin films has been revealed by a combined study of normal-incident reflectance and spectroscopic ellipsometry. The application of this procedure enabled us to determine the complete set of optical response functions and to show that the dominant effect responsible for the anisotropy is due to interband transitions, which distinctly screen the plasma edge depending on the polarization of incident radiation. The most important transition occurs at 23,800 cm− 1 and is polarized in the ab-plane. This is in good agreement with the results obtained previously for single crystals. Our results are also in a qualitative agreement with those obtained by band structure calculations.
Optical properties of electrochromic iridium oxide and iridium–tantalum oxide thin films in different colouration states
Authors: Jonas Backholm and Gunnar A. Niklasson
DOI:10.1016/j.solmat.2008.05.015
Abstract: Electrochromic iridium oxide (IrOx) and iridium–tantalum oxide (IrTaOx) thin films were prepared by sputtering. Complex refractive indices were determined for samples deposited on indium-tin oxide covered glass in different colouration states, and for as-deposited samples on sapphire and Corning glass. The refractive index was found to be practically constant for both IrOx ( 1.3) and IrTaOx ( 2). The extinction coefficient was found to vary between the coloured and bleached states with 35% for IrOx and 55% for IrTaOx at 660 nm. This is believed to be a result of the removal of intraband transitions within the Ir t2g band during bleaching.
Study of the optimal film structure by using conventional ellipsometry
Authors: Sheng MY, Wu YH, Zhao Y, Chen YR, Zheng YX, Chen LY
JOURNAL OF THE KOREAN PHYSICAL SOCIETY 53 (2) 564-567 (2008)
Abstract: The optimal film structure affected by the space effect has been studied for SiO2 film samples deposited onto Si wafers by using the e-beam evaporation method. The ellipsometric data were measured at different incidence angles and in the 300-800-nm wavelength range. In the range where the phase delay delta is close to pi, the film thickness deduced from the conventional ellipsometry model varied with the phase delay. The optimal SiO2 film-thickness was achieved with a modified ellipsometric model, including the space effect. The results given in this work can generally be applied to other optical measurement methods used to study film structures.
Spectroscopic ellipsometry investigations of the thermally induced first-order transition of RbMn[Fe(CN)(6)]
Authors: Loutete-Dangui ED, Codjovi E, Tokoro H, Dahoo PR, Ohkoshi S, Boukheddaden K
PHYSICAL REVIEW B 78 (1) 014303 (2008)
DOI: 10.1103/PhysRevB.78.014303
Abstract: We report on detailed spectroscopic ellipsometry investigations on the thermally induced first-order phase transition of rubidium manganese hexacyano-ferrate (RbMn[Fe(CN)(6)]) pellet sample. This switchable solid shows a cooperative Jahn-Teller distortion coupled with a local charge transfer between Fe and Mn ions. Optical spectra of the real, epsilon', and imaginary, epsilon", parts of the complex dielectric constant have been recorded in the interval of temperature, i.e., 250-350 K, around the transition region and in the optical range of 190-830 nm. Four (two) optical bands have been identified and assigned in the low-temperature (high-temperature) phase, corresponding to the Fe-II-CN-Mn-III (Fe-III-CN-Mn-II) state. We performed a quantitative analysis by fitting our spectra with Gauss-Lorentz (GL) line shapes and determined the energy positions, oscillator strengths, and widths of individual transitions, as well as their thermal variation. It has been found that the GL profiles excellently approximate the optical response. Moreover, we observed a significant shift of the metal-ligand charge-transfer band8 upon the thermal transition and correlated it quantitatively to the volume change at the transition. We then derived the coefficient of the volumetric thermal expansion of the title compound and found alpha=(partial derivative V/partial derivative T)/(V) over bar similar or equal to 3.0x10(-3) K-1 in the transition region and alpha(LT)(T)similar or equal to 4.0x10(-5) K-1 (alpha(HT)(T)=8.7x10(-5) K-1) in the low-temperature (high-temperature) region, in very good agreement with the reported zero thermal-expansion character of this compound. Finally, from the analysis of the integrated absorption spectra, we derived the thermal hysteresis of the high-temperature fraction, which was found in very good agreement with that of magnetic data recorded on the same sample.
Dielectric properties of Ti2AlC and Ti2AlN MAX phases: The conductivity anisotropy
Authors: Haddad N, Garcia-Caurel E, Hultman L, Barsoum MW, Hug G
JOURNAL OF APPLIED PHYSICS 104 (2) 023531 (2008)
DOI: 10.1063/1.2960340
Abstract: The optical properties of Ti2AlN and Ti2AlC were determined in the 2-80 eV energy range by electron energy loss spectroscopy and in the visible-ultraviolet range, from 1.6 to 5.5 eV, by spectroscopic ellipsometry. Both experimental techniques are angular resolved and in very good agreement over their overlapping energy range. We observe a dependence of the dielectric function as a function of the crystallographic orientation of the crystals. In particular, we notice a shift of the energy position of the plasmon absorption of Ti2AlC with respect to Ti2AlN. Moreover, a drastic change is also observed in the shape of the dielectric function as a function of the composition (or valence electron concentration). The dielectric functions are fitted to an empirical semiclassic Drude-Lorentz model to obtain physical parameters such as the relaxation times. These microscopic parameters are then used in a macroscopic model to yield the transport properties such as the static conductivity as function of the crystal orientation. Ti2AlN is found to be a better conductor than Ti2AlC in all orientations, which is consistent with experimental measurements. A comparison of the electrical and optical properties of these two compounds is made in terms of different electronic properties and interband-intraband transitions deduced from our mode.
Influence of shadowing on ellipsometric quantities of randomly rough surfaces and thin films
Authors: Ohlidal I, Necas D
JOURNAL OF MODERN OPTICS 55 (7) 1077-1099 (2008)
DOI: 10.1080/09500340701618379
Abstract: In this paper the formulae enabling us to calculate the values of the ellipsometric parameters of randomly rough surfaces and very thin films with randomly rough boundaries with respect to the influence of the shadowing between the irregularities of roughness are presented. These formulae are derived within the scalar diffraction theory of light. The first formula allows the calculation of the ellipsometric parameters using a numerical method, while the second formula is the approximative one but it expresses the ellipsometric parameters in a closed form. The numerical analysis of both formulae is performed for several examples of randomly rough surfaces and thin films. Moreover, the comparison of the results achieved using both formulae respecting the shadowing and an earlier formula not including this effect is performed. The experimental data of two samples of the randomly rough silicon surfaces covered with very thin surface layers are interpreted using all the formulae mentioned. Using this experimental study, the correctness of both formulae taking into account the shadowing, is confirmed.
Moderate temperature sol-gel deposition of magnesium fluoride films for optical UV-applications: A study on homogeneity using spectroscopic ellipsometry
Authors: Kruger H, Kemnitz E, Hertwig A, Beck U
DOI: 10.1002/pssa.200777856
PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE 205 (4) 821-824 (2008)
Abstract: Thin films of MgF2 have been deposited on silicon wafers in optical quality with a novel sol-gel deposition process at temperatures as low 100 degrees C. The properties of the fluoride layers are compared to bulk MgF2 with respect to the optical constants. By employing spectroscopic mapping ellipsometry, the uniformity of the thickness of fluoride layers is confirmed to be within acceptable limits for optical applications. The optical constants are close to the bulk data. High-quality low-index films of suitable and homogeneous thickness have already been produced on a laboratory scale.
Email: andreas.hertwig@bam.de