Showing papers on "Ellipsometry published in 2005"

Handbook of Ellipsometry

Abstract: Polarized Light and Ellipsometry- Optical Physics of Materials- Data Analysis for Spectroscopic Ellipsometry- Optical Components and the Simple PCSA (polarizer, compensator, sample, analyzer) Ellipsometer- Rotating Polarizer and Analyzer Ellipsometry- Polarization Modulation Ellipsometry- Multichannel Ellipsometry- SiO2 Films- Theory and Application of Generalized Ellipsometry- VUV Ellipsometry- Spectroscopic Infrared-Ellipsometry- Ellipsometry in Life Sciences

Multiferroic BiFeO3 thin films processed via chemical solution deposition: Structural and electrical characterization

Abstract: Polycrystalline BiFeO3 thin films were fabricated on (111)Pt∕Ti∕SiO2∕Si substrates via Bi-acetate- and Fe-acetylacetonate-based chemical solution deposition and spin-coating techniques. The processing parameters were optimized in order to obtain films with high resistivity. The optical properties (refractive indices and extinction coefficients) were measured by means of ellipsometry (HeNe laser, λ=632.8A). Microstructure characterization was made by means of atomic force microscopy, grazing incidence x-ray diffractometry (XRD), and texture analysis. Additionally, powders prepared from a stoichiometric precursor were investigated by means of thermogravimetric and differential thermal analyses and XRD. It is demonstrated that the formation of perovskite-type BiFeO3 is accompanied by the appearance of bismuth oxide at low temperatures which then transforms into Bi36Fe2O57. For the films it was found that annealing in oxygen leads to higher indices of refraction, lower roughness, and smaller grain size. Compl...

Atmospheric pressure plasma deposition of thin films by Townsend dielectric barrier discharge

Abstract: The aim of this study is to contribute to the understanding of the thin film growth mechanism using an Atmospheric Pressure Townsend-like Discharge (APTD). Films obtained in dielectric barrier discharges fed with N2 and small admixtures of hexamethyldisiloxane (HMDSO) and nitrous oxide (N2O) as oxidizer gas have been investigated. Results are compared to those obtained with SiH4, in similar conditions. The discharge dissipated power and the feed composition ([N2O]/[HMDSO] ratio) on film properties have been investigated by means of Fourier Transform Infrared Spectroscopy (FTIR), X-ray Photoelectron Spectroscopy (XPS) and Ellipsometry. The film thickness homogeneity and deposition rate have been measured by means of a profilometer and an ellipsometer at the same time. Then silicon oxide thin film properties obtained with SiH4 and HMDSO containing APTD are compared. Concerning chemical composition results are similar. In the two cases, a rather low adding of N2O allows to get SiOx layer without N and C incorporation. Si–OH bounds are always observed. The relative contribution of homogeneous and heterogeneous growth mechanisms is very dependent on the nature of the precursor. Because of its high reactivity, SiH4 induces particles formation in the plasma. These particles are efficiently included in the coating, decreasing drastically the layer density. Thin films made with HMDSO are always dense.

Convective Assembly of Antireflective Silica Coatings with Controlled Thickness and Refractive Index

Abstract: Convective assembly at high volume fraction was used to deposit silica nanoparticle coatings onto glass and silicon substrates. By allowing control of the film structure and thickness, this technique provides a means for making large-scale coatings with antireflective properties. The reflectance was reduced by 50% for silicon (at 600 nm) and by 70% for single glass/air surface. Microstructural investigations using SEM, AFM, profilometry, and ellipsometry provided good correlation to the observed macroscopic optical properties. By virtue of the coatings' uniformity, the reflectance and transmission spectra from both substrates could be modeled well by classical reflection relations, using a volume-averaged refractive index. Data analysis showed that the relatively high packing fraction in nanocoatings made from monodisperse spheres is responsible for the limit on antireflective capabilities. To overcome this restriction, low-density silica coatings were made from binary colloidal mixtures of different diam...

Effects of nitrogen doping on optical properties of TiO2 thin films

Abstract: The potential for extending the optical absorption range of TiO2 by doping with nonmetallic elements was examined in nitrogen-containing TiO2 thin films Thin films of TiO2-xNx were synthesized on glass and silicon substrates by ion-beam-assisted deposition to obtain a wide range of nitrogen concentrations The compositions of the films were determined by Rutherford backscattering spectrometry and X-ray photoelectron spectroscopy The structures of the films were analyzed by X-ray diffraction, transmission electron microscopy, and atomic force microscopy The optical properties of the films were measured by UV-Vis spectroscopy and ellipsometry A characteristic decreasing trend in band-gap values of the films was observed within a certain range of increasing dopant concentrations As the nitrogen concentration increased, the structure of the films evolved from a well-defined anatase to deformed anatase The reduced band gaps are associated with the N 2p orbital in the TiO2-xNx films

On the optical anisotropy of conjugated polymer thin films

Abstract: In this paper the problem of optical anisotropies in conjugated polymer thin films is revisited and the results in the literature are critically reappraised. Several models for upper bounds on the different types of anisotropies are developed and these are compared with experiment. We analyze both in-plane/out-of-plane and in-plane anisotropies in spin coated and oriented films, respectively. For the in-plane/out-of-plane anisotropy in spin coated films we study the reasons for the large disparity amongst the results reported in the literature, and propose the method of interference enhancement variable angle spectroscopic ellipsometry to retrieve this anisotropy more accurately. Experimental results are reported for poly(9,9-dihexyl fluorene) (spin coated), poly(9,9-dioctylfluorene) (both spin coated and uniaxially aligned), and poly(9,9-dioctylfluorene-co-benzothiadiazole) (both spin coated and uniaxially aligned). Our results concerning the measurement of optical anisotropy can be applied equally well to other molecular systems, such as self-assembled monolayers or Langmuir--Blodgett films.

Microphase Separation in Thin Films of Poly(styrene-block-4-vinylpyridine) Copolymer-2-(4`-Hydroxybenzeneazo)benzoic Acid Assembly

Abstract: The fine structure of thin films of poly(styrene-block-4-vinylpyridine) copolymer−2-(4‘-hydroxybenzeneazo)benzoic acid (PS-PVP+HABA) assembly has been studied using the combination of atomic force microscopy, ellipsometry, X-ray reflectivity, GISAXS, XPS, and XPEEM. The films consist of cylindrical nanodomains formed by PVP+HABA associates surrounded by PS matrix. Alignment of the domains can be switched upon exposure to vapors of different solvents from the parallel to perpendicular orientation and vice versa with respect to the surface plane. Swelling in 1,4-dioxane leads the system from the cylindrical to the spherical morphology. Solvent evaporation results in a shrinkage of the matrix in the vertical direction and subsequent merging of the spheres into the perpendicularly aligned cylinders. The cylinders form a regular hexagonal lattice with a spatial period of 25.5 nm. On the other hand, vapors of chloroform induce in-plane alignment. The films consist of parallel layers of the cylinders separated b...

Optical optimization of polyfluorene-fullerene blend photodiodes

Abstract: Blends of polyfluorene-fullerenes are promising materials for polymer-based photovoltaic devices (PPVD). Using spectroscopic ellipsometry we deduce the dielectric function for the blend of the fullerene derivative [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) and the alternating polyfluorene copolymer, poly [2,7-(9,9-dioctyl-fluorene)-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)] DiO-PFDTBT (4:1 by weight), for the wavelength interval 250–1300nm. n reaches above 2 and saturates to 1.9 for high wavelengths. Absorption starts at 720nm (1.72eV) and reaches a crest around 550nm (2.25eV). The spin coating introduces anisotropy in the blend, manifested in birefringence as well as in dichroism. The dielectric function for the blend versus its constituents is not additive. There are indications that the constituents lost their dielectric identity, as screening cannot explain the experimental data. Simulations of optical absorption inside a PPVD are performed for both monochromatic and polychromatic ...

Optical properties of δ-Bi2O3 thin films grown by reactive sputtering

Abstract: The optical properties of δ-Bi2O3 thin films were investigated using spectroscopic ellipsometry and optical absorption spectrum. δ-Bi2O3 thin films were grown on Si and quartz substrates under different oxygen flow ratios (OFR) by radio frequency reactive magnetron sputtering. The Tauc-Lorentz dispersion method was adopted to model the optical dispersion functions of the thin films. The optical bandgap was obtained by three different methods. It was found that refractive index and extinction coefficient decrease, and the optical bandgap has a slight blue shift with increasing the OFR. Factors influencing the optical constants and optical bandgap are discussed.

Structural, electrical, and optical properties of transparent gallium oxide thin films grown by plasma-enhanced atomic layer deposition

Abstract: Gallium oxide (Ga2O3) thin films were deposited on silicon (100) and sapphire (001) substrates using the plasma-enhanced atomic layer deposition (PEALD) technique with an alternating supply of reactant source, [(CH3)2GaNH2]3, and oxygen plasma. The thin films were annealed at different temperatures (500, 700, and 900°C, respectively) in a rapid thermal annealing system for 1min. It was found that Ga2O3 thin films deposited by PEALD showed excellent step coverage characteristics. X-ray diffraction measurements showed that the as-deposited thin film was amorphous. However, the thin films annealed at temperatures higher than 700°C showed a (400) orientation of the monoclinic structure. An atomic force microscope was used to investigate the surface morphologies of the thin films. The thin films showed very smooth surfaces; the roughness of the as-deposited thin film was about 4A. With increasing annealing temperature, the thin film became rougher compared with that annealed at lower temperatures. A double-bea...

Surface characterization of 3-glycidoxypropyltrimethoxysilane films on silicon-based substrates.

Abstract: Silane coupling agents are commonly used to activate surfaces for subsequent immobilization of biomolecules. The homogeneity and surface morphology of silane films is important for controlling the structural order of immobilized single-stranded DNA probes based on oligonucleotides. The surfaces of silicon wafers and glass slides with covalently attached 3-glycidoxypropyltrimethoxysilane (GOPS) have been characterized by using angularly dependent X-ray photoelectron spectroscopy (XPS), time-of-flight secondary-ion mass spectrometry (ToF-SIMS), atomic force microscopy (AFM), scanning electron microscopy (SEM), and monochromatic and spectroscopic ellipsometry. XPS and ToF-SIMS data provided evidence of complete surface coverage by GOPS. Data from angularly resolved XPS and ellipsometry methods suggested that the GOPS films were of monolayer thickness. AFM and SEM data indicated the presence of films that consisted of nodules approximately 50-100 nm in diameter. Modeling suggested that the nodules may lead to a nanoscale structural morphology that might influence the hybridization kinetics and thermodynamics of immobilized oligonucleotides.

Depolarization of diffusely reflecting man-made objects

Abstract: The polarization properties of light scattered or diffusely reflected from seven different man-made samples are studied. For each diffusely reflecting sample an in-plane Mueller matrix bidirectional reflectance distribution function is measured at a fixed bistatic angle using a Mueller matrix imaging polarimeter. The measured profile of depolarization index with changing scattering geometry for most samples is well approximated by an inverted Gaussian function. Depolarization is minimum for specular reflection and increases asymptotically in a Gaussian fashion as the angles of incidence and scatter increase. Parameters of the Gaussian profiles fitted to the depolarization data are used to compare samples. The dependence of depolarization on the incident polarization state is compared for each Stokes basis vector: horizontal, vertical, 45 degrees, 135 degrees, and right- and left-circular polarized light. Linear states exhibit similar depolarization profiles that typically differ in value by less than 0.06 (where 1.0 indicates complete depolarization). Circular polarization states are depolarized more than linear states for all samples tested, with the output degree of polarization reduced from that of linear states by as much as 0.15. The depolarization difference between linear and circular states varies significantly between samples.

Impact of titanium addition on film characteristics of HfO2 gate dielectrics deposited by atomic layer deposition

Abstract: The impact of 8-to45-at.% Ti on physical and electrical characteristics of atomic-layer-deposited and annealed hafnium dioxide was studied using vacuum-ultraviolet spectroscopic ellipsometry, secondary ion mass spectroscopy, transmission electron microscopy, atomic force microscopy, x-ray diffraction, Rutherford backscattering spectroscopy, x-ray photoelectron spectroscopy, and x-ray reflectometry. The role of Ti addition on the electrical performance is investigated using molybdenum (Mo)-gated capacitors. The film density decreases with increasing Ti addition. Ti addition stabilizes the amorphous phase of HfO2, resulting in amorphous films as deposited. After a high-temperature annealing, the films transition from an amorphous to a polycrystalline phase. Orthorhombic Hf–Ti–O peaks are detected in polycrystalline films containing 33-at.% or higher Ti content. As Ti content is decreased, monoclinic HfO2 becomes the predominant microstructure. No TiSi is formed at the dielectric/Si interface, indicating fil...

Analysis of organic films and interfacial layers by infrared spectroscopic ellipsometry.

Abstract: Organic films and surfaces have been shown to be of increasing technological importance. The exploration of their potential for applications in fields such as nanotechnology or for the development of ‘‘smart materials’’ is the focus of numerous R&D projects. Appropriate characterization methods are mandatory for the design and analysis of devices on the basis of organic films. This focal point article focuses on presenting infrared spectroscopic ellipsometry (IRSE) as an emerging powerful technique for the structural analysis of organic films. IRSE has been successfully applied to the study of inorganic materials and films as, for

Spectroscopic ellipsometry characterization of nitrogen-incorporated HfO2 gate dielectrics grown by radio-frequency reactive sputtering

Abstract: Spectroscopic ellipsometry with photon energy 0.75–6.5 eV at room temperature has been used to derive the optical properties of nitrogen-incorporated HfO2 films on Si(100) substrates grown by radio-frequency reactive sputtering using different N2∕(N2+O2+Ar) gas ratios from 20% to 50%. Excellent agreement has been found between the experimental and the simulated spectra, in which an empirical dielectric dispersion relation based on Tauc-Lorentz model has been successfully adopted. Increases in the refractive index n and the extinction coefficient. k, with increases in nitrogen-incorporation content are observed due to the nitrogen-incorporation-induced higher packing density. The change of the complex dielectric functions and reduction in the optical band gap with an increase in nitrogen concentration resulting from the effect of the nitrogen-incorporation on the structure are discussed in detail.

Growth of vacuum evaporated ultraporous silicon studied with spectroscopic ellipsometry and scanning electron microscopy

Abstract: Using a combination of variable-angle spectroscopic ellipsometry and scanning electron microscopy, we investigated the scaling behavior of uniaxially anisotropic, ultraporous silicon manufactured with glancing angle deposition. We found that both the diameter of the nanocolumns and the spacing between them increase with film thickness according to a power-law relationship consistent with self-affine fractal growth. An ellipsometric model is proposed to fit the optical properties of the anisotropic silicon films employing an effective medium approximation mixture of Tauc-Lorentz oscillator and void. This study shows that the optical response of silicon films made at glancing incidence differs significantly from that of amorphous silicon prepared by other methods due to highly oriented nanocolumn formation and power-law scaling.

Optical band gaps and composition dependence of hafnium–aluminate thin films grown by atomic layer chemical vapor deposition

Abstract: We report the optical properties of unannealed hafnium–aluminate (HfAlO) films grown by atomic layer chemical vapor deposition (ALCVD) and correlate them with the aluminum contents in the films. Vacuum ultraviolet spectroscopic ellipsometry (VUV-SE), high-resolution transmission electron microscopy (HRTEM), channeling Rutherford backscattering spectrometry (RBS), and resonant nuclear reaction analysis (NRA) were employed to characterize these films. In the analyses of ellipsometry data, a double Tauc–Lorentz dispersion produces a best fit to the experimental VUV-SE data. As a result, the determined complex pseudodielectric ⟨e⟩ functions of the films clearly exhibit a dependency on the aluminum densities measured by RBS and NRA. We show that the optical fundamental band gap Eg shifts from 5.56±0.05eV for HfO2 to 5.92±0.05eV for HfAlO. The latter was grown by using an equal number of pulses of H2O∕HfCl4 and H2O∕TMA (trimethylaluminum) precursors in each deposition cycle for HfO2 and Al2O3, respectively. The...

Fiber-based polarization-sensitive Mueller matrix optical coherence tomography with continuous source polarization modulation.

Abstract: We report on a new configuration of fiber-based polarization-sensitive Mueller matrix optical coherence tomography that permits the acquisition of the round-trip Jones matrix of a biological sample using only one light source and a single depth scan. In this new configuration, a polarization modulator is used in the source arm to continuously modulate the incident polarization state for both the reference and the sample arms. The Jones matrix of the sample can be calculated from the two frequency terms in the two detection channels. The first term is modulated by the carrier frequency, which is determined by the longitudinal scanning mechanism, whereas the other term is modulated by the beat frequency between the carrier frequency and the second harmonic of the modulation frequency of the polarization modulator. One important feature of this system is that, for the first time to our knowledge, the Jones matrix of the sample can be calculated with a single detection channel and a single measurement when diattenuation is negligible. The system was successfully tested by imaging both standard polarization elements and biological samples.

Temperature-dependent dielectric and electro-optic properties of a ZnO-BaTiO3-ZnO heterostructure grown by pulsed-laser deposition

Abstract: Temperature-dependent dielectric and electro-optic properties of a ZnO-BaTiO3-ZnO heterostructure grown by pulsed-laser deposition on (0001) sapphire are reported. The wurtzite-structure ZnO layers serve as transparent conducting electrodes. Previously observed coupling effects within the wurtzite-perovskite heterostructure by spectroscopic electro-optic ellipsometry birefringence measurements manifest themselves as a “pinning” of the ferroelectric polarization in the BaTiO3 layer by the cladding ZnO layers. Temperature-controlled electro-optic Raman measurements assign the electro-optic birefringence results to a temperature-driven phase transition resulting from the leakage current within the sample. High-temperature small-signal capacitance measurements exploiting the conductive electrode properties of the cladding layers reveal occurrence of the Curie temperature of the BaTiO3 layer at 384 K.

Evaluation of lanthanum based gate dielectrics deposited by atomic layer deposition

Abstract: In this article, we evaluated physical and electrical characteristics of La-based gate dielectrics (La2O3 and LaAlxOy) deposited by atomic layer deposition (ALD). The precursors used for La2O3 and LaAlxOy are lanthanum tris[bis(trimethylsilyl)amide] La[N(SiMe3)2]3, trimethyl aluminum [Al(CH3)3], and water. Physical properties of these dielectric films were studied using ellipsometry, x-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). To investigate electrical properties of these La-based dielectrics, metal oxide semiconductor capacitors (MOSCAPs) were fabricated using metal gates (Ta–Si–N, TiN and Pt). Linear growth rate characteristics were observed for ALD (La2O3 and LaAlxOy films deposited at temperatures of 225to275°C. XPS and XTEM analysis of La-based films grown on a chemical oxide starting surface revealed a rough La-based dielectric/Si interface and chemical interaction with the Si substrate. In general, adding Al into La2O3 improved electrical properties of the fi...

Effect of Quantum Confinement on Optical Properties of Ge Nanocrystals in GeO[sub 2] Films

Abstract: Germanium dioxide films containing Ge nanocrystals are studied. The films have been prepared by two methods: (i) deposition from supersaturated GeO vapors with subsequent decomposition of metastable germanium monoxide into a heterophase Ge:GeO2 system, and (ii) formation of anomalously thick native germanium oxides with a GeO2(H2O) chemical composition by a catalyst-accelerated oxidation of germanium. The films, which have been prepared on various substrates, are studied using the photoluminescence technique, Raman spectroscopy, spectral ellipsometry, and high-resolution electron microscopy. In the GeO2 films with built-in Ge nanoclusters, intense photoluminescence is detected at room temperature. The nanocluster sizes are estimated from the position of the Raman peak related to localized optical phonons. The correlation between a decrease in the nanocluster size and the shift of the photoluminescence peaks to the blue spectral region as the relative Ge content decreases is revealed. The presence of nanoclusters is confirmed by the data obtained from high-resolution electron microscopy. The correlation of the optical gap calculated taking into account the quantum confinement of electrons and holes in the nanoclusters with the experimentally observed luminescence peak is established. It can be concluded from the data obtained that the Ge nanoclusters constructed in the GeO2 matrix represent type I quantum dots.

In situ study of the thermoresponsive behavior of micropatterned hydrogel films by imaging ellipsometry.

Abstract: A patterned hydrogel was immobilized on a polymer substrate by low-pressure argon plasma treatment using a masking technique. The polymer sample showed a thermoresponsive aggregation behavior in the region of 35−37 °C. The micropatterned, thermoresponsive hydrogel film has been characterized with imaging ellipsometry. The characterization was carried out on the dry film as well as on a swollen sample in water. The thermoresponsive behavior was studied in deionized water by temperature-dependent measurements in a solid−liquid cell. Through imaging ellipsometry, it was possible to distinguish the different regions of interest on a micrometer scale and to follow the swelling of the hydrogel part as a function of the temperature. It was possible to visualize the swelling as 3D profiles of Δ at various temperatures. Long-term changes of the sample could also be detected, which cannot be picked up by conventional ellipsometry.