Piezoelectric and Ferroelectric Films

• Optical Properties of BST Thin Films by Spectroscopic Ellipsometry and Optical Reflectivity
  D. Chvostova, V. Zelzny, L. Pajasova, D. Simek, M. Jelinek, Z. Matej
  FERROELECTRICS 370 126-131 (2008)
  Abstract: Optical properties of Ba0.25Sr0.75TiO3 thin films fabricated by pulsed laser deposition (PLD) have been investigated using variable angle spectroscopic ellipsometry (VASE) and near-normal spectroscopic reflectivity (NNSR). The measurements were carried out from 5 K to 450 K in the spectral range 1-6 eV by VASE, and in the range 1-12 eV by NNSR at the room temperature. Both types of the experimental data (VASE and NNSR) were simultaneously fitted to obtain the optical functions (e.g. complex refractive index, dielectric function) and thicknesses of the films. To determine the optical response functions and parameters of the material we used several models to fit the experimental data. The Cauchy-Urbach formula was applied in the transparent spectral range and the direct fit procedure and the Cody-Lorentz model were applied around and beyond absorption edge. In the entire spectral range the reflectivity spectra were analyzed by Kramers-Kronig analysis. The behavior of the refractive index obtained in this way was studied and some anomalies were found. The x-ray diffraction was used for a study of sample texture. Some correlation with the optical study was found. The optimal deposition temperature can be found from both studies.
  Email: chvostov@fzu.cz
  
  
• The preparation and refractive index of BST thin films
  Authors: Li SZ, Yang YQ, Liu L, Liu WC, Wang SB
  PHYSICA B-CONDENSED MATTER 403 (17) 2618-2623 (2008)
  DOI: 10.1016/j.physb.2008.01.024
  Abstract: Radio-frequency magnetron sputtering technique is used to deposit Ba0.65Sr0.35TiO3 (BST) thin films on fused quartz substrates. In order to prepare the high-quality BST thin films, the crystallization and microstructure of the films were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM). More intense characteristic diffraction peaks and better crystallization can be observed in BST thin films deposited at 600 degrees C and subsequently annealed at 700 degrees C. The refractive index of the films is determined from the measured transmission spectra. The dependences of the refractive index on the deposition parameters of BST thin films are different. The refractive index of the films increases with the substrate temperature. At lower sputtering pressure, the refractive index increases from 1.797 to 2.197 with pressure increase. However, when the pressure increases up to 3.9 Pa, the refractive index reduces to 1.86. The oxygen to argon ratio also plays an important effect on the refractive index of the films. It has been found that the refractive index increases with increase in the ratio of oxygen to argon. The refractive index of BST thin films is strongly dependent on the annealing temperature, which also increases as the annealing temperature ascends. In a word, the refractive index of BST thin films is finally affected by the films' microstructure and texture.
  
  
• Infrared optical properties of Ba(Zr0.20Ti0.80)O-3 and Ba(Zr0.30Ti0.70)O-3 thin films prepared by sol-gel method
  APPLIED SURFACE SCIENCE 254 (18) 5660-5663 (2008)
  DOI: 10.1016/j.apsusc.2008.03.178
  Abstract: Ba(ZrxTi1 (x))O-3 (BZT) (x = 0.20 and 0.30) thin films are deposited on Pt(1 1 1)/Ti/SiO2/Si(1 0 0) substrate by sol-gel method. X-ray diffraction patterns show that the thin. lms have a good crystallinity. Optical properties of the. lms in the wavelength range of 2.5-12 mm are studied by infrared spectroscopic ellipsometry (IRSE). The optical constants of the BZT thin. lms are determined by fitting the IRSE data using a classical dispersion formula. As the wavelength increases, the refractive index decreases, while the extinction coefficients increase. The effective static ionic charges are derived, which are smaller than that in a purely ionic material for the BZT thin films.
  
  
• Structure and optical properties of ferroelectric PbZr0.40Ti0.60O3 films grown on LaNiO3-coated platinized silicon determined by infrared spectroscopic ellipsometry
  Authors: Hu ZG, Li YW, Zhu M, Zhu ZQ, Chu JH
  JOURNAL OF PHYSICAL CHEMISTRY C 112 (26) 9737-9743 (2008)
  DOI: 10.1021/jp801566b
  Abstract: The PbZr0.40Ti0.60O3 (PZT)/LaNiO3 (LNO) multilayer films with different associated thickness have been deposited on Pt/Ti/SiO2/Si substrates by a modified sol-gel technique. X-ray diffraction analysis shows that the PZT and LNO films are polycrystalline with the (100)-preferential orientation and perovskite phase. The optical properties of PZT films have been investigated using infrared spectroscopic ellipsometry (IRSE) in the photon frequency range of 800-4000 cm(-1) (2.5-12.5 mu m). By fitting the measured ellipsometric parameters with a four-phase layered model (air/PZT/LNO/Pt) and a derived classical dispersion relation, the optical function and thickness of the films have been uniquely extracted. The refractive index of the PZT films increases and the extinction coefficient decreases with increasing grain size in the mid-infrared region. Correspondingly, infrared absorption coefficient of the films linearly increases with increasing thickness. It can be concluded that the discrepancy of infrared optical properties is mainly ascribed to the crystalline quality, the grain size effect, and the influence from the interface layer. The present results can be crucial for future application of ferroelectric PZT-based infrared optoelectronic devices.
  
  
• Spectroscopic Ellipsometry Studies of Ferroelectric SbSexS1xI Crystals
  Authors: A. Audzijonis, A. Reza, R. Zaltauskas, L. Zigas, R. Sereika, C. Paskevic, A. Pauliukas,
  FERROELECTRICS 366 45-54 (2008)
  Abstract: In the present paper the optical spectra were measured by spectroscopic ellipsometry method in the range of 0.5-5.0 eV making use of a computer-controlled photometric ellipsometer with a rotating analyzer. The measurement data were traded in terms of a pseudodielectric function (PDF) in framework of the two-phase isotropic ambient-anisotropic homogeneous sample approximation. Anisotropic properties of the sample were revealed by performing the measurement with the sample at two orthogonal orientations with respect to the plane incidence. Two components of the dielectric tensor for crystal of orthorhombic symmetry were determined. The experimental spectra of the dielectric tensor components were approximated by the contributions of Laurence oscillators in order to determine the main optical transitions to the optical response.
  Email: sereika@vpu.lt
  
  
• Growth and ellipsometric characterizations of highly (111)-oriented Bi2Ti2O7 films on platinized silicon by metal organic decomposition method
  Authors: Hu ZG, Li YW, Zhu M, et al.
  JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A 26 (5) 1287-1292 (2008)
  DOI: 10.1116/1.2970142
  Abstract: Optical properties and electronic structure of Bi2Ti2O7 (BTO) films on platinized silicon substrates have been investigated using near-infrared-ultraviolet spectroscopic ellipsometry. The optical dispersion in the photon energy range of 0.73-5.8 eV has been extracted by fitting the experimental data with a four-phase layered model. The Tauc-Lorentz dispersion function has been fundamentally applied and describes the optical response of the BTO films well. The refractive index in the transparent region can be reasonably fitted by a single oscillator function and the maximum electronic transition occurs near 4.2 eV for the BTO material. The long wavelength refractive index n(0) can be estimated to about 1.7 at zero point. The fundamental band gap energy was determined to be about 3.2 eV, which was supported by different theoretical evaluation methods. The present results can be important for future applications of BTO-based electro-optics and optoelectronic devices. (C) 2008 American Vacuum Society.