Oxides

• Relationship between nanostructure and optical properties of ZnO thin films
  Authors: Malandrino G, Blandino M, Fragala ME, Losurdo M, Bruno G
  JOURNAL OF PHYSICAL CHEMISTRY C 112 (26) 9595-9599 (2008)
  DOI: 10.1021/jp8001492
  Abstract: Nanostructured ZnO thin films have been grown on quartz substrates by metal organic chemical vapor deposition. Zn(tta)2 center dot tmeda (H-tta = 2-thenoyltrifluoroacetone, tmeda = N,N,N',N'-tetramethylethylenediamine) has been used as Zn precursor. The impact of deposition temperature, in the range 400-750 degrees C, on film nanostructure and optical properties has been investigated. The X-ray diffraction patterns show that film crystallinity improves upon increasing the substrate temperature. This is consistent with morphologies observed through scanning electron microscopy (SEM) and atomic force microscopy (AFM), which indicate that grain dimensions increase ranging from 80 nm rounded grains at 400 degrees C to barlike grains of about 200-400 nm at the highest investigated temperature of 750 degrees C. The AFM investigation shows that the roughness is also a function of the substrate temperatures and parallels the grains size of ZnO films. The UV-vis transmission spectrum shows that ZnO films grown at 600 degrees C on quartz are highly transparent in the visible region. Furthermore, spectroscopic ellipsometry is used for investigating the dependence of the ZnO dielectric function and optical gap on film nanostructure
  Email: maria.losurdo@ba.imip.cnr.it
  
  
• Ellipsometrically determination of the optical constants of ZnO in ZnO/Ag/ZnO multilayer system
  Authors: S.H. Mohamed, S.A. Ahmed
  EUROPEAN PHYSICAL JOURNAL-APPLIED PHYSICS 44 (2) 137-141 (2008)
  Abstract: The variable angle spectroscopic ellipsometer in conjunction with computer simulation were employed to determine the optical constants of ZnO in the ZnO/Ag/ZnO (ZAZ) multilayer system. A. five-phase, glass/ZnO/Ag/ZnO/air, model was used to. fit the calculated data to the experimental spectra. The ellipsometrically determined ZnO and Ag layers thicknesses were found to be agreed well with those previously determined by X-ray reactivity. The effects of Ag layer thickness (Ag-d) and ZnO top layer thickness (ZnOd) on the optical constants of ZnO in the ZAZ multilayer system were discussed. The refractive index values determined at 550 nm, remains almost constant as Ag-d increases while the refractive index values decrease with decreasing ZnOd. Over the whole visible spectral range the extinction coefficient values of the Ag-d group are very close to zero and does not depend on Ag-d while the extinction coefficient values of the ZnOd group increase with decreasing ZnOd. The optical band gap values are found to be affected strongly by both Ag-d and ZnOd.
  
  
• Growth, optical and nanostructural properties of magnetron sputtered ZnO thin films deposited on polymeric substrates
  Authors: Koidis C, Logothetidis S, Georgiou D, Laskarakis A, Lousinian S, Tsiaoussis I, Frangis N
  PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE 205 (8) 1988-1992 (2008)
  DOI: 10.1002/pssa.200778917
  Abstract: ZnO thin films were deposited onto flexible Poly-Ethylene Terephthalate and Poly-Ethylene Naphthalate substrates in all ultra-high vacuum chamber by Pulsed DC Magnetron Sputtering. The process took place at room temperature and in argon atmosphere with fixed pressure, by applying two different power values on the target, in order to investigate their effect on the growth, optical, nanostructural and topographical properties of the films. In-situ and real-time Spectroscopic Ellipsometry in the 1.5-6.5 eV energy region has been employed to monitor the ZnO deposition, which revealed information about the growth mechanisms, interface phenomena and optical properties of the films. Transmission Electron Microscopy was used in order to investigate the structural characteristics of the films and to examine the film/polymer interface properties. The X-ray Diffraction measurements revealed the changes in films structure caused by the change of the target power, nevertheless all films were preferentially grown along the (002) axis. Finally, with Atomic Force, Microscopy the surface roughness of the films was defined correlated also with the target power applied.
  
  
• Correlation between structure and properties of Er2O3 nanocrystalline thin films
  Authors: Giangregorio MM, Sacchetti A, Losurdo M, Capezzuto P, Bruno G
  JOURNAL OF NON-CRYSTALLINE SOLIDS 354 (19-25) 2853-2857 (2008)
  DOI: 10.1016/j.jnoncrysol.2007.10.102
  Abstract: Er2O3 thin films have been deposited by low-pressure metalorganic chemical vapor deposition (MOCVD) also plasma assisted (RP-MOCVD), using tris(isopropylcyclopentadienyl)erbium and O2 on Si(100), Si(111) and corning glass substrates. The RP-MOCVD approach produced highly (100)-oriented, dense and mechanically stable Er2O3 films with columnar structure, while films with (111) texture are deposited by MOCVD. A high refractive index of 2.1 at 589.3 nm comparable to that of bulk single crystalline Er2O3, a high transparency in the vis-near UV range and an optical band-gap of 6.5 eV have been found, which make Er2O3 interesting as antireflective and protective coating. A static dielectric constant k similar to 12, a density of interface traps as low as 4.2 x 1010 cm(2) eV(-1), for 5-10 nm thick Er2O3 layers grown on Si(100), render the present Er2O3 films interesting also as high-k dielectric in CMOS devices
  Email: maria.losurdo@ba.imip.cnr.it
  
  
• Structure, composition and evolution of dispersive optical constants of sputtered TiO2 thin films: effects of nitrogen doping
  Authors: He G, Zhang LD, Li GH, Liu M, Wang XJ
  JOURNAL OF PHYSICS D-APPLIED PHYSICS 41 (4) 045304 (2008)
  DOI: 10.1088/0022-3727/41/4/045304
  Abstract: Films of nitrogen-doped TiO2 have been successfully deposited on a Si substrate by radio frequency reactive sputtering in a mixture of argon, oxygen and nitrogen. The nitrogen gas ratio varies in the range 0.2-0.4 during the deposition, resulting in TiOxNy films with 3% <= y <= 6.55% as determined by x-ray photoelectron spectroscopy (XPS). Chemical bond state analysis by XPS indicates that nitrogen is effectively incorporated and produces an oxynitride centre as oxygen is replaced by nitrogen. Characterization by atomic force microscopy demonstrates that the incorporation of nitrogen has a significant effect on the morphology of the targeted TiO2 thin films. Spectroscopic ellipsometry with a photon energy of 0.75-6.5 eV at room temperature has been carried out to derive the refractive index n and the extinction coefficient k on the basis of a new amorphous dispersive model. The optical constants such as absorption coefficient, complex dielectric functions and the optical band gap have been determined. The trend of a decrease in the optical band gap with an increase in nitrogen concentration is consistent with the observation determined by UV-visible spectroscopy. The reduced band gap is associated with the N 2p orbital in the TiOxNy films.
  Email: ganghe01@issp.ac.cn
  
  
• Lanthanum oxyfluoride sol-gel thin films by a simple single-source precursor route
  Authors: Armelao L, Bottaro G, Bruno G, Losurdo M, Pascolini M, Soini E, Tondello E
  JOURNAL OF PHYSICAL CHEMISTRY C 112 (37) 14508-14512 (2008)
  DOI: 10.1021/jp804351y
  Abstract: Highly transparent and homogeneous nanostructured LaO1-xF1+2x (0 <= x <= 1) thin films have been synthesized by 0 a simple sol-gel procedure using La(hfa)(3)center dot diglyme (Hhfa = 1,1,1,5,5,5-hexafluoro-2,4-pentailedione; diglyme = bis(2-metoxyethyl) ether) as source compound for both lanthanum and fluorine. While thermal treatments up to 500 degrees C resulted in highly fluorinated nanosystems, i.e., LaF3 at 300 degrees C and LaF3 + LaOF at 500 degrees C, pure and single-phase nanostructured lanthanum oxyfluoride thin films with a mean crystallite size of similar to 15 nm have been obtained at 700 degrees C. The microstructure and composition of the samples and their interplay with the synthesis procedure were investigated by glancing incidence X-ray diffraction, X-ray photoelectron, and X-ray excited Auger electron spectroscopy. Finally, the optical properties of the films were studied by UV-vis-NIR spectroscopy and spectroscopic ellipsometry.
  Email: maria.losurdo@ba.imip.cnr.it
  
  
• Ellipsometric analysis of mixed metal oxides thin films
  Authors: Buiu O, Davey W, Lu Y, Mitrovic IZ, Hall S
  THIN SOLID FILMS 517(1) 453-455 (2008)
  DOI: 10.1016/j.tsf.2008.08.119
  Abstract: The optical dielectric function of hafnium oxide and hafnium silicate thin films was extracted from spectroscopic ellipsometry measurements. The dielectric function is further used for extracting the film density and also to investigate the relation with composition, deposition method and layer stoichiometry. The density of a hafnium silicate film was found to vary between 5563 and 8223 kg/m(-3), for hafnium content (x) between 0.3 and 0.7. We demonstrate that the density of pure hafnium oxide film depends on the deposition method employed and the chemical nature of the starting surface. Also, we investigate the "zero" frequency contribution to the dielectric constant as a function of hafnium silicate film composition.
  Email: w.m.davey@liv.ac.uk
  
  
• Exploring the thermal transformation of mesoporous titania using spectroscopic ellipsometry
  Authors: Choi SY, Mamak M, Ozin GA, Peiris FC
  PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE 205 (4) 825-828 (2008)
  DOI: 10.1002/pssa.200777878
  Abstract: Spectroscopic ellipsometry was used to investigate the optical properties of a series of 2D-hexagonal and 3D-cubic mesoporous titania samples subjected to different annealing temperatures. Below a critical temperature, the dispersion of the index of refraction of the composite structure exhibits strong anisotropy, while above the critical temperature the structure reverts to an isotropic medium. Scanning electron microscopy and X-ray measurements corroborate the ellipsometry results.
  Email: mailto:peirisf@kenyon.edu%20
  
  
• Characterization of sputtered and annealed niobium oxide films using spectroscopic ellipsometry, Rutherford backscattering spectrometry and X-ray diffraction
  Authors: M. Serenyi, T. Lohner, P. Petrik, Z. Zolnai, Z.E. Horvath, N.Q. Khanh
  THIN SOLID FILMS 526 (22) 8096-8100 (2008)
  
  
• Optical gradient of the trapezium-shaped NaNbO3 thin films studied by spectroscopic ellipsometry
  Authors: Aulika I, Dejneka A, Zauls V, Kundzins K
  JOURNAL OF THE ELECTROCHEMICAL SOCIETY Volume: 155 Issue: 10 Pages: G209-G213 (2008)
  DOI: 10.1149/1.2965786
  Abstract: Ellipsometric studies of the optical gradient of NaNbO3 thin films were performed in the photon energy range of 1.24-4.96 eV. Effective values of the complex refractive index and thickness nonuniformity, roughness, and depth profile of the real part of the refractive index were evaluated. An increase of the refractive index with increasing of the sample thickness was observed and discussed.
  
  
• Structural, optical, and electrical properties of epitaxial titanium oxide thin films on LaAlO3 substrate
  Authors: Sbai N, Perriere J, Gallas B, Millon E, Seiler W, Bernard MC
  JOURNAL OF APPLIED PHYSICS 104 (3) 033529 (2008)
  DOI: 10.1063/1.2964114
  Abstract: Titanium oxide thin films were prepared by pulsed-laser deposition on LaAlO3 single crystal substrate at 700 degrees C. Pure anatase films are obtained at high oxygen pressure (10(-1) mbar), while the rutile phase is evidenced at low oxygen pressure (10(-5) mbar) despite a large oxygen deficiency (O/Ti=1.75). From asymmetric x-ray diffraction measurements, the in-plane epitaxial relationships be0tween the substrate and the titanium oxide phases are highlighted. Optical constants (refractive index n and extinction coefficient k) were deduced from ellipsometric measurements. The optical band gap energies of the anatase and rutile films are found to be 3.4 and 3.3 eV, respectively. Since the nearly stoichiometric anatase films are resistive (>10(3) Omega cm), the large oxygen deficiency in rutile films leads to noticeable increase in the conductivity due to the Ti3+ species, which supply electrons in the conduction band. At low temperature (T < 200 K) the resistivity of rutile films versus temperature may be explained by a variable range hopping mechanism based on both two or three dimensional electron transfer between the Ti3+ and Ti4+ species.