Optical properties of CeO<Subscript>2</Subscript> thin films

Cerium oxide (CeO₂) thin films have been prepared by electron beam evaporation technique onto glass substrate at a pressure of about 6 × 10⁻⁶ Torr. The thickness of CeO₂ films ranges from 140–180 nm. The optical properties of cerium oxide films are studied in the wavelength range of 200–850 nm. The film is highly transparent in the visible region. It is also observed that the film has low reflectance in the ultra-violet region. The optical band gap of the film is determined and is found to decrease with the increase of film thickness. The values of absorption coefficient, extinction coefficient, refractive index, dielectric constant, phase angle and loss angle have been calculated from the optical measurements. The X-ray diffraction of the film showed that the film is crystalline in nature. The crystallite size of CeO₂ films have been evaluated and found to be small. The experimental d-values of the film agreed closely with the standard values.     

Effect of V<Subscript>2</Subscript>O<Subscript>5</Subscript> content on the optical,structural and electrochromic properties of TiO<Subscript>2</Subscript> and ZrO<Subscript>2</Subscript> thin films

Vanadium oxide (V₂O₅) mixed titanium oxide (TiO₂) and zirconium oxide (ZrO₂) thin films were fabricated on glass substrates (corning 2947) and on indium tin oxide (ITO) coated glass substrates by sol gel spin coating process. Their optical, structural and electrochromic properties were investigated. The results were compared with pure TiO₂ and ZrO₂ thin films. Mixture of V₂O₅ with both types of film reduces the transmittance at the higher wavelengths. The refractive index of the V₂O₅ mixed TiO₂ and ZrO₂ films increases when compared with pure TiO₂ and ZrO₂ films. AFM images demonstrate no significant topographical changes for V₂O₅ mixed TiO₂ whereas for V₂O₅ mixed ZrO₂ films a topographical change is observed. V₂O₅ mixed TiO₂ showed slight increase in their charge capacity.     

Enhanced electrochemical performance of Na<Subscript>3</Subscript>V<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>2</Subscript>F<Subscript>3</Subscript> for Na-ion batteries with nanostructure and carbon coating

Carbon-coating Na₃V₂(PO₄)₂F₃ nanoparticles (NVPF@C NP) were prepared by a hydrothermal assisted sol–gel method and applied as cathode materials for Na-ion batteries. The as-prepared nanocomposites were composed of Na₃V₂(PO₄)₂F₃ nanoparticles with a typical size of ~?100 nm and an amorphous carbon layer with the thickness of ~?5 nm. Cyclic voltammetry, rate and cycling, and electrochemical impedance spectroscopy tests were used to discuss the effect of carbon coating and nanostructure. Results display that the as-prepared NVPF@C NP demonstrates a higher rate capability and better long cycling performance compared with bare Na₃V₂(PO₄)₂F₃ bulk (72 mA h g^?1 at 10 C vs 39 mA h g^?1 at 10 and 1 C capacity retention of 95% vs 88% after 50 cycles). The remarking electrode performance was attributed to the combination of nanostructure and carbon coating, which can provide short Na-ion diffusion distance and rapid electron migration.     

Synthesis and optical properties of CeO<Subscript>2</Subscript> nanocrystalline films grown by pulsed electron beam deposition

The nanocrystalline cerium dioxide (CeO₂) thin films were deposited on soda lime (SLG) and Corning glass by pulsed e-beam deposition (PED) method at room temperature. The structure of the produced CeO₂ thin films was investigated by X-ray diffraction (XRD) analysis, X-ray photoelectron spectroscopy (XPS), and micro Raman spectroscopy. The surface topography of the films was examined by atomic force microscopy (AFM). Film thickness and growth morphologies were determined with FEG-SEM from the fracture cross sections. XPS studies gave a film composition composed of +4 and +3 valent cerium typical to nanocrystalline ceria structures deficient in oxygen. The ceria films were polycrystalline in nature with a lattice parameter (a) of 0.542 nm. The Raman characteristics of the source material and the films deposited were very similar in character. Raman lines for thin film and bulk CeO₂ was observed at 465 cm⁻¹. The optical properties of the CeO₂ films were deduced from reflectance and transmittance measurements at room temperature. From the optical model, the refractive index was determined as 1.8–2.7 in the photon energy interval from 3.5 to 1.25 eV. The optical indirect band gap (E _g) of CeO₂ nanocrystalline films was calculated as 2.58 eV.     

Dependence of Microstructure and <Emphasis Type="Italic">J</Emphasis><Subscript>c</Subscript> of YBCO Films on CeO<Subscript>2</Subscript> Cap Layers Deposited by Multi-plume PLD

In order to achieve high-performance YBa₂Cu₃O_7?x (YBCO)coated conductors (CCs) fabricated in industrial scale, it is necessary to enhance the transport properties and production speed of the CCs for use in various application forms. The transport performance of CCs depends upon the inner structure of the conductors, which make it important to analyze the microstructure and transport properties. The thickness of the buffer layer is a factor in improving speed. In this work, we deposited YBCO films on CeO₂ cap layers with different thicknesses ranging from 21 to 563 nm by multi-plume pulsed laser deposition (PLD) and investigated the dependence of the microstructure and superconducting properties of YBCO film on the thickness of CeO₂ films. The crystalline structure and surface morphology of YBCO films are systematically characterized by means of XRD, AFM, SEM and TEM. The critical current of YBCO film was measured by the conventional four-probe method at 77 K, in self-field. The results showed that the microstructure and superconducting performance of YBCO film were strongly dependent on the thickness of CeO₂ films. At the optimal CeO₂ layer thickness of 221 nm, the YBCO film exhibited a sharp in-plane and out-of-plane texture of full width at half maximum (FWHM) values of 1.5° and 2.4°, respectively, and smooth morphology of root mean square (RMS) value as low as 4.0 nm. The sharply biaxially textured YBCO films with the critical current density as high as 4.7 × 10⁶ A/cm² (77 K, in self-field) were obtained on CeO₂/MgO/Y₂O₃/Al₂O₃/C276 architecture.     

Spectral optoelectronic features of Cu-containing arsenic sulfide (As<Subscript>2</Subscript>S<Subscript>3</Subscript>)<Subscript>0.95</Subscript>Cu<Subscript>0.05</Subscript>

Chalcogenide amorphous thin films of the modification (As₂S₃)_0.95Cu_0.05 were prepared using a thermal evaporation technique. The optical properties of the resultant films were investigated based on the transmittance spectra in the photon energy range 1.6–2.82 eV. Thicknesses of the films under study were determined using the envelope technique based on the transmittance spectra. The optical measurements were carried out over the conditional temperature extending from 77 to 300 K. The results of the mentioned measurements are conductive tools in investigating the electronic structures of the Chalcogenide Glasses, however the analysis of the experimental results provide information about the optical gap width and elucidate the broadness of the band tail that may disturb the band gap edges. Moreover, the single-effective oscillator was implemented in calculating both the oscillation and dispersion energies of the films under investigation. The static refractive index and the static dielectric constant were also determined for these films.     

Growth of Y<Subscript>3</Subscript>Fe<Subscript>5</Subscript>O<Subscript>12</Subscript> films on Si with AlO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> and SiO<Subscript>2</Subscript> buffer layers by ion beam sputtering

Amorphous yttrium iron garnet films ranging in thickness from 100 to 600 nm have been produced on single-crystal silicon substrates by sputtering a polycrystalline target with the composition Y₃Fe₅O₁₂ (yttrium iron garnet) by a mixture of argon and oxygen ions. Before film growth, AlO _x or SiO₂ buffer layers up to 0.8 μm in thickness were grown on the Si surface. The heterostructures were crystallized by annealing in air at a temperature of 950°C for 30 min. The properties of the films were studied by magneto-optical techniques, using Kerr effect and ferromagnetic resonance measurements. The Gilbert damping parameter reached 2.8 × 10^–3 and the effective planar magnetic anisotropy field was independent of the nature of the buffer layer. This suggests that the thin-film heterostructures obtained in this study are potentially attractive for use in spin-wave semiconductor devices.     

Effect of N<Subscript>2</Subscript> gas annealing and SiO<Subscript>2</Subscript> barrier on the optical transmittance and electrical resistivity of a transparent Sb-doped SnO<Subscript>2</Subscript> conducting film

During the fabrication process of transparent conducting thin films of ATO (antimony-doped tin oxide) on a soda lime glass substrate by a sol-gel dip coating method, the effects of the SiO₂ buffer layer formed on the substrate and N₂ annealing treatment were investigated quantitatively. The deposited ATO thin film was identified as a crystalline SnO₂ phase and the film thickness was about 100 nm/layer at a withdrawal speed of 50 mm/min. Optical transmittance and electrical resistivity of the 400 nm-thick ATO thin film that was deposited on SiO₂ buffer layer/soda lime glass and then annealed under nitrogen atmosphere were 84% and 5.0 × 10^–3cm, respectively. The XPS analysis confirmed that a SiO₂ buffer layer inhibited Na ion diffusion from the substrate, preventing the formation of a secondary phase such as Na₂SnO₃ and SnO and increasing Sb ion concentration and ratio of Sb⁵⁺/Sb³⁺ in the film. It was found that N₂ annealing treatment leads to the reduction of Sn⁴⁺ as well as Sb⁵⁺, however the reduction of Sn⁴⁺ is more effective, and consequently results in a decrease in the electrical resistivity to produce excellent electrical properties in the film. © Springer Science + Business Media, Inc.     

Piezoelectric and optical properties of ZnO thin films deposited using various O<Subscript>2</Subscript>/(Ar+O<Subscript>2</Subscript>) gas ratios

In this study, ZnO thin films were fabricated on a Pt(111)/TiO_x/SiO₂/Si substrate using the RF magnetron sputtering method. Then, the effect of the crystallization orientation and microstructure on the piezoelectric and optical properties of the ZnO thin film was investigated for various O₂/(Ar+O₂) gas ratios. When the O₂/(Ar+O₂) gas ratio was 50%, the intensity of the (002) peak corresponding to the preferred orientation of the ZnO thin film was a maximum and the minimum FWHM value of 0.56° was observed. The surface roughness of the ZnO thin film measured using AFM also had a minimum value of 16.43 °C at an O₂/(Ar+O₂) gas ratio of 50%. The piezoelectric characteristics of the ZnO thin film were measured using the pneumatic loading method (PLM) and the corresponding constant had the largest value of 11.9 pC/N at an O₂/(Ar+O₂) gas ratio of 50%. The transmittance of the ZnO thin film obtained from the transmittance curve using a spectrophotometer was slightly greater than 80% in the human visible light region at an O₂/(Ar+O₂) gas ratio of 50%. By using the refractive index data obtained from the transmittance curve and the Sellmeir dispersion relation, we can also predict the refractive index at a wavelength of 400 nm. When the O₂/(Ar+O₂) gas ratio was 50%, the refractive index was 2.043 and, at other gas ratios, the corresponding refractive indices were 2.004∼2.006. The band gap energies of the ZnO thin film were 3.27∼3.33 eV depending on the O₂/(Ar+O₂) gas ratio and were little affected by the variation of the oxygen inflow volume.     

Structure and physical properties of tetragonal PbMg<Subscript>1/3</Subscript>Nb<Subscript>2/3</Subscript>O<Subscript>3</Subscript>-PbTiO<Subscript>3</Subscript> solid solutions

The principal bond distances in the structure of tetragonal PbMg_1/3Nb_2/3O₃-PbTiO₃ (PMN-PT) solid solutions have been determined by the Rietveld method. The ferroelectric state of (PbMg_1/3Nb_2/3O₃)_0.62(PbTiO₃)_0.38 samples is shown to be governed by the displacement of the Pb ions from their ideal crystallographic site. In the frequency range 4000–5000 cm^?1, the refractive index of the samples is 2.70–2.75, as determined by the Kramers-Kronig method.     

Surface modification and enhanced multiferroic behavior of BiFe<Subscript>0.25</Subscript>Cr<Subscript>0.75</Subscript>O<Subscript>3</Subscript> films with different thickness over Pt(111)/Ti/SiO<Subscript>2</Subscript>/Si substrate

Polycrystalline BiFe_0.25Cr_0.75O₃ thin films have been fabricated via a chemical deposition technique at various thicknesses (60-, 130-, 190-, 240 nm). The effect of Cr substitution on BiFeO₃ structures have been briefly discussed by performing X-ray diffraction and SAED pattern. The nature of the films surface at different thicknesses were briefly discussed using scanning electron microscope and transmission electron microscope. Roughness and other amplitude parameters of the film at different thickness are studied through atomic force microscopy. The result indicates that, when changing the thickness of the film, the average bond length gets changed causing difference in electrical and magnetic properties. Electrical and dielectric study reveals thickness dependent property and is deeply understood from space charge, oxygen vacancies and super-exchange interaction. Film at 60 nm shows higher magnetization with 8.5042 emu/cm³ and with a retentivity of 3.852 emu/cm³ than the thick film. Further, the spin-cooling behavior and magnetization below room temperature from 2 to 300 K were analyzed briefly for spintronics applications.     

Micro-Raman spectroscopy and X-ray diffraction studies of atomic-layer-deposited ZrO<Subscript>2</Subscript> and HfO<Subscript>2</Subscript> thin films

Raman spectroscopy and X-ray diffraction (XRD) methods were applied to characterize ZrO₂ and HfO₂ films grown by atomic layer deposition (ALD) on silicon substrates in chloride- based processes. A dramatic enhancement in spectral quality of Raman data resulted from the use of the film’s freestanding edges for experimental runs between 80 and 800 cm⁻¹. Both techniques detected a preferential formation of a metastable phase in ZrO₂ and HfO₂ films at 500 and 600^∘C, respectively, during the initial stages of ALD. In the case of ZrO₂ films this phase was identified as the tetragonal polymorph of ZrO₂ (t-ZrO₂). XRD and Raman spectroscopy data showed that, in contrast to the monoclinic phase (m-ZrO₂), the absolute amount of t-ZrO₂ remained approximately constant while its relative amount decreased with the increase of the film thickness from 56 to 660 nm. Neither XRD nor Raman spectroscopy allowed unambiguous identification of the metastable phase formed in otherwise monoclinic HfO₂ films.     

Electrical properties of pulsed laser deposited Bi<Subscript>2</Subscript>Zn<Subscript>2/3</Subscript>Nb<Subscript>4/3</Subscript>O<Subscript>7</Subscript> thin films for high K gate dielectric application

Metal Insulator Semiconductor (MIS) capacitors with monoclinic bismuth zinc niobate pyrocholre having the composition Bi2Zn2_/3Nb_4/3O₇ (m-BZN) dielectric layer were fabricated and characterized. Capacitance voltage (C–V) and current voltage measurements were utilized to obtain the dielectric properties, leakage current density and interface quality. The results shows that the obtained m-BZN thin films presents a high dielectric constant in between 30 and 70, a good interface quality with silicon and a leakage current density of 10 μA/cm² for a field strength of 100 kV/cm which is acceptable for high performance logic circuits. The equilent oxide thickness for the films annealed at 200 °C was 10 nm. These results suggest that m-BZN thin films can be potentially integrated as gate dielectric materials in CMOS technology.     

Fabrication of SiO<Subscript>2</Subscript>/TiO<Subscript>2</Subscript> double layer thin films with self-cleaning and photocatalytic properties

Transparent antireflective SiO₂/TiO₂ double layer thin films were prepared using a sol–gel method and deposited on glass substrate by spin coating technique. Thin films were characterized using XRD, FE-SEM, AFM, UV–Vis spectroscopy and water contact angle measurements. XRD analysis reveals that the existence of pure anatase phase TiO₂ crystallites in the thin films. FE-SEM analysis confirms the homogeneous dispersion of TiO₂ on SiO₂ layer. Water contact angle on the thin films was measured by a contact angle analyzer under UV light irradiation. The photocatalytic performance of the TiO₂ and SiO₂/TiO₂ thin films was studied by the degradation of methylene blue under UV irradiation. The effect of an intermediate SiO₂ layer on the photocatalytic performance of TiO₂ thin films was examined. SiO₂/TiO₂ double layer thin films showed enhanced photocatalytic activity towards methylene blue dye.     

Preparation,characterization and photocatalytic activity of TiO<Subscript>2</Subscript> / Methylcellulose nanocomposite films derived from nanopowder TiO<Subscript>2</Subscript> and modified sol–gel titania

TiO₂—methylcellulose (MC) nanocomposite films processed by the sol-gel technique were studied for phocatalytic applications. Precalcined TiO₂ nanopowder was mixed with a sol and heat treated. The sol suspension was prepared by first adding titanium tetra isopropoxide (Ti(OPr)₄ or TTP) to a mixture of ethanol and HCl (molar ratio TTP:HCl:EtOH:H₂O = 1:1.1:10:10) and then adding a 2 wt.% solution of methylcellulose (MC). The TiO₂ nanopowder was dispersed in the sol and the mixture was deposited on a microscope glass slide by spin coating. Problems of film inhomogeneity and defects which caused peeling and cracking during calcinations, because of film shrinkage, were overcome by using MC as a dispersant. Effect of MC on the structure evaluation, crystallization behavior and mechanical integrity with thermal treatment up to 500 °C are followed by SEM, XRD and scratch test. XRD Scanning electron microscopy (SEM) showed that the composite films with MC have much rougher surface than films made without MC. Composite films heat treated at approximately 500 °C have the greatest hardness values. For the composite thick film, the minimum load which caused the complete coating removal was 200 g/mm², an indication of a strong bond to the substrate. Photocatalytic activities of the composite film were evaluated through the degradation of a model pollutant, the textile dye, Light Yellow X6G (C.I. Reactive Yellow 2) and were compared with the activity of (i) a similar composite film without MC, and (ii) a TiO₂ nanopowder. The good mechanical integrity make this composite film an interesting candidate for practical catalytic applications.     

Orientation controlling of Pb(Zr<Subscript>0.53</Subscript>Ti<Subscript>0.47</Subscript>)O<Subscript>3</Subscript> thin films prepared on silicon substrates with the thickness of La<Subscript>0.5</Subscript>Sr<Subscript>0.5</Subscript>CoO<Subscript>3</Subscript> electrodes

Pb(Zr_0.53Ti_0.47)O₃ (PZT) thin films were prepared on La_0.5Sr_0.5CoO₃ (LSCO) coated Si substrates by a sol–gel route. The thickness of LSCO electrode was found to modify the preferential orientation of PZT thin films, which consequently affected the dielectric and ferroelectric properties. (100) textured PZT films with dense columnar structure could be obtained on the top of (110) textured LSCO with thickness of 230 nm. PZT thin films prepared on the optimized LSCO films exhibit the enhanced dielectric constant and remnant polarization of 980 and 20 μC/cm², respectively.     

Synthesis and characterization of nanocrystalline TiO<Subscript>2</Subscript> thin films

Nanocrystalline thin films of TiO₂ have been synthesized by sol gel spin coating technique Thin films of TiO₂ annealed at 700 °C were characterized by X-ray diffraction(XRD), Atomic Force Microscopy, High resolution TEM and Scanning Electron Microscopy (SEM), The XRD shows formation of tetragonal anatase and rutile phases with lattice parameters a = 3.7837 Å and c = 9.5087 Å. The surface morphology of the TiO₂ films showed that the nanoparticles are fine with an average grain size of about 60 nm. Optical studies revealed a high absorption coefficient (10⁴ cm^?1) with a direct band gap of 3.24 eV. The films are of the n type conduction with room temperature electrical conductivity of 10^?6 (Ω cm)^?1.     

Preparation of K<Subscript>2</Subscript>Ti<Subscript>6</Subscript>O<Subscript>13</Subscript>/TiO<Subscript>2</Subscript> bio-ceramic on titanium substrate by micro-arc oxidation

K₂Ti₆O₁₃/TiO₂ bio-ceramic coatings are prepared successfully by micro-arc oxidation on titanium substrate in pure KOH electrolyte solution. The coating is prepared at various applied current density (150–500 mA/cm²) and in KOH electrolyte with different concentrations (0.5–1.2 mol/L). The composition and surface morphologies of coatings are strongly dependent on the applied current density and the electrolyte concentration. On the condition of lower current density and electrolyte concentration, K₂Ti₆O₁₃ phase almost cannot be formed. The phase is mainly composed of rutile and K₂Ti₆O₁₃ with increasing current density and electrolyte concentration. The surface morphologies are composed of whiskers and porous structures. The ability of K₂Ti₆O₁₃/TiO₂ bio-ceramic films inducing apatite deposition is evaluated by soaking it in biological model fluids. The results show the K₂Ti₆O₁₃/TiO₂ bio-ceramic coatings possess excellent capability of inducing bone-like apatite to deposit.     

Spectroscopic ellipsometry study of In<Subscript>2</Subscript>O<Subscript>3</Subscript> thin films

In₂O₃ films grown by helicon magnetron sputtering with different thicknesses were characterized by spectroscopic ellipsometry in the energy range from 1.5 to 5.0 eV. Aside from one amorphous sample prepared at room substrate temperature, polycrystalline In₂O₃ films with cubic crystal structure were confirmed for other four samples prepared at the substrate temperature of 450 °C. Excellent SE fittings were realized by applying 1 and/or 2 terms F&B amorphous formulations, building double layered film configuration models, and further taking account of void into the surface layer based on Bruggeman effective medium approximation for thinner films. Spectral dependent refractive indices and extinction coefficients were obtained for five samples. The curve shapes were well interpreted according to the applied dispersion formulas. Almost similar optical band gap values from 3.76 to 3.84 eV were obtained for five samples by Tauc plot calculation using extinction coefficients under the assumption of direct allowed optical transition mode.     

Studies on Micro-Structure of Nano-ZrO<Subscript>2</Subscript> Films

In this paper, the micro-structure and laser damage threshold of nano-ZrO₂ thin films were investigated. High-purity nano-ZrO₂ particles as the coating materials of samples were prepared by electron beam evaporation. The crystallitic size and surfaces’ roughness of the samples were analyzed. The laser damage threshold test used a 1064 nm, 10 ns, 3 Hz Nd:YAG laser. The experimental results showed that oxygen partial pressure has an important influence on the micro-structure of nano-ZrO₂ films, and also we found that the laser damage threshold was dependent on the micro-structure.