Dielectric Properties of Pulsed Excimer Laser Ablated BaBi2Nb2O9 Thin Films

The dielectric response of BaBi2Nb2O9 (BBN) thin films has been studied as a function of frequency over a wide range of temperatures. Both dielectric constant and loss tangent of BBN thin films showed a ‘power law’ dependence with frequency, which was analyzed using the Jonscher's universal dielectric response model. Theoretical fits were utilized to compare the experimental results and also to estimate the value of temperature dependence parameters such as n(T) and a(T) used in the Jonscher's model. The room temperature dielectric constant (ε') of the BBN thin films was 214 with a loss tangent (tanδ) of 0.04 at a frequency of 100 kHz. The films exhibited the second order dielectric phase transition from ferroelectric to paraelectric state at a temperature of 220 °C. The nature of phase transition was confirmed from the temperature dependence of dielectric constant and sponteneous polarization,respectively. The calculated Currie constant for BBN thin films was 4 × 105°C.

Microstructural Studies of Ferroelectric Bi2VO5.5 Thin Films With LaNiO3 Electrodes

Thin films of Bi2VO5.5 (BVO), a vanadium analog of the n = I member of the Aurivillius family, have been prepared by pulsed laser deposition. The BVO films grow along the [001] direction on LaNiO3(LNO) and YBa2Cu3O7 (YBCO) electrode buffer layers on LaA- IO3(LAO) substrates as obtained from X-ray diffraction studies. The microstructure of the films and of the interfaces within the film and between the film and the substrate were characterized using transmission electron microscopy. The in-plane epitaxial relationship of the rhombohedral LNO on perovskite LAO was [100] LNO // [100] LAO and [001] LNO // [001] LAO. High resolution lattice images showed a sharp interface between LNO and LAO. However, the LNO film is twinned with a preferred orientation along the growth direction. The BVO layer is single crystalline on both LNO/LAO and YBCO/LAO with the caxis parallel to the growth direction except for a thin layer of about 400 Å at the interface which is polycrystalline.

Growth and Characterization Studies of ABi2ta2o9 (A = Ba, Sr and Ca) Ferroelectric Thin Films

Thin films of ferroelectric ABi2Ta2O9 bismuth-layered structure, where A = Ba, Sr and Ca, were prepared by pulsed laser deposition technique on Pt/TiO2/SiO2/Si(100) substrates. The influence of substrate temperature between 500 to 750°C, and oxygen partial pressure 100-300 mTorr, on the structural and electrical properties of the films was investigated. The films deposited above 650°C substrate temperature showed complete Aurivillius layered structure. Films annealed at 750°C for 1h in oxygen atmosphere have exhibited better electrical properties. Atomic force microscopy study of surface topography shows that the films grown at lower temperature has smaller grains and higher surface roughness. This paper discusses the pronounced influence of A-site cation substitution on the structural and ferroelectric properties with the aid of Raman spectroscopy, X-ray diffraction and electrical properties. The degradation of ferroelectric properties with Ba and Ca substitution at A-sites is attributed to the higher structural distortion caused by changing tolerance factor. A systematic proportionate variation of coercive field is attributed to electronegativity difference of A-site cations.

Structural, optical and nanomechanical properties of (1 1 1) oriented nanocrystalline ZnTe thin films

Structural, optical and nanomechanical properties of nanocrystalline Zinc Telluride (ZnTe) films of thickness upto 10 microns deposited at room temperature on borosilicate glass substrates are reported. X-ray diffraction patterns reveal that the films were preferentially oriented along the (1 1 1) direction. The maximum refractive index of the films was 2.74 at a wavelength of 2000 nm. The optical band gap showed strong thickness dependence. The average film hardness and Young's modulus obtained from load-displacement curves and analyzed by Oliver-Pharr method were 4 and 70 GPa respectively. Hardness of (1 1 1) oriented ZnTe thin films exhibited almost 5 times higher value than bulk. The studies show clearly that the hardness increases with decreasing indentation size, for indents between 30 and 300 nm in depth indicating the existence of indentation size effect. The coefficient of friction for these films as obtained from the nanoscratch test was ~0.4.

Structural, optical and nanomechanical properties of (1 1 1) oriented nanocrystalline ZnTe thin films

Structural, optical and nanomechanical properties of nanocrystalline Zinc Telluride (ZnTe) films of thickness upto 10 microns deposited at room temperature on borosilicate glass substrates are reported. X-ray diffraction patterns reveal that the films were preferentially oriented along the (1 1 1) direction. The maximum refractive index of the films was 2.74 at a wavelength of 2000 nm. The optical band gap showed strong thickness dependence. The average film hardness and Young's modulus obtained from load-displacement curves and analyzed by Oliver-Pharr method were 4 and 70 GPa respectively. Hardness of (1 1 1) oriented ZnTe thin films exhibited almost 5 times higher value than bulk. The studies show clearly that the hardness increases with decreasing indentation size, for indents between 30 and 300 nm in depth indicating the existence of indentation size effect. The coefficient of friction for these films as obtained from the nanoscratch test was ~0.4.

Formation of amorphous xenon nanoclusters and microstructure evolution in pulsed laser deposited Ti62.5Si37.5 thin films during Xe ion irradiation

As deposited amorphous and crystallized thin films of Ti 37.5% Si alloy deposited by pulsed laser ablation technique were irradiated with 100 keV Xe+ ion beam to an ion fluence of about 1016 ions-cm−2. Transmission electron microscopy revealed that the implanted Xe formed amorphous nanosized clusters in both cases. The Xe ion-irradiation favors nucleation of a fcc-Ti(Si) phase in amorphous films. However, in crystalline films, irradiation leads to dissolution of the Ti5Si3 intermetallic phase. In both cases, Xe irradiation leads to the evolution of similar microstructures. Our results point to the pivotal role of nucleation in the evolution of the microstructure under the condition of ion implantation.

Fabrication of Yy‐Pr1‐y ‐Ba‐Cu‐O Thin Films and Superlattices of ‐Ba‐Cu‐O/Yy‐Pr1‐y ‐Ba‐Cu‐O

We have prepared epitaxial thin films of Yy‐Pr1‐y‐Ba‐Cu‐O (y= 1 to 0) and superlattices of Y‐Ba‐Cu‐O/Yy‐Pr1‐y ‐Ba‐Cu‐O using pulsed laser deposition technique. The zero resistance transition temperatures of Yy‐Pr1‐y‐Ba‐Cu‐O bulk samples are reproduced in the films. The composition oscillations in the superlattices are observed by SIMS. The films and superlattices are found to have c‐axis orientations and good crystallinity.

High energy Li ion irradiation effects in ferroelectric PZT and SBT thin films

The ferroelectric Pb(Zr0.53Ti0.47)O-3 (PZT) and SrBi2Ta2O9 (SBT) thin films were prepared by laser ablation technique. The dielectric analysis, capacitance-voltage, ferroelectric hysteresis and DC leakage current measurements were performed before and after 50 MeV Li3+ ion irradiation. In both thin films, the irradiation produced some amount of amorphisation, considerable degradation in the ferroelectric properties and change in DC conductivity. On irradiation of these thin films, the phase transition temperature [T-c] of PZT decreased considerably from 628 to 508 K, while SBT exhibited a broad and diffuse transition with its T-c decreased from 573 to 548 K. The capacitance-voltage curve at 100 kHz showed a double butterfly loop with a large decrease in the capacitance and switching voltage. There was decrease in the ferroelectric hysteresis loop, remanant polarisation and coercive field. After annealing at a temperature of 673 K for 10 min while PZT partially regained the ferroelectric properties, while SBT did not. The DC conductivity measurements showed a shift in the onset of non-linear conduction region in irradiated SBT. The degradation of ferroelectric properties of the irradiated thin films is attributed to the irradiation-induced partial amorphization and the pinning of the ferroelectric domains by trapped charges. The regaining of properties after annealing is attributed to the thermal annealing of the defects generated during the irradiation. (C) 2003 Elsevier Science B.V. All rights reserved.

Transient analysis in Al-doped barium strontium titanate thin films grown by pulsed laser deposition

Thin films of (Ba0.5Sr0.5)TiO3 (BST) with different concentrations of Al doping were grown using a pulsed laser deposition technique. dc leakage properties were studied as a function of Al doping level and compared to that of undoped BST films. With an initial Al doping level of 0.1 at. % which substitutes Ti in the lattice site, the films showed a decrease in the leakage current, however, for 1 at. % Al doping level the leakage current was found to be relatively higher. Current time measurements at elevated temperatures on 1 at. % Al doped BST films revealed space-charge transient type characteristics. A complete analysis of the transient characteristics was carried out to identify the charge transport process through variation of applied electric field and ambient temperature. The result revealed a very low mobility process comparable to ionic motion, and was found responsible for the observed feature. Calculation from ionic diffusivity and charge transport revealed a conduction process associated with an activation energy of around 1 eV. The low mobility charge carriers were identified as oxygen vacancies in motion under the application of electric field. Thus a comprehensive understanding of the charge transport process in highly acceptor doped BST was developed and it was conclusive that the excess of oxygen vacancies created by intentional Al doping give rise to space-charge transient type characteristics. © 2001 American Institute of Physics.

Role of rigidity and temperature in the kinetics of photodarkening in Ge(x)As((45-x))Se(55) thin films

We present insightful results on the kinetics of photodarkening (PD) in Ge(x)As(45-x)Se(55) glasses at the ambient and liquid helium temperatures when the network rigidity is increased by varying x from 0 to 16. We observe a many fold change in PD and its kinetics with decreasing network flexibility and temperature. Moreover, temporal evolution of PD shows a dramatic change with increasing x. (C)2011 Optical Society of America

Microwave ECR Plasma Assisted MOCVD of Y(2)O(3) Thin Films Using Y(tod)(3) Precursor and Their Characterization

Yttrium oxide (Y(2)O(3)) thin films were deposited by microwave electron cyclotron resonance (ECR) plasma assisted metal organic chemical vapour deposition (MOCVD) process using indigenously developed metal organic precursors Yttrium 2,7,7-trimethyl-3,5-octanedionates, commonly known as Y(tod)(3) which were synthesized by an ultrasound method. A series of thin films were deposited by varying the oxygen flow rate from 1-9 sccm, keeping all other parameters constant. The deposited coatings were characterized by X-ray photoelectron spectroscopy, glancing angle X-ray diffraction and infrared spectroscopy. Thickness and roughness for the films were measured by stylus profilometry. Optical properties of the coatings were studied by the spectroscopic ellipsometry. Hardness and elastic modulus of the films were measured by nanoindentation technique. Being that microwave ECR CVD process is operating-pressure-sensitive, optimum oxygen activity is very essential for a fixed flow rate of precursor, in order to get a single phase cubic yttrium oxide in the films. To the best of our knowledge, this is the first effort that describes the use of Y(tod)(3) precursor for deposition of Y(2)O(3) films using plasma assisted CVD process.