Ilze Aulika

Formation of Optical Gradient in Chemical Solution-Derived PbZr0.52Ti0.48O3 Thin Films: Spectroscopic Ellipsometry Investigation

Investigation using a variable angle spectroscopic ellipsometer revealed the influence of sample preparation conditions on sol-gel PbZr 0.52 Ti 0.48 O 3 (PZT 52/48) thin-film homogeneity that allows identification and further optimization of thin-film performance. Separate crystallization of the layers determined the optical gradient appearance, irrespective of the chemical solvents used in this work. A more refined analysis showed that a refractive index gradient was apparent in the samples in which lattice parameters strongly changed with thickness. For these films, energy-dispersive X-ray spectroscopy analysis showed significant variation in Pb and Zr. Additionally, complex dielectric functions for each PZT 52/48 thin film in the wide phonon energy (1.03-5.39 eV) range were evaluated.

Optical Spectra and Direct Optical Transitions in Amorphous and Crystalline ZnO Thin Films and Powders

Comparative studies of ZnO crystalline and amorphous thin films and nanocrystalline powders are reported. The UV-visible optical spectra were analyzed with special attention paid to the direct optical bandgap. Atmospheric radio-frequency barrier torch discharge and pulsed hollow cathode sputtering techniques for the film fabrication were used. For the crystalline films, similar values of the direct optical bandgap were found independent of the growth method used. The analysis of the amorphous films and powders revealed a pronounced Urbach-like exponential absorption tail approaching the bandedge. For the powders, the bandgap energies were larger than those for the crystalline and amorphous films. A decrease in the powder particle size in the powders leads to an increased direct optical bandgap.

Optical Gradient of the Trapezium-Shaped NaNbO3 Thin Films Studied by Spectroscopic Ellipsometry

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 therefractive index were evaluated. An increase of the refractive index with increasing of the sample thickness was observed anddiscussed.© 2008 The Electrochemical Society. DOI: 10.1149/1.2965786 All rights reserved.Manuscript submitted May 27, 2008; revised manuscript received July 7, 2008. Published August 19, 2008.

Irradiation effects in lead zirconate thin films

Lead zirconate PbZrO3 (PZ) and PbZr0.53Ti0.47O3 (PZT) sol-gel films with a thickness of up to 1.5 μm were deposited on TiO2/Pt/TiO2/SiO2/Si substrates by spin coating technique and heterostructures of the same composition as well as on Pb0.92La0.08 (Zr0.65Ti0.35)O3 (PLZT-8) (with a thickness of 0.4 μm) were pulse laser deposited (PLD) on Pt/Ti/SiO2/Si. Observation of a typical antiferroelectric (AFE) double hysteresis loop in obtained PZ heterostructures at room temperature was attributed to the superior dielectric strength in case of thin film materials. The thermal behavior of dielectric permittivity ε of PZ film reveals a maximum near 225°C on heating and 219°C on cooling. The higher resistance of antiferroelectric PZ thin films as compared to ferroelectric (e.g., PZT, PLZT-8) heterostructures to neutron irradiation (up to fluence 2x1022m-2)* is recognized and discussed.

Thermo-optical studies of NaNbO3 thin films

Thermo-optical studies of sodium niobate NaNbO3 (NN) thin films, deposited by the pulsed laser ablation technique on Si/SrRuO3 substrates, were performed by spectroscopic ellipsometry in the temperature range 300-550°C. Optical constants at the room temperature were measured in the spectral range 250-1000 nm. Substantial changes in the refractive index temperature behaviour (taken at λ = 300 nm) were found at temperatures 370, 445, 503, 520, and 532°C, where the first and the last temperatures are the phase transitions P → R and S → T1, respectively. Other temperatures (445, 503, and 520°C) are suggested as the points of some local structural changes in the NN film.

Structure and Properties of Pb(LuNb)O3-PbTiO3 Ceramics and Thin Films

The crystallographic features of binary system Pb(LuNb)O3-PbTiO3 (PLuNT) including the morphotropic phase boundary (MPB) region between tetragonal P4mm and pseudo-monoclinic M phases are reported and discussed with respect to dielectric, polarization and electromechanical characteristics. Non-isovalent doping of PLuNT in the Pb sublattice according to 2Pb2+ → 2La3+ + □A either in both components or maintaining the PbTiO3 unmodified: (i) shifts the MPB to the pseudo-monoclinic side of the phase diagram; (ii) diminishes the distortion of the unit cell (c/a −1 = 0.009 at 2 mol.% of La); (iii) reduces the coercive field to 15.8 kV/cm in the first case and below 10 kV/cm in the latter case. Simultaneously high values of maximum polarization Pm = 50.3 μC/cm2 and remnant polarization Pr ≅ 40.3 μC/cm2 maintain. The films of PLuNT with composition near the MPB formed by in situ pulsed laser deposition (PLD) onto LSCO/(100)MgO exhibited ferroelectric (FE) behaviour with Pm ≅ 29 μC/cm2, Pr ≅ 14 μC/cm2, Ec ≅ 70 kV/cm. The zero-field dielectric permittivity ϵ = 300–450 at room temperature, and demonstrates a relaxor type broad peak around 350°C. Au/PLuN/LSCO thin film heterostructures exhibit FE behaviour as well in contrast to typical AFE features of PLuN ceramic; a diffuse peak of ϵ was observed around 100°C. The lower degree of structural ordering is considered to be the main factor in the different behaviour of thin films and bulk ceramic material.

Effect of Nanotube Aspect Ratio on Chemical Vapour Sensing Properties of Polymer/MWCNT Composites

The main topic of this paper is the study of polyisoprene-multi wall carbon nanotubes (PiMWCNT) composites electrical conductivity and volatile organic compound sensing properties with respect to type of multi wall carbon nanotubes used. Electrical percolation parameters like percolation threshold and critical exponent of produced composites are determined and analyzed. PiMWCNT composites exhibit a promising sensitivity to the presence of volatile organic compounds. Therefore the composites sensing mechanism of volatile organic compounds are analyzed in more detail by applying an original measuring technique which enables simultaneous measurement of an electrical resistance, mass and length change measurement of the sample in the presence and subsequent absence of a vapour. Measurement results enabled the evaluation of both vapour diffusion behavior in the composite and electrical resistance change mechanism.

Compositional and Optical Gradient in Films of PbZrxTi1-xO3 (PZT) Family

Pb(ZrxTi1-x)O3 (PZT) (x = 0-1) films have attracted the attention of researchers for the past 30 years due to their excellent ferroelectric (FE) and electromechanical properties, which have led to the commercialization of thin PZT films for ferroelectric random access memory (FeRAM), forming a market of several millions USD annually. Ferroelectricity of perovskite oxide thin films, especially PZT thin films, can be exploited in semiconductor devices to achieve non-volatile random access memory (NVRAM) with high-speed access and long endurance, which can overcome the barriers, encountered in current semiconductor memory technologies. The ferroelectricity can be also exploited to voltage dependent and thermally sensitive resistors, gas and humidity sensors. Besides, due to large pyroelectric coefficient of PZT, it has drawn interest for use in pyroelectric devices (Izyumskaya et al., 2007; Muralt, 2000; Whatmore et al., 2003). PZT thin films have remarkable advantages over bulk materials: • Can be directly deposited on platinized silicon to allow direct integration with electronics; • Have superior electromechanical properties compared to other ferroelectric ceramics. Thanks to that, PZT films have formed an integral part of the microelectromechanical systems (MEMS) in various applications such as sensors, actuated micromirrors for finetracking high-density optical data storage mechanisms (Yee et al., 2001), and tunable capacitors for high-frequency microwave applications, microelectromechanical systems, infrared detectors, applications in optical devices, for instance, rugate filters (Bovard, 1990), anti-reflection coatings (Oulette et al., 1991), and electro-optic modulators, to name a few. Low density embedded FE memories are being considered for implementation not only in commercial devices, such as smart cards and cellular phones, but also for adaptive FE

Nanocrystalline Ferroelectric/Relaxor Multilayers

After investigations on sputtered nanocrystalline ferroelectric Pb 0.76 Ca 0.24 TiO 3 (PTC) films and nanocrystalline relaxor films, namely Pb(Sc 0.5 Ta 0.5 )O 3 (PST), Pb(Sc 0.5 Nb 0.5 )O 3 (PSN) and Pb(Mg 1/3 Nb 2/3 )O 3 (PMN) we started to investigate effects in multilayers of nanocrystalline ferroelectric and relaxor films. The increasing size of the crystallites, the crystal structure and the phase purity were characterized by profile analysis of the XRD spectra which reveal that the perovskite peaks of the PTC films in the multilayers are very well developed and the large amount of pyrochlore phase found in the single layers has almost been completely reduced. Temperature and frequency dependent dielectric measurements show not only typical relaxor properties but the existence of two maxima as well. Hysteresis loops have been recorded to look for thickness dependence.