PT Thin Films Research Articles

Fabrication and characterization of high curie temperature BiSc 1/2Fe 1/2O 3–PbTiO 3 piezoelectric films by a sol–gel process

(1 − x)BiSc 1/2Fe 1/2O 3– xPbTiO 3 (BSF–PT) thin films with the composition of x = 0.45–0.6 were fabricated on the Pt(1 1 1)/Ti/SiO 2/Si substrates via an aqueous sol–gel method. The structure and electric properties of these BSF–PT thin films were investigated. The films showed a maximum dielectric and piezoelectric activities for x = 0.55 which was around the morphotropic phase boundary (MPB) composition in BFS–PT ceramics. The local effective piezoelectric coefficient d 33 * of the BSF–PT film for x = 0.55 was approximately 50 pm/V, which was comparable to that of the BiScO 3–PbTiO 3 (BSPT) thin films, and the curie temperature was about 420 °C, also similar to that of BSPT films, but higher than that of PZT thin films. Therefore, the relative low cost of the BFS–PT films compared with that of BSPT films suggests potential device applications in high temperature.

Unusual piezoresponse behavior across the grain boundary of PbMg1/3Nb2/3O3–0.33PbTiO3 thin films

Ferroelectric PbMg1/3Nb2/3O3–0.33PbTiO3 (PMN–0.33PT) polycrystalline thin film near MPB was grown on Ir with LaNiO3 buffer layer by pulsed laser deposition technology. Piezoresponse force microscopy (PFM) was employed to investigate the role of grain boundary on the domains formation and their local physical properties in PMN–PT thin film. Unusual piezoresponse behaviors were firstly observed across the grain boundary of PMN–PT thin film via PFM. Such abnormal phenomenon is ascribed to the structural incompatibility-induced local stress across the grain boundary, which gives a deep influence on the local imprint behavior of PMN–PT thin film.

Epitaxial PMN–PT thin films grown on buffered Si substrates using ceramic and single-crystal targets

Epitaxial 0.65Pb(Mg 1/3Nb 2/3)O 3–0.35PbTiO 3 (PMN–PT) thin films were deposited on LSCO/CeO 2/YSZ tri-buffered Si substrate by pulsed laser deposition (PLD) using sintered ceramic and single-crystal targets. The PMN–PT films deposited using both targets were single crystalline and exhibited cube-on-cube growth epitaxy with the substrate. The films deposited using the single-crystal target showed higher crystallinity and a smoother surface morphology than those grown using the ceramic target. The crystallinity of films can be affected by the in-plane lattice mismatch of PMN–PT/LSCO interfaces. The low density and low absorption coefficient of the sintered ceramic target were responsible for the severe compositional deviation from the desired stoichiometry of the PMN–PT films. Dielectric constants of approximately 1926 and 1540 at 10 kHz were obtained for the films deposited using the single-crystal and sintered ceramic target, respectively. In addition, the PMN–PT films fabricated using the single-crystal target exhibited well-developed polarization hysteresis loops with a remnant polarization of 11.9 μC/cm 2. Single-crystal targets are an indispensable candidate for the growth of epitaxial PMN–PT films with high crystallinity and good electrical properties.

Large electrocaloric effect of highly (100)-oriented 0.68PbMg1/3Nb2/3O3–0.32PbTiO3 thin films with a Pb(Zr0.3Ti0.7)O3/PbOx buffer layer

0.68PbMg1/3Nb2/3O3–0.32PbTiO3 (PMN–PT) thin films with a lead zirconate titanate Pb(Zr0.3Ti0.7)O3 (PZT)/PbOx buffer layer were deposited on Pt/TiO2/SiO2/Si substrates by radio frequency magnetron sputtering technique, and pure perovskite crystalline phase with highly (100)-preferred orientation was formed in the ferroelectric films. We found that the highly (100)-oriented thin films possess not only excellent dielectric and ferroelectric properties but also a large electrocaloric effect (13.4K at 15V, i.e., 0.89K/V) which is attributed to the large electric field-induced polarization and entropy change during the ferroelectric–paraelectric phase transition. The experimental results indicate that the use of PZT/PbOx buffer layer can induce the crystal orientation and phase purity of the PMN–PT thin films, and consequently enhance their electrical properties.

Microstructural and electrical properties of 0.65Pb(Mg 1/3Nb 2/3)O 3–0.35PbTiO 3 (PMN–PT) epitaxial films grown on Si substrates

Epitaxially grown PMN–PT thin films using the PMN–PT single crystal targets were prepared at 550 °C on appropriate buffer layers of LSCO/CeO 2/YSZ deposited on a Si substrate using pulsed laser deposition. The micro-structural and the electrical properties of the films were investigated as a function of the film thickness. The PMN–PT films with the thickness from 200 to 600 nm exhibited an epitaxial nature with a pure perovskite structure. On the other hand, the films above 700 nm included a pyrochlore phase embedded in the perovskite structure although they exhibited an epitaxial nature. A pyrochlore phase included in the films above 700 nm thickness decreased the dielectric constant and the ferroelectric properties of the PMN–PT films.

Epitaxial 0.65PbMg 1/3Nb 2/3O 3–0.35PbTiO 3 (PMN–PT) thin films grown on LaNiO 3/CeO 2/YSZ buffered Si substrates

Ferroelectric PMN–PT thin films with a thickness of 600 nm were epitaxially grown on buffered Si (0 0 1) substrates at a substrate temperature that ranged from 550 to 700 °C using pulsed laser deposition (PLD). LaNiO 3 (LNO) electrode thin films with a resistivity of ∼1900 μΩ cm were epitaxially grown on CeO 2/YSZ buffered Si (0 0 1) substrates. The PMN–PT thin films grown at 600 °C on LNO/CeO 2/YSZ/Si substrates had a pure perovskite and epitaxial structure. The PMN–PT films exhibited a high dielectric constant of about 1818 and a low dissipation factor of 0.04 at a frequency of 10 kHz. Polarization-electric-field (P-E) hysteresis characteristics, with a remnant polarization of 11.1 μC/cm 2 and a coercive field of 43 kV/cm, were obtained in the epitaxial PMN–PT films.

Electrochemical Characterization of Thin Film Electrodes Toward Developing a DNA Transistor

The DNA-Transistor is a device designed to control the translocation of single-stranded DNA through a solid-state nanopore. Functionality of the device is enabled by three electrodes exposed to the DNA-containing electrolyte solution within the pore and the application of a dynamic electrostatic potential well between the electrodes to temporarily trap a DNA molecule. Optimizing the surface chemistry and electrochemical behavior of the device is a necessary (but by no means sufficient) step toward the development of a functional device. In particular, effects to be eliminated are (i) electrochemically induced surface alteration through corrosion or reduction of the electrode surface and (ii) formation of hydrogen or oxygen bubbles inside the pore through water decomposition. Even though our motivation is to solve problems encountered in DNA transistor technology, in this paper we report on generic surface chemistry results. We investigated a variety of electrode-electrolyte-solvent systems with respect to their capability of suppressing water decomposition and maintaining surface integrity. We employed cyclic voltammetry and long-term amperometry as electrochemical test schemes, X-ray photoelectron spectroscopy, atomic force microscopy, and scanning, as well as transmission electron microscopy as analytical tools. Characterized electrode materials include thin films of Ru, Pt, nonstoichiometric TiN, and nonstoichiometric TiN carrying a custom-developed titanium oxide layer, as well as custom-oxidized nonstoichiometric TiN coated with a monolayer of hexadecylphosphonic acid (HDPA). We used distilled water as well as aqueous solutions of poly(ethylene glycol) (PEG-300) and glycerol as solvents. One millimolar KCl was employed as electrolyte in all solutions. Our results show that the HDPA-coated custom-developed titanium oxide layer effectively passivates the underlying TiN layer, eliminating any surface alterations through corrosion or reduction within a voltage window from -2 V to +2 V. Furthermore, we demonstrated that, by coating the custom-oxidized TiN samples with HDPA and increasing the concentration of PEG-300 or glycerol in aqueous 1 mM KCl solutions, water decomposition was suppressed within the same voltage window. Water dissociation was not detected when combining custom-oxidized HDPA-coated TiN electrodes with an aqueous 1 mM KCl-glycerol solution at a glycerol concentration of at least 90%. These results are applicable to any system that requires nanoelectrodes placed in aqueous solution at voltages that can activate electrochemical processes.

The Impact of PZT Seed Layer on Microstructure, Dielectric and Ferroelectric Properties of 0.93PMN-0.07PT Thin Films

This paper investigated the effect of PZT30/70 seed layer as a nucleation aid on the microstructure and electrical properties of 0.93PMN-0.07PT thin films. Pyrochlore phase was totally eliminated at an annealing temperature as low as 650°C. Seeded 0.93PMN-0.07PT thin film possessed a denser structure, larger grain size, and thus higher permittivity, spontaneous polarization and pyrocoefficient than unseeded film. The slim P-E loops and the frequency dependent T m observed in both films indicated a relaxor-like behavior.

Control of π−π Interactions in Epitaxial Films of Platinum(II) Octaethyl Porphyrin

Epitaxial thin films of Pt(II) octaethyl porphyrin were grown on the cleavage surface of graphite and potassium hydrogen phthalate. The structure of the films was characterized by high resolution atomic force microscopy, showing that the two substrates template the growth of two layered phases with dramatic structural differences, strongly influencing π-stacking of adjacent molecules. The impact of these characteristics on the electronic structure of the film phases is illustrated by a thorough optical investigation.

Fabrication of pure-perovskite PMN –PT thin films on SrTiO 3 substrates using pulsed laser deposition

Lead magnesium niobate–lead titanate ((1− x)Pb(Mg 1/3Nb 2/3)O 3– xPbTiO 3 ( x=0.20,0.33,0.50), PMN–PT) thin films have been successfully deposited on SrTiO 3(1 0 0) substrates by pulsed laser deposition (PLD). The result of X-ray diffraction (XRD) showed that the PMN–PT thin films were c-orientated. The effects of deposition conditions, such as deposition temperature, deposition oxygen pressure, pulsed laser repeated frequency, cooling rate, pulsed laser energy and post annealing, were studied first on thin-film quality. It was found that the deposition temperature was very different for the different mole fractions of the thin films. The range of the deposition temperature of high-qualitied thin films is very narrow, about ±2 °C. Such harsh conditions are rare in other thin films, which is also the main reason why PMN–PT thin films are very difficult to prepare.

PVP‐Mediated Crystallization of Perovskite Phase in the PMN–PT Thin Films Prepared by Sol–Gel Processing

A modified sol–gel processing has been developed by using polyvinylpyrrolidone (PVP) as modifier and lead nitrate as lead source to synthesize (1−x)Pb(Mg1/3,Nb2/3)O3−xPbTiO3 (PMN–PT) thin films with x=0.23–0.43. The composition distribution and morphology of the gel particles in the PMN–PT solutions have been investigated. It shows that PVP addition results in spatial separation between Pb and Nb ions in the gel particles, leading to the perovskite crystallization via a columbite‐like route in the resultant PMN–PT thin films. Pyrochlore phase is circumvented and perovskite phase can directly crystallize from amorphous films at the temperature as low as 460°C, while in the non‐PVP films, B‐site rich pyrochlore phase (Pb1.83Nb1.71Mg0.29O6.39) is always formed in the temperature range used (460°–650°C).

Highly (1 1 1)-oriented and pyrochlore-free PMN–PT thin films derived from a modified sol–gel process

Ferroelectric PMN–PT (68/32) thin films, about 250 nm in thickness, have been successfully grown on Pt/Ti/SiO 2/Si substrate by a modified sol–gel process. Pure perovskite phase with highly (1 1 1)-preferred orientation, determined by X-ray diffraction, was formed in the PMN–PT thin films when annealed at 650 °C. The pyrochlore phase has been effectively avoided through a variation of the processing parameters such as Mg content, Mg precursor and annealing temperature during thin film deposition. FE-SEM investigation showed that the films have a smooth and crack-free surface with densely packed grains after annealed at 650 °C. The annealed films exhibited well-defined hysteresis loops, with a respective remanent polarization P r of 16.1 μC/cm 2 and coercive field E c of 71.2 kV/cm at an applied electric field of 400 kV/cm at room temperature.

Investigation of the electrocaloric effect in a PbMg2/3Nb1/3O3-PbTiO3 relaxor thin film

Permittivity measurements of a 0.93PMN-0.07PT thin film show a broad maximum near 35 °C, and an anomaly at the depolarizing temperature Td=18 °C on heating only, suggesting a dipolar glass-relaxor phase transition. No structural phase transition at 18 °C is apparent from ferroelectric hysteresis loops taken on field cooling and field heating. These loops show the thermal hysteresis expected for ferroelectric relaxors, which has not hitherto been experimentally verified in PbMg2/3Nb1/3O3-PbTiO3 thin films. Our data suggest the intriguing possibility of a giant electrocaloric effect (ΔT=9 K, ΔE=720 kV cm−1) at and near room temperature.

Optical properties of PMN–PT thin films prepared using pulsed laser deposition

(1 − x)Pb(Mg 1/3Nb 2/3)O 3– xPbTiO 3 (PMN–PT) thin films have been deposited on quartz substrates using pulsed laser deposition (PLD). Crystalline microstructure of the deposited PMN–PT thin films has been investigated with X-ray diffraction (XRD). Optical transmission spectroscopy and Raman spectroscopy are used to characterize optical properties of the deposited PMN–PT thin films. The results show that the PMN–PT thin films of perovskite structure have been formed, and the crystalline and optical properties of the PMN–PT thin films can be improved as increasing the annealing temperature to 750 °C, but further increasing the annealing temperature to 950 °C may lead to a degradation of the crystallinity and the optical properties of the PMN–PT thin films. In addition, a weak second harmonic intensity (SHG) has been observed for the PMN–PT thin film formed at the optimum annealing temperature of 750 °C according to Maker fringe method. All these suggest that the annealing temperature has significant effect on the structural and optical properties of the PMN–PT thin films.

Near-white and tunable electrophosphorescence from bis[3,5-bis(2-pyridyl)-1,2,4-triazolato]platinum(II)-based organic light emitting diodes

A new phosphorescent platinum(II)-pyridyltriazolate complex, bis[3,5-bis(2-pyridyl)-1,2,4-triazolato]platinum(II), Pt(ptp) 2, was synthesized and incorporated into organic light emitting diodes for evaluation as electrophosphorescent dopant. Single crystal X-ray diffraction shows that the complex forms columnar stacks stabilized via strong intermolecular Pt(II) ⋯ Pt(II) interactions (3.289 Å), making it amenable to form excimers. Three types of phosphorescent emissions are seen for neat and doped thin films of Pt(ptp) 2 into 4,4′-bis(carbazol-9-yl)triphenylamine (CBP): structured monomer emission in the blue–green region ( λ max ∼ 480 nm), unstructured excimer emission in the yellow region ( λ max ∼ 550 nm), and rather broad unstructured extended excimer emission in the orange–red region ( λ max ∼ 600 nm). By varying the doping level in x% Pt(ptp) 2:CBP thin films, the ratio of monomer to excimer emission could be adjusted leading to tuning both the photoluminescence (PL) and electroluminescence (EL) wavelengths. Doping levels of ∼5–10%v were found to be optimal for both EL efficiency and white color coordinates resulting from simultaneous monomer and excimer emissions. Peak power and luminous efficiencies obtained were 9.8 lm/W and 14 cd/A, respectively, while the peak external quantum efficiency was 6.6% in a standard OLED device structure. The emissions for the 7.5–15%v Pt(ptp) 2:CBP devices are characterized by CIE coordinates of ∼(0.3, 0.5), rendering near-white EL with green hue. The CRI increased with dopant concentration, reaching 56 at the 45% doping level. More optimal white EL color could not be attained by fine-tuning the doping level. The devices exhibit good stability at higher current density and brightness levels, which is atypical of phosphorescent organic light emitting diodes. Strategies to attain higher efficiencies and CRI are proposed based on the results of this work.

Direct crystallization of perovskite phase in PMN–PT thin films prepared by polyvinylpyrrolidone modified sol–gel processing and their properties

A modified sol–gel processing has been developed by using polyvinylpyrrolidone (PVP) as modifier and lead nitrate as lead source to synthesize (1− x)Pb(Mg 1/3,Nb 2/3)O 3– xPbTiO 3 (PMN–PT) thin films with x=0.23–0.43. With PVP additions, perovskite phase could directly crystallize from amorphous films at the temperature as low as 430 °C via bypassing the metastable phase-pyrochlore and crystallinity was significantly enhanced. The PVP addictives have been optimized with molecular weight <630 K and the ratio of PVP monomer/PMN–PT at 0.25–1.0. XPS analysis indicates that the chemical states of the elements in the well-crystallized PMN–PT films are close to the literature data for the PMN–PT single crystals and the films possess highly desired electrical and optical properties.

Stability of thin platinum films implemented in high-temperature microdevices

In this paper we report on structural and electrical properties of thin films of Pt with Ti, Ta, or no adhesion, which were annealed in different ambient at temperatures in the range 400–950 °C. Correlations are made between the mechanical strain and grain size values obtained from X-ray diffraction, electrical measurements, and optical microscope images of film sintering after annealing at high temperature. A method to obtain highly adhesive, patterned Pt films without adhesion layer is presented, which films show the highest reliability, in terms of structural integrity and electrical properties. Therefore this is the best option for implementation in high-temperature microdevices like microreactors and gas sensors operating at temperatures above 750 °C.

Valence-EELS analysis of local electronic and optical properties of PMN–PT epitaxial film

This study investigated local electrical and optical properties of Pb(Mg 0.39Nb 0.61)–0.34 mol%PbTiO 3 solid solution (PMN–PT) film stacked on Si (0 0 1) wafer with (La,Sr)CoO 3− x /CeO 2/YSZ buffer layers. TEM-VEELS analysis of the PMN–PT thin film, which was grown epitaxially on the Si substrate with two coexisting phases of pseudocubic and tetragonal morphology, was firstly conducted using the TEM-VEELS method. The ELF has shown a bulk plasmon peak and two interband plasmon peaks. The interband transition has been interpreted in comparison with the joint density of state obtained from the measured dielectric function and the density of state calculated by the density functional theory. The interband transition from the O 2p band to Nb 4d/Ti 3d bands determines the optical properties around the band gap. The optical absorption of PMN–PT film has shown the band gap of 3.5 ± 0.2 V. The refractive index derived from the TEM-VEELS analysis in the nano-region of the film has agreed with that obtained with the conventional optical measurement from the macroscopic region.

Electrochemical Properties of Pt Coatings on Ni Prepared by Atomic Layer Deposition

Presented herein is an approach to fabrication of Pt coatings on non-noble metals with (sub)monolayer thickness. The Pt coatings were prepared using atomic layer deposition (ALD) in which Ni-disk substrate is exposed to and in alternating cycles. The structure and electrocatalytic activity of the coatings were characterized using elemental analysis and various electrochemical techniques. We found that the ALD results in micrometer-size Pt islands up to ca 3.7 monolayers of Pt loading and continues more uniformly at higher loadings. The islandlike growth at low Pt loadings is attributed to the presence of adsorbed O on atomically rough facets of polycrystalline Ni substrate. The thin films of Pt on Ni show enhancement factors in the oxygen reduction reaction similar to what has been reported for PtNi alloys. Potential applications of the methodology demonstrated in this work for the development of the third-generation polymer electrolyte fuel cell catalytic layers with ultralow Pt loading are briefly discussed.

Piezoelectric thin films for MEMS applications—A comparative study of PZT, 0.7PMN–0.3PT and 0.9PMN–0.1PT thin films grown on Si by r.f. magnetron sputtering

PMN–PT (0.7), PMN–PT (0.9) and PZT (54/46) thin films were deposited by sputtering on silicon substrate covered bottom TiO x /Pt electrodes. The top and lower electrodes are grown by r.f. sputtering. The objective in this paper here is to compare the dielectric, ferroelectric and piezoelectric properties of different materials, and material compositions, in thin films form. For these films the electric, ferroelectric and piezoelectric properties have been determined and compared to PZT films of the same thickness. The comprehensive characterization process clearly reveals the merits of each film composition for a particular application. The results for the three film compositions are presented and discussed.