Epitaxial PbTiO3 Research Articles

Measurement Technique for the Evaluation of Residual Stress in Epitaxial Thin Film by Asymmetric X-Ray Diffraction.

An analytical technique to determine residual stress in eqitaxial thin film by asymmetric X-ray diffraction (XRD) was studied. The residual stresses of PbTiO3 films were determied by XRD technique and displace measurement technique. Measurement results by these techniques were compared with each other to consider the respective advantages of each technique. The stresses measured by XRD technique were not consistent with those by displacement measurement technique, because the latter technique involves errors which origined from the shape and the size of the substrate. The stress in a polycrystalline film measured by modified sin2ψ method was in good agreement with that measured by normal sin2ψ method. This result suggests that modified sin2ψ method can be applied to stress measurement not only in epitaxial thin films, but also in polycrystalline thin films. We further discuss the precision of the stress determination technique. Residual stress of epitaxial PbTiO3 film on (100)SrTiO3 substrate measured by modified sin2ψ method was comparable to the theoretical stress estimated from the difference in thermal expansion coefficients between the film and the substrate. Stress values measured by modified sin2ψ method may thus have the precision required for actual application.

Structural studies of epitaxial PbTiO 3 films by optical second harmonic generation

Second harmonic generation has been applied for a structural study of thin epitaxial PbTiO 3 films on a YBaCuO/SrTiO 3 substrate. From the azimuthal anisotropic dependence the crystallographic orientation and the texturing parameters are obtained with a high accuracy.

PbTiO3 epitaxial thin films as optical waveguides

Thin films of lead titanate (PbTiO 3 -PT) have been prepared in-situ on SrTiO 3 (100) substrates using radio-frequency sputtering. The epitaxial quality of the films has been investigated as a function of the substrate temperature. Stoichiometric films have been obtained in the temperature range 550°C-600°C. Films have a high degree of c-axis oriented crystalline structure. The optimum conditions for growing epitaxial PbTiO 3 layers are reported in this study. Thin films grown at 550°C exhibited a rocking curve full width at a half maximum (FWHM) of 0.26°. The refractive index calculated from optical transmission method has been evaluated to 2.61 @ 632.8nm. which represents 98% of the corresponding bulk material.

Domain structure and surface morphology of epitaxial PbTiO 3/SrRuO 3 heterostructures on vicinal (001) SrTiO 3 substrates

Epitaxial ferroelectric PbTiO 3/SrRuO 3 heterostructures have been grown on (001) SrTiO 3 substrates with 1.7 and 5° miscut toward [010] by rf magnetron sputtering. X-ray diffraction indicates that heterostructures with thin PbTiO 3 layer (120, 400, and 1250 Å) consist of purely c-axis PbTiO 3 domain, while the thicker PbTiO 3 layer (2500 Å) contains both a-axis and c-axis PbTiO 3 domains. The bottom SrRuO 3 layer is single domain with [110] normal orientation. Furthermore, both PbTiO 3 and SrRuO 3 layers are of very good crystalline quality from the measurements of the full width at half maximum of rocking curve and in-plane φ scans. Atomic force microscopy studies show that both SrRuO 3 and PbTiO 3 layers are grown by step flow mechanism, which results in very smooth surfaces (the root mean square roughness ≈12 Å for a 400 Å PbTiO 3/SrRuO 3 heterostructure on a 1.7° miscut substrate over a 2×2 μm area). Our results demonstrate that the high quality epitaxial ferroelectric PbTiO 3 heterostructures can be prepared by using SrRuO 3 bottom electrodes on miscut (001) SrTiO 3 substrates for ferroelectric device applications.

Single crystal thin films of conductive oxides SrRuO3 and ferroelectric heterostructures

We have grown epitaxial thin films of the conductive oxide SrRuO3 with well controlled surface morphology and domain structure using vicinal (001) SrTiO3 substrates. Scanning tunneling microscopy and x-ray diffraction show that the SrRuO3 thin films on miscut (001) SrTiO3 substrates with miscut angle > 2° grow by step flow in one direction leading to single crystal films. In contrast, the SrRuO3 thin films on exact (001) SrTiO3 substrates grow by two dimensional nucleation resulting in a two domain in-plane structure. The single crystal thin films have been used as electrodes for the growth of epitaxial ferroelectric PbTiO3 and PZT layers. The PbTiO3/SrRuO3 and PZT/SrRuO3 heterostructures have high crystalline quality, coherent interfaces and a cube-on-cube epitaxial growth with respect to the substrate. These epitaxial heterostructures have superior fatigue characteristics and look promising for the fabrication of integrated single crystal ferroelectric devices.

Adsorption-controlled growth of PbTiO 3 by reactive molecular beam epitaxy

Epitaxial lead titanate films have been grown on (001) SrTiO 3 substrates by reactive molecular beam epitaxy (MBE). Growth of stoichiometric phase-pure epitaxial PbTiO 3 films is achieved by supplying a continuous excess of lead and ozone to the surface of the depositing film. Results obtained from RBS composition analysis, measured film thicknesses and flux measurements using atomic absorption spectroscopy (AA) indicate that the film growth rate is completely determined by the incident titanium flux supplied to the surface. Atomic force microscopy (AFM) results show that films grow smoothly in a layer-by-layer fashion with an RMS roughness of <0.5 nm. The sticking coefficient of titanium is determined to be approximately unity while the excess lead, lead oxide and ozone desorb. Lead and ozone beam equivalent pressures have been measured in the MBE environment. Thermodynamic analysis is used to help describe the processes that prevent the incorporation of PbO into films under adsorption-controlled growth conditions.

Thickness and substrate effects of epitaxial PbTiO3 thin films

Ferroelectric PbTiO3 thin films were epitaxially grown on LaAlO3, and SrTiO3 single crystal substrates by metalorganic chemical vapor deposition and investigated by x-ray diffraction and x-ray photoelectron spectroscopy. The as-deposited films showed clearly thickness and substrate dependence. The thin films on LaAlO3 displayed 90° alternating a-c domain configurations and the a-domain population decreases with decreasing film thickness. The thin films on SrTiO3 were epitaxial and single-domain. Non-stoichiometric surface layer with lead abundance were observed in the 700 Å-thick PbTiO3 films on both LaAlO3 and SrTiO3 substrates, and there might be oxygen vacancy at the surface of 700 Å PbTiO3 films on SrTiO3. Decrease of tetragonal distortion were found with decreasing film thickness, which may indicate weakening of ferroelectricity in the PbTiO3 thin films as compared with bulk material or thicker films.

Ferroelectric domains in epitaxial PbTiO3 and BaTiO3 thin films on MgO(100)

Epitaxial PbTiO3 and BaTiO3 thin films were prepared on MgO(100) by laser ablation and RF magnetron sputter deposition, respectively. X-ray diffraction (XRD), transmission electron microscopy (TEM), and atomic force microscopy (AFM) were used to investigate the ferroelectric domains in the grown films. In the PbTiO3 film, significant portions of a-domains were distributed in c-domains, which causes abundant 90° domain population. On the other hand, the BaTiO3 film was mainly single c-domains without any meaningful domain structure. We attribute the difference in domain population of the two reasons. One is the smaller phase transformation strain which comes from smaller tetragonality of BaTiO3, and the other is the larger compressive stress due to thermal mismatch which comes from lower Tc of BaTiO3 than those of PbTiO3.

Mild hydrothermal synthesis of titanate films: from polycrystalline BaTiO3 to epitaxial PbTiO3

Mild hydrothermal synthesis of titanate films: from polycrystalline BaTiO3 to epitaxial PbTiO3

Preparation of epitaxial PbTiO3 thin films by pulsed laser deposition

Epitaxial PbTiO3 thin films were prepared in situ by pulsed laser deposition on MgO(001) and SrTiO3(001) single crystal substrates. The effects of oxygen pressure and substrate temperature on the growth of films were investigated. The favorable conditions for the fabrication of epitaxial films were identified. Appropriate control of oxygen pressure in the range of 200–250 mTorr was necessary for epitaxial PbTiO3 thin films and higher substrate temperature up to 700°C was preferred. The epitaxial relation between film and substrate is PbTiO3{001}//MgO(001), PbTiO3〈100〉//MgO[100]. The chemical composition of the film was very similar to the ideal stoichiometry of PbTiO3.

Evaluation of metalorganic precursors for fabrication of lead-based ferroelectric thin films

Eight kinds of metalorganic precursors for metalorganic chemical vapor deposition of lead-based ferroelectric thin films were used to evaluate residual carbon concentration and growth rate of the oxide films. Secondary ion mass spectroscopy measurements indicated that Pb(DPM)2, Zr(O-tC4H9)4, and Ti(O-iC3H7)4 are the most suitable precursors for reducing the carbon concentration in PbO, ZrO2 and TiO2 films, respectively. Using these precursors, a Pb(Zr0.52, Ti0.48)O3 thin film with a residual carbon concentration as low as 0.02mol% was grown at 763 K. Growth rates for various temperature were measured for six precursors. The rates obtained from alcoxide precursors, such as (C2H5)PbOCH2C(CH3)3, Zr(O-tC4H9)4 and Ti(O-iC3H7)4, were saturated in a wide temperature range. An epitaxial PbTiO3 film was obtained on a (100)Pt/(100)MgO substrate at 763K using (C2H5)PbOCH2C(CH3)3 and Ti(O-iC3H7)4 Precise control of the film composition is indispensable for low temperature fabrication of Pb-based ferroelectric thin films.

Observation of the polarization of domains in ferroelectric thin films using x-ray interference

We report that the sign of the polarization of an epitaxial ferroelectric film can be determined from the interference between the x-ray scattering from the film and the substrate. X-ray scattering measurements of a 10 nm epitaxial PbTiO3 film grown by metal-organic chemical vapor deposition on a SrTiO3 substrate are presented. The scattering profile near the 001 peaks of the film and substrate shows clear evidence of the interference effects. Analysis indicates that this film is a single domain of specific polarity.

A study of the structure and composition of Si-doped PbTiO3

It is very useful to grow epitaxial PbTiO 3 films on Si substrates for applications in integrated devices. At high growth temperatures, this leads to the formation of an intermediate metastable Pb 2 − x Ti 2 − y Si x + y O 6 phase (with a pyrochlore structure) and the consequent partial incorporation of Si into the PbTiO 3 lattice. To understand the effect of Si on the ferroelectric characteristics of the material, it is important to determine the position and state of aggregation of Si in the PbTiO 3 lattice. We have attempted to investigate this aspect by a neutron diffraction study of silicon doped ceramic lead titanate. Our results indicate that the silicon may exist in the form of a glassy lead silicate phase dispersed at the grain boundaries. Some of the Si atoms may also occupy interstitial positions in the lattice.

Formation of the ferroelectric domains in epitaxial PbTiO 3 thin films grown by metalorganic chemical vapor deposition

thin films have been prepared by metalorganic chemical vapor deposition under reduced pressure. The formation of ferroelectric domains in films grown on SrTiO3 and LaAlO3 substrates was investigated by synchrotron radiation and Rutherford backscattering spectroscopy. Single-domain (3000-A thick) and multi-domain (4500-A thick) PbTiO3 films were produced on SrTiO3. For multi-domain PbTiO3 film, the c-domain presented epitaxial structure with its c-axis perpendicular to the substrate surface, while a-domains aligned four-fold symmetrically with c-domains by 2.79° off the c-axis of c-domains. In the film, the measured lattice constants (a, b and c) of the a- and c-domains were different from each other, indicating that the films suffered a modulated strain during domain formation. In contrast, both the a and c domains of films on LaAlO3 were alternatively aligned on substrate with the a-axis of the a-domain and the c-axis of c-domains perpendicular to the substrate surface. Two-dimensional distribution of these domains is proposed and the formation of these kinds of domains is discussed. The surface morphology and phase transition process of single and multi domain PbTiO3 film on SrTiO3 were studied by atomic force microscope (AFM) and high temperature X-ray diffraction, respectively.

Domain structure of epitaxial PbTiO3 films grown on vicinal (001) SrTiO3

Epitaxial PbTiO3 films have been grown on vicinal (001) SrTiO3 substrates by pulsed laser deposition. Vicinal SrTiO3 substrates with misorientations up to 9° from (001) were used, and the influence of the direction of misorientation on the resulting domain structure was studied. 4-circle x-ray diffraction analysis indicates that thin (40 nm) PbTiO3 films are completely c-axis oriented [rocking curve full-width-at-half-maximum (FWHM) of 0.25° for the 002 reflection] and that thicker films (∼ 200 nm) contain mixed a-axis and c-axis PbTiO3 domains due to twinning along {011} planes. The [100] axis of the a-axis domains is misoriented by 2.1° to 3.3° toward 〈100〉 substrate directions with respect to the substrate normal. In contrast to growth on well-oriented (001) SrTiO3 surfaces where the four equivalent tilts of the [100] axis of the a-axis domains are equally likely, on vicinal SrTiO3 the a-axis domains are preferentially oriented in an uphill direction with respect to the crystallographic miscut.

Epitaxial lead titanate grown by MBE

Epitaxial PbTiO 3 films have been grown by reactive molecular beam epitaxy (MBE) on (100) LaAlO 3 substrates. Lead is supplied from a conventional effusion cell. Titanium is sublimated from a Ti-Ball™, and oxygen is supplied in the form of purified ozone. Atomic layer-by-layer composition control is obtained using real-time atomic absorption spectroscopy (AA) feedback. The titanium flux is controlled with a shutter directly coupled to the titanium AA feedback to deliver a burst corresponding to one monolayer of titania. Similarly, lead is monitored in situ using an atomic absorption signal. An adsorption-controlled growth mechanism leads to the use of a lead overpressure to insure films with proper stoichiometries. Film structure is studied during growth using in situ RHEED. 4-circle X-ray diffraction analysis indicates that films grown on LaAlO 3 are epitaxial and are mixed a- and c-axis oriented.

Structure Analysis of Sputtered PbTiO3 Thin Films.

Thin films of PbTiO3(PT), 5-360 nm in thickness, were grown on miscut (001)SrTiO3(ST) substrate (miscut angle of 1.7°) at 600°C by rf planar magnetron sputtering. The sputtered PT thin films showed three-dimensional crystal orientation, and the surfaces were extremely smooth over a large area. The crystal form of bulk PT is cubic at 600°C, but the epitaxial PT thin films on ST substrate become deformed from cubic to tetragonal form by compressive force in the a-b plane during film growth since the lattice parameter of ST is smaller than that of PT. The deformed crystal structure was quenched during a cooling cycle in the deposition process. The PT thin films were coherent to the substrate and tightly bonded on the surface of the substrate. The transition from tetragonal to cubic phase could not be observed even when the temperature of the PT thin films was elevated from room temperature to Curie temperature.

A high-temperature x-ray-diffraction study of epitaxial PbTiO3 thin films on MgO(100) grown by metal-organic chemical-vapor deposition

Epitaxial lead titanate (PbTiO3) thin films were grown on MgO(100) single-crystal substrate by metal-organic chemical-vapor deposition at a growth temperature of 650 °C. The films were dense, stoichiometric, and epitaxial. The domain structure was studied via x-ray-diffraction ω scans and in-plane Φ scans. Existence of c and a domains in the PbTiO3 films was evident. Consistent with literature reports, the a domains were found to have four variants 90° apart from each other, tilting about 2.2° away from the surface normal. The population ratio between c and a domain of the PbTiO3 films was determined to be approximately 2.3 to 1. The domain structure was found to be stable and reproducible during repeated thermal cycling above and below Tc. Furthermore, lattice parameters and Curie temperatures of PbTiO3 thin films were measured during the thermal cycles. The lattice parameters were found to be smaller and the Curie temperatures were shifted lower than the corresponding bulk values. This is attributed to the film stress effect. A theory based on the Landau–Ginzburg–Devonshire function has been developed to explain the shift of the Curie temperatures.

Influence of the growth temperature on the epitaxial quality of PbTiO3 films deposited in-situ by sputtering

Abstract Thin films of lead titanate were prepared in-situ on SrTiO3 substrates using radio-frequency magnetron sputter deposition. The epitaxial quality of the films has been studied as a function of the substrate temperature. Stoichiometric films have been obtained in the temperature range [550°C, 600°C]. The films deposited in the equilibrium zone have a high degree of c-axis oriented epitaxial crystalline structure as shown by X-ray diffraction in the 2θ/θ, θ, and ϕ scans configuration as well as by electron channeling pattern. The optimum conditions for growing epitaxial PbTiO3 layers were determined. The crystallinity of films deposited at 550°C is suprior to those deposited at 600°C. The PbTiO3 films grown at 550°C have a rocking curve full width at half maximum (FWHM) of 0.2°; Normaski optical and atomic force microscopy show that the surface is apparently free of grain boundaries and very smooth. The refractive index of these films has been evaluated from transmission spectra; it is very close to...

Microstructural instability in single-crystal thin films

Epitaxial PbTiO3 thin films were produced from a mixed Pb–Ti double-alkoxide precursor by spin-coating onto single crystal (001) SrTiO3 substrates. Heat treatment at 800 °C produces a dense and continuous, epitaxial lead titanate film through an intermediate Pb-Ti fluorite structure. A microstructural instability occurred when very thin single crystal films were fabricated; this instability caused the films to become discontinuous. Scanning electron microscopy and atomic force microscopy observations show that single crystal films with a thickness less than ∼80 nm developed holes that expose the substrate; thinner films broke up into isolated, single crystal islands. The walls of the holes were found to be (111) perovskite planes. A free energy function, which considered the anisotropic surface energies of different planes, was developed to describe the microstructural changes in the film and to understand the instability phenomenon. The function predicted that pre-existing holes greater than a critical size are necessary to initiate hole growth, and it predicted the observed morphological changes in the current system. Morphological stability diagrams that explain the stability fields for different film configurations, i.e., either completely covered, with holes, or single crystal islands, can be calculated for any film/substrate system.