Titanium dioxide thin films were grown on sapphire (11$\overline 1$0) substrates in a low-pressure metal-organic chemical vapor deposition system at temperatures ranging from 400 to 800 °C. Raman scattering, x-ray diffraction, transmission electron microscopy, and high resolution electron microscopy techniques were employed to characterize the structural properties of the deposited films. The resultant phases and structures of the deposited films depended on both the growth temperature and the substrate surface properties (surface imperfections, steps, etc.). At the growth temperature of 800 °C, single-crystal rutile films were obtained reproducibly with two possible epitaxial relationships. At lower temperatures (400 to 775 °C), the deposited films can be epitaxial or polycrystalline with highly oriented grains. The similarity between the atomic arrangements of the substrate and the film is discussed in detail to explain the observed epitaxial relationships and abruptness of the interfaces.

Lead- and titanium-based oxide thin films were prepared by the metal-organic chemical vapor deposition technique (MOCVD) and the relationship between the film structures and the processing parameters, such as the ratio of Pb/Ti precursors in the gas phase, substrate materials, substrate surface orientation, and growth temperature, was systematically studied. It was found that whether a single-phase stoichiometric PbTiO3 film could be obtained depended on both the Pb/Ti precursor ratio in the gas phase and the deposition temperature. Under appropriate conditions, stoichiometric PbTiO3, films could be obtained on all the substrates including silicon, MgO, α-Al2O3, SrTiO3, and LaAlO3. The PbTiO3 films grown on silicon substrates were always polycrystalline, whereas epitaxial PbTiO3 films were obtainable on all the other substrates. For epitaxial PbTiO3 films, the epitaxial relationship, crystallinity, and domain structures were found to be a function of both the substrate materials and surface orientation as well as the deposition temperature. X-ray rocking curves (ω scan) of the (100) and (001) planes of PbTiO3 epitaxial film and PbTiO3 single crystal revealed the inherent nature of the domain structures in PbTiO3.

The preferred orientation, grain morphology, and composition heterogeneity of the polycrystalline Pb(ZrxTi1–x)O3 (PZT) thin films were characterized by x-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), transmission electron microscopy (TEM), and x-ray energy dispersive spectroscopy (EDS). PZT thin films with nominal x = 0.5 were grown by metal-organic chemical vapor deposition (MOCVD) on (110)- and (101)-textured RuO2 bottom electrodes at temperatures ≤525 °C. Columnar grain microstructure with strongly faceted surface morphology was observed in both films. The grain morphology and surface roughness of the PZT films were observed to depend on those of the underlying RuO2 layers. TEM-EDS analysis shows notable cation composition heterogeneity in length scales of 0.2–2 μm. Pronounced Pb composition deficiency and heterogeneity were also observed in PZT/(110)RuO2 in length scales above 40 μm. The grain morphology and cation heterogeneity of the PZT films are discussed on the basis of diffusion-limited columnar growth mechanism.

The submitted manuscript haa been created by the University of CMIcago as Operator of Argonne National Laboratory (“Argonne”) under Contract No. W-3 I-109 -ENG-38 with the U.S. Department of Energy. The U.S. Government retains for itself, and others acting on its behalf, a paid-up, nonexclusive, irrevocable worldwide license in said article to reproduce, prepare derivative works, distribute copies to the public, and perform publicly and display publicly, by or on behalf of the Government.

Ferroelectricity in solids originates from the relative shifts of the anion and cation atomic sublattices [1] resulting in a net dipole moment (spontaneous polarization) along a certain crystallographic axis. Under an applied electric field, the direction of the polarization vector can be switched. This bi-stable property, in conjunction with thin-film heteroepitaxy, can provide the basis for nonvolatile random access memory (NVFRAM) [2]. Electrical measurements can be used to study such structures on a macroscopic scale. In our study, we use the thin-film x-ray standing wave (XSW) method to probe the polarity of as-grown PbTiO3 (PTO) ferroelectric thin films on an atomic scale.

Polycrystalline Pb(Zr0.6Ti0.4)O-3 (PZT) thin films, 3000-6000 Angstrom thick, have been grown by metal-organic chemical vapor deposition (MOCVD) on (111)Pt/Ti/SiO2/Si substrates at temperatures as low as 450-525 degrees C. Random and (Ill)-oriented, or occasionally (100)-oriented, PZT films can be deposited directly on (111)Pt/Ti/SiO2/Si. In addition, highly (100)-oriented films can be deposited consistently by using 150-250 Angstrom thick (100)-oriented PbTiO3 (PT) or TiO2 as a template. Films were characterized by X-ray diffraction, electron microscopy, and electrical measurements. The as-grown (100)-oriented films on (111)Pt/TiSiO2/Si substrates exhibited dielectric constants (epsilon(r)) of up to 600, remnant polarization (P-r) of 40 mu C/cm(2), coercive field of 55 kV/cm, and breakdown field of 2-6 x 10(7) V/m.

Possible domain patterns are developed for (001) oriented (pseudocubic indexing) epitaxial rhombohedral perovskite ferroelectric (FR) films. We assume that the films are grown above their Curie temperature (TC) in a cubic paraelectric (PC) state. The rhombohedral distortion consists of a “stretch” along one of the four 〈111〉 crystallographic directions of the cubic perovskite unit cell. Domain pattern formation is concurrent with the PC→FR transformation on cooling from the growth temperature. The domain patterns form to minimize elastic energy in the film, at the energetic expense of both forming domain boundaries and developing local stresses in the substrate. Eight possible domains may form, half of which are related by inversion, thus leading to four mechanically distinct variants. The possible domain walls are determined by mechanical and charge compatibility and follow closely from the analysis of Fousek and Janovec [J. Appl. Phys. 40, 135 (1969)]. Domain patterns may develop with either {100} or {101} boundaries. In both cases, the individual domains in the patterns are energetically degenerate and thus equal width lamellar patterns are predicted. When polarization is included in the analysis, the {100} boundary patterns have no normal component of the net polarization, whereas the {101} boundary patterns correspond to the fully poled state. We report on experimental observation of {100} domain patterns in epitaxial PbZr0.80Ti0.20O3 and PbZr0.65Ti0.35O3 films.

YVO4 films were reproducibly prepared on (0001) and (112̄0) sapphire (α-Al2O3) substrates using metal organic chemical vapor deposition. X-Ray diffraction, transmission electron microscopy and X-ray energy dispersive spectroscopy were used to characterize the deposited films. It was found that under most growth conditions the films deposited on (0001) sapphire consisted of two layers, i.e. a stoichiometric bottom layer of YVO4 which was epitaxially grown on the substrate and a polycrystalline top layer of Y8V2O17. The effect of growth parameters, in particular the growth temperature, on the stability of the dual layer structured films was studied and a working model explaining the origin of dual layer structure was suggested. Based on these observations the method for the preparation of stoichiometric epitaxial one layer-structured YVO4 films with either an in-plane variant or a single crystal structure on (0001) and (112̄0) sapphire (α-Al2O3) substrates, respectively, was presented.

Abstract Pb(Zr0.5Ti0.5)O3/RuO2 (PZT/RuO2) thin film heterostructures with controlled PZT and RuO2 orientation were successfully grown in-situ on SiO2/(001)Si substrates at 525°C, using metal-organic chemical vapor deposition (MOCVD). XRD analysis revealed that the textured orientation of the PZT films is strongly dependent on the orientation of RuO2 bottom electrode layers. PZT layers grown on (101)-textured RuO2 exhibit a predominant (001) orientation, while those grown on (110)-textured RuO2 present a mixed (001)-(111)-(110) polycrystalline structure. Highly (110)-oriented RuO2 layers were grown using relatively high deposition temperatures and low rates (∼350°C and 3 nm/min, respectively). The RuO2 layers exhibited resistivities of 34-40 μΩ-cm, average grain size of 65±15 nm, and surface roughness of 3-10 nm (rms), while the PZ...

The coherency defect technique is developed for the domain pattern energetics in rhombohedral (001) epitaxial ferroelectric films. The coherency defects that are necessary to maintain the epitaxy during the ferroelectric phase transition are considered to be the only sources of elastic strains and stresses (and, correspondingly energy) in the film/substrate system. The coherency defects include: (i) a uniform distribution of edge dislocations which are responsible for the in-plane tension or compression and have Burgers vectors parallel to the interface; and two kinds of mesoscale defects: (ii) Somigliana screw dislocations which are responsible for in-plane shear; and (iii) wedge disclinations which are responsible for the out of plane rotations in neighboring domains. Using this approach, analytical expressions were found for the elastic energy in the film/substrate system for both the {101}-ri/rj and the {100}-ri/rj domain patterns. These two configurations differ by the orientation of domain walls, coherency defect content, and also the morphology of the free surface (flat versus puckered surfaces). Calculations are performed for screened mesoscale coherency defect configurations that represent a single embedded domain pattern and multidomain patterns. The following mesoscale defect configurations are used for these calculations: Somigliana dislocation dipoles, wedge disclination dipoles, Somigliana dislocation quadrupoles, and disclination quadrupoles. It is predicted that there is no critical thickness for domain pattern formation in rhombohedral ferroelectric epitaxial films. Agreement is shown between experimentally observed domain widths and theoretically predicted values.

Highly oriented, polycrystalline Pb(Zr0.5Ti0.5)O3 (PZT) thin films were successfully grown on RuO2/SiO2/(001)Si using metal–organic chemical vapor deposition (MOCVD) at 525 °C. The orientation of the PZT film was controlled by using MOCVD-deposited highly textured RuO2 bottom electrodes. A (001)-oriented PZT film was observed for growth on (101)-textured RuO2. In contrast, for (110) RuO2, the growth of (001) PZT was greatly suppressed while the growth of both (110) and (111) were enhanced, resulting in a poorly (001)-textured polycrystalline film. The as-grown PZT films exhibited a dense columnar microstructure with an average grain size of 150–250 nm. Both PZT films showed excellent ferroelectric properties without any postgrowth annealing. The (001) highly oriented PZT films showed significantly higher values of remnant polarization (Pr=49.7 μC/cm2) and saturation polarization (Ps=82.5 μC/cm2). In comparison, for the PZT films grown on (110) RuO2, Pr and Ps were 21.5 and 35.4 μC/cm2, respectively.

Recent electron diffraction and microscopy studies of GaN nucleation layers have shown that faults in the stacking of the close-packed planes result in the coexistence of cubic and hexagonal phases within the layers. Using grazing incidence x-ray scattering, we have quantified the proportion of the cubic and hexagonal phases throughout the nucleation layer. We compare the structure of a 20 nm nucleation layer grown on sapphire by atmospheric pressure metal-organic chemical vapor deposition at 525 °C to that of an identical layer heated to 1060 °C. The fractions of cubic and hexagonal phases in the layers are determined by a comparison of the scattering data with a Hendricks–Teller model. High temperature exposure results in a decrease of the cubic fraction from 0.56 to 0.17. The good agreement with the Hendricks–Teller model indicates that the positions of the stacking faults are uncorrelated.

Polycrystalline RuO2 thin films were grown by metal-organic chemical vapor deposition (MOCVD) on both SiO2/Si(001) and Pt/Ti/SiO2/Si(001) substrates. Films having a controllable and reproducible structural texture and phase purity were synthesized by carefully controlling deposition parameters. Moderate growth temperatures (∼350 °C) and low growth rates (<30 Å/min) produced highly (110)-textured RuO2 films. Highly (101)-textured RuO2 films were favored at slightly lower temperatures (∼300 °C) and much higher growth rates (>30 Å/min). The most conductive RuO3 films had resistivities of 34 to 40 µΩ−cm at 25 °C, an average grain size of 65 ± 15 nm, and a surface roughness (rms) of 3 to 10 nm. Both single-phase Ru and mixed Ru/RuO2 phase material were also fabricated at low temperatures (<350 °C) by using lower oxygen flow concentrations (<10%).

In this talk we treat domain patterns that develop in epitaxial ferroelectric (FE) films. The models are applicable to ferroelectric films grown epitaxially in their paraelectric cubic state (PE) on single crystal substrates. We explicitly treat misfit strain relaxation by both misfit dislocations and by domain pattern formation. We have developed temperature dependent stability maps that predict the energetically favorable domain structure that will form at the PE → FE transition. The stability maps incorporate the role of: (i) the substrate lattice parameter; (ii) differential thermal expansion; (iii) cooling rate; (iv) depolarizing fields and electrode geometry; and (v) applied electric fields. We treat the formal defect description both the … a1/a2/a1/a2… and the …a1/c/a1/c… domain patterns and show rigorous mechanics solutions for the elastic energy of both configurations. As a result of the PE → FE transition, the crystal axes of individual domain are rotated in the far-field. The concepts of the domain stability map, the relative coherency strain, and far field rotation of crystals axes in the domain are verified by three independent measurements (integrated x-ray peak intensity, partitioning of crystals tilts, and domain volume fraction by TEM) for MOCVD PbTiO3 films grown on MgO(001), SrTiO3(001), LaAlO3(001) and SrRuO3/SrTiO3(001).

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.