C. M. Foster

Single-crystal Pb(ZrxTi1−x)O3 thin films prepared by metal-organic chemical vapor deposition: Systematic compositional variation of electronic and optical properties

Single-crystal thin films of Pb(ZrxTi1−x)O3 (PZT) covering the full compositional range (0⩽x⩽1) were deposited by metal-organic chemical vapor deposition. Epitaxial SrRuO3(001) thin films grown on SrTiO3(001) substrates by rf-magnetron sputter deposition served as template electrode layers to promote the epitaxial growth of PZT. X-ray diffraction, energy-dispersive x-ray spectroscopy, atomic force microscopy, transmission electron microscopy, and optical waveguiding were used to characterize the crystalline structure, composition, surface morphology, microstructure, refractive index, and film thickness of the deposited films. The PZT films were single crystalline for all compositions exhibiting cube-on-cube growth epitaxy with the substrate and showed very high degrees of crystallinity and orientation. The films exhibited typical root mean square surface roughness of ∼1.0–2.5 nm. For tetragonal films, the surface morphology was dominated by grain tilting resulting from ferroelectric domain formation. We r...

Domain patterns in epitaxial rhombohedral ferroelectric films. I. Geometry and experiments

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 {1...

Substrate effects on the structure of epitaxial PbTiO3 thin films prepared on MgO, LaAlO3, and SrTiO3 by metalorganic chemical‐vapor deposition

Epitaxial PbTiO3 films were prepared by metalorganic chemical‐vapor deposition on MgO(001)‐, SrTiO3(001)‐, and LaAlO3(001)‐oriented substrates. Four‐circle x‐ray diffraction, transmission electron microscopy, Rutherford backscattering (RBS) channeling, and optical waveguiding were performed to characterize the deposited films. Epitaxial, single‐crystal films were obtained on all three substrate materials under the same growth conditions. However, the defect structure of the films, including grain tilting, threading dislocation density, and 90° domain formation, was strongly dependent on the choice of substrate material. Films grown on MgO(001) and LaAlO3(001) (pseudocubic indices) substrates are nominally c‐axis oriented; however, the PbTiO3 grains in the film form a fourfold domain structure, with the grains tilted ∼0.6° and ∼0.7°, respectively, toward the [100] directions (cubic or pseudo‐cubic) of the substrates. In addition, these films contain a significant volume fraction of 90°‐domain (a‐axis) stru...

Dimension and Size Effects in Ferroelectrics

The characteristic sizes of perovskite ferroelectrics have been examined by mean-field theory in a three dimensional base, leading to a detailed evaluation of the ultimate limits of physical sizes in nanostructured ferroelectrics with the stable polar phase in situations where the influence of depolarizing field can be neglected. Consequently, the dielectric susceptibility of nanostructured ferroelectrics is also derived for a three dimensional case. The size dependencies on the phase transition temperatures of perovskite ferroelectris, such as BaTiO3, PbTiO3, and Pb(Zr0.5Ti0.5)O3, are calculated by considering crystallographic anisotropy. In addition we have numerically evaluated the dielectric coefficient of Pb(Mg,Nb)O3 near the Curie temperature range based on its microstructure.

Deposition and characterization of nanocrystalline diamond films

Highly uniform, smooth nanocrystalline diamond films have been fabricated with a magnetoactive microwave chemical vapor deposition system. The top and bottom magnet currents were 145 and 60 A, respectively, while the microwave power and substrate temperature were controlled at 1500 W and 850 °C, respectively during deposition. The total processing pressure was regulated at 40 Pa (300 mTorr) with gas‐flow rates of 30 sccm of hydrogen, 2.4 sccm of methane, and 1 sccm of oxygen. Diamond films obtained under these conditions have grain sizes between 0.1 and 0.3 μm, and a mean roughness of 14.95 nm. The growth rate is 0.1 μm/h. Characterization techniques have involved x‐ray diffraction, Raman spectroscopy, scanning electron microscopy, atomic force microscopy, and transmission electron microscopy. Both x‐ray and electron diffraction patterns show no evidence of graphitic phase. Although a high density of twins and stacking faults was revealed by high‐resolution electron microscopy, compact diamond grains, and...

Piezoelectrically‐induced switching of 90° domains in tetragonal BaTiO3 and PbTiO3 investigated by micro‐Raman spectroscopy

Domain switching of 90° ferroelectric domains in tetragonal BaTiO3 and PbTiO3 is induced by the application of stress along specific crystallographic axes. For BaTiO3, single‐domain crystals are obtained from twinned specimens by the application of ∼1.1 MPa of stress parallel to the a axis and twin boundaries are induced by application of ∼0.22 MPa of stress parallel to the c axis. Similar piezoelectrically‐induced domain switching was observed in PbTiO3 at elevated temperature. We observed the rotation of the crystallographic axes associated with domain switching via micro‐Raman spectroscopy. These results were consistent with optical microscope images of the domain switching which demonstrates the usefulness of micro‐Raman spectroscopy for the study of ferroelectric domain structures. A phenomenological treatment of domain switching in a piezoelectrically‐coupled system is described.

Characteristics of PZT thin films as ultra-high density recording media

Abstract Ferroelectric thin films as the recording media of scanning probe microscope-based storage devices were investigated using an atomic force microscope(AFM) technique. Polarization domains were formed in the PbZrxTi1-xO3(PZT) thin films epitaxialy grown on the epitaxial SrRuO3(SRO) thin films on SrTiO3 substrate by applying a pulse voltage between the conductive tip of AFM and SRO as a bottom electrode. The polarized domains were observed by detecting the inverse-piezoelectricity-induced surface vibration of the PZT thin film caused by applying an ac modulation voltage to the conductive tip. The recording density of polarized domains, domain switching speed and preliminary retention characteristics of polarized domains were studied. The polarized domains as small as 30 nm are formed in the PZT thin film with the thickness of 45 nm. The small domains can be formed by applying a 100 ns pulse of 10 V to the conductive tip. As for the retention characteristics of polarized domains with a size of 90–110...

Dielectric and elastic properties of ferroelectric materials at elevated temperature

Abstract The temperature dependence of the velocities of sound propagating along various directions in high quality mono-domain single crystals of BaTiO 3 and PbTiO 3 have been measured by Brillouin scattering. Using the velocities and dielectric permittivities measured by the impedance method, the elastic stiffness moduli, C ijkl , piezoelectric constants, e rij and dielectric permittivity, ϵ ij , have been determined at elevated temperature through the ferroelectric phase transition. Only the longitudinal compressive modulus along the polar c -axis of tetragonal PbTiO 3 exhibits a distinctive soft mode behavior. In BaTiO 3 the electromechanical properties are found to be significantly different at different frequencies. It is suggested that high frequency relaxation occurs in BaTiO 3 .

Low-temperature growth and orientational control in RuO2 thin films by metal-organic chemical vapor deposition

For growth temperatures in the range of 275°C to 425°C, highly conductive RuO2 thin films with either (110)- or (101)-textured orientations have been grown by metal-organic chemical vapor deposition (MOCVD) on both SiO2/Si(001) and Pt/Ti/SiO2/Si(001) substrates. Both the growth temperature and growth rate were used to control the type and degree of orientational texture of the RuO2 films. In the upper part of this growth temperature range (∼ 350°C) and at a low growth rate ( 3.0 nm/min.), the RuO2 films favored a (101)-textured orientation. In contrast, higher growth temperatures (> 425°C) always produced randomly-oriented polycrystalline films. For either of these low-temperature growth processes, the films produced were crack-free, well-adhered to the substrates, and had smooth, specular surfaces. Atomic force microscopy showed that the films had a dense microstructure with an average grain size of 50–80 nm and a rms. surface roughness of ∼ 3–10 nm. Four-probe electrical transport measurements showed that the films were highly conductive with resistivities of 34–40 μΩ-cm (at 25°C).

The relationship between the MOCVD parameters and the crystallinity, epitaxy, and domain structure of PbTiO 3 films

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 PbTiO[sub 3] film could be obtained depended on both the Pb/Ti precursor ratio in the gas phase and the deposition temperature. Under appropriate conditions, stoichiometric PbTiO[sub 3] films could be obtained on all the substrates including silicon, MgO, [alpha]--Al[sub 2]O[sub 3], SrTiO[sub 3], and LaAlO[sub 3]. The PbTiO[sub 3] films grown on silicon substrates were always polycrystalline, whereas epitaxial PbTiO[sub 3] films were obtainable on all the other substrates. For epitaxial PbTiO[sub 3] 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 ([omega] scan) of the (100) and (001) planes of PbTiO[sub 3] epitaxial films and PbTiO[sub 3] single crystal revealed the inherent nature of the domain structures in PbTiO[sub 3].