Volume 95, Issue 2, 15 January 2004
Index of content:
- DIELECTRICS AND FERROELECTRICITY (PACS 77)
95(2004); http://dx.doi.org/10.1063/1.1633342View Description Hide Description
We present a detailed study of the evolution with annealing temperature (in an oxygen environment) of the morphological and structuralproperties of thin erbium oxide films evaporated in an electron beam gun system. The electrical characteristics of metal-oxide-semiconductor structures are also described. Atomic force microscope and x-ray difractometry were used to map out the morphology and crystalline nature of films ranging in thickness from 4.5 to 100 nm. High-resolution cross-sectional transmission electron microscopy imaging and Auger electron spectroscopy reveal three sublayers: an outer dense nanocrystalline layer, a middle transition layer and amorphous film placed close to the Si substrate. The effective dielectric constant depends on the thickness and the annealing temperature. A 1–2.8 nm interfacial layer as well as an ErO inclusion with low polarizability are formed during the deposition and the annealing process has a profound effect on the dielectric constant and the leakages. The minimum effective oxide thickness is 2.4–2.8 nm and in the thinnest films we obtained a leakage current density as low as at an electric field of 1 MV/cm. We observe a shift of the flatband voltage to the positive side and significant lowering of the positive charge down to For a 4.5 nm film, the maximum total breakdown electric field was approximately
95(2004); http://dx.doi.org/10.1063/1.1633648View Description Hide Description
Anisotropicdielectric response occurs naturally due to the presence of gradation, like in functionally graded materials or graded biological cells. However, these materials with locally anisotropicdielectric responses can have macroscopically isotropic responses. In treating graded particles of anisotropicmaterials, traditional isotropic gradation methods need to be modified. In this work, we developed a first-principles approach, as well as an anisotropic differential effective dipole approximation, for calculating the dipole moment of these particles. To this end, the two methods are shown in excellent agreement. As a result, these approaches offer convenient and effective ways to investigate the dielectric properties and optical responses of graded spherical particles of anisotropicmaterials, as well as the electrokinetic phenomena of biological cells.
95(2004); http://dx.doi.org/10.1063/1.1631732View Description Hide Description
thin films were deposited on MgO single crystal substrates by the spin coating method. Films with different grain sizes (50–500 nm) were obtained by preparing at different temperatures. Films were polycrystalline in nature and oriented preferentially in the (001) direction. Electrical resistivity and thermopower were measured to study the effect of the grain size on the thermoelectric properties. Hall carrier concentrations of the films are dependent on the grain size. The film with a smaller grain size has a lower carrier concentration, a larger resistivity, and a higher thermopower. The thermoelectric power factor is related to the grain size and shows a maximum for the film with grain size of about 100 nm.
95(2004); http://dx.doi.org/10.1063/1.1632019View Description Hide Description
Residual stress development during processing of sol-gel derived ferroelectric thin films influences electromechanical properties and performance. The present work investigates the effects of stress on field-induced polarization switching in ferroelectric(PZT) (52/48) thin films. Film response is measured as a function of externally applied mechanical stress using a double-beam laser-Doppler heterodyneinterferometer. This apparatus successfully eliminates any displacement contribution from flexural vibration of the substrate and enables measurement of the strain-electric field hysteresis loops as a function of applied stress. The field-induced strain in the PZT film increases with increasing compressive stress, while the opposite trend is observed for applied tensile stress. The dependence of electromechanical response on the external stress is attributed to the initial tensile residual stress state in the film. Tensile stress creates an in-plane clamping effect on the domains in the film, hindering polarization switching. The application of a compressive stress reduces tensile residual stress in the film and the constraint on the domains, leading to higher field-induced strains. Applied tensile stress amplifies the clamping effect, leading to lower field-induced strains.
95(2004); http://dx.doi.org/10.1063/1.1635970View Description Hide Description
Ferroelectric domain structures of a 〈001〉-oriented lead magnesium niobate–lead titanate tetragonal crystal were examined under cyclic bipolar electric fields. Complex patterns of orthogonal domain strips were found to emerge from a simple structure of parallel strips of domains. Near the boundary between the two orthogonal sets of the domain strips, domains were forced to intersect, creating charged domain walls at the intersections. With continued electric cycling, direct impingement of individual domains resulted in domain interpenetration and fine domain cells in the boundary region. Away from the boundary region, initial domain walls were withdrawn and replaced by the walls along a different orientation, resulting in separate areas that each contained a single set of parallel strips of domains. A model based on domain switching is suggested to explain interpenetration of the domains and the withdrawal of the original domain walls.