High-resolution electron energy-loss spectroscopy of Ba Ti O 3∕ Sr Ti O 3 multilayers

The dielectric properties of BaTiO3 thin films and multilayers are different from bulk materials because of nanoscale dimensions, interfaces, and stress-strain conditions. In this study, BaTiO3/SrTiO3 multilayers deposited on SrTiO3 substrates by pulsed laser deposition have been investigated by high-energy-resolution electron energy-loss spectroscopy. The fine structures in the spectra are discussed in terms of crystal-field splitting and the internal strain. The crystal-field splitting of the BaTiO3 thin layer is found to be a little larger than that of bulk BaTiO3, which has been interpreted by the presence of the internal strain induced by the misfit at the interface. This finding is consistent with the lattice parameters of the BaTiO3 thin layer determined by the selected area diffraction pattern. The near-edge structure of the oxygen K edge in BaTiO3 thin layers and in bulk BaTiO3 are simulated by first-principle self-consistent full multiple-scattering calculations. The results of the simulations are in a good agreement with the experimental results. Moreover, the aggregation of oxygen vacancies at the rough BaTiO3/SrTiO3 interface is indicated by the increased [Ti]/[O] element ratio, which dominates the difference of dielectric properties between BaTiO3 layer and bulk materials.

Formation of epitaxial BaTiO3/SrTiO3 multilayers grown on Nb-doped SrTiO3 (001) substrates

The formation of epitaxial BaTiO3/SrTiO3 multilayers; is studied in terms of the growth mechanism by investigating surface morphologies, crystalline orientations, microstructures, and structures of the interfaces, as well as by determining the dielectric properties. Under specific conditions, the epitaxial BaTiO3 films follow a layer-then-island (Stranski-Krastanov) mechanism on SrTiO3 (001)-oriented substrates. In view of actual efforts made to grow epitaxial superlattices involving very thin individual layers of BaTiO3 and/or SrTiO3, we have determined that the BaTiO3 films Of up to 6,nm thickness do not show any defects and have a sharp BaTiO3-on-SrTiO3 interface. On the contrary, SrTiO3-on-BaTiO3 interfaces within multilayers are rough, probably due to the different growth mechanisms of the two different materials, or due to a difference in the morphological stability of the growth surfaces caused by different surface energies of BaTiO3 and SrTiO3 and by different mobilities of the Ba and Sr atoms reaching the SrTi3 and BaTiO3 layers, respectively.

Control of leaky-mode propagation and radiation properties in hybrid dielectric-waveguide printed-circuit technology: Experimental results

Experimental results are presented to show how a planar circuit, printed on a laterally shielded dielectric waveguide, can induce and control the radiation from a leaky-mode. By studying the leaky-mode complex propagation constant, a desired radiation pattern can be synthesized, controlling the main radiation characteristics (pointing direction, beamwidth, sidelobes level) for a given frequency, This technique leads to very flexible and original leaky-wave antenna designs. The experiments show to be in very good agreement with the leaky-mode theory.

Low temperature surface nitridation processes for dielectric-Ge interfaces

Germanium MOS capacitors have been fabricated with a high-? HfO dielectric using ALD. An in-situ low temperature (250°C) nitrogen plasma treatment on the germanium surface prior to the deposition of HfO was found to be beneficial to the electrical properties of the devices. Germanium MOS capacitors have also been fabricated with a SiO dielectric deposited by an atmospheric pressure CVD 'silox' process. The same low temperature plasma nitridation was found to degrade the electrical properties of the silox devices. The effect of a post-metal anneal in H and N on both types of capacitor structure was also found to degrade device electrical properties. copyright The Electrochemical Society.

Metamaterial made of paired planar conductors: Particle resonances, phenomena and properties

The properties and characteristics of a recently proposed anisotropic metamaterial based upon layered arrays of tightly coupled pairs of "dogbone" shaped stripe conductors have been explored in detail. It has been found that a metamaterial composed of such stacked layers exhibits artificial magnetism and may support backward wave propagation. The equivalent network models of the constitutive conductor pairs arranged in the periodic array have been devised and applied to the identification of the specific types of resonances, and to the analysis of their contribution into the effective dielectric and magnetic properties of the artificial medium. The proposed "dogbone" configuration of conductor pairs has the advantage of being entirely realizable and assemblable in planar technology. It also appears more prospective than simple cut-wire or metal-plate pairs because the additional geometrical parameters provide an efficient control of separation between the electric and magnetic resonances that, in turn, makes it possible to obtain a fairly broadband left-handed behaviour of the structure at low frequencies.

Correlation Between the Electrical and Optical Properties of an Atmospheric Pressure Plasma During Siloxane Coating Deposition

The effect of varying process parameters on atmospheric plasma characteristics and properties of nanometre thick siloxane coatings is investigated in a reel-to-reel deposition process. Varying plasma operation modes were observed with increasing applied power for helium and helium/oxygen plasmas. The electrical and optical behaviour of the dielectric barrier discharge were determined from current/voltage, emission spectroscopy and time resolved light emission measurements. As applied power increased, multiple discharge events occurred, producing a uniform multi-peak pseudoglow discharge, resulting in an increase in the discharge gas temperature. The effects of different operating modes on coating oxidation and growth rates were examined by injecting hexamethyldisiloxane liquid precursor into the chamber under varying operating conditions. A quenching effect on the plasma was observed, causing a decrease in plasma input power and emission intensity. Siloxane coatings deposited in helium plasmas had a higher organic component and higher growth rates than those deposited in helium/oxygen plasmas.

Real-time approach to the optical properties of solids and nanostructures: Time-dependent Bethe-Salpeter equation

Many-body effects are known to play a crucial role in the electronic and optical properties of solids and nanostructures. Nevertheless, the majority of theoretical and numerical approaches able to capture the influence of Coulomb correlations are restricted to the linear response regime. In this work, we introduce an approach based on a real-time solution of the electronic dynamics. The proposed approach reduces to the well-known Bethe-Salpeter equation in the linear limit regime and it makes it possible, at the same time, to investigate correlation effects in nonlinear phenomena. We show the flexibility and numerical stability of the proposed approach by calculating the dielectric constants and the effect of a strong pulse excitation in bulk h-BN.

Optimisation and scaling of interfacial GeO2 layers for high-k gate stacks on germanium and extraction of dielectric constant of GeO2

Germanium is an attractive channel material for MOSFETs because of its higher mobility than silicon. In this paper, GeO2 has been investigated as an interfacial layer for high-kappa gate stacks on germanium. Thermally grown GeO2 layers have been prepared at 550 degrees C to minimise GeO volatilisation. GeO2 growth has been performed in both pure O-2 ambient and O-2 diluted with N-2. GeO2 thickness has been scaled down to approximately 3 nm. MOS capacitors have been fabricated using different GeO2 thicknesses with a standard high-kappa dielectric on top. Electrical properties and thermal stability have been tested up to at least 350 degrees C. The K value of GeO2 was experimentally determined to be 4.5. Interface state densities (D-it) of less than 10(12) CM-2 eV(-1) have been extracted for all devices using the conductance method.

ARTIFICIAL SURFACES WITH INTERWOVEN AND TESSELLATED PATTERNED CONDUCTORS: PROPERTIES AND PHENOMENOLOGY

The features of artificial surfaces composed of doubly periodic patterns of interwoven planar conductors are discussed. The free-standing intertwined quadrifilar spirals and modified Brigid's crosses are presented as illustrative examples to demonstrate the highly stable angular reflection and transmittance response with low cross-polarisation and a broad fractional bandwidth. The main mechanisms contributing to the substantially sub-wavelength response of these arrays are discussed showing that interweaving their conductor patterns provides concurrent control of both the equivalent capacitance and inductance of the unit cell. The effects of dielectric substrate and conductor thickness on the properties of intertwined spiral and modified Brigid's cross arrays are discussed to provide insight in the effect of the structure parameters on array performance.

Three-wave Nonlinear Scattering by Quasiperiodic Dielectric Structure

The combinatorial frequency generation by a Fibonacci type quasi-periodic dielectric multilayered structure illuminated by two plane waves has been analysed. The effects of the layer parameters and Fibonacci sequence order on the properties of the combinatorial frequency waves emitted from the stacked nonlinear layers are discussed.

Metasurfaces with interwoven conductor patterns on dielectric substrates

The properties of metasurfaces comprised of interwoven conductor patterns on dielectric substrates have been examined. The significant reduction of the fundamental resonance frequency fr and expanded fractional bandwidths (FBWs) offered by the intertwined spirals and Brigid’s crosses extended beyond a single unit cell has been achieved with the aid of thin dielectric substrates. A qualitative model has been proposed and proved to adequately predict the main properties of entwined spiral arrays on dielectric substrates.

Near-Field Plasmonics of an Individual Dielectric Nanoparticle above a Metallic Substrate

We simulate and discuss the local electric-field enhancement in a system of a dielectric nanoparticle placed very near to a metallic substrate. We use finite-element numerical simulations in order to understand the field-enhancement mechanism in this dielectric NP-on-mirror system. Under appropriate excitation conditions, the gap between the particle and the substrate becomes a "hot spot", i.e., a region of intense electromagnetic field. We also show how the optical properties of the dielectric NP placed on a metallic substrate affect the plasmonic field enhancement in the nanogap and characterize the confinement in the gap. Our study helps to understand and design systems with dielectric NPs on metallic substrates which can be equally as effective for SERS, fluorescence, and nonlinear phenomena as conventional all plasmonic structures.

Studies of the Room-Temperature Multiferroic Pb(Fe0.5Ta0.5)0.4(Zr0.53Ti0.47)0.6O3: Resonant Ultrasound Spectroscopy, Dielectric, and Magnetic Phenomena

Recently, lead iron tantalate/lead zirconium titanate (PZTFT) was demonstrated to possess large, but unreliable, magnetoelectric coupling at room temperature. Such large coupling would be desirable for device applications but reproducibility would also be critical. To better understand the coupling, the properties of all 3 ferroic order parameters, elastic, electric, and magnetic, believed to be present in the material across a range of temperatures, are investigated. In high temperature elastic data, an anomaly is observed at the orthorhombic mm2 to tetragonal 4mm transition, Tot = 475 K, and a softening trend is observed as the temperature is increased toward 1300 K, where the material is known to become cubic. Thermal degradation makes it impos- sible to measure elastic behavior up to this temperature, however. In the low temperature region, there are elastic anomalies near ≈40 K and in the range 160–245 K. The former is interpreted as being due to a magnetic ordering transition and the latter is interpreted as a hysteretic regime of mixed rhom- bohedral and orthorhombic structures. Electrical and magnetic data collected below room temperature show anomalies at remarkably similar temperature ranges to the elastic data. These observations are used to suggest that the three order parameters in PZTFT are strongly coupled.