Atomically Defined Rare‐Earth Scandate Crystal Surfaces

The fabrication of well‐defined, atomically sharp substrate surfaces over a wide range of lattice parameters is reported, which is crucial for atomically regulated epitaxial growth of complex oxide heterostructures. By applying a framework for controlled selective wet etching of complex oxides on the stable rare‐earth scandates (REScO₃), a_pseudocubic = 0.394 – 0.404 nm, the large chemical sensitivity of REScO₃ to basic solutions is exploited, which results in reproducible, single‐terminated surfaces. Time‐of‐flight mass‐spectroscopy measurements show that after wet etching the surfaces are predominantly ScO₂ ‐terminated. Moreover, the morphology study of SrRuO₃ thin‐film growth gives no evidence for mixed termination. Therefore, it is concluded that the REScO₃ surfaces are completely ScO₂ ‐terminated.     

Electrical and structural characterization of PLD grown CeO2–HfO2 laminated high-k gate dielectrics

The electrical and physical properties of CeO₂–HfO₂ nanolaminates deposited by pulsed laser deposition (PLD) are investigated. The properties of the nanolaminates are compared with binary CeO₂ and HfO₂ thin films. Layers were deposited using CeO₂ and HfO₂ targets at substrate temperatures between 220 and 620 °C in 10 Pa Ar+H₂ or O₂. In situ post deposition anneal (PDA) was achieved by controlled cooling down to room temperature with . Nanolaminates starting with CeO₂ show lower EOT and leakage compared to layers starting with HfO₂. TEM and XRD analyses showed thickness-dependent crystallinity of the layers, varying from amorphous to highly oriented polycrystalline phase.C–V and I–V measurements were done on the capacitors. Lowest fixed-charge density was found for the nanolaminates deposited at 520 °C. The k values of the nanolaminates extracted by the EOT-physical thickness plots were found to be 141, 48 and 22, for deposition temperatures 420, 520 and 620 °C, respectively. Higher k value for lower deposition temperatures is explained by the thickness dependent morphology of the layers. An with was found for binary HfO₂ layer with 4 nm physical thickness. Lowest leakage current density was for a 4 nm laminate deposited at 420 °C and with a cooling rate of 2 °C/min during PDA.     

Epitaxy on Demand

Perovskite oxide heteroepitaxy is realized on the top of inorganic nanosheets that are covering the amorphous oxide surfaces of Si substrates. Utilizing pulsed laser deposition, thin films of SrRuO₃ in a (001)_pc and (110)_pc orientation on nanosheets of Ca₂Nb₃O₁₀ and Ti_0.87O₂ are grown, respectively. The two types of nanosheets are patterned to locally tailor the crystallographic orientation and properties of SrRuO₃. The success of our approach is demonstrated by electron backscatter diffraction and spatial magnetization maps. An unprecedented control of perovskite film growth on arbitrary substrates is illustrated in this work, and the methods that are developed to deposit SrRuO₃ thin films are a viable starting point for growth of artificial heteroepitaxial thin films that require a bottom electrode. Control is not just reached in the direction of film growth, as the crystal orientation and film properties are regulated laterally on the surface of micropatterned nanosheets. Local control of magnetic properties is illustrated, which holds out prospects for the fabrication of next‐generation devices like noncollinear magnetic random access memories.     

Admixtures to d-wave gap symmetry in untwinned YBa2Cu3O7 superconducting films measured by angle-resolved electron tunneling

We report on an ab anisotropy of Jc parallel b/Jc parallel a approximately/= 1.8 IcRn parallelb/IcRn parallel a approximately/= 1.2 and in ramp-edge junctions between untwinned YBa2Cu3O7 and s-wave Nb. For these junctions, the angle theta with the YBa2Cu3O7 crystal b axis is varied as a single parameter. The RnA(theta) dependence presents twofold symmetry. The minima in IcRn at theta approximately/= 50 degrees suggest a real s-wave subdominant component and negligible d(xy)-wave or imaginary s-wave admixtures. The IcRn(theta) dependence is well fitted by 83% dx2-y2-, 15% isotropic s-, and 2% anisotropic s-wave order parameter symmetry, consistent with deltab/deltaa approximately/= 1.5.     

Numerical simulation of the vertical structure of discontinuous flows

A numerical method to solve the Reynolds‐averaged Navier–Stokes equations with the presence of discontinuities is outlined and discussed. The pressure is decomposed into the sum of a hydrostatic component and a hydrodynamic component. The numerical technique is based upon the classical staggered grids and semi‐implicit finite difference methods applied for quasi‐ and non‐hydrostatic flows. The advection terms in the momentum equations are approximated in order to conserve mass and momentum following the principles recently developed for the numerical simulation of shallow water flows with large gradients. Conservation of these properties is the most important aspect to represent near local discontinuities in the solution, following from sharp bottom gradients or hydraulic jumps. The model is applied to reproduce the flow over a step where a hydraulic jump forms downstream. The hydrostatic pressure assumption fails to represent this type of flow mainly because of the pressure deviation from the hydrostatic values downstream the step. Fairly accurate results are obtained from the numerical model compared with experimental data. Deviation from the data is found to be inherent to the standard k–ε model implemented. Copyright © 2001 John Wiley & Sons, Ltd.     

Semi‐implicit subgrid modelling of three‐dimensional free‐surface flows

In this paper, a semi‐implicit numerical model for two‐ and three‐dimensional free‐surface flows will be formulated in such a fashion as to intrinsically account for subgrid bathymetric details. It will be shown that with the proposed subgrid approach the model accuracy can be substantially improved without increasing the corresponding computational effort. Copyright © 2010 John Wiley & Sons, Ltd.     

Tailoring Vanadium Dioxide Film Orientation Using Nanosheets: a Combined Microscopy,Diffraction, Transport,and Soft X‐Ray in Transmission Study

Vanadium dioxide (VO₂) is a much‐discussed material for oxide electronics and neuromorphic computing applications. Here, heteroepitaxy of VO₂ is realized on top of oxide nanosheets that cover either the amorphous silicon dioxide surfaces of Si substrates or X‐ray transparent silicon nitride membranes. The out‐of‐plane orientation of the VO₂ thin films is controlled at will between (011)_M1/(110)_R and (?402)_M1/(002)_R by coating the bulk substrates with Ti_0.87O₂ and NbWO₆ nanosheets, respectively, prior to VO₂ growth. Temperature‐dependent X‐ray diffraction and automated crystal orientation mapping in microprobe transmission electron microscope mode (ACOM‐TEM) characterize the high phase purity, the crystallographic and orientational properties of the VO₂ films. Transport measurements and soft X‐ray absorption in transmission are used to probe the VO₂ metal–insulator transition, showing results of a quality equal to those from epitaxial films on bulk single‐crystal substrates. Successful local manipulation of two different VO₂ orientations on a single substrate is demonstrated using VO₂ grown on lithographically patterned lines of Ti_0.87O₂ and NbWO₆ nanosheets investigated by electron backscatter diffraction. Finally, the excellent suitability of these nanosheet‐templated VO₂ films for advanced lensless imaging of the metal–insulator transition using coherent soft X‐rays is discussed.     

High-performance flexible all-digital quadrature up and downconverter chip

In this paper, the design of an all-digital quadrature up and down converter with high accuracy and flexible intermediate frequency (IF) settings is presented. The signal up or down conversion is achieved by interpolation and decimation combined with a programmable anti-alias filter to preserve the selected frequency band during the sample rate conversion. This way a high-speed solution with low power consumption is obtained. A novel technique, based on the use of canonic signed digit (CSD) code, was utilized to implement the programmable anti-alias filter structure. The resulting chip fabricated in a 0.5-μm CMOS process is capable of handling sample rates up to 160 megasamples per second (MSPS) and is suitable for coaxial access network modem applications     

Domain Selectivity in BiFeO3 Thin Films by Modified Substrate Termination

Ferroelectric domain formation is an essential feature in ferroelectric thin films. These domains and domain walls can be manipulated depending on the growth conditions. In rhombohedral BiFeO₃ thin films, the ordering of the domains and the presence of specific types of domain walls play a crucial role in attaining unique ferroelectric and magnetic properties. In this study, controlled ordering of domains in BiFeO₃ film is presented, as well as a controlled selectivity between two types of domain walls is presented, i.e., 71° and 109°, by modifying the substrate termination. The experiments on two different substrates, namely SrTiO₃ and TbScO₃, strongly indicate that the domain selectivity is determined by the growth kinetics of the initial BiFeO₃ layers.