Smart contact lenses have been put forward for years, but there is still no commercial product in the market; the high cost due to expensive fabrication techniques could be one of the reasons. In this paper, first, a cost-efficient and reliable route to fabricate graphene grating on contact lens was designed and demonstrated based on the direct laser interference patterning graphene film on commercial contact lenses using an Nd:YAG laser. The thickness of the film and the interference angle have been taken into consideration. Optical characterization and simulation have been applied to evaluate the quality of our final achieved grating patterns with a grating size from 0.92 to 3.04 μm. Two-dimensional (2D) patterns could also be obtained through double-time laser interference. Contact angles for samples with different interference angles were presented considering the service environment of smart contact lenses. Of course, the conductivity of the samples was evaluated using a four-probe method. The most conductive sample had the sheet resistance lower than 30 Ω/sq. This research study highlighted the possibility of patterning graphene with the laser ablation method and provided a candidate solution for the fabrication of smart contact lenses under controlled cost.

Here, the authors present a new type of split-ring resonator (SRR) constructed from high dielectric constant material. Compared to conventional metal SRRs, such resonators have significantly higher unloaded quality factor (Q(u)). A new class of microwave filter is presented using the dielectric SRR. Two examples of different filter configurations are investigated, and the measured results show excellent performance. Good agreement between measurements and simulations has been achieved.

A quantitative analysis of the dielectric properties of a multiphase sample using a scanning microwave microscope (SMM) is proposed. The method is demonstrated using inhomogeneous samples composed of a resin containing micrometric inclusions of a known ceramic material. The SMM suitable for this task employs relatively large tips (tens of micrometers in diameter). Additionally, in order to make the instrument more suitable for high-throughput analysis, an original design for rapid tip changes is implemented. Single-point measurements of dielectric constant at random locations on the sample were performed, leading to histograms of dielectric constant values. These are related to the dielectric constants of the two phases using Maxwell-Garnett effective medium theory, taking into account the volume-of-interaction in the sample beneath the tip.

In this letter, a microstrip-fed open-ended resonant antenna (RA) based on an extended composite right/left-handed (ECRLH) unit cell structure is presented for multiband operations. This antenna includes an asymmetric ECRLH unit cell as the main resonator and a short microstrip line as the feeding line. This designed RA, of overall size of 56 × 64 × 1.575 mm 3 , generates ten operating resonances covering several commercial frequency bands over 0.5-6 GHz. Measured and simulated results have close agreement. Furthermore, the equivalent circuit model of the proposed RA is developed. For each operating resonance, the major control parts in this antenna structure and the primary radiation sources for each operating resonance are analyzed and summarized.

Uncertainties of the order of 8 % in the accuracy of lithography used to define co-planar waveguides on ferroelectric thin films lead to a similar uncertainty in the value of relative permittivity of the film extracted from measurements. When such films are used as the tunable elements in a tunable composite right/left handed leaky wave antenna, such variations of the capacitance of the varactors can lead to a reduction in radiation and total efficiency around of the order of 1 dB in 5 dB due to the appearance of a bandgap in the frequency response.

The microwave microscope is a device which utilises near fields to characterise material properties of samples on length scales smaller than the operating wavelength. The errors associated with extracting the permittivity of a high permittivity thin film on a low permittivity substrate from measurements using such a device are found to be of the order of 25% when using a widely used image charge model of the tip-sample interaction. The uncertainties arise from the model-based extraction of the permittivity from the raw frequency shift data, and in the current case are shown to come from the assumption in the model that the tip of the microwave probe can be modelled as a sphere.The raw data from the microscope contain random uncertainties of the order of 1% and reveal variations in the properties of the thin film with sub-wavelength resolution demonstrating the microwave microscope as a sub-wavelength characterisation technique for thin films.

The crystal structure and the dielectric properties of LaYbO3 films grown by pulsed laser deposition and integrated in SrRuO3/LaYbO3/SrRuO3 capacitive structures are reported. Two different fabrication procedures are assessed. When the SrRuO3/LaYbO3/SrRuO3 stack is grown in-situ, the relative permittivity of the LaYbO3 is 35. When instead the lower SrRuO3 electrode layer is patterned by contact photolithography and argon ion milling, prior to the deposition of the LaYbO3, the relative permittivity of the LaYbO3 is 55. In this case, post-growth annealing brings the relative permittivity towards that of the film grown in-situ. In both cases the relative permittivity is higher than the value measured in bulk material. This is attributed to the permittivity being highest along the orthorhombic c-axis. The annealing procedure produced a recrystallization of the LaYbO3 and of the SrRuO3.

This paper outlines four related developments in frequency reconfigurable antennas: using negative impedance converters to enhance the tuning range of tunable antennas; tuning the isolation between closely spaced antennas; reducing the size of a filter/antenna module by direct impedance matching; and using ferroelectric varactors tuning elements.

Two and three dimensional growth of SrTiO3 films on (001) MgO substrate was achieved by pulsed laser interval and pulsed laser deposition respectively. The growth mode was monitored by in-situ reflection high energy electron diffraction. Interval deposition forces layer-by-layer growth of materials even with such a large lattice misfit (~7.9%). A titanium dioxide buffer monolayer was deposited to allow the film to wet the substrate to encourage two dimensional growth of the strontium titanate. A variety of defects was investigated using transmission electron microscopy and high resolution scanning transmission electron microscopy. Misfit dislocations, steps at the interface, Ti-rich defects and regularly shaped nano-holes connected by anti-phase boundaries were found to be the dominant defects in these films grown layer by layer. The edges of the nano-holes were mainly along [010] and [100] for a [001] growth direction. The large strain between the two crystal systems with large lattice mismatch leads to in-plane tensile stress during the layer-by-layer growth. The stress is relieved in part by the holes. The films with a three dimensional growth mode possess a uniform surface with dislocations as the dominant defects. The individual densities of the various defects, including a Ti-rich phase and misfit and threading dislocations, are determined by the kinetics of the deposition method.

Bismuth sodium titanate (BNT)-derived materials have seen a flurry of research interest in recent years because of the existence of extended strain under applied electric fields, surpassing that of lead zirconate titanate (PZT), the most commonly used piezoelectric. The underlying physical and chemical mechanisms responsible for such extraordinary strain levels in BNT are still poorly understood, as is the nature of the successive phase transitions. A comprehensive explanation is proposed here, combining the short-range chemical and structural sensitivity of in situ Raman spectroscopy (under an applied electric field and temperature) with macroscopic electrical measurements. The results presented clarify the causes for the extended strain, as well as the peculiar temperature-dependent properties encountered in this system. The underlying cause is determined to be mediated by the complex-like bonding of the octahedra at the center of the perovskite: a loss of hybridization of the 6s2 bismuth lone pair interacting with the oxygen p-orbitals occurs, which triggers both the field-induced phase transition and the loss of macroscopic ferroelectric order at the depolarization temperature.

Dense Bi2Te2W3O16 ceramics were prepared by the conventional solid-state reaction route. X-ray diffraction data show the room-temperature (RT) crystal symmetry of Bi2Te2W3O16 to be well described by the centrosymmetric monoclinic C2/c space group [a=21.280(5)angstrom, b=5.5663(16)angstrom, c=12.831(3)angstrom and =124.014(19)degrees and Z=4]. Raman spectroscopy analyses are in broad agreement with space group assignment, but also revealed the presence of Bi2W2O9 as a secondary phase. This phase is present as plate-like grains embedded on a fine-grained equiaxed matrix, as revealed by scanning electron microscopy. From the fitting of infrared reflectivity data the relative permittivity, epsilon(r), was estimated as 34.2, and the intrinsic quality factor, Q(u)xf as 57500GHz. At RT and microwave frequencies, Bi2Te2W3O16 ceramics sintered at 720 degrees C for 6h exhibit epsilon(r similar to)34.5, Q(u)xf=3173GHz (at 7.5GHz), and temperature coefficient of resonant frequency, (f)=-92ppm/degrees C. This shows a good agreement between the estimated and measured epsilon(r) values, but also shows that, in principle, the dielectric losses of the ceramics are of extrinsic origin.

An investigation of all oxide ferroelectric capacitors based on SrRuO3/BaTiO3/SrRuO3 multi-layers grown on sacrificial oxide layers of YBa2Cu3O7 and MgO for Micro-Electro-Mechanical systems applications is reported. By insertion of additional MgO or SrTiO3 buffer layers the orientation of the BaTiO3 film can be controlled allowing the fabrication of suspended cantilevers using the 31 and the 33 piezoelectric modes. The electrical properties of SrRuO3/BaTiO3/SrRuO3 capacitors are changed compared with those grown directly on a single crystal substrate by the introduction of sacrificial layers. Circuit modeling of the electrical characteristics of these devices shows that a reduction of the deposition pressure for BaTiO3 produces a decrease of the parasitic shunting conductance (modeled with a resistor in parallel to the capacitance of the device) which reduces the resistive losses present in the BaTiO3 film. However for extremely low deposition pressure the quality of the polarization hysteresis loops is compromised. Particulates present on the surface of the YBa2Cu3O7 increase the parasitic conductance at low frequency in the capacitive structure grown on this sacrificial layer. Good electrical properties are obtained for the capacitive structures grown on top of the MgO sacrificial layers at pressures equal or lower than 8 Pa. (C) 2011 Elsevier B.V. All rights reserved.

We have used a method to experimentally determine the curvature of thin film multilayers in all oxide cantilevers. This method is applicable for large deflections and enables the radius of curvature of the beam, at a certain distance from the anchor, to be determined accurately. The deflections of the suspended beams are measured at different distances from the anchor point using SEM images and the expression of the deflection curve is calculated for each cantilever. With this expression it is possible to calculate the value of the radius of curvature at the free end of the cantilever. Together with measured values for the Youngs Modulus, this enabled us to determine the residual stress in each cantilever. This analysis has been applied to SrRuO 3/BaTiO 3/SrRuO 3, BaTiO 3/MgO/SrTiO 3 and BaTiO3/SrTiO3 piezoelectric cantilevers and the results compared to two models in which the stresses are determined by lattice parameter mismatch or differences in thermal expansion coefficient. Our analysis shows that the bending of the beams is mainly due the thermal stress generated during the cooling down stage subsequent to the film deposition.

This study presents a direct comparison between semiconductor and barium strontium titanate (BST) tuning technologies. Tapped line combline two-pole and four-pole bandpass filters were designed in a coplanar waveguide configuration. Discrete BST interdigital capacitors were fabricated and integrated into the filter circuits in a hybrid manner. The BST varactors performed as tuning elements in the filters. The same filter was also made using gallium arsenide (GaAs) varactors and the tuning and loss performance were compared with the BST filters. The centre frequency of the two-pole BST filter tuned 30.3% from 1.55 to 2.02 GHz with insertion loss ranging from 3.7 to 1.1 dB, at an electric field of 6.5 V/mu m. This filter has a figure of merit of 0.87 dB(-1). The two-pole GaAs filter showed a wide tuning range from 0.94 to 2.44 GHz at 14 V with insertion loss ranging from 4.2 to 0.8 dB. The results are discussed in detail, as it is important to clarify the comparison with relation to the quality of the materials, as well as the particular filter designs and centre frequencies involved.

The fabrication and characterization of released cantilevers in new multilayer thin films architectures is reported. In contrast to previous works, the cantilevers are produced without etching of the substrate and are based on lead free piezoelectric materials. The three architectures are: SrRuO 3 /BaTiO 3 /MgO/SrTiO 3 /YBa 2 Cu 3 O 7 , SrRuO 3 /BaTiO 3 /SrRuO 3 /YBa 2 Cu 3 O 7 and SrRuO 3 /BaTiO 3 /SrRuO 3 /SrTiO 3 /YBa 2 Cu 3 O 7 . It is shown that the different architectures allow a choice of the orientation of the polar axis in piezoelectric layers, in plane (d 33 mode) or out of plane (d 31 mode). Both configurations may be utilized in piezoelectric energy harvesting devices. Released cantilevers with the above layer sequences have been produced with lengths ranging from, 100 μm to 250 μm. The residual stress after the release of the cantilevers produces an upward bending, the distance between the cantilever tips and the substrate varies between 20 μm and 45 μm. This distance would allow the sufficient vibration amplitude to enable the cantilevers to be used as micro-generators. Measurements of Young Modulus of the cantilevers and of polarization hysteresis loop are reported.

Strontium titanate films were grown by standard and interval pulsed laser interval deposition on (001) strontium titanate and magnesium oxide substrates. Reflection high-energy electron diffraction (RHEED) was used to monitor the growth mode of the films. The microstructures were investigated using transmission electron microscopy. The temporal evolution of the RHEED intensity confirmed a layer-by-layer growth mode in the homoepitaxial case. In heteroepitaxy, three dimensional growth occurred. Misfit dislocations and threading dislocations were the dominant defects. The film grown using the standard deposition was relaxed; the film grown using interval deposition was under in-plane tension and showed fewer threading dislocations.

Based on deployment throughout a term, this paper suggests the potential of a computer-based approach to promote learner awareness of their knowledge states. We consider in particular the extent to which students are interested in finding out about their misconceptions in the context of independent study. It was found that many first-year students held misconceptions in introductory electrical circuits and mathematics courses at some stage of their learning, and most viewed information about their misconceptions to assist them in identifying their problems. We suggest, therefore, that an approach of highlighting an individual's misconceptions can be found useful by students to help them recognise their knowledge, difficulties and misconceptions to support self-assessment and facilitate their identification of an appropriate focus of their efforts, to meet their learning needs.

Vacancy defects in thin film laser ablated SrTiO3 on SrTiO3 were identified using variable energy positron annihilation lifetime measurements. Strontium vacancy related defects were the dominant positron traps and, apart from in the top ~ 50 nm, were found to be uniformly distributed. The surface layer showed an increase in annihilation from larger open-volume defects, large vacancy clusters or nanovoids.

This paper presents an investigation of tunable bandstop filter using slotted ground structure. A Barium-Strontium-Titanate (BST) varactor chip is used to tune each resonator and its location is determined by electromagnetic simulation for an optimum frequency tuning. 2-pole bandstop filter is measured at the center frequency from 1.2 to 1.4 GHz and its rejection is more than 15 dB at the stop band while the insertion loss at the pass band is less than 1 dB.