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Dielectric Materials (dielectric + material)
Selected AbstractsRaman spectroscopy of optical phonon confinement in nanostructured materialsJOURNAL OF RAMAN SPECTROSCOPY, Issue 6 2007Akhilesh K. Arora Abstract If the medium surrounding a nano-grain does not support the vibrational wavenumbers of a material, the optical and acoustic phonons get confined within the grain of the nanostructured material. This leads to interesting changes in the vibrational spectrum of the nanostructured material as compared to that of the bulk. Absence of periodicity beyond the particle dimension relaxes the zone-centre optical phonon selection rule, causing the Raman spectrum to have contributions also from phonons away from the Brillouin-zone centre. Theoretical models and calculations suggest that the confinement results in asymmetric broadening and shift of the optical phonon Raman line, the magnitude of which depends on the widths of the corresponding phonon dispersion curves. This has been confirmed for zinc oxide nanoparticles. Microscopic lattice dynamical calculations of the phonon amplitude and Raman spectra using the bond-polarizability model suggest a power-law dependence of the peak-shift on the particle size. This article reviews recent results on the Raman spectroscopic investigations of optical phonon confinement in several nanocrystalline semiconductor and ceramic/dielectric materials, including those in selenium, cadmium sulphide, zinc oxide, thorium oxide, and nano-diamond. Resonance Raman scattering from confined optical phonons is also discussed. Copyright © 2007 John Wiley & Sons, Ltd. [source] High Quality Factor Metallodielectric Hybrid Plasmonic,Photonic CrystalsADVANCED FUNCTIONAL MATERIALS, Issue 12 2010Xindi Yu Abstract A 2D polystyrene colloidal crystal self-assembled on a flat gold surface supports multiple photonic and plasmonic propagating resonance modes. For both classes of modes, the quality factors can exceed 100, higher than the quality factor of surface plasmons (SP) at a polymer,gold interface. The spatial energy distribution of those resonance modes are carefully studied by measuring the optical response of the hybrid plasmonic,photonic crystal after coating with dielectric materials under different coating profiles. Computer simulations with results closely matching those of experiments provide a clear picture of the field distribution of each resonance mode. For the SP modes, there is strong confinement of electromagnetic energy near the metal surface, while for optical modes, the field is confined inside the spherical particles, far away from the metal. Coating of dielectric material on the crystal results in a large shift in optical features. A surface sensor based on the hybrid plasmonic,photonic crystal is proposed, and it is shown to have atomic layer sensitivity. An example of ethanol vapor sensing based on physisorption of ethanol onto the sensor surface is demonstrated. [source] Miniaturized planar ferrite junction circulator in the form of substrate-integrated waveguideINTERNATIONAL JOURNAL OF RF AND MICROWAVE COMPUTER-AIDED ENGINEERING, Issue 1 2008Wenquan Che Abstract The theoretical analysis and engineering implementation of the planar substrate-integrated waveguide (SIW) ferrite junction circulator have been proposed in this article. The ferrite junction circulator is implemented in the form of SIW, taking the features of low profile, small volume and easy integration with other planar circuits. The design strategies of the device have been introduced, including the design consideration of the microstrip transition. One C-band prototype of SIW ferrite junction circulator has been fabricated and measured. The experimental results indicate the bandwidth is about 33% at ,15 dB isolation and the maximum isolation is near 40 dB. However, the insertion loss is a little big, owing to the imperfect dielectric material and fabrication inaccuracy. The SIW ferrite junction circulator and the microstrip transition are integrated into a same substrate, resulting in a very compact planar ferrite junction circulator and indicating potential applications in integrated communication and radar systems. © 2007 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2008. [source] Styrene 4-vinylbenzocyclobutene copolymer for microelectronic applicationsJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 8 2008Ying-Hung So Abstract Styrene and 4-vinylbenzocyclobutene (vinyl-BCB) random copolymers were prepared by free radical polymerization and studied for suitability as a dielectric material for microelectronic applications. The percentage of vinyl-BCB in the copolymer was varied from 0 to 26 mol % to optimize the physical and mechanical properties of the cured copolymer as well as the cost. Copolymer in which 22 mol % of vinyl-BCB was incorporated along with styrene produced a thermoset polymer which, after cure, did not show a Tg before decomposition at about 350 °C. The polymeric material has a very low dielectric constant, dissipation factor, and water uptake. The fracture toughness of the copolymer was improved with the addition of 20 wt % of a star-shaped polystyrene- block -polybutadiene. Blends of the poly(styrene- co -vinyl-BCB) with the thermoplastic elastomer provided material that maintained high Tg of the cured copolymer with only a slight decrease in thermal stability. The crosslinked styrenic polymer and toughened blends possess many properties that are desirable for high frequency-high speed mobile communication applications. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2799,2806, 2008 [source] Low-Loss Microwave Dielectrics Using Mg2(Ti1,xSnx)O4 (x=0.01,0.09) Solid SolutionJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 10 2009Cheng-Liang Huang Low-loss ceramics having the chemical formula Mg2(Ti1,xSnx)O4 for x ranging from 0.01 to 0.09 have been prepared by the conventional mixed oxide route and their microwave dielectric properties have been investigated. X-ray powder diffraction patterns indicate the corundum-structured solid solutions for the prepared compounds. In addition, lattice parameters, which linearly increase from 8.4414 to 8.4441 Å with the rise of x from 0.01 to 0.09, also confirm the forming of solid solutions. By increasing x from 0.01 to 0.05, the Q×f of the specimen can be tremendously boosted from 173 000 GHz to a maximum 318 000 GHz. A fine combination of microwave dielectric properties (,r,15.57, Q×f,318 000 GHz at 10.8 GHz, ,f,,45.1 ppm/°C) was achieved for Mg2(Ti0.95Sn0.05)O4 ceramics sintered at 1390°C for 4 h. Ilmenite-structured Mg(Ti0.95Sn0.05)O3 (,r,16.67, Q×f,275 000 GHz at 10.3 GHz, ,f,,53.2 ppm/°C) was detected as a second phase. The presence of the second phase, however, would cause no significant variation in the dielectric properties of the specimen, because the second phase properties are very similar to the primary phase. These unique properties, in particular, low ,r and high Q×f, can be utilized as a very promising dielectric material for ultra-high-frequency applications. [source] Low-Temperature Sintering and Microwave Dielectric Properties of Li2MgSiO4 CeramicsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 6 2009Sumesh George Development of a low-temperature sintered dielectric material derived from Li2MgSiO4 (LMS) for low-temperature cofired ceramic (LTCC) application is discussed in this paper. The LMS ceramics were prepared by the solid-state ceramic route. The calcination and sintering temperatures of LMS were optimized at 850°C/4 h and 1250°C/2 h, respectively, for the best density and dielectric properties. The crystal structure and microstructure of the ceramic were studied by the X-ray diffraction and scanning electron microscopic methods. The microwave dielectric properties of the ceramic were measured by the cavity perturbation method. The LMS sintered at 1250°C/2 h had ,r=5.1 and tan ,=5.2 × 10,4 at 8 GHz. The sintering temperature of LMS is lowered from 1250°C/2 h to 850°C/2 h by the addition of both lithium borosilicate (LBS) and lithium magnesium zinc borosilicate (LMZBS) glasses. LMS mixed with 1 wt% LBS sintered at 925°C/2 h had ,r=5.5 and tan ,=7 × 10,5 at 8 GHz. Two weight percent LMZBS mixed with LMS sintered at 875°C/2 h had ,r=5.9 and tan ,=6.7 × 10,5 at 8 GHz. [source] Low-Loss Microwave Dielectrics in the (Mg1,xZnx)2TiO4 CeramicsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 10 2008Cheng-Liang Huang The microwave dielectric properties and the microstructures of (Mg1,xZnx)2TiO4 ceramics prepared by the conventional solid-state route were investigated. Lattice parameters were also measured for samples with different x. As x increased from 0 to 0.05, the Q×f of the specimen can be promoted from 150 000 GHz to a maximum 275 300 GHz. It also showed a remarkable lowering in the sintering temperature (,100°C). Ilmenite-structured (Mg0.95Zn0.05)TiO3 was detected as a second phase. The coexistence of the second phase, however, is not harmful to the dielectric properties of the specimen because it possesses compatible ones. A fine combination of microwave dielectric properties (,r,15.48, Q×f,275 300 GHz, ,f,,34 ppm/°C) was obtained for (Mg0.95Zn0.05)2TiO4 specimen sintered at 1330°C for 4 h. It is proposed as a very promising dielectric material for low-loss microwave and millimeter wave applications. [source] The assessment of microscopic charging effects induced by focused electron and ion beam irradiation of dielectricsMICROSCOPY RESEARCH AND TECHNIQUE, Issue 3 2007Marion A. Stevens-Kalceff Abstract Energetic beams of electrons and ions are widely used to probe the microscopic properties of materials. Irradiation with charged beams in scanning electron microscopes (SEM) and focused ion beam (FIB) systems may result in the trapping of charge at irradiation induced or pre-existing defects within the implanted microvolume of the dielectric material. The significant perturbing influence on dielectric materials of both electron and (Ga+) ion beam irradiation is assessed using scanning probe microscopy (SPM) techniques. Kelvin Probe Microscopy (KPM) is an advanced SPM technique in which long-range Coulomb forces between a conductive atomic force probe and the silicon dioxide specimen enable the potential at the specimen surface to be characterized with high spatial resolution. KPM reveals characteristic significant localized potentials in both electron and ion implanted dielectrics. The potentials are observed despite charge mitigation strategies including prior coating of the dielectric specimen with a layer of thin grounded conductive material. Both electron- and ion-induced charging effects are influenced by a delicate balance of a number of different dynamic processes including charge-trapping and secondary electron emission. In the case of ion beam induced charging, the additional influence of ion implantation and nonstoichiometric sputtering from compounds is also important. The presence of a localized potential will result in the electromigration of mobile charged defect species within the irradiated volume of the dielectric specimen. This electromigration may result in local modification of the chemical composition of the irradiated dielectric. The implications of charging induced effects must be considered during the microanalysis and processing of dielectric materials using electron and ion beam techniques. Microsc. Res. Tech., 2007. © 2007 Wiley-Liss, Inc. [source] Effective dielectric constant and design of sliced Lüneberg lensMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 10 2007Georgios Zouganelis Abstract In this article, a design of Lüneberg lens with slices made from low loss dielectric material with hemispherical air-holes drilled appropriately on the top and bottom surface of each of them is presented. A formula to estimate the values of radial dependent effective dielectric constant of air-holes dielectric composite material is suggested. The estimated values are compared with the ones calculated from finite difference time domain method electromagnetic simulations of a periodic lattice of spherical and cylindrical air-holes embedded in a dielectric slab using Nicolson,Ross method. Calculation of S-parameters and near field of lens with hemispherical air-holes under an incident plane wave, using estimated effective constants by the suggested formula are compared with ones using precise theoretical values of dielectric constants. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 2332,2337, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22751 [source] Fabrication of carbon nanotube-based field-effect transistors for studies of their memory effectsPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 11 2007M. Y. Zavodchikova Abstract Carbon nanotube-based field-effect transistors (CNTFETs) have been fabricated using nanometer thin dielectric material as the gate insulator film. The demonstrated fabrication technique is highly suitable for preparing devices with low contact resistances between the electrodes and the carbon nanotube, down to 14 k,. Electronic transport measurements of the fabricated devices have been conducted on more than 70 FETs. Hysteretic behavior in the transfer characteristics of some CNTFETs was observed. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Atomic Layer Deposition of High- k Oxides of the Group 4 Metals for Memory Applications,ADVANCED ENGINEERING MATERIALS, Issue 4 2009Jaakko Niinistö Abstract This paper reviews several high-k ALD processes potentially applicable to the production of capacitors, concentrating on very recent developments. A list of the dielectric materials under investigation consists of the oxides of several metals, including the Group 4 (Ti, Zr, Hf) elements. The binary oxides of Group 4 metals, as well as their mixtures with other oxides, doped hosts, or multi-layers in the form of nano-laminates are of interest.Several examples of our recent results are shown, including possible ALD routes to materials not previously grown, as well as advances in process development. [source] Perovskite BaHfO3 Dielectric Layers for Dynamic Random Access Memory Storage Capacitor Applications,ADVANCED ENGINEERING MATERIALS, Issue 4 2009Grzegorz Lupina Very thin layers of dielectric materials are of high importance for many advanced microelectronic applications. In this work, properties of very thin (<50,nm) BaHfO3 layers prepared using molecular beam deposition and chemical vapor deposition are examined. We conclude that polycrystalline cubic BaHfO3 films appear to be promising candidates for future memory capacitor applications. [source] High Quality Factor Metallodielectric Hybrid Plasmonic,Photonic CrystalsADVANCED FUNCTIONAL MATERIALS, Issue 12 2010Xindi Yu Abstract A 2D polystyrene colloidal crystal self-assembled on a flat gold surface supports multiple photonic and plasmonic propagating resonance modes. For both classes of modes, the quality factors can exceed 100, higher than the quality factor of surface plasmons (SP) at a polymer,gold interface. The spatial energy distribution of those resonance modes are carefully studied by measuring the optical response of the hybrid plasmonic,photonic crystal after coating with dielectric materials under different coating profiles. Computer simulations with results closely matching those of experiments provide a clear picture of the field distribution of each resonance mode. For the SP modes, there is strong confinement of electromagnetic energy near the metal surface, while for optical modes, the field is confined inside the spherical particles, far away from the metal. Coating of dielectric material on the crystal results in a large shift in optical features. A surface sensor based on the hybrid plasmonic,photonic crystal is proposed, and it is shown to have atomic layer sensitivity. An example of ethanol vapor sensing based on physisorption of ethanol onto the sensor surface is demonstrated. [source] Engineering Disorder in Superdiffusive Lévy GlassesADVANCED FUNCTIONAL MATERIALS, Issue 6 2010Jacopo Bertolotti Abstract Disorder is known to have a substantial impact on light transport in optical materials. In particular, when properly tuned, disorder can unveil optical properties that common, periodically patterned materials do not possess. In this paper, a method to realize disordered dielectric materials dubbed Lévy glasses, in which light transport is superdiffusive, is presented. The degree of superdiffusion is set by engineering the spatial inhomogeneity of the scatterer density in the material. A model that relates the microscopic parameters to the macroscopic transport properties of Lévy glasses is given and the signature of superdiffusion on the transmission profile in a slab configuration is shown experimentally. [source] Electrocaloric Materials for Solid-State RefrigerationADVANCED MATERIALS, Issue 19 2009Sheng-Guo Lu Abstract The electrocaloric effect (ECE) in dielectric materials has great potential in realizing solid-state cooling devices with compact size and high efficiency, which are highly desirable for a broad range of applications. This paper presents the general considerations for dielectric materials to achieve large ECE and reviews the experimental efforts investigating ECE in various polar dielectrics. For practical cooling devices, an ECE material must possess a large isothermal entropy change besides a large adiabatic temperature change. We show that polar dielectrics operated at temperatures near order,disorder transition have potential to achieve large ECE due to the possibility of large change in polarization induced by electric field and large entropy change associated with the polarization change. We further show that indeed the ferroelectric poly(vinylidene fluoride,trifluoroethylene)-based polymers display a large ECE, i.e., an isothermal entropy change of more than 55,J,(kgK),1 and an adiabatic temperature change of more than 12,°C, at temperatures above the order,disorder transition. [source] Molecular Self-Assembled Monolayers and Multilayers for Organic and Unconventional Inorganic Thin-Film Transistor ApplicationsADVANCED MATERIALS, Issue 14-15 2009Sara A. DiBenedetto Abstract Principal goals in organic thin-film transistor (OTFT) gate dielectric research include achieving: (i) low gate leakage currents and good chemical/thermal stability, (ii) minimized interface trap state densities to maximize charge transport efficiency, (iii) compatibility with both p- and n- channel organic semiconductors, (iv) enhanced capacitance to lower OTFT operating voltages, and (v) efficient fabrication via solution-phase processing methods. In this Review, we focus on a prominent class of alternative gate dielectric materials: self-assembled monolayers (SAMs) and multilayers (SAMTs) of organic molecules having good insulating properties and large capacitance values, requisite properties for addressing these challenges. We first describe the formation and properties of SAMs on various surfaces (metals and oxides), followed by a discussion of fundamental factors governing charge transport through SAMs. The last section focuses on the roles that SAMs and SAMTs play in OTFTs, such as surface treatments, gate dielectrics, and finally as the semiconductor layer in ultra-thin OTFTs. [source] Simulation of general linear dielectric properties in TLMINTERNATIONAL JOURNAL OF NUMERICAL MODELLING: ELECTRONIC NETWORKS, DEVICES AND FIELDS, Issue 5-6 2002John Paul Abstract The simulation of linear dispersive dielectric materials in time-domain TLM requires the inclusion of frequency-dependent material properties in the scattering process. For media having frequency dependencies described by a single pole or a pair of complex poles, for example Debye, Drude or Lorentz, it is straightforward to develop individual algorithms on a case-by-case basis. However, this approach lacks generality and when applied to the modelling of media displaying more complicated frequency dependencies, somewhat lengthy calculations need to be evaluated each time a new material is required. To address this difficulty, this paper describes methods for obtaining the iteration algorithm for general linear isotropic dielectric media. The results obtained using different ,,-transform methods are compared and an example of a frequency-dependent structure is simulated. Copyright © 2002 John Wiley & Sons, Ltd. [source] Support vector design of the microstrip linesINTERNATIONAL JOURNAL OF RF AND MICROWAVE COMPUTER-AIDED ENGINEERING, Issue 4 2008Filiz Güne Abstract In this article, the support vector regression is adapted to the analysis and synthesis of microstrip lines on all isotropic/anisotropic dielectric materials, which is a novel technique based on the rigorous mathematical fundamentals and the most competitive technique to the popular artificial neural networks (ANN). In this design process, accuracy, computational efficiency and number of support vectors are investigated in detail and the support vector regression performance is compared with an ANN performance. It can be concluded that the ANN may be replaced by the support vector machines in the regression applications because of its higher approximation capability and much faster convergence rate with the sparse solution technique. Synthesis is achieved by utilizing the analysis black-box bidirectionally by reverse training. Furthermore, by using the adaptive step size, a much faster convergence rate is obtained in the reverse training. Besides, design of microstrip lines on the most commonly used isotropic/anisotropic dielectric materials are given as the worked examples. © 2008 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2008. [source] Manipulation of image intensity distribution at 7.0 T: Passive RF shimming and focusing with dielectric materials,JOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 1 2006Qing X. Yang Abstract Purpose To investigate the effects of high dielectric material padding on RF field distribution in the human head at 7.0 T, and demonstrate the feasibility and effectiveness of RF passive shimming and focusing with such an approach. Materials and Methods The intensity distribution changes of gradient-recalled-echo (GRE) and spin-echo (SE) images of a human head acquired with water pads (dielectric constant = 78) placed in specified configurations around the head at 7.0 T were evaluated and compared with computer simulation results using the finite difference time domain (FDTD) method. The contributions to the B1 field distribution change from the displacement current and conductive current of a given configuration of dielectric padding were determined with computer simulations. Results MR image intensity distribution in the human head with an RF coil at 7.0 T can be changed drastically by placing water pads around the head. Computer simulations reveal that the high permittivity of water pads results in a strong displacement current that enhances image intensity in the nearby region and alters the intensity distribution of the entire brain. Conclusion The image intensity distribution in the human head at ultra-high field strengths can be effectively manipulated with high permittivity padding. Utilizing this effect, the B1 field inside the human head of a given RF coil can be adjusted to reduce the B1 field inhomogeneity artifact associated with the wave behavior (RF passive shimming) or to locally enhance the signal-to-noise ratio (SNR) in targeted regions of interest (ROIs; RF field focusing). J. Magn. Reson. Imaging 2006. © 2006 Wiley-Liss, Inc. [source] Central brightening due to constructive interference with, without, and despite dielectric resonance,JOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 2 2005Christopher M. Collins PhD Abstract Purpose To aid in discussion about the mechanism for central brightening in high field magnetic resonance imaging (MRI), especially regarding the appropriateness of using the term dielectric resonance to describe the central brightening seen in images of the human head. Materials and Methods We present both numerical calculations and experimental images at 3 T of a 35-cm-diameter spherical phantom of varying salinity both with one surface coil and with two surface coils on opposite sides, and further numerical calculations at frequencies corresponding to dielectric resonances for the sphere. Results With two strategically placed surface coils it is possible to create central brightening even when one coil alone excites an image intensity pattern either bright on one side only or bright on both sides with central darkening. This central brightening can be created with strategic coil placement even when the resonant pattern would favor central darkening. Results in a conductive sample show that central brightening can similarly be achieved in weakly conductive dielectric materials where any true resonances would be heavily damped, such as in human tissues. Conclusion Constructive interference and wavelength effects are likely bigger contributors to central brightening in MR images of weakly conductive biological samples than is true dielectric resonance. J. Magn. Reson. Imaging 2005;21:192,196. © 2005 Wiley-Liss, Inc. [source] Effect of sample size on microwave power absorption within dielectric materials: 2D numerical results vs. closed-form expressionsAICHE JOURNAL, Issue 6 2009S. Curet Abstract This study deals with the analytical and numerical solutions of the heat source term because of microwave heating for high and low dielectric materials in 1D and 2D configurations. The authors compare closed-form expressions dedicated to microwave power calculation to numerical simulations. A comprehensive and accurate analysis of the microwave power reflected from the surface of the sample is also carried out during microwave heating. The influence of sample length is studied using an original numerical procedure. The study highlights that 1D closed-form expressions can be extended to 2D configurations in the case of sufficiently high dielectric properties. Examples of heating rate during 2D microwave heating in TE10 mode are finally presented. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source] Structural, Dielectric, and Thermal Properties of Strontium Barium Niobate-Doped Fused Silica NanocompositesJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 8 2003Sheng-Guo Lu Ferroelectric strontium barium niobate (SBN)-doped Na2O,B2O3,SiO2 (NBS) glass nanocomposites were prepared by dispersing sol,gel-derived SBN powder into fused NBS glass. Their structures were characterized by X-ray diffractometry and Raman spectroscopy. The dielectric constants were measured as functions of frequency and temperature using an impedance analyzer. The ferroelectric-to-paraelectric-phase transition was studied by differential scanning calorimetric analysis. Our results revealed that the embedded SBN has lower phase transition temperature and phase transition heat than those of SBN bulk materials. Their activation energy, however, is larger than that of SBN ultra-fine powders. Pure tetragonal-phase SBN nanocomposites can be obtained at annealing temperatures of 750°,1000°C. Their dielectric constants are ,32,46 and ,20,25 at low frequencies and radio frequencies, respectively, and the loss tangent is <0.1 at room temperature in the radio frequencies range. Our studies suggested that additional reduction in the loss properties must be made before these systems can be considered for application as microwave dielectric materials. [source] The assessment of microscopic charging effects induced by focused electron and ion beam irradiation of dielectricsMICROSCOPY RESEARCH AND TECHNIQUE, Issue 3 2007Marion A. Stevens-Kalceff Abstract Energetic beams of electrons and ions are widely used to probe the microscopic properties of materials. Irradiation with charged beams in scanning electron microscopes (SEM) and focused ion beam (FIB) systems may result in the trapping of charge at irradiation induced or pre-existing defects within the implanted microvolume of the dielectric material. The significant perturbing influence on dielectric materials of both electron and (Ga+) ion beam irradiation is assessed using scanning probe microscopy (SPM) techniques. Kelvin Probe Microscopy (KPM) is an advanced SPM technique in which long-range Coulomb forces between a conductive atomic force probe and the silicon dioxide specimen enable the potential at the specimen surface to be characterized with high spatial resolution. KPM reveals characteristic significant localized potentials in both electron and ion implanted dielectrics. The potentials are observed despite charge mitigation strategies including prior coating of the dielectric specimen with a layer of thin grounded conductive material. Both electron- and ion-induced charging effects are influenced by a delicate balance of a number of different dynamic processes including charge-trapping and secondary electron emission. In the case of ion beam induced charging, the additional influence of ion implantation and nonstoichiometric sputtering from compounds is also important. The presence of a localized potential will result in the electromigration of mobile charged defect species within the irradiated volume of the dielectric specimen. This electromigration may result in local modification of the chemical composition of the irradiated dielectric. The implications of charging induced effects must be considered during the microanalysis and processing of dielectric materials using electron and ion beam techniques. Microsc. Res. Tech., 2007. © 2007 Wiley-Liss, Inc. [source] Characterization of spin crossover crystal surface by AFMPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 5 2010C. Chong Abstract Imaging nano-domains in spin crossover (SCO) compounds remains so far an unreached goal. We report on the first AFM tapping-mode investigation of SCO single crystals, performed at room temperature with the well known mononuclear compound [Fe(ptz)6](BF4)2 (ptz,=,1-propyl-tetrazole) and the trinuclear supramolecular compound [Fe3(hyetrz)6(H2O)6](CF3SO3)6 (hyetrz,=,4-(2,-hydroxyethyl)-1,2,4-triazole) which shows a gradual spin conversion centred at room temperature. The natural surface of the former crystal revealed a volatile coating of the scanned area attributed to the transport of adsorbed water under the effect of interaction with the AFM tip. The second one showed astonishing leopard-skin patterns assigned to the effect of atmospheric humidity on this hygroscopic compound. Their origin is discussed. We suggest the use of fluid coating layers as a general method for revealing the nano-patterning of physical properties (e.g. like-spin domains) at the surface of dielectric materials. AFM-tapping images of [Fe3(hyetrz)6(H2O)6](CF3SO3)6 at room temperature and ambient atmosphere. [source] Temperature and frequency investigations of the electrical parameters in the TGS ferroelectric transitionPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 5 2010Ciceron Berbecaru Abstract Pure and D: alanina doped triglycin sulphate (TGS) crystals were grown from aqueous solutions. Fresh cleaved, polished and silver paste painted samples were temperature and frequency investigated. Pure crystals show nonreproducible values of the permittivity and dielectric loss crossing up and down the Curie point. More stable and much lower values of the permittivity and dielectric loss could be noticed for D: alanina doped crystals. Permittivity and loss values show different frequencies behavior related to polar or nonpolar state of crystals. Frequency dependence of permittivity and loss behavior could be related to the general picture of relaxation of different polarization mechanisms and their contributions to permittivity and loss values for dielectric materials. Much smaller and stable values of permittivity and loss, vs. temperature and frequency, were found for doped crystals. Experimental results point out for a more stable structure with dipoles mobility decreased of doped vs. pure TGS crystals. Thus, higher figure of merit of doped TGS crystals point to a major advantage for technical applications (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Omni-directional gap of 1-D photonic crystals based on porous silicon with a Gaussian profile refractive indexPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 2 2007J. Arriaga Abstract Using the transfer matrix method we calculate the omni-directional band gap of a 1-D photonic crystal consisting of alternating layers of two dielectric materials A and B with refractive index nA and nB, respectively. The refractive index of layer A is constant and the refractive index of layer B varies according to the envelope of a Gaussian function. We find that under certain circumstances it is possible to obtain 100% reflectivity for both polarizations and any value of the incident angle of the electromagnetic waves. Although the structure considered does not posses a higher omni-directional band gap than the periodic sequence of low and high constant refractive indexes, it can be used to produce a new type of omni-directional mirrors without abrupt interfaces. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Application of the RASCAN holographic radar to cultural heritage inspectionsARCHAEOLOGICAL PROSPECTION, Issue 3 2009L. Capineri Abstract This paper explores the application of the RASCAN holographic radar for non-destructive subsurface imaging of works of art and architecture. This radar provides high-resolution plan-view images of the shallow subsurface in dielectric materials. The radar is particularly sensitive to small metallic targets, but also to variations in moisture content. Originally developed for detection of hidden bugging devices, sounding of building construction details, and detection of landmines, here the utility of the RASCAN radar for art and architectural preservation studies is demonstrated by several bench-top experiments on stone and wood items with different subsurface defects and features, as well as actual field tests on a decorative marble medallion in the floor of the Temple of San Biagio in Montepulciano, Italy, and Frescoes in the Church of San Rocco in Cornaredo, Italy. Historical research indicates that the medallion in San Biagio was laid circa 1590 during the funeral ceremony of a Prelatio of the family Casata Cervini. The actual burial place of the Prelatio is not recorded, but a radar scan of the medallion, and follow-up scans of a bench-top model suggest the possibility of a cavity that could contain remains or relics. In San Rocco, small delaminations were detected behind the frescos. Copyright © 2009 John Wiley & Sons, Ltd. [source] | ||||||||||||||||||||||