Core-current-enhanced domain-wall pinning in nanocrystalline Fe/sub 73.5/Cu/sub 1/Nb/sub 3/Si/sub 15.5/B/sub 7/ ribbon

We have studied the influence of surface fields H/sub p/ (generated by either direct or alternating core current) on soft magnetic properties of amorphous and nanocrystalline Fe/sub 73.5/Cu/sub 1/Nb/sub 3/Si/sub 15.5/B/sub 7/ ribbon. While in an amorphous ribbon the coercive field H/sub c/ decreases with H/sub p/, in the same optimally annealed ribbon (H/sub c/=1.3 A/m, M/sub m//spl ap/M/sub s/) H/sub c/ increases with H/sub p/ for all the explored types of H/sub p/ (static and dynamic with different phases with respect to that of the magnetizing field H). The unexpected increase of H/sub c/ in nanocrystalline ribbon is associated with the influence of H/sub p/ on the surface and main (inner) domain structure. Here, we develop a model that takes into account this influence and explains the experimental results.     

Optical and electrical H/sub 2/- and NO/sub 2/-sensing properties of Au/In/sub x/O/sub y/N/sub z/ films

In this paper, we describe the optical and electrical gas-sensing properties of In/sub x/O/sub y/N/sub z/ films with an ultrathin gold promoter overlayer. We have fabricated In/sub x/O/sub y/N/sub z/ films with a nanocrystalline porous structure by RF-sputtering in Ar/N/sub 2/ followed by an annealing process. Gold particles with 20-30-nm diameter have been formed on top of the In/sub x/O/sub y/N/sub z/ films by dc sputtering and an annealing process. We have investigated the optical H/sub 2/and NO/sub 2/-sensing properties (change of absorbance) and also the electrical sensing effect (change of electrical resistance) for these two gases. A combined optical/electrical sensor for H/sub 2//NO/sub 2/ is proposed.     

X-ray Topography of Piezoelectric La/sub 3/Ta/sub 0.5/Ga/sub 5.5/O/sub 14/ Crystal Grown by Czochralski Method

We performed synchrotron X-ray topography on a La₃Ta_0.5Ga_5.5O₁₄ (LTG) crystal grown by the Czochralski method. Since a synchrotron X-ray source can provide high-energy X-rays, one can detect bulk structures by X-ray topography. LTG is one of the most attractive piezoelectric crystals along with La₃Ga₅SiO₁₄ (LGS) because of its excellent acoustic properties (temperature compensation of acoustic losses). Since LTG single crystals can be grown from a stoichiometric melt, it was expected that single crystals with better quality than the LGS crystal, which cannot be grown from a stoichiometric system but only from a congruent melt, can be obtained. However, 60 keV X-ray topography revealed that the LTG crystal quality was not as high as the LGS crystal quality. The crystal quality of the central region was lower than that of the surrounding region.     

Evolution of nanodomains in the uniaxial relaxor Sr/sub 0.61/Ba/sub 0.39/Nb/sub 2/O/sub 6/:Ce

The evolution of the nanodomain pattern of the uniaxial relaxor ferroelectric strontium barium niobate doped with cerium was studied by piezoresponse force microscopy (PFM). The fractal-like nanodomains observed at room temperature decay on heating. At temperatures up to about 15 K above the Curie temperature, T_c = 320 K, areas of correlated polarization are still visible. On cooling from the paraelectric state to below T_c, a slow isothermal growth of nanodomain was found. The mean domain size increases according to a logarithmic law as predicted for the three-dimensional random field Ising model     

The Dielectric Properties of Ba/sub 0.6S/r/sub 0.4/Cr/sub x/Ti/sub 1-x/O/sub 3/Thin Films Prepared by Pulsed Laser Deposition

Ba_0.6Sr_0.4Cr_xTi_1-xO₃ (BSCT) films were prepared by pulsed laser deposition with the value of x varying from 0 mol% to 2.0 mol%. X-ray diffraction analysis detected an increase in the lattice parameters, which could be due to the characteristics of the growth process. Dielectric properties and tunability of the BSCT films were measured. The dissipation factors of the films decreased with increasing Cr-concentration. The highest figure of merit (FOM) value of 33.3 was obtained in 1.0 mol%-doped BSCT film. As a result, the effect of Cr doping is positive.     

Generation-recombination noise in pseudomorphic Modulation-doped Al/sub 0.2/Ga/sub 0.8/As/In/sub 0.1/Ga/sub 0.9/As/GaAs micro-Hall devices

The noise spectrum in micro-Hall devices based on pseudomorphic Al/sub 0.2/Ga/sub 0.8/As/In/sub 0.1/Ga/sub 0.9/As/GaAs modulation-doped heterostructures was measured between 4 Hz and 65 kHz, allowing components due to thermal, 1/f, and generation-recombination to be characterized. Applying deep level noise spectroscopy (DLNS) in the temperature range of 77-300 K to analyze the generation-recombination part of the spectrum, two electron traps contributing to noise density were identified. An emission activation energy of 474 meV was measured for the dominant trap, corresponding to the well-known DX center originating from the AlGaAs barrier. The other deep level, with an emission activation energy of 242 meV, is probably related to defects in the InGaAs layer. The structures under investigation resulted in high-performance micro-Hall devices: a supply-current-related sensitivity up to 725 V/spl middot/A/sup -1//spl middot/T/sup -1/ at 77 K independent of bias current, a signal-to-noise sensitivity of 155 dB/spl middot/T/sup -1/ and a detection limit of 340 pT/spl middot/mm/spl middot/Hz/sup -1/2/ at 77 K were measured.     

Phase-transition temperatures and piezoelectric properties of (Bi/sub 1/2/Li/sub 1/2/)TiO/sub 3/-(Bi/sub 1/2/K/sub 1/2/)TiO/sub 3/ lead-free ferroelectric ceramics

The phase-transition temperatures and piezoelectric properties of x(Bi_1/2Na_1/2)TiO_3-y(Bi_1/2Li_1/2)TiO_3-z(Bi_1/2K_1/2)TiO₃ [x + y + z = 1] (abbreviated as BNLKT100y-100z) ceramics were investigated. These ceramics were prepared using a conventional ceramic fabrication process. The phase-transition temperatures such as depolarization temperatures T_d, rhombohedral-tetragonal phase transition temperature T_R-T, and dielectric-maximum temperature T_m were determined using electrical measurements such as dielectric and piezoelectric properties. The X-ray powder diffraction patterns of BNLKT100y-100z show the morphotropic phase boundary (MPB) between rhombohedral and tetragonal at approximately z = 0.20, and the piezoelectric properties show the maximum at the MPB. The electromechanical coupling factor &33, piezoelectric constant d₃₃ and T_d of BNLKT4-20 and BNLKT8-20 were 0.603, 176 pC/N, and 171degC, and 0.590, 190 pC/N, and 115degC, respectively. In addition, the relationship between d₃₃ and T_d of tetragonal side and rhombohedral side for BNLKT4-100z and BNLKT8-100z were presented. Considering both high T_d and high d₃₃, the tetragonal side of BNLKT4-100z is thought to be the superior composition. The d₃₃ and T_d of BNLKT4-28 were 135 pC/N and 218degC, respectively. Moreover, this study revealed that the variation of Td is related to the variation of lattice distortion such as rhombohedrality 90-alpha and tetragonality c/a.     

O/sub 2/ sensing properties of Zn- and Au-doped Fe/sub 2/O/sub 3/ thin films

Zn- and Au-doped iron oxide thin films have been prepared by liquid phase deposition. These films have been characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Their performance as oxygen gas sensors has been measured. It has been shown that both the Zn and Au dopants increase the oxygen response of the pure iron oxide films. The XRD and SEM results show that Zn changes both the microstructure and the particles size of the sensing layer through the formation of a solid solution with iron oxide. However, the strong increase in sensitivity to oxygen of the Au-doped Fe/sub 2/O/sub 3/ film has been related to the more favorable chemisorption of oxygen on the small gold particles at the interface with the semiconductor oxide. The results show that Au-doped iron oxide sensors are most promising for oxygen gas sensing.     

Temperature stability of magnetic field-induced strain and field-controlled shape memory effect on Ni/sub 52/Mn/sub 16.4/Fe/sub 8/Ga/sub 23.6/ single crystals

The temperature dependence of the magnetic field-induced strain (MFIS) and the field-controlled shape memory effect in Ni/sub 52/Mn/sub 16.4/Fe/sub 8/Ga/sub 23.6/ single crystals were investigated by measuring the MFIS and measuring the magnetic field-enhanced transformation strain with a field bias applied in the [001] and [010] directions of the parent phase, respectively. The results show that such material combined with the martensitic transformation can product large field-enhanced transformation strain and large MFIS. The strain accompanying the martensitic transformation is -1.61% in zero field and can be enhanced to -3.30% by a field of 960 kA/m. A MFIS of 1.04% has been induced along [001] in unstressed crystals with saturated magnetic field of 600 kA/m applied along the same direction at near martensitic transformation temperature. It was found that the MFIS is almost temperature independent; the maximum decrease of the saturated MFIS is less than 10%, from 265 K to 100 K. This well-behaved temperature response makes this alloy particularly valuable for industrial and military smart actuators and transducers. Furthermore, it was found that the direction in which the MFIS has the largest value is always the [001], namely, the growth direction of the crystals.     

KTa/sub 0.6/Nb/sub 0.4/O/sub 3/ ferroelectric thin film behavior at microwave frequencies for tunable applications

In this study about the relationships between structural and microwave electrical properties of KTa_1-xNb_xO₃ (KTN) ferroelectric materials, a KTN thin film was deposited on different substrates to investigate how KTN growth affects the microwave behavior. Interdigital capacitors and stubs were made on these films through a simple engraving process. Microwave measurements under a static electric field showed the importance of the substrate on the circuit behavior and, notably, on the tuning factor     

High tunnel magnetoresistance in epitaxial Co/sub 2/Cr/sub 0.6/Fe/sub 0.4/Al/MgO/CoFe tunnel junctions

We have fabricated fully epitaxial magnetic tunnel junctions (MTJs) using a Co-based full-Heusler alloy Co/sub 2/Cr/sub 0.6/Fe/sub 0.4/Al (CCFA) thin film and an MgO tunnel barrier. The CCFA thin film for the lower ferromagnetic electrode was deposited by magnetron sputtering on an MgO-buffered MgO single-crystal substrate, and the MgO tunnel barrier was formed by electron beam evaporation. The microfabricated epitaxial CCFA/MgO/CoFe MTJs showed high tunnel magnetoresistance ratios of 42% at room temperature and 74% at 55K.     

Preparation of ferroelectric Ba(Ti/sub 0.85/Sn/sub 0.15/)O/sub 3/ thin films by metal-organic decomposition

Ferroelectric Ba(Ti/sub 0.85/Sn/sub 0.15/)O/sub 3/ (BTS/sub 15/) thin film is newly prepared on the Pt/Ti/SiO/sub 2//Si substrate by metal-organic decomposition. The firing condition is determined by thermogravimetric and differential thermal analysis. The BTS/sub 15/ thin film with a flat surface and uniform thickness is obtained by spin coating in N/sub 2/ atmosphere that avoids moisture. The BTS/sub 15/ film has a perovskite phase and a preferential [110] texture. It is also found that the crystalline structure is cubic at 24/spl deg/C with a lattice constant of 4.01 /spl Aring/, and a grain size of about 30 nm was estimated by Scherrer equation and SEM image. From P-E hysteresis loop at 20/spl deg/C, the polarization at E=0 and the electric field at P=0 are found to be 1.07 /spl mu/C/cm/sup 2/ and 24.0 kV/cm, respectively. It is observed that the dielectric constant decreases monotonously from about 830 to 630 with increasing temperature ranging from 20/spl deg/C to 50/spl deg/C. Finally, it is found that the BTS/sub 15/ thin film shows a sufficient ferroelectricity and is an attractive material for functional ferroelectric devices, such as thermal-type infrared sensors.     

Preparation and characterization of yBiGaO/sub 3/-(1-x-y)BiScOs/sub 3-x/PbTiO/sub 3/ piezoelectric ceramics

The ternary system of j/BiGaO₃-(1-x-y) BiScO₃-xPbTiO₃ (BGS-PT) ceramics was prepared by using conventional mixing oxide processing. X-ray diffraction analysis revealed that the BGS-PT ceramics showed the perovskite structure. The Curie temperature (T_C) of BGS-PT ceramics was found to increase with increasing BiGaO₃ content. However, a larger BiGaO₃ content led to sharply decreased piezoelectric properties, and the secondary phase was formed in the BGS-PT system. BGS-PT ceramics with x = 0.56, y = 0.19 showed a high Curie temperature T_C and a large piezoelectric constant d₃₃ of 501degC and 152 pC/N, respectively. The high T_C of BGS-PT ceramics with usable piezoelectric properties suggests future high-temperature applications.     

Comparison of Fe/Al/sub 2/O/sub 3/ and Fe, Co/Al/sub 2/O/sub 3/ catalysts used for production of carbon nanotubes from acetylene by CCVD

Characterization of iron containing alumina supported catalysts was performed by transmission electron microcopy (TEM), Mo/spl uml/ssbauer, and XPS spectroscopy during formation of multiwall carbon nanotubes from acetylene at 1000 K. TEM images showed that carbon fibers (outer diameter is around 20-40 nm) were generated on Fe/Al/sub 2/O/sub 3/ samples while on the bimetallic Fe,Co/Al/sub 2/O/sub 3/ carbon nanotubes with an average diameter of 8-12 nm were formed. XPS spectra revealed that Fe-Co alloy formed during the interaction of Fe,Co/Al/sub 2/O/sub 3/ and acetylene at 1000 K. The formation of the bimetallic alloy was proven by Mo/spl uml/ssbauer spectroscopy as well.     

Recent determinations of R/sub H/ in terms of Omega /sub 69-BI/

A system based on a cryogenic current comparator is used to measure the quantized Hall resistance R/sub H/ in terms of Omega /sub 69-BI/, the Bureau International des Poids et Mesures (BIPM) representation of the ohm, with an uncertainty of 1.5*10/sup -8/. This measurement system and the former potentiometric one are in good agreement within their combined uncertainties (5.1*10/sup -8/).<>     

Mg/sub x/Zn/sub 1-x/O: a new piezoelectric material

Piezoelectric ZnO thin films have been successfully used for multilayer surface acoustic wave (SAW) and bulk acoustic wave (BAW) devices. Magnesium zinc oxide (Mg/sub x/Zn/sub 1-x/O) is a new piezoelectric material, which is formed by alloying ZnO and MgO. Mg/sub x/Zn/sub 1-x/O allows for flexibility in thin film SAW device design, as its piezoelectric properties can be tailored by controlling the Mg composition, as well as by using Mg/sub x/Zn/sub 1-x/O/ZnO multilayer structures. We report the metal-organic chemical vapor deposition (MOCVD) growth, structural characterization and SAW evaluation of piezoelectric Mg/sub x/Zn/sub 1-x/O (x<0.35) thin films grown on (011~2) r-plane sapphire substrates. The primary axis of symmetry, the c-axis, lies on the Mg/sub x/Zn/sub 1-x/O growth plane, resulting in the in-plane anisotropy of piezoelectric properties. SAW test devices for Rayleigh and Love wave modes, propagating parallel and perpendicular to the c-axis, were designed and fabricated. Their SAW properties, including velocity dispersion and piezoelectric coupling, were characterized. It has been found that the acoustic velocity increases, whereas the piezoelectric coupling decreases with increasing Mg composition in piezoelectric Mg/sub x/Zn/sub 1-x/O films.     

Fabrication and Optical Properties of Pb(Mg/sub 1/3/Nb/sub 2/3/)O/sub 3/-PbTiO/sub 3/Thin Films on Si Substrates Using the PLD Method

Epitaxial 0.67Pb(Mg_1/3Nb_2/3)O₃-0.33PbTiO₃ (PMN-PT) thin films with electro-optic effects were fabricated on (La_0.5Sr_0.5)CoO₃(LSCO)/CeO₂/YSZ-buffered Si(001) substrates using double-pulse excitation pulsed laser deposition (PLD) method with a mask placed between the target and the substrate. Epitaxial growth of PMN-PT thin films was undertaken using the two-step growth method of PMN-PT film. The PMN-PT seed layer was deposited at 500degC on the LSCO/CeO₂/YSZ/Si, which temperature was the same as that used for LSCO deposition. The PMN-PT thin films were deposited on the PMN-PT seed layer at 600degC, which enables growth of high-crystallinity PMN-PT films with smooth surfaces. We obtained optimum fabrication conditions of PMN-PT film with micrometer-order thickness. Resultant films showed high crystallinity with full width at half maximum (FWHM)=0.73 deg and 1.6 mum thickness. Electro-optic properties and the refractive index value were measured at 633 nm wavelength using the prism coupling method. The obtained refractive index was 2.59. The electro-optic coefficients r₁₃ and r₃₃ were determined by applying the electrical field between a semitransparent, thin top electrode of Pt and a bottom LSCO electrode. The electro-optic coefficient was r₁₃=17 pm/V at transverse electric field (TE) mode and r₃₃=55 pm/V at transverse magnetic field (TM) mode.     

Fabrication of Lead-Free Piezoelectric (Na/sub 0.5/K/sub 0.5/)NbO/sub 3/Ceramics by a Modified Solid-State Reaction Method

Sodium potassium niobate, (Na_0.5K_0.5)NbO₃, fine powder has been successfully synthesized at the low temperature of 550degC through a modified solid-state reaction method, in which urea [CO(NH₂)₂] plays an important role. High-density (Na_0.5K_0.5)NbO₃ ceramics could be obtained by conventional sintering of the synthesized (Na_0.5K_0.5)NbO₃ fine powder with the addition of 0.03 mol% Co₃O₄ as a sintering additive. The crystal structure, microstructure, and dielectric and piezoelectric properties were characterized. The (Na_0.5K_0.5)NbO₃ ceramic showed a comparatively saturated P-E hysteresis loop. The (Na_0.5K_0.5)NbO₃ ceramic also displayed piezoelectricity with a piezoelectric constant d₃₃ of 126 pC/N and a planar electromechanical coupling factor k_p of 33%.     

CO-sensing properties of In/sub 2/O/sub 3/-doped SnO/sub 2/ thick-film sensors: effect of doping concentration and grain size

In/sub 2/O/sub 3/-doped SnO/sub 2/ nanoparticles were prepared using sol-gel technique from 0.1-M solutions of both stannic chloride (SnCl/sub 4/ 5H/sub 2/O) and indium nitrate. The doping concentration was varied from 7.718/spl times/10/sup -5/ to 3.859/spl times/10/sup -4/ moles. The average particle size, as measured from XRD, SEM, and TEM analyses, varies from 34-130 nm as a result of powder calcination at different temperatures ranging from 300/spl deg/C-900/spl deg/C. Thick-film samples with a thickness of /spl sim/15 /spl mu/m, were tested for low concentration (15-1000 ppm) of CO in air ambient. The optimal temperature for CO sensing is found to be 220/spl deg/C-240/spl deg/C. A blue shift in the sensing temperature and increase in sensitivity factor (S/sub f/) is observed with increasing doping concentration of indium oxide. Maximum sensitivity factor of /spl sim/5 is found for the highest doping concentration (3.859/spl times/10/sup -4/ moles) at 1000 ppm of CO concentration. The morphological and elemental studies of the film are carried out using SEM, TEM, XRD, and EDAX techniques. The results are discussed based on elemental analyses and available theories.     

A Pt/Ga/sub 2/O/sub 3/-ZnO/SiC Schottky diode-based hydrocarbon gas sensor

In this paper, a novel metal-reactive insulator-silicon carbide device with a catalytic layer for hydrocarbon gas-sensing is presented. This structure, employed as a Schottky diode, utilizes sol-gel prepared Ga/sub 2/O/sub 3/-ZnO layer as the reactive insulator. The sensor has been exposed to propene gas, which lowers the barrier height of the diode. The responses were stable and repeatable at operating temperatures between 300 and 600/spl deg/C. The response to propene in different ambients was examined. The effect of diode bias has been investigated by analyzing the sensors response to various propene concentrations when held at constant currents of 2 and 8 mA.