Nm For Samples Research Articles

Surface and Structural Features of Co‐Fe Oxide Nanoparticles Deposited on a Silica Substrate

AbstractMono‐ and dimetallic cobalt‐ and iron oxide nanoparticles deposited on the surface of a silica substrate have been prepared by an impregnation technique. Both the bulk and surface structures of these particles have been characterised by different physical and chemical techniques. The results provided by X‐ray diffraction, Mössbauer and X‐ray photoelectron spectroscopy show the formation of separate Co3O4 and Fe2O3 nanoparticles in oxide samples, but in no case were cobalt–iron mixed oxides detected. Quantitative data also showed that the dispersion degree of cobalt‐ and iron oxides is rather low. It was also observed that pretreatment of the supported metal oxide nanoparticles under a hydrogen atmosphere does not promote the formation of a metal–support interaction, although a cobalt–iron interaction is observed in the dimetallic systems. The diffraction patterns and photoelectron and Mössbauer spectra of these dimetallic samples provide conclusive proof for the formation of both metallic Co0 and iron‐cobalt (Co7Fe3) alloy phases in the hydrogen‐reduced samples. It was also found that the crystallite size of the alloyed Co7Fe3 phase increases with increasing iron content, i.e. 11 and 23 nm for samples containing 1 % and 5 % Fe added to the base Co sample, respectively, while that of Co0 was constant (10 nm). (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

Patterning porous matrices and planar substrates with quantum dots

Silica hydrogels and planar substrates were patterned with CdS nanoparticles using a photolithographic method based on the photo dissociation of thiols and cadmium-thiolate complexes. Silica hydrogels were prepared via a standard base-catalyzed route. The solvent was exchanged with an aqueous solution of CdSO4 and 2-mercaptoethanol, and the samples were then exposed to a focused ultraviolet beam. Planar substrates were patterned by illuminating a precursor solution spin coated on the substrates. CdS nanoparticles formed in the illuminated spots, and had a diameter below about 2 nm. The diameter of the spots illuminated by the UV beam could be varied from a few hundred to a few μm, on both hydrogels and planar substrates. Samples were characterized with transmission electron microscopy, X-ray photoelectron spectroscopy, X-ray diffraction, and optical absorption, photoluminescence and Raman spectroscopies. All these techniques confirmed the chemical identity of the CdS nanoparticles. To investigate the mechanism of nanoparticle formation, we took absorption spectra of the precursor solution as a function of irradiation time. In unirradiated solutions, we noticed a maximum at 250 nm, characteristic of Cd-thiolate complexes. The absorption at 250 nm decreased with increasing irradiation time. A new band appeared at 265 nm for exposures around 5 min, and that band shifted to 290 nm in samples exposed for 10 min. A yellow precipitate formed after about 30 min. XRD showed that the precipitate was cubic CdS, with a mean particle size of 1.4 nm. We attribute formation of CdS to the photodissociation of the thiols and of the Cd-thiolates. UV irradiation of these precursors yields a series of species that can react with Cd2+, such as RS·, S2− and H2S. Small CdS nanoparticles form in the initial stages of illumination, and present absorption bands in the 265–290 nm region. These CdS aggregates grow, coalesce and precipitate for longer irradiation times.

Dilatometry of attrition milled nanocrystalline titanium powders

The sintering behavior of nanosized titanium powders was investigated by dilatometry. The nanosized Ti powders (40 nm) were produced by the attrition milling of micron sized Ti powders (12 μm) in Ar atmosphere. Sintering was carried out in Ar atmosphere in the temperature range of 450–1250 °C for nanosized Ti and 650–1250 °C for micron sized Ti by heating at 10 °C/min, up to the sintering temperature followed by isothermal holding for 1 h. The nanosized Ti powders exhibited a lower sintering onset temperature, larger shrinkage, larger shrinkage rate, and lower activation energy for sintering as compared to the micron sized Ti powders. The sintered micron sized Ti specimens exhibited both intraagglomerate and interagglomerate porosity while the nanosized Ti specimens exhibited well densified agglomerates (almost no interagglomerate porosity) and large intraagglomerate porosity. In nanosized Ti grain growth was found to take place beyond 700 °C and reached a maximum of 66 nm in samples sintered at 1100 °C.

Chain-Folding and Overall Molecular Conformation in a Novel Amphiphilic Starlike Macromolecule

The crystallization and self-assembly behavior of an amphiphilic starlike macromolecule (ASM) with a lipophilic core and four poly(ethylene oxide) (PEO) arms (Mn = 2000 g/mol) were characterized by synchrotron small-angle X-ray scattering (SAXS) and wide-angle X-ray diffraction at different crystallization temperatures (Tc). The overall d-spacing of the alternating amorphous core and crystalline PEO lamellae almost doubled from 11.4 nm for samples quenched into liquid nitrogen to 21.0 nm for Tc = 42 °C, indicating gradual transitions from nearly once-folded to fractionally folded and finally to extended chain crystals with increasing the Tc. On the basis of SAXS, transmission electron microscopy, and computer simulation results, it was suggested that the lamellae contained an interdigitated, single-layered PEO crystal, and an amorphous layer consisted of a double-layered lipophilic core and amorphous PEO. A folded (four PEO arms at one side of the core) rather than an extended (two PEO arms on each side o...

Swift heavy ion induced structural and optical modifications in LiF thin film

Thermally deposited 200 nm polycrystalline films of lithium fluoride (LiF) grown on glass substrates were irradiated with 150 MeV Ag ions at various fluences between 1 × 1011 and 2 × 1013 ions cm−2. The irradiation induced structural and optical modifications were studied using glancing angle x-ray diffraction (GAXRD), optical absorption and photoluminescence (PL) spectroscopy. The GAXRD results show that the films are polycrystalline and the average grain size (estimated from the widths of the GAXRD peak using the Scherrer formula) decreases systematically from 46.3 nm for the pristine sample to 18.3 nm for the sample irradiated at a fluence of 3 × 1012 ions cm−2. Thereafter, it remains constant. This reduction is attributed to strain induced fragmentation of grains. The optical absorption studies show dominant absorption bands of F3 (385 nm) and F2 (445 nm) colour centres. It is observed that the concentration of the colour centres increases with ion fluence and gets saturated at higher fluences. This can be correlated with GAXRD results in the sense that as the density of grain boundaries increases the concentration of colour centres also increases. The variation with fluence in PL intensities of the F2 and colour centres is studied. The intensity of both bands (F2 and ) increases up to a fluence of 1 × 1012 ions cm−2, followed by an exponential decrease, which is due to the increase in the non-radiative transition rate in the presence of defect-rich material.

Fabrication of functional protein–organoclay lamellar nanocomposites by biomolecule-induced assembly of exfoliated aminopropyl-functionalized magnesium phyllosilicates

An aminopropyl-functionalized magnesium phyllosilicate clay was synthesized and used as an exfoliated precursor for the intercalation of myoglobin (Mb), haemoglobin (Hb) or glucose oxidase (GOx). Intercalation was achieved by exfoliation of the as-synthesized organoclay in water followed by room temperature re-assembly of the lamellar phase in the presence of negatively charged protein molecules. X-Ray diffraction data of the resulting nanocomposites showed an expansion of the interlayer d001 spacing from 1.6 nm in the parent organoclay to 4.3 and 6.4 nm for samples prepared with Mb and GOx, respectively, indicating that these biomolecules were successfully incorporated into the gallery regions. In both cases, FTIR and circular dichroism spectroscopies showed that secondary structures of the intercalated biomolecules were preserved. In addition, UV-vis spectroscopy revealed that the redox and CO/O2 binding properties of the intercalated Mb, as well as the enzymatic activity of GOx, were retained in the protein–organoclay nanocomposites. Significantly, the relative catalytic activities of GOx between pH values of 3 to 10, and up to temperatures of 65 °C, were higher in the hybrid nanocomposites compared with the native enzyme in solution. Similar experiments with Hb produced composites consisting of structurally and functionally intact protein molecules immobilized within a disordered matrix of organoclay lamellae.

Novel method of synthesis for double-perovskite Sr2FEMoO6

Polycrystalline double perovskite Sr2FeMoO6 nanosized powders have been prepared using a wet chemical coprecipitation method of synthesis. The products were ignited in nitrogen at different temperatures in order to examine thermal evolution of precursors. Powders that were fired at an above 850°C for two hours have almost a single-phase structure. Some intermediate phases have been found at low temperatures. Powder X-ray diffraction linewith measurements show an average particle size in the order of 40 nm for samples annealed in 600–1000°C. It is suggested that the samples annealed at these temperatures were both simultaneously paramagnetic and ferromagnetic in nature. The advantages of this method are the low temperature involve in the sample preparation and the use of a non-reducing atmosphere.

Physicochemical Characterization and Catalytic Properties of Titania Gel Doped with Lithium and Rubidium

The effect on titania of doping with lithium and rubidium titania gels has been studied in samples prepared with titanium (IV) tetra-n-butoxide co-gelling with the alkaline metal precursors. Titania and doped titania were characterized by X-Ray diffraction, which showed that the catalysts were nanostructured. In samples calcined at 400°C, the crystallite size of the anatase phase was 17 and 14 nm, and 78 and 38 nm for samples calcined at 600°C, for Li/TiO2 and Rb/TiO2, respectively. The specific surface areas of doped samples (400°C) are lower in Li/TiO2 (90 m2/g) than in Rb/TiO2(125 m2/g). Evaluation of their basic properties has been carried out in the acetone condensation reaction. It was found that the activity strongly depended on the Li and Rb ionic radii.

Electric Dichroism Studies on an Aqueous Dispersion of Unilamellar Titanium Oxides: Optical Anisotropy near the Absorption Edge

Electric dichroism measurements have been performed on an aqueous dispersion of unilamellar titanium oxides produced by the exfoliation of the following three kinds of titanium oxides: (A) lepidocrocite-type titanate (Cs0.7Ti1.825□0.175O4), (B) tetratitanate (K2Ti4O9), and (C) pentatitanate (Cs2Ti5O11). The AFM images showed that these exfoliated titanium oxides consisted of flakelike particles with an average diameter ranging from 0.1 to 2 μm. Under the applied voltage pulse [(1−20) × 103 V cm-1], an aqueous dispersion of titanium oxides exhibited orientational dichroism in the UV region with a maximum around 300 nm. From the reduced linear dichroism at complete orientation, the orientation of the effective transition moment (μeff) was determined with respect to the oriented axis of a particle. Here μeff was defined as the vector sum of three orthogonal transition moments of a particle. As a result, an angle (α) between μeff and the oriented axis of a particle was determined to be α = 41.6°, 24.6°, and 23.6° at 300 nm for samples A−C, respectively. The results were compared with the recent theoretical calculations of these samples. Electric dichroism was also measured for an aqueous dispersion containing sample A and a cationic molecule, [Ru(phen)3]2+. From the reduced linear dichroism in the visible region, an [Ru(phen)3]2+ ion was concluded to be adsorbed with its 3-fold symmetry axis nearly perpendicular to a surface.

Highly Efficient Spectral Hole-Burning in Oxygen-Evolving Photosystem II Preparations

quinone (QA) either neutral or photoreduced to QA - via a low-temperature pre-illumination. Remarkably efficient hole-burning is observed within the chlorophyll Qy(0,0) absorption envelope in the wavelength range of 676695 nm. The hole-burning action spectrum of a sample poised in the S1(QA - ) state is dominated by a narrow feature (40 cm -1 ) at 684 nm, where hole depths of 30% are attainable. The photoproduct for spectral holes burnt in this region is distributed across the 50 cm -1 absorption feature centered at 683.5 nm, independent of the excitation wavelength within this band. Saturated hole-burning experiments indicate weak electron phonon coupling near 684 nm but stronger coupling for holes burnt near 690 nm. Selective excitation near 690 nm of samples in the S1(QA) state also results in efficient Q A - formation. Negligible hole-burning activity is observed at higher energies (<676 nm). Holewidths extrapolated to zero fluence and temperature are 2.0 ( 0.5 GHz near 685 nm for PSII samples in the S1(QA - ) state. Holewidths are twice as large and holeburning quantum efficiencies are up to an order of magnitude greater (approaching 1%) for samples in the S1(QA) state. We ascribe hole-burning near 684 nm to slow (40-210 ps) excitation transfer from a CP43 chlorophyll to the PSII reaction center, and we ascribe hole-burning at 690 nm to excitation transfer from a chlorophyll in CP47. The unusually high hole-burning efficiency that we observe is attributed to a mechanism that involves charge separation in the reaction center that follows excitation transfer from these “slow transfer” states in CP43 and CP47. A key result of this work is the observation that selective excitation in the range 685-695 nm leads to efficient charge separation, as indicated by QA - formation. This indicates the presence of (a relatively weak) P680 absorption in a native PSII, extending to low energy and underlying the CP47 chlorophyll trap absorption.

Synthesis and acidic properties of the SiO 2/SnO 2 mixed oxides obtained by the sol–gel process. Evaluation of immobilized copper hexacyanoferrate as an electrochemical probe

SiO 2/SnO 2 mixed oxides were prepared by the sol–gel processing method using SnI 4 as the tin oxide precursor reagent. Solids with Sn compositions (in wt.%) of 4.1, 12.9 and 18.4 and presenting specific surface areas (determined by the BET method) of 492, 658 and 712 m 2 g −1, respectively, were obtained. Transmission microscopic images showed nanosized SnO 2 particles with average dimensions of (5.3±0.5) nm for samples having 12.9 wt.% Sn and (7.0±0.7) nm for samples having 18.4 wt.% Sn. For the sample presenting 4 wt.% of Sn the crystallites were poorly defined, barely being observed. The amorphous SnO 2 particles started to crystallize at different temperatures, i.e., 1273, 1173 and 1073 K for samples with 4.1, 12.9 and 18.4 wt.% of Sn, respectively. The X-ray diffraction patterns showed that only cassiterite crystallites were present in every case and, even at a temperature of 1473 K, the SiO 2 remained as an amorphous matrix. The Lewis and Brønsted acid sites were thermally stable up to a temperature of 523 K for all the compositions, as probed using pyridine molecules. The infrared spectra showed that Si–O–Sn bonds are formed at the interface between SiO 2 and SnO 2 particles. These bonds are the ones mainly responsible for the low mobility of the oxide particles, avoiding crystallization of SnO 2. Copper hexacyanoferrate was prepared in situ on the SiO 2/SnO 2 surface and cyclic voltammetry tests were carried out by sweeping the potential between 0.2 and 1.0 V. The midpoint potential corresponding to the redox process: SnOH 2 +/{KCu[Fe(CN) 6} −⇄SnOH 2 +/{Cu[Fe(CN) 6} −+K ++e − was observed at about 0.7 V. The electrochemical impedance spectroscopic data showed a charge transfer resistance of 17.8 Ω. This low value favors the oxidation–reduction process in the pores of the material.

Spectrophotometric Measurement of Asphaltene Concentration

Typically, when ultraviolet and visible absorbance of asphaltenes is employed to measure asphaltene concentration, linear calibrations of absorbance vs. asphaltene concentration are prepared from a sample of asphaltenes in a given solvent. This calibration is shown to be sensitive to: (a) the inorganic solids content of the asphaltenes; (b) physical–chemical differences between asphaltenes from different sources or extracted with different methods; and (c) selective adsorption of asphaltenes on liquid–liquid or solid–liquid interfaces. Calibration constants were determined at wavelengths of 288 and 800 nm for samples of Athabasca and Cold Lake asphaltenes obtained using different extraction methods, from precipitation experiments, and from adsorption experiments on water-in-hydrocarbon emulsions and on powdered metals. It was found that the inorganic solids content did not affect absorbance but the asphaltene concentrations must be corrected to a solids-free basis for accurate results. Calibration constants were found to correlate to the average associated molar masses of the asphaltenes. Therefore, any change in molar mass of asphaltenes during the course of an experiment may change the calibration constant. Partial precipitation and the selective adsorption of asphaltenes can lead to a change in the molar mass of asphaltenes left in solution. The corresponding change in the calibration constants can lead to errors of 5–25% in the estimated concentration.

Ultrathin Resist Pattern Transfer Process by Filling Mask Material in the Resist Pattern

We performed experiments to transfer the pattern of ultrathin resists with the reversal mask process. Resist film thickness was 100 nm for samples using the KrF resist (KrF sample) and the ArF resist (ArF sample), and 70 nm for the sample using the EB resist (EB sample). Resist patterns were formed on an organic film, and then cured by EB. Spin-on-glass (SOG) was coated over the resist patterns and etched back. Finally, we obtained organic film patterns using the remaining SOG as an etch mask. In the case of the KrF sample, it was possible to transfer three resist patterns (lines and spaces (LS), isolated line (iL), isolated space (iS)) to the organic film simultaneously. In case of the ArF sample and the EB sample, it was possible to transfer each pattern. However, the transfers were not simultaneous. In order to transfer different patterns simultaneously, strengthening etch resistance of mask material, improving uniformity of SOG thickness over the resist pattern and suppression of shrinkage of resist pattern thickness caused by EB cure are important to achieve.

The effects of a progesterone metabolite, 5β-dihydroprogesterone, on oxytocin receptor binding in human myometrial membranes

Objective To determine the effect of the progesterone metabolite 5β-dihydroprogesterone on human oxytocin receptor binding in myometrial membranes and on whole-cell calcium current in single myometrial cells. Design Receptor binding studies in human myometrial membranes prepared from biopsies taken before or after the onset of labour and in Chinese hamster ovary cells expressing the human oxytocin receptor. Whole cell patch-clamp experiments were undertaken on isolated myometrial cells. Setting University research laboratories and University hospital. Population Patients undergoing caesarean section at term either prior to or following onset of labour. Methods Myometrial biopsies were taken from women undergoing caesarean section. The binding affinities of oxytocin, 5β-dihydroprogesterone and atosiban were determined in myometrial membranes and Chinese hamster ovary cells expressing the human oxytocin receptor. The effect of 5β-dihydroprogesterone on inward current was also determined in isolated myometrial cells. Main outcome measures Receptor binding affinity and electrophysiological inward current. Results 5β-Dihydroprogesterone did not reduce oxytocin receptor binding in myometrial membranes or Chinese hamster ovary cells expressing the human oxytocin receptor. Nor did it influence calcium current under whole-cell patch conditions in single myometrial cells. In contrast, atosiban inhibited binding in myometrial membranes prepared from samples taken either prior to or following labour ( K i = 112 and 108 nM, respectively). The affinity of atosiban for the oxytocin receptor was much lower than oxytocin ( K i = 5 and 6 nM in samples taken before or after labour, respectively) in myometrial membranes and in Chinese hamster ovary cells expressing the human oxytocin receptor ( K i = 63 M and 1 nM for atosiban and oxytocin, respectively). Conclusions We conclude that 5β-dihydroprogesterone is unlikely to regulate myometrial activity as a result of a direct effect on oxytocin receptor binding or inward calcium current.

The effects of a progesterone metabolite, 5 beta-dihydroprogesterone, on oxytocin receptor binding in human myometrial membranes.

To determine the effect of the progesterone metabolite 5 beta-dihydroprogesterone on human oxytocin receptor binding in myometrial membranes and on whole-cell calcium current in single myometrial cells. Receptor binding studies in human myometrial membranes prepared from biopsies taken before or after the onset of labour and in Chinese hamster ovary cells expressing the human oxytocin receptor. Whole cell patch-clamp experiments were undertaken on isolated myometrial cells. University research laboratories and University hospital.Patients undergoing caesarean section at term either prior to or following onset of labour. Myometrial biopsies were taken from women undergoing caesarean section. The binding affinities of oxytocin, 5 beta-dihydroprogesterone and atosiban were determined in myometrial membranes and Chinese hamster ovary cells expressing the human oxytocin receptor. The effect of 5 beta-dihydroprogesterone on inward current was also determined in isolated myometrial cells. Receptor binding affinity and electrophysiological inward current. 5 beta-Dihydroprogesterone did not reduce oxytocin receptor binding in myometrial membranes or Chinese hamster ovary cells expressing the human oxytocin receptor. Nor did it influence calcium current under whole-cell patch conditions in single myometrial cells. In contrast, atosiban inhibited binding in myometrial membranes prepared from samples taken either prior to or following labour (K(i) = 112 and 108 nM, respectively). The affinity of atosiban for the oxytocin receptor was much lower than oxytocin (K(i) = 5 and 6 nM in samples taken before or after labour, respectively) in myometrial membranes and in Chinese hamster ovary cells expressing the human oxytocin receptor (K(i) = 63 M and 1 nM for atosiban and oxytocin, respectively). We conclude that 5 beta-dihydroprogesterone is unlikely to regulate myometrial activity as a result of a direct effect on oxytocin receptor binding or inward calcium current.

NiCr Alloy As Both Absorption Layer and Top Electrode onto Pb(Zr0.3Ti0.7)O3 Thin Films for Infrared Sensors

NiCr alloys prepared by dc magnetron sputtering are considered to apply simultaneously both the absorption layer and the top electrode on PZT thin films for infrared sensors. NiCr alloys deposited with dc powers of Ni 80 and Cr 50 W showed the most stable oxidation resistance even at 600°C in an oxygen ambient. They have a resistivity of approximately 70 μΩ-cm and a rms roughness of 2.0 nm in samples annealed at 600°C for 5 min in O2. The NiCr/PZT/Pt capacitors showed a well-saturated hysteresis loop having a remanent polarization of 20 μC/cm2. Ultra-thin NiCr alloys showed a possibility as a top electrode for infrared sensors.

Visible–blind GaN p–i–n photodiodes with an Al 0.12Ga 0.88N/GaN superlattice structure

GaN ultraviolet photodiodes with (i.e. sample 1) and without (i.e. sample 2) Mg-doped AlGaN/GaN strained-layer superlattice structure were both fabricated. It was found that we could achieve a near constant dark current of around 3 and 7 nA/cm 2 for sample 1 and sample 2, respectively. It was also found that we could achieve a larger photocurrent and a larger photocurrent to dark current contrast ratio from sample 1. The zero-bias peak responsivity was found to be around 0.05 A/W at 356 nm and 0.006 A/W at 363 nm for sample 1 and sample 2, respectively. However, the transient response full-width-half-maximum (FWHM) of sample 1 was found to be longer. For devices with a 500 μm diameter, it was found that the transient response FWHM was 0.6 μs for sample 1 and 0.2 μs for sample 2. The difference in response time between sample 1 and sample 2 should be attributed to the distribution of depletion layer in between the p-layer and the n-type i-layer.

Co-Pt multilayers perpendicular magnetic recording media with thin Pt layer and high perpendicular anisotropy

It was found that Co-Pt multilayer films had high perpendicular magnetic anisotropy when the thickness of the Co layer was greater than that of Pt. Hc increased with decreasing Pt layer thickness and had a maximum at 0.13 nm for samples of Pt underlayer/[Co(0.44 nm)/Pt(0 /spl sim/ 1.2 nm)]/sub 20/ deposited by sputtering at 4 Pa Ar gas pressure. K/sub /spl perp// also increased with decreasing Pt layer thickness, 3 /spl times/ 10/sup 6/ to 10 /spl times/ 10/sup 6/ erg/cm/sup 3/. Hc increased with Co-Pt multilayer deposition Ar gas pressure, and /spl alpha/(dM/dH/sub at/ /sub Hc/) decreased with Pt underlayer deposition Ar gas pressure. By increasing deposition pressures of Co-Pt multilayers and Pt underlayer to 7.5 Pa, the characteristics of Hc: 4.7 kOe, S: 0.96, /spl alpha/: 4, and K/sub /spl perp//: 10 /spl times/ 10/sup 6/ erg/cm/sup 3/ were obtained. By inserting FeTaC soft magnetic layers between the glass substrate and Pt underlayer, Hc: 5.8 kOe, S: 0.87, and /spl alpha/: 1.8 were obtained. These characteristics imply that Co-Pt multilayers with thin Pt layers have potential for perpendicular magnetic recording media at high recording density because of the high K/sub /spl perp// and thin recording layer (less than 10 nm).

Effect of Zr substitution for rare earth on microstructure and magnetic properties of melt-spun (Nd0.75Pr0.25)12.5−xZrxFe82B5.5 (x=0–3) ribbons

The effect of Zr substitution for rare earth on the microstructure and hard magnetic properties of melt-spun composition of (Nd0.75Pr0.25)12.5−xZrxFe82B5.5 (x=0–3) has been investigated. It has been found that the coercivity decreases monotonically with the increasing Zr content, from 12.0 kOe at x=0 to 10.1 kOe with x=3. Unlike the coercivity, the remanence first increased with Zr substitution, from 8.65 up to 8.93 kG at x=2, and then decreased with further Zr substitution. The energy product behaved similarly, increasing from 15.7 MGOe to a maximum of 16.5 MGOe at x=2. X-ray diffraction (XRD), transmission electron microscope (TEM), and thermogravimetric analyzer studies have shown that all the samples were primarily composed of the single R2Fe14B phase. No additional phase was observed with Zr substitution. The lattice constants and the Curie temperature of the 2:14:1 phase were found to decrease monotonically with increasing Zr content, suggesting that all the Zr is situated into the 2:14:1 matrix, occupying the rare earth sites. TEM and XRD studies also revealed a significant grain size reduction with Zr substitution. The average grain size was reduced from approximately 40 nm in Zr-free samples to about 20 nm in samples with x=2. The observed change in magnetic properties with Zr substitution is explained by the grain size reduction.

Microwave measurement of energy gap and penetration depth of MgB 2 thin film

Using a dielectric resonator technique the magnetic field penetration depth λ and the energy gap Δ of two MgB 2 thin films were determined by measuring changes of resonance frequency with temperature. The exponential temperature dependence of λ is revealed at low temperatures ( T< T c/4, T c is the critical temperature of the thin film). It indicates that a finite energy gap exists for thermal excitation of quasiparticles. From our measurements values of Δ/ kT c=1.25 and λ 0=290 nm for sample A and Δ/ kT c=1.20 and λ 0=160 nm for sample B give the best fit to the experimental results. The corresponding values for the energy gap Δ are 3.4 meV for sample A and 3.8 meV for sample B. In the high temperature region ( T> T c/2) the temperature dependence of λ can be well fitted by λ 0/[1−( T/ T c) 2] 1/2. Our results strongly support the absence of nodes in the gap and a possible multigap scenario.