Improvement of thickness and uniformity of isotopically enriched C targets on backings by the HIVIPP method

We have made enriched ¹²C targets to accurately measure the cross-section of the ¹²C(α,γ)¹⁶O reaction, which is very important in nuclear astrophysics. Isotopically enriched ¹²C targets for studying this small cross-section, especially for use with an intense pulsed α beam was desired to meet the following requirements: (1) use of impurity-free enriched ¹²C, (2) stability for a long time measurement and (3) uniform thickness in the range 200–300 μg/cm². To meet these experimental requirements, isotopically enriched amorphous ¹²C powder was converted into graphite powder in an electric furnace at a temperature of 3000 K and subsequently the graphite powder was deposited on a thick Au backing via the HIVIPP method. Targets thus prepared could be made thicker than 200 μg/cm². They had a good uniformity and a very high stability against irradiation with high intensity ion beams.     

Titanium diffusion in gold thin films

In the present study, diffusion phenomena in titanium/gold (Ti/Au) thin films occurring at temperatures ranging between 200 and 400 °C are investigated.The motivation is twofold: the first objective is to characterize Ti diffusion into Au layer as an effect of different heat-treatments. The second goal is to prove that the implementation of a thin titanium nitride (TiN) layer between Ti and Au can remarkably reduce Ti diffusion.It is observed that Ti atoms can fully diffuse through polycrystalline Au thin films (260 nm thick) already at temperatures as a low as 250 °C. Starting from secondary ion mass spectroscopy data, the overall diffusion activation energy ΔE = 0.66 eV and the corresponding pre-exponential factor D₀ = 5 × 10^− 11 cm²/s are determined. As for the grain boundary diffusivity, both the activation energy range 0.54 < ΔE_gb < 0.66 eV and the pre-exponential factor s₀D_gb0 = 1.14 × 10^− 8 cm²/s are obtained. Finally, it is observed that the insertion of a thin TiN layer (40 nm) between gold and titanium acts as an effective diffusion barrier up to 400 °C.     

Properties of Au nanolayer sputtered on polyethyleneterephthalate

AFM, XRD, zeta (ζ) potential measurement and spectroscopic ellipsometry were used for characterization of thin (20 nm) Au films sputtered onto polyethyleneterephthalate (PET). Sputtered Au film shows significantly different surface morphology and roughness in comparison with pristine PET. From XRD measurement of 20 nm thick sputtered Au layers it was found that Au crystalizes preferentially in (111) direction with lattice parameter of a = 0.40769 nm, density of ρ = 19.338 g cm^− 3 and lattice stress of about 230 MPa. Higher surface conductance of Au/PET by ζ-potential measurement was found. Au layer thickness of 19.4 nm determined from spectroscopic ellipsometry was in good agreement with the AFM estimated value of 20 nm.     

Effect of annealing temperature on electrical properties of Au/polyvinyl alcohol/n-InP Schottky barrier structure

In the present work, thin film of polyvinyl alcohol (PVA) is fabricated on n-type InP substrate as an interfacial layer for electronic modification of Au/n-InP Schottky contact. The electrical characteristics of Au/PVA/n-InP Schottky diode are determined at annealing temperature in the range of 100-300 °C by current-voltage (I-V) and capacitance-voltage (C-V) methods. The Schottky barrier height and ideality factor (n) values of the as-deposited Au/PVA/n-InP diode are obtained at room temperature as 0.66 eV (I-V), 0.82 eV (C-V) and 1.32, respectively. Upon annealing at 200 °C in nitrogen atmosphere for 1 min, the barrier height value increases to 0.81 eV (I-V), 0.99 eV (C-V) and ideality factor decreases to 1.18. When the contact is annealed at 300 °C, the barrier height value decreases to 0.77 eV (I-V), 0.96 eV (C-V) and ideality factor increases to 1.22. It is observed that the interfacial layer of PVA increases the barrier height by the influence of the space charge region of the Au/n-InP Schottky junction. The discrepancy between Schottky barrier heights calculated from I-V and C-V measurements is also explained. Further, Cheung's functions are used to extract the series resistance of Au/PVA/n-InP Schottky diode. The interface state density as determined by Terman's method is found to be 1.04 × 10¹² and 0.59 × 10¹² cm^− 2 eV^− 1 for the as-deposited and 200 °C annealed Au/PVA/n-InP Schottky diodes. Finally, it is seen that the Schottky diode parameters changed with increase in the annealing temperature.     

Removal of acid orange 7 by guava seed carbon: A four parameter optimization study

The preparation of carbon from waste materials is a recent and economic alternative for the removal of dyes. In this study four samples of carbon were obtained by thermal treatment at 1000 °C using as precursor the guava seed with different particle sizes. The Taguchi method was applied as an experimental design to establish the optimum conditions for the removal of acid orange 7 in batch experiments. The chosen experimental factors and their ranges were: pH (2–12), temperature (15–35 °C), specific surface area (50–600 m² g⁻¹) and adsorbent dosage (16–50 mg ml⁻¹). The orthogonal array L₉ and the larger the better response category were selected to determine the optimum removal conditions: pH 2, temperature 15 °C, S_esp 600 m² g⁻¹ and dosage 30 mg ml⁻¹. Under these conditions a total removal of acid orange 7 was achieved. Moreover, the most significant factors were the carbon specific surface area and the pH. The influence of the different factors on the adsorption of acid orange 7 from solution is explained in terms of electrostatic interactions by considering the dye species and the character of the surface.     

Preparation and properties of negative thermal expansion Zr2WP2O12 ceramics

Using solid-state reaction method, Zr₂WP₂O₁₂ powder was synthesized for this study. The optimum heating condition was 1200 °C for 4 h. The obtained powder was compacted and sintered. The relative density of the Zr₂WP₂O₁₂ ceramics with no sintering additive was 60%. That of samples sintered with more than 0.5 mass% MgO was about 97%. The average grain size (D₅₀), as estimated from the polished surface of a sample sintered at 1200 °C for 4 h was about 1 μm. The obtained ceramics showed a negative thermal expansion coefficient of about −3.4 × 10⁻⁶ °C⁻¹. Young's modulus, Poisson's ratio, three-point bending strength, Vickers microhardness, and fracture toughness of the obtained ceramics were, respectively, 74 GPa, 0.25, 113 ± 13 MPa, 4.4 GPa and 2.3 MPa m^1/2.     

Fabrication of carbon nanotubes by electrical breakdown of carbon-coated Au nanowires

A carbon nanotube has been generated by the electrically-induced breakdown of a carbon-coated Au nanowire. Under high current density the Au in the nanowire migrates towards both the anode and cathode resulting in a free-standing carbon nanotube and a 73% reduction in resistance. The resistivity of the carbon nanotube was < 8 × 10^− 5 Ω m and it could cope with a current density > 1.8 × 10¹¹ A/m², indicating a structural change from amorphous to graphitic carbon. The dimensions of carbon nanotubes produced in this way have an internal diameter controlled by the parent metal nanowire template.     

Effect of bead milling on heat generation ability in AC magnetic field of FeFe2O4 powder

Nano-sized FeFe₂O₄ ferrite powder having a heat generation ability in an AC magnetic field was prepared by bead milling for a thermal coagulation therapy application. A commercial powder sample (non-milled sample) of ca. 2.0 μm in particle size showed a temperature enhancement (ΔT) of 3 °C in an AC magnetic field (powder weight 1.0 g, 370 kHz, 1.77 kA m⁻¹) in ambient air. The heat generation ability in the AC magnetic field improved with the milling time, i.e., due to a decrease in the average crystallite size for all the examined ferrites. The highest heat ability (ΔT = 26 °C) in the AC magnetic field in ambient air was for the fine FeFe₂O₄ powder with a 4.7 nm crystallite size (the samples were milled for 6 h using 0.1 mm? beads). However, the heat generation ability decreased for the excessively milled FeFe₂O₄ samples having average crystallite sizes of less than ca. 4.0 nm. The heat generation of the samples showed some dependence on the hysteresis loss for the B–H magnetic property. The reasons for the high heat generation properties of the milled samples would be ascribed to an increase in the Néel relaxation of the superparamagnetic material. The hysteresis loss in the B–H magnetic curve would be generated as the magnetic moment rotates (Néel relaxation) within the crystal. The heat generation ability (W g⁻¹) can be estimated using a 1.07 × 10⁻⁴fH² frequency (f, kHz) and the magnetic field (H, kA m⁻¹) for the samples milled for 6 h using 0.1 mm? beads. Moreover, an improvement in the heating ability was obtained by calcination of the bead-milled sample at low temperature. The maximum heat generation (ΔT = 59 °C) ability in the AC magnetic field in ambient air was obtained at ca. 5.6 nm for the sample calcined at 500 °C. The heat generation ability (W g⁻¹) for this heat treated sample was 2.54 × 10⁻⁴fH².     

Piezoelectric and ferroelectric properties of K0.5Na0.5NbO3 ceramics synthesized by spray drying method

Potassium-sodium niobate was synthesized at 800 °C for 1 h using dried precursors in a powder form obtained by the spray drying method. Different samples were sintered from 1060 to 1120 °C for 2 h reaching a relative density as high as 96% of the theoretical value. Piezoelectric and ferroelectric properties were studied for these samples and some of the most prominent results are: k_p, d₃₁, 2P_r, and 2E_C of 0.36, 39 pC/N, 29 μC/cm² and 16.5 kV/cm, respectively, for the sample sintered at 1080 °C. The methodology presented in this study can be used to synthesize submicrometer powders.     

Electrical properties of Sm-doped bismuth titanate thin films prepared on Si (100) by metalorganic decomposition

Samarium-doped bismuth titanate [Bi_4−xSm_xTi₃O₁₂ (BSmT)] thin films have been grown on n-type Si (100) substrates using metalorganic decomposition and subsequent annealing at 700 °C for 1 h. X-ray diffraction analysis showed layered perovskite structures with a single phase in the films. The current-voltage characteristics displayed ohmic conductivity in the lower voltage range and space-charge-limited conductivity in the higher voltage range. The capacitance-voltage characteristics of Au/BSmT/Si (100) exhibited hysteresis loops due to the ferroelectricity and did not show large carrier injections. The fixed charge density and the surface state density of BSmT films on Si substrate were calculated to be in the range of 10¹¹ cm⁻² and 10¹² cm⁻² eV⁻¹, respectively.     

Synthesis of nanocrystalline magnesium titanate by an auto-igniting combustion technique and its structural, spectroscopic and dielectric properties

Nanocrystalline magnesium titanate was synthesized through an auto-ignited combustion method. The phase purity of the powder was examined using X-ray diffraction, thermo gravimetric analysis, differential thermal analysis, Fourier transform infrared spectroscopy and Raman spectroscopy. The transmission electron microscopy study showed that the particle size of the as-prepared powder was in between 20 and 40 nm. The nanopowder could be sintered to 98% of the theoretical density at 1200 °C for 3 h. The microstructure of the sintered surface was examined using scanning electron microscopy. The dielectric constant (?_r) of 16.7 and loss factor (tan δ) of the order of 10⁻⁴ were obtained at 5 MHz when measured using LCR meter. The quality factor (Q_u × f) 73,700 and temperature coefficient of resonant frequency (τ_f) −44.3 ppm/°C, at 6.5 GHz are the best reported values for sintered pellets obtained from phase pure nanocrystalline MgTiO₃ powder.     

Rare-earth doped solid-state phosphor with temperature induced variable chromaticity

Temperature induced variable chromaticity lanthanide multidoped solid-state phosphors are presented. The phosphors are composed of ytterbium-sensitized multiple-doped (Tm, Er, Ho) PbGeO₃-PbF₂-CdF₂ glass excited at 1.064 µm. The temperature induced color variation exploits the heat enhanced effective absorption cross-section of the ytterbium sensitizer under quasi-resonance excitation. The temperature enhancement of the energy-transfer mechanism between the sensitizer and the appropriate active light emitter allows the selective intensity control of the RGB emissions due to distinct excitation routes. The suitable combination of active ions generated variable chromaticity light with CIE-1931 coordinates changing from CIE-X = 0.283; Y = 0.288 at 20 °C to CIE-X = 0.349;Y = 0.412 at 190 °C, and CIE-X = 0.285; Y = 0.361 at 25 °C to CIE-X = 0.367; Y = 0.434 at 180 °C in Yb³⁺/Tm³⁺/Ho³⁺ and Yb³⁺/Tm³⁺/Er³⁺ samples, respectively.     

Design of magnetic akaganeite-cyanobacteria hybrid biofilms

Common Anabaena cyanobacteria are shown to form intra-cellularly akaganeite β-FeOOH nanorods of well-controlled size and unusual morphology at room temperature. High-resolution transmission electron microscopy showed that these nanorods present a complex arrangement of pores forming a spongelike structure. These hybrid akaganeite-cyanobacteria were used to form “one-pot” hybrid biofilms. The hybrid biofilm presents higher coercivity (H_c = 44.6 kA m^− 1 (560 Oe)) when compared to lyophilized akaganeite-cyanobacteria powder (H_c = 0.8 kA m^− 1 (10 Oe)) due to the quasi-assembly of the cells on the glass substrate compared to the lyophilized randomly akaganeite-cyanobacteria powder.     

Enhancement of optical nonlinearity in binary metal-nanoparticle arrays

Periodic binary metal-nanoparticle arrays, comprising of Au and Fe, were fabricated on quartz substrates using nanosphere lithography and pulsed laser deposition technique. The dimension of the obtained triangular Au(Fe) particles was about 80 nm which was defined by the single-layer masks prepared by self-assembly of polystyrene nanospheres with radius R = 100 nm. The structural characterization of the particle arrays was investigated by atomic force microscopy. In the optical absorption spectra, the metal-nanoparticle arrays show a strong absorption peak of ~ 550 nm due to the surface plasmon resonance of metal particles. The nonlinear optical properties of the nanoparticle arrays were determined using a single beam z-scan method at a wavelength of 532 nm with laser duration of 55 ps. By adding Fe, the resonant absorption of Au particles was quenched, and the figure of merit χ⁽³⁾/α (with χ⁽³⁾ being the third-order nonlinear susceptibility, α being the absorption coefficient) was obviously increased. The obtained maximum χ⁽³⁾/α is about 6.15 × 10^− 12 esu cm. The results show that periodic Au + Fe nanoparticle arrays exhibit a large nonlinear optical property with fast response.     

Synthesis, morphology and optical properties of multi-pods Au/FeO(OH) and Au/Fe2O3 nanostructures

Multi-pods Au/FeOOH nanostructures were synthesized by a hydrothermal treatment of an aqueous solution of mixed micellar formed by gold nanoparticles, hexadecyltrimethyl ammonium bromide (CTAB), and (NH₄)₃[FeF₆] at 160 °C for 48 h and sequential calcined at 290 °C for 1.5 h, resulting in the formation of multi-pods Au/Fe₂O₃ nanostructures. The as-obtained products were characterized by powder X-ray diffraction, transmission electron microscopy, selected area electron diffraction, field emission scanning electron microscopy, and UV-vis spectroscopy. Surface plasmon resonance band of gold nanoparticles was observed in the multi-pods Au/FeOOH nanostructures. However, a similar behavior was not seen with multi-pods Au/Fe₂O₃ nanostructures. The critical role of F⁻ ions and CTAB molecules in the formation of FeO(OH) multipods and the probable mechanism of the formation of multi-pods Au/FeOOH and Au/Fe₂O₃ nanostructures were discussed.     

Effect of thermal annealing on Ni/Au contact to a-InGaZnO films deposited by dc sputtering

We deposited Ni (15 nm)/Au (30 nm) layers on a-InGaZnO in order to produce low-resistance ohmic contacts by using a dc sputtering method. The samples were annealed at various temperatures for 5 min in Ar ambient. The electrical and the structural properties of the Ni/Au contact to a-InGaZnO were investigated. According to the current-voltage measurements, both the as-deposited and low-temperature annealed samples showed an ohmic behavior. The specific contact resistance of the as-deposited sample was 4.1 × 10^− 5 Ω cm², which was the lowest value. Further increasing the temperature above 400 °C led to an increase in the specific contact resistance. This is due to the chemical intermixing and formation of the oxide in the contact interface caused by the post-growth thermal annealing.     

Atomistic simulations of shearing friction and dynamic adhesion of double-walled carbon nanotubes on Au substrates

Functional gecko-mimetic adhesives have attracted a lot of research interest in recent years. In this paper, the physical adhesion behavior of (5, 5)@(10, 10) double-walled carbon nanotubes (DWCNTs) on an Au substrate is investigated by performing detailed, fully atomistic molecular dynamics (MD) simulations. The effects of adhesion temperature, tube length, and peeling velocity on the binding energy, normal adhesion force, lateral shearing friction, and adhesion time are thoroughly analyzed. The simulation results indicate that the binding energy (per unit length) of the DWCNT–Au adhesive system is −26.7 × 10⁻² eV/Å, which is 7.2% higher than that of single-walled counterparts. The tip-surface adhesion force for a single DWCNT is calculated to be 1.4 nN, and thus the adhesive strength of a DWCNT array is about 1.4 × 10¹–1.4 × 10³ N/cm² (corresponding to an aerial density of 10¹⁰–10¹² tubes/cm²). Two distinctive friction modes, namely (i) sliding friction (by the nanotube wall) and (ii) sticking friction (by the nanotube tip), are elucidated in term of the phase relationship of atomic friction forces. Moreover, the effective Young’s moduli of double- and single-walled CNTs are obtained using MD simulations combined with Euler–Bernoulli beam theory. The calculation results show good agreement with previously reported numerical and experimental results.     

The effect of high temperature annealing on Schottky diode characteristics of Au/n-Si contacts

The current-voltage and capacitance-voltage characteristics of Au/n-Si/Al Schottky barrier diode were measured in the temperature range of 100-800 °C. Au/n-Si/Al Schottky barrier diode annealed at temperatures from 100 °C to 400 °C for 5 min and from 500 °C to 800 °C for 7 min in N₂ atmosphere. The electronic parameters such as barrier height and ideality factor (n) of the device were determined using Cheung's method. To determine whether or not a Schottky diode is ideal it can be used the ideality factor (n) found from its forward current-voltage (I-V) characteristics. It has been found that the value of Φ_b (0.82 or 0.83 eV) remains constant up to 500 °C and 0.80 and 0.79 eV in 600, 750 °C respectively in the forward I-V mode. An ideality factor value of 1.04 was obtained for as-deposited sample. The ideality factor n varied from 1.04 to 2.30. The experimental results have shown that the ideality factor (n) values increases with increasing annealing temperature up to 750 °C. This has been explained in terms of the presence of different metallic-like phases produced by chemical reactions between the Au and Si substrate because of the annealing process. The Φ_b (C-V) values obtained from the reverse-bias C⁻²-V curves of the as-deposited and annealed diode are in the range 0.99-1.12 eV. The difference between Φ_b (C-V) and the Φ_b (I-V) is in close agreement with values reported in literature. Besides Fermi energy level and carrier concentration determined by using thermionic emission (TE) mechanism show strong temperature dependence. It has been seen current-voltage characteristics of the diode show an ideal behavior.     

Combustion synthesis of Sr0.5Ba0.5Nb2O6 and effect of fuel on its microstructure and dielectric properties

Nano-sized Sr_0.5Ba_0.5Nb₂O₆ (SBN50) powder has been synthesized, at very short reaction time, for the first time by a novel combustion method. Ba(NO₃)₂ and Sr(NO₃)₂ were used as source of Sr and Ba, respectively, while Nb-oxalate was used as the source of niobium. Urea, hexamethyltetramine (HMT) and glycine were used as fuel. The crystallite sizes in the powder ranged between 14-125 nm. X-ray diffraction analysis showed complete SBN50 phase formation at 700 °C, when urea/HMT was used as fuel, and at 800 °C when glycine was used as fuel. Ferroelectric-paraelectric phase transition temperature (T_c) close to 40 °C was observed when urea and HMT were used and the T_c was −49 °C when glycine was used. When urea was used as fuel highest dielectric constant was observed for the pellets sintered at 1250 °C for 4 h. Low dielectric loss was observed when HMT was used as fuel. Larger grain sizes in the sintered pellets were observed when glycine was used as fuel.     

Preparation and dielectric properties of B-doped SiC powders by combustion synthesis

The SiC(B) solid solution powders were synthesized via combustion reaction of Si/C system in Ar atmosphere, using boron powder as the dopant and polytetrafluoroethylene as the chemical activator, which were investigated by X-ray diffraction (XRD), scanning electronic microscope (SEM) and Raman spectra. Results show that the prepared powders are C-enriched SiC with C antisites and sp² carbon defects in which the sp² carbon is transformed to the sp³ carbon due to boron doping. The electric permittivities of the prepared powders were determined in the frequency range of 8.2-12.4 GHz. The dielectric real part ?′ and dielectric loss tan δ of undoped powder have maximum values (?′ = 5.5-5.3, tan δ = 0.23-0.20), and decrease with increasing boron content. The mechanism of dielectric loss by doping has been discussed.