Pyroelectric behaviour of laser-evaporated poly(vinyl fluoride) films

Laser-evaporated poly(vinyl fluoride) films were prepared with a view to their use as pyroelectric sensing elements. A high power (60 W) CO₂ laser was employed to prepare these films (0.1–1 microm thick) in a vacuum of better than 1 × 10^?5Torr. The films were characterized by determining their structure and molecular weight using IR spectroscopy and mass spectrometry. The pyroelectric currents developed in these films by poling them in electric fields of strength (1–5) × 10⁵ V cm^?1 and at poling temperatures of 303–450 K were measured. Various metal electrodes were used and the effect of the electrode material on the pyroelectric activity was also studied. The results are used to interpret the origin of the pyroelectricity in these films. The experimental details of the preparation of the films, their characterization and the pyroelectric current measurements are discussed.     

Structural and electrical properties of Ho<Superscript>3+</Superscript>-modified Pb(Zn<Subscript>1/3</Subscript>Nb<Subscript>2/3</Subscript>)O<Subscript>3</Subscript>–9PbTiO<Subscript>3</Subscript> single crystals

Ho³⁺-modified Pb(Zn_1/3Nb_2/3)O₃–9PbTiO₃ (PZN–9PT) single crystals were grown through a flux method. Phase structure and microstructural morphology of the as-grown single crystals were performed by X-ray diffraction analysis and scanning electron microscopy. The refinement of the lattice parameters were obtained by the Rietveld method. The electrical properties of PZN–9PT single crystals were improved significantly by the modification of Ho³⁺ ions. The rhombohedral–tetragonal phase transition temperature, Curie temperature, coercive field at 15 kV cm^?1, and remnant polarization of Ho³⁺-modified PZN–9PT single crystals were increased by 14, 42 K, 2.4 kV cm^?1, and 7.5 μC cm^?2, respectively (i.e., 375.45, 448.45 K, 5.9 kV cm^?1, and 38.40 μC cm^?2, respectively). Furthermore, Lorentz-type law was used to describe the dielectric relaxor behavior of the as-grown single crystals.     

Dielectric and pyroelectric properties of a composite of ferroelectric ceramic and polyurethane

Flexible piezo- and pyroelectric composite was made in the thin film form by spin coating. Lead Zirconate Titanate (PZT) ceramic powder was dispersed in a castor oil-based polyurethane (PU) matrix, providing a composite with 0–3 connectivity. The dielectric data, measured over a wide range of frequency (10^–5 Hz to 10⁵ Hz), shows a loss peak around 100 Hz related with impurities in the polymer matrix. There is also an evidence of a peak in the range 10^–4 Hz, possibly originating from the glass transition temperature T_g of the polymer. The pyroelectric coefficient at 343 K is 7.0×10^–5 C·m^–2·K^–1 which is higher than that of β-PVDF (1×10^–5 C·m^–2·K^–1). Electronic Publication     

Structural and magnetic properties of nanocomposites based on nanostructured polyaniline and titania nanotubes

Nanocomposites consisting of self-assembled polyaniline (PANI) nanostructures and titania nanotubes (TiO₂-NT) were synthesized by the oxidative polymerization of aniline with ammonium peroxydisulfate in an aqueous dispersion of TiO₂-NT (outer diameter ~10 nm), without added acid. The influence of initial mole ratio of aniline to TiO₂ (80, 20, and 5) on the morphology, electrical conductivity, molecular structure, crystallinity, and magnetic properties of synthesized PANI/TiO₂ nanocomposites was studied. Transmission electron microscopy, Raman spectroscopy, and X-ray powder diffraction proved that the shape and structure of TiO₂-NT in the final nanocomposites were preserved. The shape of PANI nanostructures formed in the nanocomposites was influenced by the initial aniline/TiO₂-NT mole ratio. Nanotubes and nanorods are predominant PANI nanostructures in the nanocomposite prepared with the highest aniline/TiO₂ mol ratio of 80. The decrease of aniline/TiO₂ molar ratio induced more pronounced formation of nanorod network. The electrical conductivity of PANI/TiO₂ nanocomposites was in the range (1.3–2.4) × 10^?3 S cm^?1. The nanocomposites exhibit weak ferromagnetic behavior. Approximately order of magnitude lower values of coercive field and remanent magnetization were obtained for nanocomposite samples in comparison to pure PANI.     

A new method of depositing high figure-of-merit porous PZT pyroelectric thick film using [001]-oriented PZT nanorod by electrophoresis deposition

The effects of hydrothermal synthesized [001]-oriented PZT nanorods on the pyroelectric properties of PZT thick film fabricated by electrophoresis deposition were studied in a range from 750 to 900 °C. It was revealed by scanning electron microscopy that the pores are mainly distributed in the film body but not at the electrode interface, which would improve the adhesion and electric contact between the thick film and electrode. The formation and distribution of the pores resulted from the PZT nanorods were schematically explained. It was found that the relative dielectric constant (ε _r ) of the PZT nanorod-doping film sintered at 800 °C was lowered by approximate 46.5 %. Accordingly, the calculated figures of merit for voltage responsivity (F_V) and detectivity (F_D) were improved by 125 and 114 %, respectively. These results demonstrated that a new way to deposit PZT porous thick film with low dielectric constant and high figures of merit was established.     

Significant G peak temperature shift in Raman spectra of graphene on copper

Linear G peak position temperature dependence in Raman spectra of graphene synthesized by chemical vapor deposition from decane on copper (220) with a shift factor of ?(5.4 ± 0.4) × 10^?2 cm^?1K^?1 was observed. The obtained value substantially exceeds values previously obtained for graphene by other authors, and was associated with the substrate interaction effects.     

Crystallographic, thermoelectric, and mechanical properties of polycrystalline type-I Ba8Al16Si30-based clathrates

Crystallographic, thermoelectric, and mechanical properties of polycrystalline Ba₈Al₁₆Si₃₀-based samples with type-I clathrate structure prepared by combining arc melting and spark plasma sintering methods were investigated. The major phase of the samples was a type-I clathrate with an actual Al/Si ratio of ~15/31, strongly suggesting that framework deficiency was absent or was present in very low concentration in the samples. The Hall carrier concentration n of the samples was approximately 1 × 10²¹ cm^?3, which is lower than the values reported so far for the Ba₈Al₁₆Si₃₀ system. Other important material parameters of the samples were as follows: the density-of-states effective mass m* = 2.3m ₀, Hall mobility μ = 7.4 cm² V^?1 s^?1, and the lattice thermal conductivity κ _L = 1.2 W m^?1 K^?1. The thermoelectric figure of merit ZT reached approximately 0.4 (900 K) for a sample with n = 9.7 × 10²⁰ cm^?3. Simulation using the experimentally determined values of material parameters showed that ZT reached values >0.5 if the carrier concentration is optimized at about 3 × 10²⁰ cm^?3. Young’s, shear, and bulk moduli were estimated to be approximately 98, 39, and 117 GPa, respectively, and Poisson’s ratio was found to be 0.25 from the longitudinal and transverse velocities of sound, v _L = 6038 m/s and v _T = 3503 m/s, respectively, for a sample with ZT = 0.4. The coefficient of thermal expansion (CTE) ranged from approximately 8 × 10^?6 K^?1 to 10 × 10^?6 K^?1 (330–690 K), which is smaller than the values reported for Ba₈Ga₁₆Ge₃₀ and Sr₈Ga₁₆Ge₃₀ clathrates.     

Effects of MgO on properties of Li2O–Al2O3–SiO2 glass–ceramics for LTCC applications

Li₂O–Al₂O₃–SiO₂ (LAS) glass–ceramics for low temperature co-fired ceramics (LTCC) application were prepared by melting method, and the effects of MgO on the sinterability, microstructure, dielectric property, thermal expansion coefficient (CTE) and mechanical character of this glass–ceramics have been studied. The X-ray diffraction images represent that the main phase is β-spodumene solid solutions. And some ZrO₂ and CaMgSi₂O₆ phases in LAS glass–ceramics are detected. The LAS glass–ceramics without additive (MgO) sintered at 800° had the dielectric properties: dielectric constant (ε_r) of 5.3, dielectric loss (tanδ) of 2.97 × 10^?3 at 1 MHz, CTE value of 1.06 × 10^?6 K^?1, bulk density of 2.17 g/cm³, and flexural strength of 73 MPa. 5.5 wt% MgO-added LAS glass–ceramic achieves densification at 800° exhibited excellent properties: low dielectric constant and loss (ε_r = 7.1, tanδ = 2.02 × 10^?3 at 1 MHz), low CTE (2.89 × 10^?6 K^?1), bulk density = 2.65 g/cm³ as well as high flexural strength (145 MPa). The results indicate that the addition of MgO is helpful to improve the dielectric and mechanical properties. The formation of CaMgSi₂O₆ crystal phase with higher CTE leads to the increase of CTE value of LAS glass–ceramics due to the increasing MgO content, and the increase of CTE is favourable for matching with silicon (3.1 × 10^?6 K^?1). The prepared LAS glass–ceramics have the potential for LTCC application.     

Pb/S/1,2-ethanedithiol composite thin films for efficient solid-state quantum-dot sensitized TiO<Subscript>2</Subscript> nanorod array solar cells

The Pb/S/1,2-ethanedithiol composite thin films were successfully deposited on TiO₂ nanorod arrays by spin-coating step-by-step 5 mmol dm^?3 Pb(NO₃)₂, Na₂S and 1% 1,2-ethanedithiol solution and their chemical compositions can be easily adjusted by changing the concentration of Na₂S solution from 5 to 3.5 mmol dm^?3 and 2 mmol dm^?3. The average crystal sizes of Pb/S/1,2-ethanedithiol quantum-dots decreased from 7.9 to 7.1 nm and 6.5 nm with the decrease of the concentration of Na₂S solution and the chemical bonding of Pb²⁺ and S in EDT was chelation of the penta-heterocycle in Pb/S/1,2-ethanedithiol composite thin films. All solid-state Pb/S/1,2-ethanedithiol composite thin film sensitized TiO₂ nanorod array solar cells using 5, 3.5, 2 mmol dm^?3 Na₂S solution exhibited the photoelectric conversion efficiency of 2.68, 3.41 and 4.51% under the illumination of simulated AM 1.5 sunlight (100 mA cm^?2).     

Ion implantation effects of negative oxygen on copper nanowires

Copper nanowires of diameter 80 nm were synthesized in polycarbonate membrane using template technique. Samples were then implanted with 160 keV O^?1 ion beam with varying particle fluence of 1?×?10¹², 5?×?10¹² and 1?×?10¹³ ions/cm². The SRIM (Stopping and range of ions in matter) software was used to study the processes involved. Compositional analysis confirms implantation of oxygen ions and the stoichiometry of Cu:O was found to be 6:1 by weight % when implanted at 1?×?10¹³ ions/cm². Scanning electron microscopy reveals no changes in morphology of nanowires on implantation. X-ray diffraction analysis showed no shifting in the ‘2θ’ position of diffraction peaks however some new diffraction peaks of oxygen were seen. Implantation with oxygen ion led to the increased crystallite size and reduced strain. The conductivity of the nanowires was found to increase linearly with the ion fluence presenting constructive effect of negative ion implantation on copper nanowires.     

Ultraviolet-assisted cold poling of Pb(Zr<Subscript>0.52</Subscript>Ti<Subscript>0.48</Subscript>)O<Subscript>3</Subscript> films

This paper discusses the advantages of a room-temperature poling procedure during exposure to ultraviolet light for Pb(Zr_0.52Ti_0.48)O₃ (PZT) films. The results of these experiments include the following: for 1.7-µm-thick chemical solution-deposited PZT films, the saturation photocurrent density after a 10 min white light exposure (190–1900 nm) (no DC bias field applied) increased up to 0.066 µA/cm² with increasing Cr thickness of top electrode in Cr/Pt bilayer electrodes. Furthermore, the d_33,f piezoelectric coefficients for UV-poled samples were 40 and 20% higher than those achieved from field-only poling at either room temperature or 150 °C. Additionally, the development of an internal bias field and pinching were investigated in major and minor polarization–electric field loops. It was found that ultraviolet illumination during the poling process produced photoinduced charge carriers that became trapped by local defects and/or grain boundaries in the films.     

Effects of annealing on thermoelectric properties of Sb2Te3 thin films prepared by radio frequency magnetron sputtering

Antimony telluride (Sb₂Te₃) thin films were deposited on silicon substrates at room temperature (300 K) by radio frequency magnetron sputtering method. The effects of annealing in N₂ atmosphere on their thermoelectric properties were investigated. The microstructure and composition of these films were characterized using scanning electron microscopy, energy dispersive X-ray spectroscopy and X-ray diffraction, respectively. The electrical transport properties of the thin films, in terms of electrical conductivity and Seebeck coefficient were determined at room temperature. The carrier concentration and mobility were calculated from the Hall coefficient measurement. Both of the Seebeck coefficient and Hall coefficient measurement showed that the prepared Sb₂Te₃ thin films were p-type semiconductor materials. By optimizing the annealing temperature, the power factor achieved a maximum value of 18.02 μW cm^?1 K^?2 when the annealing temperature was increased to 523 K for 6 h with a maximum electrical conductivity (1.17 × 10³ S/cm) and moderate Seebeck coefficient (123.9 μV/K).     

Synthesis of zirconium silicide in Zr thin film on Si and study of its surface morphology

Zirconium silicide was synthesized on Si (100)/zirconium interface by means of swiftly moving 150 MeV Au ion beam. Thin films of zirconium (~60 nm) were deposited on Si (100) substrates in ultra high vacuum conditions using the electron-beam evaporation technique. The system was exposed to different ion fluencies ranging from 3 × 10¹³ to 1 × 10¹⁴ ions/cm² at room temperature. Synthesized zirconium silicide thin film reasonably affects the resistivity of the irradiated system and for highest fluence of 1 × 10¹⁴ ions/cm² resistivity value reduces from 84.3 to 36 μΩ cm. A low resistivity silicide phase, C-49 ZrSi₂ was confirmed by X-ray analysis. Schottky barrier height was calculated from I–V measurements and the values drops down to 0.58 eV after irradiation at 1 × 10¹⁴ ions/cm². The surface and interface morphologies of zirconium silicide were examined by atomic force microscopy (AFM) and scanning electron microscopy (SEM). AFM shows a considerable change in the surface structure and SEM shows the ZrSi₂ agglomeration and formation of Si-rich silicide islands.     

Structural and pyroelectric properties of sol–gel derived multiferroic BFO thin films

Multiferroic BFO/PZT multilayer films were fabricated by spin-coating method on the (1 1 1)Pt/Ti/SiO₂/Si substrate alternately using PZT(30/70), PZT(70/30) and BFO alkoxide solutions. The structural and ferroelectric properties were investigated for uncooled infrared detector applications. The coating and heating procedure was repeated six times to form BFO/PZT multilayer films. All films showed the typical XRD patterns of the perovskite polycrystalline structure without presence of the second phase such as Bi₂Fe₄O₃. The thickness of BFO/PZT multilayer film was about 200–220 nm. The ferroelectric properties such as dielectric constant, remnant polarization and pyroelectric coefficient were superior to those of single composition BFO film, and those values for BFO/PZT(70/30) multilayer film were 288, 15.7 μC/cm² and 9.1 × 10^?9 C/cm² K at room temperature, respectively. Leakage current density of the BFO/PZT(30/70) multilayer film was 3.3 × 10^?9 A/cm² at 150 kV/cm. The figures of merit, F_V for the voltage responsivity and F_D for the specific detectivity, of the BFO/PZT(70/30) multilayer film were 6.17 × 10^?11 Ccm/J and 6.45 × 10^?9 Ccm/J, respectively.     

Linear and quadratic magnetoelectric effect in CNMFO:PZT magnetoelectric composite

Dynamic magnetoelectric voltage measurements of 30 % Co_0.7?xNi_xMn_0.3Fe₂O₄:70 % Pb(Zr_0.52Ti_0.48)O₃ composites with x = 0.00, 0.05, 0.10, 0.15 synthesized by ceramic method were carried out by linear and quadratic method. Maximum linear magnetoelectric coefficient (α) of 14.7 mv Oe^?1 cm^?1 and maximum quadratic coefficient (β) of 2.26 × 10^?4 mv Oe^?2 cm^?1 were obtained for composition with x = 0.05. Maximum values of α and β for composition with x = 0.05 may be due to more connectivity between grains than in other compositions observed from scanning electron micrographs. Higher values of dielectric constant and ac conductivity for particular composition could also be possible reasons for maximum magnetoelectric coefficients. Smaller dielectric loss at higher frequencies was observed for the same composition which may result into less leakage of charges consequently increasing the resultant magnetoelectric coefficients.     

Effect of Cu additions on morphology and optical properties of ZnO nanorod arrays by two-step method

ZnO, Zn_0.9Cu_0.1O, Zn_0.8Cu_0.2O and Zn_0.7Cu_0.3O nanorod arrays are produced via a two-step process including an initial sol–gel method followed by hydrothermal growth. Effects of the Cu on microstructure, surface topography and optical properties of the nanorod arrays were studied and discussed. The results indicate that the nanorod arrays with a highly preferred orientation along the c axis were obtained on glass substrate. The Zn_0.7Cu_0.3O possesses the maximum density of nanorod arrays of 6.0 × 10⁹ cm^?2. The optical band-gap energy E _g decreases first and then increases with Cu additions increase. The broadening of the optical band-gap can be explained by Moss–Burstein effect. The Cu additions will effective enhance the violet emission and suppress the green emission. The violet and green emissions are likely due to the electron transition from the localized level below conduction band and oxygen vacancy to the valance band.     

Adsorption of Thorium from Aqueous Solution using Nanoporous Adsorbents: Effect of Contact Time,pH, Initial Concentration,and Temperature

Nanoporous silicates MCM-41 have been prepared using different surfactants such as cetyltrimethylammonium bromide (C₁₆TAB) and dodecyltrimethylammonium bromide (C₁₂TAB) as template. The adsorbents are characterized using powder x-ray diffraction, nitrogen adsorption-desorption isotherm data, scanning electron microscopy, and transmission electron microscopy. The thorium sorption was studied as a function of shaking time, pH, initial concentration, and temperature. The sorption of thorium at the determined optimum conditions follows Langmuir and Freundlich isotherms. The results show that the nanoporous MCM-41 synthesized by C₁₂TAB has more adsorption capacity than the MCM-41 synthesized by C₁₆TAB (77.6 µmol · g^?1 vs. 52.1 µmol · g^?1) at 25°C. Th(IV) adsorption onto nanoporous adsorbents was very fast process and therefore, this adsorbent is suitable for column separation. Thermodynamic parameters such as ΔH°, ΔS° and ΔG° were found to be 47.76 KJ · mol^?1, 196.21 J · mol^?1 · K^?1, and 19.00 KJ · mol^?1, respectively (at 298 K). The positive value ΔH° suggested the endothermic nature of adsorption and negative ΔG° indicates the feasibility and spontaneity of the adsorption process.     

Laser annealing of Pb(Zr0.52Ti0.48)O3 thin films for the pyroelectric detectors

Lead zirconate titanate (Pb(Zr_0.52Ti_0.48)O₃, PZT) thin films fabricated by magnetron sputtering technique on the Pt/Ti/SiO₂/Si substrates at room temperature, were annealed by means of CO₂ laser with resulting average substrate temperature below 500 °C. The crystal structure, surface morphology and pyroelectric properties of the PZT films before and after annealing were investigated by X-ray diffraction, atomic force microscopy, and pyroelectric measurements. The results show that the annealed PZT thin film with a laser energy density of 490 W/cm² for 25 s has a typical perovskite phase, uniform crystalline particles with a size of about 90 nm, and a high pyroelectric coefficient with 1.15 × 10^− 8 Ccm^− 2 K^− 1.     

Growth of polycrystalline Cd3As2 films on room temperature substrates by a pulsed-laser evaporation technique

Cd₃As₂ films were prepared by a pulsed-laser evaporation technique. The deposition onto fused quartz substrates was carried out in a vacuum chamber under a background pressure of about 0.6 × 10^?4 Pa. Energy-dispersive X-ray analysis, scanning electron microscopy, transmission electron microscopy and Hall measurements were used to characterize the films. The properties of the film as a function of their thickness and of the deposition parameters are discussed. It is shown that polycrystalline layers of Cd₃As₂ grow on substrates held at temperatures as low as 295 K. The room temperature electron concentrations and mobilities for such layers were (3.5–5.3) × 10¹⁸ cm^?3 and (0.6–1.06) × 10³ cm² V^?1 s^?1 respectively.     

Preparation of rare earth CeO<Subscript>2</Subscript> thin films using metal organic decomposition method for metal-oxide–semiconductor capacitors

Investigation of metal organic decomposed rare earth cerium oxide thin films deposited on Si substrate by sol–gel spin coating technique was carried out. The structural properties have been examined by using XRD, Fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM). The XRD confirms the cubic phase of CeO₂ thin films with (111) plane observed at 28.54°. The FTIR and EDAX spectra confirm the formation of CeO₂ films with atomic percentage of 19.39 and 54.82% of Ce and O₂, respectively. Thickness of 60.11 nm of CeO₂ film measured by cross sectional FESEM image, the average roughness of ~0.6 nm of 400?°C annealed CeO₂ films were observed from AFM micrograph. The MOS capacitors were fabricated by using Ti/Au bilayer metal contact depositing by E-beam evaporator on CeO₂/Si thin film for electrical measurements. Capacitance and conductance voltage measurement was carried out to determine the effective oxide charges (Q_eff), interface trap density (D_it) and dielectric constant (k) and are 2.48?×?10¹² cm^?2, 1.26?×?10¹² eV^?1cm^?2 and ~39, respectively. The effective metal work function of 5.68 for Ti/Au bilayer is observed to be higher than the work function of Ti or Au metals in vacuum.