Lithium ion conducting PVA:PVdF polymer electrolytes doped with nano SiO2 and TiO2 filler

The effect of nano SiO₂ and TiO₂ fillers on the thermal, mechanical and electrochemical properties of PVA:PVdF:LiCF₃SO₃ have been investigated by three optimized systems of SPE (80PVA:20PVdF:15LiCF₃SO₃), CPE-I (SPE:8SiO₂) and CPE-II (SPE:4TiO₂). From the TGA curve least weight loss has been observed for CPE-II indicating high thermal stability compared to other systems. Stress–strain curve of the prepared samples confirm the enhancement of tensile strength in CPE-II compared to CPE-I and SPE. Conductivity studies show that addition of TiO₂ filler slightly enhances ionic conductivity 3.7×10⁻³ S cm⁻¹ compared to filler free system at 303 K. Dielectric plots have been analyzed and CPE-II possesses higher dielectric constant compared to CPE-I and filler free system. Temperature dependence of modulus plots has been studied for highest conductivity possessing sample. Wider electrochemical stability has been obtained for nano-composite polymer electrolytes. The results conclude that the prepared CPE-II shows the best performance and it will be well suited for lithium ion batteries.     

Measurements of neutron radiation and induced radioactivity for the new medical linear accelerator,the Varian TrueBeam

Contemporary linear accelerators applied in radiotherapy generate X-ray and electron beams with energies up to 20 MeV. Such high-energy therapeutic beams induce undesirable photonuclear (γ,n) and electronuclear (e,e'n) reactions in which neutrons and radioisotopes are produced. The originated neutron can also induce reactions such as simple capture, (n,γ), reactions that produce radioisotopes. In this work measurements of the non-therapeutic neutrons and the induced gamma radiation were carried out in the vicinity of a new medical accelerator, namely the Varian TrueBeam. The TrueBeam is a new generation Varian medical linac making it possible to generate the X-ray beams with a dose rate higher than in the case of the previous models by Varian. This work was performed for the X-ray beams with nominal potentials of 10 MV (flattening filter free), 15 MV and 20 MV, and for a 22 MeV electron beam. The neutron measurements were performed by means of a helium chamber and the induced activity method. The identification of radioisotopes produced during emission of the therapeutic beams was based on measurements of the energy spectra of gammas emitted in decays of the produced nuclei. The gamma energy spectra were measured with the use of the high-purity germanium detector. The correlation between the neutron field and the mode and nominal potential was observed. The strongest neutron fluence of 3.1 × 10⁶ cm⁻² Gy⁻¹ and 2.0 × 10⁶ cm⁻² Gy⁻¹ for the thermal and resonance energies, respectively, was measured during emission of the 20 MV X-ray beam. The thermal and resonance neutron fluence measured for the 15 MV X-rays was somewhat less, at 1.1 × 10⁶ cm⁻² Gy⁻¹ for thermal neutrons and 6.7 × 10⁵ cm⁻² Gy⁻¹ for resonance neutrons. The thermal and resonance neutron fluences were smallest for the 10 MV FFF beam and the 22 MeV electron beam and were around two orders of magnitude smaller than those of the 20 MV X-ray beam. This work has shown that the neutron reactions are dominant because of relatively high cross sections for many elements used in the accelerator construction. The detailed analysis of the measured spectra made it possible to identify 11 radioisotopes induced during TrueBeam delivery. In this work the following radioisotopes were identified: ⁵⁶Mn, ¹²²Sb, ¹²⁴Sb, ¹³¹Ba, ⁸²Br, ⁵⁷Ni, ⁵⁷Co, ⁵¹Cr, ¹⁸⁷W, ²⁴Na and ³⁸Cl.     

Neutron fluence spectrometry using disk activation

A simple and robust detector for spectrometry of environmental neutrons has been developed. The technique is based on neutron activation of a series of different metal disks followed by low-level gamma-ray spectrometry of the activated disks and subsequent neutron spectrum unfolding. The technique is similar to foil activation but here the applied neutron fluence rates are much lower than usually in the case of foil activation. The detector has been tested in quasi mono-energetic neutron fields with fluence rates in the order of 1000–10000 cm⁻² s⁻¹, where the obtained spectra showed good agreement with spectra measured using a Bonner sphere spectrometer. The detector has also been tested using an AmBe source and at a neutron fluence rate of about 40 cm⁻² s⁻¹, again, a good agreement with the assumed spectrum was achieved.     

Electrical characterization of nano-composite polymer gel electrolytes containing NH4BF4 and SiO2: role of donor number of solvent and fumed silica

Nano-composite polymer gel electrolytes were synthesized by using polyethylene oxide (PEO), ammonium tetrafluoroborate (NH₄BF₄), fumed silica (SiO₂), dimethylacetamide (DMA), ethylene carbonate (EC), and propylene carbonate (PC) and characterized by conductivity studies. The effect of donor number of solvent on ionic conductivity of polymer gel electrolytes has been studied. The mechanical strength of the gel electrolytes has been increased with the addition of nano-sized fumed silica along with an enhancement in conductivity. Maximum room temperature ionic conductivity of 2.63 × 10⁻³ and 2.92 × 10⁻³ S/cm has been observed for nano-composite gel electrolytes containing 0.1 and 0.5 wt% SiO₂ in DMA+1 M NH₄BF₄+10 wt% PEO, respectively. Nano-composite polymer gel electrolytes having DMA have been found to be thermally and electrically stable over 0 to 90 °C temperature range. Also, the change in conductivity with the passage of time is very small, which may be desirable to make applicable for various smart devices.

     

Optical and electrical properties of Ge-implanted SiO2 layers on n-Si and p-Si

Ge ions of 100 keV were implanted into a 120 nm-thick SiO₂ layer on n-Si at room temperature while those of 80 keV were into the same SiO₂ layer on p-Si. Samples were, subsequently, annealed at 500°C for 2 h to effectively induce radiative defects in the SiO₂. Maximum intensities of sharp violet photoluminescence (PL) from the SiO₂/n-Si and the SiO₂/p-Si samples were observed when the samples have been implanted with doses of 1×10¹⁶ and 5×10¹⁵ cm⁻², respectively. According to current–voltage (I–V) characteristics, the defect-related samples exhibit large leakage currents with electroluminescence (EL) at only reverse bias region regardless of the type of substrate. Nanocrystal-related samples obtained by an annealing at 1100°C for 4 h show the leakage at both the reverse and the forward region.     

The spatial distribution of thermal and epithermal neutrons in a graphite moderated spallation neutron field

The Gamma-3 assembly is located at the Joint Institute for Nuclear Research, Dubna, Russia. It consists of a cylindrical lead target (ø = 8 cm, L = 58.8 cm) surrounded by reactor grade graphite (110 × 110 × 60 cm). The target was irradiated with a beam of 1.6 GeV deuterons from the Nuclotron accelerator and CR-39 track detectors coupled to LR-115 2B film were used to measure the slow neutron distribution on the surface of the graphite. The detection efficiency of the CR-39 in the CR-39/LR-115 2B system was measured using a custom made calibration setup and found to be (1.12 ± 0.05) × 10⁻³ and (6.1 ± 1.2) × 10⁻⁴ tracks per neutron, for thermal and epithermal neutrons respectively, under the etching and counting procedures described in this work. The irradiation of the Gamma-3 was also simulated using MCNPX 2.7 Monte Carlo code and good agreement between the experimental and calculated track densities was found. This serves as a good validation for the computational models used to simulate spallation neutron production, transport and moderation.     

Development of proton conducting biopolymer membrane based on agar–agar for fuel cell

A proton-conducting polymer electrolyte based on agar and ammonium nitrate (NH₄NO₃) has been prepared through solution casting technique. The prepared polymer electrolytes were characterized by impedance spectroscopy, X-ray diffraction, and Fourier transform infra-red spectroscopy. Impedance analysis shows that sample with 60 wt.% NH₄NO₃ has the highest ionic conductivity of 6.57 × 10⁻⁴ S cm⁻¹ at room temperature. As a function of temperature, the ionic conductivity exhibits an Arrhenius behaviour increasing from 6.57 × 10⁻⁴ S cm⁻¹ at room temperature to 1.09 × 10⁻³ S cm⁻¹ at 70 °C. Transport parameters of the samples were calculated using Wagner’s polarization method and thus shows that the increase in conductivity is due to the increase in the number of mobile ions. Fuel cell has been constructed with the highest proton conductivity polymer 40agar/60NH₄NO₃ and the open circuit voltage is found to be 558 mV.

     

Optical properties of amorphous Si/SiO2superlattice

Amorphous Si/SiO₂(a-Si/SiO₂) superlattices have been fabricated by the magnetron sputtering technique. The superlattice with an Si layer thickness of 1.8 nm has been characterized by transmission electron microscopy (TEM). The result indicates that most of the regions in the Si layer consist of amorphous phase, while regular structure appears in some local regions. This is in agreement with the Raman scattering spectroscopy. The optical absorption spectrum and photoluminescence (PL) spectrum have been measured. Moreover, the third-order optical nonlinearity χ⁽³⁾of this superlattice has been measured. To our knowledge, this is the first investigation of the nonlinear absorption and refractive index of an a-Si/SiO₂superlattice using the Z -scan technique. The real and imaginary parts of χ⁽³⁾have been found to be 1.316  ×  10 ^− 7eus and  − 5.596  ×  10 ^− 7eus, respectively, which are about two orders of magnitude greater than those of porous silicon. The results may be attractive for potential application in electro-optics devices.     

Synthesis and electrochemical properties of Li2S–B2S3–Li4SiO4

New Li⁺ ion-conductive glasses Li₂S–B₂S₃–Li₄SiO₄ were synthesized by rapid quenching, and they were transformed into glass ceramics by heat treatment. The heat treatment increased the ionic conductivities of the Li₄SiO₄-doped glasses, and the highest ionic conductivity observed in the system was 1.0 × 10^− 3 S cm^− 1 at room temperature. The glass ceramics were highly stable against electrochemical oxidation with a wide electrochemical window of 10 V.     

Electrical and optical characterization of SiOxNy and SiO2 dielectric layers and rear surface passivation by using SiO2/SiOxNy stack layers with screen printed local Al-BSF for c-Si solar cells

In c-Si solar cells, surface recombination velocity increases as the wafer thickness decreases due to an increase in surface to volume ratio. For high efficiency, in addition to low surface recombination velocity at the rear side, a high internal reflection from the rear surface is also required. The SiO_xN_y film with low absorbance can act as rear surface reflector. In this study, industrially feasible SiO₂/SiO_xN_y stack for rear surface passivation and screen printed local aluminium back surface field were used in the cell structure. A 3 nm thick oxide layer has resulted in low fixed oxide charge density of 1.58 × 10¹¹ cm⁻² without parasitic shunting. The oxide layer capped with SiO_xN_y layer led to surface recombination velocity of 155 cm/s after firing. Using single layer (SiO₂) rear passivation, an efficiency of 18.13% has been obtained with V_oc of 625 mV, J_sc of 36.4 mA/cm² and fill factor of 78.7%. By using double layer (SiO₂/SiO_xN_y stack) passivation at the rear side, an efficiency of 18.59% has been achieved with V_oc of 632 mV, J_sc of 37.6 mA/cm², and fill factor of 78.3%. An improved cell performance was obtained with SiO₂/SiO_xN_y rear stack passivation and local BSF.     

Optically stimulated luminescence (OSL) and thermally assisted OSL in Eu2+ – Doped BaSO4 phosphor

BaSO₄:Eu²⁺ phosphor has been investigated for its photoluminescence (PL), thermoluminescence (TL), TL kinetics, optically stimulated luminescence (OSL) and thermally assisted OSL (TA-OSL) response. PL spectra showed the characteristic emission of Eu²⁺ ion at 375 nm when excited by 320 nm. The luminescence lifetime has been measured as 40 and 628 μs of fast and slow components respectively. The TL parameters such as trap depth (E), frequency factor (s) and the order of kinetics (b) are determined. The phosphor is found to be 6 and 4 times more sensitive than CaSO₄:Dy and α-Al₂O₃:C, respectively, in TL mode. However, its OSL sensitivity is 75% of α-Al₂O₃:C. It is found to possess three OSL components having photoionization cross-sections of 1.4 × 10⁻¹⁷, 1.2 × 10⁻¹⁸ and 5.2 × 10⁻¹⁹ cm² respectively. The temperature dependence of OSL studies showed that integrated TA-OSL signal increases with stimulation temperature between 50 and 250 °C, while between 260 and 450 °C the signal intensity decreases. This behavior is interpreted to arise from competing effects of thermal assistance (activation energy E_A = 0.063 ± 0.0012 eV) and depletion of trapped charges. This increase of OSL at elevated temperature can be employed for enhancing the sensitivity of phosphor for radiation dosimetry.     

Structural,thermal and ion transport studies on nanocomposite polymer electrolyte-{(PEO + SiO<Subscript>2</Subscript>):NH<Subscript>4</Subscript>SCN} system

Development and characterisation of polyethylene oxide (PEO)-based nanocomposite polymer electrolytes comprising of (PEO-SiO₂): NH₄SCN is reported. For synthesis of the said electrolyte, polyethylene oxide has been taken as polymer host and NH₄SCN as an ionic charge supplier. Sol–gel-derived silica powder of nano dimension has been used as ceramic filler for development of nanocomposite electrolytes. The maximum conductivity of electrolyte ∼2.0 × 10⁻⁶ S/cm is observed for samples containing 30 wt.% silica. The temperature dependence of conductivity seems to follow an Arrhenius-type, thermally activated process over a limited temperature range.     

Small-angle neutron scattering studies on the structure of radiation defects in neutron-irradiated synthetic quartz

The supra-atomic structure of single crystals of synthetic quartz with a dislocation density of 54 cm^?2 in their initial state and after irradiation in a VVR-M reactor by fast neutrons with the energy, E _n > 0.1 MeV, at fluences of 2.3 × 10¹⁹ and 4.5 × 10¹⁹ N/cm², has been studied by the method of small-angle thermal neutron scattering. It has been established that fast neutrons create point, linear, and bulk defects throughout the entire material. It has been shown that extended defects have a significant integral length per volume unit equal to ??3 × 10¹¹ cm/cm³, and can form a consolidated network in the sample with a cell size of ??30 nm, through the channels of which the migration of impurity atoms and molecules is possible.     

Effects of neutron irradiation and subsequent annealing on the optical characteristics of sapphire

In this paper, the effect of neutron irradiation on sapphire single crystal with fast neutron of 1.0×10¹⁸ and 1.0×10¹⁹ neutrons/cm² has been investigated along with the effect of annealing temperature. It is found that the colorless transparent sapphire single crystals were turned yellow after 10 MeV fast neutron irradiation at room temperature. There are peaks at 206, 230, 258, 305, 358 and 452 nm after neutron irradiation. And the intensity of optical absorption bands decrease with wavelength and annealing temperature. A new absorption peak at 452 nm was found after isothermal annealing at 400 °C for 10 min, which was ascribed to F₂⁺ color center. Because of the recombination of interstitial ions and vacancies, color centers were almost removed after annealing at 1000 °C. The TL peaks were found to shift to higher temperature after neutron irradiation. And a higher fluence of the neutron irradiation would result in deep traps revealed as the new TL peaks at 176 and 227 °C.     

Charge storage characteristics of nonvolatile memories with chemically-synthesized and vacuum-deposited gold nanoparticles

Carrier injection and charge loss characteristics of nonvolatile memories with chemically-synthesized (CS) and vacuum-deposited (VD) gold nanoparticles (Au-NPs) have been investigated. Compared to CS counterparts, the memories with VD Au-NPs exhibit a higher dot density of 3.77 × 10¹¹ cm⁻², leading to a larger memory window. Further, the energy from valence-band edge to vacuum level (E_{VB_vac}) of tunneling oxide for the samples with CS and VD Au-NPs is found to be 9.04 and 9.85 eV respectively. The small E_{VB_vac} value of the memories with CS Au-NPs is resulted from the formation of a thin chemical oxide (SiO_x) on thermally-grown SiO₂ tunneling layer during the chemically synthesized process, contributing to a slow erasing behavior. Besides, the programming of the memories with VD Au-NPs is saturated at high gate bias, which has been well-explained by the electrons induced potential coupling between Au-NPs. Superior data retention property and high temperature dependence of charge loss are observed for the memories with CS Au-NPs, which can be ascribed to the thick tunneling oxide layer by the additional SiO_x film.     

A study of ZnS(Ag)/6LiF with different mass ratios

The properties of ZnS(Ag)/⁶LiF samples with three different mass ratios were studied. The study showed that the EJ426 sample with the mass ratio of 3:1 had the highest detection efficiency of thermal neutrons, which was 32.4% in the experiment. Furthermore, this sample had the largest charge spectrum. The light yield of its surface at the average value of the charge spectrum was approximately 8.01 × 10³ photons/neutron. The gamma sensitivity of the sample was better than 10⁻⁶ at the threshold of 350 photoelectrons. Therefore, EJ426 is a good candidate for a position-sensitive thermal neutron detector.     

NH4PO3/SiO2 composite as electrolyte for intermediate temperature fuel cells

NH₄PO₃/SiO₂ composite based electrolyte with SiO₂ as supporting matrix was prepared. A thermogravimetric analysis was performed. Its electrochemical properties were investigated by an impedance spectroscopy within the temperature range of 100–300 °C under dry and humid atmospheres. The maximum conductivity is 6 mS cm^− 1 at 300 °C under dry N₂ and 0.1 S cm^− 1 at 200 °C under humid N₂.     

Effect of series resistance on the performance of silicon Schottky diode in the presence of tin oxide layer

The current–voltage (I–V) characteristics of Al/SnO₂/p-Si (MIS) Schottky diodes prepared by means of spray deposition method have been measured at 80, 295 and 350 K. In order to interpret the experimentally observed non-ideal Al/SnO₂/p-Si Schottky diode parameters such as, the series resistance R_s, barrier height Φ_B and ideality factor n, a novel calculation method has been reported by taking into account the applied voltage drop across interfacial oxide layer V_i and ideality factor n in the current transport mechanism. The values obtained for V_i were subtracted from the applied voltage values V and then the values of R_s were recalculated. The parameters obtained by accounting for the voltage drop V_i have been compared with those obtained without considering the above voltage drop. It is shown that the values of R_s estimated from Cheung’s method were strongly temperature-dependent and decreased with increasing temperature. It is shown that the voltage drop across the interfacial layer will increase the ideality factor and the voltage dependence of the I–V characteristics. The interface state density N_ss of the diodes has an exponential growth with bias towards the top of the valance band for each temperature; for example, from 2.37 × 10¹³ eV⁻¹ cm⁻² in 0.70−E_v eV to 7.47 × 10¹³ eV⁻¹ cm⁻² in 0.62−E_v eV for 295 K. The mean N_ss estimated from the I–V measurements decreased with increasing the temperature from 8.29 × 10¹³ to 2.20 × 10¹³ eV⁻¹ cm⁻².     

Optical spectra and excited state relaxation dynamics of Sm<Superscript>3+</Superscript> in Gd<Subscript>2</Subscript>SiO<Subscript>5</Subscript> single crystal

Single crystals of gadolinium orthosilicate Gd₂SiO₅ containing 0.5 at% and 5 at% of Sm³⁺ were grown by the Czochralski method. Optical absorption spectra, luminescence spectra and luminescence decay curves were recorded for these systems at 10 K and at room temperature. Comparison of optical spectra recorded in polarized light revealed that the anisotropy of this optically biaxial host affects the intensity distribution within absorption and emission bands related to transitions between multiplets rather than the overall band intensity. It has been found that among four bands of luminescence related to the ⁴G_5/2→⁶H_J (J=5/2–11/2) transitions of Sm³⁺ in the visible and near infrared region the ⁴G_5/2 →⁶H_7/2 one has the highest intensity with a peak emission cross section of 3.54×10⁻²¹ cm² at 601 nm for light polarized parallel to the crystallographic axis c of the crystal. The luminescence decay curve recorded for Gd₂SiO₅:0.5 at% Sm³⁺ follows a single exponential time dependence with a lifetime 1.74 ms, in good agreement with the ⁴G_5/2 radiative lifetime τ _rad=1.78 ms calculated in the framework of Judd-Ofelt theory. Considerably faster and non-exponential luminescence decay recorded for Gd₂SiO₅:5 at% Sm³⁺ sample was fitted to that predicted by the Inokuti-Hirayama theory yielding the microparameter of Sm³⁺–Sm³⁺ energy transfer C _da=1.264×10⁻⁵² cm⁶×s⁻¹.     

Influences of LiCF3SO3 and TiO2 nanofiller on ionic conductivity and mechanical properties of PVA:PVdF blend polymer electrolyte

In recent years, solid polymer electrolytes have been extensively studied due to its flexibility, electrochemical stability, safety, and long life for its applications in various electrochemical devices. Interaction of LiCF₃SO₃ and TiO₂ nanofiller in the optimized composition of PVA:PVdF (80:20—system-A possessing σ ~ 2.8 × 10⁻⁷ Scm⁻¹ at 303 K) blend polymer electrolyte have been analyzed in the present study. LiCF₃SO₃ has been doped in system-A, and the optimized LiCF₃SO₃ doped sample (80:20:15-system-B possessing σ ~ 2.7 × 10⁻³ Scm⁻¹ at 303 K) has been identified. The effect of different concentration of TiO₂ in system-B has been analyzed and the optimized system is considered as system-C (σ ~ 3.7 × 10⁻³ Scm⁻¹ at 303 K). The cost effective, solution casting technique has been used for the preparation of the above polymer electrolytes. Vibrational, structural, mechanical, conductivity, thermal, and electrochemical properties have been studied using FTIR, XRD, stress-strain, AC impedance spectroscopic technique, DSC and TGA, LSV, and CV respectively to find out the optimized system. System-C possessing the highest ionic conductivity, higher tensile strength, low crystallinity, high thermal stability, and high electrochemical stability (greater than 5 V vs Li/Li⁺) is well suitable for lithium ion battery application.