Development of sulphurized SnS thin film solar cells

Thin films of tin sulphide (SnS) have been grown by sulphurization of sputtered tin precursor layers in a closed chamber. The effect of sulphurization temperature (T_s) that varied in the range of 150–450 °C for a fixed sulphurization time of 120 min on SnS film was studied through various characterization techniques. X-ray photoelectron spectroscopy analysis demonstrated the transformation of metallic tin layers into SnS single phase for T_s between 300 °C and 350 °C. The X-ray diffraction measurements indicated that all the grown films had the (111) crystal plane as the preferred orientation and exhibited orthorhombic crystal structure. Raman analysis showed modes at 95 cm⁻¹, 189 cm⁻¹ and 218 cm⁻¹ are related to the A_g mode of SnS. AFM images revealed a granular change in the grain growth with the increase of T_s. The optical energy band gap values were estimated using the transmittance spectra and found to be varied from 1.2 eV to 1.6 eV with T_s. The Hall effect measurements showed that all the films were p-type conducting nature and the layers grown at 350 °C showed a low electrical resistivity of 64 Ω-cm, a net carrier concentration of 2 × 10¹⁶ cm⁻³ and mobility of 41 cm² V⁻¹ s⁻¹. With the use of sprayed Zn_0.76Mg_0.24O as a buffer layer and the sputtered ZnO:Al as window layer, the SnS based thin film solar cell was developed that showed a conversion efficiency of 2.02%.     

Reactions of hydrazine with the amidogen radical and atomic hydrogen

The rate coefficient k₁ for NH₂ + N₂H₄ was measured to be (5.4 ± 0.4) × 10⁻¹⁴ cm³ molecule⁻¹ s⁻¹ at 296 K. NH₂ was generated by pulsed laser photolysis of NH₃ at 193 nm, and monitored as a function of time by pulsed laser-induced fluorescence excited at 570.3 nm under pseudo-first order conditions in the presence of excess N₂H₄ in an Ar bath gas. This reaction was also investigated computationally, with geometries and scaled frequencies obtained with M06-2X/6-311+G(2df,2p) theory, and single-point energies from CCSD(T)-F12b/cc-pVTZ-F12 theory, plus a term to correct approximately for electron correlation through CCSDT(Q). Three connected transition states are involved and rate constants were obtained via Multistructural Improved Canonical Variational Transition State Theory with Small Curvature Tunneling. Combination of experiment and theory leads to a recommended rate coefficient for hydrogen abstraction of k₁ = 6.3 × 10⁻²³ T^3.44 exp(+289 K/T) cm³ molecule⁻¹ s⁻¹. The minor channel for H + N₂H₄ forming NH₂ + NH₃ was characterized computationally as well, to yield 5.0 × 10⁻¹⁹ T^2.07 exp(-4032 K/T) cm³ molecule⁻¹ s⁻¹. These results are compared to several discordant prior estimates, and are employed in an overall mechanism to compare with measurements of half-lives of hydrazine in a shock tube.     

Impact of flow rate on sensitivity of semiconductor type thoron monitor

The commercially available continuous thoron monitor, RAD7, applies electrostatic collection of charged thoron progeny followed by alpha spectrometry with a semiconductor detector. Because of the short half life of thoron, the sensitivity of this monitor should vary with the flow rate of gas through it. In the work, direct correlation has been demonstrated between a theoretical model and the measured monitor sensitivity. Comparative thoron measurements were carried out using scintillation cells and double-filter method. It was found that the RAD7 thoron sensitivity increased with increasing flow of gas, reaching a maximum value 33.33 × 10⁻⁶ m³ s⁻¹ and decreased thereafter. To obtain improved thoron concentration accuracy at the standard 10.83 × 10⁻⁶ m³ s⁻¹ flow rate of the RAD7 monitor, a correction factor was estimated.     

Oxygen diffusion and surface exchange studies on (La0.75Sr0.25)0.95Cr0.5Mn0.5O3−δ

Oxygen tracer diffusion coefficient (D^⁎) and surface exchange coefficient (k^⁎) have been measured for (La_0.75Sr_0.25)_0.95Cr_0.5Mn_0.5O_3−δ using isotopic exchange and depth profiling by secondary ion mass spectrometry technique as a function of temperature (700–1000 °C) in dry oxygen and in a water vapour-forming gas mixture. The typical values of D^⁎ under oxidising and reducing conditions at ∼ 1000 °C are 4 × 10^− 10 cm² s^− 1 and 3 × 10^− 8 cm² s^− 1 respectively, whereas the values of k^⁎ under oxidising and reducing conditions at ∼ 1000 °C are 5 × 10^− 8 cm s^− 1 and 4 × 10^− 8 cm s^− 1 respectively. The apparent activation energies for D^⁎ in oxidising and reducing conditions are 0.8 eV and 1.9 eV respectively.     

Biosynthesis of gold nanoparticles by Aspergillum sp. WL-Au for degradation of aromatic pollutants

A simple method for synthesis of gold nanoparticles (AuNPs) using Aspergillum sp. WL-Au was presented in this study. According to UV–vis spectra and transmission electron microscopy images, the shape and size of AuNPs were affected by different parameters, including buffer solution, pH, biomass and HAuCl₄ concentrations. Phosphate sodium buffer was more suitable for extracellular synthesis of AuNPs, and the optimal conditions for AuNPs synthesis were pH 7.0, biomass 100 mg/mL and HAuCl₄ 3 mM, leading to the production of spherical and pseudo-spherical nanoparticles. The biosynthesized AuNPs possessed excellent catalytic activities for the reduction of 2-nitrophenol, 3-nitrophenol, 4-nitrophenol, o-nitroaniline and m-nitroaniline in the presence of NaBH₄, and the catalytic rate constants were calculated to be 6.3×10⁻³ s⁻¹, 5.5×10⁻³ s⁻¹, 10.6×10⁻³ s⁻¹, 8.4×10⁻³ s⁻¹ and 13.8×10⁻³ s⁻¹, respectively. The AuNPs were also able to catalyze the decolorization of various azo dyes (e.g. Cationic Red X-GRL, Acid Orange II and Acid scarlet GR) using NaBH₄ as the reductant, and the decolorization rates reached 91.0–96.4% within 7 min. The present study should provide a potential candidate for green synthesis of AuNPs, which could serve as efficient catalysts for aromatic pollutants degradation.     

The effect of annealing in forming gas on the a-IGZO thin film transistor performance and valence band cut-off of IGZO on SiNx

In this investigation, the carrier concentration gradient between channel and contact region is achieved to improve the Thin film Transistors (TFT) performance by employing annealing at 350 °C in forming gas (N₂ + 5% H₂). The contact region is covered with Mo metal and the channel region is only exposed to forming gas to facilitate the diffusion controlled reaction. The TFT using a-IGZO active layer is fabricated in ambient of Ar:O₂ in ratio 60:40 and the conductivity of the order of 10⁻³ S/cm is measured for as-deposited sample. The electrical conductivity of an annealed sample is of the order of 10² S/cm. The device performance is determined by measuring merit factors of TFT. The saturation mobility of magnitude 18.5 cm²V⁻¹ s⁻¹ has been determined for W/L (20/10) device at 15 V drain bias. The extrapolated field effect mobility for a device with channel width (W) 10 μm is 19.3 cm²V⁻¹ s⁻¹. The on/off current ratio is 10⁹ and threshold voltage is in the range between 2 and 3 V. The role of annealing on the electronic property of a-IGZO is carried out using X-ray photoelectron spectroscopy (XPS). The valance band cut-off has been approximately shifted to higher binding energy by 1 eV relative to as-deposited sample.     

Structural and electrical properties of fluorine-doped zinc tin oxide thin films prepared by radio-frequency magnetron sputtering

Transparent and conductive thin films of fluorine doped zinc tin oxide (FZTO) were deposited on glass substrates by radio-frequency (RF) magnetron sputtering using a 30 wt% ZnO with 70 wt% SnO₂ ceramic targets. The F-doping was carried out by introducing a mixed gas of pure Ar, CF₄, and O₂ forming gas into the sputtering chamber while sputtering ZTO target. The effect of annealing temperature on the structural, electrical and optical performances of FZTO thin films has been studied. FZTO thin film annealed at 600 °C shows the decrease in resistivity 5.47 × 10⁻³ Ω cm, carrier concentration ∼10¹⁹ cm⁻³, mobility ∼20 cm² V⁻¹ s⁻¹ and an increase in optical band gap from 3.41 to 3.60 eV with increasing the annealing temperatures which is well explained by Burstein–Moss effect. The optical transmittance of FZTO films was higher than 80% in all specimens. Work function (ϕ) of the FZTO films increase from 3.80 eV to 4.10 eV through annealing and are largely dependent on the amounts of incorporated F. FZTO is a possible potential transparent conducting oxide (TCO) alternative for application in optoelectronics.     

Ultrasmall iron oxide nanoparticles: Magnetic and NMR relaxometric properties

Ultrasmall iron oxide (USPIO) nanoparticles, with diameter mostly less than 3 nm dispersed in an organic carrier fluid were synthesized by polyol route. The evolution of ZFC-FC magnetization curves with temperature, as well as the shift of the ac susceptibility peaks upon changing the frequency, reveal that the nanoparticles in the fluid are non-interacting and superparamagnetic with the blocking temperature T_B ∼10 K. The Mössbauer spectra analysis proposed the core/shell structure of the nanoparticles consisting of stoichiometric γ-Fe₂O₃ core and non-stoichiometric shell. The nanoparticle surface layer has a great influence on their properties which is principally manifested in significant reduction of the magnetization and in a large increase in magnetic anisotropy. Magnetic moments do not saturate in fields up to 5 T, even at the lowest measured temperature, T = 5 K. The average magnetic particle diameter is changed from 1.3 to 1.8 nm with increasing magnetic field from 0 to 5 T which is noticeably smaller than the particle sizes measured by TEM. The estimated effective magnetic anisotropy constant value, K_eff = 2 × 10⁵ J/m³, is two orders of magnitude higher than in the bulk maghemite. Measurements of the longitudinal and transverse NMR relaxivity parameters on water diluted nanoparticle dispersions at 1.5 T gave the values r₁ = 0.028 mmol⁻¹ s⁻¹, r₂ = 0.050 mmol⁻¹ s⁻¹ and their ratio r₂/r₁ = 1.8. Continuous increase of the T₁-weighted MRI signal intensity with increasing Fe concentration in the nanoparticle dispersions was observed which makes this ferrofluid to behave as a positive T₁ contrast agent.     

A study of electrical enhancement of polycrystalline MgZnO/ZnO bi-layer thin film transistors dependence on the thickness of ZnO layer

A polycrystalline MgZnO/ZnO bi-layer was deposited by using a RF co-magnetron sputtering method and the MgZnO/ZnO bi-layer TFTs were fabricated on the thermally oxidized silicon substrate. The performances with varying the thickness of ZnO layer were investigated. In this result, the MgZnO/ZnO bi-layer TFTs which the content of Mg is about 2.5 at % have shown the enhancement characteristics of high mobility (6.77–7.56 cm² V⁻¹ s⁻¹) and low sub-threshold swing (0.57–0.69 V decade⁻¹) compare of the ZnO single layer TFT (μ_FE = 5.38 cm² V⁻¹ s⁻¹; S.S. = 0.86 V decade⁻¹). Moreover, in the results of the positive bias stress, the ΔV_on shift (4.8 V) of MgZnO/ZnO bi-layer is the 2 V lower than ZnO single layer TFT (ΔV_on = 6.1 V). It reveals that the stability of the MgZnO/ZnO bi-layer TFT enhanced compared to that of the ZnO single layer TFT.     

Ultrasonically assisted synthesis of barium stannate incorporated graphitic carbon nitride nanocomposite and its analytical performance in electrochemical sensing of 4-nitrophenol

We describe the ultrasonic assisted preparation of barium stannate-graphitic carbon nitride nanocomposite (BSO-gCN) by a simple method and its application in electrochemical detection of 4-nitrophenol via electro-oxidation. A bath type ultrasonic cleaner with ultrasonic power and ultrasonic frequency of 100 W and 50 Hz, respectively, was used for the synthesis of BSO-gCN nanocomposite material. The prepared BSO-gCN nanocomposite was characterized by employing several spectroscopic and microscopic techniques such as X-ray diffraction, X-ray photoelectron spectroscopy, fourier transform infra-red, field emission scanning electron microscopy, and high resolution transmission electron microscopy, to unravel the structural and electronic features of the prepared nanocomposite. The BSO-gCN was drop-casted on a pre-treated glassy carbon electrode (GCE), and their sensor electrode was utilized for electrochemical sensing of 4-nitrophenol (4-NP). The BSO-gCN modified GCE exhibited better electrochemical sensing behavior than the bare GCE and other investigated electrodes. The electroanalytical parameters such as charge transfer coefficient (α = 0.5), the rate constant for electron transfer (k_s = 1.16 s⁻¹) and number of electron transferred were calculated. Linear sweep voltammetry (LSV) exhibited increase in peak current linearly with 4-NP concentration in the range between 1.6 and 50 μM. The lowest detection limit (LoD) was calculated to be 1 μM and sensitivity of 0.81 μA μM⁻¹ cm⁻²_. A 100-fold excess of various ions, such as Ca²⁺, Na⁺, K⁺, Cl⁻, I⁻, CO₃²⁻, NO₃, NH₄⁺ and SO₄²⁻ did not able to interfere with the determination of 4-NP and high sensitivity for detecting 4-NP in real samples was achieved. This newly developed BSO-gCN could be a potential candidate for electrochemical sensor applications.     

Investigating gate metal induced reduction of surface donor density in GaN/AlGaN/GaN heterostructure by electroreflectance spectroscopy

The internal field of GaN/AlGaN/GaN heterostructure on Si-substrate was investigated by varying the thickness of an undoped-GaN capping layer using electroreflectance spectroscopy. The four samples investigated are AlGaN/GaN heterostructure without a GaN cap layer (reference sample) and three other samples with GaN/AlGaN/GaN heterostructures in which the different thickness of GaN cap layer (2.7 nm, 7.5 nm, and 12.4 nm) has been considered. The sheet carrier density (n_s) of a two-dimensional electron gas has decreased significantly from 4.66 × 10¹² cm⁻² to 2.15 × 10¹² cm⁻² upon deposition of a GaN capping layer (12.4 nm) over the reference structure. Through the analysis of internal fields in each GaN capping and AlGaN barrier layers, it has been concluded that the undiminished surface donor states (n_s) of a reference structure and the reduced n_s caused by the Au gate metal are approximately 5.66 × 10¹² cm⁻² and 1.08 × 10¹² cm⁻², respectively.     

Direct determination of gas velocity and gas temperature in an atmospheric-pressure argon-hydrogen plasma jet

Direct gas temperature and gas velocity measurements made in the exit plane of a subsonic argon-hydrogen thermal plasma jet from high-resolution lineshape analysis of laser light scattered by the plasma are reported. The lineshapes are in general a superposition of the ion feature of the Thomson-scattered light and the lineshape of Rayleigh scattered light. In the center of the jet Thomson scattering dominates while at larger radii Rayleigh scattering dominates. Because of the complexity of the lineshapes of light scattered by multicomponent plasmas, only those that are predominantly due to Thomson scattering can in practice be analyzed for gas temperature. Gas velocity can be determined from the Doppler shift of the lineshapes relative to the frequency of the incident laser if the velocity is greater than about 50 m s⁻¹. The maximum gas temperature measured was 14,500 K±5%. The maximum gas velocity measured was 1100 m s⁻¹±3%. Temperature values and the radial velocity profile are compared with those previously obtained from a subsonic all-argon plasma jet operated under similar conditions.     

Synergetic effects of ultrasound and sodium alginate coating on mass transfer and qualities of osmotic dehydrated pumpkin

This research studied the effects of combined ultrasound and 3% sodium alginate (SA) coating pretreatment (US + Coat) on mass transfer kinetics, quality aspects, and cell structure of osmotic dehydrated (OD) pumpkin. The results of the pretreatment were compared with the results of control (non-pretreated osmotic dehydration) and other three pretreatment methods, which were 1) ultrasound in distilled water for 10 min (USC), 2) ultrasound in 70% (w/w) sucrose solution (US) for 10, 20 and 30 min, and 3) coating with 1%, 2%, 3% (w/w) SA. The coating pretreatments with SA resulted in a higher water loss (WL) but lower water activity and solid gain (SG) than other treatments. US pretreatments resulted in the highest effective diffusion coefficients of water (D_w) and solid (D_s) but the cell structure of the product was deformed. The 3% SA coating treatment had the highest WL/SG (5.28) but with the longest OD time (12 h). Using the US + Coat pretreatment gave satisfactory high WL/SG (5.18), D_w (1.09 × 10⁻¹⁰ m²s⁻¹) and D_s (5.15 × 10⁻¹¹ m²s⁻¹), reduced the OD time to 9 h, and preserved the cell structure of the product. This research suggests that US + Coat pretreatment can be an effective processing step in the production of OD pumpkin.     

Thermoluminescence (TL) properties of Al2O3: C,Mg exposed to cobalt-60 gamma radiation doses

TL characteristics of powder form of Al₂O₃ doped with 0.1 mol% carbon and co-doped with different magnesium concentrations of 0.1 mol% and 0.2 mol% exposed to Cobalt-60 gamma ray at doses ranging from 5 Gy to 70 Gy were investigated. The recorded glow curves consist a dominant peak at 180 °C for a heating rate of 1 °C s⁻¹. The TL sample with 0.2 mol% Mg concentration have higher response compared to the sample with 0.1 mol% Mg concentration for a delivered dose of 5 Gy. The TL response has linear relationship with delivered dose for both samples. The TL sensitivity was found as 277.9 nC mg⁻¹ Gy⁻¹ for the sample with Mg concentration 0.2 mol% and 128.2 nC mg⁻¹ Gy⁻¹ for 0.1 mol% Mg. However, the sample with 0.1 mol% Mg concentration has better fading properties compared to the sample with 0.2 mol% Mg concentration. Both samples show good reproducibility with value less than 13%. The experimental value of effective atomic number, Z_eff is 9.21 and 9.44 for the sample with Mg concentration 0.1% mol and 0.2% mol, respectively, which are near to Z_eff of bone with a value of about 11.6.     

Preparation of ZIF-8 membranes supported on macroporous carbon tubes via a dipcoating–rubbing method

In the present work, a new dipcoating–rubbing method (DCRM) was developed to seed the surface of a macroporous carbon tube with a mixture of graphite and ZIF-8 nanoparticles. A continuous and low-defect ZIF-8 membrane was well formed on the seeded carbon tube by solvothermal growth. The DCRM involved a two-step process including first dipcoating a thin layer of the composite of graphite and ZIF-8 nanoparticles on the carbon surface and then rubbing the layer to form a stable seed layer. The graphite in the composite acting as binding agent could have two functions: (1) anchoring the ZIF-8 seeds onto the carbon surface; (2) smoothing the coarse surface of the macroporous carbon tube, thus forming a high quality ZIF-8 membrane. The as-prepared membrane was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and single gas permeation and was proved to be continuous and low-defect. The ideal selectivity of H₂/CH₄ is 7.9 with a H₂ permeance of 7.15×10⁻⁸ mol Pa⁻¹ s⁻¹ m⁻², which is higher than its corresponding Knudsen diffusion value. We could therefore expect the ZIF-8 membrane supported on macroporous tubular carbon to achieve a high selectivity of H₂ over CH₄ through a molecular sieving effect.     

High-speed laser cutting of superposed thermoplastic films: thermal modeling and process characterization

Common thermoplastic films used in the packaging industry have a thickness lower than 100 μm, and present low absorption to CO₂ laser radiation. This characteristic renders the use of cutting parameters, predicted by models developed for thicker thermoplastics inappropriate. In addition, the usual procedures involve the use of an assisting gas, responsible for removing the melted material, which, when processing thin films, induces changes in position in the material. A new theoretical model describing the temperature distribution on thin thermoplastic material during laser cutting was later developed. The heat conduction was solved analytically by the Green function method and heating and cooling thermal stress evolution was taken into consideration. The laser beam diameter over the samples provides the possibility of obtaining two cut operations: a simple cut, on beam focus, and a cut with welding, defocusing the beam. Engineering parameters predicted by the model were applied to cutting superposed high- and low-density polyethylene and polypropylene samples, transparent and white, with thicknesses between 10 and 100 μm, and experimentally validated.Proper modeling and the introduction of a reflective substrate under the samples allowed the improvement of process efficiency and the achievement of cutting operations up to 20 m s⁻¹, and cut with welding up to 14 m s⁻¹; an order of magnitude of improvement on industrial speeds previously attained for this operation.     

Novel wet electrostatic precipitator for collection of fine aerosol

A novel wet electrostatic precipitator (WESP) is designed for effective control of fine aerosol from humid gases. It operates on the principle of unipolar particle charging in the corona discharge and particle precipitation under the field of their own space charge. The new precipitator is characterized by high gas velocity in the ionizing stage. Tests were carried out for gas with (NH₄)₂SO₄, HCl and (NH₄)Cl aerosol at particle number concentration up to 5·10⁷#/cm³ and mass concentration 10–1000 mg/Nm³. For test conditions one-field WESP ensures mass collection efficiency 90–97% and two-field electrostatic precipitator up to 99%.     

On the structural stability and oxygen permeation behavior of inorganic SrCo0.8Fe0.2O3−δ membranes

The high oxygen permeability combined with reasonable structural stability of perovskite-type ABO_3−δ compounds is vital for their potential applications in gas separation, solid oxide fuel cells, sensors, etc. Hence, an attempt is made to develop SrCo_0.8Fe_0.2O_3−δ-based dense membranes with sol-gel-derived oxalates and study their phase stability and oxygen permeation. While X-ray diffraction confirms the presence of a perovskite-type cubic phase above 800 °C, X-ray photoelectron spectroscopy reveals the presence of cobalt and iron in 3+ and 4+ oxidation states with O₂ ²⁻, O₂ ⁻ and O⁻ species. The electrical conductivity increases up to a characteristic temperature and decreases slowly thereafter via pronounced carrier scattering. A 1.5-mm-thick membrane displays reasonable oxygen permeability of 1.05 × 10⁻⁶ mol cm⁻² s⁻¹ at 900 °C but has inadequate stability. Partial substitution of iron with zirconium is shown to improve permeability and stability significantly. Thus, SrCo_0.8Fe_0.15Zr_0.05O_3−δ membrane shows promise for oxygen permeation purposes.

     

A Boubaker polynomials expansion scheme (BPES)-related protocol for measuring sprayed thin films thermal characteristics

Measurements of In₂S₃ and ZnIn₂S₄ sprayed thin films thermal characteristics have been carried out using the photodetection technique. The thermal conductivity k and diffusivity D were obtained using a new protocol based on photothermal signal parameters analysis. Measured values of k and D were respectively, (15.2 ± 0.85) W m⁻¹K⁻¹ and (69.8 ± 7.1) × 10⁻⁶ m²s⁻¹ for In₂S₃, (7.2 ± 0.7) W m⁻¹K⁻¹ and (32.7 ± 4.3) × 10⁻⁶ m²s⁻¹ for ZnIn₂S₄. These values are extremely important since similar compounds are more and more proposed as Cd-free alternative materials for solar cells buffer layers.     

Polyethylene oxide and ionic liquid-based solid polymer electrolyte for rechargeable magnesium batteries

Solid polymer electrolytes (SPEs) based on polyethylene oxide (PEO) complexed with magnesium triflate Mg(Tf)₂ or Mg(CF₃SO₃)₂) and incorporating the ionic liquid (IL) (1-butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (PYR₁₄TFSI)) were prepared by solution cast technique. The electrolyte was optimized and characterized using electrical conductivity, cationic transport number measurements, and cyclic voltammetry. The highest conductivity of the PEO/Mg(Tf)₂, 15:1 (molar ratio), electrolyte at room temperature was 1.19 × 10⁻⁴ S cm⁻¹ and this was increased to 3.66 × 10⁻⁴ S cm⁻¹ with the addition of 10 wt.% ionic liquid. A significant increase in the Mg²⁺ ion transport number was observed with increasing content of the ionic liquid in the PEO-Mg(Tf)₂ electrolyte. The maximum Mg²⁺ ion transport number obtained was 0.40 at the optimized electrolyte composition. A battery of the configuration Mg/ and [(PEO)₁₅:Mg(Tf)₂+10%IL]/TiO₂-C was assembled and characterized. Preliminary studies showed that the discharge capacity of the battery was 45 mA h g⁻¹.