Synthesis and characterization of low particle size nanocrystalline SnSe thin films

Tin selenide (SnSe) nanocrystalline thin films of different thickness from 15 to 70 nm were prepared by inert gas condensation technique. Argon gas flow and substrate temperature were kept constant during deposition process at 2 × 10^?3 Torr and 27 °C respectively. Polycrystalline orthorhombic phase structured was deduced for the prepared SnSe ingot powder by X-ray diffraction pattern. The grazing incident in-plane X-ray diffraction (GIIXD) pattern showed nanocrystalline orthorhombic structure for deposited SnSe thin film. The TEM micrographs showed that thin films were nanocrystalline with particle size in the range from 2 to 5.7 nm. The optical band gap E_g of the thin films due to direct allowed transition have values ranging from 2.5 to 2.13 eV as the particle size increases from 2 to 5.7 nm. The photoconductivity spectra of the nanostructured SnSe thin films of different particle size showed transitions at 2.45, 2.34 and 2.21 eV for films of different particle size.     

The fabrication of SnSe/Ag nanoparticles on TiO2 nanotubes

SnSe and silver (Ag) nanoparticles were sequentially deposited on TiO₂ nanotube (NT) by pulsed electrochemical deposition and polyol chemistry process, respectively. The morphological observation under scanning electron microscope (SEM) showed that the average size of SnSe was about 30 nm and the Ag was about 5 nm. Transmission electron microscopy (TEM) combined with selected area electron diffraction (SAED) examination indicated that Ag nanoparticles exhibited a well-defined crystallinity. However, SnSe nanoparticles were amorphous and they turned to crystalline after being annealed at 300 °C in the atmosphere. The photocatalytic behavior of SnSe/Ag-TiO₂ NT was evaluated by UV–vis diffuse reflectance spectra (DRS). The results showed that the deposition of SnSe and Ag nanoparticles increased light absorption intensity in the wavelength range of visible light, which implied that the SnSe/Ag-TiO₂ NT is a promising ternary hybrid material in photocatalysis.     

Low-temperature ultrasound synthesis of nanocrystals CoTiO3 without a calcination step: Effect of ultrasonic waves on formation of the crystal growth mechanism

CoTiO₃ nanocrystallites with an average diameter of 50 nm were synthesized successfully by the sonochemical method without a calcination step and using C₁₀H₁₆N₂O₈ (EDTA) as the chelating agent. To reach an in-depth understanding of the scientific basis of the proposed process, an in-detail analysis was carried out for characterization of nanoscale CoTiO₃ particles via XRD, FTIR, FE-SEM and UV–vis diffuse reflectance spectroscopy (DRS). The crystallite size, average particle size and band gap are found to be 10.7 nm, in the range of 50 nm and 4.64 eV, respectively. The mechanism and the formation process of CoTiO₃ in the sonochemical process were proposed. It was found that nanocrystals were formed directly before being oriented and aggregated into large particles in aqueous solution under ultrasonic irradiation. The nucleation in the sonocrystallization process was accelerated by the implosive collapse of bubbles, while the crystal growth process was inhibited or delayed by shock waves and turbulent flow created by ultrasonic radiation. A pure complex perovskite phase of spherical shape was formed completely in a short irradiation time without the calcination process. Sonochemical irradiation could accelerate spherical shape formation of the particles significantly. These results provide new insights into the development and design of better nanomaterial synthesis methods.     

Influence of microstructure on macroscopic elastic properties and thermal expansion of nickel‐base superalloys ERBO/1 and LEK94

In the present work the thermal expansion and the elastic properties of second generation nickel‐base superalloy single crystals ERBO/1 (CMSX‐4 variation) and LEK94 have been studied between about 100 K and 1273 K using dilatometry and resonant ultrasound spectroscopy, respectively. Inhomogeneity related to the large scale microstructure of the samples can act as a potential source of scatter for the propagation of ultrasonic waves. This can be overcome by choosing samples of sufficient size so that they appear as homogeneous media at the scale of the elastic wave length. Our final results are in good agreement with data reported in literature for similar alloy systems. In particular, the elastic material properties are only weekly affected by moderate variations in chemical composition and microstructure. Taking into account literature data for other superalloys like CMSX‐4, we derive general polynomial functions which describe the temperature dependence of the elastic moduli E_〈100〉, E_〈110〉 and E_〈111〉 in nickel‐base superalloys to within about ±3%. It was also observed that the alloys ERBO/1 and LEK94 show weak but significant anomalies in both thermal expansion and temperature coefficients of elastic constants above about 900 K. These anomalies are probably related to the gradual dissolution of the γ′‐precipitates at higher temperatures.     

The effects of S-doping concentration on the photocatalytic performance of SnSe/S-GO nanocomposites

The effects of S-doped graphene oxide (S-GO) on the photocatalytic performance of SnSe nanostructures have been investigated. Different concentrations of S-doping as 2S-GO, 4S-GO, and 6S-GO (2, 4, and 6% in weight) have been synthesized. Characterization results indicated sulfur not only has successfully placed in the GO structure and a part of the GO sheet has been changed into reduced GO (rGO) by sulfur doping but also the surface morphology of the GO sheets has been changed from a smooth surface to fractured crack surfaces. The results showed that the increase of sulfur content caused the morphology of the SnSe nanostructures was changed from nanoparticles (NPs) into nanorods (NRs). The photocatalytic activity of the samples to degrade dyes under the visible-light irradiation conditions was carried out and it was observed an enhancement photocatalytic performance for the SnSe/2S-rGO nanocomposites in comparison to the other samples. More than 95% of dyes were degraded by the SnSe/2S-rGO nanocomposites for only 60 min. Brunauer–Emmett–Teller (BET) and electrical measurement results indicated the textural properties and conductivity of GO sheets were improved by sulfur doping. In addition, the photogenerated electron lifetime (τ_r) of the SnSe/rGO and SnSe/S-rGO nanocomposites has been measured by the Bode phase plot and it was observed a lifetime of τ_r = 71.1 and 31.7 μs for the SnSe/S-rGO and SnSe/rGO nanocomposites, respectively.     

Effect of structural defects on optical properties of amorphous selenium films

Thickness of film, energy of incident photons and glass transition temperature all affect the structural bonding between neighbours and are considered to be the main factors in studying the optical properties of amorphous selenium films. The results indicate that in the lowtemperature range (T <T _g), a shift in the absorption edge to lower photon energies with increasing film thickness occurs. Increasing the thickness is accompanied by a decrease in the optical energy gap,E _g ^opt , with a gradient of 5×10^–4eV nm^–1. In the high-temperature range (T >T _g), the value ofE _g ^opt for a given thickness decreases by more than 50% due to pronounced modulation of the structural defects under incidence of isoenergetic photons of 1.8 eV. The isothermal curves ofT,R=f(t), atT >T _g, take place via three time-dependent stages. These results are interpreted and are correlated with the temperature dependence of the morphological changes declaring the formation of spherulites having a lamellar structure. The kinetic parameters controlling the structural transition are computed and the results are discussed.     

Structural,optical, electrical properties,and relative humidity sensor application of PVA/Dextrin polymeric blend loaded with silicon dioxide nanoparticles

In the current study, polymer composite films (PCFs) of polyvinyl alcohol (PVA) and Dextrin (60/40) wt% without and with 0.03 and 0.06 wt% silicon dioxide nanoparticles (SiO₂NPs) were synthesized via casting way. The structural properties of the matrix polymer blend (MPB) were investigated using X-ray diffraction and revealed an amorphous structure. However, some kind of crystallinity has appeared after embedding the SiO₂NPs. The chemical functional groups were analyzed via FTIR spectra. The surface morphology characteristics were performed utilizing an optical microscope (OPM), and the images showed that SiO₂NPs were well diffused in MPB without any agglomerations. The optical properties were studied in the wavelength range between 190 and 1100 nm. Up to 97% of UV rays were blocked by PCFs at λ?=?270 nm and the absorption edges decreased from 4.05 to 3.80 eV. The values of the allowed and forbidden energy gap (E_g) decreased from 4.18 to 3.75 eV and from 3.98 to 3.73 eV, respectively, with the existence of the NPs. In addition, the electrical conductivity (σ_ac) values were increased with the increase in frequency f and NPs content. The use of SiO2NPs has shown highly improved dielectric and energy dissipation characteristics and has a high sensitivity to relative humidity in various NPs ratios, temperatures, time and RH ranges.

     

Sonocatalytic degradation of azo fuchsine in the presence of the Co-doped and Cr-doped mixed crystal TiO2 powders and comparison of their sonocatalytic activities

In order to degrade some pollutants effectively under ultrasonic irradiation, the Co-doped and Cr-doped mixed crystal TiO₂ powders, with high sonocatalytic activity, were prepared as sonocatalyst. The Co-doped and Cr-doped mixed crystal TiO₂ powders as sonocatalyst were prepared through sol–gel and heat-treated methods from tetrabutylorthotitanate, and then were characterized by XRD and TG–DTA technologies. In order to compare and evaluate the sonocatalytic activity of the Co-doped and Cr-doped mixed crystal TiO₂ powders, the low power ultrasound was as an irradiation source and the azo fuchsine was chosen as a model compound to be degraded. The degradation process was investigated by UV–vis, TOC, ion chromatogram and HPLC techniques. The results indicated that the sonocatalytic activity of Cr-doped mixed crystal TiO₂ powder was higher than that of Co-doped and undoped mixed crystal TiO₂ powder during the sonocatalytic degradation of the azo fuchsine in aqueous solution. These results may be of great significance for driving sonocatalytic method to treat non- or low-transparent industrial wastewaters.     

A change in the structure of an ultrasonically processed MMA-MAA based photoresist

The structure of a photoresist based on a MMA-MAA copolymer was modified by exposure to an ultrasound with a frequency of 21 kHz and a power density of 300 W/m². The results of the UV and IR spectroscopic measurements show that the ultrasonic processing leads to the formation of C=O double bonds and to the growth of absorption in the 260–360 nm wavelength range.     

Influence of RF power on structural optical and electrical properties of hydrogenated nano-crystalline silicon (<Emphasis Type="Italic">nc</Emphasis>-Si:H) thin films deposited by PE-CVD

We report synthesis of hydrogenated nanocrystalline silicon (nc-Si:H) thin films by using conventional plasma enhanced chemical vapor deposition (PE-CVD) system from gas mixture of pure silane (SiH₄) and hydrogen (H₂). We investigated the effect of RF power on structural, optical and electrical properties using various characterization techniques including Raman spectroscopy, FTIR spectroscopy, UV–visible spectroscopy etc. Low angle XRD and Raman spectroscopy analysis revealed that the RF power in PE-CVD is a critical process parameter to induce nanocrystallization in Si:H films. The FTIR spectroscopy analysis results indicate that with increase in RF power the predominant hydrogen bonding in films shifts from Si–H to Si–H₂ and (Si–H₂)_n bonded species bonded species. However, the bonded hydrogen content didn’t show particular trend with change in RF power. The UV–visible spectroscopy analysis shows that the band tail width (E₀₄–E_Tauc) with increase in RF power. The defect density and Urbach energy also increases with increase in RF power. The highest dark conductivity (and lowest charge carrier activation energy) was obtained for the film deposited at RF power of 125 W indicating that 125 W is optimized RF power of our PE-CVD unit. At this optimized RF power nc-Si:H films with crystallite size ~3.7 nm having good degree of crystallinity (~86.7 %) and high band gap (E_Tauc ~ 2.01 eV and E₀₄ ~ 2.58 eV) were obtained with a low hydrogen content (6.2 at.%) at moderately high deposition rate (0.24 nm/s).     

Reflectivity spectrum and electrical properties of TlIn0.98Ce0.02Se2 single crystals

The room-temperature reflectivity spectrum of TlIn_0.98Ce_0.02Se₂ crystals is measured at photon energies from 1 to 6 eV, and their conductivity, Hall coefficient, and thermoelectric power are determined in the temperature range 80–460 K. The results are used to evaluate the ionization energy of impurities (ΔE _a = 0.09 eV), the band gap of the crystals (E _g = 1.30 eV), and their refractive index (n = 2.5).     

Effect of pyrolysis temperature on structural,microstructural and optical properties of nanocrystalline ZnO powders synthesised by ultrasonic spray pyrolysis technique

In this article, we report on the effect of pyrolysis temperature on structural, microstructural and optical properties of nanocrystalline ZnO powder synthesised by ultrasonic spray pyrolysis (USP) technique. Powder samples P1, P2 and P3 were prepared at various pyrolysis temperatures (temperature of 2nd zone) of 973, 1073 and 1273?K, respectively. Phases were identified and crystallite sizes were calculated from X-ray diffraction (XRD) diagrams. The morphology and size of ZnO nanocrystallites associated with nanopowder were studied using transmission electron micrograph (TEM). It revealed that the powder consisted of crystallites ranging in size from 9 to 20?nm. These values were matching with the crystallite sizes calculated from XRD. Both XRD and TEM studies of ZnO nanopowders showed that the crystallite sizes increased with an increase in the pyrolysis temperature. The synthesised nanopowders exhibited direct band gap (E _g) in the range 3.37–3.40?eV.     

Highly Efficient Semitransparent Solar Cells with Selective Absorption and Tandem Architecture

Semitransparent (ST) photovoltaics (PVs) with selective absorption in the UV or/and near‐infrared (NIR) range(s) and reduced energy losses, are critical for high‐efficiency solar‐window applications. Here, a high‐performance tandem ST‐PV with selected absorption in the desirable regions of the solar spectrum is demonstrated. An ultralarge‐bandgap perovskite film (FAPbBr_2.43Cl_0.57, E_g ≈ 2.36 eV) is first developed to fulfil efficient selective absorption in the UV region. After optimization, the corresponding ST single junction (SJ) PV exhibits an averaged transmittance (AVT) of ≈68% and an efficiency of ≈7.5%. By sequentially reducing the visible absorbing component in a low‐bandgap organic bulk‐heterojunction layer, an ST‐PV with selective absorption in the NIR is achieved with a power conversion efficiency (PCE) of 5.9% and a high AVT of 62%. The energy loss associated with the SJ ST‐PVs is further reduced with a tandem architecture, which affords a high PCE of 10.7%, an AVT of 52.91%, and a light utilization efficiency up to 5.66%. These results represent the best balance of AVT and PCE among all ST‐PVs reported so far, and this design should pave the road for solar windows of high performance.     

Polyaniline/CuCl nanocomposites prepared by UV rays irradiation

In present paper, polynailine (PANI)/CuCl nanocomposites were prepared by UV rays irradiation method. In this method, photons in the UV rays and Cu²⁺ ions replaced conventional oxidant such as ammonium persulfate (APS) to promote polymerization of aniline monomer. The PANI/CuCl nanocomposites were characterized by infrared spectroscopy (FT-IR), X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution transmission electron microscope (HRTEM), and electron diffraction (ED). The results indicated that aniline could polymerize to PANI by UV rays irradiation. Meanwhile, the results of HRTEM and ED confirmed that the CuCl dispersed into PANI was single crystal with cubic crystal structure. A potential formation mechanism of PANI/CuCl nanocomposites was investigated and suggested.     

Détermination de la résistance à la compression du béton d'après la vitesse transversale de propagation des ultrasons et les méthodes combinées qui en découlent

On expose les résultats d'une recherche, qui permettent de formuler un jugement sur le degré de corrélation entre la résistance du béton à la compression et ses caractéristiques aux ultrasons, soit la vitesse de propagation des ultrasons par impulsons d'ondes transversales, une caractéristique complexe composée de la vitesse d'impulsion des ondes transversales et de la vitesse d'impulsion des ondes longitudinales, le module d'élasticité dynamique en compression et en tractionE _bu du béton, le module d'élasticité dynamique transversaleG _bw, ces relations étant comparées avec la relation employée jusqu'alors pour déterminer la résistance du béton, et la vitesse de propagation des ultrasons par impulsion d'ondes longitudinales. Summary This research is founded on new knowledge of the possibility of measuring the propagation time of transverse ultrasonic waves in concrete and on a measurement method devised by the author. This uses the measured and theoretical characteristics of concrete obtained by the ultrasonic method, that is to say the velocity of propagation of transverse ultrasonic waves vt, the dynamic modulus of elasticity in compressive and tensile loading E_bw, the dynamic modulus of transverse elasticity G_bw, determined on the bases of their ultrasonic parameters, the velocity of propagation of longitudinal waves and a complex characteristic composed of two pulse velocities (v_t and v_L). Extensive study of the degree of correlation between the compressive strength and the two characteristics of concrete mentioned above led the author to formulate the following statements: Correlations R=F (v_t), R=f₂(E_bw), R=f₃(G_bw) and the multiple correlation R=F₁(v_t, v_L) show an analogous degree of correlation which is always higher than the correlation R=f₁ (v_L) used up till now. From the practical point of view, the result is that to determine the strength of a concrete in a building or a structural member, it suffices to measure the propagation time of transverse ultrasonic waves and to apply R=f(v_t) expressed by a regression equation. Introducing other parameters (velocity of longitudinal ultrasonic waves, the concrete density and the Poisson ratio) which implies undertaking additional measurements, will no longer give rise to appropriate effects. By varying the aggregate content and the concrete density at certain points in the concrete, it is possible to reach greater accuracy in the determination of compressive strength of concrete with the correlation R=f₃(G_bw).      

A facile way to optimize thermoelectric properties of SnSe thin films via sonication-assisted liquid-phase exfoliation

In our work, SnSe nanosheets and nanostructured thin films were successfully synthesized via sonication-assisted exfoliation and coating process. The SnSe nanosheets respond to a uniform lateral size, with two to three single layers by 2.82 nm and 280 nm² of average thickness and average area, respectively. The results were confirmed by Scanning Electron Microscope, Transmission Electron Microscope, and Atomic Force Microscope. X-ray diffraction and Raman spectra indicate that the SnSe nanosheets have high crystalline quality along a-axis. The SnSe nanostructured thin films were prepared in various thicknesses from 350 to 650 nm. The highest power factor value is achieved at 450 nm in 375–600 K temperature range. A simple method of fabrication and controllable thermoelectric properties of SnSe nanostructured thin films as well as other two-dimensional (2D) materials are introduced.

     

Investigation of Phase Formation and Magnetic Properties of Mn Ferrite Nanoparticles Prepared via Low-Power Ultrasonic Assisted Co-precipitation Method

MnFe₂O₄ nanoparticles were synthesized by low-power ultrasonic assisted co-precipitation at two different aging times. In order to investigate the effect of ultrasonic waves on phase formation and magnetic properties of Mn ferrite nanoparticles, two other samples were synthesized in the same conditions but in the absence of ultrasonic waves. Structural and morphological properties of the nanoparticles were examined by using X-ray diffraction (XRD) and scanning electron microscope (SEM). The presence of ultrasonic waves through the reaction medium led to form a single phase of MnFe₂O₄ at 15 min aging time, while this time was insufficient to form a single phase in the absence of ultrasonic waves. At 60 min aging time, the crystallinity of the sample synthesized in the presence of ultrasonic waves was greater and its particle size was bigger than those of the sample synthesized in the absence of ultrasonic waves. The observed results were evaluated from physico-chemical point of view. It was concluded that the ultrasonic waves led to a slower nucleation rate. The magnetic properties of the nanoparticles were examined by permeameter and Faraday-balance equipment. The saturation magnetization of the sample prepared in the presence of ultrasonic waves was enhanced and its Curie temperature was reduced.     

Optical constants and band gap determination of Pb0.95La0.05Zr0.54Ti0.46O3 thin films using spectroscopic ellipsometry and UV–visible spectroscopy

We report the structural evolution and optical properties of lanthanum doped lead zirconate titanate (PLZT) thin films prepared on Pt/TiO₂/SiO₂/Si substrates by chemical solution deposition. X-ray diffraction demonstrates the post-deposition annealing induced crystallization for PLZT films annealed in a temperature (T_a) range of 550–750 °C. PLZT films annealed at higher temperature exhibit polycrystalline structure along with larger grain size. Optical band gap (E_g) values determined from UV–visible spectroscopy and spectroscopic ellipsometry (SE) for PLZT films were found to be in the range of 3.5–3.8 eV. E_g decreases with increasing T_a. The optical constants and their dispersion profiles for PLZT films were also determined from SE analyses. PLZT films show an index of refraction in the range of 2.46–2.50 (λ = 632.8 nm) with increase in T_a. The increase in refractive index at higher T_a is attributed to the improved packing density and crystallinity with the temperature.     

The effects of substrate temperature on the structure and properties of ZnO films prepared by pulsed laser deposition

ZnO thin films were prepared by pulsed laser deposition (PLD) on glass substrates with growth temperature from room temperature (RT) to 500 °C. The effects of substrate temperature on the structural and optical properties of ZnO films have been investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission spectra, and RT photoluminescence (PL) measurements. The results showed that crystalline and (0 0 2)-oriented ZnO films were obtained at all substrate temperatures. As the substrate temperature increased from RT to 500 °C, the ratio of grain size in height direction to that in the lateral direction gradually decreased. The same grain size in two directions was obtained at 200 °C, and the size was smallest in all samples, which may result in maximum E_g and E₀ of the films. UV emission was observed only in the films grown at 200 °C, which is probably because the stoichiometry of ZnO films was improved at a suitable substrate temperature. It was suggested that the UV emission might be related to the stoichiometry in the ZnO film rather than the grain size of the thin film.     

Structural evolution, dielectric and electro-optic properties of sol-gel derived potassium titanyl phosphate thin films

Transparent potassium titanyl phosphate (KTiOPO₄) thin films were prepared by a sol-gel coating technique. The structural evolution of the KTP thin films was examined by means of DTA/TGA, FT-IR, XRD and SEM. The effect of UV irradiation on the crystallization behavior was investigated and it was found that the UV irradiation decreases the crystallization temperature of the KTP thin films and dried gels. The dielectric and electro-optic properties were evaluated. The dielectric measurement results show that the KTP thin films have a low dielectric constant of 12 in the temperature range of 25–100 °C and frequency range of 1–1000 kHz. The electro-optic results indicate that the KTP thin films exhibit a quadratic electro-optic effect and may have potential applications for electro-optic devices.