Photoelectrochemical oxidation of organic substances and electricity generation in the presence of nanocrystalline titania photocatalyst

A chemically biased, two compartment cell has been used to photoelectrochemically degrade several substances and produce electricity. The photoanode of the cell was made of nanocrystalline Titania deposited on a conductive transparent fluorine-doped tin oxide electrode. The dark cathode was made of an identical electrode as the photoanode with Pt nanoparticles deposited on the nanocrystalline Titania film. The photoanode was activated by UVA radiation emitted by Black-light tubes or directly by natural (Solar) light. Photo-oxidation of several substances produced electricity. Efficiency calculations have been made in all studied cases.     

Synthesis and optical characterization of n-ZnO and p-Cu2ZnSnS4 nanocrystalline thin films for low cost solar cells

High quality ZnO/Cu₂ZnSnS₄ thin films as a window/absorber layers were successfully synthesized via spin coating the sol-gel precursor of each composition without using any vacuum facilities. In this study, the impact of annealing temperature (400 °C, 3 h) on the ZnO window layer and different thickness (3 and 5 layers) of the Cu₂ZnSnS₄ (CZTS) absorber layer were investigated. X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDX), scanning electron microscope (SEM) and UV–vis–NIR spectroscopy were used for the structural, compositional, morphological and optical absorption analysis of each layer. ZnO exhibits wurtzite hexagonal crystal structure with particle size equals to 8.60 and 28.59 nm for fresh and annealed films, respectively. Micro-strain and dislocations density decreased with the annealing temperature. X-ray diffraction patterns for CZTS films show small peak at (112) according to the kesterite structure with particle size in nano-scale for the two thicknesses. ZnO films demonstrated direct optical band gap of 3.23 and 3.21 eV for fresh and annealed films, respectively. CZTS films (3 and 5 layers) also have direct optical band with optimum value (1.51 eV) for thickness of 5 layers. The J-V characteristics of the CZTS-based thin film solar cells (CZTS/ZnO/ZnO:Ag) were measured under air mass AM 1.5 and 100 mW/cm² illumination. The values of the short circuit current (J_sc), open circuit voltage (V_oc) and fill factor (FF) also have been obtained.     

Carbon incorporation process in GaAsN films grown by chemical beam epitaxy using MMHy or DMHy as the N source

Crystal quality of GaAsN films can be improved by using CBE for low-temperature growth. However, low-temperature growth increases C incorporation in the films, which degrades their electrical properties. Consequently, C incorporation was investigated in view of the surface reaction of N sources on a substrate surface, and MMHy and DMHy were compared. When MMHy was used as an N source, C concentration in GaAsN drastically increases below 380 °C than that in GaAs due to insufficient CH_x desorption. In the case of DMHy, N(CH₃)₂ is desorbed more readily than CH_x, therefore, the C concentration can then be reduced using DMHy.     

Calculation of the integrated coefficients of absorption and transmission of solar radiation for semiconductor films

A Method is described for calculating the absorption and transmission of solar radiation by thin semiconductor films as a function of the thickness of the films. Computational results are presented.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 53, No. 3, pp. 402–406, September, 1987.     

Raman spectroscopic investigation of solid samples using a low-repetition-rate pulsed Nd:YAG laser as the excitation source

We tried to investigate the possibility of using a low-repetition-rate pulsed Nd:YAG laser as an excitation source in Raman measurements for solid samples. Based on the results from the Raman spectra excited by continuous wave (CW) 532 and 325 nm lasers, we studied the influence of laser energy and irradiation time of 532 and 355 nm pulsed Nd:YAG lasers (10 Hz repetition rate) on the thermal stability of (NH4)6Mo7O(24).4H2O, NH4VO3, and Ce(NO3)(3).6H2O samples, which usually decompose at relatively low temperatures. It is observed that the heating temperature estimated at these samples caused by the irradiation of 532 nm pulsed laser with 22 mJ is no higher than 100 degrees C even for 60 min exposure. The 355 nm pulsed laser with energies below 8.0 mJ hardly causes thermal damage to hydrated (NH4)6Mo7O24 and hydrated Ce(NO3)3 SAMPLES: However, a 355 nm pulsed laser with only 2.2 mJ causes heating temperatures as high as 200 degrees C in the NH4VO3 SAMPLE: These great differences should be attributed to the electronic absorbance of the above three samples at 355 nm. We also found that a 532 nm pulsed laser with even 22 mJ and a 355 nm pulsed laser with even 8.0 mJ do not cause the phase transition of TiO2 and ZrO2, whose phase transformation easily takes place at elevated temperatures, but pulsed lasers could remove some oxygen atoms from these samples. In addition, for L-alanine and DL-beta-phenylalanine biological samples, it is surprisingly found that they are not damaged by the 355 nm pulsed laser even when the laser energy is increased to 8.0 mJ, possibly because they do not absorb the 355 nm laser. Based on these results, it is demonstrated that low-repetition-rate pulsed lasers with appropriate wavelength and energy can be employed as the excitation sources of Raman spectroscopy for characterizing some solid samples, even the thermally unstable samples.     

Preparation and properties of transparent conductive N-doped CuAlO2 films using N2O as the N source

N-doped CuAlO₂ films were prepared by RF magnetron sputtering on quartz substrates using N₂O as the N source. N concentration in the films is detected by Auger electron spectroscopy in detail, which confirms that N is indeed incorporated into the films. The optical and electrical properties of transparent conductive N-doped CuAlO₂ films are modulated by the N₂O flow ratio in sputtering gas. The N-doped films have a visible transmittance of 60–70 % and a high infrared transmittance of ~85 %. The film deposited by using 15 % N₂O flow ratio with the optimal crystalline is provided with a conductivity of 3.75 × 10^?2 S cm^?1 at room temperature, which improves over one order of magnitude compared with the undoped film. The enhanced conductive property is mainly originated from the ionization of acceptor impurities.     

Effect of temperature on the evolution of diffusivity, microstructure and hardness of nanocrystalline nickel films electrodeposited at low temperatures

Most nickel (Ni) films galvanostatically electrodeposited at 40-50 °C exhibited low hardness about 4 GPa and rough surface. In this article, we have investigated Ni electrodeposition at low temperatures of 5-20 °C in order to enhance the hardness and smoothness of films and performed by potentiostatic mode instead of galvanostatic mode to avoid the low-temperature precipitation of electrolyte agents. Effect of temperature on the evolution of diffusion coefficient, deposition rate, morphology and hardness was studied. Electrodeposition at low temperature without hard-element addition can reduce diffusion rate and produce the fine-grain, smooth morphology and dense film together with compressive residual stress to enhance hardness up to 6.18 GPa at 5 °C. The growth and hardening mechanism of low-temperature electrodeposited Ni were further discussed in details.     

Growth of p-type ZnO thin films by using an atomic layer epitaxy technique and NH3 as a doping source

Nitrogen-doped, p-type ZnO thin films have been grown successfully on sapphire (0001) substrates by atomic layer epitaxy (ALE) using Zn(C₂H₅)₂ [Diethylzinc, DEZn], H₂O and NH₃ as a zinc precursor, an oxidant and a doping source gas, respectively. The lowest electrical resistivity of the p-type ZnO films grown by ALE was 210 Ω cm with a hole concentration of 3.41 × 10¹⁶ cm^− 3. Low temperature-photoluminescence analysis results support that the nitrogen ZnO after annealing is a p-type semiconductor. Also a model for change from n-type ZnO to p-type ZnO by annealing is proposed.     

Deposition of nanocrystalline ZnO thin films on p-Si by novel galvanic method and application of the heterojunction as methane sensor

Undoped nanocrystalline n-ZnO thin films were deposited by a novel galvanic technique at room temperature on p-Si 〈100 〉 substrates to fabricate ZnO–Si heterojunctions. The I–V characteristics were studied at different temperatures with two different metallic contacts e.g., gold and palladium–silver (26%), in air and in presence of different concentrations (0.1, 0.5 and 1%) of methane gas. A shift in I–V characteristics in presence of methane was observed. The sensitivity and response time were studied at different temperatures (30 through 350 °C). Pd–Ag (26%) catalytic contacts showed much improved sensor performance.     

Design, fabrication and performance evaluation of a 22-channel direct reading atomic emission spectrometer using inductively coupled plasma as a source of excitation

The indigenous design, fabrication and performance evaluation of a polychromator, using inductively coupled plasma (ICP) as a source of excitation, are described. A concave holographic grating is used as the dispersing element and a Paschen — Runge mount is chosen to focus the spectra over a wide range along the Rowland circle. Twenty-two exit slits, mounted along the circle, precisely correspond to the wavelengths used for determination of up to twenty elements present in the plasma. Radiations emerging from the exit slits are detected by photomultiplier tubes placed behind them. The photomultiplier signal is recorded by an electronic system consisting of an integrator and a PC-based data acquisition system. The performance of the spectrometer has been evaluated with an ICP excitation source. Synthetic standards in deionized water containing a mixture of twenty impurities have been analysed. Typical determination limits observed for elements range from sub-ppm to ppm levels. All the elements present as impurities can be detected simultaneously. It is also observed that each element has a different emitting region in the ICP flame for which the maximum signal to the background is obtained. The determination limits obtained corresponding to these zones are the lowest. A study of the sensitive emitting zones for several elements has been carried out and the results are demonstrated by photographs of the ICP flame. The study will help in achieving the minimum value of determination limit for an impurity element.     

Growth of single-phase CuInGaSe2 photo-absorbing alloy films by the selenization method using diethylselenide as a less-hazardous Se source

Selenization growth of purely single-phase, polycrystalline CuIn_1 − xGa_xSe₂ (0 ≤ x ≤ 1) alloy films was demonstrated using a less-hazardous metalorganic selenide, diethylselenide [(C₂H₅)₂Se: DESe], without additional thermal annealing. Approximately 2.0-μm-thick films of the alloys exhibited X-ray diffraction peaks originating exclusively from the chalcopyrite structure. Low temperature photoluminescence spectra of the alloy films were dominated by a couple of characteristic donor-acceptor pair emissions that are particular to the state-of-the-art CuInGaSe₂ photo-absorbing layers.     

History of the solar particle event radiation doses on-board aeroplanes using a semi-empirical model and Concorde measurements

Measurements during solar particle events with dosemeters flying permanently on-board Concorde are used to develop a semi-empirical model, called SiGLE. The model is intended to calculate, for a given flight plan, the dose equivalent received during a solar particle event observed with ground-based neutron monitors. It is successfully in operation in the SIEVERT computerised system intended to improve monitoring of radiation dose received by aircrews, in application to a European Directive. The semi-empirical model is applied to evaluate, for most exposed routes, the radiation doses corresponding to the GLEs observed since 1942 with ion chambers or neutron monitors. The results for the largest GLEs observed in the past are discussed in terms of radiation risk, and guidelines are suggested concerning possible alerts to the aeroplanes in case of events of exceptional magnitude.     

Synthesis of titania microspheres with hierarchical structures and high photocatalytic activity by using nonanoic acid as the structure-directing agent

The titania, as the heterogeneous photocatalyst, has attracted much attention in attempts to eliminate pollutants, especially organic compounds in water and air. In this study, the titania microspheres with hierarchical structures were prepared by a combined sol–gel and solvothermal method. The X-ray powder diffraction (XRD) result indicated that the synthesized titania microspheres were of anatase phase. Field-emission scanning electron microscope (FESEM) and high-resolution transmission electron microscope (HRTEM) showed that the microspheres with well-dispersity had an average diameter of 651 nm and were composed of nanoparticles with about 20 nm in diameter. The Brunauer–Emmett–Teller (BET) results showed that the microspheres possessed high surface areas and lots of mesopores. Further study indicated that the synthesized titania microspheres exhibited high photocatalytic activity and had an important advantage over the commercial P25.     

Synthesis of the nanocrystalline CoFe2O4 ferrite thin films by a novel sol-gel method using glucose as an additional agent

Polycrystalline and nanometer-sized CoFe₂O₄ ferrite thin films are successfully synthesized using glucose as an addition agent. The thermal gravimetric/differential thermal analyzer, X-ray diffractometer, electron diffraction, scanning electron microscope, atomic force microscope and vibrating sample magnetometer are used to characterize the effects of the calcination temperature on the crystalline structure, morphology and magnetic properties of the Co-ferrite thin films. CoFe₂O₄ ferrite thin films have a single phase inverse spinel structure and are crystallized at and above 300 °C which is much lower than the required temperature in the traditional ceramic method (about 500-600 °C). Co-ferrite thin films annealed at relative low temperature of 400 °C show very small particle size with average of 32 nm and excellent magnetic properties for information storage applications.     

Investigation of thin-film samples by the method of photothermal reflection with harmonic excitation, using the heterodyning of exciting and sampling radiation

A method of determining the phase shift and thermal parameters of thin films is suggested and experimentally tested.     

Synthesis and structure characterization of low dielectric constant MSQ films by using octamethyl cyclotetrasiloxane (D4) as a porosity promotion agent

Low dielectric methylsilsesquioxane (MSQ) film can be synthesized by spin-coating on P–Si (100) wafer. Octamethyl cyclotetrasiloxane (D4) was used as a porosity promotion agent to MSQ film. Seven samples with different treatment were prepared. The dielectric constants of these MSQ films significantly lowered from 3.0 to 2.1. Fourier transform infrared spectroscopy was used to identify the Si–O–Si network structure, Si–O–Si cage structure and other bonds. The change of structure resulted in significant lowering of the dielectric constant (k). The capacitance–voltage (C–V) characteristic by HP4294A was used to determine the dielectric constant. Current–voltage (I–V) measurement by Keithley6517A was used to determine the breakdown electric field.     

Effect of doping (C or N) and co-doping (C+N) on the photoactive properties of magnetron sputtered titania coatings for the application of solar water-splitting

The photocatalytic splitting of water into hydrogen and oxygen using a photoelectrochemical (PEC) cell containing titanium dioxide (TiO2) photoanode is a potentially renewable source of chemical fuels. However, the size of the band gap (-3.2 eV) of the TiO2 photocatalyst leads to its relatively low photoactivity toward visible light in a PEC cell. The development of materials with smaller band gaps of approximately 2.4 eV is therefore necessary to operate PEC cells efficiently. This study investigates the effect of dopant (C or N) and co-dopant (C+N) on the physical, structural and photoactivity of TiO2 nano thick coating. TiO2 nano-thick coatings were deposited using a closed field DC reactive magnetron sputtering technique, from titanium target in argon plasma with trace addition of oxygen. In order to study the influence of doping such as C, N and C+N inclusions in the TiO2 coatings, trace levels of CO2 or N2 or CO2+N2 gas were introduced into the deposition chamber respectively. The properties of the deposited nano-coatings were determined using Spectroscopic Ellipsometry, SEM, AFM, Optical profilometry, XPS, Raman, X-ray diffraction UV-Vis spectroscopy and tri-electrode potentiostat measurements. Coating growth rate, structure, surface morphology and roughness were found to be significantly influenced by the types and amount of doping. Substitutional type of doping in all doped sample were confirmed by XPS. UV-vis measurement confirmed that doping (especially for C doped sample) facilitate photoactivity of sputtered deposited titania coating toward visible light by reducing bandgap. The photocurrent density (indirect indication of water splitting performance) of the C-doped photoanode was approximately 26% higher in comparison with un-doped photoanode. However, coating doped with nitrogen (N or N+C) does not exhibit good performance in the photoelectrochemical cell due to their higher charge recombination properties.     

Investigating the effect of using granite and marble as a building material on the radiation exposure of humans

The aim of this study was to comprehensively study the radiological hazards of granite and marble used as a building material in Egypt. The activity concentrations of (226)Ra, (232)Th and (40)K were determined using high-resolution hyper-pure germanium detectors in 25 samples of different types of commercially available granite and marble. The measured activity concentrations for these natural radionuclides were compared with the reported data for Egypt and other countries. In order to assess the radiological impact, the radiation hazard parameters such as radium equivalent activity (Ra(eq)) and hazard level index (I(γ)) were calculated. The internal and external dose rates due to natural radionuclides in granite and marble were also calculated. The data obtained were considered as helpful in regulating the use of building materials in Egypt.