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Abstract

Nanocrystalline zinc sulfide thin films were prepared on glass substrates by chemical bath deposition method using aqueous solutions of zinc chloride, thiourea ammonium hydroxide along with non-toxic complexing agent trisodium citrate in alkaline medium at 80 °C. The effect of deposition time and annealing on the properties of ZnS thin films was investigated by X-ray diffraction, scanning electron microscopy, optical transmittance spectroscopy and four-point probe method. The X-ray diffraction analysis showed that the samples exhibited cubic sphalerite structure with preferential orientation along 〈2 0 0〉 direction. Scanning electron microscopy micrographs revealed uniform surface coverage, UV-Vis (300 nm to 800 nm) spectrophotometric measurements showed transparency of the films (transmittance ranging from 69 % to 81 %), with a direct allowed energy band gap in the range of 3.87 eV to 4.03 eV. After thermal annealing at 500 °C for 120 min, the transmittance increased up to 87 %. Moreover, the electrical conductivity of the deposited films increased with increasing of the deposition time from 0.35 × 10−4 Ω·cm−1 to 2.7 × 10−4 Ω·cm−1.

Abstract

CdS thin films with (1 1 1) orientation were prepared by chemical bath deposition technique at 80±5 °C using the reaction between NH4OH, CdCl2 and CS(NH2)2. The influence of annealing temperature varying from 150 °C to 250 °C was studied. X-ray diffraction studies revealed that the films are polycrystalline in nature with cubic structure. Various parameters, such as dislocation density, stress and strain, were also evaluated. SEM analysis indicated uniformly distributed nano-structured spherically shaped grains and net like morphology. Optical transmittance study showed the wide transmittance band and absence of absorption in the entire visible region. I-V characterization of p-Si/n-CdS diode and photoluminescence studies were also carried out for the CdS films.

Vplyv relaxačného času na kvalitu pigmentovanej vrstvy solárneho kolektora

Skúmal sa vplyv relaxačného času periodického reverzného prúdu na kvalitu vyfarbovania povrchu anodicky oxidovaného hliníka. Na vyfarbovanie sa použil elektrolyt bez komplexotvorného činidla a s komplexotvorným činidlom. Študoval sa aj vplyv frekvencie impulzového prúdu. Kvalita vyfarbených povrchov sa hodnotila spektrokolorimetricky a množstvo vylúčeného niklu sa určilo atómovou absorpčnou spektroskopiou. Zistilo sa, že relaxačný čas periodického reverzného prúdu významne ovplyvňuje kvalitu vyfarbených povlakov pre elektrolyty bez komplexotvorného činidla.

Abstract

LaCrO3 perovskite nanopowders were successfully prepared via a sol-gel method using stoichiometric proportion of materials containing lanthanum and chromium in stearic acid complexing agent. Structural analysis of LaCrO3 indicated an octahedral framework in its XRD pattern bearing crystallite size in the range of 28 nm. The particle sizes were confirmed by morphological scanning of the sample. The optical properties of LaCrO3 nanopowders clearly indicated an interesting optical activity of LaCrO3 in the UV and visible ranges. The degradation activation energy (Ed) was calculated from the output of a moderate thermal programming profile at about 207.97 kJ·mol-1 using Kissinger equation. Capacity, impedance and AC resistance of the perovskites was obtained at 2.970 nF, 2.522 MΩ and 16.19 MΩ, respectively.

Abstract

Magnesium-aluminum-bismuth layered double hydroxides (Mg3Al1−xBix; LDHs) were prepared using both coprecipitation and sol-gel methods. For the preparation of Mg/Al/Bi LDH by the co-precipitation method, the appropriate amounts of dissolved starting materials (Al(NO3)3 · 9H2O, Mg(NO3)2 · 6H2O and Bi(NO3)3 · 5H2O) were mixed with a solution of NaHCO3:NaOH. In the sol-gel processing, the precursor Mg–Al–Bi–O gels were synthesized using the same starting materials and ethylene glycol as complexing agent. The mixed-metal oxides obtained by subsequent heating of Mg–Al–Bi–O gels at 650 °C were reconstructed to Mg3Al1−xBix LDHs in water at 80 °C. All the synthesized products were characterized by X-ray diffraction (XRD) analysis, scanning electron microscopy (SEM) and dielectric measurements.

Abstract

For the first time, the studies on 2 to 10 at.% neodymium (Nd3+) ion doped Yttrium Aluminum Garnet (Nd:YAG) nanopowders obtained by microwave assisted citrate nitrate gel combustion synthesis is described in this work. This paper reports on high doping of Nd3+ ions with retaining the cubic garnet structure of YAG as evidenced from XRD, except the case of 8 at.% doped Nd:YAG. Phase pure YAG formation with 8 at.% Nd3+ doping was explored by using urea and alanine as alternative to citric acid complexing agents. Complete crystallization of YAG as a result of 2 hour thermal treatment at 900 °C under oxygen supply was studied by using Fourier Transform Infra-Red Spectroscopy (FTIR) and X-Ray Diffraction (XRD) techniques. With an increase in the dopant concentration a red shift in the FTIR peaks was observed. Using the XRD data, the cell parameter of Nd3+ (2 to 6 and 10 at.%) YAG was found to increase with an increase in the dopant concentration. The average primary particle size calculated using Scherrer’s equation was ∼25 nm which was additionally supported by Transmission Electron Microscopy (TEM) results yielding particle sizes in the range of ∼25 to 30 nm for all the cases.

Abstract

Ho doped Ag2S thin films were grown on the glass substrate by chemical bath deposition (CBD) method at room temperature. The bath contained aqueous solution of silver nitrate, thiourea, EDTA, ammonia and holmium nitrate. Silver nitrate was used as a silver (Ag+) ion source; thiourea as sulfur (S) ion source, EDTA was a complexing agent while ammonia was used to maintain pH, Ho(NO3)3 was taken as a source of Ho ions. The optical absorption edge of undoped (pure) and Ho doped silver sulfide films was determined between 324 nm and 298 nm showing blue shift as compared to bulk Ag2S. Band gaps calculated from Tauc plot also showed an increase in values for doped samples. The increase in band gap indicates reduced particle size in the prepared Ho doped films. The photoluminescence emission peaks were observed at around 578 nm to 601 nm wavelength and excitation peaks were found at 351 nm to 294 nm for undoped and doped films. The SEM micrograph consists of globular ball type and flower type structures observed in the prepared films of Ho doped Ag2S.

of macro- and nanocrystalline PbS and CdS have been described in literature. Among the chemical methods, chemical bath deposition (CBD) is of special interest because it is simple and highly efficient. CBD allows adjustable control of size and surface density of nanoparticles, and can be used for preparation of high-quality nanocrystalline PbS and CdS films [ 4 , 6 ]. This method has been shown to allow control of stirring period, reaction time, bath temperature, pH of solution, complexing agent and impurities [ 7 , 8 ]. Among several n-type semiconductor

the synthesis of CdS nanoparticles were cadmium chloride anhydrous (CdCl 2 H 2 O) as the source of Cd 2+ ions, thiourea (CS(NH 2 ) 2 ) as the source of S 2- ions and ammonia solution (NH 4 OH) as the complexing agent to control precipitation. To prepare CdS nanoparticles, the equimolar (0.2 M) aqueous solutions of the reactants, cadmium chloride and thiourea were prepared using double distilled water (Millipore, 15 MΩ·cm) separately. The ammonia solution (25 %) was added dropwise through a burette into 25 mL of cadmium chloride solution under slow stirring. It was

3 were obtained at 1200 to 1250 °C. For all investigated compositions of (Ba 1-x Ca x )(Ce 0.9 Y 0.1 )O 3 , a rhombohedral structure was found. As for the calcium modified barium zirconate series, such as the (Ba 1-x Ca x )(Zr 0.9 Y 0.1 )O 3 samples, a cubic perovskite structure was detected. The application of the sol-gel method with EDTA as a complexing agent enabled the temperature to be lowered to approximately 100 to 200 °C compared with the Pechini and citrate methods for both the investigated BCY and BZY series [ 25 , 26 ]. On the basis of X