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Fabrication, characterization and photocatalytic properties of CdS nanoparticles modified by N-doped TiO2 NTs

Abstract

Highly ordered TiO2 nanotube arrays (TiO2 NTs) were prepared by anodic oxidizing method on a surface of Ti substrate. Fabrication of nitrogen-doped TiO2 nanotube arrays (N-TiO2 NTs) was carried out by immersion in ammonia solution. CdS nanoparticles loaded N-doped TiO2 nanotube arrays (CdS/N-TiO2 NTs) were obtained by successive ionic layer adsorption and reaction (SILAR) technique. The samples were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), photoluminescence (PL) emission spectra and ultraviolet-visible (UV-Vis) diffuse reflectance spectroscopy (DRS). The results indicate that the TiO2 nanotube diameter and wall thickness are 100 nm to 120 nm and 20 nm to 30 nm, respectively. Moreover, the morphology and structure of the highly ordered TiO2 NTs are not affected by N-doping. Furthermore, CdS nanoparticles are evenly distributed on the surface of TiO2 NTs. Finally, the photocatalytic activity of CdS/N-TiO2 NTs was evaluated by degradation of MO under visible-light irradiation. Compared with TiO2 NTs, N-TiO2 NTs, CdS/N-TiO2 NTs exhibited enhanced photocatalytic properties, and the highest degradation rate of CdS/N-TiO2NTs could reach 97.6 % after 90 min of irradiation.

Open access
Fabrication of temperature sensor based on copper oxide nanowires grown on titanium coated glass substrate

Abstract

Single phase, adherent films of copper oxide nanowires (CuO NWs) were successfully grown on a glass substrate. Titanium nanofilm was pre-coated on the glass substrate to assist the growth of a layer adherent to the substrate. The copper film of 1.5 μm thickness was deposited via physical vapor deposition technique followed by thermal oxidation in air at various temperatures for 4 h. The product was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), ultraviolet-visible (UV-Vis) and Fourier transformation infrared (FT-IR) spectroscopy to find the crystal structure, morphology, phases, and optical properties of the deposited films. The CuO NWs film with 60% transmittance at wavelengths greater than 800 nm was obtained. It can be used as an infrared thermal imaging filter and in optoelectronic devices. The fabricated temperature sensor exhibited high sensitivity in the temperature range of 20 °C to 180 °C.

Open access
High transparency and conductivity of heavily In-doped ZnO thin films deposited by dip-coating method

Abstract

Heavily In doped zinc oxide (IZO) thin films were deposited on glass substrates by dip-coating method with different concentrations of indium. The effect of heavy In doping on the structural, morphological, optical and electrical properties of ZnO was discussed on the basis of XRD, AFM, UV-Vis spectra and Hall effect measurements. The diffraction patterns of all deposited films were indexed to the ZnO wurtzite structure. However, high In doping damaged the films crystallinity. The highest optical transmittance observed in the visible region (>93 %) exceeded that of ITO: the absolute rival of the most commercial TCOs. The grain size significantly decreased from 140 nm for undoped ZnO to 17.1 nm for IZO with the greatest In ratio. The roughness decreased with increasing In atomic ratio, indicating an improvement in the surface quality. Among all synthesized films, the sample obtained with 11 at.% indium showed the best TCO properties: the highest transmittance (93.5 %) and the lowest resistivity (0.41 Ωcm) with a carrier concentration of 2.4 × 1017 cm−3. These results could be a promising solution for possible photonic and optoelectronic applications.

Open access
Improving color uniformity and color rending index of remote-phosphor packaging white LEDs by co-doping SiO2 and Sr2Si5N8:Eu2+ particles

Abstract

Based on some advantageous properties, such as fast response time, environment friendliness, small size, long lifetime, and high efficiency, white LEDs are increasingly used in common illumination applications. In this research, by co-doping of redemitting Sr2Si5N8:Eu2+ phosphor and adding SiO2 particles to yellow-emitting YAG:Ce phosphor compounds, a new approach for improving color uniformity and color rending index of remote-phosphor structure white LEDs is proposed and demonstrated. The obtained results clearly indicate that the color rendering index (CRI) and color uniformity (ΔCCT) significantly depend on Sr2Si5N8:Eu2+ concentration. The results provide a potential practical solution for manufacturing remote-phosphor white LEDs (RP-WLEDs) in the near future.

Open access
Investigation of Cu(In, Ga)Se2 solar cell performance with non-cadmium buffer layer using TCAD-SILVACO

Abstract

The purpose of this work is to achieve the best efficiency of Cu(In, Ga)Se2 solar cells by replacing the CdS buffer layer with other nontoxic materials. The simulation tool used in this study is Silvaco-Atlas package based on digital resolution 2D transport equations governing the conduction mechanisms in semiconductor devices. The J-V characteristics are simulated under AM1.5G illumination. Firstly, we will report the modeling and simulation results of CdS/CIGS solar cell, in comparison with the previously reported experimental results [1]. Secondly, the photovoltaic parameters will be calculated with CdS buffer layer and without any buffer layer to understand its impact on the output parameters of solar cells. The simulation is carried out with the use of electrical and optical parameters chosen judiciously for different buffers (CdS, ZnOS and ZnSe). In comparison to simulated CdS/CIGS, the best photovoltaic parameters have been obtained with ZnOS buffer layer. The structure has almost the same open circuit voltage Voc and fill factor FF, and higher short circuit current density Jsc, which results in slightly higher conversion efficiencies.

Open access
Investigations of reconstruction of passivation layer on stainless steel surface using AFM-based techniques

Abstract

Continuous development of stainless steel technology forced by the increase in the growing demands on the operating parameters of various stainless steel alloys, is the motivation for implementation of research for understanding the complexity of electrochemical processes ongoing on the surface of a material during various technological processes and during exploitation of the finished components. In this paper, the use of atomic force microscopy (AFM) is presented as a tool for observation of reconstruction process of passivation layers on the surface of previously electropolished stainless steel. For this purpose, a technique called nanoscratching was used, in which scratches are made on the surface of a material by means of diamond scanning probe, which violates the continuity of the passivation layer. Then, the dynamics of the process of reconstruction of that layer was assessed using continuous imaging of the scratched area in AFM semicontact mode. Studies of this type can be used to evaluate the impact of various factors on the spontaneous reconstruction of the passivation layer as well as possible susceptibility of the material on the course of corrosion processes initiated as a result of mechanical defects arising during operation of the material. By using the AFM, it was possible to observe changes in the depth of scratches with a subnanometer resolution. Obtained results proved that the presented AFM application allowed observation of the dynamics of passivation layer reconstruction process in a quantitative fashion, therefore it seems to be a very useful tool in the investigation of the impact of various conditions on this phenomenon. The results showed that changes in surface modification were occurring in a continuous manner. Changing dynamics of said process was presented. It should be underlined that no such experiments have been reported so far.

Open access
Magnetic properties of ZnO:Co layers obtained by pulsed laser deposition method

Abstract

We have studied magnetic properties of zinc oxide (ZnO) composite doped with Co ions. The samples were obtained by pulsed laser deposition (PLD) method. Electron magnetic resonance (EMR) measurements were carried out and temperature dependence of EMR spectra was obtained. Analysis of temperature dependence of the integral intensity of EMR spectra was carried out using Curie-Weiss law. Reciprocal of susceptibility of an antiferromagnetic (AFM) material shows a discontinuity at the Néel temperature and extrapolation of the linear portion to negative Curie temperature. The results of temperature dependence of EMR spectra for the ZnO:Co sample and linear extrapolation to the Curie-Weiss law indicated the AFM interaction between Co ions characterized by the Néel temperatures TN = 50 K and TN = 160 K for various samples. The obtained g-factor is similar to g-factors of nanocrystals presented in literature, and the results confirm that in the core of these nanocrystals Co was incorporated as Co2+, occupying Zn2+ sites in wurtzite structure of ZnO.

Open access
New kind of Cu based paste for Si solar cells front contact formation

Abstract

Potential impact of copper replacing silver in the paste used for the front electrode fabrication in crystalline silicon solar cells was investigated. The copper was applied as a new CuXX component with about 2 wt.% to 6 wt.% share of XX modifier. The generated CuXX molecules were analyzed using transmission microscopy. Based on the commercial Du Pont PV19B paste, CuXX and XX materials, the new PV19B/CuXX paste with 51 wt.% share of Cu and the PV19B/XX paste with 51 wt.% share of XX only were developed. Comparative studies of the effect of the commercial PV19B paste made by DuPont Company, and the pastes with the CuXX component and with the modifier XX alone on the electrical parameters of solar cells produced on crystalline silicon were carried out. The solar cells were characterized by the current-voltage technique. As a final result, the Cz-Si solar cell with the 51 wt.% share of Cu in the front electrode having a series resistance of 0.551 Ω·cm2, an efficiency of 14.08 % and, what is more important, the fill factor of 0.716, was obtained. It is the best result ever obtained concerning direct Cu application for solar cells fabricated in thick-film technology.

Open access
Optical properties of Sr2SiO4:Eu2+, Dy3+ phosphors prepared by combustion method

Abstract

In the present paper, TL and PL study of Dy3+ doped Sr2SiO4:Eu2+ phosphor is reported. A polycrystalline sample of Sr2SiO4:Eu2+, Dy3+ was prepared by combustion method. The obtained phosphor was characterized by powder X-ray diffraction, scanning electron microscopy, UV-Vis spectroscopy, PL and thermoluminescence. The results of the XRD studies obtained for Sr2SiO4:Eu2+, Dy3+ phosphor revealed its monoclinic structure. The average crystallite size was calculated as 12.77 nm. Thermoluminescence study was carried out for the phosphor using UV irradiation and a single glow peak was found. The thermoluminescence glow curves of the samples were measured at various concentrations of co-dopant. The kinetic parameter has been calculated using Chen’s glow curve method. In this paper, the photoluminescence and afterglow behavior of these phosphors are reported.

Open access
Physical properties of ZnTe semiconductor thin films prepared by high vacuum resistive system

Abstract

Zinc telluride (ZnTe) polycrystalline films have been grown on well-cleaned glass substrates by thermal vacuum evaporation technique using 99.99 % pure ZnTe powder as an evaporant. The samples were prepared at different substrate temperatures, rates of evaporation and thicknesses. The X-ray diffraction was used to study the structure of the films. The structures of the samples were found to be polycrystalline with preferred (1 1 1) orientation. Transmission spectra of all ZnTe films were recorded in the range of 300 nm to 2500 nm. The films were electrically characterized using Hall effect measurements at room temperature. It has been stated that the electrical resistivity, mobility and carrier concentration are strongly influenced by the substrate temperature. From the SEM results, it is clear that the surface of ZnTe is very smooth with occasional large particles on it.

Open access