Dependence of Sheet Resistivity on Urbach Energy of Nano TiO2 - Graphene-based Electrode for DSSC Application

The importance of renewable energy cannot be over-emphasized. Titanium IV oxide (TiO2 ) is the most suitable semiconductor for dye-sensitized solar cells (DSSC) due to its chemical stability, non-toxicity and excellent optoelectronic properties. In this research, TiO2 is coated on Graphene to enhance its charge transport, aiming to reduce recombination, a main setback in DSSCs. Understanding Graphene- TiO2 contact is, therefore, essential for DSSC application. Using doctor blading, TiO2 thin films were deposited on single-layer graphene (SLG) and fluorine tin oxide (FTO). The films were annealed at 2 °C /min and 1 °C/min up to a temperature of 450 °C, then sintering at this temperature for 30 minutes. Four four-point probes SRM -232 were used to measure the samples' sheet resistance. The film thickness was obtained from transmittance using pointwise unconstrained minimization approximation (PUMA). UV–VIS spectrophotometer was employed to measure transmittance. The resistivity of TiO2 on both FTO and Graphene was of order 10-4 Ω cm. However, TiO2 annealed on graphene matrix exhibited a slightly lower resistivity, 5.6 x10-4 Ω cm, compared to 6.0 x10-4 Ω cm on FTO. Optical transmittance on the visible region was lower for TiO2 on FTO than on SLG, 71.48% and 80.11%, respectively. The annealing rate decreased the weak absorption region's Urbach energy (Eu). Urbach energies for 1oC/min TiO2 on FTO and SLG were 361 meV and 261 meV, respectively. This accounted for the decrease in film disorders due to annealing. A striking relation between sheet resistivity and Urbach was reported, suggesting SLG as a suitable candidate for the photoanode of a DSSC

Applied Technological Direction of Power Plant Ash and Slag Waste Management when Kuznetsk Bituminous Coal is Burned

Currently a lot of power plants have a problem with storage of coal combustion solid by-products (ash and slag). Holding capacity of existing power plants available ash dumps were enlarged and modernized repeatedly. Many plants have two or even three of them. Today new ash dump construction is economically inconvenient due to need to assign new plots of land and their inconveniently big distance from a plant, which increase ash and slag transportation expenses. The goal of our research work is to find promising directions for ash and slag waste mass utilization based on Kuznetsk bituminous coals experimental data on ultimate composition and properties. The experimental research of ash, slag and their mixture samples from ash dumps brought us to conclusion that the most promising direction for these materials application in large quantities is construction industry including road construction. Be-sides, we lined up some other directions for ash, slag, and ash and slag mixture possible application. These directions might not provide mass utilization but they are promising from a point of view of the researched waste properties

Fundamental processes in growth of reactive DC magnetron sputtered thin films

This work seeks an atomistic understanding of fundamental processes in DC reactive magnetron sputtering of optical functional coatings. From a comparative study for different metal-oxygen combinations, which is illustrated by two oxide deposition reports on neighbouring elements - hafnium and tantalum, a surprising structural trend is revealed. While films are obtained crystalline at room temperature for group IV oxides, amorphous films were obtained for groups V and VI oxides. This observation can not be explained by the known growth laws including the Thornton model. The trend is attributed to the impact of energetic particles, originating from the oxidized target, which bombard the growing film. This scenario is supported by the measured target characteristics and evolution of deposition stress of the films and related to the variation in the activation energy for negative oxygen ion formation. Besides comparing the findings with other reports, possible chemical effects on structure are also ruled out. Observed backsputtering for the amorphous films provides further evidence for a model based on energetic particle bombardment. To improve on the low growth rates and high film surface roughness characterizing sputtered oxides, the approach of adding nitrogen to the sputter atmosphere leads to films with superior properties and growth conditions. An understanding to the cause of these beneficial effects was sought by examining the film composition and crystallographic structure for grown zirconium oxynitrides. Based on a thermochemical description together with a modeling of formation kinetics a film formation mechanism is proposed, which explains many of the observations. Rutherford backscattering spectroscopy (RBS) shows early nitrogen incorporation at 64% N2 flow in disagreement with the predictions of thermochemistry. The stoichiometry is only successfully simulated with the use of an expanded Berg-Larsson model with a low replacement coefficient of about 0.1 of nitrogen by oxygen after metal-nitrogen bond formation. The deviation from complete replacement as predicted by thermodynamics illustrates the importance of kinetics in film formation. The model further successfully predicts the variation of the mass deposition rate. The X-ray diffraction analyses suggest that, within the crystalline phase, nitrogen atoms occupy oxygen sites, resulting in an unchanged zirconium oxide structure

Enhanced Electron Transport in Epitaxial Annealed Graphene Titanium Dioxide Heterojunction

Titanium dioxide (TiO2) photocatalyst is a widely acceptable photo catalyst candidate due to its environment friendliness, cost-effectiveness, intrinsic electronics, photostability, good surface properties, and non-toxicity. However, TiO2 faces significant challenges for commercial exploitations, including high recombination rates, low quantum yield, and low visible light photo conversion efficiency. In this research, the optical properties of graphene TiO2 heterojunction were evaluated in measurements of Transmittance and Reflectance. Optical parameters in terms of WDD dispersion energy and dielectric constants were studied by annealing the films in the air up to 450 °C at 1 step, 2 °C/min and 1 °C/min annealing rates. Transmittance for the film annealed at 1 °C/min showed the highest transmittance of 86.57% and 74.07% for graphene and graphene TiO2, respectively. SCOUT software modelled Transmittance data to obtain refractive index. Refractive indices for pristine, 1 step, 2 °C/min, and 1 °C/min TiO2 films obtained at 550 nm were found to be 0.51, 034, 0.40 and 0.49, respectively. Porosity and dispersion energy for the lowest annealing rates (1 oC/min) was found to be 49 % and 12.7 eV in that order. Real and imaginary Interband transition (2.33–4.04) x 10-6 and (0.23–2.73) x 10-6 in that order, linear and nonlinear optical susceptibility (1.42–2.18) x 10-1 and (4.12–22.50) x 10-14, optical conductivity (2.51–13.2) x 1013 and electrical conductivity (3.89–4.60) x 1010 were enhanced with decreasing annealing rates. This is due to pole filing, film densification, increased lattice absorption and scattering centres and improved crystallinity of the films due to heat treatment and large-area graphene anchoring. The findings revealed that annealing graphene - TiO2 passivates its surface, reducing its boundary traps owing to quantum confinement effects and improving the electron transport throughout the heterojunction

Algorithm and Software for Operative Calculations of the Short Circuits Modes

Smart power grids provide efficient control of power flows or other grid variables, such as voltages or short circuit currents. Most essential the control has become, if the consumers are electrical systems of high power capacity. These systems are able to reconfigure the grid structure for emergency situations. The developed algorithm is intended for carrying out operational calculations of short-circuits modes in electrical grids of voltage 0,4kV to 220kV. In the calculation the following methods have been used: methods of node voltages, method of superposition and method of branch expansion to form the node voltage matrix according to the graphs theory. In the software the short circuit inflow from all electrical motors and nodes with generalized load is taken into account as opposed to other algorithms. The calculated circuit can have up to 700 nodes; there is ability to decrease number of branches and nodes and to form the calculative model of the grid part. Calculation algorithm of the short circuit currents is implemented as a sequence of software calculations. Software of systems and grids, in which short circuits are altered, allows carrying out operational calculations of the short circuit modes to adjust settings of relays protection devices, to check electrical equipment and to replace it, to choose optimal operational circuits. Actuality of the calculations is caused by need of the software implementation to maintain, upgrade and design the electrical grids of enterprises that have their own power plants