Papers by Keyword: Passivation

Abstract: Thermal and photo instabilities are two major issues for organic-inorganic lead halide perovskite solar cells. Mixing of A site cations and X cite halogens are tried to address these issues, but the performance is still not reached the theoretical Shockley Quissier limit. One of the reasons for this is the energy loss ratio with band gap energy. Despite the high open circuit voltage, this ratio is lower for perovskite solar cell in competition with silicon technology. Open circuit voltage can be increased by different ways, but short circuit current is compromised. To increase open circuit voltage without affecting the short circuit current is the surface passivation technique. Numerous studies have been conducted on electron transport layer and perovskite interface, with a very few on hole transport layer and perovskite interface. Both interfaces are equally important. Here we passivated the later interface by inserting a 10 nm thick layer of caesium-formamide based lead mixed halide perovskite in FAMA mixed perovskite solar cell. Our proposed model achieved an efficiency of 31.42 % with a high fill factor of 86.4 %. At the same time, we recorded higher open circuit voltage of 1.46 V and 25.49 mA/cm² short circuit current. Our proposed model will help in experimental work for making highly efficient perovskite solar cells.

Abstract: Black Carbon (BC) is a solid material obtainable from the remnants of incomplete burning of biological organisms or fossil fuels, which benefits pollution alleviation and soil amendment. In this study MBC was prepared using acidic potassium permanganate for inactivating heavy metal in soils. The specific surface area and pore volume of BC and MBC were measured by nitrogen adsorption and the space around the black carbon particles was observed by Scanning Electron Microscopy (SEM). The contents of carboxyl, ester and phenol hydroxyl group on their surface have been determined. The effect on availability of Cu in soils and soil enzyme activity of MBC was also investigated. Scanning electron microscopy analysis of MBC demonstrated large micropores with looser aggregate structure. MBC featured a higher surface area (956.88m²·g^-1), larger average pore size and pore volume than BC, which can improve its excellent adsorption ability. Using as a soil heavy metal passivator, MBC reduced the available content of copper in three soils significantly and MBC has the best passivation effect on copper in cinnamon soil. Comparison of the enzyme activities in three soils amended with MBC under constant moisture conditions revealed that MBC increased the activities of catalase, urease in different degrees and inhibited the activities of dehydrogenase in three soils. These findings suggest that MBC has a strong passivation ability to Cu and would be applied to the remediation of copper contaminated soil.

Abstract: Stainless steel reinforcing bars show excellent corrosion resistance in concrete exposed to harsh environments. In this combined electrochemical and surface analytical work, an explanation for this behavior is proposed. XPS surface analytical results (thickness, composition of the passive film and of the interface beneath the film) obtained on black steel, FeCr alloys, and a series of stainless steels after exposure to alkaline solutions simulating concrete are reported. Pitting potentials were determined in the same solutions with electrochemical experiments. It is shown that the pitting potentials of the steels can be related to the Cr (III) oxy-hydroxide and Mo (VI) content in the passive film. It is proposed to calculate a Cr and Mo oxide equivalent similar to the well-known pitting resistance equivalent number (PREN). A correlation between the critical chloride content in concrete (reported in literature for CEM II A/LL and CEM I) and the pitting potential for carbon steel, Fe12%Cr alloy, DIN 1.4301 and DIN 1.4571 stainless steels is proposed to link results of solution analysis and performance in concrete.

Abstract: The general and localized corrosion resilience of 2101 LDX duplex stainless steel (2101ST) was assessed in specific concentrations of H₂SO₄ electrolyte by Potentiodynamic polarization, potentiostatic evaluation, open circuit potential analysis and optical illustration characterization. Data output shows 2010ST exhibited sufficient resistance to general corrosion (0.28 mm/y and 1.01 mm/y) at low concentrations of H₂SO₄ solution (1M and 2 M H₂SO₄) whose values correlates to polarization resistance of 42.47 Ω and 19.74 Ω. Further increment in H₂SO₄ concentration results in substantial increase in degradation rate which culminated at 58.32 mm/y at 6M H₂SO₄ and polarization resistance of 0.10 Ω. Due to the destructive action of SO₄^2- anions. Corrosion potential shifts indicates dominant anodic dissolution reactions with respect to H₂SO₄ concentration. Metastable pitting activity was observed on the plot following anodic polarization but prior to passivation of the steel. The metastable pitting current and passivation potential of the steel grew with increase in H₂SO₄ concentration. This weakened the localized corrosion resistance of the steel at higher H₂SO₄ solution. This is evident in the decrease in passivation range values plot configuration. Open circuit potential plots depict significant passivation of the steel at 1M H₂SO₄ solution compared to the plot at 6M H₂SO₄ which indicates strong tendency to corrode despite its thermodynamic stability. Optical images of 2101ST exterior after corrosion at 1M H₂SO₄ solution shows mild surface deterioration coupled with miniature corrosion pits. This contrasts the morphology of the steel at 6M H₂SO₄ which showed the presence of deep and enlarged, corrosion pits, and a badly etched surface showing the grain boundary coupled with a severely degraded exterior.

Abstract: The research data on the specific features of the formation of oxide films on the Ti6Al4V alloy in the ethylene glycol-water electrolytes have been given. The kinetic dependences obtained for the alloy allowed us to establish that the specific features of the formation of oxide films during the electrochemical oxidation of the alloy surface depend on the solution composition and the current density. For the water-to-alcohol ratio of 50:50 the kinetic dependences show the sections that correspond to the formation of the barrier oxide layer and also to the formation of the pores due to the desorption of fluoride ions and the growth of the porous portion of oxide. As the water-to- alcohol ratio is decreased the indicated peculiarities of kinetic dependences are met not so often and do not obey any regularity. The obtained data are explained by the fact that an increase in the portion of the organic component of the solution results in a decreased etching capacity of the electrolyte due to the controlled activity of fluoride ions. The anode current density value has a similar effect on the variation of kinetic dependences. Its effect is explained by that an increase in the alloy oxidation rate results in the fast formation of the surface oxide and the specific features of kinetic curves are concealed. The linear relationship between the formation time of oxide of a minimum thickness for given conditions and the current density is unavailable and it is conditioned by the chemical interaction of the oxide film with electrolyte components. The obtained research data can be used for the formation of the individual bioinert and bioactive coatings for the implants of a medical purpose or for the formation of the matrix used for the production of composite coatings.

Abstract: The inhibition effect of Cefalexin on the corrosion of mild steel in sodium chloride has been examined with the use of weight loss and potentiodynamic polarization methods at ambient temperature. Cefalexin showed good protection ability by adsorbing on the mild steel surface. The mixed inhibition characteristics of Cefalexin were revealed by the Potentiodynamic polarization results. The inhibitor efficiency was found to be above 65% obeying the Langmuir and Freundlich isotherm law with correlation regression coefficients of R² = 0.9984 and R² = 0.9488, respectively. The closeness of these R² values to unity established the reliability of Cefalexin as an inhibitor.

Abstract: In this study, the effect of chloride in marine environment on carbon steel reinforcement corrosion was investigated. The nature of corrosion products produced was analyzed through visual inspection and X Ray Diffraction (XRD). It was very difficult using gain and loss technique alone to evaluate passivation conditions and corrosion reactions. It was found that the corrosion rate of steel increases with the increasing of sodium chloride (NaCl) concentration when steel bars without concrete were used. However, a passive film was formed on all steel samples embedded in concrete due to concrete alkalinity. Results reveal that most corrosion products were mainly FeO(OH) along with FeCO₃ and Fe₂O₃.

Abstract: Charge trapping at 4H-SiC/dielectric interfaces in 4H-SiC MOS capacitors has been investigated using constant capacitance deep level transient spectroscopy (CCDLTS). The experiments were focused on further understanding of the following aspects related to 4H-SiC/SiO₂ interfaces: (i) Origin of near interface oxide traps (NITs), (ii) Effect of interfacial impurity/passivation methods and (iii) Characterization of near-interface oxide traps for different SiC wafer orientations. For the (0001) Si-face 4H-SiC/ SiO₂ interface, two types of NITs are typically detected by CCDLTS, named ‘O1’ and ‘O2’ traps with emission activation energies of about 0.15±0.05 eV and 0.39±0.1 eV respectively below the 4H-SiC conduction band. Based on comparison with previous ab initio calculations, the physical identities of these defects have been suggested to be carbon dimers substituted for O dimers (‘O1’) and interstitial silicon atoms (‘O2’) in the near interfacial SiO₂ respectively. In this work, it is shown for the first time that such traps are not observed for 4H-SiC/ Al₂O₃ interfaces, proving that these traps are inherent to the near-interfacial SiO₂. In addition, the summary of CCDLTS results for Si-face with different interface trap passivation methods are included in this study. Finally, a comparison is presented for NO annealed (0001) Si-face, (11-20) a-face and (000-1) C-face interfaces that highlight the difference of CCDLTS signatures for the different crystal faces.

Abstract: The contribution is aimed at corrosion propertied and wettability of basic graded of stainless steel commonly used in medicine as a standard for construction of instruments and other applications. Samples of AISI 304 (1.4301) steel were chemical passivated by nitric acid and tested for corrosion resistance in environment of sodium hypochlorite (NaClO), which is commonly used for basic disinfection of surfaces or devices in hospital facilities. It was found that chemical passivation of stainless steel surface increases its corrosion resistance and lower corrosion rate. Passivation layer also shows more polarization resistance. The wettability of passivated surface was measured by sessile drop method. Wettability itself determinates effectivity of disinfection process as the surfaces with lower contact angle may be cleaned and disinfected with more efficiency. It was proofed that chemical passivation increases wettability by lowering contact angle of treated surface.

Abstract: ZnO NWFETs were fabricated with and without Al₂O₃ passivation. This was done by developing a new recipe for depositing the thin film of ZnO. By using a high donor concentration of 1.7 x 10¹⁸ cm^-3 for the thin film, contact resistance values were lowered (passivated device had R_con = 2.5 x 10⁴ Ω; unpassivated device had R_con = 3.0 x 10⁵ Ω). By depositing Zn first instead of O₂, steep subthreshold slopes were obtained. The passivated device had a subthreshold slope of 225 mV/decade and the unpassivated device had a slope of 125 mV/decade. Well-behaved electrical characteristics have been obtained and the passivated device shows field effect mobility of 10.9 cm²/Vs and the un-passivated device shows a value of 31.4 cm²/Vs. To verify the results, 3D simulation was also carried out which shows that the obtained values of sub-threshold slope translate into interface state number densities of-1.86 x 10¹³ cm^-2 for the unpassivated device and 3.35 x 10¹⁴ cm^-2 for the passivated device. The passivated device is suitable for biosensing applications.