Structural and oxidative changes in the kidney of crucian carp induced by silicon-based quantum dots

Silicon-based quantum dots were intraperitoneally injected in Carassius auratus gibelio specimens and, over one week, the effects on renal tissue were investigated by following their distribution and histological effects, as well as antioxidative system modifications. After three and seven days, detached epithelial cells from the basal lamina, dilated tubules and debris in the lumen of tubules were observed. At day 7, nephrogenesis was noticed. The reduced glutathione (GSH) concentration decreased in the first three days and started to rise later on. The superoxide dismutase (SOD) activity increased only after one week, whereas catalase (CAT) was up-regulated in a time-dependent manner. The activities of glutathione reductase (GR) and glutathione peroxidise (GPX) decreased dramatically by approximately 50% compared to control, whereas the glutathione-S-transferase (GST) and glucose-6-phosphate dehydrogenase (G6PDH) increased significantly after 3 and 7 days of treatment. Oxidative modifications of proteins and the time-dependent increase of Hsp70 expression were also registered. Our data suggest that silicon-based quantum dots induced oxidative stress followed by structural damages. However, renal tissue is capable of restoring its integrity by nephron development.     

Nanotwinning and structural phase transition in CdS quantum dots

Nanotwin structures are observed in high-resolution transmission electron microscopy studies of cubic phase CdS quantum dots in powder form by chemical co-precipitation method. The deposition of thin films of nanocrystalline CdS is carried out on silicon, glass, and TEM grids keeping the substrates at room temperature (RT) and 200°C by pulsed laser ablation. These films are then subjected to thermal annealing at different temperatures. Glancing angle X-ray diffraction results confirm structural phase transitions after thermal annealing of films deposited at RT and 200°C. The variation of average particle size and ratio of intensities in Raman peaks I_2LO/I_1LO with annealing temperature are studied. It is found that electron-phonon interaction is a function of temperature and particle size and is independent of the structure. Besides Raman modes LO, 2LO and 3LO of CdS at approximately 302, 603, and 903 cm⁻¹ respectively, two extra Raman modes at approximately 390 and 690 cm⁻¹ are studied for the first time. The green and orange emissions observed in photoluminescence are correlated with phase transition.     

Growth kinetics of MPS-capped CdS quantum dots in self-assembled thin films

For this study, we prepared colloidal CdS quantum dots using 3-mercaptopropyltrimethoxysilane as capping agent. Colloidal CdS quantum dots were directly deposited on glass substrates by a spin-coating process. Coated substrates were heat-treated between 225°C and 325°C for various heat treatment time intervals to investigate the growth kinetics of the quantum dots. Results showed that sizes of the CdS quantum dots grew approximately from 2.9 to 4.6 nm, and the E_1s1s energy values shifted approximately from 3.3 to 2.7 eV. Results showed that the average size of quantum dots increase by thermal treatment due to Ostwald ripening. The thermal process used to grow the size of quantum dots was examined according to the Lifshitz-Slyozov-Wagner theory. The activation energy of CdS quantum dots in thin films was calculated at approximately 44 kJ/mol.     

Exciton-related nonlinear optical properties in cylindrical quantum dots with asymmetric axial potential: combined effects of hydrostatic pressure, intense laser field, and applied electric field

ABSTRACT: The exciton binding energy of an asymmetrical GaAs-Ga1-xAlxAs cylindrical quantum dot is studiedwith the use of the effective mass approximation and a variational calculation procedure. Theinfluence on this quantity of the application of a direct-current electric field along the growthdirection of the cylinder, together with that of an intense laser field, is particularly considered. Theresulting states are used to calculate the exciton-related nonlinear optical absorption and opticalrectification, whose corresponding resonant peaks are reported as functions of the external probes,the quantum dot dimensions, and the aluminum molar fraction in the potential barrier regions.