Semiconductor nanostructures for device applications
This thesis demonstrates a synthesis and device application of some semiconductors nanostructure. Section 1 layered hexagonal disks of CuO were synthesized on a large scale via low-temperature hydrothermal growth process. The detailed morphological investigations by field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). The detailed structural characterizations of the hexagonal CuO disks were done by high-resolution TEM (HRTEM) and X- ray diffraction (XRD) which confirmed that the synthesized structures possessing well nanocrystalline nature and monoclinic structure. The purity and composition of the synthesized products were examined by using energy dispersive spectroscopy (EDS), elemental mapping and Fourier transform infrared spectroscopy (FTIR). Using UV-Vis spectroscopy at room temperature we obtained indirect and direct band gap values slightly blue shifted to the bulk values. Finally, a plausible growth mechanism has been proposed for the formation of CuO layered hexagonal disks. Section2 reports the fabrication of highly-sensitive, robust, reliable and reproducible 4-nitrophenol (4-NP) chemical sensor based on CuO nanocubes. The structural characterizations confirmed the nanocrystalline nature and monoclinic structure for as-synthesized nanocubes. The optical property of CuO nanocubes exhibits indirect and direct band gap values examined by UV-Vis. spectroscopy at room-temperature. The as-synthesized CuO nanocubes were used as efficient electron mediators for the fabrication of 4-nitrophenol chemical sensor by simple I-V technique. High-sensitivity of ~132.84 ± 0.02 mA.cm-2.(mol L-1)-1 and detection limit of ~5×10-9 mol L-1 in a short response time of ~10.0 s were observed for the fabricated 4-nitrophenol sensor. This work shows that simply synthesized CuO nanostructures have great potential for the fabrication of efficient and reliable chemical sensors. Section3 , we reported the high-yield facile synthesis, detailed characterization and photocatalytic application of α-Fe2O3 nanoparticles. The UV-Vis absorption spectrum of the synthesized nanoparticles demonstrated the existence of two optical band gaps which correspond to direct and indirect transitions, respectively. The as-synthesized α-Fe2O3 nanoparticles exhibit good photocatalytic properties on photocatalytic degradation of methylene blue. Section4 reports the facile synthesis of α-Fe2O3 nanoellipsoids by low-temperature hydrothermal process and effectively utilized for the fabrication of highly sensitive aqueous ammonia chemical sensor by I-V technique. The detailed structural and optical properties confirmed the rhombohedral α-Fe2O3 structure and indirect (1.87 eV) and direct (2.15 eV) band gap, respectively, for synthesized nanoellipsoids. The fabricated aqueous ammonia sensor based on nanoellipsoids exhibits very high and reproducible sensitivity of ~4.678 µA.cm-2.mM-1 and detection limit ~0.04 nM with correlation coefficient (R) of 0.995 in short response time (10.0 sec). The presented work demonstrates that simply synthesized iron oxide nanostructures can efficiently be used for the fabrication of reliable and reproducible chemical sensors. Section 5 this section demonstrates the successful and facile large-scale synthesis and characterizations of SnS2 nanoflakes. The photocatalytic properties of SnS2 nanoflakes towards the photocatalytic degradation of Rhodamine B under visible light irradiation showed reasonably good degradation of ~61%. Moreover, the as-synthesized SnS2 nanoflakes were used as efficient electron mediators for the fabrication of nitroaniline chemical sensor by simple I-V technique. Very high-sensitivity of ~ (505.82 ± 0.02) mA.cm-2.(mole/L)-1 and experimental detection limit of ~15*10-6 (mole/L) in a short response time of ~10.0 sec with LDR in the range of 15.6*10-6 (mole/ L) to 0.5*10-3 mole L-1 were observed for the fabricated nitroaniline chemical sensor. The observed results indicated that the SnS2 nanoflakes can efficiently be used as visible-light-driven photocatalysts and the fabrication of ultra-high sensitive chemical sensors. Section 6 , in this section a heterojunction device was fabricated with solution processed SnS nanosheets (p-type)/TiO2 nanoparticles (n-type) and a top Pt thin layer to form Pt/SnS/TiO2/FTO diode assembly. The fabricated heterostructure device presented considerably improved electrical properties with high current of 0.78 mA at 1V, reasonable ideality factor of 31 and relatively high effective barrier height of 0.634 eV.
Semiconductor nanostructures, Copper oxide, Iron oxide, Tin sulphides, Hydrothermal process, Optical band gap, Chemical sensors, Photocataltic degradation, Heterojunction diode, 620.115, Ημιαγώγιμες νανοδομές, Οξείδιο του χαλκού, Οξείδιο του σιδήρου
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