Influence of ZnO nanostructure configuration on tailoring the optical bandgap: Theory and experiment

Exploiting the link between form and function of semiconductor nanostructure provides a new prospect for tailoring the features of nanoscale materials. However, achieving this remains a challenge in the fabrication of optoelectronic devices. Therefore, this research systematically presents theoretical and experimental investigations of shape dependent structural and optical properties of ZnO nanostructures (nanoparticles, vertically oriented nanorods and compact ZnO) synthesized using the electroless deposition technique to understand the principles of bandgap modification. FESEM, XRD, Photoluminescence (PL) and UV–Vis spectroscopic characterizations were employed. The characterizations show increase in lattice parameters, bandgap and density of dislocations from 0.3236 nm to 0.3258 nm, ~3.14 eV to ~3.51 eV and ~17 × 10-4 to ~39 × 10-4 , respectively as the ZnO nanostructures are transformed from compact ZnO to ZnO nanoparticles. The expansion in lattice parameter is attributed to lower compressive stress that exists in ZnO nanoparticles compared to compact ZnO. The blue shift (0.06 eV) in bandgap is ascribed to overlapping of the orbitals and energy level in ZnO nanoparticles which causes a substantial increase in energy gap between valence and conduction bands. The small size-induced hardening in ZnO nanoparticles accounts for their comparatively higher dislocation density. Theoretically, conversion from compact ZnO to ZnO nanoparticles extends the bandgap from 3.38 eV to 3.44 eV, which is consistent with the experimental results. This study confirms the shape dependency of the structure and bandgap of ZnO nanostructures, which may provide a new insight into future integrated optoelectronic device applications

Continuous monitoring of crude oil movement in an electromagnetic-assisted enhanced oil recovery process using a modified fiber Bragg grating sensor

The Fiber Bragg grating (FBG) sensor used for distinguishing the oil movement offers detailed insights about the reservoir oil and is the key to quantifying the impact on improvement and the integrity and efficiency of the wells. The modified FBG sensors proposed in this paper through a partially un-cladding process and magnetostrictive nanolayer coating could advantageously monitor the crude oil mobility in electromagnetic-assisted enhanced oil recovery operations. The remaining ∼400 nm thickness of cladding after partial removal was coated with ∼100 nm magnetostrictive Ni-Fe nanolayer. The structures of Ga-doped magnetite and Ga-doped hematite were found orthorhombic with Pnma space group and rhombohedral with R3C space group, with the corresponding remnant magnetization (retentivity) value of 94 Oe and 150 Oe, respectively. The magnetization values at 1.5 T were 30 for Ga-doped magnetite and 21 emu/g for Ga-doped hematite nanoparticles. The interfacial tension of crude oil and brine dropped for 16.9 % and 4.1 % when the Ga-doped magnetite and the Ga-doped hematite nanofluid were injected, respectively. The correlated contact angle for the Ga-doped magnetite was 65.2˚, while for the Ga-doped hematite, it was 57.4˚. The FBG's responses to different nanofluids and surfactant injection at the presence of electromagnetic field indicated the high sensitivity of the probe against the induced magnetic field, which was varied as a function of distance, nanofluids type, and nanoparticles accumulation near the FBG sensing point. The increase in the wavelength shift of FBG by flowing the nanofluids through the sandstone and opposite behavior was recorded by surfactant flowing. The maximum wavelength shift was 0.21 nm when Ga-doped magnetite nanofluid was injected, whereas it was 0.14 when Ga-doped hematite was injected. © 2020 Elsevier B.V