C. Siva

Ultrasonic-assisted synthesis of ZnTe nanostructures and their structural, electrochemical and photoelectrical properties

Colloidal zinc telluride (ZnTe) nanostructures were successfully processed through a simple and facile ultrasonic (sonochemical) treatment for photoelectronic applications. The particle-like morphological features, phase and nature of valence state of various metal ions existing in ZnTe were examined using electron and X-ray photoelectron spectroscopic tools. Raman spectroscopic measurements revealed the dominance of exciton-phonon coupling and occurrence of TeO2 traces in ZnTe through the corresponding vibrations. Optical bandgap of the ZnTe suspension was estimated to be around 2.15eV, authenticating the direct allowed transitions. The p-type electrical conductivity and charge carrier density of ZnTe were additionally estimated from the Bode, Nyquist and Mott-Schottky type impedance plots. The photoelectrical properties of ZnTe were investigated by fabricating p-ZnTe/n-Si heterostructures and studying their corresponding current-voltage characteristics under dark and white light illumination. The diodes revealed excellent rectifying behaviour with significant increase in reverse current under illumination. The stability of the devices were also affirmed through the time-dependent photoresponse characteristics, which actually suggested the improved and effective separation of photo generated electron hole pairs across the integrated heterojunctions. The obtained results also augment the potential of sonochemically processed ZnTe for application in photo detection and sensor related functions.

Optical and electrical properties of n-ZnAgAuO/p-Si heterojunction diodes

Chemical synthesis of nanostructured materials has nowadays attracted significant interest for a number of electronic and optoelectronic applications. In this regard, the influence of co-doping on the electrical characteristics of zinc oxide (ZnO) was systematically investigated using noble metals such as silver (Ag) and gold (Au). The doped nanostructures were actually synthesized by a simple wet chemical route and studied using X-ray diffraction (XRD) and electron microscopic tools to validate the successful incorporation of metal ions and their other structural and morphological characteristics. The optical band gaps of the processed materials were further estimated using the Tauc’s plot. p-n junctions were then fabricated using a colloidal dispersion of the obtained samples via spray pyrolysis on p-Si. The current–voltage (I–V) characteristics of the fabricated diodes revealed an improved electrical conductivity in the co-doped systems. The findings were justified to the newly generated energy levels in ZnO, which might have acted as trap centers and resulted with the downward shift in their Fermi level.

Blue luminescence and Schottky diode applications of monoclinic HfO2 nanostructures

Schottky diodes based on metal–semiconductor (MS) and metal–insulator–semiconductor (MIS) configurations are nowadays widely regarded as key components for the realization of a number of improved electronic and optoelectronic functions. In this regard, hafnium dioxide (HfO2) nanostructures were processed through a facile chemical route for application in MIS Schottky diodes. Their monoclinic phase and micro-structural characteristics were studied in detail using the X-ray diffraction, Raman and electron microscopic measurements. The nanostructures were studied to evolve in form of particulate structures at an average scale of 8–10 nm. The low-temperature photoluminescence measurements revealed the optical activity of HfO2 to spread across the blue region of electromagnetic spectrum. And their origin has been related to the transitions taking place across the intermediary energy levels established by the oxygen related vacancies. The power of incident laser irradiation was also noted to have a significant influence on the surface-state related defect emissions. The electrical properties of HfO2 were studied using the Bode, Nyquist and Mott–Schottky type plots extracted from the impedance spectroscopic measurements. MIS Schottky diode architectures were finally fabricated using the HfO2 thin films that were spin cast on n-Si. A significant improvement in the diode characteristics were noted for the heat treated devices, suggesting the improved tunnelling and limiting of charge leakages across the integrated heterojunctions.

Optoelectronic characteristics of chemically processed ultra-thin InyZn1−yO nanostructures

InyZn1−yO nanostructures were processed through a solution-based strategy for optoelectronic-related functions. Their crystalline structure, phase purity and valence states of various transition metal ions existing within them were studied in detail using X-ray diffraction, Raman and X-ray photoelectron spectroscopic measurements. The morphological dimension of the nanostructures was observed to be of sheet-like form from the electron microscopic results, while the optical band gap was estimated to be around 3.13 eV using Taucs plot. The luminescence measurements revealed the nanosheets to be associated with multiple defects through the wide sub-band edge emissions in the visible region. The origin of defect-related emission was also substantiated using Raman spectroscopy. The electrical properties of the nanosheets were studied from the Nyquist and Mott–Schottky plots, which were established through electrochemical impedance spectroscopic measurements. The optoelectronic capabilities of InyZn1−yO were investigated via establishing p–n architectures using silicon (p-Si) and studying their corresponding current–voltage (I–V) characteristics. UV photon irradiation was found to substantiate the potential of the fabricated heterostructures for optoelectronic functions.

Facile synthesis of ZnAgO nanoflakes and their improved photocatalytic activities under sun light

Silver (Ag) doped zinc oxide (ZnO) nanoflakes were processed through a facile wet-chemical route. Their phase purity and wurtzite crystalline characteristics were studied using the results of X-ray diffraction measurements. The flake-like morphological nature of the processed materials was examined through scanning electron microscopy. The optical absorbance of undoped ZnO was noted to improve significantly along the visible region on Ag doping. The absence of surface plasmon resonance in Zn1−xAgxO nanostructures characterized the effective substitution of Ag dopant ions in the host matrix. The photocatalytic activity of undoped ZnO and Zn1−xAgxO was evaluated via performing degradation reactions using methylene blue (MB) under visible light. The degradation kinetics was also noted to improve significantly in the doped materials while compared with that of the undoped ZnO.

Magnetic and optical property studies on cubic Gd3Fe5−xCoxO12 nanogarnets for spintronics

Investigations on wide band gap nanocrystalline magnetic materials are the subject of recent research interest for establishing functional spin-based nanodevices. In this regard, gadolinium-based rare earth garnets (Gd3Fe5−xCoxO12) were processed in the form of nanostructures by a facile chemical route involving high-temperature annealing treatments. The garnet configuration and the existence of secondary phase characteristics were identified using Raman and X-ray diffraction analysis, respectively. The average size of the nanoparticles was estimated to be around 50–60 nm using Scherrers formula and further confirmed using scanning/transmission electron microscopy imaging techniques. The wide band gap of Gd3Fe5−xCoxO12 systems was studied using the Tauc plot extracted from UV-vis absorbance measurements. A broad luminescence was also observed along the ultraviolet and green regions of the photoluminescence spectrum, which was attributed to the intermediate defect levels existing within the band gap of the material. The electrochemical characteristics of the Gd3Fe5−xCoxO12 nanostructures were further identified using the Nyquist-type impedance plots. Additionally, the saturation magnetization observed in the room-temperature magnetic (M–H) measurements was attributed to the complex magnetic structure of the garnet. Finally, in the present study, the investigation results suggest Gd3Fe5−xCoxO12 as an ideal candidate for applications in magneto-optical devices and spintronics.