P. Ilanchezhiyan

Highly efficient CNT functionalized cotton fabrics for flexible/wearable heating applications

In this work, a highly efficient, flexible electro thermal heater based on highly conductive carbon nanotube functionalized cotton fabrics has been studied. Cotton fabrics were functionalized with single walled carbon nanotubes through a simple dip coating method. To explore their potential as heaters, electrothermal performances of the devices were studied in terms of applied voltage, heating rate and input power density. The highly flexible heater is constructed based on uniformly interconnected CNT networks, which yields an effective and rapid heating of the heater at low input power. The investigation results suggest promising applications of these devices in wearable electronics and beyond and they could also be woven into textile materials.

MoS2 memristor with photoresistive switching.

A MoS2 nanosphere memristor with lateral gold electrodes was found to show photoresistive switching. The new device can be controlled by the polarization of nanospheres, which causes resistance switching in an electric field in the dark or under white light illumination. The polarization charge allows to change the switching voltage of the photomemristor, providing its multi-level operation. The device, polarized at a voltage 6 V, switches abruptly from a high resistance state (HRSL6) to a low resistance state (LRSL6) with the On/Off resistance ratio of about 10 under white light and smooth in the dark. Analysis of device conductivity in different resistive states indicates that its resistive state could be changed by the modulation of the charge in an electric field in the dark or under light, resulting in the formation/disruption of filaments with high conductivity. A MoS2 photomemristor has great potential as a multifunctional device designed by using cost-effective fabrication techniques.

Chemically-derived CuO/In2O3-based nanocomposite for diode applications

Nowadays, oxide-based semiconducting nanostructures are widely regarded as one of the most essential elements of the modern semiconductor industry and for a number of advanced technological functions in electronics and optoelectronic platforms. In this regard, a CuO-based nanocomposite was synthesized through a facile surfactant-free wet chemical strategy, and its potential for photoelectronic applications has been demonstrated. The nature of the composite phase and its other structural characteristics were studied in detail using Raman and X-ray photoelectron spectroscopic tools. The particulate characteristics of the composite were inferred using transmission electron microscopic measurements. Room temperature luminescence measurements revealed that the optical activity of the composite spreads across the red and near-infrared region of the electromagnetic spectrum through corresponding transitions. The optoelectronic capabilities of the processed composite were investigated through fabricating a CuO composite/ZnO nanowire-based p–n heterostructure and studying its associated current–voltage (I–V) characteristics under photon illumination. The nature of charge carriers, flat band potential, charge transfer resistance and carrier density were also studied individually and collectively for each component comprising the heterostructure through Mott–Schottky and Nyquist type impedance plots.

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.

Enhanced photoelectrical performance of chemically processed SnS2 nanoplates

In this work, tin disulfide (SnS2) nanoplates have been synthesized through a facile hydrothermal method. The structural and morphological properties of SnS2 were investigated via scanning electron microscopy (SEM) which actually revealed the nanoplates like morphology of the obtained samples. Heterojunction diodes comprising SnS2 nanoplates and p-type silicon (Si) were fabricated and been demonstrated. Their electrical properties were studied using current–voltage characteristics and impedance spectroscopy. The diodes were found to exhibit excellent rectifying behavior with significant increase in reverse current under illumination. Impedance results identified the resistance of the device to reduce considerably under light irradiation. The enhanced photoelectrical properties of the heterojunctions were actually promoted by the electric field at the heterojunction interface, which further results with the effective separation of photogenerated electron hole pairs. The obtained results also suggest the potential of chemically processed SnS2 nanoplates for applications in photodetection and sensors applications.

Structural and optical properties of Dy doped ZnO thin films prepared by pyrolysis technique

Structural, optical and Raman scattering studies have been performed on the Dy substituted zinc oxide (ZnO) thin films (1, 3 & 5 wt%) fabricated through a sol gel based spray pyrolysis technique on preheated glass substrates. The hexagonal crystal structure with (002) preferred orientation was confirmed from the X-ray diffraction analysis for the undoped and Dy doped ZnO films. The crystallinity of the films decreased with increasing Dy content with a corresponding decease in the intensity of (002) orientations. Reduction in grain size with increase in Dy content was observed. The shift of E2 (high) mode observed in the Raman spectra towards the lower wave numbers with increase in Dy concentration was correlated with the increase in stress on the ZnO matrix upon Dy substitution. The optical band gap was found to increase from 3.17 eV to 3.27 eV with a transparency of 80% for higher Dy concentrations. A blue shift in the NBE emission was also observed for Dy doping.

Vertically aligned ZnCdS nanowire arrays/P3HT heterojunctions for solar cell applications

Nowadays, solid-state inorganic-organic hybrid solar cells based on one-dimensional (1D) inorganic semiconducting nanostructures and organic polymers are believed to offer convincing solutions for the realm of next generation solar cells. In this regard, 1D ZnCdS nanowire (NW) arrays were fabricated on transparent conducting substrates through a catalyst free co-evaporation method and their wurtzite structural characteristics, 1D morphological layout and valence state/composition were studied in detail using X-ray diffraction, high-resolution electron microscopy and X-ray photoelectron spectroscopy, respectively. The existence of deep level traps and optical band gap of ZnCdS NWs were additionally studied using room-temperature cathodoluminescence and UV-vis absorbance measurements. The inorganic-organic hybrid cells were then fabricated using these NWs via spin coating poly(3,4-ethylenedioxythiophene) and poly(styrene sulfonate) based polymers. The morphological dissemination of the polymer deposits on NWs were also studied individually by electron microscopy. The solar cell (J-V) characteristics of the fabricated architectures were investigated at room-temperature and as a function of temperature and different intensities of incident light irradiation. The trap energy of the devices was noted to decrease from 68.1 to 40.7eV, suggesting the active role of trap sites that could have originated from the surface defects and other structural disorders across the hybrid heterostructures.

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.

Self-assembled MoS2/rGO nanocomposites with tunable UV-IR absorption

MoS2/reduced graphene oxide (rGO) nanocomposites were synthesized using an ultrasonic pretreatment with a single-stage hydrothermal and reduction process. Self-assembled MoS2 layers in the rGO matrix were obtained. The effect of quantum confinement in the structure, controlled by the degree of reduction of graphene oxide and the size of the 2D MoS2 nanocrystals, made it possible to obtain tunable optical absorption. MoS2/rGO layered nanocomposites exhibit a wide UV-IR absorption in the wavelength range from 280 nm to 973 nm, which is attractive for highly efficient multiband solar cells and advanced photonics.

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.