A. Kathalingam

Shape-dependent electrical property of solution synthesized ZnO nanorods

Synthesis of linked-ZnO nanorods by the aqueous solution method and its electrical characterization by constructing metal-ZnO nanorod?metal devices are reported. Aluminum and gold metals were used to produce electrical contacts to the ZnO nanorods using the lithography and lift-off processes. Current?voltage (I?V) characteristics of the aligned ZnO nanorod devices were analyzed, and they showed shape-dependent electrical property for both aluminum and gold contacts. Linked-ZnO nanorods of dissimilar ends have been found to show a nonlinear and asymmetrical I?V plot, showing rectifying diode-like behavior with the rectification ratio 103?at a bias of 2?V. The formation of Schottky diodes is suggested due to the asymmetric contacts resistance of metal-ZnO NR-metal devices. Space-charge-limited current conduction is found to influence the charge conduction in the nanorod under room-ambient condition. Photoresponse of the ZnO rods under different illumination is also demonstrated. It revealed that the photo absorption eliminates the effect of surface adsorbates on the ZnO nanorods.

Thermally stable memory devices using graphene flakes sandwiched polymethyl methacrylate polymer layers

Fabrication and characterization of graphene flakes sandwiched polymethyl methacrylate (PMMA) hybrid bistable devices (HBD) is reported in this paper. Graphene flakes (GFs) sandwiched polymer layers were prepared through a simple solution process. The fabricated memory devices have exhibited remarkable electrical bistable behavior even at 150°C. Bistable memory behavior of the fabricated devices have been described on the basis of current-voltage characteristics. Reasonably good ON/OFF current ratio (∼103) and retention property have been obtained from the constructed memory devices. The device showed excellent stability up to 105 switching cycles without any degradation both in ON and OFF states. The results obtained have indicated that the HBD fabricated by embedding graphene flakes in an insulating polymer matrix have potential applications in organic nonvolatile flash memory devices.

Hysteresis I–V nature of mechanically exfoliated graphene FET

Graphene is an attractive material for device applications due to its excellent electrical and mechanical properties. The mechanical exfoliation is an attractive method to fabricate graphene devices using mono and multilayer graphene flakes. As the graphene is very sensitive to atmosphere the occurrence of hysteresis and p-doping is common. This paper reports electrical characterization and hysteresis effect of graphene field effect transistor (FET) fabricated using mechanically exfoliated graphene flakes. Raman spectra and atomic force microscopy techniques have been used to examine the quality and thickness of the exfoliated graphene. This fabricated graphene FET has shown hysteresis nature with p-type doping. The possible reason for the observed hysteresis and p-doping has been explained.

An enhanced electrochemical and cycling properties of novel boronic Ionic liquid based ternary gel polymer electrolytes for rechargeable Li/LiCoO 2 cells

A new generation of boronic ionic liquid namely 1-ethyl-3-methylimidazolium difluoro(oxalate)borate (EMImDFOB) was synthesized by metathesis reaction between 1-ethyl-3-methylimiazolium bromide and lithium difluoro(oxalate)borate (LiDFOB). Ternary gel polymer electrolyte membranes were prepared using electrolyte mixture EMImDFOB/LiDFOB with poly vinylidenefluoride-co-hexafluoropropylene (PVdF-co-HFP) as a host matrix by facile solvent-casting method and plausibly demonstrated its feasibility to use in lithium ion batteries. Amongst ternary gel electrolyte membrane, DFOB-GPE3, which contained 80 wt% of EMImDFOB/LiDFOB and 20 wt% PVdF-co-HFP, showed excellent electrochemical and cycling behaviors. The highest ionic conductivity was found to be 10−3 Scm−1 at 378 K. Charge-discharge profile of Li/DFOB-GPE3/LiCoO2 coin cell displayed a maximum discharge capacity of 148.4 mAhg−1 at C/10 rate with impressive capacity retention capability and columbic efficiency at 298 K.

Synthesis of ZnO nanorods using different precursor solutions and their two terminal device characterization

Abstract ZnO nanostructures such as nanoparticles, nanorods, nanotubes and nanoplates were prepared by the novel chemical solution route using different combinations of precursors such as zinc nitrate [Zn(NO3)2·6H2O] and sodium hydroxide [NaOH], zinc nitrate [Zn(NO3)2·6H2O] and hexamethylenetetramine (HMT) (C6H12N4), and zinc acetate [Zn(CH3COO)2·2H2O] and NaOH at low temperature. The effects of temperature and bath concentration for the synthesis of various ZnO nanostructures have been studied. Synthesized powders were characterized by X-ray diffraction, scanning electron microscope and photoluminescence. The crystalline structure, size and shape of the synthesized particles have been analyzed. Energy band gap values and photoluminescence emissions of the nanostructures were found to change according to the kind of the particles. Rod shaped ZnO have been obtained from the combination of zinc nitrate and HMT. The synthesized ZnO nanorods were aligned between lithographically patterned finger type metal contacts and their current–voltage response were measured.

Effect of indium on photovoltaic property of n-ZnO/p-Si heterojunction device prepared using solution-synthesized ZnO nanowire film

Abstract. Preparation of n-ZnO/p-Si heterostructures using solution-synthesized ZnO nanowire films and their photovoltaic characterization is reported. The solution-grown ZnO nanowire film is characterized using scanning electron microscope, electron dispersive x-ray, and optical absorption studies. Electrical and photovoltaic properties of the fabricated heterostructures are studied using e-beam-evaporated aluminum as metal contacts. In order to use transparent contact and to simultaneously collect the photogenerated carriers, sandwich-type solar cells were fabricated using ZnO nanorod films grown on p-silicon and indium tin oxide (ITO) coated glass as ITO/n-ZnO NR/p-Si. The electrical properties of these structures are analyzed from current-voltage (I−V) characteristics. ZnO nanowire film thickness-dependent photovoltaic properties are also studied. Indium metal was also deposited over the ZnO nanowires and its effects on the photovoltaic response of the devices were studied. The results demonstrated that all the samples exhibit a strong rectifying behavior indicating the diode nature of the devices. The sandwich-type ITO/n-ZnO NR/p-Si solar cells exhibit improved photovoltaic performance over the Al-metal-coated n-ZnO/p-Si structures. The indium deposition is found to show enhancement in photovoltaic behavior with a maximum open-circuit voltage (Voc) of 0.3 V and short-circuit current (Isc) of 70×10−6 A under ultraviolet light excitation.

Fabrication of two-terminal devices using solution-synthesized Cu-doped ZnO nanorods and their photosensing properties

The fabrication and characterization of two-terminal devices using solution-synthesized Cu-doped ZnO nanorods and their photosensitive properties are reported in this work. Hydrothermally prepared ZnO and Cu:ZnO nanorods were characterized by SEM, EDS and PL studies. Two-terminal devices of ZnO and Cu:ZnO nanorods were prepared using a simple drop-casting on E-beam evaporated metal patterns. The aluminum metal patterns were produced using lithography and the lift-off technique. The current–voltage (I–V) characteristics of the nanorod devices show different shapes and current levels depending on the contact resistance and size of the nanorods. The photoresponse of the nanorods under different illumination conditions was analyzed. Both ZnO and Cu-doped ZnO show enhanced response under UV light excitation compared to halogen light excitation. The Cu-doped ZnO nanorods show an enhanced photosensitive property compared to undoped ZnO. This work demonstrates a simple fabrication technique of ZnO nanorod-based planar two-terminal devices.

Facile Preparation of Nanocrystalline ZnO Powder for Non-Volatile Memory Application

In this work, synthesis of ZnO nanoparticle by solution method and its application in non-volatile memory is reported. Nanocrystalline ZnO particles were prepared by a novel chemical route using the combination of zinc nitrate [Zn (NO3)2 6H2O] and sodium hydroxide [NaOH] at low temperature. The effects of temperature and bath concentration for the synthesis of ZnO powder have been studied. Synthesized powder was characterized by X-ray diffraction (XRD), UV-Vis spectrometer, transmission electron microscopy (TEM) and photoluminescence. Using the prepared ZnO nanoparticles with organic PMMA; non-volatile memory cells were prepared and studied its switching property.

Studies on structural, optical, electrical and morphological properties of LiCoO2 thin films prepared by sol–gel method

Abstract In the present investigation, lithium cobalt oxide (LiCoO2) thin films were synthesised by the sol–gel process coupled with a cost-effective spin coating method using citric acid as a chelating agent. The films prepared on mineral glass substrates were annealed at different temperatures of 548–748 K in steps of 50 K. The XRD studies revealed that the LiCoO2 thin films annealed at a lower temperature exhibit semi-crystalline nature and transform to crystalline structure with an increase in the annealing temperature. The optical band gap energy of the films was found to vary from 2.51 to 3.24 eV for films annealed at temperatures in the range of 548–748 K. The electrical conductivity of the LiCoO2 thin films varied from 10−3 to 10−9 Ω−1 cm−1 due to variation in the annealing temperature.

A Rapid One-Pot Synthesis of Novel High-Purity Methacrylic Phosphonic Acid (PA)-Based Polyhedral Oligomeric Silsesquioxane (POSS) Frameworks via Thiol-Ene Click Reaction

Herein, we demonstrate a facile methodology to synthesis a novel methacrylic phosphonic acid (PA)-functionalized polyhedral oligomeric silsesquioxanes (POSSs) via thiol-ene click reaction using octamercapto thiol-POSS and ethylene glycol methacrylate phosphate (EGMP) monomer. The presence of phosphonic acid moieties and POSS-cage structure in POSS-S-PA was confirmed by Fourier transform infrared (FT-IR) and nuclear magnetic resonance (1H, 29Si and 31P-NMR) analyses. Matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectrum of POSS-S-PA acquired in a dithranol matrix, which has specifically designed for intractable polymeric materials. The observed characterization results signposted that novel organo-inorganic hybrid POSS-S-PA would be an efficacious material for fuel cells as a proton exchange membrane and high-temperature applications due to its thermal stability of 380 °C.