Structural,optical, photoluminescence,electrochemical, and photoelectrochemical properties of Fe doped ZnSe hexagonal nanorods

The present investigation describes that the iron (Fe) doped ZnSe hexagonal nanorods were successfully synthesized via chemical synthesis specifically galvanostatic mode of electrodeposition and addition of Fe in order to improve the PEC performance of ZnSe electrodes using a galvanostatic mode. These crystalline Fe doped ZnSe hexagonal nanorods electrodes are characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), and optical properties, such as UV–vis spectroscopy, photoluminescence spectroscopy, electrochemical impedance spectroscopy (EIS), Raman spectroscopy and photoelectrochemical properties. It is seen that at 5% Fe doped ZnSe hexagonal nanorods show the open circuit voltage (V_oc) was 100 mV, and short circuit current (I_sc) was 110 μA. The observed fill factor and efficiency were found to be 44% and 0.15%, respectively.     

Metal-catalyzed synthesis of ultralong tin dioxide nanobelts: Electrical and optical properties with oxygen vacancy-related orange emission

Tin dioxide (SnO₂) ultralong nanobelts were fabricated on silicon substrate by metal catalyzed Chemical Vapor Deposition (CVD) approach. An optical bandgap of 3.66 eV was calculated by optical absorbance data. Three Raman active modes peaks were observed at 474.4, 633 and 774.4 cm⁻¹. Room temperature photoluminescence (PL) exhibited an orange emission at 600 nm. A vapor–liquid–solid (VLS) process based growth mechanism for the formation of SnO₂ nanobelts was proposed and discussed briefly. Electrical transport characteristics of nanobelts were studied in dark and under ultraviolet (UV) laser. The fabricated device exhibited high photo-response properties under UV light, indicating their potential application as photo-switches and UV detectors.     

Temperature dependent study of basal plane stacking faults in Ag:ZnO nanorods by Raman and photoluminescence spectroscopy

We report the specific features of basal plane stacking faults (BSFs) in ZnO nanorods (NRs), studied by temperature dependent photoluminescence and Raman spectroscopy. At low temperature (4 K) the intense band of emission at 3.321 eV is attributed to the presence of BSFs defects and Ag as an acceptor dopant in ZnO. This specific peak red-shifts with the temperature increase, occupying the position 3.210 eV at RT. The nature of the emission is explained as exciton recombination of the electrons, confined in the homo-heterojunction QW, with the holes, localized near the Ag atoms close to SFs. Raman spectroscopy revealed that Ag:ZnO nanorods have slightly downshifted positions of the modes 330 cm⁻¹ and 440 cm⁻¹ by 4 cm⁻¹, which we explain as due to the presence of BSFs. It was also observed, that the longitudinal optical phonon mode A^LO, which is common polar mode for ZnO, was not detected by Raman spectroscopy in the samples with high BSFs density. This feature can be explained as due to existence of the bound charge induced by the BSFs in the NRs.     

Development of sensitive non-enzymatic glucose sensor using complex nanostructures of cobalt oxide

The study reports the synthesis of cobalt oxide (Co₃O₄) nanostructures and their application in enzyme free electrochemical sensing of glucose. The synthesized nanostructures were elaborately characterized via number of analytical techniques including scanning electron microscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR). The as-synthesized nanostructures of Co₃O₄ were found to exhibited nanodisc like morphology with the size dimension in range of 300–500 nm. The obtained morphological features were evaluated for their electrochemical potential towards oxidation of glucose which enabled development of sensitive (27.33 µA mM⁻¹ cm⁻²), and stable enzyme free glucose sensor. In addition, the developed sensor showed excellent linearity (r²=0.9995), wide detection range (0.5–5.0 mM), lower detection limit (0.8 µM) and extreme selectivity towards glucose in the presence of common interferents like dopamine (DP), ascorbic acid (AA) and uric acid (UA). The successfully application of developed sensor for real blood glucose analysis further reflects its capability for routine glucose measurement.     

The excellent spontaneous ultraviolet emission of GaN nanostructures grown on silicon substrates by thermal vapor deposition

In this study, GaN nanostructures were grown on p-Si (111) substrate by thermal chemical vapor deposition (TCVD). Ga vapor directly reacted with NH₃ solution in N₂ carrier gas flow of 2 L/min at different temperatures (950–1050 °C). The influence of NH₃ solution and growth temperature on the morphology, structure, optical and photoresponse properties of GaN nanostructures was investigated. Scanning electron microscopy images showed that the densities of the NWs varied with increasing temperature. The use of NH₃ solution and increased growth temperature improved the crystalline quality of GaN nanostructures. The photoluminescence (PL) spectra of nanostructures displayed a near band-edge (NBE) emission at around 363–367 nm. Higher growth temperature (1050 °C) resulted in a strong NBE emission with no yellow emission peak. With +5 V applied bias, the NWs metal–semiconductor–metal UV photodetector exhibited a high photocurrent of 1.6×10⁻³ A. The photocurrent to dark current contrast ratio was 120.     

Fabric electrodes coated with polypyrrole nanorods for flexible supercapacitor application prepared via a reactive self-degraded template

Wearable energy storage devices that can be used in the garment industry are strongly required to power E-textiles. In this article, polypyrrole (PPy) nanorods were deposited on cotton fabrics via in situ polymerization of pyrrole in the presence of the fibrillar complex of FeCl₃ and methyl orange as a reactive self-degraded template. The obtained fabrics could be directly used as supercapacitor electrodes, with a maximum specific capacitance of 325 F g⁻¹ and an energy density of 24.7 Wh kg⁻¹ at a current density of 0.6 mA cm⁻². The capacitance remained higher than 200 F g⁻¹ after 500 cycles.     

Effect of swift heavy ion (SHI) irradiation on the structural and optical properties of N implanted CVT grown ZnSe single crystals

Present study reports the variation of structural and optical properties of N implanted ZnSe single crystals grown by a Chemical Vapor Transport (CVT) technique due to120 MeV Au ion irradiation. The grazing incidence X-ray diffraction (GIXRD) results show that the full width at half maximum (FWHM) increases on irradiation. The surface morphology of irradiated sample shows the pits and islands by AFM studies. The optical absorption cut off wavelength is 493 nm for as grown ZnSe whereas for the implanted and irradiated samples cut off wavelength shift towards red region. The photoluminescence spectrum shows the emission wavelength is at 592 nm whereas for the implanted-irradiated samples PL emission shift towards red region. The intensity of defect level emission decreases due to Au irradiation. The FT-Raman spectrum shows the peak at 252 cm⁻¹ due to LO mode of Zn–Se lattice vibrations. The X-ray absorption near edge structure (XANES) study was performed for the as grown and irradiated samples. The detailed investigation on the structural and optical properties of the N implanted and Au irradiated ZnSe single crystal was carried out.     

One step hydrothermal synthesis of SnO2-RGO nanocomposite and its field emission studies

Field emission (FE) properties of hydrothermally synthesized, SnO₂-RGO nanocomposite have been investigated at a base pressure of 1×10⁻⁸mbar. The results reveal that the SnO₂-RGO nanocomposite emitter prevails over the pristine RGO emitter. The values of turn-on field, defined at emission current density of 1 μA/cm², are found to be 1.8 and 2.2 V/μm for the SnO₂-RGO and pristine RGO emitters, respectively. Furthermore, the SnO₂-RGO emitter delivers maximum emission current density of ~800 µA/cm² at an applied field of 5 V/μm. The observed values of applied field corresponding to emission current densities of 1 μA/cm² and 10 µA/cm² are superior to those reported for various emitters due to SnO₂ nanostructures and their composites. The emission current at the pre-set value of 1 µA is found to be very stable over a period of 3hrs. The enhanced FE behaviour of SnO₂-RGO nanocomposite emitter has been attributed to synergic effect due to its nanometric dimensions offering high aspect ratio and modulation of electronic properties via formation of heterostructure. The results obtained herein propose the SnO₂-RGO nanocomposite as a prospective candidate for FE based vacuum microelectronic devices.     

The influence of high energy electron irradiation on the Schottky barrier height and the Richardson constant of Ni/4H-SiC Schottky diodes

The influence of high energy electron (HEE) irradiation from a Sr-90 radio-nuclide on n-type Ni/4H–SiC samples of doping density 7.1×10¹⁵ cm⁻³ has been investigated over the temperature range 40–300 K. Current–voltage (I–V), capacitance–voltage (C–V) and deep level transient spectroscopy (DLTS) were used to characterize the devices before and after irradiation at a fluence of 6×10¹⁴ electrons-cm⁻². For both devices, the I–V characteristics were well described by thermionic emission (TE) in the temperature range 120–300 K, but deviated from TE theory at temperature below 120 K. The current flowing through the interface at a bias of 2.0 V from pure thermionic emission to thermionic field emission within the depletion region with the free carrier concentrations of the devices decreased from 7.8×10¹⁵ to 6.8×10¹⁵ cm⁻³ after HEE irradiation. The modified Richardson constants were determined from the Gaussian distribution of the barrier height across the contact and found to be 133 and 163 A cm⁻² K⁻² for as-deposited and irradiated diodes, respectively. Three new defects with energies 0.22, 0.40 and 0.71 eV appeared after HEE irradiation. Richardson constants were significantly less than the theoretical value which was ascribed to a small active device area.     

Growth enhancement and field emission characteristics of one-dimensional 3,4,9,10-perylenetetracarboxylic dianhydride nanostructures on pillared titanium substrate

We have utilized the π–π interactions between 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) molecules and temperature-induced morphology changes to synthesize one-dimensional (1D) nanostructures of PTCDA on a heated (ca. 100 °C) titanium substrate through vacuum sublimation. Because of the pillared Ti structures and the presence of reactive Ti–Cl sites, the titanium substrate played a crucial role in assisting the PTCDA molecules to form 1D nanostructures. The average diameter of the nanofibers deposited on the Ti-CVD substrate, a Ti substrate formed by chemical vapor deposition (CVD), at 100 °C was ca. 84 nm, with lengths ranging from 100 nm to 3 μm. When the PTCDA nanofibers were biased under vacuum, the emission current remained stable. The turn-on electric field for producing a current density of 10 μA/cm² was 8 V/μm. The maximum emission current density was 1.3 mA/cm², measured at 1100 V (E = 11 V/μm). From the slope of the straight line obtained after plotting ln(J/E²) versus 1/E, we calculated the field enhancement factor β to be ca. 989. These results demonstrate the PTCDA nanofibers have great potential for applicability in organic electron-emitting devices.     

Surfactant free hydrothermally derived ZnO nanowires,nanorods, microrods and their characterization

ZnO nanowires, nanorods and microrods have been prepared by an organic-free hydrothermal process using ZnSO₄ and NaOH/NH₄OH solutions. The powder X-ray diffraction (PXRD) patterns reveal that the ZnO nano/microrods are of hexagonal wurtzite structure. The Fourier transform infrared (FT-IR) spectrum of ZnO powder shows only one significant spectroscopic band at around 417 cm^?1 associated with the characteristic vibrational mode of Zn–O bonding. The thickness 75–300 nm for ZnO nanorods and 0.2–1.8 μm for microrods are identified from SEM/TEM images. UV–visible absorption spectra of ZnO nano/microrods show the blue shift. The UV band and green emission observed in photoluminescence (PL) spectra are due to free exciton emission and singly ionized oxygen vacancy in ZnO. Finally, the mechanism for organic-free hydrothermal synthesis of the ZnO nano/microrods is discussed.     

Fabrication and performance evaluation of symmetrical supercapacitor based on manganese oxide nanorods–PANI composite

Manganese oxide nanorods distributed over polyaniline (PANI) network was prepared by one step facile synthesis condition. pH of the reactant solution was tuned using sulfuric acid. Effect of pH on the morphology, chemical composition, structure and electrochemical performance of the prepared materials were studied. Thermal investigation reveals the decomposition of PANI at temperatures below 600 °C. Structural details and chemical composition of the compound was obtained from XRD, FTIR and XPS studies. α type MnO₂ was found to be crystallized in the prepared MnO₂–PANI composite. Single crystal manganese oxide nanorods distributed over the PANI network was cognizant from the FESEM and HRTEM investigations. Nanorods of average diameter 82 nm and length 482 nm were obtained without deploying any surfactants or templates. Electrochemical techniques like Cyclic Voltammetry (CV), Chronopotentiometry (CP) and Electrochemical Impedance Spectroscopy (EIS) were utilized. Study results indicate that the composites prepared shows excellent electrochemical performance. Among the prepared materials, MnP-46 exhibits a maximum specific capacitance of 687 Fg⁻¹ at 5 mV s⁻¹ scan rate and a capacitance retention of 95% over 2000 cycling. Promising performance of MnP-46 was further tested in a symmetrical two cell configuration. The cell was operative upto 1 V potential window. MnP-46 in a symmetrical arrangement demonstrates 179 Fg⁻¹ at 5 mV/s scan rate. High conductivity of the electrode material was confirmed from the Nyquist plot.     

Nanostructured nickel oxide ultrafine nanoparticles: Synthesis,characterization, and supercapacitive behavior

Well-dispersed NiO nanoparticles were prepared via cathodic electrodeposition followed by a heat-treatment method. The supercapacitive performance of the prepared nanoparticles was analyzed by means of cyclic voltammetry (CV) and galvanostatic charge–discharge tests at −0.2–0.5 V potential windows in 1 M KOH. The nanoparticles exhibited high specific capacitance (1623.1 F g⁻¹ at the scan rate of 5 mV s⁻¹) and good long-term cycling stability (9.6% capacity decay after 1000 cycling at the current density of 2 A g⁻¹).     

Green and blue–green light-emitting electrochemical cells based on cationic iridium complexes with 2-(4-ethyl-2-pyridyl)-1H-imidazole ancillary ligand

The ionic iridium complexes, [Ir(ppy)₂(EP-Imid)]PF₆ (Complex 1) and [Ir(dfppy)₂(EP-Imid)]PF₆ (Complex 2) are used as the light-emitting material for the fabrication of light-emitting electrochemical cells (LECs). These complexes have been synthesized, employing 2-(4-ethyl-2-pyridyl)-1H-imidazole (EP-Imid) as the ancillary ligand, 2-phenylpyridine (ppy) and 2-(2,4-difluorophenyl)pyridine (dfppy) as the cyclometalated ligands, which were characterized by various spectroscopic, photophysical and electrochemical methods. The photoluminescence (PL) emission spectra in acetonitrile solution show blue–green and blue light emission for Complexes 1 and 2 respectively. However, LECs incorporating these complexes resulted in green (522 nm) light emission for Complex 1 with the Commission Internationale de L’Eclairage (CIE) coordinates of (0.33, 0.56) and blue–green (500 nm) light emission for Complex 2 with the CIE coordinates of (0.24, 0.44). Using Complex 1, a maximum luminance of 1191 cd m⁻² and current efficiency of 1.0 cd A⁻¹ are obtained while that of Complex 2 are 741 cd m⁻² and 0.88 cd A⁻¹ respectively.     

Effect of aqueous electrolyte on pseudocapacitive behavior of chemically synthesized La2S3 electrode

Lanthanum sulfide electrode (La₂S₃) is prepared by a low cost, simple and room temperature chemical route for energy storage. The surface morphology of La₂S₃ film is revealed through field emission scanning electron microscopy. For the energy storage purpose, the pseudocapacitive behavior of La₂S₃ electrode is studied in 1 M aqueous Na₂SO₄ and 1 M KOH electrolytes. La₂S₃ electrode achieved maximum specific capacitance of 358 F g⁻¹ at 5 mV s⁻¹ scan rate with 78% electrochemical cyclic stability over 1000 cycles in 1 M Na₂SO₄ electrolyte. The galvanostatic charge–discharge study demonstrated the energy density of 35 Wh kg⁻¹ at power density of 1.26 kW kg⁻¹. The electrochemical impedance study showed field assisted charge transfer process with relaxation time of 32 ms in 1 M Na₂SO₄ electrolyte ensuring fast redox reaction.     

Nanostructured CuO/PANI composite as supercapacitor electrode material

An in-situ polymerization method has been employed to prepare CuO/PANI nanocomposite. The prepared samples have been characterized by X-ray diffraction (XRD), FTIR spectroscopy, field emission scanning electron microscopy (FESEM), and BET analysis. Application of the prepared samples has been evaluated as supercapacitor material in 1 M Na₂SO₄ solution using cyclic voltammetry (CV) in different potential scan rates, ranging from 5 to 100 mV s⁻¹, and electrochemical impedance spectroscopy (EIS). The specific capacitance of CuO/PANI has been calculated to be as high as 185 F g⁻¹, much higher than that obtained for pure CuO nanoparticles (76 F g⁻¹). Moreover, the composite material has shown better rate capability (75% capacitance retention) in various scan rates in comparison with the pure oxide (30% retention). EIS results show that the composite material benefits from much lower charge transfer resistance, compared to CuO nanoparticles. Moreover, much better cyclic performance has been achieved for the composite material.     

High electron mobility triazine for lower driving voltage and higher efficiency organic light emitting devices

The triazine compound 4,4′-bis-[2-(4,6-diphenyl-1,3,5-triazinyl)]-1,1′-biphenyl (BTB) was developed for use as an electron transport material in organic light emitting devices (OLEDs). The material demonstrates an electron mobility of ∼7.2 × 10⁻⁴ cm² V⁻¹ s⁻¹ at a field of 8.00 × 10⁵ V cm⁻¹, which is 10-fold greater than that of the widely used material tris(8-hydroxyquinoline) aluminum (AlQ₃). OLEDs with a BTB electron transport layer showed a ∼1.7–2.5 V lower driving voltage and a significantly increased efficiency, compared to those with AlQ₃. These results suggest that BTB has a strong potential for use as an OLED electron transport layer material.     

Enhanced field emission and hysteresis characteristics of aligned carbon nanotubes with Ti decoration

The field emission behavior of aligned carbon nanotubes (CNTs) is remarkably improved by decorating their surfaces with Ti nanoparticles through a sputtering process. The CNT/Ti(4 nm) sample shows a low turn-on field of 0.63 V/μm at 10 μA/cm², low threshold field of 1.06 V/μm at 1 mA/cm², and maximum field emission current density of 23 mA/cm² at 1.80 V/μm. The enhanced field emission properties of the CNT/Ti samples are attributed to the added defect sites and Ti nanoparticles, which increase the field enhancement factor and density of emission sites. Stability measurements indicate that the Ti coating, which acts as a protective layer, also strengthens the field emission stability of the CNT arrays. Moreover, the extent of hysteresis in the current–voltage sweep highly depends on the voltage-sweep speed.     

Effect of electron irradiation on morphological,compositional and electrical properties of nanocluster carbon thin films grown using room temperature based cathodic arc process for large area microelectronics

The influence of 8 MeV electron beam bombardment on room temperature grown nanocluster carbon using cathodic arc process has been studied here. Atomic force microscopy (AFM) study shows that surface roughness varies with varying electron doses. High doses of electrons could causes thermal induce graphitization and morphological changes in the films. Raman spectroscopy analysis reveals that G-peak vary from 1555 cm⁻¹ to 1570 cm⁻¹ and D-peak varying from 1361 cm⁻¹ to 1365 cm⁻¹ indicating the disorderness and presence of both graphitic and diamond-like phases. Room temperature conductivity changes by two to three orders in magnitude. The conductivity in the films could be due to conduction of charge carriers through neighboring islands of conductive chains. Defect states calculated using the differential technique varies from 8 × 10¹⁷cm⁻³ eV⁻¹ to 1.5 × 10¹⁹ cm⁻³ eV⁻¹. Irradiation of nanocluster carbon thin films could be helpful to tune the electrical properties and defect densities of the nanocluster carbon films for various large area, flexible electronic and nano electronic applications.     

Simple-structured efficient white organic light emitting diode via solution process

High-efficiency white emission is crucial to the design of energy-saving display and lighting panels, whereas solution-process feasibility is highly desirable for large area-size and cost-effective roll-to-roll manufacturing. In this study, we demonstrate highly-efficient, bright and chromaticity stable white organic light emitting diodes (OLEDs) with solution-processed single emissive layer. The resultant best white OLED shows excellent electroluminescence performance with forward-viewing external quantum efficiency, current efficiency and power efficiency of 22.7%, 48.8 cd A^− 1 and 27.8 lm W^− 1 at 100 cd m^− 2, respectively, with a maximum luminance of 19,590 cd m^− 2. Furthermore, we also observed an increment of 112% in the power efficiency, 86.9% in the current efficiency and a decrement of 39.2% in the external quantum efficiency at 100 cd m^− 2 as the doping concentration of blue dye was increased from 10 wt% to 25 wt% in the devices. The better efficiency performance may be attributed to the effective exciton-confining device architecture and low-energy barrier for electrons to inject from the hole-blocking electron-transport layer to the host layer.