Electric field dependence of Raman-active modes in single-wall carbon nanotube thin films

We report on electrical Raman measurements in transparent and conducting single-wall carbon nanotube (SWNT) thin films. Application of external electric field results in downshifts of the D and G modes and in reduction of their intensity. The intensities of the radial breathing modes increase with electric field in metallic SWNTs, while decreasing in semiconducting SWNTs. A model explaining the phenomenon in terms of both direct and indirect (Joule heating) effects of the field is proposed. Our work rules out the elimination of large amounts of metallic SWNTs in thin film transistors using high field pulses. Our results support the existence of Kohn anomalies in the Raman-active optical branches of metallic graphitic materials [Phys. Rev. Lett. 93 (2004) 185503].Comment: 17 pages, 4 figure

Enhanced Second Harmonic Generation from Coupled Asymmetric Plasmonic Metal Nanostructures

We show that second harmonic generation can be enhanced by Fano resonant coupling of asymmetric plasmonic metal nanostructures. We develop a theoretical model examining the effects of electromagnetic interaction between two metal nanostructures on the second harmonic generation. We compare the second harmonic generation efficiency of a single plasmonic metal nanostructure with that of two coupled ones. We show that second harmonic generation from a single metal nanostructure can be enhanced about 30 times by attaching a second metal nanostructure with a 10 times higher quality factor than that of the first one. The origin of this enhancement is Fano resonant coupling of the two metal nanostructures. We support our findings on Fano enhancement of second harmonic generation by an experimental study of a coupled plasmonic system composed of a silver nanoparticle and a silver nanowire on glass surface in which the ratio of the quality factors are also estimated to be around 10 times

Hydrothermal zinc oxide nanowire growth using zinc acetate dihydrate salt

Hydrothermal approach is widely used for the synthesis of zinc oxide (ZnO) nanowires. Zinc nitrate hexahydrate, zinc acetate and zinc chloride are three common salts that are used for synthesis. Among these, zinc nitrate hexahydrate is primarily used in many studies and zinc chloride is preferred for electrodeposition. In this work, zinc acetate dihydrate salt is used for the growth of ZnO nanowires and the effects of time, temperature, solution concentration and concentration ratios of the precursor chemicals are investigated. It is found that the growth time and solution concentration control the lengths of the nanowires, whereas the precursor concentration ratio and solution concentration control their diameter. High solution concentrations and high zinc acetate dihydrate concentrations lead to the development of thin film morphology. Optimum growth parameters are obtained and suggested for the use of zinc acetate dihydrate as a zinc source for growing ZnO nanowires with high aspect ratio (AR). The use of zinc acetate dihydrate leads to the formation of ZnO nanowires without impurities and eliminates the need for using extra capping agents

Nanometer-thick Mn:NiO and Co:NiO films for high performance nonenzymatic biosensors

© 2021 American Chemical Society.People with diabetes require regular blood sugar level monitoring, using commercial enzyme-based biosensors. There is a considerable need to develop biosensors with nonenzymatic electrodes to eliminate the drawbacks of enzymes. Nanostructured nickel oxide (NiO) thin films are highly promising materials for the development of nonenzymatic glucose and hydrogen peroxide (H2O2) biosensors. Although the biosensor performance can be easily attained with nonenzymatic electrodes, their commercialization still requires development of cost-effective and mass-production methods. In this work, we demonstrate the use of ultrasonic spray deposited, nanometer-thick, manganese and cobalt doped NiO (Mn:NiO and Co:NiO) films on indium tin oxide (ITO) coated glass substrates for glucose sensing. Sensor characterization followed detailed materials characterization. Nanometer-thick Co:NiO film electrodes showed better glucose sensor performance than those of bare NiO and Mn:NiO electrodes. High sensitivity of 1.67 μA/μM·cm2, a low detection limit of 231 nM, and a fast response time of 5.4 s within the linear range of 16-308 μM were obtained from nanometer-thick Co:NiO film electrodes. Amperometric measurements showed significant electrode reproducibility and stability. Nanometer-thick Co:NiO film electrode was also used to demonstrate actual clinical glucose measurements using human blood serum as a glucose source. Moreover, all fabricated nanometer-thick film electrodes were also utilized as H2O2 sensors. This work provides a novel approach for monitoring the biosensor performance using nanometer-thick doped NiO film electrodes. Obtained results demonstrated the potential of ultrasonic spray deposition method for the mass-production of high-performance nonenzymatic nanometer-thick film biosensors

Polyol Synthesis of Silver Nanowires: An Extensive Parametric Study

Silver nanowires have been synthesized by a polyol process. A detailed parametric study determining the relationship between final morphology of the products and temperature, injection rate, molar ratio of poly(vinylpyrrolidone) to silver nitrate, sodium chloride amount, and stirring rate is presented. The as-synthesized silver nanowires are analyzed by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD). The dependency of nanowire morphology and aspect ratio on synthesis parameters is shown via SEM images. Furthermore, the nanowire diameter is found to decrease with stirring rate, poly(vinylpyrrolidone) to silver nitrate molar ratio, and temperature and to increase with injection rate. The lack of sodium chloride and its presence in excess amounts resulted in the formation of particles with different sizes in addition to nanowires. In addition, poly(vinylpyrrolidone) to silver nitrate molar ratio is found to affect the morphology of the resulting nanostructure, leading to formation of particles at high and low ends. The results reported in this paper provide a basis for optimizing silver nanowire growth through the self-seeding polyol method

Zinc Oxide Nanowire Photodetectors with Single-Walled Carbon Nanotube Thin-Film Electrodes

In this study, transparent and flexible zinc oxide (ZnO) nanowire ultraviolet (UV) photodetectors prepared via a solution-based method in which single-walled carbon nanotube (SWNT) thin films were used as transparent electrodes are reported. The photoresponse current was found to be in proportion with the ZnO nanowire density, and the nanowire density could be tuned to increase the photocurrent by a factor of 300. The decay time for the fabricated photodetectors was found to be as low as 16 s. This study suggests the possibility of fabricating inexpensive, visible-blind UV photodetectors via solution-based methods

Fabrication and characterization of copper oxide-silicon nanowire heterojunction photodiodes

WOS: 000331468100013In this study, copper oxide (CuO) thin film/silicon (Si) nanowire heterojunctions have been fabricated and their optoelectronic performances have been investigated. Vertically aligned n-type Si nanowires have been fabricated using metal-assisted etching (MAE) technique. CuO thin films were synthesized by the sol-gel method and deposited onto the nanowires through spin-coating. Fabricated nanowire heterojunction devices exhibited excellent diode behaviour compared to the planar heterojunction control device. The rectification ratios were found to be 105 and 101 for nanowire and planar heterojunctions, respectively. The improved electrical properties and photosensitivity of the nanowire heterojunction diode was observed, which was related to the three-dimensional nature of the interface between the Si nanowires and the CuO film. Results obtained in this work reveal the potential of Si nanowire-based heterojunctions for various optoelectronic devices.Scientific and Technical Research Council of Turkey (TUBITAK); Turkish Academy of Sciences (TUBA)GA and FAA would like to thank The Scientific and Technical Research Council of Turkey (TUBITAK) Post-Doctoral Fellowship for financial support. HEU acknowledges support from the Distinguished Young Scientists award of the Turkish Academy of Sciences (TUBA). Middle East Technical University (METU) Central Laboratory facilities are also greatly acknowledged

Zinc Oxide Nanowire Decorated Single-Use Electrodes for Electrochemical DNA Detection

WOS: 000348662400048The surfaces of pencil graphite electrodes (PGEs) were decorated with zinc oxide nanowires (ZnO NWs) for the electrochemical detection of nucleic acids. ZnO NWs were synthesized through simple hydrothermal method. PGEs decorated with ZnO NWs (ZnO NW/PGEs) were electrochemically characterized through cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) following morphological characterization through transmission (TEM) and scanning electron microscopy (SEM). Enhanced sensor response obtained using ZnO NW/PGEs contrary to the bare PGE (control) samples. Our preliminary results simply reveal the potential of combining ZnO NWs with disposable sensor technology for the electrochemical detection of DNA.Turkish Academy of Sciences (TUBA)Turkish Academy of Sciences; Scientific and Technological Research Council of Turkey (TUBITAK)Turkiye Bilimsel ve Teknolojik Arastirma Kurumu (TUBITAK) [109M084, 109M487]; TUBATurkish Academy of Sciences; TUBITAKTurkiye Bilimsel ve Teknolojik Arastirma Kurumu (TUBITAK) [111T073]A.E. would like to express her gratitude to the Turkish Academy of Sciences (TUBA) as an Associate member for its partial support. H.E.U. acknowledges support from the Scientific and Technological Research Council of Turkey (TUBITAK) under grant no. 109M084 and 109M487 and the Distinguished Young Scientist Award of TUBA. G.C. acknowledges a PhD project scholarship through TUBITAK (Project No. 111T073)