Cu-Pd bimetal and CuPt alloy nanotubes derived from Cu nanowires:novel amplification media for surface-enhanced Raman spectroscopy

Abstract Surface-plasmons of metals have been utilized to enhance the Raman spectra of various adsorbed moieties for over decades. While amplification of the spectral intensity takes place on most of the metals, due to their superb properties, Au, Ag and Cu surfaces represent the benchmark in surface-enhanced Raman spectroscopy. In this paper, we show that Cu-Pd bimetal and CuPt alloy nanotubes derived from Cu nanowires by simple galvanic exchange reactions are suitable for the efficient enhancement of Raman spectra when dispersed on Si surfaces. Amplification factors of 120× on Cu nanowires, 150× on Cu-Pd bimetal nanotubes and 250× on CuPt alloy nanotubes in reference to the substrate are measured for rhodamine 6G and methyl violet model compounds. We also show that the nanotubes dispersed on Au surfaces can contribute to a further intensity enhancement of the substrate and detect analytes adsorbed from 10 −6 M analyte concentrations. Our results obtained using bimetallic and alloy nanomaterials shed light on a new strategy to synthetize and apply new types of metal nanostructures and compositions for surface-enhanced Raman spectroscopy in the future

Grid-type transparent conductive thin films of carbon nanotubes as capacitive touch sensors

Abstract Transparent conductive films are used in a wide variety of devices. While solar cell top electrodes as well as tablet and mobile phone screens require high optical transparency and low sheet resistance (>80% and <10 Ω/❑) to maximize power efficiency; other, less demanding applications, such as those in capacitive touch panels and antistatic coatings, in which only small currents are involved, can be managed with coatings of moderate conductivity. In this paper, we show that area-selective argon plasma treated polyethylene terephthalate surfaces are suitable for localized deposition of carbon nanotubes from their aqueous dispersions by a simple dip coating and subsequent drying processes. The as-deposited carbon nanotubes form entangled networks in microscopic patterns over the plasma-treated surface areas with sheet resistance of <1 kΩ/❑ and optical transparency of ~75%. Based on this process, we demonstrate grid-type transparent conductive thin films of carbon nanotubes as capacitive touch sensors. Since each process step is robust, easy to up and downscale, and may be implemented even in roll-to-roll and sheet-to-sheet fabrication, the demonstrated technology is promising to produce grid-type structures even at an industrial scale in the future

Size-dependent H₂ sensing over supported Pt nanoparticles

Abstract Catalyst size affects the overall kinetics and mechanism of almost all heterogeneous chemical reactions. Since the functional sensing materials in resistive chemical sensors are practically the very same nanomaterials as the catalysts in heterogeneous chemistry, a plausible question arises: Is there any effect of the catalyst size on the sensor properties? Our study attempts to give an insight into the problem by analyzing the response and sensitivity of resistive H₂ sensors based on WO₃ nanowire supported Pt nanoparticles having size of 1.5±0.4 nm, 6.2±0.8 nm, 3.7±0.5 nm and 8.3±1.3 nm. The results show that Pt nanoparticles of larger size are more active in H₂ sensing than their smaller counterparts and indicate that the detection mechanism is more complex than just considering the number of surface atoms of the catalyst

High photoresponse of individual WS₂ nanowire-nanoflake hybrid materials

Abstract van der Waals solids have been recognized as highly photosensitive materials that compete conventional Si and compound semiconductor based devices. While 2-dimensional nanosheets of single and multiple layers and 1-dimensional nanowires of molybdenum and tungsten chalcogenides have been studied, their nanostructured derivatives with complex morphologies are not explored yet. Here, we report on the electrical and photosensitive properties of WS₂ nanowire-nanoflake hybrid materials we developed lately. We probe individual hybrid nanostructured particles along the structure using focused ion beam deposited Pt contacts. Further, we use conductive atomic force microscopy to analyze electrical behavior across the nanostructure in the transverse direction. The electrical measurements are complemented by in situ laser beam illumination to explore the photoresponse of the nanohybrids in the visible optical spectrum. Photodetectors with responsivity up to ∼0.4 AW⁻¹ are demonstrated outperforming graphene as well as most of the other transition metal dichalcogenide based devices

Ultrasensitive H₂S gas sensors based on p-type WS₂ hybrid materials

Abstract Owing to their higher intrinsic electrical conductivity and chemical stability with respect to their oxide counterparts, nanostructured metal sulfides are expected to revive materials for resistive chemical sensor applications. Herein, we explore the gas sensing behavior of WS₂ nanowire-nanoflake hybrid materials and demonstrate their excellent sensitivity (0.043 ppm⁻¹) as well as high selectivity towards H₂S relative to CO, NH₃, H₂, and NO (with corresponding sensitivities of 0.002, 0.0074, 0.0002, and 0.0046 ppm⁻¹, respectively). Gas response measurements, complemented with the results of X-ray photoelectron spectroscopy analysis and first-principles calculations based on density functional theory, suggest that the intrinsic electronic properties of pristine WS₂ alone are not sufficient to explain the observed high sensitivity towards H₂S. A major role in this behavior is also played by O doping in the S sites of the WS₂ lattice. The results of the present study open up new avenues for the use of transition metal disulfide nanomaterials as effective alternatives to metal oxides in future applications for industrial process control, security, and health and environmental safety