Nanowires represent numerous opportunities for nanoelectronics and sensorics, while metal contact fabrication makes the device development rather challenging. Here, we demonstrate that silicon (Si) nanowires deposited on interdigital metal contacts via simple drop casting exhibit an abrupt increase in conductivity upon exposure to ammonia vapors and aqueous solutions due to adsorption of the analyte species. To reduce the noise of the DC resistance measurements lacking ohmic conductivity, we exploit electronic impedance spectroscopy. The resistive response is found to be dependent on the ammonia content in vapor and liquid matter. The results demonstrate a detection limit of 4 μmol•L −1 (80 ppb), a sensitivity of 0.2% μmol −1 •l (0.01%•ppb −1 ), and applicability for the low-concentration detection of up to 400 μmol•L −1 (8 ppm) ammonia in aqueous solutions both directly and indirectly with a response rate of up to 0.43%•s −1 and a recovery rate of 0.31%•s −1 and show selectivity to oxidizing species. Thus, we demonstrate that the use of semiconductor nanowires in adsorption sensorics does not require the fabrication of ohmic contacts and present a simple fabrication protocol perspective for the development of highly sensitive room-temperature multi-environment sensors.

Tailorable synthesis of axially heterostructured epitaxial nanowires (NWs) with a proper choice of materials allows for the fabrication of novel photonic devices, such as a nanoemitter in the resonant cavity. An example of the structure is a GaP nanowire with ternary GaPAs insertions in the form of nano-sized discs studied in this work. With the use of the micro-photoluminescence technique and numerical calculations, we experimentally and theoretically study photoluminescence emission in individual heterostructured NWs. Due to the high refractive index and near-zero absorption through the emission band, the photoluminescence signal tends to couple into the nanowire cavity acting as a Fabry–Perot resonator, while weak radiation propagating perpendicular to the nanowire axis is registered in the vicinity of each nano-sized disc. Thus, within the heterostructured nanowire, both amplitude and spectrally anisotropic photoluminescent signals can be achieved. Numerical modeling of the nanowire with insertions emitting in infrared demonstrates a decay in the emission directivity and simultaneous rise of the emitters coupling with an increase in the wavelength. The emergence of modulated and non-modulated radiation is discussed, and possible nanophotonic applications are considered.

Semiconductor nanowires are the perfect platform for nanophotonic applications owing to their resonant, waveguiding optical properties and technological capabilities providing control over their crystalline and chemical composition. Vapor-liquid-solid growth mechanism...

Carbon monoxide and ammonia are inorganic agents found both in nature and in the human body, which is of great interest for modern sensing. First, in concentrations of the order of 1 ppm agents are produced by human and can be markers of changes in human health. Second, at concentrations of the order of 100 ppm, carbon monoxide and ammonia are toxic and hazardous. This work is aimed at fabrication and study of precise, technological and relatively cheap sensors compatible with a gas and liquid medium for CO and NH3 detection, respectively.

This work is aimed at the development of a highly sensitive silicon (Si)-based sensor allowing for the selective detection and analysis of liquid solution compositions containing ammonia (NH3) and hydrochloric acid (HCl) in an indirect manner using electrochemical impedance spectroscopy (EIS). For optimization of the performance, we develop three types of sensors based on as-fabricated Si nanowires, nanowires treated with hydrofluoric acid (HF), and nanowires decorated with silver (Ag) nanoparticles. The fabricated sensors exhibit good performance governed by the sensitivity of the nanoscale Schottky barriers at the interface between the golden pads and Si nanowires. The best results on sensitivity are obtained with untreated Si nanowires providing a detection limit at the level of 4 μmol·L–1 and resistive sensitivities of 0.8% per μmol·L–1 for HCl and 4 μmol·L–1, −0.2% per μmol·L–1 for NH3, correspondingly. Treatment with HF stimulates the surface oxidation providing higher density of the adsorption sites and found promising for the detection with the analyte content up to 1000 μmol·L–1. In the end, we study the sensor response upon simultaneous exposure under NH3 and HCl vapors using developed approach for the EIS data analysis involving characterization of the sensor response with two parametersresistance and EIS frequency corresponding to the change in the operation regime. Due to the use of two parameters simultaneously, this approach is found as a pathway for qualitative analysis of the gas mixture composition using only one sensor. The results of the work shed light on the development of feasible highly sensitive sensors for health monitoring, allowing for selective mixed analytes detection.