Sensors Based on Nanoscale Silicon 1D Structures for Industrial, Environmental and Medical Monitoring

Abstract

Article is devoted to the analysis of modern sensors based on silicon nanowires (SiNWs) to determine the influence of SiNWs synthesis parameters and their structural features on device characteristics. A modern trend in the development of electronic sensing devices is the use of various types of nanomaterials in order to increase sensor sensitivity and miniaturize of their size. 1D nanomaterials, namely SiNWs, have several advantages for sensor applications, such as a large surface-to-volume ratio and an increased rate of diffusion of the main charge carriers. Based on the literature analysis, an overview of modern SiNWs sensors was made. The advantages of silicon 1D structures were shown by comparison with other types of nanostructures. Also sensors were classified according to the methods of synthesis of SiNWs, sensor principle operation, kind of input value and types of applied modifiers. Silicon nanowires were most often synthesized by the method of metal-stimulated chemical etching, the advantages of which include the simplicity of implementation, low cost, and the ability to synthesize nanostructures with a high aspect ratio. The vapor-liquid-solid synthesis was also used, the advantages of which include the ability to be adapted to any technology of supplying a gas mixture with the target component and the possibility of obtaining nanowires with a diameter of 10 nm or less. According to the principle operation, the most of sensors developed on the basis of silicon nanowires are of electrical type (resistive, capacitive, electrochemical, diode or transistor type), optical sensors (fluorescent) are developed to a much lesser extent. Gas sensors (ethanol, oil vapor, formaldehyde, ammonia, nitrogen oxide, hydrogen, carbon dioxide,), liquid sensors (glucose, hydrogen peroxide, ethanol, heavy metal ions, pH), and physical values (humidity, temperature and illumination) have been developed on the basis of silicon 1D nanoscale structures. The following surface modifiers of nanowires were used to improve the performance characteristics: noble metal nanoparticles, metal-organic framework structures, carbon nanotubes, graphene, self-assembled monolayers, metal and metal oxide thin films. In particular, it was shown that the modification of the surface of the array of SiNWs with noble metals led to an increase in the sensitivity of the hydrogen sensor by 80%. Modification of formaldehyde sensor using reduced graphene oxide resulted in an improvement of sensor sensitivity by more than 2 times. The influence of SiNWs synthesis parameters on sensor performance characteristics was also determined. In particular, it was shown that increasing of SiNWs width from 20–30 nm to 500–600 nm led to an increase in the sensitivity of humidity sensor from 4.5 to 7.5%. Increasing the etching time caused the synthesis of longer nanowires, which improved the sensitivity of carbon dioxide sensors from 0.6 to 2.5%. Dependences established in this work will make it possible to develop the production technology of various types of sensors based on silicon nanowires with high sensitivity, selectivity, stability and operation speed.