High-performance humidity sensor using Schottky-contacted SnS nanoflakes for noncontact healthcare monitoring

Abstract

Humidity sensors based on flexible sensitive nanomaterials are very attractive in noncontact healthcare monitoring. However, the existing humidity sensors have some shortcomings such as limited sensitivity, narrow relative humidity (RH) range, and a complex process. Herein, we show that a tin sulphide (SnS) nanoflakes-based sensor presents high humidity sensing behaviour both in rigid and flexible substrate. The sensing mechanism based on the Schottky nature of a SnS-metal contact endows the asfabricated sensor with a high response of 2491000% towards a wide RH range from 3% RH to 99% RH. The response and recovery time of the sensor are 6 s and 4 s, respectively. Besides, the flexible SnS nanoflakes-based humidity sensor with a polyimide substrate can be well attached to the skin and exhibits stable humidity sensing performance in the natural flat state and under bending loading. Moreover, the first-principles analysis is performed to prove the high specificity of SnS to the moisture (H 2 O) in the air. Benefiting from its promising advantages, we explore some application of the SnS nanoflakes-based sensors in detection of breathing patterns and non-contact finger tips sensing behaviour. The sensor can monitor the respiration pattern of a human being accurately, and recognize the movement of the fingertip speedily. This novel humidity sensor shows great promising application in physiological and physical monitoring, portable diagnosis system, and noncontact interface localization.

High-performance resistive humidity sensor based on Ag nanoparticles decorated with graphene quantum dots

“…High humidity sensing response of GQDs/AgNPs over pristine GQDs and pristine AgNPs may be attributed to two main aspects: (i) formation of Schottky junctions at the metal–semiconductor interfaces that play a crucial role for charge transfer enhancements [ 53 , 54 ]. Energy band diagrams of GQDs and AgNPs before contact are displayed in figure 6 c .…”

“…When GQD are well embedded on AgNPs, the electrons can be transferred between two sensing nanomaterials to equilibrate the Fermi energy level. The band bending occurs and forms Schottky barrier [ 53 , 54 ] ( figure 6 d ). At low RH level (25% RH), Schottky barrier ( ɸ B ) exhibits a high value based on the Schottky junction formation with intrinsic conductions of metal–semiconductor nanocomposites.…”

“…interfaces that play a crucial role for charge transfer enhancements [53,54]. Energy band diagrams of GQDs and AgNPs before contact are displayed in figure 6c.…”

Human Respiratory Monitoring Based on Schottky Resistance Humidity Sensors

“…Wearable electronic textile humidity sensors based on carbon nanotubes and composite fibers have also been developed [14,15]. The Schottky structure has been used extensively in photoelectric sensing, and Schottky structure humidity sensors for noncontact medical monitoring have been reported in recent years [16]. Inspired by the excellent performance of graphene and metal oxide, SiNW/ZnO/rGO and SiNW/TiO 2 /rGO Schottky composite metal nanomaterials were developed and used for sensitive detection of trace explosive vapors [17,18], and we found that their response to humidity is very sensitive and that they can be used for human respiration monitoring.…”

Temperature dependence of the dielectric function and critical points of α-SnS from 27 to 350 K

“…Its direct bandgap energy is a desirable ~ 1.3 eV with an indirect bandgap near 1.1 eV 6 , 7 and a high optical absorption coefficient 8 . Also, SnS-based materials have interesting properties, leading to applications such as high-performance humidity sensors 9 , ion batteries 10 , thermoelectric devices 11 , exciton-driven chemical sensors 12 , and Schottky barrier diodes 13 . They also exhibit valley-selective linear dichroism 14 .…”