No abstract

Flexible pressure sensors have gained considerable attention for their potential applications in wearable electronics and human−machine interfacing. However, two major bottlenecks in their widespread usage (i) achieving high sensitivity over a wide working pressure range and (ii) constituent material platform for manufacturability and environmental safety still limits its utility. Herein, we suggest a low-cost hierarchical construction strategy, which enhances the sensitivity of a paper-based piezoresistive pressure sensor over a wide working range. This strategy uses a special multilayered cellulose paper structure composed of alternate layers of plain and corrugated paper sheets, coated with 2D tin-monosulfide (SnS). This design of the paper pressure sensor allows it to achieve high sensitivity up to 14.8 kPa−1 and a broad working range of 0−120 kPa with good durability and repeatability. Further, to confirm practical applicability, we utilized an array of these multilayered flexible pressure sensors for monitoring human activity and developing a biodegradable and foldable keypad. The proposed paper-based green electronic platform can potentially be used in a variety of applications including healthcare and human−machine interfacing.

Direct growth of transition metal dichalcogenides over large areas within the back-end-of-line (BEOL) thermal budget limit of silicon integrated circuits is a significant challenge for 3D heterogeneous integration. In this work, we report on the growth of MoS 2 films (∼1-10 nm) on SiO 2 , amorphous-Al 2 O 3 , c-plane sapphire, and glass substrates achieved at low temperatures (350 • C-550 • C) by chemical vapor deposition in a manufacturing-compatible 300 mm atomic layer deposition reactor. We investigate the MoS 2 films as a potential material solution for BEOL logic, memory and sensing applications. Hall-effect/4-point measurements indicate that the ∼10 nm MoS 2 films exhibit very low carrier concentrations (10 14 -10 15 cm −3 ), high resistivity, and Hall mobility values of ∼0.5-17 cm 2 V −1 s −1 , confirmed by transistor and resistor test device results. MoS 2 grain boundaries and stoichiometric defects resulting from the low thermal budget growth, while detrimental to lateral transport, can be leveraged for the integration of memory and sensing functions. Vertical transport memristor structures (Au/MoS 2 /Au) incorporating ∼3 nm thick MoS 2 films grown at 550 • C (∼0.75 h) show memristive switching and a stable memory window of 10 5 with a retention time >10 4 s, between the high-low resistive states. The switching set and reset voltages in these memristors demonstrate a significant reduction compared to memristors fabricated from pristine, single-crystalline MoS 2 at higher temperatures, thereby reducing the energy needed for operation. Furthermore, interdigitated electrode-based gas sensors fabricated on ∼5 nm thick 550 • C-grown (∼1.25 h) MoS 2 films show excellent selectivity and sub-ppm sensitivity to NO 2 gas, with a notable self-recovery at room temperature. The demonstration of large-area MoS 2 direct growth at and below the BEOL thermal budget limit, alongside memristive and gas sensing functionality, advances a key enabling technology objective in emerging materials and devices for 3D heterogeneous integration. Recently, transition metal dichalcogenides (TMDs) have emerged from the graphene initiatives due to the diverse functionality offered by the incorporation of this class of 2D layered material. More specifically,

A chemiresistive, 1T-TiS2 nanosheet (TNS) based gas sensor has been developed, and its ultrahigh sensitivity toward hydrogen sulfide (H2S) and oxygen (O2) gas at room temperature has been experimentally demonstrated. The sensor displayed room-temperature detection with a maximum response of 395% to 4 ppm H2S (reducing gas) in dry air and a response of 234% to 100% oxygen (oxidizing gas) in ambient conditions. The H2S and O2 sensing in humid environment (40% and 80%) has also been demonstrated so as to ensure the reliable operation of sensor in real-time applications. The ultrasensitive nature and linear behavior of the sensor enable it to operate reliably in the wide range of 300 ppb to 4 ppm H2S and 1% to 100% oxygen. Density functional theory (DFT) simulations were carried out to study the structural and electronic properties of TNS. Adsorption behavior of these gas molecules on TNS nanosheets was also studied theoretically. A plausible sensing mechanism based on the theoretical model has been detailed, and interestingly, it suggests physisorption phenomena between the adsorbate and adsorbent which enables fast recovery of the sensor without any external stimulation. The rather low lower limit of detection (LLoD) for H2S and O2 reported here, specifically at room temperature, is unique and competes favorably with reported studies. This outstanding sensor performance can be attributed to small adsorption energy and van der Waals interaction between analyte and the receptor.

A 2D/0D heteronanostructure (HNS) employing WSe2 as 2D nanosheets and Fe3O4 as 0D nanoparticles has been facilely synthesized at room temperature using a simple wet chemical route. The process involved liquid-phase exfoliation of WSe2 nanosheets, followed by a coprecipitation method for the subsequent nucleation of nanoparticles on the former. The hence-formed hybrid along with its pristine counterparts has been investigated for ammonia-sensing properties. Herein, WSe2 behaves as a p-type semiconductor and Fe3O4 as an n-type semiconductor as per the trends observed in the modulation of electrical conductivity in the presence of ammonia. As expected, the HNS demonstrated ultrasensitive (R % = 510% to 3 ppm) and selective response toward ammonia at room temperature when compared to WSe2 (53.2% to 3 ppm) and Fe3O4 (128% to 3 ppm) alone. The 10-fold increase in sensitivity for ammonia sensing achieved by fabricating a heterostructure enabled the detection down to 50 ppb with a response magnitude of 2.4%. Moreover, our sensor exhibits an ultrafast recovery of 13 s toward 50 ppb NH3 at room temperature without any external stimulus. Importantly, the repeatability and long-term stability over a period of few months seem to be promising. Therefore, the sensor can reliably be deployed in a real environment for practical gas-sensing applications. The exemplary gas-sensing performance achieved here can be ascribed to the enlarged specific surface area (219 m2/g) and the electronic effect of type II p–n heterostructures. This work can pave the way for the utilization of HNS of other 2D/0D materials for the ultrasensitive and selective gas-sensing applications.