Mechanical strain induced changes in the electronic properties of two-dimensional (2D) materials is of great interest for both fundamental studies and practical applications. The anisotropic 2D ...materials may further exhibit different electronic changes when the strain is applied along different crystalline axes. The resulting anisotropic piezoresistive phenomenon not only reveals distinct lattice-electron interaction along different principle axes in low-dimensional materials but also can accurately sense/recognize multidimensional strain signals for the development of strain sensors, electronic skin, human-machine interfaces, etc. In this work, we systematically studied the piezoresistive effect of an anisotropic 2D material of rhenium disulfide (ReS
), which has large anisotropic ratio. The measurement of ReS
piezoresistance was experimentally performed on the devices fabricated on a flexible substrate with electrical channels made along the two principle axes, which were identified noninvasively by the reflectance difference microscopy developed in our lab. The result indicated that ReS
had completely opposite (positive and negative) piezoresistance along two principle axes, which differed from any previously reported anisotropic piezoresistive effect in other 2D materials. We attributed the opposite anisotropic piezoresistive effect of ReS
to the strain-induced broadening and narrowing of the bandgap along two principle axes, respectively, which was demonstrated by both reflectance difference spectroscopy and theoretical calculations.
Full text
Available for:
IJS, KILJ, NUK, PNG, UL, UM
Two‐dimensional (2D) materials have attracted extensive research interests due to their excellent properties related to unique structure. Strain engineering, as an important strategy for tuning the ...lattice and electronic structure of 2D materials, has been widely used in the modulation of physical properties, which broadens their applications in flexible nanoelectronic and optoelectronic devices. In this review, we first summarize the methods of inducing strain to 2D materials and discuss the advantages and problems of various methods. We then introduce the strain‐induced effects on optical, electrical, and magnetic properties, together with the phase transition of 2D materials. Finally, we illustrate the potential applications of strained 2D materials and further look forward to their opportunities and challenges in practical applications in the future.
The methods of inducing strain to 2D materials are systematically classified, and the advantages and disadvantages of various methods are discussed. Moreover, the strain‐modulated outstanding optical, electrical, and magnetic properties are summarized. Based on strain‐induced effects, the applications of strained 2D materials including flexible strain sensors and photodetectors are further illustrated.
Full text
Available for:
FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
To realize long-term and stable applications of wearable and flexible sensors for motion detection, health analysis and wisdom medication in harsh environments, self-healing, self-adhesive, ...electrically conductive and biocompatible polyacrylamide (PAM) nanocomposite hydrogels are fabricated as flexible strain or pressure sensors by in situ polymerization of acrylamide in the presence of polydopamine-modified carbon nanotubes (PDA@CNTs) for effectively detecting human motions, identifying materials and their shapes, and transmitting health information. The resultant PDA@CNT/PAM nanocomposite hydrogel exhibits a high self-healing efficiency of 97.3%, excellent biocompatibility, and strong adhesion with substrates based on hydrogen bonding and π–π stacking interactions. Based on the piezoresistive effect, the nanocomposite hydrogel-based strain sensor exhibits a high sense gauge factor of 3.93 at a strain of 400% and responds quickly with a fast response time of 76 ms when detecting human movement. Thanks to the contact electrification and the electrostatic induction, the nanocomposite hydrogel-based pressure sensor can respond to pressure linearly and generate voltage signals in the absence of an additional power supply. Furthermore, the self-powered smart ring made of the silicone rubber-coated PDA@CNT/PAM hydrogel enables efficient and concise information transmission via Morse code.
Display omitted
•Self-healing, self-adhesive, conductive and biocompatible hydrogels are fabricated as flexible strain or pressure sensors.•The nanocomposite hydrogel shows high self-healing efficiency, good biocompatibility, and strong adhesion with substrates.•The sensors are efficient in detecting human motions, identifying materials and shapes, and transmitting health information.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPUK, ZAGLJ, ZRSKP
Skin sensors are of paramount importance for flexible wearable electronics, which are active in medical diagnosis and healthcare monitoring. Ultrahigh sensitivity, large measuring range, and high ...skin conformability are highly desirable for skin sensors. Here, an ultrathin flexible piezoresistive sensor with high sensitivity and wide detection range is reported based on hierarchical nanonetwork structured pressure-sensitive material and nanonetwork electrodes. The hierarchical nanonetwork material is composed of silver nanowires (Ag NWs), graphene (GR), and polyamide nanofibers (PANFs). Among them, Ag NWs are evenly interspersed in a PANFs network, forming conductive pathways. Also, GR acts as bridges of crossed Ag NWs. The hierarchical nanonetwork structure and GR bridges of the pressure-sensitive material enable the ultrahigh sensitivity for the pressure sensor. More specifically, the sensitivity of 134 kPa–1 (0–1.5 kPa) and the low detection of 3.7 Pa are achieved for the pressure sensor. Besides, the nanofibers act as a backbone, which provides effective protection for Ag NWs and GR as pressure is applied. Hence, the pressure sensor possesses an excellent durability (>8000 cycles) and wide detection range (>75 kPa). Additionally, ultrathin property (7 μm) and nanonetwork structure provide high skin conformability for the pressure sensor. These superior performances lay a foundation for the application of pressure sensors in physiological signal monitoring and pressure spatial distribution detection.
Full text
Available for:
IJS, KILJ, NUK, PNG, UL, UM
Currently, extensive research has been conducted on carbon fabric−reinforced cementitious matrix (CFRCM) composites, impressed current cathodic protection (ICCP), and the piezoresistive effect in the ...field of strengthening of reinforced concrete (RC) structures, corrosion protection of steel reinforcement, and structural health monitoring, respectively. This study utilized two types of matrix materials: normal matrix (sand conforming to ISO standard) and seawater sea-sand matrix. The mechanism by which the ICCP procedure affects the degradation of tensile performance in CFRCM plates with these two types of matrix materials was investigated in the study. Additionally, the piezoresistive effects of CFRCM with the two types of matrix materials after the ICCP procedure were analyzed, and the impact of ICCP on the piezoresistive effect was also investigated. By observing the piezoresistive effect of each CFRCM segment, the sequence of crack propagation and an approximate crack location can be inferred. Finally, the tensile performance of CFRCM with charge density was investigated. Leveraging the dual functionality of carbon fiber reinforcement and sensing, this study lays the groundwork for the development of a triple-functional system encompassing impressed current cathodic protection, structural strengthening, and structural health monitoring (ICCP-SS-SHM). Seawater sea-sand has the potential to be used as an alternative to freshwater river sand, which is beneficial for addressing the shortage of freshwater river sand resources.
•The seawater sea-sand matrix was utilized.•The crack identification based on piezoresistive effect was explored.•A triple-functional system ICCP-SS-SHM was developed.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPUK, ZAGLJ, ZRSKP
Conducting polymer nanocomposites filled with carbon nanotubes (CNTs) have attracted great interest in developing flexible sensors. This paper reported the preparation of cotton-based CNT foam by ...using a chemical vapor deposition method. The prepared foam was incorporated into epoxy or polydimethylsiloxane (PDMS) to fabricate corresponding nanocomposites. The results showed that CNT foam exhibited excellent adsorption performance for liquid polymer, thus eliminating the variations on the dispersion, concentration and formation of CNT networks in nanocomposites. CNT/Epoxy nanocomposites had a comparable electrical conductivity (1.2 S/m) with that of CNT foam (1.5 S/m), and a much higher value than that of CNT/PDMS counterpart (0.06 S/m). Interesting, CNT/Epoxy showed a negative piezoresistance, whereas the one with PDMS had a positive effect. It was found that the Poisson's ratio of the matrix and its wettability with nanofiller controlled the contact and tunneling resistance in the system, which in turn affecting piezoresistive behavior of bulky nanocomposites.
Carbon nanotube foam was prepared and the corresponding nanocomposites was developed by spontaneous monomer infusion process. The prepared nanocomposites exhibited positive or negative piezoresistive effect and the mechanism behind such observations was illustrated. Display omitted
•CNT foam eliminated the variations of CNT networks in nanocomposites.•CNT/PDMS nanocomposites showed positive piezoresistivity.•CNT/Epoxy nanocomposites showed negative piezoresistivity.•The mechanism of matrix modulating the contact and tunneling resistance was investigated.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPUK, ZAGLJ, ZRSKP
A conformal tactile sensor based on MoS2 and graphene is demonstrated. The MoS2 tactile sensor exhibits excellent sensitivity, high uniformity, and good repeatability in terms of various strains. In ...addition, the outstanding flexibility enables the MoS2 strain tactile sensor to be realized conformally on a finger tip. The MoS2‐based tactile sensor can be utilized for wearable electronics, such as electronic skin.
Full text
Available for:
BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
The piezoresistive pressure sensor, a kind of widely investigated artificial device to transfer force stimuli to electrical signals, generally consists of one or more kinds of conducting materials. ...Here, a highly sensitive pressure sensor based on the semiconductor/conductor interface piezoresistive effect is successfully demonstrated by using organic transistor geometry. Because of the efficient combination of the piezoresistive effect and field‐effect modulation in a single sensor, this pressure sensor shows excellent performance, such as high sensitivity (514 kPa−1), low limit of detection, short response and recovery time, and robust stability. More importantly, the unique gate modulation effect in the transistor endows the sensor with an unparalleled ability—tunable sensitivity via bias conditions in a single sensor, which is of great significance for applications in complex pressure environments. The novel working principle and high performance represent significant progress in the field of pressure sensors.
A highly sensitive pressure sensor based on the semiconductor/conductor interface piezoresistive effect in organic field‐effect transistors is demonstrated. This sensor simultaneously displays high and tunable sensitivity due to combining the advantages of the piezoresistive effect and the field‐effect modulation. In addition, the quick response speed and robust working performance show its potential in subtle and complex pressure environments.
Full text
Available for:
BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Display omitted
•A stress amplification structure employing free-standing SiC sensing elements was utilised to enhance 3C-SiC/Si pressure sensor sensitivity to 0.276 mV/V/kPa.•Analytical and ...numerical methods show that the stress in the structure is amplified by more than 750% compared to a traditional structure.•The fabricated sensor had a non-linearity of 2.2% and was highly repeatable with a low hysteresis of 0.91%.•The dual 3C-SiC thin film on the sensor provides a strong chemical protective capability due to its chemical inertness.
SiC based pressure sensors show tremendous promise for harsh environment applications thanks to their excellent mechanical, electrical, thermal, and chemical properties. This paper presents the design, fabrication, and characterisation of a highly sensitive and robust 3C-SiC/Si pressure sensor. The sensor utilises a stress amplification structure consisting of four Si pillars built up from the 3C-SiC/Si membrane, supporting a series of released n-type 3C-SiC sensing elements. When pressure is applied to the diaphragm, the pillars act to locally concentrate and amplify strain in the 3C-SiC sensing elements, resulting in over 7 times higher stresses/strains in these sensing elements compared to a traditional structure. Additionally, the front side of the sensor is fully covered by a 3C-SiC thin film, which provides a strong chemical protective capability, allowing the sensor to operate in harsh chemically corrosive environments. The robust device utilises the full Wheatstone bridge to negate the effects of temperature. Experimental results show that the fabricated sensor is highly stable, repeatable, has a high sensitivity of 0.276 mV/V/kPa and a maximum non-linearity of 2.2 % in the 0–100 kPa region. The results indicate that this smart-structure pressure sensor is promising for applications that require highly precise pressure sensing in aggressively corrosive environments.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPUK, ZAGLJ, ZRSKP
•A tough highly-conductive thermogalvanic hydrogel is developed via a solvent-exchange salt-out strategy.•The gel and electrode forms a tight electrical connection by non-covalent bonding.•The gel ...module can realize self-powered pressure detection by coupling thermogalvanic and piezoresistive effects.•By implanting a gel module array on a glove, highly accurate sign language and object recognition is achieved with the aid of deep learning.
The human hand provides rich sensory information for proper interaction with the environment. However, designing passive hand-sensing arrays with robust mechanical properties, high conductivity, ease of integration and reliability remains a long-term challenge. Here, we develop a robust dynamic crystalline ion-injected thermoelectric gel (DCI-TEG) via a simple solvent-exchange salt-out strategy. The resultant DCI-TEG exhibits high tensile strength (3.8 MPa), toughness (7.5 MJ m−3), and ionic conductivity of 1.84 S m−1. Benefiting from non-covalent crosslinking, the gel electrolyte and electrodes can be fully integrated into modules with tight physical and electrical contact, facilitating a stable and reliable signal output. By coupling thermogalvanic and piezoresistive effects, the DCI-TEG permits self-powered timely sensing of pressure using current signals. By implanting ionic thermoelectric module arrays on a glove, a wearable pressure sensing route is demonstrated with the merits of self-power, low cost and simple preparation. With the help of deep learning algorithms, a self-powered recognition for sign language and objects is realized in wearable/portable scenarios by active high-accuracy pressure detection. This work gives people a new direction toward barrier-free passive communication and human–machine interaction in the next-generation artificial intelligence.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPUK, ZAGLJ, ZRSKP
PDF
