Recently, wearable and flexible pressure sensors have sparked tremendous research interest, and considerable applications including human activity monitoring, biomedical research, and artificial intelligence interaction are reported. However, the large-scale preparation of low-cost, high-sensitivity piezoresistive sensors still face huge challenges. Inspired by the specific structures and excellent metal conductivity of a family of two-dimensional (2D) transition-metal carbides and nitrides (MXene) and the high-performance sensing effect of human skin including randomly distributed microstructural receptors, we fabricate a highly sensitive MXene-based piezoresistive sensor with bioinspired microspinous microstructures formed by a simple abrasive paper stencil printing process. The obtained piezoresistive sensor shows high sensitivity (151.4 kPa −1 ), relatively short response time (<130 ms), subtle pressure detection limit of 4.4 Pa, and excellent cycle stability over 10,000 cycles. The mechanism of the high sensitivity of the sensor is dynamically revealed from the structural perspective by means of in situ electron microscopy experiment and finite element simulation. Bioinspired microspinous microstructures can effectively improve the sensitivity of the pressure sensor and the limit of the detectable subtle pressure. In practice, the sensor shows great performance in monitoring human physiological signals, detecting quantitatively pressure distributions, and remote monitoring of intelligent robot motion in real time.

can effectively capture subtle changes of pressures is much needed. To date, plenty of pressure sensors have been explored, including capacitive, [2,3] piezoelectrical, [4][5][6] and piezoresistive [7,8] pressure sensors. Among them, piezoresistive sensors stand out as promising candidates due to their low-cost fabrication, stability to temperature, sensitivity to pressure, etc. Piezoresistive pressure sensors can transduce changes of mechanical strain into changes of electrical resistance, and are broadly used due to their simple work mechanism and sensitivity to pressure. [9] Conventional piezoresistive pressure sensors, however, are usually based on rigid substrates like Si, [10] which are not skin-mountable and cannot meet the needs for portability and flexibility of smart wearable electronic devices. To tackle this problem, one possible way is the combination of flexible insulating matrices with carbonaceous nanomaterials as conductive fillers, such as graphene, [11] reduced graphene oxide (rGO), [12] and carbon nanotubes (CNTs). [13] For example, Park et al. combined wrinkled CNT and PDMS to build a pressure sensor [14] and more recently, Pang et al. prepared a pressure sensor based on rGO and micro-patterned PDMS substrate. [15] However, composite flexible pressure sensors like these often suffer from a performance compromise between sensor sensitivity and linear region. [16] Apart from that, the signal stability of the sensor may be influenced by the thermal expansion of the polymer substrate. [9] Another way is the utilization of the carbonaceous nanomaterials as the building blocks for making highly elastic materials. In particular, carbon aerogels prepared by this method have demonstrated extraordinary mechanical properties, [17] good flexibility, [18] high aspect ratio, [19] and exceptional thermal stability. [20] Over the past few years, a considerable amount of reports have focused on piezoresistive pressure sensors based on reduced graphene oxide (rGO) aerogel or rGO composite aerogel. For instance, Ha et al. prepared a PAA/ rGO composite aerogel for pressure sensing, [21] and recently, Peng et al. made a piezoresistive sensor based on CNT/rGO-CNF aerogel. [22] However, it still remains a challenge to further improve the sensitivity and the detecting range of these carbon aerogel based pressure sensors.Recently, a new kind of 2D transitional metal carbide/carbonitride materials (MXenes) with metal conductivity have Pressure sensing is key to smart wearable electronics and human-machine interaction interfaces. To achieve a high-performance pressure sensor that has broad linear range and is capable of detecting subtle changes of pressure, the good choice of sensing materials and rational design of structures are both needed. A novel piezoresistive sensor based on hollow MXene spheres/ reduced graphene composite aerogel and flexible interdigital electrodes is presented. Benefiting from the unique microstructure of the composite aerogel, the prepared pressure sensor exhibits high sensitivity (609 kPa −...

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Multiferroic tunnel junctions (MFTJs) have aroused significant interest due to their functional properties useful for non-volatile memory devices. So far, however, all the existing MFTJs have been based on perovskite-oxide heterostructures limited by a relatively high resistance-area (RA) product unfavorable for practical applications. Here, using first-principles calculations, we explore spin-dependent transport properties of van der Waals (vdW) MFTJs which consist of two-dimensional (2D) ferromagnetic FenGeTe2 (n = 3, 4, 5) electrodes and 2D ferroelectric In2Se3 barrier layers. We demonstrate that such FemGeTe2/In2Se3/FenGeTe2 (m, n = 3, 4, 5; m ≠ n) MFTJs exhibit multiple non-volatile resistance states associated with different polarization orientation of the ferroelectric In2Se3 layer and magnetization alignment of the two ferromagnetic FenGeTe2 layers. We find a remarkably low RA product (around 1 Ω•μm 2) which makes the proposed vdW MFTJs superior to the conventional MFTJs in terms of their promise for non-volatile memory applications.

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environmentalmonitoring, infrared imaging, and optical communication. [1,2] Semiconductor nanomaterials and hybrid films (HFs) have attracted much attention for their potential applications in novel photodetectors. [3] In the family of graphene-like 2D materials used in novel optoelectronics, layered transition metal dichalcogenides (TMDs) have a broad application prospect [4][5][6] due to their unique physical features and optoelectronic properties. [7] As a representative material of TMDs, MoS 2 possesses several advantages, including a direct bandgap of ≈1.8 eV, high carrier mobility, and favorable chemical stability, [8] which are especially suitable for sensing light. However, the atomically thin nature of 2D MoS 2 crystals results in an extremely inefficient light-trapping ability, [9] which is a fatal flaw for photodetector devices. The practical application of MoS 2 -based photodetectors is also hindered by severely limited photoresponse and detecting capability, slow response rate, [10] etc. As a result, many efforts have been made to optimize the performance of atomic-layer MoS 2 -based optoelectronics. [10][11][12][13][14][15][16][17][18] Many studies have shown that the use of hybrid photodetectors (HPs) can mitigate the disadvantages of atomically thin MoS 2 crystals. Under the synergistic effect of multimaterials, hybrid MoS 2 -based devices show improved response rates and responsivities. [10][11][12][13][14][15][16][17][18] For example, the photoresponse rate of a MoS 2 -based device increased by almost three orders of magnitude by constructing the heterojunctions with GaSe flakes, [10] and a greatly increased responsivity (10 6 A W −1 ) was achieved in a TiO 2 -encapsulated MoS 2 transistor-modified by HgTe quantum dots. [18] Therefore, a heterojunction structure improves the performance of MoS 2 -based photodetectors, and the successful integration of dissimilar materials may pave the way toward successful high-performance hybrid optoelectronic devices.Currently, lead halide perovskite materials have been widely used in optoelectronic applications, especially solar cells and lightemitting diodes (LEDs), owing to their attractive optoelectronic characteristics, such as high optical absorbance, long diffusion length of charge carriers, and high carrier mobility. [19][20][21] Perovskite materials with different dimensions have been integrated into optoelectronic devices to improve the performance. [22] The past several years have seen the rapid development of fully inorganic trihalide perovskite nanocrystals (PNCs) in the field of hybrid optoelectronic devices due to their outstanding photophysical properties and environmental stability. In this study, novel and easily implementable strategies are proposed to regulate the photoresponse performance of monolayer MoS 2 /PNC hybrid photodetectors (HPs) without the photogating effect. The optoelectronic properties of these HPs are tuned by regulating the characteristic factors of colloidal PNCs (solution concentration and surface ligand content), ...

lithium-ion batteries, [12,13] and electromagnetic interference shielding. [14,15] In addition to these above-mentioned applications, the excellent performance of MXenes makes them ideal for the research in MXene-semiconductor devices. [16] To be specific, MXenes colloidal solution can be fabricated into high-quality thin film through simple methods, such as drop casting and spin-coating, [17,18] thus simplifying the fabrication process of the devices. Besides, MXenes thin film possesses high transmittance and low sheet resistance, [19] which benefits their applications in photodetectors and LEDs. Moreover, the work function of MXene is adjustable in a large range from 2.14 to 5.65 eV, [20,21] which allows it to form Schottky junctions with different semiconductor materials, thereby broadening its application situations.So far, van der Waals heterostructures formed by other 2D materials (such as graphene and TMDs) and conventional semiconductor materials have been investigated widely in various fields and exhibits excellent characteristics. [22][23][24] However, van der Waals heterostructures fabricated by MXene and semiconductor materials have rarely been investigated so far and still need further study. Moreover, as an ideal candidate for optoelectronic devices, GaN has been widely used in photodetectors and LEDs. [25][26][27][28] In this work, Ti 3 C 2 T X /(n/p)-GaN van der Waals heterostructures were fabricated and studied. Ultraviolet photoelectron spectroscopy (UPS) confirms that Ti 3 C 2 T X can form Schottky contacts with both n-GaN and p-GaN at room temperature. By taking the advantages of the Ti 3 C 2 T X /(n/p)-GaN Schottky junctions, we fabricated high-speed photodetectors and stable orange LEDs, respectively. Under the illumination of a 365 nm light source with an intensity of 96.9 µW cm −2 , the Ti 3 C 2 T X /n-GaN photodetector shows a short rise time (60 ms) and decay time (20 ms), a high responsivity (44.3 mA W −1 ) and on/off ratio (≈11 300). And the Ti 3 C 2 T X /p-GaN LED device remains stable orange light emission under bias voltage from 4 to 22 V. We believe that this work gives an essential strategy for photodetectors and LEDs by taking the advantages of MXenes. Due to their excellent electrical conductivity, high transmittance, and adjustable work function, 2D transition-metal carbides and nitrides have shown great promise in optoelectronic applications, especially in MXenesemiconductor devices. In this work, Ti 3 C 2 T X /(n/p)-GaN van der Waals heterostructures are fabricated and studied. The Ti 3 C 2 T X /(n/p)-GaN Schottky junctions are confirmed by ultraviolet photoelectron spectroscopy (UPS) with a work function ≈4.2 eV of Ti 3 C 2 T X . Based on the Ti 3 C 2 T X /(n/p)-GaN Schottky junctions, high-speed photodetectors and stable orange light emitting diodes (LEDs) are fabricated. The Ti 3 C 2 T X /n-GaN heterostructure photodetector shows a short rise time (60 ms) and decay time (20 ms), a high responsivity (44.3 mA W −1 ) and on/off ratio (≈11300) under a light source of 365 nm wa...

AbstractThe hybrid structures of graphene with semiconductor materials based on photogating effect have attracted extensive interest in recent years due to the ultrahigh responsivity. However, the responsivity (or gain) was increased at the expense of response time. In this paper, we devise a mechanism which can obtain an enhanced responsivity and fast response time simultaneously by manipulating the photogating effect (MPE). This concept is demonstrated by using a graphene/silicon-on-insulator (GSOI) hybrid structure. An ultrahigh responsivity of more than 107 A/W and a fast response time of 90 µs were obtained. The specific detectivity D* was measured to be 1.46 ⨯ 1013 Jones at a wavelength of 532 nm. The Silvaco TCAD modeling was carried out to explain the manipulation effect, which was further verified by the GSOI devices with different doping levels of graphene in the experiment. The proposed mechanism provides excellent guidance for modulating carrier distribution and transport, representing a new route to improve the performance of graphene/semiconductor hybrid photodetectors.