An Intrinsically Stretchable Nanowire Photodetector with a Fully Embedded Structure

on. [1][2][3][4][5][6][7] Among these 1D nanomaterials, many novel synthesis techniques have then been developed, including chemical vapor deposition (CVD), [8][9][10] hydrothermal methods, [11][12][13] and template-assisted electrodeposition, etc; [14][15][16] however, all of these fabrication schemes come with different process-related disadvantages. For example, CVD has been widely employed for the growth of 1D semiconductor nanostructures, [17,18] in which this technique is still far from being compatible with the large-scale manufacturing platform due to the rather high fabricating cost, rigorous process control, low production throughput, and complicated subsequent device fabrication scheme. [9,19] Although hydrothermal methods are seem to be the simple process and capable to produce large amounts of 1D nanomaterials with the relatively low cost, they are challenging to precisely control the diameter, morphology, and crystal structure of the nanomaterials obtained, seriously influencing their chemical and physical properties, eventually limiting their practical utilizations. [13,20] In general, electrospinning is well accepted to its simplicity and versatility to yield organic, inorganic or composite nanofibers (NFs). [21,22] This technique can not only fabricate NFs with well-controlled properties, such as the excellent crystallinity, homogeneous chemical composition, and uniform diameters but also deliver the high throughput Although significant progress has been made towards using ZnO nanofibers (NFs) in future high-performance and low-cost electronics, they still suffer from insufficient device performance caused by substantial surface roughness (i.e., irregularity) and granular structure of the obtained NFs. Here, a simple onestep electrospinning process (i.e., without hot-press) is presented to obtain controllable ZnO NF networks to achieve high-performance, large-scale, and low-operating-power thin-film transistors. By precisely manipulating annealing temperature during NF fabrication, their crystallinity, grain size distribution, surface morphology, and corresponding device performance can be regulated reliably for enhanced transistor performances. For the optimal annealing temperature of 500 °C, the device exhibits impressive electrical characteristics, including a small positive threshold voltage (V th ) of ≈0.9 V, a low leakage current of ≈10 −12 A, and a superior on/off current ratio of ≈10 6 , corresponding to one of the best-performed ZnO NF devices reported to date. When high-κ AlO x thin films are employed as gate dielectrics, the source/drain voltage (V DS ) can be substantially reduced by 10× to a range of only 0-3 V, along with a 10× improvement in mobility to a respectable value of 0.2 cm 2 V −1 s −1 . These results indicate the potential of these nanofibers for use in next-generation low-power devices. Thin-Film Transistors

Rationally designed sinusoidal gold nanobelts are fabricated as stretchable electrodes, and they do not show obvious change of resistance under large deformation after 10,000 cyclic stretching/relaxing processes. As a proof of concept, they are successfully used to record intracranial electroencephalogram or electrocorticogram signals from rats.

humidity level, and concentration of harmful gases, and airborne particulates can provide valuable information for the prediction, management, and treatment of chronic diseases. [4,5] In addition to the applications in wearable health monitoring, continuous tracking of daily and sports activities can offer an efficient way to assess the well-being and athletic performances. [6] In order to ensure a robust and conformal contact with the curvilinear, coarse, and dynamic surface of skin without impeding daily activities, the wearable sensor should have low modulus and high stretchability. The epidermis has a modulus of 140-600 kPa while the dermis has an even lower modulus of 2-80 kPa. [7] Skin itself can be stretched elastically up to 15% and with the help of wrinkles and creases, the overall stretchability can reach as high as 100% during daily motions. [8] In addition to good wearability, wearable sensors should be highly sensitive, lightweight, low-cost, and with low power consumption. To achieve these features, nanomaterials that are compliant, possessing larger surface area and exceptional material properties, and compatible with low-cost fabrication processes are widely employed as building blocks for developing wearable sensors.In this review, we start from a brief overview of nanomaterials, their related structural designs and fabrication processes (Section 2). Following that, recent advances of nanomaterialenabled wearable sensors including temperature, electrophysiological, strain, tactile, electrochemical, and other sensors will be summarized (Section 3). A survey on the integration of multiple sensors and other components into wearable systems will be given in Section 4. The application of nanomaterialenabled wearable sensors for healthcare including health monitoring, activity tracking, and electronic skin will be presented in Section 5. The challenges and opportunities will be discussed at the end. Nanomaterials, Structural Designs, and Fabrication ProcessesNanomaterials can be classified into two categories-top-down fabricated ones and bottom-up synthesized ones. [9] The focus of this review is on the wearable sensors based on bottom-up synthesized nanomaterials. Nanomaterials can be synthesized into various dimensions, from 0D such as metallic nanoparticles (NPs), to 1D such as carbon nanotubes (CNTs), and metallic nanowires (NWs), to 2D such as graphene and transition metal Highly sensitive wearable sensors that can be conformably attached to human skin or integrated with textiles to monitor the physiological parameters of human body or the surrounding environment have garnered tremendous interest. Owing to the large surface area and outstanding material properties, nanomaterials are promising building blocks for wearable sensors. Recent advances in the nanomaterial-enabled wearable sensors including temperature, electrophysiological, strain, tactile, electrochemical, and environmental sensors are presented in this review. Integration of multiple sensors for multimodal sensing and integration with...