We have fabricated and characterized suspended single-layer MoS2 devices to investigate the substrate effect on the electrical properties of MoS2. The MoS2 devices were fabricated on Si/SiO2 first by using e-beam lithography and were suspended by etching away half of the SiO2 layer with buffered oxide etchant and drying them with critical point dryer. Compared with SiO2 substrate-supported devices, the suspended devices show 2-10 times of mobility and on/off ratio improvement. While measuring the electronic properties, we observed that the suspended devices were annealed by joule heating and showed the performance improvement, whereas the supported devices did not. Our observations reveal that MoS2 devices are substrate-sensitive in their electrical properties and that proper substrates and cleaning is necessary for the optimal device performance.

Highly sensitive and flexible pressure sensors were developed based on dielectric membranes composed of insulating microbeads contained within polyvinylidene fluoride (PVDF) nanofibers. The membrane is fabricated using a simple electrospinning process. The presence of the microbeads enhances porosity, which in turn enhances the sensitivity (1.12 kPa −1 for the range of 0−1 kPa) of the membrane when used as a pressure sensor. The microbeads are fixed in position and uniformly distributed throughout the nanofibers, resulting in a wide dynamic range (up to 40 kPa) without any sensitivity loss. The fluffy and nonsticky PVDF nanofiber features low hysteresis and ultrafast response times (∼10 ms). The sensor has also demonstrated reliable pressure detection over 10 000 loading cycles and 250 bending cycles at a 13 mm bending radius. These pressure sensors were successfully applied to detect heart rate and respiratory signals, and an array of sensors was fabricated and used to recognize spatial pressure distribution. The sensors described herein are ultrathin and ultralight, with a total thickness of less than 100 μm, including the electrodes. All of the materials comprising the sensors are flexible, making them suitable for on-body applications such as tactile sensors, electronic skins, and wearable healthcare devices.

We report high and versatile performances of 3D macroporous dielectric layers fabricated rapidly and easily using a baking-inspired foaming process.