Ning-Qin Deng

Flexible, Highly Sensitive, and Wearable Pressure and Strain Sensors with Graphene Porous Network Structure

A mechanical sensor with graphene porous network (GPN) combined with polydimethylsiloxane (PDMS) is demonstrated by the first time. Using the nickel foam as template and chemically etching method, the GPN can be created in the PDMS-nickel foam coated with graphene, which can achieve both pressure and strain sensing properties. Because of the pores in the GPN, the composite as pressure and strain sensor exhibit wide pressure sensing range and highest sensitivity among the graphene foam-based sensors, respectively. In addition, it shows potential applications in monitoring or even recognize the walking states, finger bending degree, and wrist blood pressure.

An intelligent artificial throat with sound-sensing ability based on laser induced graphene

Traditional sound sources and sound detectors are usually independent and discrete in the human hearing range. To minimize the device size and integrate it with wearable electronics, there is an urgent requirement of realizing the functional integration of generating and detecting sound in a single device. Here we show an intelligent laser-induced graphene artificial throat, which can not only generate sound but also detect sound in a single device. More importantly, the intelligent artificial throat will significantly assist for the disabled, because the simple throat vibrations such as hum, cough and scream with different intensity or frequency from a mute person can be detected and converted into controllable sounds. Furthermore, the laser-induced graphene artificial throat has the advantage of one-step fabrication, high efficiency, excellent flexibility and low cost, and it will open practical applications in voice control, wearable electronics and many other areas.

Fabrication techniques and applications of flexible graphene-based electronic devices

In recent years, flexible electronic devices have become a hot topic of scientific research. These flexible devices are the basis of flexible circuits, flexible batteries, flexible displays and electronic skins. Graphene-based materials are very promising for flexible electronic devices, due to their high mobility, high elasticity, a tunable band gap, quantum electronic transport and high mechanical strength. In this article, we review the recent progress of the fabrication process and the applications of graphene-based electronic devices, including thermal acoustic devices, thermal rectifiers, graphene-based nanogenerators, pressure sensors and graphene-based light-emitting diodes. In summary, although there are still a lot of challenges needing to be solved, graphene-based materials are very promising for various flexible device applications in the future.

Enhancement of carrier mobility in MoS2 field effect transistors by a SiO2 protective layer

Molybdenum disulfide is a promising channel material for field effect transistors (FETs). In this paper, monolayer MoS2 grown by chemical vapor deposition (CVD) was used to fabricate top-gate FETs through standard optical lithography. During the fabrication process, charged impurities and interface states are introduced, and the photoresist is not removed cleanly, which both limit the carrier mobility and the source-drain current. We apply a SiO2 protective layer, which is deposited on the surface of MoS2, in order to avoid the MoS2 directly contacting with the photoresist and the ambient environment. Therefore, the contact property between the MoS2 and the electrodes is improved, and the Coulomb scattering caused by the charged impurities and the interface states is reduced. Comparing MoS2 FETs with and without a SiO2 protective layer, the SiO2 protective layer is found to enhance the characteristics of the MoS2 FETs, including transfer and output characteristics. A high mobility of ∼42.3 cm2/V s is achi...

Improved electrothermal performance of custom-shaped micro heater based on anisotropic laser-reduced graphene oxide

In this paper, a flexible heater based on anisotropic laser-reduced graphene oxide (LRGO) is established. Attributing to precision and shape design of laser processing and excellent adhesion of graphene oxide, the LRGO-based heater can be microminiaturized with custom patterns and integrated on various substrates, which is what the existing film heaters cannot do and can be widely used for wearable heating devices, flexural warming systems in medical science, and light deicing equipment and heaters for aero vehicles. The electrothermal performance of the anisotropic LRGO is investigated systematically through a series of experiments including Raman spectra, SEM, white-light interferograms, IV testing, and infrared thermography. The electrothermal performance of the LRGO with the parallel aligned direction is better than the LRGO with the vertical aligned direction. The electrothermal performance can be improved greatly through radiating repeatedly. The saturated temperature and heating rate of the LRGO ra...

3D Stretchable Arch Ribbon Array Fabricated via Grayscale Lithography.

Microstructures with flexible and stretchable properties display tremendous potential applications including integrated systems, wearable devices and bio-sensor electronics. Hence, it is essential to develop an effective method for fabricating curvilinear and flexural microstructures. Despite significant advances in 2D stretchable inorganic structures, large scale fabrication of unique 3D microstructures at a low cost remains challenging. Here, we demonstrate that the 3D microstructures can be achieved by grayscale lithography to produce a curved photoresist (PR) template, where the PR acts as sacrificial layer to form wavelike arched structures. Using plasma-enhanced chemical vapor deposition (PECVD) process at low temperature, the curved PR topography can be transferred to the silicon dioxide layer. Subsequently, plasma etching can be used to fabricate the arched stripe arrays. The wavelike silicon dioxide arch microstructure exhibits Young modulus and fracture strength of 52 GPa and 300 MPa, respectively. The model of stress distribution inside the microstructure was also established, which compares well with the experimental results. This approach of fabricating a wavelike arch structure may become a promising route to produce a variety of stretchable sensors, actuators and circuits, thus providing unique opportunities for emerging classes of robust 3D integrated systems.

High performance photodetector based on Pd-single layer MoS2 Schottky junction

Due to excellent photoelectric property of single layer molybdenum disulphide (SL MoS2), different kinds of photodetectors based on SL MoS2 have been reported. Although high photosensitivity was obtained, the rising and decay time of photocurrent were relatively large (>300 ms) when the current reached up to μA order. In this paper, we demonstrate a high sensitive and fast barrier type photodetector based on Pd-SL MoS2 Schottky junction. The photosensitivity can reach up to 0.88 A/W at 425 nm laser. Compared with SL MoS2 photodetectors based on ohmic contact, our device shows much shorter rising and a decay time of 24.7 ms and 24.5 ms, respectively, exhibiting the merit of barrier type photodetector.

The use of graphene-based earphones in wireless communication

Graphene-based materials have attracted much attention in recent years. Many researchers have demonstrated prototypes using graphene-based materials, but few specific applications have appeared. Graphene-based acoustic devices have become a popular topic. This paper describes a novel method to fabricate graphene-based earphones by laser scribing. The earphones have been used in wireless communication systems. A wireless communication system was built based on an ARM board. Voice from a mobile phone was transmitted to a graphene-based earphone. The output sound had a similar wave envelope to that of the input; some differences were introduced by the DC bias added to the driving circuit of the graphene-based earphone. The graphene-based earphone was demonstrated to have a great potential in wireless communication.

A large-strain, fast-response, and easy-to-manufacture electrothermal actuator based on laser-reduced graphene oxide

In this paper, we have developed a high-performance graphene electrothermal actuator (ETA). The fabrication method is easy, fast, environmentally friendly, and suitable for preparing both large-size and miniature graphene ETAs. When applied with the driving voltage of 65 V, the graphene ETA achieves a large bending angle of 270° with a fast response of 8 s and the recovery process costs 19 s. The large bending deformation is reversible and can be precisely controlled by the driving voltage. A simple robotic hand prepared by using a single graphene ETA can hold the object, which is more than ten times the weight of itself. By virtue of its large-strain, fast response, and easy-to-manufacture, we believe that the graphene ETA has tremendous potential in extensive applications involving biomimetic robotics, artificial muscles, switches, and microsensors in both macroscopic and microscopic fields.

A universal method to grow and etch graphene film

This paper reports a novel universal method to grow and etch graphene film using a one-step laser-scribing process. The grown and etched regions were observed when a graphene oxide (GO) film was exposed to different laser power. The resulting profiles, Raman spectra, optical and electrical properties were thoroughly analyzed. This work indicates that the laser-scribing technique is promising for the rapid and cost efficient large-scale production of graphene for various applications, such as NEMS resonator, NEMS pressure sensor, NEMS gas sensor, etc.