Characteristics and Controlling Factors of Methane Adsorption of the Longmaxi Shale in Northeastern Chongqing: Implications for Shale Gas Occurrence in Complex Structural Areas.

Accurately determining the adsorption capacity of Longmaxi shale in complex structural areas is crucial for evaluating the shale gas resources in northeastern Chongqing. However, studies on the pore characteristics and methane adsorption capacity of these Longmaxi shales are currently limited. In this paper, we collected core samples from the YDB-1 well in northeastern Chongqing and determined the pore structure and adsorption capacity of the Longmaxi shale using low-pressure gas adsorption and high-temperature, high-pressure methane adsorption experiments, respectively. The results indicate that the adsorption capacity of shale in complex structural areas is significantly positively correlated with the organic matter (OM) content, weakly positively correlated with the quartz content, and weakly negatively correlated with clay minerals. Meanwhile, gas-in-place content is simultaneously controlled by the pressure and temperature of the reservoir, and with increasing depth, the adsorbed gas rapidly increases to a maximum value (at 0.8 km) and then slowly decreases, whereas the free gas continuously increases. Compared with the shale in the stable structural areas, the Longmaxi shale in complex structural areas usually develops OM-hosted pores and intergranular pores of OM and minerals and contains more micropores due to tectonic compression, resulting in a relatively larger specific surface area and adsorption capacity. This is the reason shale in complex structural areas has high development potential. The final result can provide an important basis for the evaluation of the gas content and the optimization of dessert areas in the Lower Paleozoic shale gas in southern China.

Provenance Analysis in the Nima Basin during Paleogene and Its Implications for the Decline of the Tibetan Central Valley.

It is unclear what caused the Bangong Nujiang suture zone in the central Tibetan plateau to rise from less than 2 km in early Cenozoic to more than 4 km at present. The zircon U-Pb ages and trace elements of samples from the Niubao Formation in the Paleogene of the Nima basin were analyzed and tested. Combined with the isostasy theory, the surface uplift height of the Nima Basin during the Cenozoic period was calculated. The zircon U-Pb age results of the Niubao formation are consistent with the ages of the Lhasa terrane on the south side of the basin, the Qiangtang terrane on the north side, and the uplift in central. The zircon Eu/Eu* results show that the crust in central part of Tibetan plateau thickened by ∼20 km in Paleogene, resulting in ∼3 km surface uplift. Sediments created a total of about 1 km of surface uplift throughout the Paleogene, and the deposition rate began to slow down significantly at ∼40 Ma. Therefore, it is inferred that in the early Cenozoic, the uplift of the valley was mainly caused by sedimentation. With the continuous downward subduction of the Indian plate, at about 40 Ma, factors such as crustal shortening dominated the uplift of the central valley, and the uplift caused by deposition only accounted for a very small part. In general, the uplift of the Central Valley in the Paleogene was mainly affected by crustal shortening, but a quarter of the surface uplift was caused by the accumulation of sediments.

A novel artificial synapse with dual modes using bilayer graphene as the bottom electrode.

Resistive Random Access Memory (RRAM) shows great potential to be used as an artificial synapse for neuromorphic applications. The resistance can be gradually reduced during reset, which can enable enough states to mimic the "forgetting" process. However, the abrupt set (Mode I) cannot generate enough states to mimic the "learning" process, which results in depression-only behavior. In this work, we introduce another mode (Mode II) in an Al/AlOx/graphene 'RRAM' stack by using oxygen vacancies as trapping centers and bottom electrode bilayer graphene as the channel material. In this way, since the pulse can gradually create the oxygen vacancies, post-synaptic current (PSC) can be gradually potentiated or depressed. By introducing Mode II, we can realize 166 potentiation states, which is higher than the previously reported conventional RRAM with insufficient potentiation states due to the abrupt set. Moreover, Mode II can help realize an inhibitory synapse. By combining modes I and II, we can realize both excitatory and inhibitory synapses in a single device. This work shows great potential to enable neuromorphic computations with greater learning and reconfigurability.

In Situ Tuning of Switching Window in a Gate-Controlled Bilayer Graphene-Electrode Resistive Memory Device.

A resistive random access memory (RRAM) device with a tunable switching window is demonstrated for the first time. The SET voltage can be continuously tuned from 0.27 to 4.5 V by electrical gating from -10 to +35 V. The gate-controlled bilayer graphene-electrode RRAM can function as 1D1R and potentially increase the RRAM density.

Graphene Dynamic Synapse with Modulatable Plasticity.

The synaptic activities in the nervous system is the basis of memory and learning behaviors, and the concept of biological synapse has also spurred the development of neuromorphic engineering. In recent years, the hardware implementation of the biological synapse has been achieved based on CMOS circuits, resistive switching memory, and field effect transistors with ionic dielectrics. However, the artificial synapse with regulatable plasticity has never been realized of the device level. Here, an artificial dynamic synapse based on twisted bilayer graphene is demonstrated with tunable plasticity. Due to the ambipolar conductance of graphene, both behaviors of the excitatory synapse and the inhibitory synapse could be realized in a single device. Moreover, the synaptic plasticity could also be modulated by tuning the carrier density of graphene. Because the artificial synapse here could be regulated and inverted via changing the bottom gate voltage, the whole process of synapse development could be imitated. Hence, this work would offer a broad new vista for the 2D material electronics and guide the innovation of neuro-electronics fundamentally.

Surface-modified piezoresistive nanocomposite flexible pressure sensors with high sensitivity and wide linearity.

Flexible pressure sensors working in a low pressure range (<10 kPa) have become an important part of recent research due to their applications in "artificial skin", foldable electronics and so on. Several efforts have been focused on the high sensitivity of devices with the neglect of linearity which is essential for real applications. Here, we present a device with a new Gaussian random distribution contact surface profile and a novel contact and piezoresistive composite working principle by numerical simulation, which predicts the combination of wide linearity and high sensitivity. With the modified surfaces' contact effect and the piezoresistive capability of these nanocomposite structures, an outstanding linearity can be achieved all along the measuring scale from 0 to 14 kPa, with a high sensitivity around 13.8 kPa(-1). The random distribution surface also provides the device with fine stability and reproducibility, which are validated in the test.

A graphene-based resistive pressure sensor with record-high sensitivity in a wide pressure range.

Pressure sensors are a key component in electronic skin (e-skin) sensing systems. Most reported resistive pressure sensors have a high sensitivity at low pressures (<5 kPa) to enable ultra-sensitive detection. However, the sensitivity drops significantly at high pressures (>5 kPa), which is inadequate for practical applications. For example, actions like a gentle touch and object manipulation have pressures below 10 kPa, and 10-100 kPa, respectively. Maintaining a high sensitivity in a wide pressure range is in great demand. Here, a flexible, wide range and ultra-sensitive resistive pressure sensor with a foam-like structure based on laser-scribed graphene (LSG) is demonstrated. Benefitting from the large spacing between graphene layers and the unique v-shaped microstructure of the LSG, the sensitivity of the pressure sensor is as high as 0.96 kPa(-1) in a wide pressure range (0 ~ 50 kPa). Considering both sensitivity and pressure sensing range, the pressure sensor developed in this work is the best among all reported pressure sensors to date. A model of the LSG pressure sensor is also established, which agrees well with the experimental results. This work indicates that laser scribed flexible graphene pressure sensors could be widely used for artificial e-skin, medical-sensing, bio-sensing and many other areas.

A pressure sensing system for heart rate monitoring with polymer-based pressure sensors and an anti-interference post processing circuit.

Heart rate measurement is a basic and important issue for either medical diagnosis or daily health monitoring. In this work great efforts have been focused on realizing a portable, comfortable and low cost solution for long-term domestic heart rate monitoring. A tiny but efficient measurement system composed of a polymer-based flexible pressure sensor and an analog anti-interference readout circuit is proposed; manufactured and tested. The proposed polymer-based pressure sensor has a linear response and high sensitivity of 13.4 kPa-1. With the circuit's outstanding capability in removing interference caused by body movement and the highly sensitive flexible sensor device, comfortable long-term heart rate monitoring becomes more realistic. Comparative tests prove that the proposed system has equivalent capability (accuracy: <3%) in heart rate measurement to the commercial product.

Graphene earphones: entertainment for both humans and animals.

The human hearing range is from 20 Hz to 20 kHz. However, many animals can hear much higher sound frequencies. Dolphins, especially, have a hearing range up to 300 kHz. To our knowledge, there is no data of a reported wide-band sound frequency earphone to satisfy both humans and animals. Here, we show that graphene earphones, packaged into commercial earphone casings can play sounds ranging from 100 Hz to 50 kHz. By using a one-step laser scribing technology, wafer-scale flexible graphene earphones can be obtained in 25 min. Compared with a normal commercial earphone, the graphene earphone has a wider frequency response (100 Hz to 50 kHz) and a three times lower fluctuation (±10 dB). A nonlinear effect exists in the graphene-generated sound frequency spectrum. This effect could be explained by the DC bias added to the input sine waves which may induce higher harmonics. Our numerical calculations show that the sound frequency emitted by graphene could reach up to 1 MHz. In addition, we have demonstrated that a dog wearing a graphene earphone could also be trained and controlled by 35 kHz sound waves. Our results show that graphene could be widely used to produce earphones for both humans and animals.

Wafer-scale integration of graphene-based electronic, optoelectronic and electroacoustic devices.

In virtue of its superior properties, the graphene-based device has enormous potential to be a supplement or an alternative to the conventional silicon-based device in varies applications. However, the functionality of the graphene devices is still limited due to the restriction of the high cost, the low efficiency and the low quality of the graphene growth and patterning techniques. We proposed a simple one-step laser scribing fabrication method to integrate wafer-scale high-performance graphene-based in-plane transistors, photodetectors, and loudspeakers. The in-plane graphene transistors have a large on/off ratio up to 5.34. And the graphene photodetector arrays were achieved with photo responsivity as high as 0.32 A/W. The graphene loudspeakers realize wide-band sound generation from 1 to 50 kHz. These results demonstrated that the laser scribed graphene could be used for wafer-scale integration of a variety of graphene-based electronic, optoelectronic and electroacoustic devices.

Scalable fabrication of high-performance and flexible graphene strain sensors.

Graphene strain sensors have promising prospects of applications in detecting human motion. However, the shortage of graphene growth and patterning techniques has become a challenging issue hindering the application of graphene strain sensors. Therefore, we propose wafer-scale flexible strain sensors with high-performance, which can be fabricated in one-step laser scribing. The graphene films could be obtained by directly reducing graphene oxide film in a Light-Scribe DVD burner. The gauge factor (GF) of the graphene strain sensor (10 mm × 10 mm square) is 0.11. In order to enhance the GF further, graphene micro-ribbons (20 µm width, 0.6 mm long) has been used as strain sensors, of which the GF is up to 9.49. The devices may conform to various application requirements, such as high GF for low-strain applications and low GF for high deformation applications. The work indicates that laser scribed flexible graphene strain sensors could be widely used in medical-sensing, bio-sensing, artificial skin and many other areas.