We demonstrate an interesting phenomenon that graphene can emit sound. The application of graphene can be expanded in the acoustic field. Graphene-on-paper sound source devices are made by patterning graphene on paper substrates. Three graphene sheet samples with the thickness of 100, 60, and 20 nm were fabricated. Sound emission from graphene is measured as a function of power, distance, angle, and frequency in the far-field. The theoretical model of air/graphene/paper/PCB board multilayer structure is established to analyze the sound directivity, frequency response, and efficiency. Measured sound pressure level (SPL) and efficiency are in good agreement with theoretical results. It is found that graphene has a significant flat frequency response in the wide ultrasound range 20-50 kHz. In addition, the thinner graphene sheets can produce higher SPL due to its lower heat capacity per unit area (HCPUA). The infrared thermal images reveal that a thermoacoustic effect is the working principle. We find that the sound performance mainly depends on the HCPUA of the conductor and the thermal properties of the substrate. The paper-based graphene sound source devices have highly reliable, flexible, no mechanical vibration, simple structure and high performance characteristics. It could open wide applications in multimedia, consumer electronics, biological, medical, and many other areas.

Single-layer graphene (SLG) was demonstrated to emit sound. The sound emission from SLG had a significant flat frequency response in the wide ultrasound range from 20 kHz to 50 kHz. SLG can produce a sound pressure level (SPL) as high as 95 dB at a distance of 5 cm with a sound frequency of 20 kHz. The SPL value is among the highest reported to date for sound-emitting devices (SEDs) based on the thermoacoustic effect. A theoretical model was established to analyze the sound emission from SLG. The theoretical results are in good agreement with the experimental results. Conventional acoustic devices with a large size can be reduced to the nano-scale by using this novel SLG-SED material. It has the potential to be widely used in speakers, buzzers, earphones, ultrasonic transducer, etc.

Giant electrocaloric effect was observed in lead-free material for the first time. A demonstration of large electrocaloric effect in 200 nm sol-gel thin film SrBi2Ta2O9 is described here. The ferroelectric hysteresis loops and the film permittivity were measured. The extracted data characterized the electrocaloric temperature change, up to 4.93K in 12V (i.e., 0.41 K V−1) near the Curie point. It is concluded that the giant electrocaloric effect exists in lead-free materials, and a large family of layered perovskite oxides may exhibit analogical property. The absence of lead allows eco-friendly application and enhances compatibility with integrated circuit process in future applications.

Recently, manipulating heat transport by phononic devices has received significant attention, in which phonon – a heat pulse through lattice, is used to carry energy. In addition to heat control, the thermal devices might also have broad applications in the renewable energy engineering, such as thermoelectric energy harvesting. Elementary phononic devices such as diode, transistor and logic devices have been theoretically proposed. In this work, we experimentally create a macroscopic scale thermal rectifier based on reduced graphene oxide. Obvious thermal rectification ratio up to 1.21 under 12 K temperature bias has been observed. Moreover, this ratio can be enhanced further by increasing the asymmetric ratio. Collectively, our results raise the exciting prospect that the realization of macroscopic phononic device with large-area graphene based materials is technologically feasible, which may open up important applications in thermal circuits and thermal management.

Graphene-on-silicon Schottky junction solar cells were prepared with pillar-array-patterned silicon substrate. Such patterned substrate showed an anti-reflective characteristic and led to an absorption enhancement of the solar cell, which showed enhanced performance with short-circuit current density, open-circuit voltage, fill factor, and energy conversion efficiency of 464.86 mV, 14.58 mA/cm 2 , 0.29, and 1.96%, respectively. Nitric acid was used to dope graphene film and the cell performance showed a great improvement with efficiency increasing to 3.55%. This is due to the p-type chemical doping effect of HNO 3 which increases the work function and the carrier density of graphene. V

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We demonstrated flexible, ultrathin, and transparent sound-emitting devices (SEDs) using silver nanowires (AgNWs). Large area of AgNWs film on substrate was made by dry transfer technique. The sound emission from the AgNWs was measured as a function of power, distance, and frequency. Significant flat and wide frequency responses occurred between 15 and 45 kHz. The sound pressure was in good agreement with theoretical results. This indicates that a thermoacoustic effect exists in AgNWs. The AgNWs-SEDs can be integrated with the liquid crystal display, which shows the potential to be an important component in flexible electronic systems. V

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