Laser directed lithography of asymmetric graphene ribbons on a polydimethylsiloxane trench structure.

Recently, manipulating heat transport by asymmetric graphene ribbons has received significant attention, in which phonons in the carbon lattice are used to carry energy. In addition to heat control, asymmetric graphene ribbons might also have broad applications in renewable energy engineering, such as thermoelectric energy harvesting. Here, we transfer a single sheet of graphene over a 5 µm trench of polydimethylsiloxane (PDMS) structure. By using a laser (1.77 mW, 1 µm diameter spot size, 517 nm wavelength) focusing on one side of the suspended graphene, a triangular shaped graphene ribbon is obtained. As the graphene has a negative thermal expansion coefficient, local laser heating could make the affected graphene area shrink and eventually break. Theoretical calculation shows that the 1.77 mW laser could create a local hot spot as high as 1462.5 °C, which could induce an asymmetric shape structure. We also find the temperature coefficient (-13.06 cm(-1) mW) of suspended graphene on PDMS trench substrate is ten times higher than that reported on SiO2/Si trench substrate. Collectively, our results raise the exciting prospect that the realization of graphene with asymmetric shape on thermally insulating substrate is technologically feasible, which may open up important applications in thermal circuits and thermal management.

An ultra-high element density pMUT array with low crosstalk for 3-D medical imaging.

A ~1 MHz piezoelectric micromachined ultrasonic transducer (pMUT) array with ultra-high element density and low crosstalk is proposed for the first time. This novel pMUT array is based on a nano-layer spin-coating lead zirconium titanium film technique and can be fabricated with high element density using a relatively simple process. Accordingly, key fabrication processes such as thick piezoelectric film deposition, low-stress Si-SOI bonding and bulk silicon removal have been successfully developed. The novel fine-pitch 6 × 6 pMUT arrays can all work at the desired frequency (~1 MHz) with good uniformity, high performance and potential IC integration compatibility. The minimum interspace is ~20 µm, the smallest that has ever been achieved to the best of our knowledge. These arrays can be potentially used to steer ultrasound beams and implement high quality 3-D medical imaging applications.

A novel flexible capacitive touch pad based on graphene oxide film.

Recently, graphene oxide (GO) supercapacitors with ultra-high energy densities have received significant attention. In addition to energy storage, GO capacitors might also have broad applications in renewable energy engineering, such as vibration and sound energy harvesting. Here, we experimentally create a macroscopic flexible capacitive touch pad based on GO film. An obvious touch "ON" to "OFF" voltage ratio up to ∼60 has been observed. Moreover, we tested the capacitor structure on both flat and curved surfaces and it showed high response sensitivity under fast touch rates. Collectively, our results raise the exciting prospect that the realization of macroscopic flexible keyboards with large-area graphene based materials is technologically feasible, which may open up important applications in control and interface design for solar cells, speakers, supercapacitors, batteries and MEMS systems.