Publications

Recent advances in flexible pressure sensors have fueled increasing attention as promising technologies with which to realize human epidermal pulse wave monitoring for the early diagnosis and prevention of cardiovascular diseases. However, strict requirements of a single sensor on the arterial position make it difficult to meet the practical application scenarios. Herein, based on three single-electrode sensors with small area, a 3 × 1 flexible pressure sensor array was developed to enable measurement of epidermal pulse waves at different local positions of radial artery. The designed single sensor holds an area of 6 × 6 mm2, which mainly consists of frosted microstructured Ecoflex film and thermoplastic polyurethane (TPU) nanofibers. The Ecoflex film was formed by spinning Ecoflex solution onto a sandpaper surface. Micropatterned TPU nanofibers were prepared on a fluorinated ethylene propylene (FEP) film surface using the electrospinning method. The combination of frosted microstructure and nanofibers provides an increase in the contact separation of the tribopair, which is of great benefit for improving sensor performance. Due to this structure design, the single small-area sensor was characterized by pressure sensitivity of 0.14 V/kPa, a response time of 22 ms, a wide frequency band ranging from 1 to 23 Hz, and stability up to 7000 cycles. Given this output performance, the fabricated sensor can detect subtle physiological signals (e.g., respiration, ballistocardiogram, and heartbeat) and body movement. More importantly, the sensor can be utilized in capturing human epidermal pulse waves with rich details, and the consistency of each cycle in the same measurement is as high as 0.9987. The 3 × 1 flexible sensor array is employed to acquire pulse waves at different local positions of the radial artery. In addition, the time domain parameters including pulse wave transmission time (PTT) and pulse wave velocity (PWV) can be obtained successfully, which holds promising potential in pulse-based cardiovascular system status monitoring.

Cobalt silicide nanostructures have been synthesized by a spontaneous chemical vapor transport and reaction method. The temperature and the vapor flow rate were shown to critically influence the growth of nanostructures. The effects of two main parameters on the growth of nanostructures were discussed. The phases formed were determined by the Gibbs free energy changes in the reactions. Various phases (CoSi, Co2Si) and morphologies, such as single-stem nanowires, three-dimensional (3D) nanowire networks, and aloelike nanostructures, have been synthesized. Very low turn-on field (1.42 V/μm) and good conductance obtained from field-emission and electrical property measurements, respectively, indicate that CoSi nanowires are potentially useful for electronic devices.

This article presents results of detailed and direct real-time observations of the wide variety of SnO(2) nanobelt motions induced by ac dielectrophoresis (DEP) in an innovative microfluidic setup. High ac electric fields were generated on a gold microelectrode (approximately 20 microm electrode gap) array, patterned on a glass substrate and covered by a approximately 10 microm tall polydimethylsiloxane (PDMS) microchannel. Ethanol suspended SnO(2) nanobelts were introduced into the microchannel, and the DEP experiments were performed. Negative DEP (repulsion) of the nanobelts was observed in the low-frequency range (<100 kHz) of the applied electric field, which caused rigid body motion as well as deformation of the nanobelts. The negative DEP effect observed in ethanol is unusual and contrary to what is predicted by the Clausius-Mossotti factor (using bulk SnO(2) conductivity and permittivity values) of the dipole approximation theory. In the high-frequency range (approximately 1-10 MHz), positive DEP (attraction) of the nanobelts was observed. Pearl chain formation involving short nanobelts and particles was also observed in the two DEP regimes.

ZnO/(La, Sr) CoO3 (ZnO/LSCO) core-shell composite nanorod arrays have been successfully synthesized by a sequential combination process of a hydrothermal synthesis followed by a pulsed laser deposition (PLD) process (or a colloidal deposition process). Compared to the colloidal deposition process, PLD produces a more uniform and efficient deposition of continuous and mesoporous LSCO thin films onto ZnO nanorod arrays. During the PLD process, the deposited film uniformity was found to be dependent on the nanorod diameter, array density, and thus specific surface area of the nanorod arrays, in addition to the PLD deposition parameters. Field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD) were used to investigate the surface morphologies and orientations of the composite nanorod arrays. With densely packed ZnO nanorod arrays as a unique support structure, the mesoporous LSCO thin film coated on top exhibited better photocatalytic properties than ZnO nanorod arrays and LSCO thin films deposited on flat Si substrates. With optimization of the structure, dimensionality, packing density, as well as the composition and interface structure, these unique composite nanoarchitectures could be a promising class of photocatalyst candidates for organic molecule degradation.

A Schottky barrier can be formed at the interface between a metal electrode and a semiconductor. The current passing through the metal-semiconductor contact is mainly controlled by the barrier height and barrier width. In conventional nanodevices, Schottky contacts are usually avoided in order to enhance the contribution made by the nanowires or nanotubes to the detected signal. We present a key idea of using the Schottky contact to achieve supersensitive and fast response nanowire-based nanosensors. We have illustrated this idea on several platforms: UV sensors, biosensors, and gas sensors. The gigantic enhancement in sensitivity of up to 5 orders of magnitude shows that an effective usage of the Schottky contact can be very beneficial to the sensitivity of nanosensors.

Interfacial contact electrification can catalyze redox reactions through a process called contact-electro-catalysis (CEC). The two main reaction paths for producing reactive oxygen species via CEC are the water oxidation reaction (WOR) and the oxygen reduction reaction (ORR). Herein, we designed a polymer/metal Janus composite catalyst that regulated the reaction rates of the WOR and ORR based on the catalyst composition. The ORR was preferentially enhanced when the polymer was negatively charged during contact electrification, while the WOR was preferentially enhanced when the polymer was positively charged. This phenomenon was observed for various conductive materials. The increase in the enhancement of the reaction rates depended on the conductivity and work function of the metal. We expect that this efficient CEC method can form a universal strategy for improving the performance of existing catalysts, as contact electrification is common in nature.

We demonstrate a dynamic surface plasmonic modulation based on graphene-nanowire hybrid structures at optical frequency, on the basis of the tunable optical absorption between SPPs and graphene through an applied external voltage.

'Plasma Grafting' published in 'Encyclopedia of Nanotechnology'