Publications

UV photodetector fabricated using a single ZnO nanobelt (NB) has shown a photoresponse enhancement up to 750 times higher than that of a bare ZnO NB after coating with ∼20nm plasma polymerized acrylonitrile (PP-AN) nanoscale film. The mechanism for this colossal photoconductivity is suggested as a consequence of the efficient exciton dissociation under UV illumination due to enhanced electron transfer from valence band of ZnO NB to the PP-AN and then back to the conduction band of ZnO. This process has demonstrated an easy and effective method for improving the performance of the nanowire∕NB-based devices, possibly leading to supersensitive UV detector for applications in imaging, photosensing, and intrachip optical interconnects.

We demonstrate the first self-powered system driven by a nanogenerator (NG) that works wirelessly and independently for long-distance data transmission. The NG was made of a free cantilever beam that consisted of a five-layer structure: a flexible polymer substrate, ZnO nanowire textured films on its top and bottom surfaces, and electrodes on the surfaces. When it was strained to 0.12% at a strain rate of 3.56% S–1, the measured output voltage reached 10 V, and the output current exceeded 0.6 μA (corresponding power density 10 mW/cm3). A system was built up by integrating a NG, rectification circuit, capacitor for energy storage, sensor, and RF data transmitter. Wireless signals sent out by the system were detected by a commercial radio at a distance of 5–10 m. This study proves the feasibility of using ZnO nanowire NGs for building self-powered systems, and its potential application in wireless biosensing, environmental/infrastructure monitoring, sensor networks, personal electronics, and even national security.

The human brain's neural network demonstrates exceptional efficiency in information processing and recognition, driving advancements in neuromimetic devices that emulate neuronal functions such as signal integration and parallel transmission. A key challenge remains in replicating these functions while minimizing energy consumption. Here, inspired by neuronal signal integration and axonal bidirectional transmission, mechano-driven hydrogel logic gates leveraging the piezoionic effect is presented, offering a novel bionic approach with significantly reduced power consumption. By exerting external force on the thick and thin sides of the geometrically asymmetric hydrogel, spike signals of differing amplitudes and opposite polarities can be generated, corresponding to '1' and '0', respectively. The differential mobility of anions and cations plays a crucial role in the piezoionic effect. This geometric asymmetry amplifies ion convection, improving force-to-electricity conversion efficiency, while the inclusion of salts with varying ion size can further enhance this disparity, even reversing the signal direction. Arranging asymmetric hydrogel iontronics in series-parallel configurations enables the emulation of complex neuronal logic operations, facilitating ionic spike signal addition and subtraction. This hydrogel-based logic control has been directly applied in human-machine interaction to control robot arms and offers significant potential for the advancement of artificial intelligence, robotics, and wearable technologies.

Controlling the morphology of the as-synthesized nanostructures is usually challenging, and there lacks of a general theoretical guidance in experimental approach. In this study, a novel way of optimizing the aspect ratio of hydrothermally grown ZnO nanowire (NW) arrays is presented by utilizing a systematic statistical design and analysis method. In this work, we use pick-the-winner rule and one-pair-at-a-time main effect analysis to sequentially design the experiments and identify optimal reaction settings. By controlling the hydrothermal reaction parameters (reaction temperature, time, precursor concentration, and capping agent), we improved the aspect ratio of ZnO NWs from around 10 to nearly 23. The effect of noise on the experimental results was identified and successfully reduced, and the statistical design and analysis methods were very effective in reducing the number of experiments performed and in identifying the optimal experimental settings. In addition, the antireflection spectrum of the as-synthesized ZnO NWs clearly shows that higher aspect ratio of the ZnO NW arrays leads to about 30% stronger suppression in the UV-vis range emission. This shows great potential applications as antireflective coating layers in photovoltaic devices.

By functionalizing the surfaces of ZnO nanobelts (NBs) with a thin self-assembled molecular layer, the electrical and optoelectronic performances of a single NB-based device are drastically improved. For a single NB-based device, due to energy band tuning and surface modification, the conductance was enhanced by 6 orders of magnitude upon functionalization; a coating molecule layer has changed a Schottky contact into an Ohmic contact without sophisticated deposition of multilayered metals. A functionalized NB showed negative differential resistance and exhibited huge improved photoconductivity and gas sensing response. The functionalized molecular layer also greatly reduced the etching rate of the ZnO NBs by buffer solution, largely extending their life time for biomedical applications. Our study demonstrates a new approach for improving the physical properties of oxide NBs and nanowires for device applications.

By assembling a ZnO nanowire (NW) array based nanogenerator (NG) that is transparent to UV light, we have investigated the performance of the NG by tuning its carrier density and the characteristics of the Schottky barrier at the interface between the metal electrode and the NW. The formation of a Schottky diode at the interface is a must for the effective operation of the NG. UV light not only increases the carrier density in ZnO but also reduces the barrier height. A reduced barrier height greatly weakens the function of the barrier for preserving the piezoelectric potential in the NW for an extended period of time, resulting in little output current. An increased carrier density speeds up the rate at which the piezoelectric charges are screened/neutralized, but a very low carrier density prevents the flow of current through the NWs. Therefore, there is an optimum conductance of the NW for maximizing the output of the NG. Our study provides solid evidence to further prove the mechanism proposed for the piezoelectric NG and piezotronics. The output current density of the NG has been improved to 8.3 μA/cm2.

The II-VI semiconductors are important optoelectronic, luminescent, and lasing materials. This paper presents a review on synthesis, structure, and growth mechanisms of one-dimensional nanostructures of ZnS, CdSe, ZnSe, CdS and CdO. The two most frequently received wurtzite structures of these materials are "nanobelts" and "nanosaws". The nanosaws are suggested to be a result of atomic-termination induced asymmetric growth due to the cation-terminated, catalytically active (0001) surface, while the anion-terminated (000 ī) is chemically inactive. It has also been shown that the phase transformation from wurtzite to zinc blend could also be a factor in initiating the growth of the saw teeth. The applications and nanodevices that have been built using nanobelts are also presented.

Fluidic flow monitoring of a non-full pipe is of great significance in the field of energy measurement and pipeline transportation. In this work, a monitoring method based on triboelectric nanogenerators for non-full pipe fluidic flow of large pipelines is proposed. Specifically, a triboelectric non-full pipe flow sensor (TNPFS) is fabricated, which can monitor the flow velocity and the liquid level simultaneously, and then the flow can be obtained by conversion. For flow velocity monitoring, the flexible blades slide between electrodes, generating periodic electrical signals. Interestingly, the frequencies of the voltage and flow velocities show a good linear relationship. For liquid level monitoring, according to the principle of liquid-solid contact electrification, a variable area interdigital electrode with a stable signal distributed on a polytetrafluoroethylene tube is designed. The experiments demonstrate that the peak number and trend of the voltage derivative curve are related to the liquid level. Finally, a real-time flow-monitoring system is established to effectively monitor the flow from 94 to 264 L/min. Compared with the actual measured flow, the error rate is under 1.95%. In addition to this, the TNPFS also has good responsiveness in sewage. This work provides a novel method for fluidic flow monitoring, especially the non-full pipe flow of large pipelines.

Water oxidation or oxygen evolution reaction (OER) electrocatalysis got much attention in the last few years because of its prime role in water splitting, rechargeable metal-air batteries and fuel cells. Therefore, the development of efficient, abundant and economical catalysts for water oxidation reaction is one of the main subjects of present study in renewable energies. This review article summarizes the very recent efforts in the field of OER electrocatalysis along with the faced challenges. The solutions to these challenges also outline with appropriate examples of scientific literatures. Significantly, the present review will provide the standards to evaluate the activity and stability for heterogeneous OER catalysts. It will clearly summarize the future directions and applications, especially the combination of sustainable energy utilization (like triboelectric nanogenerator) with water splitting. The providing study will help to explore and develop better catalysts and units for practical applications and will offer basic understanding of OER process along with the standard parameters to evaluate the performance.

The response of a single CdS-nanowire-based nanogenerator to excitation by visible light is investigated. White light reduces the height of the Schottky barrier that existis at the tip nanowire contact, leading to possible barrier breakthrough and a contact-mode change from Schottky to quasi-Ohmic. This work demonstrates the triple coupling among semiconducting, piezoelectric, and optoelectric properties, which may be useful for designing new optopiezotronic devices.

Flexible and self-powered photodetectors (PDs) are highly desirable for applications in image sensing, smart building, and optical communications. In this paper, a self-powered and flexible PD based on the methylammonium lead iodide (CH3 NH3 PBI3 ) perovskite is demonstrated. Such a self-powered PD can operate even with irregular motion such as human finger tapping, which enables it to work without a bulky external power source. In addition, with high-quality CH3 NH3 PBI3 perovskite thin film fabricated with solvent engineering, the PD exhibits an impressive detectivity of 1.22 × 1013 Jones. In the self-powered voltage detection mode, it achieves a large responsivity of up to 79.4 V mW-1 cm-2 and a voltage response of up to ≈90%. Moreover, as the PD is made of flexible and transparent polymer films, it can operate under bending and functions at 360 ° of illumination. As a result, the self-powered, flexible, 360 ° omnidirectional perovskite PD, featuring high detectivity and responsivity along with real-world sensing capability, suggests a new direction for next-generation optical communications, sensing, and imaging applications.