Publications

Portable and wearable personal electronics and smart security systems are accelerating the development of transparent, flexible, and thin-film electronic devices. Here, we report a transparent and flexible self-charging power film (SCPF) that functions either as a power generator integrated with an energy storage unit or as a self-powered information input matrix. The SCPF possesses the capability of harvesting mechanical energy from finger motions, based on the coupling between the contact electrification and electrostatic induction effects, and meanwhile storing the generated energy. Under the fast finger sliding, the film can be charged from 0 to 2.5 V within 2094 s and discharge at 1 μA for approximately 1630 s. Furthermore, the film is able to identify personal characteristics during a sliding motion by recording the electric signals related to the person's individual bioelectricity, applied pressing force, sliding speed, and so on, which shows its potential applications in security systems in touchpad technology.

We report the effect of dissimilar anion anneals on the properties of layered quantum dot structures exhibiting vertical self-organization. Such anneals may provide an additional means of controlling dot properties, such as composition, size, and position. In addition, the modification of surface strain is critical to the subsequent nucleation of dots after the initial seed layer. Anion exchange may modify the strain at the semiconductor surface. We find that the effects of P2 and As4 anneals on InAs quantum dot size distributions are different. P2 anneals at relatively high temperatures (350 °C) can cause the loss of the three-dimensional morphology due to surface exchange. P2 anneals at lower temperatures (300 °C) appear to improve the uniformity of the dot size distribution. This behavior is not observed for anneals under As4. The dot size uniformity decreases by annealing dots under As4 at 300 °C.

The hydrolysis of starch converting into glucose, cyclodextrins and other monomer products is very critical in food and pharmaceutical industries. The conventional methods of testing the hydrolysis products are cumbersome and time consuming. The single-crystal zinc oxide (ZnO) structures are quasi-one dimensional semiconducting nanostrucrures, and open a new field of biosensor technology for fabricating highly sensitive biosensors for the detection of protein, peptide, DNA/RNA, and enzyme-catalyst events in real-time mode. We synthesized ZnO nanobelts/wires, and modified surfaces by coating with silicon nitride (Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> ) to protect nanostructure from process treatment. The nanostrucrures were coated with dilute aqueous starch solution, and electrical impedance measurements were recorded for both control and test samples. The test samples were hydrolyzed using amyloglucosidase enzyme (AMG). The SEM analysis showed degradation of the starch on the surface of ZnO nano-belts, whereas the starch remained intact on the control samples. The electrical impedance measurements showed shift in electrical impedance on test samples, whereas in control samples it remained static. The details of experimental results of electronic sensing of hydrolysis and advantages of the lab-on chip are discussed. This is the first report of electronic detection of starch hydrolysis using ZnO nanobelts/wires

Contact electrification (CE) involves a complex interplay of physical interactions in realistic material systems. For this reason, scientific consensus on the qualitative and quantitative importance of different physical mechanisms on CE remains a formidable task. The CE mechanism at a water/polymer interface is a crucial challenge owing to the poor understanding of charge transfer at the atomic level. First-principle density functional theory (DFT), used in the present work, proposes a new paradigm to address CE. Our results indicate that CE follows the same trend as the gap between the highest occupied and lowest unoccupied molecular orbitals (HOMO and LUMO) of polymers. Electron transfer occurs at the outmost atomic layer of the water/polymer interface and is closely linked to the functional groups and atom locations. When the polymer chains are parallel to the water layer, most electrons are transferred; conversely, if they are perpendicular to each other, the transfer of charges can be ignored. We demonstrate that a decrease in the interface distance between water and the polymer chains leads to CE in quantitative agreement with the electron cloud overlap model. We finally use DFT calculations to predict the properties of CE materials and their potential for triboelectric nanogenerator energy harvesting devices.

The development of the Internet of Things has brought new challenges to the corresponding distributed sensor systems. Self-powered sensors that can perceive and respond to environmental stimuli without an external power supply are highly desirable. In this paper, a self-powered wind sensor system based on an anemometer triboelectric nanogenerator (a-TENG, free-standing mode) and a wind vane triboelectric nanogenerator (v-TENG, single-electrode mode) is proposed for simultaneously detecting wind speed and direction. A soft friction mode is adopted instead of a typical rigid friction for largely enhancing the output performance of the TENG. The design parameters including size, unit central angle, and applied materials are optimized to enhance sensitivity, resolution, and wide measurement scale. The optimized a-TENG could deliver an open-circuit voltage of 88 V and short-circuit current of 6.3 μA, corresponding to a maximum power output of 0.47 mW (wind speed of 6.0 m/s), which is capable of driving electronics for data transmission and storage. The current peak value of the a-TENG signal is used for analyzing wind speed for less energy consumption. Moreover, the output characteristics of a v-TENG are further explored, with six actual operation situations, and the v-TENG delivers fast response to the incoming wind and accurately outputs the wind direction data. As a wind sensor system, wind speed ranging from 2.7 to 8.0 m/s can be well detected (consistent with a commercial sensor) and eight regular directions can be monitored. Therefore, the fabricated wind sensor system has great potential in wireless environmental monitoring applications.

When ZnO nanobelts are exposed to a high-dose electron probe of several nanometers to hundred nanometers in diameter inside a transmission electron microscope, due to the radiolysis effect, part of oxygen atoms will be ejected into the vacuum and leaving a Zn-ion rich surface with a pit appearance at both the electron-entrance and electron-exit surfaces. At the same time, a temperature distribution is created around the electron probe due to local beam heating effect, which generates a unidirectional pyroelectric field. This pyroelectric field is strong enough to drive Zn ions moving along its positive c-axis direction as interstitial ions. In the first case, for the ZnO nanobelts with c-axis lie in their large surfaces, defects due to the aggregation of Zn interstitial ions will be formed at some distances of 30–50 nm approximately along the c-axis direction from the electron beam illuminated area. Alternatively, for the ZnO nanobelts with ±(0001) planes as their large surfaces, the incident electron beam is along its c-axis and the generated pyroelectric field will drive the interstitial Zn-ions to aggregate at the Zn terminated (0001) surface where the local electrical potential is the lowest. Such electron beam induced damage in ZnO nanostructures is suggested as a result of Zn ion diffusion driven by the temperature gradient induced pyroelectric field along c-axis. Our study shows a radiation damage caused by electron beam in transmission electron microscopy, especially when the electron energy is high.

Abstract Combined surface, structural and opto-electrical investigations are drawn from the chemically fashioned ZnO nanotubes and its heterostructure with p-GaN film. A strong correlation has been found between the formation of radiative surface defect states in the nanotubes and the pure cool white light possessing averaged eight color rendering index value of 96 with appropriate color temperature. Highly important deep-red color index value has been realized &gt; 95 which has the capability to render and reproduce natural and vivid colors accurately. Diverse types of deep defect states and their relative contribution to the corresponding wavelengths in the broad emission band is suggested.

ABSTRACT The flexoelectric effect, a polarization phenomenon unrestricted by material symmetry, holds great promise for next‐generation energy harvesting and sensing. However, conventional flexoelectric devices require external mechanical stress, which severely limits their practical applicability. Here, we present a heterojunction‐based dual‐mode flexoelectric nanogenerator that is driven by light and heat, requiring no external mechanical or electrical input. Under illumination (photodetection mode) or temperature variation (thermal response mode), the heterojunction components undergo differential deformation, generating a pronounced interfacial strain gradient that drives strong flexoelectric polarization and flexo‐photovoltaic currents. The photodetection mode demonstrates a broad spectral response from 250 to 600 nm, with a peak responsivity of 2.2 mA W −1 . The thermal response mode exhibits an effective pyroelectric coefficient as high as 7518 µC m −2 K −1 , surpassing conventional pyroelectric materials by over an order of magnitude. By eliminating the need for external stress, this work enables direct coupling among optical, thermal, mechanical, and electrical energies, opening a new avenue for self‐powered photodetectors and thermal sensors based on flexoelectricity.

We demonstrated a flexible strain sensor based on ZnSnO(3) nanowires/microwires for the first time. High-resolution transmission electron microscopy indicates that the ZnSnO(3) belongs to a rhombohedral structure with an R3c space group and is grown along the [001] axis. On the basis of our experimental observation and theoretical calculation, the characteristic I-V curves of ZnSnO(3) revealed that our strain sensors had ultrahigh sensitivity, which is attributed to the piezopotential-modulated change in Schottky barrier height (SBH), that is, the piezotronic effect. The on/off ratio of our device is ∼587, and a gauge factor of 3740 has been demonstrated, which is 19 times higher than that of Si and three times higher than those of carbon nanotubes and ZnO nanowires.