Tetrapod ZnO Nanostructures Research Articles

A wearable exhaling-oxygen-sensing mask based on piezoelectric/gas-sensing coupling effect for real-time monitoring and uploading lung disease information

Comprehensive analysis of respiratory gases may provide noninvasive health monitoring of lung diseases, such as corona virus 2019 pneumonia. Here, a self-powered wearable mask has been fabricated for real-time monitoring and uploading exhaling oxygen information. Tetrapod ZnO (T-ZnO) nanostructures are hybridized with polyvinylidene fluoride (PVDF) that adhere to flexible fabric substrate on a mask. The piezoelectric effect of T-ZnO/PVDF is coupled with the gas sensing properties. The sensing unit can convert breath energy into piezoelectric signal without any external power supply, and the outputting piezoelectric voltage increases with increasing oxygen concentration, acting as the sensing signal. The sensing unit integrated with data processing module and wireless Bluetooth module can transmit the exhaling oxygen information to the mobile device, realizing real-time monitoring the oxygenation capacity of the lungs. This self-powered wearable approach can promote the lung diagnosis outside of clinical settings.

A self-powered intelligent glove for real-time human-machine gesture interaction based on piezoelectric effect of T-ZnO/PVDF film

In the emerging field of human-machine interaction, intelligent gesture recognition techniques have great application prospects. The traditional use of rigid and over-sized power units has restrained the development of wearable gesture recognition systems. Here, we present a self-powered intelligent glove based on piezoelectric motion sensor arrays for real-time gesture recognition. The system can be confortably worn on human hands, and mainly consists of three parts: a flexible piezoelectric motion sensor based on T-ZnO/PVDF film (T-ZnO, tetrapod ZnO nanostructures), a signal processing module for analyzing the sensing information, and a Bluetooth unit for wireless communication. The system can work without external power, and the piezoelectric output can act as both the energy source of the system and the sensing signal. The working mechanism can be attributed to the piezoelectric effect of T-ZnO/PVDF composites and with flexion and extension of the fingers, a series of pulse signals can be generated and converted into specific corresponding codes. The sensing signal can be wirelessly transmitted to smartphones through the Bluetooth unit, and the phone can recognize the codes corresponding to sign language actions and translate them. This work can potentially promote the development of the next generation of human-machine interaction systems and expand the scope of self-powered techniques and wearable electronics.

A flexible self-powered T-ZnO/PVDF/fabric electronic-skin with multi-functions of tactile-perception, atmosphere-detection and self-clean

A flexible self-powered e-skin has been presented with multi-functions of tactile-perception, atmosphere-detection and self-clean. Piezoelectric PVDF and tetrapod ZnO (T-ZnO) nanostructures are hybridizing on the flexible fabric substrate. The piezoelectric, gas sensing and photocatalytic properties of T-ZnO nanostructures are combined together. The piezoelectric effect of T-ZnO/PVDF leads to the motion-powered tactile-perception behavior, e.g. the e-skin can detect elbow bending or finger pressing. The piezoelectric/gas-sensing coupling effect of T-ZnO nanostructures delivers the motion-powered atmosphere-detection performance, and the piezoelectric output of the e-skin is different upon exposure to different atmosphere conditions, acting as the gas-sensing signal. The piezo-photocatalytic activity of T-ZnO nanostructures results in the distinct self-clean characteristics, and the organic-pollutants/bacteria can be degraded/sterilized on the surface of the e-skin. This novel material system and device architecture can promote the development of flexible self-powered multi-functional e-skin.

Luminescence properties of tetrapod ZnO nanostructures

The tetrapod ZnO nanostructures are synthesized on the Si (100) substrates using the chemical vapor deposition (CVD) method at 1000 °C. Each nanostructure has four arms which are about 3–10 μm in length and 0.2–1.5 μm in diameter. Further analyses on structure demonstrate that the tetrapod ZnO nanostructures have single crystalline wurtzite hexagonal structure preferentially oriented in c-axis. The photoluminescence (PL) measurements of the tetrapod ZnO nanostructures revealed a UV peak at 382 nm corresponding to the free exciton emission, and a green peak at 523 nm arising from deep level emission. For comparative analysis, cathodoluminescence (CL) spectra obtained from different regions of an individual tetrapod are investigated. Moreover, a possible growth mechanism of the tetrapod ZnO nanostructures is also discussed based on the experimental results.

Facilitating ZnO nanostructure growths by making seeds for self-catalytic reactions

Long and straight single-crystalline ZnO nanowires were successfully synthesized on ZnCl2-coated Zn foils in oxygen environment by using simple thermal annealing processes. With relatively low reaction temperatures (410 and 700°C), nanowires whose lengths and diameters are up to ∼50μm and 10–100nm were obtained. We found that ZnO seeds created from ZnCl2 played an important role in facilitating the ZnO nanowire growth via self-catalytic reactions. Systematic studies by altering critical synthesis factors that determine shape, length, diameter, and density of the nanowires were performed in order to unveil the growth mechanisms. We also compared the nanowires synthesized from Zn foils with tetrapod ZnO nanostructures synthesized from Zn powders at various temperatures.

Facile fabrication of UV photodetector based on spatial network of tetrapod ZnO nanostructures

A highly sensitive UV photodetector based on a spatial network of tetrapod ZnO nanostructures was fabricated by a new simple and cost-effective method. The device showed a drastic and fast response to UV illumination in atmosphere at room temperature, but no response to visible light. The photocurrent and dark current contrast ratio is up to approximately six orders of magnitude at an applied bias of 1 V. The photoresponse mechanism is also analysed and discussed. The proposed approach provides a facile and effective way to fabricate high- performance photodetector or other nanodevices.

Synthesis of zinc oxide nanotetrapods by a novel fast microemulsion-based hydrothermal method

ZnO nanotetrapods have been successfully synthesized via a novel microemulsion-mediated hydrothermal route at 120 °C for 12 h. X-ray power diffraction (XRD), field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), selected-area electron diffraction analysis (SAED), and electrochemical analysis (EA) were employed to study the structural features and electrochemical behavior of the products. It was found that these tetrapod ZnO nanostructures had a single crystal hexagonal wurtzite structure with lattice constants of a = 0.3249 nm and c = 0.5205 nm. And they exhibited a clearly electrocatalytic response, showing potential applications for sensor constructions.

Evaporation of Tetrapod ZnO Nanostructures and Its Influence on the Field-Emission Performance

The ZnO cathode is a promising electron source due to its excellent field-emission performance. In this letter, we investigate the evaporation characteristics of the field emitters in a screen-printed ZnO cathode by a quadrupole mass spectrometer, energy-dispersive X-ray, and scanning electron microscopy. As the experiments show, the oxygen and zinc start to be evaporated if the temperature is higher than 1273 K. The quantity of evaporative materials increases with the increment of temperature, and the quantity of evaporated oxygen is much larger than that of zinc. The evaporations of oxygen and zinc have considerable effects on the field-emission properties of the ZnO cathode, particularly the turn-on field, the threshold electric field, and the emission current density. Therefore, the evaporation of field emitters is an important factor for the stability of the field-emission current.

Morphology-controlled growth of tetrapod ZnO nanostructures by direct arc discharge

A novel buttress-root shaped ZnO tetrapod-like nanostructure and a classic tetrapod ZnO nanostructure were synthesized by a direct reaction of high-purity Zn granules with oxygen using an arc discharge method. The morphology of the products could be controlled by adjusting the oxygen partial pressure. The buttress-root shaped tetrapod-like nanostructure contains three triangular nanosheets, the diameters of nanoarms vary between 50 and 80 nm, and the angle between every two arms is about 109.5°. A nanorod-centered growth model has been proposed to explain the novel nanostructure. An ultraviolet (UV) emission band located at 389 nm (3.18 eV) and a broad blue emission band centered at 484 nm (2.57 eV) were observed at room temperature.

Effect of ion bombardment on the field emission property of tetrapod ZnO

The influences of ion bombardment on the field emission performance of tetrapod ZnO nanostructures are reported. As the scanning electron microscopy images and photoluminescence spectrum show, the tips of the field emitters are destroyed and the surface state of the field emitters is also changed after the ion bombardment. The ion bombardment has a considerable effect on the field emission properties of the tetrapod ZnO field emitters. After Ar+ ion bombardment with the energy of 3 keV and the ion current of 0.05 μA for 30 min, the turn-on field increases about 63% and the threshold field increases about 77%, respectively. There are two main reasons for the variation in field-emission property: (1) the decrement of the field enhancement factor β, which is caused by the variation in morphology of field emitter; (2) the increment of work function φ, which is caused by the changed concentration of the surface oxygen vacancy.

Growth kinetic and characterization of tetrapod ZnO nanostructures

Tetrapod ZnO nanostructures ( T -ZnO) were synthesized by an oxidation reaction technique by heating the mixture of zinc powder and hydrogen peroxide solution at 1000 ∘C under normal atmospheric pressure. The cross-sectional size which was determined at the middle of the legs and the length of T -ZnO is about 200–1000 nm and 1–5 μm, respectively. XRD, EDS and TEM results confirmed that T -ZnO is a hexagonal structure and has a growth direction along [0001] direction. A growth model of T -ZnO by anisotropic growth via a vapor–solid mechanism with 3D tetrahedral nucleus as a seed was proposed. The 3D tetrahedral nuclei form by accumulation and then, condensation of ZnO vapor due to a supersaturation condition. These 3D nuclei first grow along the c -axis in four variants of tetrahedral axes due to symmetrical structure before finally forming the four-leg structure of T -ZnO. Evidence to confirm this growth model were the kinked Y-shape, X-shape, and H-shape of the projected images of grain boundaries observed by TEM. This growth model could be generalized to explain other materials having a similar hexagonal structure such as GaN.

High field emission enhancement of ZnO-nanorods via hydrothermal synthesis

We describe the synthesis of zinc oxide nanorods by a hydrothermal method in this paper. The reactants were zinc nitrate hexahydrate and hexamethylenetetramine (HMT, (CH2)6N4) and the solvent was absolute alcohol. The ZnO-nanostructures have been characterized with X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM): the nanorods had a length of 9–10μm and a diameter 0.5μm. From the field emission characteristics of the ZnO-nanorods the following properties were derived: a low turn-on electric field of 1.9V/μm at a current density of 0.2μA/cm2, maximum current density was 1mA/cm2 at a threshold field of 7.4V/μm and a field emission enhancement factor β of 2510. Furthermore, ZnO-nanorods show a higher stability and longer lifetime as compared with those of ZnO-nanoparticles and tetrapod ZnO-nanostructures.

Synthesis and photoluminescence of tetrapod ZnO nanostructures

Tetrapod ZnO nanostructures with three different morphologies (rod–wire junction, dumbbell-like and cone-like) and high aspect ratios were synthesized by a vapor oxidation method. It was found that these tetrapod ZnO nanostructures had a single crystal hexagonal wurtzite structure with lattice constants of a = 0.325 nm and c = 0.521 nm. Photoluminescence characterization of such ZnO nanostructures shows that they exhibit a strong UV emission (about 380 nm) and three broad green emission peaks, showing good potential for photoluminescent application.

Nucleation mechanism of the seed of tetrapod ZnO nanostructures

Tetrapod zinc oxide (T-ZnO) nanorods have been synthesized by evaporation and recondensation of metallic Zn under ambient conditions. The total sizes of the T-ZnO nanostructures range from 300nmto15μm with leg diameters of about 30to650nm, depending on the deposition temperature. A detailed high-resolution electron microscopy analysis showed that the center core of T-ZnO nanorods consists of four hexagonal grains with a twinlike relation. The nucleation and growth mechanism has been generated on the basis of energy considerations during a phase transition from a fullerenelike ZnO cluster to a nanometer-sized tetrahedron, which is directly visible in our high-resolution transmission electron microscopy investigations.

Tailoring the Optical Property by a Three-Dimensional Epitaxial Heterostructure: A Case of ZnO/SnO2

Epitaxial growth, as a best strategy to attain a heterostructure with a well-defined and clean interface, usually takes place on a planar substrate. In this paper, using a ZnO/SnO2 core-shell heterostructure as an example, we demonstrate the possibility of establishing a three-dimensional epitaxial interface between two materials with different crystal systems for the first time and show possible tailoring optical properties by building the heteroepitaxial crystal interface. The characterization results of element mapping, high-resolution transmission electron microscopy, and selected area electric diffraction reveal that the as-prepared ZnO/SnO2 heterostructure has a tetrapod-like ZnO core and a SnO2 shell with 15-30 nm, and their special epitaxial relation is (010)SnO2//(010)ZnO and [100]SnO2//[0001]ZnO. Such three-dimensional epitaxy between the ZnO core and SnO2 shell is quite different from the usual planar epitaxy or three-dimensional epitaxy between materials having the same crystal structure. A rational model of such complicated epitaxy has been proposed through investigating the certain structural comparability between the wurtzite ZnO and rutile SnO2 crystals. The as-prepared T-ZnO/SnO2 epitaxial heterostructure exhibits unique luminescence properties in contrast with individual tetrapod ZnO and SnO2 nanostructures, in which the epitaxial interface induces new luminescence properties. This result may inspire great interest in exploring other complicated epitaxy systems and their potential applications in laser, gas sensor, solar energy conversion, photo catalysis, and nanodevices in the future.

Microwave plasma growth and high spatial resolution cathodoluminescent spectrum of tetrapod ZnO nanostructures

A novel microwave plasma assisted by tube furnace heating system is designed to grow tetrapod ZnO nanostructures. Under optimal reaction conditions, Zn powder is oxidated to form the tetrapod ZnO with straight and uniform four legs (nanorods), bearing diameters ranging from 10 to 25 nm and lengths up to 160 nm. High-resolution transmission electron microscopy analyses reveals that the tetrapod ZnO nanostructures are perfect crystalloid. High spatial resolution cathodoluminescent spectrum for individual tetrapod ZnO nanostructure shows only a strong ultraviolet emission at 385 nm.