Zinc Oxide Nanobelts Research Articles

Field emission from zinc oxide nanostructures and its degradation

Arrays of zinc oxide (ZnO) nanowires and nanobelts were synthesized by the thermal evaporation of mixed powders of ZnO and graphite. Neither catalyst nor vacuum environment was involved in the fabrication. For comparison, the ZnO nanowires were grown on a pre-deposited transitional ZnO film on a brass substrate and the ZnO nanobelts were grown directly on a Si substrate. Their field emission properties were systematically measured. Current density of 10 μA/cm 2 was achieved at the fields of 5.7 and 6.2 V/μm from the nanowires and nanobelts, respectively. Also, the emission sites were found to distribute uniformly on the whole cathode. In the preliminary test on the stability, the ZnO nanobelts, which were sharp at the tip but wide at the root, exhibited better robustness than the ZnO nanowires. The post-test scanning electron microscopy (SEM) observation showed that the degradation of their field emission capability resulted from the breaking of the nanowires, which was tentatively attributed to the resistive heating during the field emission. In contrast, the shedding of the ZnO from the substrate was not so serious as imagined.

Anomalous photoconductivity of cobalt-doped zinc oxide nanobelts in air

The decrease of photoconductivity from 1.3 to 0.25 μA in ambient air or in water vapor atmosphere has been observed when the cobalt-doped zinc oxide nanobelts are irradiated with 630 nm light. This kind of negative photoconductivity is attributed to the photodesorption of water molecules from nanobelts’ surface, and the mechanism was discussed. This result supplies a potential method to detect water vapor with a low concentration in environment.

Effect of Sn concentration on structural and optical properties of zinc oxide nanobelts

We investigated structural and optical properties of Sn-doped ZnO nanobelts with different Sn concentrations. X-ray diffraction and Raman spectra showed that the Sn-doped ZnO nanobelts have wurtzite structure at low Sn concentration (<2.1 at%) and over 2.1 at% a part of them starts to have the inverse spinel Zn 2SnO 4 structure phase. In addition, for Sn-doped ZnO nanobelts, the photoluminescence spectra indicate that ultraviolet emission peak appears first a blue shift with the increase of Sn concentration due to Burstein–Moss effect and then exhibits a red shift due to band gap renormalization effect.

Synthesis and Elastic Characterization of Zinc Oxide Nanowires

Zinc oxide nanowires, nanobelts, and nanoneedles were synthesized using the vapor‐liquid‐solid technique. Young′s modulus of the nanowires was measured by performing cantilever bending experiments on individual nanowires in situ inside a scanning electron microscope. The nanowires tested had diameters in the range of 200–750 nm. The average Young′s modulus, measured to be 40 GPa, is about 30% of that reported at the bulk scale. The experimental results are discussed in light of the pronounced electromechanical coupling due to the piezoelectric nature of the material.

Characterization of ZnO Nanobelt-Based Gas Sensor for ${\rm H}_{2}$, ${\rm NO}_{2}$, and Hydrocarbon Sensing

A conductometric H2, NO2, and hydrocarbon gas sensor based on single-crystalline zinc oxide (ZnO) nanobelts has been developed. The nanobelt sensitive layer was deposited using a radio frequency (RF) magnetron sputterer. The microcharacterization study reveals that the nanobelts have a single crystal hexagonal structure with average thickness and width of about 10 and 50nm, respectively. The sensor was exposed to H2, NO2 and propene gases at operating temperatures between 150 degC and 450 degC. The study showed that optimum operating temperatures for the sensor are in the range of 300 degC-400degC for H2, 300 degC-350 degC for NO2, and 350 degC-420 degC for propene sensing

Zinc oxide nanobelts by RF sputtering for ethanol sensor

Zinc oxide nanobelts were RF sputtered onto a copper tube. Their nanostructure has been confirmed by FE-SEM and Raman spectroscopy. The copper tube coated with these ZnO nanobelts was then employed as an ethanol gas sensor. To characterize the sensor, experiments with ethanol at concentration levels of 50–2000 ppm and at operating temperatures ranging from 200 to 290 °C were performed. The sensitivity and response time of the sensor's resistance for several ethanol concentrations and operating temperatures was determined. The relationship between the sensor's sensitivity and ethanol concentration level suggests that the adsorbed oxygen species at the sensor's surface is O 2−.

In situ TEM probing properties of individual one-dimensional nanostructures

One-dimensional nanomaterials are a fundamental component of nanoscience and nanotechnology. Property measurements of individual one-dimensional nanostructures, including nanowires and nanotubes, are challenging due to their small size, which constrains the applications of the well-established testing and measurement techniques. We have developed an alternative novel approach that allows the direct measurements of the mechanical and physical properties of individual nanostructures inside high-resolution transmission electron microscopy (TEM), by which microstructures of the nanomaterials can be characterised in situ. Thus the properties of nanostructures can be directly correlated with their well-defined structures by this technique. This paper will review our progress in using in situ TEM method to measure the mechanical and field emission properties of individual nanowires and nanotubes. Mechanical resonance of zinc oxide (ZnO) nanobelt, as a new important class of nanowire, was induced by an alternating electric field. Due to the rectangular cross-section of the nanobelt, two fundamental resonance modes have been observed, corresponding to the two orthogonal transverse vibration directions, showing the versatile applications of nanobelts as nanocantilevers and nanoresonators. The elastic modulus of the ZnO nanobelts was measured to be ∼52 GPa and the damping time constant of the resonance in vacuum of 10-8 Torr was ∼1.2 ms. Field emission properties of individual carbon nanotubes have been systematically studied. The field emission behaviours have been directly linked with in situ nanotube tip morphology and their real work function. The dynamic field emission of a nanotube at mechanical resonance was also studied by in situ TEM method.

NANOMECHANICS OF INDIVIDUAL ZINC OXIDE NANOBELTS MEASURED BY IN SITU TRANSMISSION ELECTRON MICROSCOPY

Zinc oxide nanobelts, grown by a solid–vapor phase thermal sublimation process, are stimulating extensive interest because of their semiconducting and piezoelectric properties, diverse functionalities and chemical stability. For nanomanipulation and nanomeasurement of an individual ZnO nanobelts, in situ transmission electron microscopy (TEM) technique is a unique approach. In this paper, mechanical resonance of a single ZnO nanobelt, induced by an alternative electric field, was studied by in situ TEM. Due to the rectangular cross-section of the nanobelt, two fundamental resonance modes have been observed in corresponding to two orthogonal transverse vibration directions, showing the versatile applications of nanobelts as nanocantilevers and nanoresonators. The bending modulus of the ZnO nanobelts was measured to be ~ 52 GPa and the damping time constant of the resonance in vacuum of 10–8 Torr was ~ 1.2 ms. The ZnO nanobelts are promising in potential applications as nanocantilevers, nanoresonators and nanoactuators.

Growth of Zinc Oxide Nanorods, Tetrapods, and Nanobelts without Catalyst

Zinc oxide (ZnO) nanostructures with various morphologies have been synthesized without catalyst in a one-step simple redox process. The results show that ZnO nanorods, nanobelts, and tetrapods with hexagonal needled arms could be synthesized via thermal treatment of a mixture of zinc oxide and charcoal powder in a muffle furnace at 1000-1200 degrees C for 240 min. XRD analyses showed that polycrystalline ZnO phase with wurtzite crystal structure was formed. At a relatively low temperature, 1000 degrees C, the ZnO structure was found to be a bundle of denser nanorods. By increasing the reaction temperature to 1100 degrees C, tetrapod-like structures of needle-like arms with pyramidal tips were formed. With the increase of temperature up to 1200 degrees C, the morphology of ZnO nanostructures changed from nanorods and tetrapods to coalescence grains. Reaction temperature was found to be the most important experimental parameter that played an important role in controlling the mode, mechanism of growth, and formation of different ZnO morphologies.

Room-temperature gas sensing based on visible photoluminescence properties of metal oxide nanobelts

The gas-sensitive light emission properties of structurally uniform and single-crystal tin dioxide and zinc oxide nanobelts are reported. Strong visible gas-sensitive photoluminescence (PL) emission was observed and the influence of the environment was studied by comparing measurements obtained in the presence of air and a low concentration of NO2 as a function of temperature from 300 to 500 K. Visible photoluminescence was reversibly quenched by nitrogen dioxide at the 5 ppm level at room temperature. Preliminary results on time-resolved PL properties of tin dioxide nanobelts are also shown.

Surface-effects-dominated thermal and mechanical responses of zinc oxide nanobelts

Molecular dynamics (MD) simulations are carried out to characterize the mechanical and thermal responses of Open image in new window-oriented ZnO nanobelts with lateral dimensions of 21.22 A×18.95 A, 31.02 A × 29.42 A and 40.81A × 39.89 A over the temperature range of 300-1000 K. The Young's modulus and thermal conductivity of the nanobelts are evaluated. Significant surface effects on properties due to the high- surface-to-volume ratios of the nanobelts are observed. For the mechanical response, surface-stress-induced internal stress plays an important role. For the thermal response, surface scattering of phonons dominates. Calculations show that the Young's modulus is higher than the corresponding value for bulk ZnO and decreases by ~ 33% as the lateral dimensions increase from 21.22 A × 18.95 A to 40.81 A × 39.89 A. The thermal conductivity is one order of magnitude lower than the corresponding value for bulk ZnO single crystal and decreases with wire size. Specifically, the conductivity of the 21.22 A × 18.95 A belt is approximately (31-18)% lower than that of the 40.81 A × 39.89 A belt over the temperature range analyzed. A significant dependence of properties on temperature is also observed, with the Young's modulus decreasing on average by 12% and the conductivity decreasing by 50% as temperature increases from 300 K to 1000 K.

Gas sensitive light emission properties of tin oxide and zinc oxide nanobelts

Light emission properties of tin oxide and zinc oxide nanobelts and nanowires have been investigated by means of continuous wave and time resolved photoluminescence. In both kind of nanostructures, photoluminescence quenching was observed at increasing temperature and at interaction with 5ppm concentration NO2. Photoluminescence time decay measurements in the visible range suggest that adsorbed NO2 induces fast non-radiative relaxation of surface electrons, competing with radiative surface-localized recombination. Such fast interaction between electrons and molecular adlayer may reduce the number of possible radiative recombination events at surface without significantly changing the subsequent slower radiative processes. Our measurements also show that adsorbate-related non-radiative recombination time should be lower than 1ns.

Optical characterization of ZnO nanobelts

Zinc oxide nanobelts have been synthesized by chemical precipitation technique using zinc acetate as starting material. Scanning electron microscopy observations indicate that the lengths of nanobelts are ranging from a few hundreds of micrometers to a few millimeters. X-Ray Diffraction pattern confirms the wurtzite structure. Nitrogen laser is employed here as an excitation source (337.1 nm, 10 ns) for phosphorescence studies. From the decay curves of time resolved laser induced photoluminescence, various optical parameters such as Einstein’s spontaneous and stimulated coefficients, oscillator strength, integrated cross-section and dipole-moment of ZnO nanobelts have been calculated and reported in this paper. Einstein’s spontaneous and stimulated coefficient values obtained from the decay curves indicate the probability of transitions from various traps. Selective excitation of the levels can make ZnO as a best suited laser medium.

ZnO nanostructures with different morphologies and their field emission properties

Zinc oxide (ZnO) products with the morphologies of balls, nunchakus and belts have been synthesized from aqueous solutions by adjusting the reagent concentration and reaction time. The X-ray diffraction (XRD) peaks of the products were indexed to ZnO materials, but exhibited different relative intensities for the (0 0 2) diffraction peak. Field emission (FE) measurements showed that the turn-on and threshold field for the ZnO nanonunchakus were 3.01 ± 0.005 and 5.47 ± 0.005, 3.71 ± 0.005 and 6.43 ± 0.005 V/μm, respectively, for the ZnO nanobelts, revealing that the products have comparable FE properties with those of the reported ZnO nanowires and carbon nanotubes (CNTs).

Modelling the shape and orientation of ZnO nanobelts

At the nanoscale, zinc oxide forms in many different shapes, the dimensions of which are often closely related to specific properties. Although much attention is focussed on finding methods for controlling the morphology, explanations of phenomena such as the change in crystallographic orientation of the principle axis of one-dimensional nanostructures (with size) are still largely empirical. We have used a shape-dependant thermodynamic model to identify the relationship between size, structure and orientation in zinc oxide nanobelts, and present results showing that growth in the ± [ 1 2 ¯ 1 0 ] direction is a decisive factor in determining the orientation.

Conversion of Zinc Oxide Nanobelts into Superlattice‐Structured Nanohelices.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Orientation and size dependence of the elastic properties of zinc oxide nanobelts

Molecular dynamics simulations are performed to characterize the response of zinc oxide(ZnO) nanobelts to tensile loading. The ultimate tensile strength (UTS) and Young’smodulus are obtained as functions of size and growth orientation. Nanobelts in threegrowth orientations are generated by assembling the unit wurtzite cell along the [0001],, and crystalline axes. Following the geometric construction, dynamic relaxation is carried outto yield free-standing nanobelts at 300 K. Two distinct configurations are observed in the[0001] and orientations. When the lateral dimensions are above 10 Å, nanobelts with rectangularcross-sections are seen. Below this critical size, tubular structures involving two concentricshells similar to double-walled carbon nanotubes are obtained. Quasi-static deformations ofbelts with and orientations consist of three stages, including initial elastic stretching, wurtzite-ZnO tographitic-ZnO structural transformation, and cleavage fracture. On the other hand, [0001]belts do not undergo any structural transformation and fail through cleavage along (0001)planes. Calculations show that the UTS and Young’s modulus of the belts are sizedependent and are higher than the corresponding values for bulk ZnO. Specifically, as thelateral dimensions increase from 10 to 40 Å, decreases between 38–76% and 24–63% areobserved for the UTS and Young’s modulus, respectively. This effect is attributed to thesize-dependent compressive stress induced by tensile surface stress in the nanobelts. and nanobelts with multi-walled tubular structures are seen to have higher values of elastic moduli(∼340 GPa)and UTS (∼36 GPa) compared to their wurtzite counterparts, echoing a similar trend in multi-walledcarbon nanotubes.

Conversion of Zinc Oxide Nanobelts into Superlattice-Structured Nanohelices

A previously unknown rigid helical structure of zinc oxide consisting of a superlattice-structured nanobelt was formed spontaneously in a vapor-solid growth process. Starting from a single-crystal stiff nanoribbon dominated by the c-plane polar surfaces, an abrupt structural transformation into the superlattice-structured nanobelt led to the formation of a uniform nanohelix due to a rigid lattice rotation or twisting. The nanohelix was made of two types of alternating and periodically distributed long crystal stripes, which were oriented with their c axes perpendicular to each other. The nanohelix terminated by transforming into a single-crystal nanobelt dominated by nonpolar (0110) surfaces. The nanohelix could be manipulated, and its elastic properties were measured, which suggests possible uses in electromechanically coupled sensors, transducers, and resonators.

Characterization of individual zincoxide nano-belts by using X-ray nano-diffraction technique

Characterization of individual zincoxide nano-belts by using X-ray nano-diffraction technique

Growth of Zinc Oxide Nanowires and Nanobelts for Gas Sensing Applications

Zinc Oxide (ZnO) is a very useful as a solid state gas sensor material. In chemical sensing the surface and interface interactions between the analyte molecules and the sensing material is all but important that is read through the changes in electrical conductance. In that sense, nano-objects with a large surface atom/bulk atom ratio, like nanoparticles and nanowires, are potentially the best chemical sensors. The mechanism envisioned involves the adsorption (and eventually diffusion) of the analyte molecule at the surface that induces a change in the electrical resistance of the nano-object. The most convenient way to measure changes in electrical resistance in such devices is to obtain the specific material as nanowires or as connected nanoparticles. Here, we will discuss about a low-temperature wet-chemical process of synthesizing ZnO nanoparticles, nanowires and nanobelts for application as gas sensors.