Porous and single crystalline ZnO nanosheets, which were synthesized by annealing hydrozincite Zn5(CO3)2(OH)6 nanoplates produced with a water/ethylene glycol solvothermal method, are used as building blocks to construct functional Pd–ZnO nanoarchitectures together with Pd nanoparticles based on a self-assembly approach. Chemical sensing performances of the ZnO nanosheets were investigated carefully before and after their surface modification with Pd nanoparticles. It was found that the chemical sensors made with porous ZnO nanosheets exhibit high selectivity and quick response for detecting acetone, because of the 2D ZnO nanocrystals exposed in (100) facets at high percentage. The performances of the acetone sensors can be further improved dramatically, after the surfaces of ZnO nanosheets are modified with Pd nanoparticles. Novel acetone sensors with enhanced response, selectivity and stability have been fabricated successfully by using nanoarchitectures consisting of ZnO nanosheets and Pd nanoparticles.

Highly enhanced acetone sensing performances of porous and single crystalline ZnO nanosheets: high percentage of exposed (100) facets working together with surface modification with Pd nanoparticles.

High-performance liquefied petroleum gas sensing based on nanostructures of zinc oxide and zinc stannate

Highly crystalline ZnO hierarchical nanostructures were prepared at room temperature through the alkaline hydrolysis of zinc salt by the forced mixing of two immiscible solutions: Zn-nitrate aqueous solution and oleic-acid-dissolved n-hexane solution. The oleic acid acted as a surfactant in the room-temperature formation of well-defined ZnO hierarchical nanostructures, which subsequently demonstrated a sensitive and selective detection of C 2 H 5 OH. The responses of these hierarchical nanostructures to 10–100 ppm C 2 H 5 OH ranged from 15.7 to 177.7, which were 7–9 times higher than those of the agglomerated nanoparticles.

ZnO hierarchical nanostructures grown at room temperature and their C2H5OH sensor applications

In this study, pure ZnO microbullets, ZnO–ZnFe2O4 composite, and ZnO–Fe2O3–ZnFe2O4 composite with micron structured balloons, rods, and particles were prepared by a simple solvent thermal process using methanol or ethanol as solvents. The influence of solvents on the composition and morphology of the products was studied, and their gas-sensing properties were also investigated. The morphology of ZnO microbullets synthesized in ethanol is similar to but more uniform than that of ZnO microbullets synthesized in methanol. The Fe-doped ZnO synthesized in ethanol contains many micron particles homogeneously dispersing on the surface of the microbullets, which is composed of hexagonal wurtzite ZnO and franklinite ZnFe2O4, while Fe-doped ZnO prepared in methanol consists of micron structured balloons, rods, and particles, which is composed of hexagonal wurtzite ZnO, hematite Fe2O3, and franklinite ZnFe2O4. Compared with pure ZnO and ZnO–ZnFe2O4 composite, the ZnO–Fe2O3–ZnFe2O4 composite presented high response, rapid response/recovery characteristics, good selectivity, and excellent stability to acetone at relatively low operating temperature of 190 °C. This sensor could detect acetone in wide range of 1–1000 ppm, which was expected to be a promising gas sensor for detecting acetone.

Solvent thermal synthesis and gas-sensing properties of Fe-doped ZnO

Using zinc naphthenate dissolved in xylene as a precursor undoped ZnO nanopowders were synthesized by the flame spray pyrolysis technique. The average diameter and length of ZnO spherical and hexagonal particles were in the range of 5 to 20 nm, while ZnO nanorods were found to be 5–20 nm wide and 20–40 nm long, under 5/5 (precursor/oxygen) flame conditions. The gas sensitivity of the undoped ZnO nanopowders towards 50 ppm of NO2, C2H5OH and SO2 were found to be 33, 7 and 3, respectively. The sensors showed a great selectivity towards NO2 at high working temperature (at 300 °C), while small resistance variations were observed for C2H5OH and SO2, respectively.

Flame-spray-made undoped zinc oxide films for gas sensing applications.

Relaxor-lead titanate (PbTiO3) crystals, which exhibit extremely high piezoelectricity, are believed to possess high electro-optic (EO) coefficients. However, the optical transparency of relaxor-PbTiO3 crystals is severely reduced as a result of light scattering and reflection by domain walls, limiting electro-optic applications. Through synergistic design of a ferroelectric phase, crystal orientation, and poling technique, we successfully removed all light-scattering domain walls and achieved an extremely high transmittance of 99.6% in antireflection film–coated crystals, with an ultrahigh EO coefficient r33 of 900 picometers per volt (pm V−1), >30 times as high as that of conventionally used EO crystals. Using these crystals, we fabricated ultracompact EO Q-switches that require very low driving voltages, with superior performance to that of commercial Q-switches. Development of these materials is important for the portability and low driving voltage of EO devices. Description Breaking down the domain walls Ferroelectric materials should make for decent optical components because of the change in refractive index with electric field. However, many of the best ferroelectrics have domain walls that scatter light and are not useful for optics applications. Liu et al. used a high-temperature poling method to remove the light-scattering domain walls in a lead ceramic ferroelectric. The material has a very high electro-optic coefficient and requires a very low driving voltage. This strategy may be useful for other materials and may help in the development of better optical devices. —BG High-temperature poling eliminates light-scattering domain walls in a relaxor ferroelectric.

Ferroelectric crystals with giant electro-optic property enabling ultracompact Q-switches

In this study, ZnO nanostructures with different morphologies including nanorods, nanowires, and nanobrushes were synthesized by a simple hydrothermal process without using any structure-directing reagent. The samples were characterized by X-ray diffraction, field emission scanning electron microscopy, and transmission electron microscopy. The influence of the preparation parameters on the morphology of ZnO is discussed. Gas-sensing properties of the materials were investigated. The results reveal that all the prepared nanostructured ZnO powders show high response to ethanol, among which, the three-dimensional nanobrushes show the highest response, demonstrating excellent potentiality for ethanol sensors.

Xue-Yong Ma

Papers

Ferroelectric crystals with giant electro-optic property enabling ultracompact Q-switches

Tunable ZnO nanostructures for ethanol sensing