Haoran Zhang

Synthesis and Luminescence Properties of Cube-Structured CaSnO3 ∕ RE3 + ( RE = Pr , Tb ) Long-Lasting Phosphors

Uniform and cube-structured RE 3+ (RE = Pr,Tb)-doped CaSnO 3 phosphors have been successfully synthesized by a two-step approach including the room-temperature synthesis of CaSn(OH) 6 precursors with the help of cetyltrimethylammoniumbromide surfactant and then converted to CaSnO 3 by calcination at 750°C. The decomposition process of the Casn(OH) 6 precursor, crystallization, and morphology of the as-synthesized CaSnO 3 phosphors have been investigated using thermal analysis, X-ray diffraction, and scanning electron microscopy. Furthermore, luminescence properties of CaSnO 3 /RE 3+ (RE = Pr,Tb) phosphors, including photoluminescence, fluorescence lifetime, afterglow decay, and thermoluminescence, are also systematically discussed in this paper. The as-synthesized Pr 3+ and Tb 3+ doped CaSnO 3 phosphors show intense luminescence under ultraviolet excitation. Moreover, the afterglow emission from CaSnO 3 /RE 3+ (RE = Pr,Tb) phosphors lasts for more than 3 h after the ultraviolet irradiation source has been removed. Both the fluorescence and afterglow decay curves of the CaSnO 3 /RE 3+ (RE = Pr,Tb) phosphors contain one fast decay component and another slow decay process. Thermoluminescence spectra indicate that the incorporation of RE 3+ ions into the CaSnO 3 host produces suitable trapping centers, which are the origin of the long-lasting phosphorescence phenomenon in this kind of material at room temperature.

High-performance transparent thin-film transistor based on Y2O3/In2O3 with low interface traps

High-performance Y2O3/In2O3-based transparent thin-film transistors were processed featuring low thermal budget. The device shows a field-effect mobility of 43.5 cm2 V−1 s−1, a subthreshold swing of 0.28 V/decade, and an on/off current ratio of 108. These results are attributed to the high dielectric constant of Y2O3 and unique electronic structure of In2O3. Furthermore, the cubic phases of crystalline Y2O3 and In2O3 films have the identical crystal structure with a small lattice mismatch, which provides a well-defined dielectric/semiconductor interface for the optimal performance.

Stripe distributions of graphene-coated Cu foils and their effects on the reduction of graphene wrinkles

Hexagonal single-crystal domains of graphene were analyzed and the wrinkle distribution was obtained using thermal hydrogen etching. We observe parallel stripes on some single-crystal domains and these stripes are associated with graphene wrinkles. The etched trenches in graphene are always perpendicular to the stripes, thereby suggesting the suppressed formation of wrinkles along the stripe direction. Results indicate that the stripes help release the internal stress of graphene to reduce its wrinkle density. Furthermore, these stripes are due to Cu surface reconstruction and relate to two main factors, namely, the distribution of Cu grains and the cooling rate after graphene growth. Continuous graphene films which are synthesized by slow cooling exhibit high stripe area coverage and low sheet resistance because of the low wrinkle density.

High pressure-assisted transfer of ultraclean chemical vapor deposited graphene

We develop a high pressure-assisted (approximately 1000 kPa) transfer method to remove polymer residues and effectively reduce damages on the surface of graphene. By introducing an ethanol pre-dehydration technique and optimizing temperature, the graphene surface becomes nearly free of residues, and the quality of graphene is improved obviously when temperature reaches 140 °C. The graphene obtained using the high pressure-assisted transfer method also exhibits excellent electrical properties with an average sheet resistance of approximately 290 Ω/sq and a mobility of 1210 cm2/V·s at room temperature. Sheet resistance and mobility are considerably improved compared with those of the graphene obtained using the normal wet transfer method (average sheet resistance of approximately 510 ohm/sq and mobility of 750 cm2/V·s).

Enhanced light scattering effect of wrinkled transparent conductive ITO thin film

Indium tin oxide (ITO) plays an important role due to its high transparency and high conductivity in various optoelectronic thin-film devices. However, ITO has the drawback of mechanical fragility, limiting its development. Wrinkling has been considered a powerful tool for improving the flexibility and surface properties of thin films, but wrinkled ITO has not been reported so far. In this work, we fabricate uniform wrinkles on ITO and systematically study the properties of the wrinkled ITO in optics, electrics and mechanics. The wrinkled ITO shows a high optical transmittance and also a high haze value due to a remarkable wrinkle-induced enhancement of light scattering, which is beneficial for solar cells and light-emitting diodes. Our experimental results also indicate that wrinkles can effectively improve the mechanical bending performance of ITO without compromising the crystallization and electrical conductivity.

Stripe distribution on graphene-coated Cu surface and its effect on oxidation and corrosion resistance of graphene

The morphology and distribution of the stripes caused by Cu surface reconstruction were measured, and the effects of stripes on graphene stability were studied by oxidation and corrosion. The results reveal that the stripes are determined by the crystal orientation of both the Cu surface and graphene, which can both change the stripe distribution, and the stripes can also be influenced by the graphene thickness. The stripes would not induce cracks or destruction to the graphene. The oxidation resistance of graphene can be improved by Cu surface reconstruction. The local nonuniform distortion of the stripe area may induce a bigger strain in the graphene which, in turn, may induce structure instability and result in local stability degeneration in the stripe area.