Li-Jiaun Lin

Photoresponsive and Ultraviolet to Visible-Light Range Photocatalytic Properties of ZnO:Sb Nanowires

Zinc oxide (ZnO) doped antimony (Sb) nanowires have been synthesized for improving ultraviolet sensing and photocatalytic properties. Upon illumination by UV light (365 nm, 2.33 mW cm -2 ), the photoelectric current of the ZnO:Sb nanowires exhibited a rapid photoresponse as compared to that of the ZnO nanowires. A highest ratio of photocurrent to dark current of around 48.8-fold was achieved in the as-synthesized ZnO:Sb nanowires. A UV-visible spectrophotometer was used to investigate the absorbance spectrum of the ZnO:Sb nanowires, which exhibited a high absorbance ratio with redshift effect in contrast to that of the ZnO nanowires. Visible-light photocatalysis and UV photoresponsive properties of the ZnO:Sb nanowires are superior to those of the ZnO nanowires.

Growth of Epitaxial Needlelike ZnO Nanowires on GaN Films

Epitaxial needlelike ZnO nanowires were grown vertically over an entire epi-GaN/sapphire substrate at 550°C by low-pressure vapor phase deposition without employing any metal catalysts. A two-step oxygen injection processis the key of successful synthesis. The length of ZnO wires was up to 3.0 μm. The diameters of the roots and tips of the ZnO nanowires were around 80-100 and 15-30 nm, respectively. X-ray diffraction showed the epitaxial orientation relationship between ZnO and GaN as [001] Z n O //[001] G a N along the normal to the plane, and [100] Z n O //[100] G a N along the in-plane direction, consistent with the selective area electron diffraction pattern taken at the ZnO/GaN heterointerface. High-resolution transmission electron microscopy confirmed that nanowire was a single crystal. A room-temperature photoluminescence spectrum of the wires revealed a low concentration of oxygen vacancy in the ZnO nanowires and showed high optical quality.

The substrate effect on the in-plane orientation of vertically well-aligned ZnO nanorods grown on ZnO buffer layers

Vertically well-aligned ZnO nanorods were synthesized without employing any metal catalysts on various substrates including glass, Si(111), 6H-SiC(0001) and sapphire (0001), which were pre-coated with c-oriented ZnO buffer layers, by simple physical vapour deposition. The alignments of the ZnO nanorods on the different substrates depend on the crystallographic alignments of the pre-coated ZnO buffer layers. The ZnO nanorods grown on glass and Si(111) are vertically aligned but randomly oriented in the in-plane direction. In contrast, the vertically aligned ZnO nanorods on 6H-SiC(0001) and sapphire (0001) show an in-plane alignment with azimuthally sixfold symmetry, which indicates the epitaxial relationship between ZnO and the substrate. Similarly, photoluminescence measurements show the distinct appearance of ZnO nanorods on different substrates. Besides the UV band, which was attributed to the recombination of free excitons near the band edge, defect-related visible emissions were also observed for the samples grown on both glass and Si(111) substrates. However, the ZnO nanorods exhibit only strong band edge emission peaks with no noticeable deep level emissions when grown on the 6H-SiC(0001) and sapphire (0001) substrates, which confirms the good crystalline and optical quality of the epitaxial ZnO nanorods.

Using an Au interlayer to enhance electron field emission properties of ultrananocrystalline diamond films

We observe that an Au interlayer markedly enhances the electrical field emission (EFE) properties of ultrananocrystalline diamond (UNCD) films on Si substrates. The EFE properties of UNCD/Au/Si films can be turned on at a lower field and attain a higher current density than in UNCD films grown on Si substrates without an Au interlayer. Transmission electron microscopy reveals that the Au interlayer induces the formation of SiC clusters, preventing the formation of a resistive amorphous carbon layer that nucleates the diamond clusters. This improves the diamond-to-substrate interfacial conductivity. Moreover, there is an abundant nano-graphite phase, which is presumably induced by the coalescence of nano-sized diamond clusters. The percolation of the nano-graphite clusters helps transport electrons, improving the conductivity of the UNCD films. We believe that the simultaneous increase in the conductivity of the UNCD-to-Si interface and the bulk of the UNCD films is the main factor enhancing electrical con...

Thermal conduction behavior in polycrystalline (Sr1−x,K2x)Zr4(PO4)6 ceramic

Single‐phase (Sr1−x,K2x)Zr4(PO4)6 ceramic (with x=0.0–0.8) demonstrated values of thermal conductivity decrease with increasing potassium content to a minimum value at x=0.5, which suggests a maximum content of lattice defect, i.e., oxygen vacancy, at this composition. The thermal conductivity of the ceramic then increased with further increase of potassium. The thermal conduction in (Sr1−x,K2x)Zr4(PO4)6 ceramic (at x=0.5) appears to exhibit a strongly lattice‐defect dependence with a calculated phonon mean free path of approximately 3.04 A, rather than a phonon‐phonon dependence as observed in a number of dielectric materials. A linear relationship of the thermal conductivity in terms of porosity with temperature up to 600 °C has been correlated and can be simply expressed as K=K0 (1−p) regardless of the influence of emissivity factor.

The induction of nanographitic phase on Fe coated diamond films for the enhancement in electron field emission properties

A thin layer of iron coating and subsequent post-annealing (Fe-coating/post-annealing) is seen to significantly enhance the electron field emission (EFE) properties of ultrananocrystalline diamond (UNCD) films. The best EFE properties, with a turn on field (E0) of 1.98 V/μm and current density (Je) of 705 μA/cm2 at 7.5 V/μm, are obtained for the films, which were Fe-coated/post-annealed at 900 °C in H2 atmosphere. The mechanism behind the enhanced EFE properties of Fe coated/post-annealed UNCD films are explained by the microstructural analysis which shows formation of nanographitic phase surrounding the Fe (or Fe3C) nanoparticles. The role of the nanographitic phase in improving the emission sites of Fe coated/post-annealed UNCD films is clearly revealed by the current imaging tunneling spectroscopy (CITS) images. The CITS images clearly show significant increase in emission sites in Fe-coated/post-annealed UNCD films than the as-deposited one. Enhanced emission sites are mostly seen around the boundarie...

Influence of machining on the strength of SiCAl2O3Y2O3 ceramic

Abstract The influence of surface machining on the mechanical strength of SiC ceramics was investigated in terms of surface roughness, residual stress, and surface morphology observation. Experimental results showed that the mechanical strength of the SiC ceramic appears to correlate with the surface roughness of the ceramics: the lower the surface roughness, the higher the flexural strength. An average four-point bending strength of as high as 700 MPa, which is higher by a factor of 1.8 than the ceramic with as-fired surface, can be achieved after the surface of the specimens is polished with a 600-grit fine diamond wheel. More extensive surface polishing deteriorates the strength by forming large surface pores which act as failure origins. Machining-induced compressive residual stress in the thin surface layer of the ceramic appears to increase the fracture stress to only a limited extent.

Therman Expansion and Crystal Chemistry of (Sr1−x, K2x)Zr4(PO4)6 Ceramic

Thermal expansion of (Sr1−x, K2x)Zr4(PO4)6 (SrKZP) (with x = 0–1) ceramic was investigated using both a dilatometer and a high-temperature X-ray diffractometer. The coefficients of thermal expansion (CTEs) of the SrKZP ceramic measured by the dilatometer demonstrate a similar trend as those from high-temperature X-ray diffraction. Both measurements show an ultra-low CTE at x = 0.5; nevertheless, this composition shows significant lattice thermal-expansion anisotropy (TEA), while the minimum TEA appears with composition x = 0.2. Although it possessed a sufficient degree of TEA, the x = 0.5 composition showed no visible microcracks or negligible microcracks over a grain size as large as 15 μm. A transition of space group from R{\bar 3} to R{\bar 3}c with composition between x = 0.3 and x = 0.5 has been observed. The crystal structure of the SrKZP ceramic with possible occupations of strontium and/or potassium within the lattice in relation to their influence on the CTEs is proposed.

The 3D-tomography of the nano-clusters formed by Fe-coating and annealing of diamond films for enhancing their surface electron field emitters

The Fe-coating and H2-annealed processes markedly increased the conductivity and enhanced the surface electron field emission (s-EFE) properties for the diamond films. The enhancement on the s-EFE properties for the diamond films is presumably owing to the formation of nano-graphite clusters on the surface of the films via the Fe-to-diamond interaction. However, the extent of enhancement varied with the granular structure of the diamond films. For the microcrystalline (MCD) films, the s-EFE process can be turned on at (E0)MCD = 1.9 V/μm, achieving a large s-EFE current density of (Je)MCD = 315 μA/cm2 at an applied field of 8.8 V/μm. These s-EFE properties are markedly better than those for Fe-coated/annealed ultrananocrystalline diamond (UNCD) films with (E0)UNCD = 2.0 V/μm and (Je)UNCD = 120 μA/cm2. The transmission electron microscopy showed that the nano-graphite clusters formed an interconnected network for MCD films that facilitated the electron transport more markedly, as compared with the isolated ...

A study of magnetic domain distribution in ferrite by magnetic force microscopy

In this study, vibration sample measurement (VSM) and magnetic force microscopy (MFM) have been used to observe the magnetic behavior and identify the magnetic domain distribution of NiZn ferrite, which was synthesized via chemical route and spray deposition method. Cases considered in the present study involve the types of NZF1 and NZF2 NiZn ferrite. VSM results show that the films with different deposition rate have the saturation magnetization from 200 to 900 emu/cm3, and the resistance of the film is about 1 Mohm. The ferromagnetic resonance frequency is 1 GHz approximately. MFM results show that images were also discussed the domain wall motion between the particle of NiZn ferrite, which generated the different magnetic moment direction. Therefore, MFM could obtain the relationship results between the qualitative magnetic domain structure distribution and surface morphology of two types of NiZn ferrite.