Cerium dioxide, CeO2, is a potentially superior material in a myriad of areas, and many methods have been proposed to deposit single crystal CeO2 thin films. A novel fabrication technique utilizing dual plasma generat...Cerium dioxide, CeO2, is a potentially superior material in a myriad of areas, and many methods have been proposed to deposit single crystal CeO2 thin films. A novel fabrication technique utilizing dual plasma generated by metal vacuum arc (MEVVA) and radio frequency (RF) is discussed in this paper. We have recently conducted a systematic investigation to determine the optimal process window to deposit CeO2 thin films'on Si(100) substrates. The X-ray diffraction results show the existence of CeO2(100) in the as-deposited sample.展开更多
Hydrogenated nanocrystalline silicon carbide （SIC） thin films were deposited on the single-crystal silicon substrate using the helicon wave plasma enhanced chemical vapor deposition （HW-PECVD） technique. The influ...Hydrogenated nanocrystalline silicon carbide （SIC） thin films were deposited on the single-crystal silicon substrate using the helicon wave plasma enhanced chemical vapor deposition （HW-PECVD） technique. The influences of magnetic field and hydrogen dilution ratio on the structures of SiC thin film were investigated with the atomic force microscopy （AFM）, the Fourier transform infrared absorption （FTIR） and the transmission electron microscopy （TEM）. The results indicate that the high plasma activity of the helicon wave mode proves to be a key factor to grow crystalline SiC thin films at a relative low substrate temperature. Also, the decrease in the grain sizes from the level of microcrystalline to that of nanocrystalline can be achieved by increasing the hydrogen dilution ratios. Transmission electron microscopy measurements reveal that the size of most nanocrystals in the film deposited under the higher hydrogen dilution ratios is smaller than the doubled Bohr radius of 3C-SiC （approximately 5.4 nm）, and the light emission measurements also show a strong blue photoluminescence at the room temperature, which is considered to be caused by the quantum confinement effect of small-sized SiC nanocrystals.展开更多
Here we develop a two-dimensional numerical model of wire and arc additive manufacturing(WAAM)to determine the relationship between process parameters and deposition geometry,and to reveal the influence mechanism of p...Here we develop a two-dimensional numerical model of wire and arc additive manufacturing(WAAM)to determine the relationship between process parameters and deposition geometry,and to reveal the influence mechanism of process parameters on deposition geometry.From the predictive results,a higher wire feed rate matched with a higher current could generate a larger and hotter droplet,and thus transfer more thermal and kinetic energy into melt pool,which results in a wider and lower deposited layer with deeper penetration.Moreover,a higher preheat temperature could enlarge melt pool volume and thus enhance heat and mass convection along both axial and radial directions,which gives rise to a wider and higher deposited layer with deeper penetration.These findings offer theoretical guidelines for the acquirement of acceptable deposition shape and optimal deposition quality through adjusting process parameters in fabricating WAAM components.展开更多
Plasma treatments of boron-doped nano-crystalline diamond （NCD） thin films were carried out in order to improve their electrical properties of the films. Boron-doped NCD thin films were fabricated on well polished p...Plasma treatments of boron-doped nano-crystalline diamond （NCD） thin films were carried out in order to improve their electrical properties of the films. Boron-doped NCD thin films were fabricated on well polished poly-crystalline diamond （PCD） thick films in a microwave plasma enhanced chemical vapor deposition （MPCVD） reactor, then they were processed in methane, ar- gon, hydrogen and B2H~ （0.1% diluted by H~） plasmas, respectively. Scanning electron microscopy （SEM） and atomic force microscope （AFM） results show that the surface morphology changed lit- tle during the 10 min treatment. Secondary ion mass spectroscopy （SIMS） results indicate that B2H6 plasma was efficient for increasing boron concentration in NCD films, while the carrier anal- yses demonstrates that CH4 plasma processing was effective to activate the dopants and resulted in good electrical properties.展开更多
为了优化Inconel 625合金快速成型零件的组织和力学性能,分析了不同工艺参数对脉冲等离子弧快速成型的沉积态组织,研究其影响规律,重点分析了工艺参数对沉积态组织中的枝晶形态、相的种类、尺寸及分布特征等的影响,同时评价了在不同线...为了优化Inconel 625合金快速成型零件的组织和力学性能,分析了不同工艺参数对脉冲等离子弧快速成型的沉积态组织,研究其影响规律,重点分析了工艺参数对沉积态组织中的枝晶形态、相的种类、尺寸及分布特征等的影响,同时评价了在不同线能量条件下沉积态组织的生长连续性。结果表明,随着峰值电流的提高,组织会逐渐由胞状晶转变为树枝晶,且枝晶间距也随之不断增大,而Laves相的尺寸以及数量都会随之变大;同时成型速度也会对沉积态组织产生影响,其影响规律与峰值电流相反。当线能量密度P/V不超过18 k W·min/m时,其组织主要是细小的胞状晶,并且多层的沉积组织没有出现明显的转变层,组织为连续的柱状晶形态,但线能量密度P/V达到36 k W·min/m时,组织为粗大的树枝晶形态。层层之间出现明显的转变,组织为不连续柱状晶形态,同时析出相Laves在转变层枝晶间隙大量析出,组织出现严重的元素偏析。展开更多
基金The work was supported by Hong Kong RGC CERG9040344 and 9040412, RGC / Germany Joint Schemes9050084 and 9050150, and CityU S
文摘Cerium dioxide, CeO2, is a potentially superior material in a myriad of areas, and many methods have been proposed to deposit single crystal CeO2 thin films. A novel fabrication technique utilizing dual plasma generated by metal vacuum arc (MEVVA) and radio frequency (RF) is discussed in this paper. We have recently conducted a systematic investigation to determine the optimal process window to deposit CeO2 thin films'on Si(100) substrates. The X-ray diffraction results show the existence of CeO2(100) in the as-deposited sample.
基金Natural Science Foundation of Hebei Province, China (503129 and E2006000999)
文摘Hydrogenated nanocrystalline silicon carbide （SIC） thin films were deposited on the single-crystal silicon substrate using the helicon wave plasma enhanced chemical vapor deposition （HW-PECVD） technique. The influences of magnetic field and hydrogen dilution ratio on the structures of SiC thin film were investigated with the atomic force microscopy （AFM）, the Fourier transform infrared absorption （FTIR） and the transmission electron microscopy （TEM）. The results indicate that the high plasma activity of the helicon wave mode proves to be a key factor to grow crystalline SiC thin films at a relative low substrate temperature. Also, the decrease in the grain sizes from the level of microcrystalline to that of nanocrystalline can be achieved by increasing the hydrogen dilution ratios. Transmission electron microscopy measurements reveal that the size of most nanocrystals in the film deposited under the higher hydrogen dilution ratios is smaller than the doubled Bohr radius of 3C-SiC （approximately 5.4 nm）, and the light emission measurements also show a strong blue photoluminescence at the room temperature, which is considered to be caused by the quantum confinement effect of small-sized SiC nanocrystals.
基金supported by National Natural Science Foundation of China(Nos.52077172,U1966602)Shaanxi Province‘Sanqin scholar-s’Innovation Team Project(Key technology of advanced DC power equipment and its industrialization demonstration innovation team of Xi’an Jiaotong University)。
文摘Here we develop a two-dimensional numerical model of wire and arc additive manufacturing(WAAM)to determine the relationship between process parameters and deposition geometry,and to reveal the influence mechanism of process parameters on deposition geometry.From the predictive results,a higher wire feed rate matched with a higher current could generate a larger and hotter droplet,and thus transfer more thermal and kinetic energy into melt pool,which results in a wider and lower deposited layer with deeper penetration.Moreover,a higher preheat temperature could enlarge melt pool volume and thus enhance heat and mass convection along both axial and radial directions,which gives rise to a wider and higher deposited layer with deeper penetration.These findings offer theoretical guidelines for the acquirement of acceptable deposition shape and optimal deposition quality through adjusting process parameters in fabricating WAAM components.
基金supported by the Research Fund of Hubei Provincial Department of Education of China (No.Q20081505)
文摘Plasma treatments of boron-doped nano-crystalline diamond （NCD） thin films were carried out in order to improve their electrical properties of the films. Boron-doped NCD thin films were fabricated on well polished poly-crystalline diamond （PCD） thick films in a microwave plasma enhanced chemical vapor deposition （MPCVD） reactor, then they were processed in methane, ar- gon, hydrogen and B2H~ （0.1% diluted by H~） plasmas, respectively. Scanning electron microscopy （SEM） and atomic force microscope （AFM） results show that the surface morphology changed lit- tle during the 10 min treatment. Secondary ion mass spectroscopy （SIMS） results indicate that B2H6 plasma was efficient for increasing boron concentration in NCD films, while the carrier anal- yses demonstrates that CH4 plasma processing was effective to activate the dopants and resulted in good electrical properties.
文摘为了优化Inconel 625合金快速成型零件的组织和力学性能,分析了不同工艺参数对脉冲等离子弧快速成型的沉积态组织,研究其影响规律,重点分析了工艺参数对沉积态组织中的枝晶形态、相的种类、尺寸及分布特征等的影响,同时评价了在不同线能量条件下沉积态组织的生长连续性。结果表明,随着峰值电流的提高,组织会逐渐由胞状晶转变为树枝晶,且枝晶间距也随之不断增大,而Laves相的尺寸以及数量都会随之变大;同时成型速度也会对沉积态组织产生影响,其影响规律与峰值电流相反。当线能量密度P/V不超过18 k W·min/m时,其组织主要是细小的胞状晶,并且多层的沉积组织没有出现明显的转变层,组织为连续的柱状晶形态,但线能量密度P/V达到36 k W·min/m时,组织为粗大的树枝晶形态。层层之间出现明显的转变,组织为不连续柱状晶形态,同时析出相Laves在转变层枝晶间隙大量析出,组织出现严重的元素偏析。
