Improved field emission properties of carbon nanotube cathodes by nickel electroplating and corrosion

Carbon nanotube（CNT） cathodes prepared by electrophoretic deposition were treated by a combination of nickel electroplating and cathode corrosion technologies.The characteristics of the samples were measured by scanning electron microscopy,energy dispersive X-ray spectroscopy,J-E and F-N plots.After the treatment,the CNT cathodes showed improved field emission properties such as turn-on field,threshold electric field,current density,stability and luminescence uniformity.Concretely,the turn-on field decreased from 0.95 to 0.45 V/μm at an emission current density of 1 mA/cm^2,and the threshold electric field decreased from 0.99 to 0.46 V/μm at a current density of 3 mA/cm^2.The maximum current density was up to 7 mA/cm2 at a field of 0.48 V/μm.In addition,the current density of the CNT cathodes fluctuated at around 0.7 mA/cm^2 for 20 h,with an initial current density 0.75 mA/cm^2.The improvement in field emission properties was found to be due to the exposure of more CNT tips,the wider gaps among the CNTs and the infiltration of nickel particles.

Field emission digital display tube with nano-graphite film cathode

The field emission digital display tube with a nano-crystalline graphite cold cathode is designed and fabricated. Under the control of the driving circuits, a dynamic digital display with uniform luminance distribution is realized. The luminance of the character segments is 190 cd/m2 at the operating voltage of 900 V. And the stable emission is attained with a fluctuation of about 3% at an average segment current of 75 μA. The results demonstrate that nano-crystalline graphite film is a promising material for cold cathode.

FePO4-coated Li[Li0.2Ni0.13Co0.13Mn0.54]O2 with improved cycling performance as cathode material for Li-ion batteries

Li[Li0.2Ni0.13Coo.13Mn0.54]O2 cathode materials were synthesized by carbonate-based co-precipitation method, and then, its surface was coated by thin layers of FePO4. The prepared samples were characterized by X-ray diffraction （XRD）, field emission scanning electron micro- scope （FESEM）, energy-dispersive spectroscopy （EDS）, and transmission electron microscopy （TEM）. The XRD and TEM results suggest that both the pristine and the coated materials have a hexagonal layered structure, and the FePO4 coating layer does not make any major change in the crystal structure. The FePO4-coated sample exhibits both improved initial discharge capacity and columbic efficiency compared to the pristine one. More significantly, the FePO4 coating layer has a much positive influence on the cycling perfor- mance. The FePO4-coated sample exhibits capacity reten- tion of 82 % after 100 cycles at 0.5℃ between 2.0 and 4.8 V, while only 28 % for the pristine one at the same charge-discharge condition. The electrochemical impe- dance spectroscopy （EIS） results indicate that this improved cycling performance could be ascribed to the presence of FePO4 on the surface of Li[Li0.2Ni0.13Co0.13Mno.54102 par- ticle, which helps to protect the cathode from chemical attacks by HF and thus suppresses the large increase in charge transfer resistance.

Transmission-mode GaN photocathode based on graded Al_xGa_(1-x)N buffer layer

We create a GaN photocathode based on graded AlxGa1-xN buffer layers to overcome the influence of buffer-emission layer interface on the photoemission of transmission-mode GaN photocathodes. A gate- shaped spectral response with a 260-nm starting wavelength and a 375-nm cut-off wavelength is obtained. Average quantum efficiency is 15% and short wavelength responses are almost equivalent to long wavelength ones. The fitted interface recombination velocity is 5×10^4 cm/s, with negligible magnitude, proving that the design of the graded buffer layers is efficient in obtaining good interface quality between the buffer and the emission laver.