Vertical few-layer graphene (FLG) sheets have been fabricated by using microwave-plasma-enhanced chemical vapour deposition. Their shape was manipulated through adjusting the growth time and hydrocarbon gas ratio. The growth mechanism during different growth stages is discussed. The field emission characteristics for different FLG shapes were tested and found to be strongly influenced by the tip shape, the height and the amorphous carbon content. The optimal shape of vertical FLG for field emission had fewer layers, sharp corners, large height and was free of amorphous carbon. The best field emission properties with the optimal shape were observed with a turn-on field of 1:8 V μm(-1) and maximum current density of 7 mA cm(-2).

Gigahertz to terahertz radiation sources based on cold-cathode vacuum electron technology are pursued, because its unique characteristics of instant switch-on and power saving are important to military and space applications. Gigahertz gyrotron was reported using carbon nanotube (CNT) cold-cathode. It is reported here in first time that a fully-sealed CNT cold-cathode 0.22 THz-gyrotron is realized, typically with output power of 500 mW. To achieve this, we have studied mechanisms responsible for CNTs growth on curved shape metal surface, field emission from the sidewall of a CNT, and crystallized interface junction between CNT and substrate material. We have obtained uniform growth of CNTs on and direct growth from cone-cylinder stainless-steel electrode surface, and field emission from both tips and sidewalls of CNTs. It is essential for the success of a CNT terahertz gyrotron to have such high quality, high emitting performance CNTs. Also, we have developed a magnetic injection electron gun using CNT cold-cathode to exploit the advantages of such a conventional gun design, so that a large area emitting surface is utilized to deliver large current for electron beam. The results indicate that higher output power and higher radiation frequency terahertz gyrotron may be made using CNT cold-cathode electron gun.

A single baffle metal–insulator–metal (MIM) waveguide coupled with a semi-circular cavity and a cross-shaped cavity is proposed based on the multiple Fano resonance characteristics of surface plasmon polaritons (SPPs) subwavelength structure. The isolated state formed by two resonators interferes with the wider continuous state mode formed by the metal baffle, forming Fano resonance that can independently be tuned into five different modes. The formation mechanism of Fano resonance is analyzed based on the multimode interference coupled mode theory (MICMT). The finite element method (FEM) and MICMT are used to simulate the transmission spectra of this structure and analyze the influence of structural parameters on the refractive index sensing characteristics. And the transmission responses calculated by the FEM simulation are consistent with the MICMT theoretical results very well. The results show that the figure of merit (FOM) can reach 193 and the ultra-high sensitivity is 1600 nm/RIU after the structure parameters have been optimized, and can provide theoretical basis for designing the high sensitive refractive index sensors based on SPPs waveguide for high-density photonic integration with excellent performance in the near future.

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Study of high-brightness flat-panel lighting source using carbon-nanotube cathodeThe authors investigated a full sealed flat-panel light source, which is based on a triode structure with a metal mesh gate electrode and uses a carbon nanotube cold cathode. It has a flat surface luminance distribution with good uniformity, a stable luminance of 12 000 cd/ m 2 , and a luminous efficiency that was measured to be 14.5 lm/ W. It also shows a high color rendering index of 88 and a wide optical emission spectrum. Further, its application as thin film transistor-liquid-crystal display ͑TFT-LCD͒ backlight was demonstrated and the resulted performance of the TFT-LCD display was studied and compared to the commercial TFT-LCD products, which use the cold-cathode fluorescent lamp backlight and light emitting diode backlight. It is shown that the light transmission ratio in the TFT-LCD module using our light source is ϳ8%, as compared to ϳ4% of the commercial products. With this and the very high luminance, our light source is very useful to the situation, in which the TFT-LCD screen is employed to work under outdoor sunshine conditions.