Stable Field Emission Characteristics Research Articles

Stable Emission Characteristics of Low Work Function Amorphous Carbon Coated Transfer Mold Nickel Field Emitter Arrays in Harsh Environment

Low work function amorphous carbon Transfer Mold field emitter arrays (a-C-FEAs) have been fabricated by combining the Transfer Mold emitter fabrication method and the emitter material coating method to realize stable vacuum nanoelectronic devices in harsh environments of aerospace. The emitter tips of a-C-FEAs are extremely sharpened to 26.7-30.7 nm of tip radii. Work function of a-C-FEAs was as low as 3.6 eV compared with those of conventional emitter materials such as carbon nanotube of 5.0 eV. Oxygen radical flux intensity of 1015 atoms/cm2•sec was used for the evaluation of field emission characteristics, whose value is 107-108 times higher than those of 107-108 atoms/cm2•sec in aerospace of satellite orbits. As the oxygen radical treatment time increased, turn-on fields of Ni-FEAs exhibited the 2.2 times degradation from 14.9 V/µm to 32.7 V/µm. Those of a-C-FEAs have been keeping almost the same value of 20.8-23.7 V/µm after oxygen radical treatment. The a-C-FEAs exhibit stable field emission characteristics in harsh environments.

Suitability of low-work-function titanium nitride coated transfer mold field-emitter arrays for harsh environment applications

Low-work-function titanium nitride (TiN) coated transfer mold field-emitter arrays (TiN-FEAs) were fabricated by the transfer metal mold method. This method has potential for realizing stable large-area aerospace nanodevices that are resistant to the harsh plasma atmospheres often experienced by electric propulsion engines in space. Another application is for production of vacuum nanoelectronic devices such as field-emission displays that are suitable for highly oxidizing atmospheres. TiN-FEAs have sharp tips with radii of 6.8 nm, and their work function is just 3.2 eV compared to approximately 5.0 eV for conventional emitter materials such as carbon nanotubes. The turn-on fields of TiN-FEAs are as low as 15.4 V/μm, and their anode-to-emitter distance is 10 μm. Field-emission characteristics of TiN-FEAs were evaluated in situ at a pressure as high as 10−3 Pa and by irradiation with oxygen radicals at 1015 cm−2 s−1, a flux several orders of magnitude higher than orbital satellites typically experience. As the treatment time increased, the turn-on fields of TiN-FEAs changed only slightly from 15.4 to 18.8 V/μm, with no observed change in the work function during the in situ oxygen radical treatment. In summary, the TiN-FEAs exhibited stable field-emission characteristics and a high level of resistance to harsh environments.

Optical, Field-Emission, and Antimicrobial Properties of ZnO Nanostructured Films Deposited at Room Temperature by Activated Reactive Evaporation

ZnO nanostructures were deposited on flexible polymer sheet and cotton fabrics at room temperature by activated reactive evaporation. Room-temperature photoluminescence spectrum of ZnO nanostructured film exhibited a week intrinsic UV emission and a strong broad yellow-orange visible emission. TEM and HRTEM studies show that the grown nanostructures are crystalline in nature and their growth direction was identified to be along [002]. ZnO nanostructures grown on the copper-coated flexible polymer sheets exhibited stable field-emission characteristics with a threshold voltage of 2.74 V/mum (250 muA) and a very large field enhancement factor (beta) of 23,213. Cotton fabric coated with ZnO nanostructures show an excellent antimicrobial activity against Staphylococcus aureus bacteria (Gram positive), and approximately 73% reduction in the bacterial population is achieved compared to uncoated fabrics after 4 h in viability. Using a shadow mask technique, we also selectively deposited the nanostructures at room temperature on polymer substrates.

Origin of Field Emission from a Nano-Diamond/Carbon Nanowall Electron Emitter

The origin of field emission from a specific nano-diamond/carbon nanowall (ND/CNW) electron emitter, which has high and stable field emission characteristics, was examined by field emission spectromicroscopy and scanning electron microscopy. It was found that graphite sticks are present on the field emission sites of the films. Energy distribution curves of electrons field-emitted from the specified sites have the same features as those field-emitted from a metallic substance (graphite). Thus, it was concluded that graphite sticks present on the ND/CNW film are responsible for the field emission.