Carbon Nanotube Field Emission Electron Research Articles

Fully 3D-printed carbon nanotube field emission electron sources with in-plane gate electrode

We report the design, fabrication, and experimental characterization of the first fully additively manufactured carbon nanotube (CNT) field emission electron sources. The devices are created via direct ink writing (DIW)—one of the least expensive and most versatile additive manufacturing methods, capable of creating monolithic multi-material objects. The devices are 2.5 cm by 2.5 cm glass substrates coated with two imprints, i.e. a trace made of a CNT ink (the emitting electrode), symmetrically surrounded on both sides by a trace made of Ag microparticle ink (the in-plane extractor gate). The CNT ink is a mixture of (–COOH)-functionalized multiwalled CNTs (MWCNTs), N,N-Dimethylformamide, and ethyl cellulose. Optimization of the formulation of the CNT ink resulted in a MWCNT concentration equal to 0.82 wt% and in imprints with an electrical resistivity equal to 0.78 Ω cm. 3D-printed devices having CNT imprints with active length equal to 25 mm (a single, straight trace with 174.5 μm gap between adjacent Ag microparticle imprints) and 135 mm (a square-loop spiral with 499 μm gap between Ag microparticle adjacent imprints) were characterized in a triode configuration (i.e. using an external anode electrode) at ∼2.5 × 10–7 Torr, yielding emission currents as large as 120 μA (60 μA cm−2), start-up voltages as low as 62 V and gate transmission as high as 99%. The low-cost cold cathode technology is compatible with compact applications such as miniaturized mass spectrometry, handheld x-ray generation, and nanosatellite electric propulsion.

A vacuum-sealed miniature X-ray tube based on carbon nanotube field emitters

A vacuum-sealed miniature X-ray tube based on a carbon nanotube field-emission electron source has been demonstrated. The diameter of the X-ray tube is 10 mm; the total length of the tube is 50 mm, and no external vacuum pump is required for the operation. The maximum tube voltage reaches up to 70 kV, and the X-ray tube generates intense X-rays with the air kerma strength of 108 Gy·cm2 min−1. In addition, X-rays produced from the miniature X-ray tube have a comparatively uniform spatial dose distribution.

Development of Carbon Nanotube Field Emission Electron Source for Diagnostic X-ray Imaging

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On-chip electron-impact ion source using carbon nanotube field emitters

A lateral on-chip electron-impact ion source utilizing a carbon nanotube field emission electron source was fabricated and characterized. The device consists of a cathode with aligned carbon nanotubes, a control grid, and an ion collector electrode. The electron-impact ionization of He, Ar, and Xe was studied as a function of field emission current and pressure. The ion current was linear with respect to gas pressure from 10−4to10−1Torr. The device can operate as a vacuum ion gauge with a sensitivity of approximately 1Torr−1. Ion currents in excess of 1μA were generated.

Prospects and Limitations of Carbon Nanotube Field Emission Electron Sources

Today the most mature technology to produce gated micro field electron emitter arrays is the so-called Spindt-type metal micro-tip process. The drawbacks of the Spindt-type process are the expensive production, the critical lifetime in technical vacuum and the high operating voltages. Carbon nanotubes (CNT) can be regarded as the potential second-generation technology to Spindt-type metal micro-tips. The use of CNT as field enhancing structures in field emission electron sources can bring several advantages such as longer lifetime and operation in poor vacuum due to the high chemical inertness as well as low operation voltages and perhaps most important very low cost production techniques. In the present contribution we show that the field electron emission (FE) of CNT thin films can be accurately described by Fowler-Nordheim tunneling and that the field enhancement factor ? influences the emission properties most prominently. We have used scanning anode field emission microscopy to investigate the local field emission properties of randomly oriented carbon nanotube deposits. In the technically interesting applied electric field range of 30 V/?m an emission site density larger than 5×106 cm?2 could be measured. We will discuss however that emitter degradation at high emission currents limits the full exploitation of this high emission site density. The emission degradation becomes apparent for emission currents in the ?A range for a single emitter and the field emission I-V characteristics suggests that power dissipation due high contact or intra CNT resistance is the cause of the emitter degradation. Therefore, although the fundamental properties of CNTs are very favorable for the use as field emission tips, these properties alone will not guarantee their success in this area. Our investigations clearly show that a perfect control of the catalytic CNT growth process is needed for successful CNT field emitter technology, at least for high current applications.