A vacuum-sealed compact x-ray tube based on focused carbon nanotube field-emission electrons

Abstract

We report on a fully vacuum-sealed compact x-ray tube based on focused carbon nanotube (CNT) field-emission electrons for various radiography applications. The specially designed two-step brazing process enabled us to accomplish a good vacuum level for the stable and reliable operation of the x-ray tube without any active vacuum pump. Also, the integrated focusing electrodes in the field-emission electron gun focused electron beams from the CNT emitters onto the anode target effectively, giving a small focal spot of around 0.3 mm with a large current of above 50 mA. The active-current control through the cathode electrode of the x-ray tube led a fast digital modulation of x-ray dose with a low voltage of below 5 V. The fabricated compact x-ray tube showed a stable and reliable operation, indicating good maintenance of a vacuum level of below 5 × 10(-6) Torr and the possibility of field-emission x-ray tubes in a stand-alone device without an active pumping system.

RETRACTED ARTICLE: Flexible Field Emitter for X-ray Generation by Implanting CNTs into Nickel Foil

“…As the emitter was fixed in a “cap,” the electric field between cathode and anode was complex. The X-ray tube can be operated under a relatively low voltage compared with other works [20–22]. A round badge with a thickness of 100 μm and diameter of 3 mm was put in front of the sensitive plate in order to create a defined pattern when exposed to radiation, the shadow of the aperture thus unequivocally confirms the X-ray emission.…”

Electrostatic Focusing Lens Module With Large Focusing Capability in Carbon Nanotube Emitter-Based X-Ray Sources

“…The CNT field emitters have 112 dots with diameters of 0.2 mm within a 10 mm × 1.6 mm rectangular area on a Kovar substrate [9]. The CNT cathode and the gate mesh are well aligned with a gap of 0.2 mm to avoid a gate leakage current inducing unstable operation [10].…”

“…The anode with a 0.1-mm-thick W target which is at an angle of 15°from the horizontal plane, is carefully aligned with the macro-FL at a distance of 24 mm. The FL module along with the CNT cathode and the anode target are integrated with an Al 2 O 3 ceramic by brazing at 715°C [9], thus producing a fully vacuum-sealed CNT X-ray tube, as shown in Fig. 1 The e-beam trajectories, even those from the outermost holes of the micro-FL, converge in the macro-FL and then they are focused onto the anode target.…”

Outstanding field emission properties of wet-processed titanium dioxide coated carbon nanotube based field emission devices

“…The high-performance solution-processed composite cathode demonstrates great potential application in vacuum electronic devices. Field emission (FE) of electrons from nanomaterials has attracted widespread attention in the past twenty years in light of potential applications in vacuum electronic devices, such as field emission displays, 1,2 X-ray sources, [3][4][5] and microwave devices. 6,7 Carbon nanotubes (CNTs) with unique properties of high aspect ratio, low work function, high mechanical strength, and thermal conductivity [8][9][10][11] have been intensively investigated as the cathode materials for the electron emission.…”

“…6,7 Carbon nanotubes (CNTs) with unique properties of high aspect ratio, low work function, high mechanical strength, and thermal conductivity [8][9][10][11] have been intensively investigated as the cathode materials for the electron emission. [1][2][3][4][5] To improve the FE performance of CNT cathodes, several techniques of controlling the emitter morphology have been developed, including optimization of the CNT density aiming at reduction of the field-screening effect, 12 increase of the emitter sharpness to achieve high electric field enhancement factor, 13,14 and preparation of vertically aligned CNT arrays to increase the number of effective emission tips. [15][16][17] On the other hand, composite CNT cathodes by doping or attaching CNTs with metal nanoparticles or metal oxide thin films have been demonstrated to greatly improve the FE performance.…”