IEEE TRANSACTIONS ON ELECTRON DEVICES, VOL. 66, NO. 12, DECEMBER 2019 5301 Design and Fabrication of CNT-Based E-Gun Using Stripe-Patterned Alloy Substrate for X-Ray Applications Jongmin Lim, Amar P. Gupta, Seung Jun Yeo, Mallory Mativenga , Moonkyoo Kong, Chong-Gil Cho, Jeung Sun Ahn, Seung Hoon Kim, and Jehwang Ryu Abstract — We report the enhancement of carbon nanotube (CNT) field emitters by growing them directly on stripe-patterned alloy substrates. For a gate voltage of 1300 V, CNT field emitters grown on full and stripe- patterned alloy substrates achieved respective emission currents of 0.22 and 2.32 mA, corresponding to tenfold performance enhancement. Performance enhancement is attributed to the reduced screening effect (as a result of the spacing between strips) during field emission and a damage-free patterning process. To verify the ability of the stripe-patterned CNT field emitters to generate X-rays, we designed and assembled an electron gun through brazing. With the open type X-ray system, an X-ray image of human teeth was successfully obtained, verifying the potential of the stipe-patterned CNT emitters in X-ray applications. Index Terms— Carbon nanotube (CNT), field emission, X-ray. I. I NTRODUCTION C ARBON nanotube (CNT) field emitters have enormous potential in many different areas, particularly in X-ray technology, where CNT-based emitters provide many new possibilities in vacuum electronic devices [1]–[3]. The CNT- based X-ray system has many advantages because of CNT‘s superior electrical and mechanical characteristics [4]. It is hard to achieve pulsed X-ray radiation with filament X-ray sources based on thermionic emission because of their long Manuscript received August 19, 2019; revised September 18, 2019; accepted September 23, 2019. Date of publication October 17, 2019; date of current version November 27, 2019. This work was supported in part by the National Research Foundation of Korea (NRF) grants funded by the Korean Government (MSIP) under Grant NRF-2018M3A9E9024942. The review of this article was arranged by Editor M Blank. (Corresponding author: Mallory Mativenga; Jehwang Ryu.) J. Lim, A. P. Gupta, S. J. Yeo, J. S. Ahn, and J. Ryu are with the Department of Physics, Kyung Hee University, Seoul 02447, South Korea (e-mail: jhryu@khu.ac.kr). M. Mativenga is with the Department of Information Display, Kyung Hee University, Seoul 02447, South Korea (e-mail: mallory@tft.khu.ac.kr). M. Kong is with the Department of Radiation Oncology, Kyung Hee University Medical Center, Kyung Hee University School of Medicine, Seoul 02447, South Korea. C.-G. Cho is with CAT Beam Tech. Co. Ltd., Seoul 02455, South Korea. S. H. Kim is with the Department of Radiology, Asan Medical Center, University of Ulsan College of Medicine, Seoul 05505, South Korea. Color versions of one or more of the figures in this article are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TED.2019.2943870 response time and high operating temperature. On the contrary, CNT field emitters can be swiftly turned on and off, allowing the generation of the pulsed emission. In addition, electron extraction from CNTs for X-ray radiation is possible at room temperature, allowing the formation of cold cathode X-ray sources [5]–[9]. During the growth of CNTs by chemical vapor deposition (CVD), it is important to select the type of substrate (e.g., silicon or metal substrate) and pretreatment process [10], [11]. The advantage of a metal substrate over silicon is its excellent electrical conductivity. Since CNTs can be directly grown on a metal substrate without external catalyst, the adher- ence between CNTs and substrate is greatly enhanced [12]. Furthermore, the synthesis of CNTs is easy to handle and process on metal substrates. In particular, the formation of holes on metal substrates can be easily achieved by simple acid etching treatments, thus enabling the formation of patterned field emitters. One of the major challenges in field emission is the screening effect, which arises when the spacing between CNTs is too small. Patterning of field emitters thus prevents the screening effect in field emission, consistent with many studies, which suggest that field emission properties of CNTs are strongly related to the shape of the emitter [13], [14]. This has necessitated the patterning of CNTs on metal substrates through photolithography in some studies [15]. In this article, instead of having to pattern the CNTs through photolithography, we explore the patterning of the metal alloy substrate into strips through a simple and inex- pensive acid etching process. Given that the etching process is performed on the substrate before CNT growth, the CNTs are expected to be damage-free, and hence, exhibit better field emission properties compared to those in previous studies. To test the application of the stripe-patterned CNT emitters in X-ray imaging, we self-design and assemble an electron gun ( E -gun) employing the stripe-patterned CNT emitters developed herein and capture an image of human teeth. II. EXPERIMENT CNTs were synthesized by thermal CVD (TCVD) on a metal alloy substrate, YEF-426, consisting of 42% nickel, 6% chromium, and 52% iron [Fig. 1(a)]. The strips that are 56-μm-wide with 142-μm spacing were achieved by acid etching with FeCl 3 [Fig. 1(b)]. Inside the chamber, the pres- sure was maintained at 10 −6 torr to prevent oxidation, and the chamber was heated up to 900 ◦ C. When the desired 0018-9383 © 2019 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. 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