- Nano Express
- Open Access
High Current Emission from Patterned Aligned Carbon Nanotubes Fabricated by Plasma-Enhanced Chemical Vapor Deposition
© Cui et al. 2015
- Received: 16 October 2015
- Accepted: 7 December 2015
- Published: 15 December 2015
Vertically, carbon nanotube (CNT) arrays were successfully fabricated on hexagon patterned Si substrates through radio frequency plasma-enhanced chemical vapor deposition using gas mixtures of acetylene (C2H2) and hydrogen (H2) with Fe/Al2O3 catalysts. The CNTs were found to be graphitized with multi-walled structures. Different H2/C2H2 gas flow rate ratio was used to investigate the effect on CNT growth, and the field emission properties were optimized. The CNT emitters exhibited excellent field emission performance (the turn-on and threshold fields were 2.1 and 2.4 V/μm, respectively). The largest emission current could reach 70 mA/cm2. The emission current was stable, and no obvious deterioration was observed during the long-term stability test of 50 h. The results were relevant for practical applications based on CNTs.
Field emission is a quantum mechanical tunneling phenomenon. Electrons in the materials can emit into vacuum from solid surface which is determined by the strength of local electric field and potential barrier to emission. Field emission occurs from a cold cathode at room temperature which is more power efficient than thermionic emission . Field emission is widely used in many kinds of vacuum electronic applications such as flat panel displays, microwave power tubes, electron sources, and electron-beam lithography. However, high local filed is required to obtain useful current. In order to reduce the extraction voltage, field emitters with sharp protruding microstructures can be used such as Spindt tip cathodes [2, 3], silicon tips [4, 5], and carbon-based materials [6–9]. Carbon nanotube (CNT) has been recognized as an ideal candidate material for field emission applications due to its unique structure and remarkable mechanical, electrical, and chemical stability. Furthermore, the small tip radius and high aspect ratio of CNT can result in electron emission at extraordinary low-threshold electric field and obtain a high-field enhancement factor. Since the first field emission behavior of CNT reported in 1995, many works showed that the CNT emitters exhibited excellent field emission properties [10–15].
The electron emission of CNTs is originated from the tip of the nanotubes because the electrons located at the tips can easily participate in the field emission [16, 17]. Furthermore, the aligned CNTs with uniform length exhibit better field emission properties than random arrangement ones . The CNT arrays can fulfill the requirements for field emission and manipulated as field emission devices directly. Thus, CNTs had better be vertically aligned and oriented toward an anode. Vertically aligned CNTs can be synthesized by chemical vapor deposition methods (CVD). The CVD methods are ideally suited to prepare CNT films on various substrates, and the process can be assisted by microwave of radio frequency plasma [19–22].
As CNTs are capable of emitting efficient high currents, they are potential as emitters in various devices [23, 24]. But nevertheless, the emission densities and short emission lifetimes present obstacles for the practically available electron field emitters based on CNTs. The challenge is to improve the field emission properties of CNTs. It is found that the applied external field is strongly screened when the spacing distance is shorter than the length of the carbon nanotubes . In order to reduce the screen effect, patterning CNT is an efficient method. In this work, the CNT emitters were fabricated using radio frequency plasma-enhanced chemical vapor deposition (PECVD) method on patterned Si substrate. The vertically aligned CNT arrays showed good field emission properties with high emission current and ultra-long-term emission stability which were better than other reported patterned vertical CNTs [26–28].
The surface morphology of samples was observed by FESEM (JSM-6701 F). A transmission electron microscopy (TEM, F-30) with an accelerating voltage of 200 kV was used to characterize the microstructure of CNTs. The microstructure was also investigated by micro-Raman spectroscopy (JY-HR800 spectrometer, the excitation wavelength of 532 nm). The field emission characteristics of the films were measured in a chamber with high vacuum better than 5 × 10−6 Pa using a parallel-plate-electrode configuration. The distance between anode and cathode was adjusted to 300 μm using a spiral micrometer. The current-voltage (I–V) characteristics were obtained by LabVIEW program through a Keithley 248 power source with a computer-controlled data-acquisition card.
Results and Discussion
The emission stability of a field emission electron source is one of the key factors that affect its potential application in vacuum electronic devices. The J-E curves can only show transitory field emission phenomenon in a short time and cannot reflect the field emission behavior sufficiently. Figure 5d showed the looping testing of the CNTs. The anode voltage was increased or decreased by 30 V/step. Seen from loop testing with increased and decreased voltage between 1.5 and 3.5 V μm−1 for 25 loops, there is no obvious deterioration of the maximum current density. Before the looping testing with maximum current of about 20 mA/cm2, the current density of 10 mA/cm2 was also tested with no deterioration. Figure 5e displayed the typical J-E curves for different loops of the loop testing. The current density was relatively stable both in the increased and decreased voltage processes. During the increased or decreased voltage process of the field emission testing, desorption and adsorption of the gas molecules will change the work function of CNT and probably lead to a phenomenon of hysteresis [9, 44]. The hysteresis was unnoticeable in this work indicated that desorption and adsorption may reach an equilibrium state. Furthermore, the long-term test of the sample exhibited good stability for 50 h (Fig. 5f). When ionization vacuum gauge was opened, the emission current increased abruptly during the stability test as shown in the arrow pointed position of Fig. 5f. The conditions in vacuum chamber and the surface state of CNT emitters may change in testing process which resulted in the rising of emission current. All these achievements underlined the potential of CNT emitters in applications.
In summary, the vertically aligned CNTs were synthesized on patterned substrates by PECVD. The field emission properties of CNTs were optimized with different H2/C2H2 mixture ratios. The CNTs exhibited excellent field emission characteristics with high current density and good emission stability. In order to achieve practically available electron field emitters based on CNTs, we should still focus on the enhancement of electron emission density and the structure design.
This work was financially supported by the Natural Science Foundation of China (Nos. 21473153 and 51002161), the Natural Science Foundation of Hebei Province (No. B2013203108), the Science Foundation for the Excellent Youth Scholars from Universities and Colleges of Hebei Province (No. YQ2013026), the Support Program for the Top Young Talents of Hebei Province, the China Postdoctoral Science Foundation (No. 2015 M580214), and the Scientific and Technological Research and Development Program of Qinhuangdao City (No. 201502A006).
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- Milne WI, Teo KBK, Amaratunga GAJ, Legagneux P, Gangloff L, Schnell JP, Semet V, Thien Binh V, Groening O (2004) Carbon nanotubes as field emission sources. J Mater Chem 14:933–943View ArticleGoogle Scholar
- Spindt CA (1968) A thin film field emission cathode. J Appl Phys 39:3504–3505View ArticleGoogle Scholar
- Spindt CA, Brodie I, Humphrey L, Westerberg ER (1976) Physical properties of thin film field emission cathodes with molybdenum cones. J Appl Phys 47:5248–5263View ArticleGoogle Scholar
- Au FCK, Wong KW, Tang YH, Zhang YF, Bello I, Lee ST (1999) Electron field emission from silicon nanowires. Appl Phys Lett 75:1700–1702View ArticleGoogle Scholar
- She JC, Deng SZ, Xu NS, Yao RH, Chen J (2006) Fabrication of vertically aligned Si nanowires and their application in a gated field emission device. Appl Phys Lett 88:013112–013113View ArticleGoogle Scholar
- Chuang FY, Sun CY, Chen TT, Lin IN (1996) Local electron field emission characteristics of pulsed laser deposited diamondlike carbon films. Appl Phys Lett 69:3504–3506View ArticleGoogle Scholar
- Zhu W, Kochanski GP, Jin S (1998) Low-field electron emission from undoped nanostructured diamond. Science 282:1471–1473View ArticleGoogle Scholar
- Li J, Chen JT, Shen BS, Yan XB, Xue QJ (2011) Temperature dependence of the field emission from the few-layer graphene film. Appl Phys Lett 99:163103–3View ArticleGoogle Scholar
- Chen JT, Li J, Yang J, Yan XB, Tay BK, Xue QJ (2011) The hysteresis phenomenon of the field emission from the graphene film. Appl Phys Lett 99:173104–3View ArticleGoogle Scholar
- Fan SS, Chapline MG, Franklin NR, Tombler TW, Cassell AM, Dai HJ (1999) Self-oriented regular arrays of carbon nanotubes and their field emission properties. Science 283:512–514View ArticleGoogle Scholar
- de Heer WA, Chatelain A, Ugarte D (1995) A carbon nanotube field emission electron source. Science 270:1179–1180View ArticleGoogle Scholar
- Bonard JM, Kindb H, Stöcklic T, Nilssona LO (2001) Field emission from carbon nanotubes: the first five years. Solid State Electron 45:893–914View ArticleGoogle Scholar
- Lee J, Jung Y, Song J, Kim JS, Lee GW, Jeong HJ, Jeong Y (2012) High-performance field emission from a carbon nanotube carpet. Carbon 50:3889–3896View ArticleGoogle Scholar
- Lahiri I, Wong J, Zhou Z, Choi W (2012) Ultra-high current density carbon nanotube field emitter structure on three-dimensional micro-channeled copper. Appl Phys Lett 101:063110–063115View ArticleGoogle Scholar
- Sridhar S, Tiwary C, Vinod S, Taha-Tijerina JJ, Sridhar S, Kalaga K, Sirota B, Hart AHC, Ozden S, Sinha RK, Harsh, Vajtai R, Choi W, Korda´s K, Ajayan PM (2014) Field emission with ultralow turn on voltage from metal decorated carbon nanotubes. ACS Nano 8:7763–7770View ArticleGoogle Scholar
- Wey Y, Weng D, Yang Y, Zhang X, Jiang K, Liu L, Fan SS (2006) Efficient fabrication of field electron emitters from the multiwalled carbon nanotube yarns. Appl Phys Lett 89:063101–063103View ArticleGoogle Scholar
- Jang HS, Jeon SK, Nahm SH (2010) Field emission properties from the tip and side of multi-walled carbon nanotube yarns. Carbon 48:4019–4023View ArticleGoogle Scholar
- Jang YT, Choi CH, Ju BK, Ahn JH, Lee YH (2003) Fabrication and characteristics of field emitter using carbon nanotubes directly grown by thermal chemical vapor deposition. Thin Solid Films 436:298–302View ArticleGoogle Scholar
- Lee CJ, Kim DW, Lee TJ, Choi YC, Park YS, Lee YH, Choi WB, Lee NS, Park GS, Kim JM (1999) Synthesis of aligned carbon nanotubes using thermal chemical vapor deposition. Chem Phys Lett 312:461–468View ArticleGoogle Scholar
- Park D, Kim YH, Lee JK (2003) Synthesis of carbon nanotubes on metallic substrates by a sequential combination of PECVD and thermal CVD. Carbon 41:1025–1029View ArticleGoogle Scholar
- Meyyappan M, Delzeit L, Cassell A, Hash D (2003) Carbon nanotube growth by PECVD: a review. Plasma Sources Sci Technol 12:205–216View ArticleGoogle Scholar
- Lee DH, Lee WJ, Kim SO (2009) Highly efficient vertical growth of wall-number-selected, N-doped carbon nanotube arrays. Nano Lett 9:1427–1432View ArticleGoogle Scholar
- Choi WB, Chung DS, Kang JH, Kim HY, Jin YW, Han IT, Lee YH, Jung JE, Lee NS, Park GS, Kim JM (1999) Fully sealed, high-brightness carbon-nanotube field emission display. Appl Phys Lett 75:3129–3131View ArticleGoogle Scholar
- Saito Y, Uemura S (2000) Field emission from carbon nanotubes and its application to electron sources. Carbon 38:169–182View ArticleGoogle Scholar
- Chen GH, Wang WL, Peng J, He CS, Deng SZ, Xu NS, Li ZB (2007) Screening effects on field emission from arrays of (5,5) carbon nanotubes: quantum mechanical simulations. Phys Rev 76:195412–195416View ArticleGoogle Scholar
- Shahi M, Gautam S, Shah PV, Jha P, Kumar P, Rawat JS, Chaudhury PK, Harsh, Tandon RP (2013) Effect of purity, edge length, and growth area on field emission of multi-walled carbon nanotube emitter arrays. J Appl Phys 113:204304–204306View ArticleGoogle Scholar
- Huang YJ, Chang HY, Chang HC, Shih YT, Su WJ, Ciou CH, Chen YL, Honda S, Huang YS, Lee KY (2014) Field emission characteristics of vertically aligned carbon nanotubes with honeycomb configuration grown onto glass substrate with titanium coating. Mater Sci Eng B 182:14–20View ArticleGoogle Scholar
- Hung YJ, Huang YJ, Chang HC, Lee KY, Lee SL (2014) Patterned growth of carbon nanotubes over vertically aligned silicon nanowire bundles for achieving uniform field emission. Nanoscale Res Lett 9:540–547View ArticleGoogle Scholar
- Yun Y, Shanov V, Tu Y, Subramaniam S, Schulz MJ (2006) Growth mechanism of long aligned multiwall carbon nanotube arrays by water-assisted chemical vapor deposition. J Phys Chem B 110:23920–23925View ArticleGoogle Scholar
- Choi YC, Shin YM, Bae DJ, Lim SC, Lee YH, Lee BS (2001) Patterned growth and field emission properties of vertically aligned carbon nanotubes. Diam Relat Mater 10:1457–1464View ArticleGoogle Scholar
- Choi YC, Shin YM, Lee YH, Lee BS, Park GS, Choi WB, Lee NS, Kim JM (2000) Controlling the diameter, growth rate, and density of vertically aligned carbon nanotubes synthesized by microwave plasma-enhanced chemical vapor deposition. Appl Phys Lett 76:2367–2369View ArticleGoogle Scholar
- Merkulov VI, Melechko AV, Guillorn MA, Lowndes DH, Simpson ML (2001) Alignment mechanism of carbon nanofibers produced by plasma-enhanced chemical vapor deposition. Appl Phys Lett 79:2970–2972View ArticleGoogle Scholar
- Honda SI, Katayama M, Lee KY, Ikuno T, Ohkura S, Oura K, Furuta H, Hirao T (2003) Low temperature synthesis of aligned carbon nanotubes by inductively coupled plasma chemical vapor deposition using pure methane. Jpn J Appl Phys 42:L441–L443View ArticleGoogle Scholar
- Zhang G, Mann D, Zhang L, Javey A, Li Y, Yenilmez E, Wang Q, McVittie JP, Nishi Y, Gibbons J, Dai H (2005) Ultra-high-yield growth of vertical single-walled carbon nanotubes: hidden roles of hydrogen and oxygen. Proc Natl Acad Sci 102:16141–16145View ArticleGoogle Scholar
- Nemanich RJ, Solin SA (1979) First- and second-order Raman scattering from finite-size crystals of graphite. Phys Rew B 20:392–401View ArticleGoogle Scholar
- Wang Y, Alsmeyer DC, McCreery RL (1990) Raman spectroscopy of carbon materials: structural basis of observed spectra. Chem Mater 2:557–563View ArticleGoogle Scholar
- Tuinstra F, Koenig JL (1970) Raman spectrum of graphite. J Chem Phys 53:1126–1130View ArticleGoogle Scholar
- Ferrari AC (2007) Raman spectroscopy of graphene and graphite: disorder, electron–phonon coupling, doping and nonadiabatic effects. Solid State Commun 143:47–57View ArticleGoogle Scholar
- Yoshimura A, Yoshimura H, Shin SC, Kobayashi K, Tanimura M, Tachibana M (2012) Atomic force microscopy and Raman spectroscopy study of the early stages of carbon nanowall growth by dc plasma-enhanced chemical vapor deposition. Carbon 50:2698–2702View ArticleGoogle Scholar
- Ni ZH, Fan HM, Feng YP, Shen ZX, Yang BJ, Wu YH (2006) Raman spectroscopic investigation of carbon nanowalls. J Chem Phys 124:204703–204705View ArticleGoogle Scholar
- Sharma H, Agarwal DC, Sharma M, Shukla AK, Avasthi DK, Vankar VD (2013) Tailoring of structural and electron emission properties of CNT walls and graphene layers using high-energy irradiation. J Phys D Appl Phys 46:315301–315308View ArticleGoogle Scholar
- Himani S, Agarwal DC, Sharma M, Shukla AK, Avasthi DK, Vankar VD (2014) Structure-modified stress dynamics and wetting characteristics of carbon nanotubes and multilayer graphene for electron field emission investigations. ACS Appl Mater Interfaces 6:12531–12540View ArticleGoogle Scholar
- Li J, Chen JT, Luo BM, Yan XB, Xue QJ (2012) The improvement of the field emission properties from graphene films: Ti transition layer and annealing process. AIP Adv 2:022101–022109View ArticleGoogle Scholar
- Li C, Fang G, Yang X, Liu N, Liu Y, Zhao X (2008) Effect of adsorbates on field emission from flame-synthesized carbon nanotubes. J Phys D Appl Phys 41:195401–195406View ArticleGoogle Scholar