Plasma composition during plasma-enhanced chemical vapor deposition of carbon nanotubes

To cite this version:M Mao, A Bogaerts. Investigating the plasma chemistry for the synthesis of carbon nanotubes/nanofibres in an inductively coupled plasma enhanced CVD system: the effect of different gas mixtures. Journal of Physics D: Applied Physics, IOP Publishing, 2010, 43 (20) Abstract. A hybrid model, called the Hybrid Plasma Equipment Model (HPEM) was used to study an inductively coupled plasma in gas mixtures of H 2 or NH 3 with CH 4 or C 2 H 2 used for the synthesis of carbon nanotubes or carbon nanofibers (CNTs/CNFs). The plasma properties are discussed for the different gas mixture at low and moderate pressure, and the growth precursors for CNTs/CNFs are analyzed. It is found that C 2 H 2 , C 2 H 4 , and C 2 H 6 are the predominant molecules in CH 4 containing plasmas beside the feedstock gas, and serve as carbon sources for CNT/CNF formation. On the other hand, long chain hydrocarbons are observed in C 2 H 2 containing plasmas. Furthermore, the background gases CH 4 and C 2 H 2 show a different decomposition rate with H 2 or NH 3 addition at moderate pressures.

“…This is consistent with the results reported by Bell et al [13]. Indeed, H 2 , N 2 and HCN were detected as major neutral species when CNTs were synthesized in the C 2 H 2 /NH 3 plasma.…”

Section: Plasma Chemistry In the Different Gas Mixturessupporting

confidence: 93%

Section: Introductionmentioning

confidence: 99%

Investigating the plasma chemistry for the synthesis of carbon nanotubes/nanofibres in an inductively coupled plasma enhanced CVD system: the effect of different gas mixtures

Mao¹,

Bogaerts²

2010

“…Indeed, it was observed in the calculation results that NH 3 decomposes easily to produce atomic H, especially at low hydrocarbon gas fraction. In general, our model predicts that a lower fraction of hydrocarbon gases (CH 4 or C 2 H 2 , i.e., below 20%) and hence a higher fraction of etchant gases (H 2 or NH 3 ) in the gas mixture result in more "clean" conditions for controlled CNT growth, due to the dominant role of atomic H [85], which is in agreement with literature observations (e.g., [76,83,[87][88][89][90]). …”

Section: (B) Cnts and Related Structuressupporting

confidence: 91%

Computer modelling of the plasma chemistry and plasma-based growth mechanisms for nanostructured materials

Bogaerts¹,

Eckert²,

Mao³

et al. 2011

In this review paper, an overview is given of different modeling efforts for plasmas used for the formation and growth of nanostructured materials. This includes both the plasma chemistry, providing information on the precursors for nanostructure formation, as well as the growth processes itself. We limit ourselves to carbon (and silicon) nanostructures. Examples of the plasma modeling comprise nanoparticle formation in silane and hydrocarbon plasmas, as well as the plasma chemistry giving rise to carbon nanostructure formation, such as (ultra)nanocrystalline diamond ((U)NCD) and carbon nanotubes (CNTs). The second part of the paper deals with the simulation of the (plasma-based) growth mechanisms of the same carbon nanostructures, i.e., (U)NCD and CNTs, both by mechanistic modeling and detailed atomistic simulations. IntroductionLow temperature plasmas are playing an increasingly important role for the formation and growth of nanostructures and nanostructured materials (e.g., [1][2][3][4][5][6][7]). To improve the performance of these plasma growth processes, a good insight is desired in the plasma and in the interaction with the growing nanostructures. This insight can be obtained by experimental research, but the latter is not always straightforward, in view of the small dimensions of the nanomaterials and the possible disturbance of the plasma characteristics, e.g., when introducing a probe. Therefore, computer simulations can be very useful to assist in the experimental developments.In the present paper, we will give an overview of different modeling efforts that have been presented in the literature for plasmas used for nanostructure formation. This includes two different aspects. First, a thorough understanding of the plasma behavior is needed. This comprises background gas flow and heating (i.e., fluid dynamics), gas breakdown, transport and heating of the electrons and the so-called heavy particles, as well as the plasma chemistry, i.e., creation and destruction of the various plasma species by chemical reactions. Modeling of the plasma chemistry can give indications on which species are important precursors for the growth of nanostructured materials and how the plasma operating conditions can be tuned to optimize the growth process. Therefore, in this paper we will mainly focus on the plasma chemistry modeling. Several plasma modeling approaches exist in literature, such as analytical models, zero-dimensional (0D) chemical kinetics simulations, fluid models (describing the chemical kinetics as well as fluid dynamics), solving the Boltzmann transport equation, Monte Carlo (MC) and particle-in-cell (PIC)-MC simulations, as well as hybrid methods, combining the above (e.g., MC + fluid) models. For describing the plasma chemistry, the 0D chemical kinetics approach is often applied, as it can take into account a large number of different species and reactions without too much computational effort. However, it assumes a spatially uniform plasma composition and does not consider transport of the plasm...

“…A variety of plasma sources have been reported in the literature for CNT/CNF growth [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24], such as direct current (dc) glow discharges [7][8][9][10], microwave discharges (MW) [11,12], radio-frequency capacitively coupled plasmas (RF-CCP) [13][14][15]and RF inductively coupled plasmas (RF-ICP) [16][17][18][19][20][21][22][23][24]. A wide range of operating conditions was reported for the CNT/CNF growth by PECVD.…”

Section: Introductionmentioning

confidence: 99%

Investigating the plasma chemistry for the synthesis of carbon nanotubes/nanofibres in an inductively coupled plasma-enhanced CVD system: the effect of processing parameters

Mao¹,

Bogaerts²

2010

To cite this version:M Mao, A Bogaerts. Investigating the plasma chemistry for the synthesis of carbon nanotubes/nanofibres in an inductively coupled plasma-enhanced CVD system: the effect of processing parameters. Journal of Physics D: Applied Physics, IOP Publishing, 2010, 43 (31) Abstract.A parameter study is carried out for an inductively coupled plasma used for the synthesis of carbon nanotubes or carbon nanofibers (CNTs/CNFs), by means of the Hybrid Plasma Equipment Model (HPEM). The influence of processing parameters including gas ratio for four different gas mixtures typically used for CNT/CNF growth (i.e., CH 4 /H 2 , CH 4 /NH 3 , C 2 H 2 /H 2 and C 2 H 2 /NH 3 ), ICP power (50~1000W), operating pressure (10mTorr~1Torr), bias power (0~1000W) and temperature of the substrate (0~1000°C) on the plasma chemistry is investigated and the optimized conditions for CNT/CNF growth are analyzed. Summarized, our calculations suggest that a lower fraction of hydrocarbon gases (CH 4 or C 2 H 2 , i.e., below 20%) and hence a higher fraction of etchant gases (H 2 or NH 3 ) in the gas mixture result in more "clean" conditions for controlled CNT/CNF growth. The same applies to a higher ICP power, a moderate ICP gas pressure above 100 mTorr (at least for SWCNTs), a high bias power (for aligned CNTs), and an intermediate substrate temperature.