Highly Efficient Synthesis of Nitrogen-Atom Endohedral Fullerene by Controlling Plasma Ion Behaviors

Abstract

The thorough investigation has been made to find an optimum condition for the synthesis of the nitrogen-atom endohedral fullerene (N@C60), which contains the atomic nitrogen inside the carbon cage of C60. Using our radio-frequency-plasma apparatus, the condition is realized to maximize the density of nitrogen-molecule ions (N2+) in the plasma under the pressure of 25 Pa and the acceleration substrate bias voltage of -90 V. As a result, the target molecule of N@C60 is produced in relatively high purity (mol concentration ratio of N@C60 to C60) of 0.25%, which is an order of magnitude higher than that reported in the other literatures.

Control of C₆₀ Behavior for High Yield Synthesis of N@C₆₀ in RF-Plasma

“…To produce N 2 + ions and N 2 * radicals from the N 2 molecule (N 2 + e -→ N 2 + + 2e -and N 2 + e -→ N 2 * + e -), an ionization energy of 15.58 eV and an excitation energy of 6.17 eV should be supplied to the N 2 molecule by energy transfer from electrons, respectively. [10,11] Figure 2 gives (a) purity and (b) solubility as a function of P N2 in the presence and absence of the mesh grid under the conditions of P RF = 500 W, V g = -90 V, V sub = -90 V and T ov = 750 0 C. As seen in Fig. 2(a), the purity in the presence of the mesh grid is higher than that in the absence of the mesh grid because the electron through mesh grid can be accelerated higher than that in the absence of mesh grid.…”

Nanocarbon materials fabricated using plasmas

“…Thus, the high-yield synthesis of N@C 60 has been an urgent issue, and the following promising approach was taken. Figure 12a schematically shows an experimental apparatus consisting of a glass chamber, which is called a ''double-plasma (DP) type electron beam'' device (Cho et al 2012. A nitrogen gas discharge plasma was generated by applying RF power with a frequency of 13.56 MHz to a spiralshaped RF antenna.…”

“…Here, the topics concerned with the laser (Ong et al 1990;Butler and Sumant 2008) 1990 Mass synthesis of C 60 Arc discharge (Haufler et al 1990) 1991 Small-quantity synthesis of La@C 82 Arc discharge (Chai et al 1991) 1991 Clear-cut discovery of MWNTs Arc discharge (Iijima 1991) 1993 Discovery of SWMTs Arc discharge (Iijima and Ichibashi 1993;Bethune et al 1993) 1994 Growth of UNCD films Microwave PECVD (Gruen et al 1994) 1996 Formation of alkali-atom@C 60 Plasma-ion irradiation Hatakeyama et al 2014) 1997 Formation of N@C 60 DC and RF discharges (Pietzak et al 1997;Cho et al 2012) 1997 Discovery of carbon nanoroses Arc discharge (Ando et al 1997) 1998 Growth of well-aligned MWNTs Hot filament PECVD (Ren et al 1998) 2001 Formation of C 60 , Cs, DNA@SWNTs…”

“…At that time, diamond films so far grown by PECVD using discharge plasmas in the microwave range of frequencies were first referred to as ''nanocrystalline-diamond'' (NCD) films in the realm of nanodiamonds (NDs) (Ong et al 1990;Butler and Sumant 2008). In the mid-1990s, ultra-nanocrystallinediamond (UNCD) films consisting of NDs smaller than NCDs were grown by microwave PECVD (Gruen et al 1994), and the plasma-ion irradiation made an appearance as an effective method of forming endohedral C 60 (alkali-atom@C 60 , N@C 60 ) (Hatakeyama et al 2014;Pietzak et al 1997;Cho et al 2012). In the second half of 1990, carbon nanoroses similar to carbon nanowalls (CNWs) were discovered by the arc-discharge method (Ando et al 1997), and large arrays of well-aligned MWNTs were grown by PECVD using hot filaments (Ren et al 1998).…”

Nitrogen-atom endohedral fullerene synthesis with high efficiency by controlling plasma-ion irradiation energy and C60 internal energy

“…Therefore, we insist that not only the amount of N@C 60 but also the purity is also important to obtain the pure (or high purity) N@C 60 . To obtain a large amount of N@C 60 with a high purity [14][15][16][17] to investigate its properties, two possible approaches can be considered. The first is to clarify the encapsulation mechanism of the nitrogen atoms into C 60 , and to subsequently optimize the plasma parameters.…”