Stabilization Mechanisms in Multiwalled Peapods
- PDF / 685,113 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 68 Downloads / 137 Views
1057-II10-45
Stabilization Mechanisms in Multiwalled Peapods Roberto Scipioni1, Atsushi Oshiyama2, and Takahisa Ohno3 1 Nanomaterials and Biomaterials, ICYS, NIMS, Japan, 1-1 Namiki, Tsukuba, Japan 2 Applied Physics, University of Tokyo, Tokyo, Japan 3 Computational Materials Science, National Institute for Materials Science, Tsukuba, Japan ABSTRACT We study the energetics of encapsulation in the small diameter peapod C60@(15,0) and its DWNT equivalent C60@(15,0)-(24,0). Using DFT (LDA) we show that the double layered structure of the DWNT allows for a less endothermic encapsulation of C60 by as much as 1.0 eV thus, indicating that encapsulation is facilitated in DWNTs peapods. A detailed analysis of the charge distribution suggests that the interlayer state in between the tubes is responsible for this increased stability because it acts as a repository of electronic charge. We conclude that the diameter of the tubes is not the only relevant parameter for the energetics: the multilayer structure of the host tube(s) encapsulating the fullerenes needs to be taken into account for a rigorous discussion. When an empirical term for the Van der Waals interactions is included in the calculation, the DWNT peapod is found to be slightly exothermic (in contrast to the SWNT peapod) This explains the recent observation of small diameter C60@DWNT peapods. INTRODUCTION Since the discovery of fullerenes and carbon nanotubes [1] much effort has been devoted to the assembly, characterization and to some extent the modeling of systems which can be obtained by combining the one dimensional nature of carbon nanotubes with the zero dimensional fullerenes [2]. In particular systems can be obtained which resemble hollow tubes filled with spherical or quasi spherical objects (peapods) [3]. The modeling of these systems indicated that the encapsulation of C60 in single walled nanotubes (SWNT) requires a minimum diameter of about 12.0 – 12.5 A [4,5]. The prediction was also made that non spherical fullerenes like C70, C78, C80 can be encapsulated with different orientations according to the tube diameters [6-8]. The main finding has been that the diameter of the tube and the spacing between the fullerene and the tube walls seem to be the fundamental parameters accounting for the stability of the systems. Some time later some observations were made of filling of Double Walled Nanotubes with C60 fullerenes. It was observed that fullerenes can be encapsulated in DWNT with diameters as small as 11 A [9,10], enhanced thermal stability [11], as well as an increase in the Raman scattering intensities [10] indicated that that encapsulation of C60 in DWNT is favored when compared to standard peapods. In this letter we attempt to shed some light into this conundrum in particular, we discuss the role of the extra layer in double walled nanotubes peapods, we aim to prove that when a multilayered structured is considered the physics becomes richer. Essentially two effects are responsible for the increased stabilization 1) The reduction of localization e
Data Loading...
