High-Pressure Optical Microspectroscopy Study on Single-Walled Carbon Nanotubes Encapsulating C₆₀

Abstract

The high-pressure behavior of single-walled carbon nanotubes (SWCNTs) filled with C 60 molecules, socalled C 60 @SWCNT peapods, has been investigated by optical spectroscopy using nitrogen and argon as pressure transmitting media. Peapods with a high filling ratio were prepared by the sublimation method and characterized by high-resolution transmission electron microscopy. Optical transmission measurements under high pressure were conducted on films of SWCNTs and C 60 @SWCNT peapods. As with SWCNTs, the absorption bands observed for peapods exhibit a red-shift under pressure. The relative energy shifts of the optical transitions under pressure are higher than those for empty SWCNTs, demonstrating enhanced hybridization and/or symmetry breaking effects. We find an anomaly in the pressure-induced shifts of the optical transitions at P c1 ≈ 6.5 GPa (P c1 ≈ 5.5 GPa) when using nitrogen (argon) as pressure transmitting medium. The anomaly signals the deformation of the nanotube from circular to an oval shape. The value of P c1 is in good agreement with theoretical predictions of the pressure-induced deformation for highly filled peapods with similar average diameter. A plateau in the pressure-induced shifts with an onset at P c2 = 12−13 GPa indicates a saturation of the pressure-induced effects above this critical pressure.

Raman study of graphene nanoribbon analogs confined in single‐walled carbon nanotubes and their high‐pressure transformations

“…High pressure can modify the interaction of the host‐guest and the framework of the host matrix . Such pressure‐induced modifications may also change the behavior of the encapsulated species inside nano‐confinement circumstance.…”

“…High pressure can modify the interaction of the host-guest and the framework of the host matrix. [28,[35][36][37][38][39] Such pressure-induced modifications may also change the behavior of the encapsulated species inside nano-confinement circumstance. On the other hand, pressure is an effective means to study the physical properties and modify structural transformation of materials.…”

“…To study the effect of different fillers on the mechanical stability of nanotubes, we compare the collapse pressure of nanotubes (similar diameter) with different fillers, e.g. iodine, [35] water, [36] fullerenes, [37,38] and argon [39] , as shown in Table 1. We note that C 60, argon and water filling can support against collapse of nanotubes, leading to higher transition pressure.…”

Properties of Sizeable [n]Cycloparaphenylenes as Molecular Models of Single‐Wall Carbon Nanotubes Elucidated by Raman Spectroscopy: Structural and Electron‐Transfer Responses under Mechanical Stress

“…First, we used a 1:1 [6]CPP and [12]CPP mixtures aiming to encapsulate [6]CPP into [12]CPP just to emulate a ultrashort double walled CNT (DWCNT). [25,26] It is p-p interactions that are responsible for the assembly of some [n]CPPs with C 60 , giving rise to the formation in solution of 1:1 stoichiometric supramolecular complexes driven by a surprisingly high exo-thermicity. Very small changes are observed in the Raman spectrum, thus indicating that pressure could promote encapsulation of [6]CPP into the internal cavity of [12]CPP, and thus preventing [6]CPP to collapse.…”

“…[24] The success of the [6]CPP encapsulation into [12]CPP under pressure, together with the fact that some [n]CPPs can also accommodate C 60 -fullerene into their internal cavities, led us to explore the properties of [n]CPPs + C 60 complexes, which is also in clear analogy with the "SWCNT + C 60 peapods". [25,26] It is p-p interactions that are responsible for the assembly of some [n]CPPs with C 60 , giving rise to the formation in solution of 1:1 stoichiometric supramolecular complexes driven by a surprisingly high exo-thermicity. [7] In particular, concave-convex p-p interactions are strongly promoted in these complexes owing to the natural curvature adjustment between the [n]CPP host and the C 60 guest.…”