Probing high-pressure properties of single-wall carbon nanotubes through fullerene encapsulation

Abstract

The high pressure behavior of bundled 1.35Ϯ 0.1 nm diameter single wall carbon nanotubes ͑SWNT͒ filled with C 70 fullerenes ͑usually called peapods͒ has been investigated by Raman spectroscopy and compared with the corresponding behavior of the nonfilled SWNT. We show experimentally that two reversible pressureinduced transitions take place in the compressed bundle SWNT. The first transition, in the 2-2.5 GPa range, is in good correspondence with predictions of the thermodynamic instability of the nanotube circular cross section for the studied tube diameter. An interaction between the fullerenes and the tube walls is then observed at about 3.5 GPa, which evidences a progressive deformation of the tube cross section. The second transition takes place at pressures between 10 and 30 GPa, and is evidenced by two effects by a strong frequency downshift of the Raman transverse modes and the concomitant disappearance of the fullerenes Raman modes in peapods. The pressure at which the second transition takes place is strongly dependent on the nature of the pressure transmitting medium. We also report irreversible effects at high pressure as the shortening of the tubes, the formation of nanostructures and the disappearance of the C 70 Raman signal in some cases. Transmission electron microscopy studies are also reported supporting these transformations.

Rotational dynamics of confined C 60 from near-infrared Raman studies under high pressure

“…A noticeable change was also found in the relative intensity at 400-500 cm Ϫ1 near the H g (2) mode, which might be due to pressure induced shortening of nanotubes (22) or to defects created in the SWNT wall during the pressure-induced polymerization process (23). A similar effect has been found in C 70 peapods (24). We know that monomeric C 60 s may possibly rotate uniaxially around the tube axis, but such uniaxial rotation should be difficult, if not impossible, for a long chain of polymeric C 60 .…”

From a one-dimensional crystal to a one-dimensional liquid: A comprehensive dynamical study of C60peapods

“…If we invoke the quasiharmonic approximation, the liquid phase at high temperature can be modelled using the harmonic Hamiltonian (1) in the high-temperature limit. The dynamical structure factor takes the form (13), and the speed of sound in the liquid phase v l is related to the FWHM of the Lorentzian line shape of the inelastic signal. We find a value of v l ∼ 1.8 km s −1 at 1040 K. This value is 51% smaller than in the crystalline phase, and is observed to be almost constant in the T range [823,1043] K. This important change in the sound velocity translates the softening of the elastic constants when the 1D solid melts, and is found to be equivalent-in amplitude-to the melting transition between ice and water.…”

“…[2][3][4][5][6][7][8] On the experimental side, the majority of the investigations published so far are concerned with electron microscopy and diffraction, as well as Raman spectroscopy, x-ray diffraction, or NMR. Most of them are related to the modifications of the optical properties 9 and to the evolution of the structure under different conditions, like pressure [10][11][12][13][14] or doping. 15 Few publications report on the fluctuations and on the low-frequency dynamics of confined C 60 molecules.…”

Graphitization of single-wall nanotube bundles at extreme conditions: Collapse or coalescence route

“…In the past decade there have been several experimental [3][4][5][6][7][8][9][10] and theoretical [11][12][13][14][15][16][17][18][19][20][21][22][23] investigations focusing on the effects of pressure on bundles of single-walled carbon nanotubes (SWCNT) at room temperature. Most experimental studies indicate that the bundles undergo a structural phase transition upon increasing the pressure to a few GPa.…”