^{N. A.Vinnikov1}, A. V. Dolbin¹, V. B. Esel'son¹, V. G. Gavrilko¹, V. G. Manzhelii¹,

S. N. Popov¹, B. Sundqvist²

¹ B. Verkin Institute for Low Temperature Physics and Engineering, 47 Lenin Ave., 61103 Kharkov, Ukraine

² Department of Physics, Umea University, SE - 901 87 Umea, Sweden

At present the development, property investigations and commercial applications of new carbon nanosystems are among the top priority trends of the world science and science-based technologies. Recently the authors have obtained fundamentally novel results pointing to a quantum character of carbon nanosystems at low temperatures. They are as follows.

1. A negative thermal expansion of fullerite has been observed at low temperatures, which suggests the tunnel origin of the rotational states of C₆₀ molecules. Impurities introduced into the voids of the C₆₀ lattice affect drastically both the magnitudes and the sign of the thermal expansion of the system [1].
2. Quantum diffusion of ³He, ⁴He, Ne atoms and H₂ molecules in C₆₀ has been detected by investigating the sorption – desorption kinetics of gases at low temperature [2-4]. The method was a direct measurement of the pressure of these gases contacting a C₆₀ powder in a closed volume.
3. An isotopic effect has been detected in the investigation of the thermal expansion of C₆₀ doped with methane and deuteromethane. The effect is caused by the tunnel rotation of the CH₄ and CD₄ molecules in the octahedral interstitials of the C₆₀ lattice [5].
4. The low temperature coefficient of the thermal expansion of bundles of single-walled carbon nanotubes in the radial direction has been measured for the first time [6]. Negative values of the thermal expansion were observed be low 5.5 K. This novel phenomenon is a manifestation of the lowest-frequency part of the vibrational spectrum of nanotubes at low temperatures. The spectrum is characterized by a negative Gruneisen coefficient, which is typical of bending vibrations of two – dimensional systems. As the temperature increases above 5.5 K, the negative values of the thermal expansion typical for two-dimensional systems change into positive ones characteristics of three-dimensional objects.
5. Saturation of nanotube bundles with gas impurities triggers an intensive increase in the radial thermal expansion of bundles of carbon nanotubes, which is attributed to the influence of the gas impurity molecules on the bending vibrations of the system. Because of the geometrical features of SWNT bundles, their saturation with an impurity leads to the formation of one-dimensional chains of the impurity molecules in the grooves of the bundles. This structural reordering of the impurity molecules produces a peak in the temperature dependence of the radial thermal expansion coefficient [7].
6. Experimental evidence has been obtained for the first time which suggests tunneling of ⁴He and ³He atoms in bundles of single-walled carbon nanotubes [8,9]. This results in a considerable increase in the magnitudes of the negative radial thermal expansion of the ⁴He-SWNT and ³He-SWNT systems at T<3.7 and 7K, respectively. An unexpectedly large isotopic effect has been observed due to the higher probability of tunneling of ³He atoms.

The results obtained point to the importance of the influence of quantum effects upon the structure and properties of new carbon nanomaterials. The above results lead us to expect that a controllable introduction of impurities (including quantum ones) will enable modification of the properties of carbon nanosystems in a wide temperature interval.

[1] A.N. Aleksandrovskii, A. S. Bakai, A. V. Dolbin, G. E. Gadd, V. B. Esel’son, V. G. Gavrilko, V.G.Manzhelii, B. Sundqvist, and B.G. Udovidchenko, Low temperature thermal expansion of pure and inert gas-doped C₆₀, Fiz. Nizk. Temp. 29, 432 (2003) [Low Temp. Phys. 29, 324(2003)].

[2] A. V. Dolbin, V. B. Esel'son, V. G. Gavrilko, V. G. Manzhelii, N. A. Vinnikov, and S. N. Popov. Kinetics of ⁴He gas sorption by fullerite C₆₀. Quantum effects. Fiz. Nizk. Temp. 36, 1352 (2010), [Low Temp. Phys. 36, 1091 (2010)].

[3] A. V. Dolbin, V. B. Esel'son, V. G. Gavrilko, V. G. Manzhelii, N. A. Vinnikov, S. N. Popov. Kinetics of the Sorption of ³He by C₆₀ Fullerite. The Quantum Diffusion of ³He and ⁴He in Fullerite. JETP Letters, 93, pp. 577–579 (2011)

[4] A. V. Dolbin, V. B. Esel'son, V. G. Gavrilko, V. G. Manzhelii, N. A. Vinnikov, S. N. Popov. Diffusion of H₂ and Ne impurities in fullerite C₆₀. Quantum effects Fiz. Nizk. Temp. 38, (2012) (to be published).

[5] A. V. Dolbin, N. A. Vinnikov, V. G. Gavrilko, V. B. Esel'son, V. G. Manzhelii, G. E. Gadd, S. Moricca, D. Cassidy, and B. Sundqvist. Thermal expansion of deuterium methane solutions in fullerite C₆₀ at low temperatures. Isotopic effect, Fiz. Nizk. Temp. 35, 299 (2009) [Low Temp. Phys. 35, 226 (2009)].

[6] A.V. Dolbin, V.B. Esel`son, V.G. Gavrilko,V.G. Manzhelii, N.A.Vinnikov, S.N. Popov, B. Sundqvist. Radial thermal expansion of single-walled carbon nanotube bundles at low temperatures. Fiz. Nizk. Temp. 34, 860 (2008). [Low Temp. Phys. 34, 678 (2008)].

[7] A. V. Dolbin, V. B. Esel’son, V. G. Gavrilko, V. G. Manzhelii, N. A. Vinnikov, S. N. Popov, N. I. Danilenko and B. Sundqvist. Radial thermal expansion of pure and Xe-saturated bundles of single-walled carbon nanotubes at low temperatures. Fiz. Nizk. Temp. 35, 613 (2009) [Low Temp. Phys. 35, 484 (2009)].

[8] A. V. Dolbin, V. B. Esel'son, V. G. Gavrilko, V. G. Manzhelii, N. A. Vinnikov, S. N. Popov and B. Sundqvist. Quantum effects in the radial thermal expansion of bundles of single-walled carbon nanotubes doped with ⁴He.Fiz. Nizk. Temp. 36, 797 (2010) [Low Temp. Phys. 36, 635 (2010)].

[9] A. V. Dolbin, V. B. Esel’son, V. G. Gavrilko, V. G. Manzhelii, N. A. Vinnikov, S. N. Popov, and B. Sundqvist. Quantum phenomena in the radial thermal expansion of bundles of single-walled carbon nanotubes doped with ³He. A giant isotope effect. Fiz. Nizk. Temp. 37, 685 (2011) [Low Temp. Phys. 37, 544 (2011)].