© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

phys. stat. sol. (b) 245, No. 10, 2051–2054 (2008) / DOI 10.1002/pssb.200879603 p s sbasic solid state physics

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Controllable electromagnetic response of onion-like carbon based materials

Vladimir Kuznetsov*,1, Sergey Moseenkov1, Arkady Ischenko1, Anatoly Romanenko2, Timofey Buryakov2, Olga Anikeeva2, Sergey Maksimenko3, Polina Kuzhir3, Dmitriy Bychanok3, Aleksander Gusinski4, Olga Ruhavets4, Olga Shenderova5, and Philippe Lambin6

1 Boreskov Institute of Catalysis SB RAS, Lavrentieva 5, 630090 Novosibirsk, Russia 2 Institute of Inorganic Chemistry SB RAS, Lavrentieva 3; Novosibirsk State University, Pirogova 2, 630090 Novosibirsk, Russia 3 Institute for Nuclear Problem, Bobruiskaia 11, Minsk 220030, Belarus 4 Belarusian State University of Informatics & Radioelectronics, Minsk, Belarus 5 International Technology Center, Raleigh, NC 27715, USA 6 FUNDP – University of Namur, Physics Department, 61 rue de Bruxelles, 5000 Namur, Belgium

Received 30 April 2008, revised 2 June 2008, accepted 6 June 2008

Published online 26 August 2008

PACS 41.20.Jb, 72.20.Ee, 72.80.Rj, 81.05.Uw, 81.07.–b

* Corresponding author: e-mail kuznet@catalysis.ru, Phone: +007 383 330 87 65, Fax: +007 383 330 80 56

© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

1 Introduction Nanocarbons have potential applica-tions for the development of electromagnetic wave absorb-ing and shielding materials. The first results of the micro-wave characterization in S-, X- and Ka-bands of onion like carbon powders (OLC) and OLC-polymer films presented in [1-3] demonstrate high attenuation of the given samples over the wide MW frequency range. Here we present the results on the electromagnetic response of OLC of variable

composition in Ka-band range (26-37 GHz) combined with measurements of temperature dependence of conductivity.

2 Experimental Controllable graphitization in vac-uum of the explosive nanodiamond within the temperature range 1200-1900 K allows to produce the diamond-nanographite composites [4]. ND (with the size of primary particle ~4-5 nm) were purchased from “New Technolo-

Here we discussed electromagnetic response of onion-like

carbon (OLC) powders with variable ratio of decreasing in

size diamond core and defective curved graphitic shells

(sp2/sp3 nanocomposites) in Ka-band (26-37 GHz) band.

sp2/sp3 ratio in OLC was regulated by increasing of annealing

temperature of explosive nanodiamond (ND) using as initial

product. The observed one dimensional variable range hop-

ping conductivity (4-300 K) combined with HR TEM data

was attributed to the formation of variable length ribbon-like

defective graphene scales. The increase of ND annealing

temperature results in the increase of density states of con-

ductive electrons and corresponding increase of conductivity

of OLC produced. The increase of conductivity of OLC pro-

vides the increase of EM wave attenuation ability along with

light increase of reflecting ability.

HR TEM image of OLC produced by annealing of ND at

1850 K. Dark contrast lines correspond to graphene-like

sheets with distance between them 0.34-0.35 nm. Arrows

show the measurable input, output and reflecting power of

EM irradiation and surface current.

2052 V. Kuznetsov et al.: Controllable electromagnetic response of carbon based materials

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gies” (Chelyabinsk, Russia–DA and DB series) and FGUP ALTAI (Biysk, Russia–DC series). As annealing tempera-ture is increased the ratio between diamond core and outer defective curved graphitic shells (sp2/sp3 nanocomposites) decreases, finally resulting in OLC structure. Due to the aggregation of primary ND its annealing products (OLC particles) are organized into aggregates with joint defective graphene shells covering several primary OLC cores. Con-tent of iron impurities in OLC does not exceed 0.1-0.2 wt %.

Figure 1 Scheme of formation of sp2/sp3composites and OLC.

The electric conductivity σ(T) was measured using the conventional four-point-probe technique with an error of about 0.1% at various temperatures in a range from 4.2 to 300 K. The OLC powders were pressed into a glass tube (dint = 2 mm) while the resistivity ceased to depend on the degree of compression. The electric contact was provided by a silver wire with a diameter of 0.1 mm. The sample temperature was measured using an iron–rhodium resis-tance thermometer. The complex elements of the scattering matrix, s11 and s21, have been measured with high accuracy within 26-37 GHz frequency range (Ka-band) by combination of waveguide and free space technique. The experimental setup includes high stability sweep generator, high sensi-tivity detectors, measurement bridges, and an indicator unit. Scalar network analyzer has been used for measurement of insertion loss, amplification, and voltage standing wave ra-tio (VSWR) and reflection loss. Samples are put into mi-crowave-transparent Plexiglas cuvette (21x21 mm with the sample workspace thickness is 0.8 mm). Attenuation of the signal transmitted through the sample (s21) was calibrated to empty cuvette. Standard procedure of the calibration on reflecting plate has been used for EM reflection measure-ments (s11).

Figure 2 The temperature dependence of conductivity σ(T) of

OLC series DC, annealed at temperature 1400 K (DC1400), 1650

K (DC1650) and 1850 K (DC1850) in coordinates ln(σ) - T–1/2.

Continuous lines correspond to dependence (1).

3 Results and discussion 3.1 Electron transport properties of OLC OLC

demonstrates variable range hopping conductivity (VRHC). Thus the temperature dependence of the dc conductivity, σ(T), for the OLC samples produced at different tempera-tures is shown in Fig. 2 plotted as ln(σ) vs T–1/2 for com-parison with the quasi-1D VRH model [5].

σ(T) = σVRH (T) = A* exp [-(T0/T)1/2] (1)

where A is constant, T0 = CTa/kBN(EF), CT ~ 16, a is the in-verse length on which the amplitude of wave function fall down (a ~ 60 Å for OLC). The slope of the temperature dependences of conductivity with variable range hopping conductivity in the carbon nanostructures (see Eq. (1)) is determined only by the density of states at Fermi level N(EF). Estimation of density of states of carriers at Fermi level N(EF) in OLC is based on the approximation of the tem-perature dependence of conductivity expression (1) was carried out for different series of OLC produced from ND of different vendors. The increase of the annealing tem-perature from 1400 K up to 1900 K leads to increase of the density of states at Fermi level (see Fig. 3) and conse-quently increasing of the carriers concentration. Some variation of density of states at the Fermi level is observed for OLC produce from ND of different vendors. That was attributed to the variation of size of agglomerate. Thus, we can operate density of states at Fermi level N(EF) in inves-tigated samples via variation of the annealing temperature, choice of background of preparation of initial nanodia-monds and separation of the large fraction of onion like carbon.

phys. stat. sol. (b) 245, No. 10 (2008) 2053

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Original

Paper

Figure 3 Dependence of density of states at the Fermi level

N(EF) calculated from the temperature dependences of conductiv-

ity of samples of DA, DB, DC and DH series annealed at differ-

ent temperatures. The observed one dimensional variable range hopping conductivity (4-300 K) combined with HR TEM data [4, 6] was attributed to the formation of continues ribbon-like de-fective graphene scales covering OLC cores of primary particles.

3.2 Electromagnetic response properties of OLC Samples generic characteristics, packed densities, and their EM response properties in Ka-band are represented in Table 1. In contrast to OLC powders of previously meas-ured series [1] and OLC-based polymer films [2], the stud-ied samples demonstrate non-monotonous frequency de-pendence of the EM attenuation (see Fig. 4a). Indeed, the samples of Da-1, Db-1 and two samples from Dc-series, Dc-1 and Dc-2, have evident attenuation maximum at 27 GHz, while the Dc-3 sample demonstrates pronounced at-tenuation at 31 GHz. Since s11 is a smooth function (see Fig. 1b), one can conclude that the EM absorption uni-formity of the EM attenuation and absorption can not be attributed to the Fresnel reflection from the cuvette sides. A correct physical interpretation of these experimental re-sults requires a special theoretical treatment and, probably, additional experiments. In particular, the existence of fre-quency ranges with pronounced nonuniformity peaks re-sides directly to the OLC powders: similar resonant-like electromagnetic response has been reported in many publi-cations (see [7, 8] for carbon nanotube-based composites) without clear interpretation of the effect. One can suppose that this is a common property of nanocarbon-based mate-rials related to their specific low-dimensional structure. New peculiarities of the EM response of OLC powders are also provided by the agglomeration of OLC particles (giv-ing new characteristic sizes). In fact, some individual structural elements interacting with EM fields can resonate, and contribute into the effective energy absorption in-microwave frequency range.

Table 1 EM response properties of ND annealed at different

temperatures (sp2/sp3composites, 1400-1650 K) and OLC (1850

K) in Ka-band (26-37 GHz).

Sample* Tan, K**

Max(|S21|), dB

Max(|S11|), dB

Packed density, g/cm3

Da-1 1400 5.175 28.19 0.220

Da-3 1850 14.668 18. 0 0.207

Db-1 1400 7.823 19.489 0.522

Db-3 1850 9.56 17.189 0.389

Dc-1 1400 9.067 17.744 0.582

Dc-2 1650 8.55 15.6 0.480

Dc-3 1850 13.807 13.859 0.437

* OLC Da series were produced from ND of “New Technolo-

gies”, agglomerate size 120-240 nm (after photon correlation

spectroscopy), OLC Db series were produced from ND of “New

Technologies”, agglomerate size 100-200 nm; OLC Dc series

were produced from ND of FGUP ALTAY, agglomerate size

122-285 nm

** ND annealing temperature

An additional reason for such a quasi-resonant absorp-tion in the Ka-band can be provided by structural features of analyzed OLCs. In particular, friability, block structure of the OLC agglomerates, relatively high order of lengthy defects inside nanocluster could make conditions of redis-tribution of the polarized carbon onions and be the reason of high sensitivity of EM response of OLC powders to mi-crowaves. Inter-shell vibrations [9, 10] can also contribute. The appearance of the attenuation peak at the long wave-length edge of the measured range can also be related to the water presented in samples. Indeed, the dielectric loss in water at room temperature decreases with frequency and demonstrate wide maximum below 30 GHz (see, e.g. [11]). It has been found that raising the annealing temperature leads to enhanced attenuation abilities of OLC powders along with slight growth of reflecting ability (see Fig. 4a). These properties of OLC samples correlate with observed the increase of density states of conductive electrons and corresponding increase of conductivity of OLC produced at high temperature. The reason is the following: OLC with the dielectric diamond core inside, being sp2/sp3 composite corresponding to 1400 K and 1650 K ND annealing tem-peratures, transforms into onions, when annealing tem-perature is 1850 K. The increase of annealing temperature does not only promote ND core graphitization but also re-sults in the formation of more perfect prolonged conduc-tive tracks within OLC agglomerates. As seen from Fig. 4b, for all samples s11 decreases with the frequency increase. The part of reflected energy at 37.5 GHz averages 10-20% from sample to sample. The EM re-sponse of OLC powders has been found (see Fig. 4) to be distinctly dependent on the OLC cluster size. Significant

2054 V. Kuznetsov et al.: Controllable electromagnetic response of carbon based materials

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Figure 4 Frequency dependence of S21 (a) and S11 (b) for sam-

ples of Da, Db, Dc series.

difference between s11 and s21 corresponding to 1400 K and 1850 K annealing temperature takes place for samples of relatively wide OLC fraction, Da and Dc types. In con-trast, for samples of narrow OLC fraction (Db type) there have not been found significant difference between EM re-sponses corresponding to 1400 K and 1850 K annealing temperature. The average values of EM attenuation for samples of Da and Dc types are higher than that for Db type (OLC with smaller aggregates), since the length of the conducting tracks within the OLC cluster depends directly on the size of OLC agglomerates. The sample Da-3 dem-onstrates maximal EM attenuation observed in our experi-ments, 14.7 dB. It means that only about 18% of incident power passes through the sample. The minimal reflection coefficient is observed for the same sample, 6.2 dB (48% power of incident signal is reflected). 4 Conclusion We have reported the first experimental study of the EM response of new types of OLC powders ob-tained by DND annealing at 1400, 1650 and 1850 K. It has been demonstrated that the increase of the ND annealing temperature leads to the increase of the EM attenuation for all types of related OLC samples. These data correlate with conductivity properties of OLC samples. The observed one

dimensional variable range hopping conductivity (4-300 K) combined with HR TEM data was attributed to the for-mation of variable length ribbon-like defective graphene scales within single OLC aggregate. The increase of ND annealing temperature results in the increase of density states of conductive electrons and corresponding increase of conductivity of OLC produced related to the formation of more perfect conductive tracks. The increase of conduc-tivity of OLC provides the increase of EM wave attenua-tion ability along with light increase of reflecting ability. Thus, EM response of novel nanocarbon powders is found to be sensitive to the OLC type and synthesis conditions in 26-37GHz frequency range, displaying at the same time non-monotonous frequency dependence. Reported results demonstrate that OLC is a perspective candidate material for applications in the microwave frequency range.

Acknowledgements The work was partially supported by

the NATO Science for Peace program (grant SfP-981051), IN-

TAS (grant 06-1000013-9225), the State Committee for Science

and Technology of Belarus and INTAS (grant 03-50-4409), the

Belarus Foundation for Basic Research (grant F06R-091), and by the Ministry of Science and Education of the Russian Federation (project no. RNP.2.1.1.1604).

References

[1] S. A. Maksimenko, V. N. Rodionova, G. Ya. Slepyan, V. A.

Karpovich, O. Shenderova, J. Walsh, V. L. Kuznetsov, I. N.

Mazov, S. I. Moseenkov, A. V. Okotrub, and Ph. Lambin,

Diam. Relat. Mater. 16, 1231 (2007).

[2] S. A. Maksimenko, P. P. Kuzhir, A. V. Gusinski, V. V. Ru-

havets, D. S. Bychanok, O. Shenderova, V. L. Kuznetsov,

R. Langlet, and Ph. Lambin, Proceedings of Metamaterials,

Rome October 22–24, 2007, edited by F. Bilotti and

L. Vegni (University ‘Roma Tre’, Rome, Italy, 2007), pp.

903–906.

[3] O. Shenderova, V. Grishko, G. Cunningham, S. Moseen-

kov, G. McGuire, and V. Kuznetsov, Diam. Relat. Mater.,

doi:10.1016/j.diamond.2007.08.023.

[4] V. L. Kuznetsov and Yu. V. Butenko, in: Ultrananocrystal-

line Diamond: Synthesis, Properties, and Applications, ed-

ited by O. Shenderova and D. Gruen (William Andrew

Publishing, 2006), pp. 405–476.

[5] V. L. Kuznetsov, Yu. V. Butenko, A. L. Chuvilin, A. I.

Romanenko, and A. V. Okotrub, Chem. Phys. Lett. 336,

397 (2001).

[6] V. L. Kuznetsov, A. L. Chuvilin, Yu. V. Butenko, I. Yu.

Malkov, and V. M. Titov, Chem. Phys. Lett. 222, 343

(1994).

[7] F. Bommeli, L. Degiorgi, P. Wachter, W. S. Bacsa, W. A.

de Heer, and L. Forro, Synth. Met. 86, 2307 (1997).

[8] N. Li, Y. Huang, F. Du, X. He, X. Lin, H. Gao, Y. Ma,

F. Li, Y. Chen, and P. C. Eklund, Nano Lett. 6, 1141(2006).

[9] T. F. Nagy, K. J. Conley, and D. Tomanek, Phys. Rev. B 50,

12207 (1994).

[10] S. Iglesias-Groth and J. Breton, Astron. Astrophys. 357,

782 (2000).

[11] http://www.lsbu.ac.uk/water/microwave.html