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X-ray photoelectron spectroscopy as a method to control the received metal–carbon nanostructures
Journal of Electron Spectroscopy and Related Phenomena 137–140 (2004) 239–242
X-ray photoelectron spectroscopy as a method to control the received metal–carbon nanostructures L.G. Makarova a , I.N. Shabanova b,∗ , V.I. Kodolov c , Ye.V. Besogonov a a
c
Udmurt State University, 1, Universitetskaya Street, 426034 Izhevsk, Russia b Physical Technical Institute, 132 Kirov Street, 426001 Izhevsk, Russia Scientific and Education Center of Chemical Physics and Mesoscopy of Udmurt Scientific Center of UB of RAS, Izhevsk, Russia Received in revised form 18 September 2003 Available online 1 April 2004
Abstract In the given paper the use of X-ray photoelectron spectroscopy (XPS) as means to control the formation of metal–carbon tubulens by the low-energy synthesis from multiring hydrocarbons in active media is discussed. Based on the results of X-ray photoelectron spectroscopy the assumption about the mechanisms of formation and growth of tubulenes was made, that is confirmed by the results obtained by transmission electron microscopy (TEM). © 2004 Elsevier B.V. All rights reserved. Keywords: X-ray photoelectron spectroscopy; Metal–carbon nanoclusters
1. Introduction The idea of nanotubular forms of substances started to develop in connection with the progress made in the sphere of studying structures and properties of carbon nanoobjects. As one of the possible metastable nanoforms of carbon a quasi-one-dimensional tubular structure was offered [1].The purpose of the work is studying the electronic and atomic structures of metal–carbon nanoclusters and carbon systems.
2. Experimental As a rule, in the world practice either catalytic techniques at temperatures of 500–700 ◦ C or arc plasma methods are used to obtain nanotubes [2–4]. In this work, the studies of carbon–metal-containing nanostructures obtained at temperatures lower than 250 ◦ C were carried out; they are pioneer studies in the sphere of synthesis of carbon nanotubes [5]. Metal–carbon cluster systems were obtained by low-temperature synthesis from aromatic hydrocarbons in active media with layer structures; the active media were
∗
Corresponding author. Fax: +7-3412250614. E-mail address: [email protected] (I.N. Shabanova).
0368-2048/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.elspec.2004.02.035
prepared by melting salts with intercalated metal ions under the action of low-power heat pulses. Anthracene was chosen among aromatic compounds. The ratio of the active medium to anthracene is 10:1. The main idea of the method lies in the use of a mineral medium which transforms graphite-like carbon formed as a result of the organic compound carbonization and results in the formation of nanotubes or metal nanoparticles covered with a carbon layer. The following metals were studied: nickel, cobalt, manganese. Obtaining the carbon nanotubes with the use of the mechanical metal-chloride mixtures requires heating to the temperature close to 250 ◦ C. The nanotubes have a much curved shape and are entangled reminiscent of “balls”; there are also a number of separate nanotubes and metal nanoparticles covered with a carbon layer. The nanotubes are bound together like bunches. The diameters of the tubes vary from 20 to 60 nm. The transmission electron microscopy (TEM) studies show that the average length of nanotubes is ∼300 nm. Purification from anthracene is performed by washing with aromatic hydrocarbons. The amount of anthracene is less than 0.1% after purification. The studies of metal–carbon systems conducted previously showed that the tubulene formation depends on the content of the initial components: anthracene–NaCl–AlCl3 – MeCl2 . In this connection, the dependence of the formation of C–C bonds on the content of the initial components in
240
L.G. Makarova et al. / Journal of Electron Spectroscopy and Related Phenomena 137–140 (2004) 239–242
the mixture prepared from fine powders of anthracene and metal chloride was analyzed. The studies were performed by means of the X-ray photoelectron spectrometer (XPS) with an apparatus resolution 0.1 eV at excitation of Al K␣-lines [6]. The investigated systems were non-conducting samples. In the process of photoemission, a positive charge accumulated on their surfaces; the charge created a retarding field and shifted the atom levels by several electron-volts [7]. To exclude the influence of the effect of charging the aluminium foil was set across the X-ray radiation path. When the foil was irradiated by X-ray radiation, additional electrons were knocked out, which neutralized the surface positive charge. Besides, the samples were rubbed into a copper substrate as a thin layer of ∼1 mkm; it makes charging unnecessary and allows obtaining less structured surface of a sample. The absence of the charging effects was determined by C1s- and O1s-lines. The displacement of the spectrum of these lines was not observed.
(d)
(c)
(b)
(a)
3. Results and discussion It is known from work [8] that in the C1s-spectrum of graphite (Eb = 284.3 eV) there is a satellite at the distance of 22 eV from the main peak; its intensity is 0.1 of the intensity of the main C1s-spectrum. In the C1s-spectrum of diamond (Eb = 286.1 eV) there is also a satellite observed at the distance of 25 eV from the main maximum; its intensity is 0.4 of the intensity of the main maximum, which corresponds to sp2 - and sp3 -types of hybridization. In the C1s-spectrum of hydrocarbons (Eb = 285.0 eV) [9] there is a satellite at the distance of 6–7 eV from the main maximum; its intensity is 8% of the intensity of the main peak. For more precise interpretation of the obtained X-ray electron spectra the following samples were studied: fullerene C60, single-walled and multi-walled carbon nanotubes (SWNT and MWNT), amorphous carbon. The samples were prepared with the arc-heating synthesis. The validation of the samples was conducted with the use of Raman spectroscopy and thermogravimetry. Fig. 1 shows the experimental X-ray electron spectra of the C1s-line. The X-ray electron spectroscopy study of the C60 fullerenes shows that the C1s-spectrum (Fig. 1a) has a complicated form and consists of four components. On the background of the gradually rising spectrum corresponding to characteristic losses, a satellite with the binding energy of 311 eV is observed. This satellite is characteristic of diamond (sp3 ). From this it follows that the most intensive peak in the carbon spectrum is characteristic of diamond-like bond (sp3 -configuration) (286.1 eV); its relative intensity is 50.0%. On the side of smaller binding energies at the distance of 1.1 eV, there is another peak (the binding energy is 285.0 eV) corresponding to C–H bond; its relative intensity is 28.5%. The third and the fourth peaks correspond to the bonds of C–O and shake up (288.0 and 290.0 eV),
260 265 270 275 280 285 290 295 300 305 310 315 320 325 330 335 340 345
Binding Energy, eV Fig. 1. XPS C1s-spectra of etalon samples: (a) C60 ; (b) single-walled carbon nanotubes; (c) multi-walled carbon nanotubes and (d) amorphous carbon.
respectively, and their percentage in the spectrum is 17.4 and 4.1%. The contrast of the O1s-spectrum is ∼0.3. When the globular graphite in aluminium cast iron was studied [8], it was noted, that the atoms of modifiers interacted with the carbon atoms and were adsorbed mostly on the crystal faces, where free bonds existed. As a result, the process of graphitization was slowed down, and the conditions for the crystal building up in the transverse direction were created; while this took place the compact graphite inclusions formed. It was also suggested that the atoms of the modifiers passed a part of the valence electrons to the graphite atoms, which caused the formation of the portion of atoms, which had energetically more stable diamond-like sp3 -hybridization of electrons. The transformation of the sp2 -configuration characteristic of plate-like graphite into the sp3 -configuration took place only on the surface of the graphite inclusions. In Fig. 1b the C1s-spectrum of SWNTs is displayed. On the background of the gradually rising spectrum in the high-energy region, two satellites can be observed characteristic of the sp2 - and sp3 -components. It means that in the C1s-spectrum of the one-wall nanotubes these two components are present. Additionally, there are components corresponding to the C–H and C–O bonds in the spectrum. Their percentage ratio is 34.4:18.4:40.8:6.4. The similar situation is observed in the C1s-spectrum of the MWNTs (Fig. 1c). The spectrum consists of four compo-
L.G. Makarova et al. / Journal of Electron Spectroscopy and Related Phenomena 137–140 (2004) 239–242
nents; their percentage ratio is 41.7:16.7:34.0:7.6. The first and third components correspond to the C–C bonds of various configurations of electrons (sp2 and sp3 ); the second component corresponds to the C–H bond, and the fourth one to the C–O bond. The content of sp2 is larger, which can be explained by the fact that in the MWNTs the distance between the layers is approximately equal to the inter-layer distance in graphite. The C1s-spectrum of amorphous carbon displayed in Fig. 1d consists of three components. The first component is characteristic of the hydrocarbon bonds with the binding energy of 285.0 eV; the second component is shifted by 2 eV to large binding energies (287.0 eV) and corresponds to the C–O bonds. At the distance of 6 eV from the first peak, there is a satellite characteristic of hydrocarbons. The percentage ratio of the components is 64.6:29.1:6.3. The XPS study of the electronic structure of the reference samples allowed to determine the type of hybridization of s and p electrons in the nanotubes. This result was used for the development of a new technique for obtaining the carbon–metal-containing nanotubes from multiring aromatic hydrocarbons in the active media: (1) the formation of the interaction between the carbon atoms, which is characteristic of the nanotubes; (2) the selection of the concentration of the ligand—a complexing agent; (3) the determination of the output percentage of the nanotubes. In Fig. 2 dependences of IC–C /IC–H on the content of 3d-metal chlorides are presented. Curve 1 corresponds to nickel chloride, curve 2 to cobalt chloride and curve 3 to manganese chloride. It seems that such behaviour of dependences could be connected with the ability of the atoms of 3d-metals to form chemical bonds. As far as, the electron density in the vicinity of the atoms of 3d-metals decreases in
Fig. 2. Dependence of IC–C /IC–H on the contents of metal chlorides.
241
case of the elements belonging to the row Ni–Co–Mn, and the energy of interaction of the metals with chlorine ions increases, then the dependences displayed in Fig. 2 behave differently. When fine powders of nickel chloride and anthracene are mixed, the saturation by C–C bonds is observed even at the salt amount equal to 2 mol. In the case of cobalt chloride, an abrupt increase of the portion of C–C bonds is observed, however, judging by the shape of the curve it impossible to say that the saturation by C–C bonds is taking place; and for manganese chloride, a slow growth of the curve of the relation IC–C /IC–H is observed. Different position of the initial points in Fig. 2 is connected with different oxidizing abilities of the ions of 3d-metals under discussion. The investigation of the microstructures was carried out by means of the transmission electron microscope JEM-200CX at the accelerating voltage of 160 kV. In the samples the presence of nanoparticles is observed; their electron diffraction patterns are similar to the ones characteristic to the amorphous state. The sizes of such particles are from 50 to 200 nm; these particles can be polyhedral, or they can have spherical form. The microcrystalline structure state, which forms also on larger objects, was observed for all the samples. The TEM data are given in work [10]. The results of the XPS and TEM studies allow stating that it is possible to control the formation and growth of tubules with the help of the data on the portions of C–C and carbide bonds in the XPS spectrum. The increase of the portions of these bonds in the spectrum correlates with the growth of metal–carbon tubules according to the TEM data. In order to clarify the character of the interaction of the carbon sphere with an incorporated metal atom, the first-principle quantum-chemical calculations of the geometry and electronic structure of the C60 fullerene in different basis and also its complexes with the atoms and ions of alkali and 3d-metals were carried out. The results received allow concluding that the metal–carbon bonds in the compounds of cobalt–carbon sphere and nickel–carbon sphere are covalent in nature. Between the carbon and the metal in the compounds of carbon sphere and alkali metal or manganese the covalent bonds are absent. In this case, one can observe only the charge transfer from the metal atom to the carbon sphere. We believe that different behaviour of the curves in Fig. 2 allows to draw a conclusion on the mechanisms of formation and growth of metal–carbon tubules. Amorphous carbon serves as a base for the formation of tubules. Amorphous carbon contains embedded nanoparticles of metal, which can be considered as “embryos growing up” into tubules. The growth of dendrite-like structures, the so-called “dendrites”, occurs on the particles of metal. In this work different stages of the formation of tubules are presented. For example, in case of manganese chloride only two structures are formed representing the base for the further growth of tubules. The second stage of tubulene formation is shown in the example of cobalt chloride. The dendrite-like structures are formed on the particle of the metal. The formation and growth of
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nanotubes take place in the case of nickel chloride. These assumptions based on the data of XPS are fully confirmed by the TEM results. The obtained regularities may facilitate the development of new trends in the synthesis of tubules with unique properties.
Acknowledgements
4. Conclusion
References
Thus, based on the given study we may draw the following conclusions:
[1] J.W. Mintmire, B.I. Dunlap, C.T. White, Phys. Rev. Lett. 68 (1992) 631. [2] S. Iijima, Nature 354 (1991) 56. [3] T.W. Ebbsen, P.M Ajayan, Nature 358 (1992) 220. [4] W.K. Hsu, M. Terrones, J.P. Hare, et al., Chem. Phys. Lett. 262 (1996) 161. [5] V.I. Kodolov, O.Yu. Boldenkov, N.V. Khokhriakov, S.N. Babushkina, et al., Anal. Control 4 (1999) 25. [6] I.N. Shabanova, V.P. Sapozhnikov, V.Y. Bayankin, V.G. Bragin, Prib. Tekh. Eksp. 1 (1981) 138. [7] V.I. Nefyodov, X-ray Photoelectron Spectroscopy of Chemical Compounds, Moscow, 1984. [8] K.M. Kolobova, I.N. Shabanova, O.A. Kulyabina, V.A. Trapeznikov, V.E. Dolgih, Fisica metallov i metallovedenie 51 (4) (1981) 893. [9] D. Briggs, M.P. Seach, Practical Surface Analysis by Auger and X-ray Photoelectron Spectroscopy, Wiley, Chichester, 1983. [10] V.I. Kodolov, I.N. Shabanova, L.G. Makarova, et al., Zhurnal strukturnoi chimii 42 (2) (2001) 260.
• There is a possibility of receiving multilayer carbon tubes from the mixtures of fine-dispersed powders of aromatic hydrocarbons and metal salts. The direct observation reveals that the formed tubes (tubules) have the sizes from 50 to 200 nm, and they are the result of the rolling up of graphite planes in a spiral on the surfaces of metallic particles. Mainly the ends of these tubes are closed and there is amorphous carbon on their surfaces. • The study of the structure of metal–carbon systems by XPS together with TEM allows using XPS to control the formation of metal–carbon tubules. • Based on the XPS spectra it is possible to conclude that the increase of the content of 3d-metal salt in the mixture of fine powders leads to the growth of the portion of C–C bonds.
The authors want to thank A.Yu. Volkov and Ye.G. Volkova for their contribution in the investigation of the samples by the TEM method.
X-ray photoelectron spectroscopy as a method to control the received metal–carbon nanostructures L.G. Makarova a , I.N. Shabanova b,∗ , V.I. Kodolov c , Ye.V. Besogonov a a
c
Udmurt State University, 1, Universitetskaya Street, 426034 Izhevsk, Russia b Physical Technical Institute, 132 Kirov Street, 426001 Izhevsk, Russia Scientific and Education Center of Chemical Physics and Mesoscopy of Udmurt Scientific Center of UB of RAS, Izhevsk, Russia Received in revised form 18 September 2003 Available online 1 April 2004
Abstract In the given paper the use of X-ray photoelectron spectroscopy (XPS) as means to control the formation of metal–carbon tubulens by the low-energy synthesis from multiring hydrocarbons in active media is discussed. Based on the results of X-ray photoelectron spectroscopy the assumption about the mechanisms of formation and growth of tubulenes was made, that is confirmed by the results obtained by transmission electron microscopy (TEM). © 2004 Elsevier B.V. All rights reserved. Keywords: X-ray photoelectron spectroscopy; Metal–carbon nanoclusters
1. Introduction The idea of nanotubular forms of substances started to develop in connection with the progress made in the sphere of studying structures and properties of carbon nanoobjects. As one of the possible metastable nanoforms of carbon a quasi-one-dimensional tubular structure was offered [1].The purpose of the work is studying the electronic and atomic structures of metal–carbon nanoclusters and carbon systems.
2. Experimental As a rule, in the world practice either catalytic techniques at temperatures of 500–700 ◦ C or arc plasma methods are used to obtain nanotubes [2–4]. In this work, the studies of carbon–metal-containing nanostructures obtained at temperatures lower than 250 ◦ C were carried out; they are pioneer studies in the sphere of synthesis of carbon nanotubes [5]. Metal–carbon cluster systems were obtained by low-temperature synthesis from aromatic hydrocarbons in active media with layer structures; the active media were
∗
Corresponding author. Fax: +7-3412250614. E-mail address: [email protected] (I.N. Shabanova).
0368-2048/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.elspec.2004.02.035
prepared by melting salts with intercalated metal ions under the action of low-power heat pulses. Anthracene was chosen among aromatic compounds. The ratio of the active medium to anthracene is 10:1. The main idea of the method lies in the use of a mineral medium which transforms graphite-like carbon formed as a result of the organic compound carbonization and results in the formation of nanotubes or metal nanoparticles covered with a carbon layer. The following metals were studied: nickel, cobalt, manganese. Obtaining the carbon nanotubes with the use of the mechanical metal-chloride mixtures requires heating to the temperature close to 250 ◦ C. The nanotubes have a much curved shape and are entangled reminiscent of “balls”; there are also a number of separate nanotubes and metal nanoparticles covered with a carbon layer. The nanotubes are bound together like bunches. The diameters of the tubes vary from 20 to 60 nm. The transmission electron microscopy (TEM) studies show that the average length of nanotubes is ∼300 nm. Purification from anthracene is performed by washing with aromatic hydrocarbons. The amount of anthracene is less than 0.1% after purification. The studies of metal–carbon systems conducted previously showed that the tubulene formation depends on the content of the initial components: anthracene–NaCl–AlCl3 – MeCl2 . In this connection, the dependence of the formation of C–C bonds on the content of the initial components in
240
L.G. Makarova et al. / Journal of Electron Spectroscopy and Related Phenomena 137–140 (2004) 239–242
the mixture prepared from fine powders of anthracene and metal chloride was analyzed. The studies were performed by means of the X-ray photoelectron spectrometer (XPS) with an apparatus resolution 0.1 eV at excitation of Al K␣-lines [6]. The investigated systems were non-conducting samples. In the process of photoemission, a positive charge accumulated on their surfaces; the charge created a retarding field and shifted the atom levels by several electron-volts [7]. To exclude the influence of the effect of charging the aluminium foil was set across the X-ray radiation path. When the foil was irradiated by X-ray radiation, additional electrons were knocked out, which neutralized the surface positive charge. Besides, the samples were rubbed into a copper substrate as a thin layer of ∼1 mkm; it makes charging unnecessary and allows obtaining less structured surface of a sample. The absence of the charging effects was determined by C1s- and O1s-lines. The displacement of the spectrum of these lines was not observed.
(d)
(c)
(b)
(a)
3. Results and discussion It is known from work [8] that in the C1s-spectrum of graphite (Eb = 284.3 eV) there is a satellite at the distance of 22 eV from the main peak; its intensity is 0.1 of the intensity of the main C1s-spectrum. In the C1s-spectrum of diamond (Eb = 286.1 eV) there is also a satellite observed at the distance of 25 eV from the main maximum; its intensity is 0.4 of the intensity of the main maximum, which corresponds to sp2 - and sp3 -types of hybridization. In the C1s-spectrum of hydrocarbons (Eb = 285.0 eV) [9] there is a satellite at the distance of 6–7 eV from the main maximum; its intensity is 8% of the intensity of the main peak. For more precise interpretation of the obtained X-ray electron spectra the following samples were studied: fullerene C60, single-walled and multi-walled carbon nanotubes (SWNT and MWNT), amorphous carbon. The samples were prepared with the arc-heating synthesis. The validation of the samples was conducted with the use of Raman spectroscopy and thermogravimetry. Fig. 1 shows the experimental X-ray electron spectra of the C1s-line. The X-ray electron spectroscopy study of the C60 fullerenes shows that the C1s-spectrum (Fig. 1a) has a complicated form and consists of four components. On the background of the gradually rising spectrum corresponding to characteristic losses, a satellite with the binding energy of 311 eV is observed. This satellite is characteristic of diamond (sp3 ). From this it follows that the most intensive peak in the carbon spectrum is characteristic of diamond-like bond (sp3 -configuration) (286.1 eV); its relative intensity is 50.0%. On the side of smaller binding energies at the distance of 1.1 eV, there is another peak (the binding energy is 285.0 eV) corresponding to C–H bond; its relative intensity is 28.5%. The third and the fourth peaks correspond to the bonds of C–O and shake up (288.0 and 290.0 eV),
260 265 270 275 280 285 290 295 300 305 310 315 320 325 330 335 340 345
Binding Energy, eV Fig. 1. XPS C1s-spectra of etalon samples: (a) C60 ; (b) single-walled carbon nanotubes; (c) multi-walled carbon nanotubes and (d) amorphous carbon.
respectively, and their percentage in the spectrum is 17.4 and 4.1%. The contrast of the O1s-spectrum is ∼0.3. When the globular graphite in aluminium cast iron was studied [8], it was noted, that the atoms of modifiers interacted with the carbon atoms and were adsorbed mostly on the crystal faces, where free bonds existed. As a result, the process of graphitization was slowed down, and the conditions for the crystal building up in the transverse direction were created; while this took place the compact graphite inclusions formed. It was also suggested that the atoms of the modifiers passed a part of the valence electrons to the graphite atoms, which caused the formation of the portion of atoms, which had energetically more stable diamond-like sp3 -hybridization of electrons. The transformation of the sp2 -configuration characteristic of plate-like graphite into the sp3 -configuration took place only on the surface of the graphite inclusions. In Fig. 1b the C1s-spectrum of SWNTs is displayed. On the background of the gradually rising spectrum in the high-energy region, two satellites can be observed characteristic of the sp2 - and sp3 -components. It means that in the C1s-spectrum of the one-wall nanotubes these two components are present. Additionally, there are components corresponding to the C–H and C–O bonds in the spectrum. Their percentage ratio is 34.4:18.4:40.8:6.4. The similar situation is observed in the C1s-spectrum of the MWNTs (Fig. 1c). The spectrum consists of four compo-
L.G. Makarova et al. / Journal of Electron Spectroscopy and Related Phenomena 137–140 (2004) 239–242
nents; their percentage ratio is 41.7:16.7:34.0:7.6. The first and third components correspond to the C–C bonds of various configurations of electrons (sp2 and sp3 ); the second component corresponds to the C–H bond, and the fourth one to the C–O bond. The content of sp2 is larger, which can be explained by the fact that in the MWNTs the distance between the layers is approximately equal to the inter-layer distance in graphite. The C1s-spectrum of amorphous carbon displayed in Fig. 1d consists of three components. The first component is characteristic of the hydrocarbon bonds with the binding energy of 285.0 eV; the second component is shifted by 2 eV to large binding energies (287.0 eV) and corresponds to the C–O bonds. At the distance of 6 eV from the first peak, there is a satellite characteristic of hydrocarbons. The percentage ratio of the components is 64.6:29.1:6.3. The XPS study of the electronic structure of the reference samples allowed to determine the type of hybridization of s and p electrons in the nanotubes. This result was used for the development of a new technique for obtaining the carbon–metal-containing nanotubes from multiring aromatic hydrocarbons in the active media: (1) the formation of the interaction between the carbon atoms, which is characteristic of the nanotubes; (2) the selection of the concentration of the ligand—a complexing agent; (3) the determination of the output percentage of the nanotubes. In Fig. 2 dependences of IC–C /IC–H on the content of 3d-metal chlorides are presented. Curve 1 corresponds to nickel chloride, curve 2 to cobalt chloride and curve 3 to manganese chloride. It seems that such behaviour of dependences could be connected with the ability of the atoms of 3d-metals to form chemical bonds. As far as, the electron density in the vicinity of the atoms of 3d-metals decreases in
Fig. 2. Dependence of IC–C /IC–H on the contents of metal chlorides.
241
case of the elements belonging to the row Ni–Co–Mn, and the energy of interaction of the metals with chlorine ions increases, then the dependences displayed in Fig. 2 behave differently. When fine powders of nickel chloride and anthracene are mixed, the saturation by C–C bonds is observed even at the salt amount equal to 2 mol. In the case of cobalt chloride, an abrupt increase of the portion of C–C bonds is observed, however, judging by the shape of the curve it impossible to say that the saturation by C–C bonds is taking place; and for manganese chloride, a slow growth of the curve of the relation IC–C /IC–H is observed. Different position of the initial points in Fig. 2 is connected with different oxidizing abilities of the ions of 3d-metals under discussion. The investigation of the microstructures was carried out by means of the transmission electron microscope JEM-200CX at the accelerating voltage of 160 kV. In the samples the presence of nanoparticles is observed; their electron diffraction patterns are similar to the ones characteristic to the amorphous state. The sizes of such particles are from 50 to 200 nm; these particles can be polyhedral, or they can have spherical form. The microcrystalline structure state, which forms also on larger objects, was observed for all the samples. The TEM data are given in work [10]. The results of the XPS and TEM studies allow stating that it is possible to control the formation and growth of tubules with the help of the data on the portions of C–C and carbide bonds in the XPS spectrum. The increase of the portions of these bonds in the spectrum correlates with the growth of metal–carbon tubules according to the TEM data. In order to clarify the character of the interaction of the carbon sphere with an incorporated metal atom, the first-principle quantum-chemical calculations of the geometry and electronic structure of the C60 fullerene in different basis and also its complexes with the atoms and ions of alkali and 3d-metals were carried out. The results received allow concluding that the metal–carbon bonds in the compounds of cobalt–carbon sphere and nickel–carbon sphere are covalent in nature. Between the carbon and the metal in the compounds of carbon sphere and alkali metal or manganese the covalent bonds are absent. In this case, one can observe only the charge transfer from the metal atom to the carbon sphere. We believe that different behaviour of the curves in Fig. 2 allows to draw a conclusion on the mechanisms of formation and growth of metal–carbon tubules. Amorphous carbon serves as a base for the formation of tubules. Amorphous carbon contains embedded nanoparticles of metal, which can be considered as “embryos growing up” into tubules. The growth of dendrite-like structures, the so-called “dendrites”, occurs on the particles of metal. In this work different stages of the formation of tubules are presented. For example, in case of manganese chloride only two structures are formed representing the base for the further growth of tubules. The second stage of tubulene formation is shown in the example of cobalt chloride. The dendrite-like structures are formed on the particle of the metal. The formation and growth of
242
L.G. Makarova et al. / Journal of Electron Spectroscopy and Related Phenomena 137–140 (2004) 239–242
nanotubes take place in the case of nickel chloride. These assumptions based on the data of XPS are fully confirmed by the TEM results. The obtained regularities may facilitate the development of new trends in the synthesis of tubules with unique properties.
Acknowledgements
4. Conclusion
References
Thus, based on the given study we may draw the following conclusions:
[1] J.W. Mintmire, B.I. Dunlap, C.T. White, Phys. Rev. Lett. 68 (1992) 631. [2] S. Iijima, Nature 354 (1991) 56. [3] T.W. Ebbsen, P.M Ajayan, Nature 358 (1992) 220. [4] W.K. Hsu, M. Terrones, J.P. Hare, et al., Chem. Phys. Lett. 262 (1996) 161. [5] V.I. Kodolov, O.Yu. Boldenkov, N.V. Khokhriakov, S.N. Babushkina, et al., Anal. Control 4 (1999) 25. [6] I.N. Shabanova, V.P. Sapozhnikov, V.Y. Bayankin, V.G. Bragin, Prib. Tekh. Eksp. 1 (1981) 138. [7] V.I. Nefyodov, X-ray Photoelectron Spectroscopy of Chemical Compounds, Moscow, 1984. [8] K.M. Kolobova, I.N. Shabanova, O.A. Kulyabina, V.A. Trapeznikov, V.E. Dolgih, Fisica metallov i metallovedenie 51 (4) (1981) 893. [9] D. Briggs, M.P. Seach, Practical Surface Analysis by Auger and X-ray Photoelectron Spectroscopy, Wiley, Chichester, 1983. [10] V.I. Kodolov, I.N. Shabanova, L.G. Makarova, et al., Zhurnal strukturnoi chimii 42 (2) (2001) 260.
• There is a possibility of receiving multilayer carbon tubes from the mixtures of fine-dispersed powders of aromatic hydrocarbons and metal salts. The direct observation reveals that the formed tubes (tubules) have the sizes from 50 to 200 nm, and they are the result of the rolling up of graphite planes in a spiral on the surfaces of metallic particles. Mainly the ends of these tubes are closed and there is amorphous carbon on their surfaces. • The study of the structure of metal–carbon systems by XPS together with TEM allows using XPS to control the formation of metal–carbon tubules. • Based on the XPS spectra it is possible to conclude that the increase of the content of 3d-metal salt in the mixture of fine powders leads to the growth of the portion of C–C bonds.
The authors want to thank A.Yu. Volkov and Ye.G. Volkova for their contribution in the investigation of the samples by the TEM method.