Method of producing low molecular polymer-dimers of fullerene c20

FIELD: physics.

SUBSTANCE: two fullerenes 1 C20 are put into a closed carbon nanotube 2, at the opposite end of which there is spherical fullerene 3 C60, acting as a plunger, applying a pressure of 43.24 hPa on two fullerenes 1 C20.

EFFECT: obtaining dimers of fullerene C20 without impurity atoms.

3 dwg, 1 tbl

 

The invention relates to the field of solid state physics (kempisty) and can be used to produce nanostructured materials with new properties. In the future it is expected the synthesis of such fullerite, which would be a superconductor even at room temperature.

A known method of producing dimer (C60)2 from fullerites, which consists in placing fullerite at one end of the cylindrical chamber (capsule), acting on fullerite pressure of 8 GPA at a temperature of 290 K (see Averkin, Yea, Bview, Aghlabid, Mphande, Way. Thermodynamic and dilatometric properties of dimeric phase of fullerene C60 // FTT, 2003, Vol.45, issue 4. S-766), or a pressure of 1.5 GPA at a temperature of 373 K and above (see Wagawaga, Listishenkova, Averina, Vmmanager, Any Vinegaroon. Determination of rate constants and activation energies induced by the pressure of the reaction 2+2 cycloaddition of fullerene C60. // FTT, 2002, t, issue 3. S-533).

However, the disadvantage of this method is the presence of impurities in the final product.

Known methods for producing dimers more polyhydric fullerenes, such as the synthesis of cross-dimer of C60-C70 mechanochemical method: in a capsule powder of fullerenes C60 and C70 in the presence of a catalyst is subjected to high frequency vibration and crushing (see .Komatsu, K, Fujiwara and Y.Murata The fullerenecross-dimer 130: synthesis and properties. // Chem. Commun., 2000, 1583-1584). The dimers miniature carbon cluster fullerene C20 and hypothetical patterns of crystals [C20]n so far studied only theoretically (see Alistratov, Ivemania, Ala. A new allotropic form of carbon [C]n based on the fullerene C20 and cubic cluster C8 and its analogues for the elements Si and Ge: computational simulation. // FTT, 2005, t, issue 1. P.184-190; Ahitophel, Liapunov. The education cluster molecules" (C20)2 and its thermal stability, " FIZ, 2006, t, vyp. C-2110). Experimental the synthesis of the dimer is hampered by the metastability of isomers (C20)2.

The disadvantage of this method is the impossibility of obtaining chemically pure powder dimers.

Closest to the claimed invention is a method of obtaining a crystal [s]n based on the fullerene C20 and cubic cluster C8. Of great interest is the synthesis of macroscopic cluster of substances on the basis of fullerenes C20. According to some theoretical studies such substance may be a superconductor with a very high critical temperature. Finding ways of formation of fullerites begin, usually with a detailed discussion of the processes of dimerization cluster Cn. For many of fullerenes already found several metastable isomers (Cn)2, distinguished by the number, strength is the length of intercluster links. Synthesized cross-dimers formed by different fullerenes, such as C60-C70.

However, the synthesized all the mentioned methods, the product is a crystalline powder, where in addition to low-molecular-weight polymer (dimer) certainly contains some impurities.

The objective of the proposed solutions is to obtain fullerene dimer With20representing low molecular weight polymer cluster not containing impurity atoms.

The problem is solved in that in the method of synthesis of fullerene dimer

C20-(C20)2, including the effects of high pressure on the source material, placed at one end of the capsule, according to the solution as a starting material selected two fullerene C20and as cylindrical chambers used a closed carbon nanotube, and the influence exercised by the encapsulated molecule steropodon fullerene C60located at the opposite end of the tube, the exposure is carried out at a pressure of 43,24 HPa.

The invention is illustrated by drawings, where figure 1 is presented the scheme of obtaining dimer (C20)2; figure 2 shows the relative orientation of the objects in the pressure in the nanotube 43.24 HPa, figure 3 - dimer (C20)2after returning molecule With60/sub> in initial position, where

1 - fullerenes (source material);

2 - closed carbon nanotube (capsule);

3 - encapsulated molecule (fullerene spheroid);

4 - electrodes to a power source.

Carbon nanotube serving cylindrical capsule, which is the process of dimerization, can be any atomic structure, as nokialino (zigzag, armchair), and chiral. Van der Waals interaction of the source material (fullerene20) with the surface of the capsule does not depend on its structure, as determined by the internuclear distance (see D. Qian, W.K. Liu, R.S. Ruoff Mechanical properties of carbon nanotubes: theory and experimental measurements // C.R.Physique 2003, No. 4. P.993-1008):

where Uithe interaction potential of the i-th pair of carbon atoms belonging to different molecules, ri- the distance between atoms i-th pair, σ=1.42 Å is the length of the C-C bond, yabout=2.7 and A=24.3·10-79J·m6- empirically chosen parameters. The absolute requirement of the nanotube is the presence of two caps on the ends. They needed to create an enclosed space. Beanies are formed by fragments of fullerenes C240etc. depending on the tube diameter. Synthesis technology of closed carbon nanotubes to date are well developed, particularly among the most promising are the CVD method is s (nanotubes are deposited by a chemical process from the gas phase) (see Niiiccee, Svilova, Najarian. About the mechanism of formation of carbon nanotubes in electrochemical processes // journal of technical physics, 2006, t, issue 3. S-63; Niiiccee, Sghittosa, Ugospel, Svilova, Kneenew, Acceration, Najarian, Sagarika. Production of carbon nanotubes in the reactions of self-propagating high temperature synthesis // technical physics letters, 2006, t, issue 2. P.84-89) and the method of synthesis in the reactor with activated hydrogen (see Laurasian, Davlatov, Tuveson, We Aim Swieradow. Synthesis of carbon nanofibers and nanotubes in the reactor with activated hydrogen // technical physics letters, 2006, t, vyp. Pp.92-97).

Encapsulated molecule, which plays the role of the piston, must carry an electrical charge and have dimensions that are in a specific agreement with the transverse dimensions of the nanotubes. The gap between the molecule and the cylinder should be such that the trajectory of the molecules moving under the action of an external electric field coincides with the axis of the cylinder, providing a uniform impact on the source material. Moreover, the encapsulated molecule must be of such chemical composition and form to ensure that the orientation of the covalent bond (maximum overlap of the electronic orbitals) of the source material - fullerenes. This requirement meets the fullerene spheroid shape, in which the atoms nah who are in state sp 2+Δ-hybridization (Δ=0.2÷0.3). The presence of molecules of atoms in state sp3-hybridization (or close to it) leads to increased chemical activity of the molecule. This, in turn, can lead to the formation of chemical bonds between the encapsulated molecule and one of the fullerene source material, which is unacceptable (education dimer will not happen). The fullerene spheroid shape is the cluster With60etc. To be encapsulated in a fullerene nanotube meet the above requirements, dimensions, distance of molecule - wall should be 3.1÷3.4 Å. Authors (see Otani M., Okada, S., and A. Oshiyama Phys. Rev. B. - 2003. - 68,12. - R(1-8)shows that the energetically favorable for fullerene C60is the placement in the tube at a distance of fullerene - wall 3.11 Å. Encapsulation With60in tubes of larger diameter is also exothermic, and smaller - indeterminism.

Encapsulation of fullerenes in nanotubes is carried out in various ways. In the work (see S.Berber, Y.-K.Kwon and D.Tomanek Microscopic Mechanismof Formation Nanotube Peapods // PhysRevLett. V.88. No. 18. 2002. P.185502 (4)) describes how the introduction of fullerene into the tube through the side surface of the cylinder, (see Z.Shi, L.Guan, K.Suenaga, Z.Gu and S.Iijima Direct Imagingof the Alkali Metal Site in K-Doped Fullerene Peapods // PhysRevLett. V.94. No. 4. 2005. P.045502 (4)) describes the method for synthesizing nanostructed (nanotubes with fullerenes inside) is here mixing in vacuum (pressure of 10 -3PA) single-layer tubes with fullerenes in the gas phase at a temperature of 773 K in 48 hours

The charge on the fullerene may report positive ion potassium or lithium, placed inside. The doped fullerenes With60the Li atoms may, for example, irradiation of fullerite60a beam of lithium ions with energies up to 30 eV (see N.Krawez, A.Gromov, R.Tellgmann, E.E.B.Campbell, Electronic properties of novel materials. - Progress in molecular nanostructures, XII International Winterschool, Kirchberg, Tyrol, Austria, 1998, p.368).

The way the dimerization is carried out as follows (an example of practical implementation of the method is demonstrated on the case of dimerization of fullerene20).

Encapsulated in the tube 2 fullerenes With20to timeresults or to cure spontaneously, i.e. under the influence solely of retaining tube potential, can't (fullerene C20tend to form with each other new complexes of one-, two - and three-dimensional spiral). To stimulate this process, producing fullerenes 1 additional pressure sufficient to overcome the repulsive potential Vander Waals forces. It is known that processes only at a sufficiently high pressure, is carried out in a closed cylinder (autoclave). So fullerenes With20placed in a closed capsule - tube 2 (nonautoclaved), which has a closed carbon single-walled nanotubes is C 740. The role of the piston, creating the desired pressure, executes the encapsulated molecule 3 - endohedral fullerene K+@C60(carrying a positive charge), moving from one end of the tube to another under the action of an external electric field. Nanotube C740is the tube from the tube (10,10), closed on two sides halves of fullerene C240.

The initial position of the molecule-of piston With60in keeping with the fundamental condition of nanoparticles: From60is one preconceive region nanotubes (about one fullerene caps), and the source material is in the opposite. As soon as the electrodes creates a certain potential difference, fullerene C60begins to move in the opposite end of the nanotube, providing closer to increasing pressure on fullerenes With20. The pressure is calculated as the volumetric energy density of the interaction of a molecule C20with surrounding objects: neighboring fullerene C20walls capsules740and the approaching piston (molecule60). Under the scope of the fullerene is the amount of the corresponding sphere diameter 4.088 Å.

At the initial moment (until an external electric field) all the molecules inside the capsule are in the ground state and the pressure is zero. When approaching fullerene C20 at a distance of ~2 Å, the interaction energy increases, significantly increasing the pressure. This relative position of the molecules is characterized by the overlap of the electron clouds of molecules With20. Phenomenological interaction energy of the electronic orbitals Urepis determined by the expression (in the framework of the strong ties) (see Oegema, Aijanov. The equilibrium state of the nanoclusters C60, C70, s and local defects in the molecular skeleton // FTT, 2003, 45, 1, S-186):

where r is the distance between atoms i, j - orbital moments of the wave function; α is the index indicating the type of communication (σ or π), N is the number of pairs of atoms belonging to different molecules. The values of the parametersbe:,,,. Because of spheroidally molecules of the piston and, consequently, low rehybridization its atoms, fullerenes With20form a dimer with each other, and not with a molecule With60. This is evidenced by the larger value of the phenomenological energy of interaction of fullerenes With20compared with the interaction With20-C60. Table 1 shows some data of the dynamics of fullerene C20and molecules With60in the tube with the approach: the distance between the fullerenes, energiasaastu electron clouds of various fullerenes and pressure, test average fullerene C20located between the other cluster C20and C60. At a distance of 1.8÷1.9 Å pressure induces the occurrence of chemical bonds between atoms are facing each other Pentagon fullerenes

C20and, as a consequence, the synthesis of dimer (C20)2. After returning molecule With60in initial position (as a result of changing the direction of the intensity of the external electric field) dimer several changes its position, remaining stable.

Table 1
The characterization of the interaction of the source material (fullerene) with encapsulated molecule
d1(C60-C20), Åd2(C20-C20), ÅUrep(C60-C20), eVUrep(C20-C20), eVP, HPa
2.732.800.0000.0001.27
2.662.460.0000.0006.27
2.602.380.0000.00012.42
2.401.900.0010.31043.24
Where d1d2- bimolecular distances (see figure 2), P is the pressure.

As can be seen from the table, under the pressure of the encapsulated molecules of the piston at a distance of ~1.9 Å observed the interaction of the electron orbitals exactly fullerene source material. Interaction with spheroidal molecule is negligible, and as with the walls of the nanotube (the distance the molecule-wall 2.4÷2.6 Å). Therefore, the formation of chemical bonds between the five atoms of one fullerene With20and five other (relevant pentagons in the field of nanotubes facing each other).

The calculations were performed by the modified method of strong ties.

Experimental studies of the presented method for the synthesis of dimers was carried out as follows.

The source material is a tube with a fullerene - derived from heptane CVD method on a silicon substrate with an underlayer of chromium (as catalyst was used iron). Then, the original samples were processed isolateto plasma in an oxygen atmosphere for 40 to 80 seconds (pressure of oxygen 0.8 mm Hg).

The height of the nanotubes, cleaning the annulus from graphite flakes, iron carbide and iron is used as catalyst, was carried out by plasma-chemical etching of the obtained films with carbon nanostructures. Nanotubes are oriented perpendicular to the surface of the substrate (this is confirmed by photographs taken with an atomic force microscope, N.I.Sinitsyn, Yu.V.Gulyaev, O.E.Glukhova et al. Thin films consisting of carbon nanotubes as a new material for emission electronics // Applied Surface Science, No. 111, p.145-150, 1997). The chemical purity of the samples was investigated by laser spectroscopy methods, which allows to determine the chemical composition of the tested object (laser emission spectrometer SPECS series LAES). Purity nanotube film is 100%. For complete cleaning of the nanotubes from the by-products of the synthesis was carried out plasma-chemical etching nanotube film in an oxygen atmosphere or additional processing by laser radiation (A Simple and Complete Purificaton of Singl-Walled Carbon Nanotube Materials // Advan. Mater., 1999, V.11, No. 16, 1354-1358). In the end, the cleanliness of the tubes was 100%. The capsule was tube (10,10), closed on both sides of fullerene caps. Tube length of 4.5 nm. Encapsulated fullerene spheroid were fullerene C60as raw materials - fullerenes With20. The experiment was conducted at a pressure 43,24 HPa and different is different potentials 2,851 In on the electrodes.

To create the necessary tension of the sample is placed on a flat surface (diameter of a few millimeters) at the cathode, the anode is located above the surface of the cathode at a distance of 15-20 microns. In table 2 below, the tension on the surface of the films synthesized at different thicknesses of the catalyst.

In our case, the tube length is 1-5 μm, a diameter of 15±5 nm. As shown in (..Glukhova, A.I.Zhbanov, G.V.Torgashov et al. Effect on the Field Emission of Corbon Nanotube Films // Applied Surface Science, 2003. V.215 (Issue 1-4) 15 June. P.149-159), the tension on the surface of the nanotubes is higher in the tens to hundreds of times compared with the plane nanotube film. The table shows the calculated values of tension near the tube, the amount of impurities. The experiment is conducted at a temperature of 290 K for 30-40 seconds in a vacuum.

The formation of dimers of fullerenes is fixed by using a transmission electron microscope, which can be seen in the cavity of the tubes.

The amount of impurities in each sample, as can be seen from table 2, is reduced in most cases, this is quite expected, since the remaining part of the metal catalyst on the walls, in the interlayer space) is transferred under the influence of an external electric field (large enough tension) from the film on the anode, which was observed earlier in the study Amy is these electrons from the nanotubes (N.I.Sinitsyn, Yu.V.Gulyaev, O.E.Glukhova et al. Thin films consisting of carbon nanotubes as a new material for emission electronics // Applied Surface Science, 1997. V.11. P.145-150; N.I.Sinitsyn, Yu.V.Gulyaev, O.E.Glukhova et al. Work function estimate for electrons emitted from carbon nanotube cluster films // J. Vac. Sci. Technol. 15(2), Mart/Apr 1997. P.422-424).

In General, it should be noted that the appearance of impurity atoms inside carbon nanotubes at room temperature and the conditions of the cold emission of electrons, it is unlikely (unless the impurities are not present initially in the cavity of the tube, since the synthesis of the tube with fullerenes). This is evidenced by the experimental data (Zujin Shi, Lunhui Guan, Kazu Suenaga, Zhennan Gu, and Sumio lijima Direct Imaging of the Alkali Metal Site in K-Doped Fullerene Peapods // Physical Review Letters, v.94, N 4, p.045502(4), 2005), according to which the process of penetration of potassium atoms through the wall nanotubes filled with fullerenes in the cavity requires high temperature and dozens of hours of time. For example, at a temperature of 473 To this process took 50 hours. In our case the temperature does not rise, and the whole process is less than a minute.

If you compare with other method of synthesis of fullerene dimers (Wagawaga, Listishenkova, Averina, Vmmanager, Ana, Vinegaroon. Determination of rate constants and activation energies induced by the pressure of the reaction 2+2 cycloaddition of fullerene C60. // FTT, 2002, t, issue 3. S-533), it should be noted that the pressure of 1.5 GPA is not secured for themselves the full erenow in the synthesis process, and for macroobject powder solid phase fullerene. The pressure is generated externally by mechanical means, not electric (that is, with the help of an external field), as in our case.

Thus, the proposed method allows to obtain a fullerene dimers without impurity atoms.

The method of synthesis of a dimer of fullerene C20-(C20)2, including the effects of high pressure on the source material, placed at one end of the capsule, wherein as a starting material selected two fullerene C20and as cylindrical chambers used a closed carbon nanotube, and the influence exercised by the encapsulated molecule steropodon fullerene C60located at the opposite end of the tube, the exposure is carried out at a pressure of 43,24 HPa.



 

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4 cl, 1 tbl, 25 ex

FIELD: chemistry.

SUBSTANCE: invention refers to the catalytic systems based on gold; usage of nanometric gold precipitation by the condensation from vapour phase to the activated carrier; system of breathing organs defence using aforesaid catalytic systems. The method of heterogenous catalytic system making is described including: 1) condensation from vapour phase of the catalytically active gold clusters with dimensions in the range from 0.5 to 50 nm to the nanoporous carrier; 2) the following stages: (a) impregnation of water-soluble salt to the catalyst nanoporous carrier; (b) thermic treatment of the said impregnated carrier at temperature more than approximately 200°C; (c) condensation from vapour phase of the catalytically active gold clusters with dimensions in the range from 0.5 to 50 nm to the said thermically treated nanoporous carrier; 3) following stages: a) aggregation of the relatively small particles multifold and of the relatively large particles multifold to the multifold of nanoporous composite particles; b) precipitation of catalytically active gold clusters with dimensions in the range from 0.5 to 50 nm gold clusters to the said composite particles by the condensation from vapour phase. The described heterogenous catalytic system contain: 1) nanoporous carrier; at least one water-soluble salt impregnated to the said carrier; clusters of catalytically active gold with dimensions in the range from 0.5 to 50 nm precipitated on the said carrier with the penetration depth index in the range from ca 1×10-9 to ca 0.1; 2) multifold of the composite catalytically active particles characterised in that said catalytically active particles are obtained from the components containing relatively small particles and relatively large particles with said composite particles containing catalytically active gold precipitated on the relatively small particles by the condensation from vapour phase. The system of breathing organs defence including any of aforesaid heterogenous catalytic systems is described.

EFFECT: invention provides essential improvement of the method of gold-containing catalytic systems preparation and enhancing of their characteristics.

22 cl, 71 ex, 4 tbl, 58 dwg

FIELD: physics.

SUBSTANCE: invention is related to micro- and nanoelectronics and may be used in production of integral silicon chemical and biosensors for automated control of environment, in ecology, in chemical production, in biology and medicine. Invention is aimed at reduction of nanosensor size, reduction of defectiveness, increased sensitivity, repeatability and efficiency, achievement of compatibility with standard industrial technology VLSI. In method for manufacture of nanosensor, which consists in the fact that dielectric layer is created on silicon substrate, and on surface of dielectric layer silicon layer is formed, from which nanowire with ohm contacts is formed via mask by etching, etching for formation of nanowire with ohm contacts of specified size is carried out in vapours of xenon difluoride with the rate of 36÷100 nm/min, at temperature of 5÷20°C, for 0.3÷1.3 min., silicon layer, from which nanowire is formed with ohm contacts by etching, is created with thickness of 11÷45 nm, and etching mask used is mask of polymer polymethyl methacrylate with thickness of 50÷150 nm.

EFFECT: reduction of nanosensor size, reduction of defectiveness, increased sensitivity, repeatability and efficiency, achievement of compatibility with standard industrial technology VLSI.

3 dwg

FIELD: physics, semiconductors.

SUBSTANCE: invention is related to methods for creation of metal nanowires on surface of semiconductor substrates and may be used in creation of solid-state electronic instruments. Substance of invention: in method for creation of conducting nanowires on surface of semiconductor substrates, copper is deposited on surface of silicon Si(lll) with formation of buffer layer of copper silicide Cu2Si at the temperature of 500°C under conditions of ultrahigh vacuum. Buffer layer of copper silicide is formed with monatomic thickness, afterwards at temperature of 20°C at least 10 layers of copper are deposited on atomic steps of buffer layer surface, which form nanowires of epitaxial copper that are oriented along atomic steps of substrate.

EFFECT: provides for creation of nanowires that possess high conductivity, with the possibility of these nanowires formation location control.

3 dwg

FIELD: chemistry.

SUBSTANCE: method includes heating of silica oxide photon crystals with modifying agent - crystal phosphor cesium iodide in vacuum at temperature not less than 800°C during not less than 15 hr. Cesium iodide can be activated with different admixtures (Na, Tl, In, CO3 etc), providing more bright (in comparison with pure CsJ) radioluminescence on the different waves of the visible-light spectrum. Usage of the scintillator - cesium iodide as filler provides good wettability (caused by capillary forces) of silica oxide microspheres with the melted cesium iodide without outer pressure. It allows to obtain optically inverted composite having approximately the same optical contrast (ratio of the refractive indexes relating to microspheres medium and to the medium filling the pores between microspheres) as initial silica oxide has.

EFFECT: obtaining of the end product with high yield.

4 cl, 1 ex, 2 dwg

FIELD: production processes.

SUBSTANCE: in compliance with the proposed method, copper matrix is pressed at 100 to 300 MPa and sintered at 5640 to 680°C for 1 to 2 h in protective-reducing gaseous atmosphere to produce apparent-porosity structure. Nonstructural component is introduced therein in vacuum impregnation of the matrix with suspension of refractory material nanoparticles in glycerin-based protective fluid at 1 to 10 kPa. Aforesaid protective fluid is removed at 80 to 95% of its boiling point. Finally, final sintering is effected at 810 to 1020°C for 1 to 2 h in protective-reducing gaseous atmosphere.

EFFECT: simplified process, expanded technological performances, improved physical-mechanical properties.

3 cl, 1 tbl, 1 ex

FIELD: carbon materials.

SUBSTANCE: weighed quantity of diamonds with average particle size 4 nm are placed into press mold and compacted into tablet. Tablet is then placed into vacuum chamber as target. The latter is evacuated and after introduction of cushion gas, target is cooled to -100оС and kept until its mass increases by a factor of 2-4. Direct voltage is then applied to electrodes of vacuum chamber and target is exposed to pulse laser emission with power providing heating of particles not higher than 900оС. Atomized target material form microfibers between electrodes. In order to reduce fragility of microfibers, vapors of nonionic-type polymer, e.g. polyvinyl alcohol, polyvinylbutyral or polyacrylamide, are added into chamber to pressure 10-2 to 10-4 gauge atm immediately after laser irradiation. Resulting microfibers have diamond structure and content of non-diamond phase therein does not exceed 6.22%.

EFFECT: increased proportion of diamond structure in product and increased its storage stability.

2 cl

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