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## Creator

Zaulychnyy Ya V, Solonin Yu M, Foya O O, Khyzhun O Yu, [VASYLKIV Oleg](https://orcid.org/0000-0002-5041-6130)

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[Energy redistribution of the valence electrons due to nanodispersion of materials and its evidence as determined by the ultrasoft X-ray emission spectra](https://mdr.nims.go.jp/datasets/e42d9c0e-e191-4c0b-985b-7a8c6085e5d2)

## Fulltext

Эффект наноразмерного сужения ультрамягких эмиссионных полос и энергетического перераспределения валентных электронов и его зависимость от типа их химической связиPAGE  Energy redistribution of the valence electrons due to nanodispersion of materials and its reflection in the ultrasoft X-ray emission spectraYa. Zaulychny, Yu. Solonin, O. Foya, O. KhyzhunInstitute for Materials Science NASUKrzhyzhanovsky str., 3, Kiev, 03680, UkraineO. Vasylkiv*  National Institute for Materials Science1-1, Namiki, Tsukuba, Ibaraki, 305-0044, Japan*Correspondent author. E-mail: oleg.vasylkiv@nims.go.jp.ABSTRACTAn investigation under equal experimental conditions of the ultrasoft X-ray emission bands of coarse and nanosize powders of different materials reveals narrowing of the spectra and changing of their shapes. It has been shown that this is a consequence of the energy redistribution of valence electron states after the breaking of interatomic bonds under dispersion of the materials into nanosizes, when a number of surface atoms with broken bonds becomes commensurable with the number of atoms inside the nanoparticles. The energy redistribution of electrons occupying mainly π-bonding states changes significantly due to the increasing curvature of the surfaces of carbon nanomaterials with the decreasing of their sizes. It has been established that specific narrowing of the emission bands reflecting valence states of atoms of the compound is proportional to occupancy of their states.Introduction. The energy state and unique properties of nanosystems are determined mainly by a considerable contribution of an interatomic interaction of the surface and nearsurface atoms. Therefore, a study of the energy distribution of the valence electrons (EDVE) directly involved in interatomic interactions in nanoparticles is of current importance. Because the number of atoms in nanoparticles with sizes of 10-100 nm is several times greater than in clusters with several hundreds of atoms the theoretical calculations employing Х(-methods1-5 do not reflect the electronic structure of the nanoparticles adequately. Admixtures chemisorbed on the surface of the nanoparticles make great contributions to the parameters of the interactions of surface atoms when investigating the EDVE of nanoparticles by means of optical6-8 and X-ray photoelectron spectroscopy (XPS)9,10 methods. Recrystallization and agglomeration of nanoparticles prevent purification of their surface by heating-up. Ion etching essentially breaks the nanoparticle morphology and removes a substantial part of them from the substrates. The adhesive contact of discontinuous thin films with the substrates affects their electronic structure. Therefore, it is necessary to study the EDVE of nanoparticles in the absence of chemical and adhesive interactions and at sufficiently low temperatures. It is possible using the mechanical adhesion of nanoparticles on cooled substrates (i.e., under rubbing of the metals with high thermal conductivity, e.g., Cu or Au) and employing excitation of the spectra reflecting the EDVE by the electron beam that purifies the nanoparticle surfaces from chemisorbed admixtures and does not heat the nanoparticles up.The X-ray ultrasoft emission spectroscopy (XRUSES) method satisfies all these conditions under the excitation of radiation by electrons with energies of 2.0 to 9.0 keV. Under such conditions, the depth of photon emission giving the main contribution to the spectra intensity does not exceed 10 atomic layers in the nanoparticles. The X-ray emission bands reflect the partial density of electronic states of different symmetries of all kinds of atoms of the compound under investigation. Changes in the shapes of the X-ray emission СK( bands due to their narrowing at І=2/3Іmax (I is the intensity) were observed when studying the electronic structure of high-pressure phases particularly of nano-diamonds (with coherent scattering areas (CSA) of 2.0, 3.0 and 5.0 nm) obtained from a highly nonequilibrium carbonic plasma as a result of explosive detonation.12 This narrowing magnitude increases with a decrease in the CSA. The above narrowing effect was recently confirmed for nano-diamonds.13 An even greater effect of narrowing and the changing shapes of the X-ray emission NK( and ВK( bands reflecting the EDVE of the р-symmetry of nitrogen and boron was revealed in the investigations of blended BN nanopowders. The effect of NK( narrowing exceeds by three times that for the ВK( band, and the value increases with decreasing nanoparticle sizes.14 Subsequent studies of XRUSES of the nanopowders of other compounds with different atomic-crystalline structures and chemical bonding types have revealed that the nanosize narrowing of the spectra was observed in all nanomaterials investigated by us because the contributions of the localized levels of the electronic states to the valence bands after the interatomic bond opening become commensurable with the contributions of states involved by unbroken bonds. Because the fine structure of the X-ray emission bands depend on many crystal-chemical characteristics and its nanosize change becomes apparent in the different energy intervals of the valence bands, the aim of the present paper is (1) to show that the effect of narrowing and changes in shapes of the ultrasoft X-ray emission bands (USXREB) reflecting the energy redistribution of valence electrons is a common electronic-structural characteristic of the transition of materials from the bulk to a nanosize state and (2) also to elucidate the dependence of the above effect upon the type of chemical bonding and atomic-crystal structure.Therefore, it is necessary to study and analyze the parameters of USXREB obtained from the bulk and nanomaterials among which are following powders:1) Covalent-ionic graphite-like (h-BN) and blended-like (c-BN) crystal modifications of boron nitride;2) Metal-covalent isostructural crystal TiC and TiN compounds with different ionicity degrees of the interatomic bonds;3) Ionic-covalent ТiО2 and ВаТiО3 with rutile- and perovskite-like structures respectively;4) Carbon nanomaterials with a high contribution of closed bonds in their total quantity (fullerenes, low-imperfect nanotubes) and of opened bonds (onions, high-imperfect nanotubes and nanofibers).2.1. Dependence of nanosize narrowing and changes in shapes of the USXREB due to the transition of covalent-ionic BN from the bulk to a nanostate upon the crystal-chemical characteristics of its modifications. Analysis of the comparison of the СK( and superimposed on a common energy scale the NK( and ВK( emission bands12, 14 with band-structure calculations of diamond and blended BN has shown that the nanosize narrowing is observed in the energy region where the sp3-hybride states involved in the С-С and B-N-bonds of bulk crystals are reflected.Essential distinctions in nanosize narrowings and changes in the shapes of the X-ray emission СK(, NK( and ВK( bands, which reflect the energy distributions of Ср-, Nр- and Вр-like electronic states, respectively, in crystal-analogues, diamond and blended BN are obviously accounted for by only the ionic component15 of the B(N-interaction. In Ref. 14, a detailed analysis of the influence of chemical bonding ionicity on the nanosize effect of the band’s narrowing was not carried out and a transfer of the electronic density from one atom to another one reflects substantially on the intensities of the corresponding spectra; therefore, it is of great importance to elucidate the specific contribution to the mentioned effect of the population of the nitrogen and boron energy levels localized after bond breaking. Taking into account the fact that the widths of the NK( and ВK( bands of the bulk blended c-BN are different (Fig. 1a), it is necessary to introduce the parameter of the specific narrowing of these bands in one or another part of the spectra. In this case we chose the spectra width at ½Іmax. The specific narrowing is then η=(ΔЕ1/2c-ΔЕ1/2n)/ΔЕ1/2c, where ΔЕ1/2c is the energy width of the X-ray emission bands at the half-maximum intensity in a coarse powder and ΔЕ1/2n is that in a nanopowder. The dependencies calculated in the present work of the ηNK( and ηВK( specific narrowing of the X-ray emission NK( and ВK( bands upon the average sizes (d) of c-BN powders (Fig. 1b) were found to be linear with different coefficients kNK( and kBK(. Their ratios ηNK(/ηВK(≈2.1±0.1 were approximately equal for all fractions of the c-BN nanopowders. The ratios were found to be close to the ratio QNрV/QВрV=2.0, where QNрV is the number of valence р-electrons located near one nitrogen atom and QВрV is that near the boron atom, calculated in Ref. 15. This indicates that the bigger the population of the levels of the atom emitting X-ray quanta the bigger is their contribution to the narrowing of the emission bands due to level’s localization as a consequence of the disappearance of their splitting when the B(N-bonds rapture.Because the EDVE15 and the shapes of the X-ray emission NK( and ВK( bands of h-BN and c-BN are different,16 the energy redistribution of the valence electrons should therefore be different on going from coarse h-BN to turbostratic h-BN (the average size of the particles is d=5 nm). Therefore, in the present paper for the first time the NK( and ВK( spectra of coarse and turbostratic h-BN were investigated under the same conditions. The number of valence electrons and charge states of the atoms do not change as a result of ultradispersion (the binding energies of the core-level В1s and N1s electrons14 are invariable); therefore, the ВK( bands, as well as the NK( spectra, obtained from the coarse and nanopowder BN were reduced to equal squares. From a comparison of these spectra on a common energy scale (Fig. 1c), it is obvious that the ВK(-bandwidth of turbostratic h-BN is smaller by 0.2(1.0 eV compared with that of coarse h-BN in its high-energy part. In the energy region where the sp2-hybrid states providing the BNσ-bonds are reflected, the intensity of the peculiarity “с” of the NK(-band decreases. This is a result of the disappearance of splitting of Вр- and Nр-energy levels due to the dehybridization of a part of the sp2-states after the breaking of B-N-bonds due to the nanodispersion of h-BN. The Np-dehybridizated states in turbostratic h-BN shift to the top of the valence band. This fact is reflected in the shift of the short-wave contour of peak “d” of the Nk( band towards high energies. From a comparison of the bandwidth reduction of c-BN (Fig. 1 a)14 and h-BN (Fig. 1 c), it is apparent that the ВK( bandwidth is reduced more in h-BN but the NK banwidth is reduced more in c-BN. This is explained obviously by the fact that in coarse c-BN all electrons, including those transferred to nitrogen, occupied the splitting levels of the sp3-hybrid states whereas in h-BN the main part of the electrons occupies the weakly bonding Nрz-states reflected in the narrow peak “d” of the NK( band.17 The Nрz-states split weakly due to the low degree of π-overlapping with low-populated Врz-orbitals. Therefore, in h-BN a smaller number of electrons is involved in splitting the sp2-states compared with that in c-BN. This fact is reflected in a smaller contribution to the emission of the NK( band of the electrons involved in the dehybridized states. Thus from the above analysis, it is clear that, during ultradispersion, the nearest surroundings essentially affect both the narrowing value and the changes in the shape of the USXREB reflecting the energy redistribution of valence electrons. 2.2. Peculiarities of nanosize narrowing of USXREB obtained for isostructural metal-covalent titanium carbides and nitrides with a face-centered cubic lattice. In order to study the dependence of the effect of nanosize narrowing of USXREB upon the presence of a metallic component of the chemical bonding, we have analyzed the X-ray emission СK(, NK( and TiL( bands (the latter reflects the energy redistribution of valence Tisd-like electrons), obtained for three nanosize fractions and coarse powders of metal-covalent ТіС and TiN18,19 with the face-centered cubic structure of the NaCl type. The Fm3m space symmetry groups of these are close to those of diamond (Fd3m) and c-BN (F43m), but the quantity of the nearest neighbors and the geometry of the neighborhoods are different. The measuring of widths of the  СK(, NK( and TiL( bands at ½Іmax of coarse and nanopowders with specific surface areas Ssp=9.4, 16.8, 24.2 m2/g for TiC18 and Ssp=10, 20, 50 m2/g for TiN19 and calculations of the specific narrowing of these bands have revealed that the narrowing increases with decreasing fraction sizes. As in the case of BN, the specific narrowing of the СK( and NK( bands is greater than that of the TiL( band, and their ratios are ηNK(/ηTiL(≈1,3 for ТіС and ηNK(/ηTiL(≈1,45 for TiN; whereas the ratios of the number of valence electrons near the constituent atoms calculated in Ref. 20 are QСрV/QTisdV≈1,3858 (ТіС) and QNрV/QTisdV≈1,64 (TiN). These facts confirm the conclusion stated in section 2.1.In metal-covalent TiN, in addition to the presence of an ionic component, the Fermi level passes through the high density of the metal-bonding band, where a significant part of the occupied anti-bonding states is also present.21 In ТіС, the number of valence electrons and the transfer of the electrons from titanium to carbon are smaller in comparison with that in TiN; therefore the anti-bonding (Tisd+Ср)*-states are unoccupied and the Fermi level passes only through the minimum density of the metal-bonding states.The analysis of a comparison of the X-ray emission СK(, NK( and TiL( bands with data from theoretical calculations of the electronic structure of ТіС and TiN20 carried out in Refs. 18 and 19 has shown that the band’s narrowing occurs in the energy regions where hybrid-bonding Tisd+Xр-states (X=C, N) are concentrated. In the energy range where the non-bonding states are mainly concentrated, the width of both the emission bands are not reduced, i.e., the contours of the bands of coarse and nanopowder materials coincide. The TiL(-band narrows in low-energy and in high-energy regions due to breaking of the covalent and metallic components of the bonds. The breaking of the metallic bonds leads to narrowing of the TiL( and СK( bands in the near-Fermi region in TiC owing to the localization of levels of high-energy Tisd+Ср states delocalized in the lattice. These states provide the metallic component of the Ті-С-interaction in TiC.Because the electrons of the localized energy levels have to increase their energy after the bond breaking, their levels have to shift to the high-energy side and can locate in the energy region corresponding to the non-bonding states in a coarse powder. This can also be due to of the fact that the high-energy contours of the СK( band (Fig. 2а) of coarse and nanopowders of ТіС coincide in the (E2 energy range. In our opinion, the above effect is not visible in the case of TiN due to the superposition of the NK( band and the TiLl-line in this compound. On the other hand, the short-wave contour of the main maximum “d” of the TiL( band obtained from TiN (Fig. 2b), due to the concentration in the energy region –(5.0-3.5) eV of the energy localized levels after the Ti-Ti- and Ti-N-bonds breaking even shifted somewhat to the high-energy side. Part of the hybrid К4 (Срx-y, Tiy), Δ5 (Cpy,z, Ti2g), Σ3 (Cpz, Tidz(x+y)) states is located in the above mentioned energy region in the bulk crystal according to the calculations.19 Their splitting should also disappear during the bond breaking. The energy redistribution of the metal-bonding Tisd-states, which splitting disappeared after the bond breaking during the ultradispersion of TiN, is reflected by the smaller width and the intensity of the “e” peak of the TiL( band. The redistribution shifts by 0.2-1.5 eV towards high energies the short-wave contour of the TiL( band at I<0.4Imax. It is worth mentioning that a high-energy shift by 0.4 eV of the whole short-wave contour of the X-ray emission NK( band obtained from the finest powder of c-BN as compared with that of the band of coarse c-BN was caused by a significant increase in the contributions of the occupied Np-like states corresponding to the broken bonds of atoms belonging to the large specific surface of c-BN nanopowders into the energy region corresponding to the top of the valence band. This fact shows that energy redistributions of valence electrons as a result of the increasing energy of states involved in the broken bonds have some differences because of the ultradispersion of crystals with covalent and metallic bonds. The differences are the consequence of the different distributions and localizations of metal- and covalent-binding states within the valence bands as well as the different magnitudes of changes in energy states when the splitting of their energy levels disappears after the metallic and covalent bonds break. After the nanopowder’s consolidation, crystallization and other processes, as a result of recombination of broken chemical bonds on the surface of the nanoparticles, the splitting of energy levels of the above mentioned electronic states should take place, and due to this fact the USXREB should broaden. Indeed, the X-ray emission СK(, NK( and TiL( bands obtained from the nanopowders of solid ТіС and TiN (Fig. 2) consolidated at 7 GPа and at room temperatures (Т=293 К) were found to be broadened in the same energy regions where they were narrowed in the spectra of the nanopowders. This is a result of the energy levels splitting as a consequence of their orbital superimposition during the rapprochement of surface atoms of contacting nanoparticles under the high-pressure contraction of the nanopowders.2.3. Estimation of band-energy changes as a result of ТіО2 and ВаТіО3 ultradispersion using the data for the narrowing and transformation of shapes of the X-ray emission TiL(  and ОK( bands. The elucidation of the dependence of the nanosize narrowing of the USXREB and energy redistributions of valence electrons on the types of chemical bonding would be incomplete without a study of these effects in an ionic ТіО2 crystal with a rutile structure (r-ТіО2). In this crystal the greater part of the occupied Op-states have to be non-bonding due to the big contribution of the Coulomb interaction between the titanium and oxygen ions to the binding energy. Therefore, in the present paper for the first time, the effect of nanosize narrowing of the X-ray emission TiL( and ОK( bands was studied during the transition from a coarse powder to two fractions of nanopowders with average sizes of d=107 and 10 nm (Fig. 3a). Also for the first time, the broadening of the ОK(-band (Fig. 3b) of r-ТіО2  nanopowder (d=10 nm) due to its recrystallization under heating (as a result of the rise from 8 to 45 Wt of the power of the electron beam exiting the spectra) was investigated.The valence band of the coarse r-ТіО2 contains mainly the Ор-states. The bonding hybrid (Tid(eg)+Ор) states and Ор-states contribute involved in the О(О-bonds contribute to the low-energy part, but the non-bonding Ор-states contribute to the high-energy part of the valence band.22-25 The first contribution is reflected by the wide feature “а” of the X-ray emission ОK( band and the second one by the peak “b”. Comparison of the X-ray ОK( and TiL( bands obtained from the coarse ТіО2 and nanopowders (Fig. 3a) has revealed that the ОK( band narrows by 0.2(0.5 eV on going from coarse ТіО2 to the nanopowder with average nanoparticles sizes of d=107 nm and by 0.2(1.1 eV when going to the fraction with d=10 nm. This narrowing is observed in the low-energy part created by the Op-bonding states (the feature “а” of the band). The difference square of the ОK( band of the coarse TiO2 and the nanopowder with d=10 nm is many times larger than that of the coarse and the nanopowder with a size of d=107 nm. At the same time, the TiL( band narrowing in the energy region –(6–4) eV is only 0.2-0.3 eV. The ratio of the calculated specific narrowing of the X-ray emission ОK( and TiL( bands at the intensities corresponding to their maximum narrowing equals ηОK(/ηTiL(=0.25/0.07=3.60±0.30, whereas the ratio of the population of Ор- and Tid-like states26 equals QОр/QTid=5.33/1.46=3.7 (this result is in accordance with those described above for c-BN, TiC, TiN). From a comparison of the ОK( bands presented in Fig. 3a), one can see that, like that during ultradispersion of covalent-ionic c-BN, in a nanopowder of ionic-covalent r-ТіО2 the Ор-states corresponding to the broken bonds of surface atoms concentrate near the top of the valence band; increasing in this energy region the density of the non-bonding Ор-states. Taking into account the fact that chemical content and the number of the valence electrons in all three powders are exactly the same, the ОK( bands were normalized so that their squares are equal (the method of normalization is similar to that employed in Ref. 27 for XPS spectra). The energy redistribution of the О2р-states when going from the coarse to nanopowder TiO2 should result in significant changes in the band energy of electrons and its contribution to the internal energy of nanopowders. The calculated ratios of the integrals 00(())(())FFEcEEnEIEEdEIEEdEòò, where I(E) is proportional to P(E)N(E) in the approximation that P(E) depends weakly upon Е and it is similar or equal for these powders, have revealed the increasing of band energy by 3% and 17% when going from the coarse TiO2 to nanopowders with d=107 and d=10 nm, correspondingly.Consequently, one can assume that significant changes or the appearance of new properties of r-ТіО2 are possible when the change in internal energy is sufficient due to changes in band energy because of nanocrystallinity of this material. The charge states of titanium and oxygen atoms are similar in ionic-covalent perovskite-like ВаТіО3 (p-BaTiO3) and r-ТіО2 compounds, taking into account XPS measurements of the binding energies of Ti2p3/2 and O1s-core-level electrons (see Ref. 28). However, due to the different geometry of the octahedral surrounding of Ті atoms by oxygen, all the О(О-distances in p-ВаТіО3 (0.28327 nm) are greater than the doubled ionic radius of oxygen (2rО2-). In contrast, in r-ТіО2 the distances are О(О=0.25327 nm<2rО2-=0.270 nm.29,30 Therefore, in r-ТіО2, the О(О-bonds exist and in p-ВаТіО3 they are absent.From the comparison on a common energy scale, the X-ray emission ОK( and TiL( bands obtained from the coarse and nanosize powders (Ssp=40 m2/g) with d=24.9 m2/g of p-ВаТіО3, it is obvious that the band narrowing occurs in the sequence “coarse ( nanopowder”, mainly due to redistribution of the Op- and Tid-states, localized as a result of the Ti(O-bands breaking, towards the higher energies. The Op- and Tid-states in the coarse powder were hybridized.28,31 The X-ray emission ОK( band of coarse ВаТіО3 powder does not contain the low-energy sub-band “а”, due to the absence of the Op-bonding states involving the О(О-bonds in this compound. Because of this fact, the ОK( band of barium titanate coarse powder is symmetric, and its halfwidth equals 3.4 eV (the half-width is smaller by 1.0 eV compared with that of r-ТіО2). The ОK(-band of barium titanate nanopowder is asymmetric, narrowed by 0.2(0.5 eV and its high-energy contour is shifted by 0.5(0.9 eV compared with that of coarse BaTiO3. This is due to the fact that, in ВаТіО3 nanopowder after the Ті-О-bonds breaks dehybridized Ор-states concentrate near the top of the valence band, where according to the calculations,32 non-hybridized “pure” non-bonding Ор-states are located. The same effect was also observed in the case of ultradispersion of the above-described covalent-ionic c-BN and ionic-covalent r-ТіО2. However, the main difference in the redistribution of the valence electron states because of ultradispertion of ТіО2 and ВаТіО3 is the fact that, in spite of the resemblance of theshapes of TiL(-bands in these compounds, the TiL(-band of barium titanate nanopowder narrows in the low-energy region by 0.2(1.0 eV and broadens by 0.3(0.5 eV in the energy region –(5.0(7.0) eV corresponding to the position of the high-energy contour of the main peak “b” of the band. This is a result of the fact that the population of the Tid+Ор-hybrid states in ВаТіО3 is significantly higher compared with that in r-ТіО2.33The calculated integrals ratio 00(())(())FFEcEEnEIEEdEIEEdEòò for ВаТіО3 has revealed that the band energy changes by 11 % when going from the coarse powder to the powder with d=24.9 m2/g, which is smaller than that in r-ТіО2, as would be expected. Thus, from the above facts, it is obvious that the redistribution of valence electronic states, due to the great contribution of broken bonds in the nanopowders, depends on the character of the chemical bonding and the atomic-crystal structure of materials. 2.4. Dependencies of the Cp-state energy distribution and of the shapes of the X-ray СK( band on the sizes of carbon materials. In contrast to crystalline nanopowders, ideal fullerene does not possess broken bonds and in ideal onions and carbon nanotubes, they exist only on the ends of the nanotubes; the contribution of the broken bonds to the total value of bonds is insignificant in the above materials. At the same time, in nanosize graphene layers which form carbon nanofibers, the numbers of the broken and closed bonds are commensurable. The X-ray emission СK( spectra of graphite, onions, nanotubes and nanofibers were studied under similar conditions and are compared in Fig. 4. Fig. 4 also shows the СK( bands of С60 and С70 (curves 1 and 2) investigated in Ref. 34 and obtained in the present work with smaller apparatus distortions (ΔEap≤0.2 eV) in comparison with ΔEap=0.4 eV34 (curve 3). The spectra were compared to elucidate whether the effects of narrowing and changes in the shape of the СK( bands with decreasing sizes of the carbon materials become apparent and in what way. From the comparison of curves 1 and 2 (Fig. 5), it is obvious that a divided sub-band of the СK( band of С60 is narrower at I>1/2Imax (by 0.2(0.5 eV) compared with that of С70 in the region of photon energies hν=274.5(276.0 eV, and also in the energy region corresponding to contributions of the π-states. The minimum of the СK( band dividing the pure π-bands (features “e” and “f”) from those mixed with the σ-states in С60 is deeper than that in С70, where there is no separation into π1 (“f”) and π2 (“е”) sub-bands.35 The π1 and π2 sub-bands are typical for С60 due to the difference in the degree of π-overlapping of orbitals above the spherical surface of С60 between atoms at the distances of 0.144 and 0.139 nm. The high intensity, symmetry and undivided shape of the π-sub-band in С70 are the result of the presence of 8 groups of interatomic distances (0.137 to 147 nm), because the degree of π-overlapping of the Срz-orbitals in this fullerene does not differ so noticeably as in С60. Such a dispersion of the lengths of σ-bonds leads obviously to greater width of the sub-band of СK( reflected in the π+σ-mixed states in С70.Fig. 4b shows a comparison of the СK(  bands of onions (curve 5), the sizes of which are about 5 nm, and graphite (curve 6). From the above figure, it is obvious that the СK( band of the onions is narrower at I>1/2Imax in comparison with that of graphite, mainly in the energy region where the π and π+σ-bonding states are reflected. In the energy region hν=273.0(275.0 eV, corresponding to the sp2-hybride states of the σ-bonds, the differences are minor. The narrowing of the spectra in the low-energy region is due to the presence of a noticeable number of broken bonds due to the fact that spherical sp2-bonding layers consist of broken, torn or bowed graphene fragments.36 The greater narrowing in the high-energy part of the СK( band is a result of breaking the π-bonds between the fragments and decreasing π-overlapping of the Ср-orbitals above the bowed surface of the fragments.From the comparison of the СK( bands (Fig. 4c, curves 7 and 8) of 200-walled nanotubes with a diameter of 140 nm and double-walled nanotubes with a diameter of 4 nm obtained in arc discharge without catalysts by “MER-corporation”, it is evident that the low-energy contours of the band reveal coincidence. However, in the high-energy part of the СK( band  reflecting the π- and π+σ-binding states, the features «с», «с’» and «d», «е», which are more clearly resolved and correspondingly reflect mixed ррσ+ррπ and pure ррπ37 interactions in the radial planes and along the axis of the nanotubes, become apparent. However, the bandwidth of СK( of double-walled carbon nanotubes is reduced in comparison with that of the 200-walled nanotubes only near the top of the band (at I>0.75Imax). This is the result of a decrease in the π+σ-overlapping in the radial plane inside the 200-walled nanotubes with an increase in diameter of every following wall (as a consequence, states involved in such bonds shifted to the side of higher energies). The comparison of the СK( spectra of nanotubes with diameters of 20 nm and 70 nm (Fig.5 curves 8, 9), the first of which contains many broken bonds after purification with a Со catalyst, reveals that the spectrum width of imperfect nanotubes is reduced in the low-energy and high-energy parts of the СK( band. All axes of the рz-orbitals will be perpendicular to the selection direction of the X-ray, when filaments of the carbon fibers are parallel to it (Fig. 5a, orientation I). Therefore, the contribution of the π-bonding рz-orbitals into the СK( band intensity is maximum in orientation I, whereas it will be much smaller in orientations II and III.38 The comparison of the СK( spectra of thick (18 μm) and nanosize (30 nm) fibers, obtained for the І- (Fig. 6c, curves 1 and 2) and ІІ-orientations (Fig. 6c, curves 3 and 4), has allowed us to determine qualitatively the ratio of contributions of the broken π- and σ-bonds to the narrowing of the СK( band when going from thick fibers to nanofibers. The specific narrowing calculations at І=0.86Imax (where the narrowings are the greatest at the І- and ІІ-orintations) have shown that ηІ≈ηІІ≈0.24±0.01. This would be expected because the ratio of the number of broken and closed π-bonds does not depend on the fiber orientation. The greater contribution of the σ-states to the emission of the СK( band at the ІІ-orientation becomes apparent in the narrowing of the band in the low-energy energy region reflecting the sp2-hybride σ-bonding states, when going from the thick to the nanofiber. This is the result of the increasing contribution of localized energy levels dehybridized due to sp2-state bonds breaking.  Conclusion. The effect of narrowing and shape changes in the X-ray emission bands reflecting the energy distribution of valence electrons of atoms forming compounds was revealed due to the excitation of x-ray spectra by electron bombardment, which allows refining the nanomaterial surfaces from chemisorbents, when going from bulk to nanomaterials that prove to be common for objects under investigation. This occurs due to the disappearance of splitting of the energy levels of states after the breaking of chemical bonds of the surface atoms, which number in nanoparticles is commensurable with the number of atoms in their volume. It was established the greater population of energy levels of anions in crystalline compounds causes a greater specific narrowing of the ultrasoft x-ray emission bands radiated by cations and anions. The specific narrowing ratios are close to the ratios of density of electrons concentrated near anions and cations. It was revealed that the energy levels of states participating in the broken bonds in ionic-covalent crystals are concentrated near the top of valence bands, increasing their energy and causing an increase in crystal band energy. 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(a) Comparison of the X-ray emission NK( and BK( bands of c-BN powders with fraction sizes of 2.0 μm (curve 1), 0.3 μm (curve 2), 0.2 μm (curve 3), 0.1 μm (curve 4) and (b) the dependence of the specific narrowing of the bands upon the average size of c-BN particles  (c) Comparison of the X-ray emission NK( and BK( bands of coarse 5.0 μm (dashed line) and turbostratic 5.0 nm h-BN (solid line); the dotted curves are spectra of turbostratic h-BN (5.0 nm) heated by an electronic beam up to yellow-and-white luminescence of the particles (T>1500 K evaluated by a pyrometer). Fig. 2. Comparison of the X-ray emission TiL(, CK( and NK( bands of coarse powders (dashed line), nanopowders (solid line) and materials consolidated from the nanopowders at high-pressure and room temperatures (chain line) of (a) TiC and (b) TiN.Fig. 3. (a) Comparison on a common energy scale of calculated densities of Tid- and Op-like states and of the X-ray emission TiL(- and OK( bands of coarse (dashed line) and nanosize (solid line) powders of (a) BaTiO3 and (b) TiO2. Solid lines are contours of spectra corresponding to the finest nanopowders with average sizes of 10 nm (TiO2) and 24 nm (BaTiO3). Dotted lines are contours of spectra of nanopowder TiO2 with a size of 105 nm (b). OK(-bands of r-TiO2 nanopowders measured at increased power of the exciting electron beam (c).Fog. 4. Comparison of the X-ray emission CK( bands of carbon nanomaterials: (a) C60 and C70 fullerenes (curve 1 – the spectrum of C60 obtained in present study; 2 and 3 – from Ref. 34; 4 – the spectrum of C70 from Ref. 34; (b) the spectrum of onions (5) and thermally exfoliated graphite (6); (c) the spectra of double-walled nanotubes with diameter of 4 nm (7) and 200-walled nanotubes with diameter of 140 nm (8) obtained in arc discharge, (d) the spectra of catalytic nanotubes with diameter 30 nm before (9) and after (10) purification.Fig. 5. The X-ray emission CK( bands of carbon fibers: (a) in orientation I: 1- fiber with a diameter of 30 nm (1) and 18 μm (2), a) in orientation II 1- fiber with a diameter of 30 nm (3) and 18 μm (4). Orientation I: the angle between the direction of X-ray emission and the main direction of the Cpz-orbitals is in the range of 0-180º. Orientation II: the angle between the direction of X-ray emission and the main direction of the Cpz-orbitals is 90º. e- are the directions of the electron beams, c are directions of the axis corresponding to graphene layers, hυ is  the direction of X-ray emission.PAGE  20_1168867008.unknown_1168867096.unknown_1168866769.unknown