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1.
The band structure of linear chains of fullerene molecules is calculated as a function of the intermolecular π-electron overlap integral T, which increases under increasing external pressure. Chains consisting of neutral (C60) and charged (C
60
−
) molecules are studied. It is shown that there is a sharp transition from a metal (or narrow-gap semiconductor) to an insulator
(with band gap ∼1 eV)with increasing T. The proposed model makes it possible to describe the formation of solid-carbon struc-tures, containing chains of covalently
bound fullerene molecules, with different pressure-dependent semiconductor properties.
Pis’ma Zh. éksp. Teor. Fiz. 65, No. 8, 647–650 (25 April 1997) 相似文献
2.
The structural analysis of linear chains of arbitrary fixed shape is discussed in the context of a spectral approach. The
shape of the chain is characterized by a set of scalar and pseudoscalar invariants, which remain constant under translations
and rotations. The statistical properties of the set of invariants are compared with the analogous characteristics for a freely
linked chain. The proposed criteria have the self-averaging property for relatively short (∼100–300 links) chains and can
be used to discern possible latent periodicities and symmetries in a system. As examples, two applications of the theory are
considered: the structural analysis of chains generated by random walks on a cubic lattice and protein Cα backbones.
Zh. éksp. Teor. Fiz. 116, 620–635 (August 1999) 相似文献
3.
V. V. Brazhkin A. G. Lyapin R. N. Voloshin S. V. Popova Yu. A. Klyuev A. M. Naletov S. C. Bayliss A. V. Sapelkin 《JETP Letters》1999,69(11):869-875
The results of an investigation of the transformation of C60 fullerite to diamond under pressure through intermediate three-dimensionally polymerized and amorphous phases are reported.
It is found that treatment of fullerite C60 at pressures 12–14 GPa and temperatures ∼1400°C produces a nanocrystalline graphite-diamond composite with a concentration
of the diamond component exceeding 50%. At lower temperatures (700–1200°C) nanocomposites consisting of diamondlike (sp
3) and graphitic (sp
2) amorphous phases are formed. The nanocomposites obtained have extremely high mechanical characteristics: hardness comparable
to that of best diamond single crystals and fracture resistance two times greater than that of diamond. Mechanisms leading
to the transformation of C60 fullerite into diamond-based nanocomposites and the reasons for the high mechanical characteristics of these nanocomposites
are discussed.
Pis’ma Zh. éksp. Teor. Fiz. 69, No. 11, 822–827 (10 June 1999) 相似文献
4.
S. A. Gusev L. A. Mazo M. Nefedov Yu. N. Nozdrin M. V. Sapozhnikov L. V. Sukhodoev A. A. Fraerman 《JETP Letters》1998,68(6):509-513
Collective effects arising in a two-dimensional lattice of nanosize magnetic particles as a result of the dipole interparticle
interaction are investigated by Hall magnetometry. The experimental system consists of 105 permalloy particles having a diameter of ∼40 nm and a height of ∼40 nm and forming a lattice with a rectangular unit cell
(90 nm×180 nm). We attribute the characteristic features observed in the magnetization curves to quasi-one-dimensionality
of the experimental lattice of particles and to the formation of solitons in chains of dipoles.
Pis’ma Zh. éksp. Teor. Fiz. 68, No. 6, 475–479 (25 September 1998) 相似文献
5.
The formation of radiating particles in the excitation of C60 fullerene molecules by electrons with energies E
e<100 eV is investigated by the method of crossed molecular and electron beams. A quasicontinuous (with a spectral resolution
of 3 nm) emission spectrum, close to the Planck emission spectrum of a heated body, is recorded in the wavelength range 300–800
nm. The temperature of the radiation corresponds to an internal energy of the C60 molecule of approximately 40 eV.
Pis’ma Zh. éksp. Teor. Fiz. 63, No. 12, 915–919 (25 June 1996) 相似文献
6.
The behavior of the thermal conductivity k(T) of bulk faceted fullerite C60 crystals is investigated at temperatures T=8–220 K. The samples are prepared by the gas-transport method from pure C60, containing less than 0.01% impurities. It is found that as the temperature decreases, the thermal conductivity of the crystal
increases, reaches a maximum at T=15–20 K, and drops by a factor of ∼2, proportional to the change in the specific heat, on cooling to 8 K. The effective phonon
mean free path λ
p, estimated from the thermal conductivity and known from the published values of the specific heat of fullerite, is comparable
to the lattice constant of the crystal λ
p∼d=1.4 nm at temperatures T>200 K and reaches values λp∼50d at T<15 K, i.e., the maximum phonon ranges are limited by scattering on defects in the volume of the sample in the simple cubic
phase. In the range T=25−75 K the observed temperature dependence k(T) can be described by the expression k(T)∼exp(Θ/bT), characteristic for the behavior of the thermal conductivity of perfect nonconducting crystals at temperatures below the
Debye temperature Θ (Θ=80 K in fullerite), where umklapp phonon-phonon scattering processes predominate in the volume of the
sample.
Pis’ma Zh. éksp. Teor. Fiz. 65, No. 8, 651–656 (25 April 1997) 相似文献
7.
Polaron states in linear chains of fullerenes are studied with the use of the generalized model of Su-Shrieffer-Heeger (SSH)
for the intermolecular and intramolecular degrees of freedom. Electron charge distributions over the molecular surface and
Jahn-Teller distortions of carbon atoms in C60 are calculated self-consistently for linear C60 polymer and C
60
−
polyanion chains. A polaron band narrowing is examined. It is shown that the polymerization of C60 molecules in phase transitions may be caused by the cooperative Jahn-Teller effect.
Pis’ma Zh. éksp. Teor. Fiz. 64, No. 8, 521–525 (25 October 1996)
Published in English in the original Russian Journal. Edited by Steve Torstveit. 相似文献
8.
Boiling occurs in a solution of oxygen and fullerenes in CCl4 upon optical pumping of C60 upon the fast appearance of incandescent fullerenes in cold solvent. Upon single-photon absorption, a spherical zone of the
critical state of CCl4 is formed within 5 ns (with a diameter of 22–25 nm, P
cr ∼ 45 atm, and T
cr ∼ 556 K). This spherical zone (gas-bubble nucleus) expands to a diameter of ∼100–400 nm for 2–5 ns. If the external pressure
(natural or artificial) is rapidly released, the bubble accelerates and emerges into a vacuum chamber within 0.7–25 μs (the
length of the passage is 0.1–5 cm depending on the construction of the singlet oxygen generator). We note that singlet oxygen
appears 50 ns after the absorption of a photon by fullerene (i.e., inside of the almost formed gas bubble that only begins
to emerge from the liquid to a low-pressure gas region). 相似文献
9.
Raman scattering of light by optical phonons in Si-Ge-Si structures with pseudomorphic germanium quantum dots has been investigated.
Resonance amplification of the scattering intensity on E
0 (Γ7−Γ8) transitions has been observed. It is shown that as a result of the formation of the layer of germanium quantum dots, the
resonance energy is ∼0.3 eV higher than in the two-dimensional case.
Pis’ma Zh. éksp. Teor. Fiz. 64, No. 3, 203–207 (10 August 1996) 相似文献
10.
N. L. Bashlov V. M. Milenin N. A. Timofeev A. Ya. Vul’ S. V. Kidalov S. V. Kozyrev 《JETP Letters》1996,63(9):713-717
Optical radiation of C60 fullerenes in the gas phase was observed. The observed emission line λ=258 nm is identified with an electronic transition into the ground state h
g
→h
u
in C
60.
Pis’ma Zh. éksp. Teor. Fiz. 63, No. 9, 683–687 (10 May 1996) 相似文献
11.
Ion-implanted buried layer in diamond as a source of ballistic phonons at liquid-helium temperatures
T. I. Galkina A. I. Sharkov A. Yu. Klokov M. M. Bonch-Osmolovskii R. A. Khmel’nitskii V. A. Dravin A. A. Gippius 《JETP Letters》1996,64(4):298-300
It is shown that an approximately 150 nm thick ion-implanted buried layer in diamond and excited by a pulsed laser at wavelength
λ=337 nm is a source of nonequilibrium acoustic phonons propagating ballistically through the diamond sample at temperatures
∼2 K.
Pis’ma Zh. éksp. Teor. Fiz. 64, No. 4, 270–272 (25 August 1996) 相似文献
12.
Studies of a classical III–V semiconductor (InSb) doped with 3d magnetic ions (Mn2+, having a localized spin S=55/2) reveal some unexpected transport properties. It is found that the transition from the metallic to the low-temperature
insulator phase occurs at an impurity concentration N
Mn∼N
cr=2× 1017 cm−3 and a temperature T<T
cr∼1 K. Under these conditions a giant negative magnetoresistance arises. The experimental results can be explained in terms
of the onset of a hard Mott-Hubbard gap Δ in the impurity band formed by the shallow manganese acceptor in InSb at N
Mn∼N
cr. A model describing the gap formation is proposed.
Pis’ma Zh. éksp. Teor. Fiz. 69, No. 5, 358–362 (10 March 1999)
Published in English in the original Russian journal. Edited by Steve Torstveit. 相似文献
13.
The specific heat C
total of crystalline and amorphous Eu2(MoO4)3 is measured in the temperature interval 4.5–30 K. The amorphous state is obtained by applying pressure ∼7 GPa at room temperature.
It is found that the specific heat of the crystal at T⩽7.5 K is described by a cubic function of temperature, while the specific
heat of the amorphous sample has a strongly non-Debye character in the entire experimental temperature interval. The curve
of C
total for amorphous europium molybdate is analyzed in a model of soft atomic potentials, and it is shown that it agrees well with
universal low-temperature anomalies of the specific heat of classical glasses obtained by quenching from the liquid.
Pis’ma Zh. éksp. Teor. Fiz. 68, No. 8, 623–627 (25 October 1998) 相似文献
14.
S. A. Gurevich V. V. Horenko T. A. Zarayskaya L. Yu. Kupriyanov M. Yu. Kupriyanov T. N. Vasilevskaya S. V. Vyshenski 《JETP Letters》1996,64(10):736-741
We study the room-temperature electrical properties of thin (≃200 nm) SiO2 films with inclusions of Cu globules with radius ≃1 nm and separation ≃20 nm. Current-voltage curves taken across the film
in different experimental arrangements show “fingerprints” that are fully reproducible within each setup. We observe multiple
peaks with a height of ≃2 pA against the Ohm’s-law background. The typical peak width is consistent with single-electron recharging
of Cu globules. We interpret these data as self-selection of energetically favorable quasi-1D chains of globules, along which
the current is mainly concentrated.
Pis’ma Zh. éksp. Teor. Fiz. 64, No. 10, 684–688 (25 November 1996)
Published in English in the original Russian journal. Edited by Steve Torstveit. 相似文献
15.
V. K. Voronkova Yu. V. Yablokov E. Huskowska J. Legendziewicz 《Physics of the Solid State》1997,39(11):1838-1842
Crystalline [CuNd2(C4O4)4(H2O)16]·2H2O constructed of complexes of trivalent neodymium and divalent copper, has been synthesized and studied by EPR. The square
anion groups (C4O4) enter as bridge ligands, forming chains of neodymium ions interconnected by (C4O4)Cu(C4O4) fragments. It is found that the relaxation rate of the neodymium subsystem at room temperature significantly exceeds the
exchange interaction rate between copper and neodymium ions. Under these conditions the magnetic properties of the crystal
are determined by two magnetically nonequivalent chains of copper ions, which do not interact. The intrachain exchange interaction
via hydrogen bonds is estimated to be ∼0.1 cm−1. As one proceeds from the high-temperature (250<T<300 K) to the low-temperature region (T<40 K), a substantial change in the nature of the interaction is revealed. An unusual magnetic structure given in a crystal
is observed at low temperatures, which is determined by the presence of two magnetically nonequivalent “ribbons,” formed by
the interacting copper and neodymium ions: chains of copper ions are framed on two sides by chains of neodymium ions. The
magnitude of the parameter of the exchange interaction between the copper and neodymium ions is estimated as J
Cu-Nd⩾0.2 cm−1. An exchange interaction between magnetically nonequivalent neodymium ions is not revealed in the EPR spectra.
Fiz. Tverd. Tela (St. Petersburg) 39, 2057–2061 (November 1997) 相似文献
16.
G. A. Petrakovskii L. I. Ryabinkina N. I. Kiselev D. A. Velikanov A. F. Bovina G. M. Abramova 《JETP Letters》1999,69(12):949-953
The magnetic, electric, magnetoresistive, and structural properties are investigated in the sulfide solid solutions FexMn1−2x
S, which are based on the antiferromagnetic semiconductor α-MnS (the fcc NaCl lattice). Colossal negative magnetoresistance
(δH∼−83% at 160 K for x ∼ 0.29), comparable to that observed in La-Ca-Mn-O polycrystals and films (δH∼−90% at 100 K and 40 kOe), is observed in compounds with intermediate concentrations 0.26<x<0.4, corresponding to the region
of incipient ferromagnetism.
Pis’ma Zh. éksp. Teor. Fiz. 69, No. 12, 895–899 (25 June 1999) 相似文献
17.
V. A. Davydov L. S. Kashevarova A. V. Rakhmanina V. N. Agafonov R. Ceolin H. Szwarc 《JETP Letters》1996,63(10):818-824
Modifications of carbon which are formed from C60 fullerite at pressures up to 10.0 GPa and temperatures up to 1900 K are studied by x-ray diffraction, Raman spectroscopy,
and atomic force microscopy methods. The pressures p and temperatures T at which atomic, molecular, and polymolecular structures form under conditions of quasihydrostatic compression are determined.
It is shown that, together with polymerization, another type of chemical interaction of the molecules, called polycondensation,
which leads to the formation of polymolecular structures with a shortest intermolecular distance of 0.65 nm, is possible in
the system. Three-dimensional polycondensation of C60 fullerene is explained by the special properties of the new carbon states.
Pis’ma Zh. éksp. Teor. Fiz. 63, No. 10, 778–783 (25 May 1996)
The spelling of the authors names are presented here in English as requested by the Russian Editorial office. 相似文献
18.
L. K. Orlov E. A. Shteinman N. L. Ivina V. I. Vdovin 《Physics of the Solid State》2011,53(9):1798-1805
The light-emitting properties of cubic silicon carbide films grown by vacuum vapor phase epitaxy on Si(100) and Si(111) substrates
under conditions of decreased growth temperatures (T
gr ∼ 900–700°C) have been discussed. Structural investigations have revealed a nanocrystalline structure and, simultaneously,
a homogeneity of the phase composition of the grown 3C-SiC films. Photoluminescence spectra of these structures under excitation of the electronic subsystem by a helium-cadmium
laser (λexcit = 325 nm) are characterized by a rather intense luminescence band with the maximum shifted toward the ultraviolet (∼3 eV)
region of the spectral range. It has been found that the integral curve of photoluminescence at low temperatures of measurements
is split into a set of Lorentzian components. The correlation between these components and the specific features of the crystal
structure of the grown silicon carbide layers has been analyzed. 相似文献
19.
The properties of the coherent x-ray transition radiation (CXTR) produced by intense, short electron beams microbunched in
various devices, with periods corresponding to x-ray wavelengths ∼0.02–14 nm and with modulation indices ∼0.001–1, are investigated
theoretically. The results of numerical calculations show that, just as in the case of incoherent and coherent transition
radiation in the optical and microwave regions, CXTR can be used to study the microbunching processes and may thus find application
for beam diagnostics in future x-ray FELs and advanced accelerator technology.
Pis’ma Zh. éksp. Teor. Fiz. 70, No. 10, 664–668 (25 November 1999)
Published in English in the original Russian journal. Edited by Steve Torstveit. 相似文献
20.
D.K. Yu R.Q. Zhang S.T. Lee 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,15(1):57-63
The structures and energetics of carbon bridged C60 clusters (C
60
)
n
Cm have been studied by simulated annealing technique within the tight-binding molecular-dynamics. The “sp2 addition” ball-and-chain dimers exhibit odd-even alternations over the number of chain atoms, with the dimers containing
even chain atoms more stable against dissociation than their immediate neighbors containing odd chain atoms. In addition to
the usual “sp2 addition” dimers, a pentagon-linked C121 isomer and a hexagon-linked C122 isomer are also found to be stable. Based on our tight-binding calculations, trimers and larger clusters can be simply regarded
as being made up of independent or weakly interacting dimers, if the C-C60 joints on a single cage are not too close to each other. Large C60 clusters connected by chains each containing only one or two carbon atoms have similar stability to that of constituent dimers,
indicating the possibility to form stable C60-carbon polymers.
Received 17 January 2001 and Received in final form 26 February 2001 相似文献