Pseudoentanglement of spin states in the multilevel 15N@C60 system

We have prepared combined electron and nuclear spin pseudoentangled states Psi+/-27 and Phi+/-18 out of the total number of eight quantum states in the multilevel quantum system of a nitrogen atom with electron spin 3/2 and nuclear spin 1/2 encaged in the endohedral fullerene (15)N@C(60). Density matrix tomography was applied to verify the degree of entanglement.     

Junction characteristics of C60/polycarbonate blend on Si substrate

We report a study of the interface between fullerene (C₆₀) doped polycarbonate (PC) blends and n-type Si substrate. C₆₀ is usually an electron acceptor in interpenetrated networks and an electron transport in photovoltaic cells. We have studied that the guest-host approach to prepare C₆₀ doped polycarbonate blend. In this article, we report the I-V characteristics of C₆₀ doped polycarbonate/n-type Si junction and the annealing effect on these characteristics. In this junction, a nanocomposite of organic semiconductor fullerene (C₆₀), used as the active medium, with an inert polycarbonate matrix was spin coated on n-type Si substrate. We found that the C₆₀ shows the junction characteristics with n-type Si substrate. The knee voltage and dynamic resistance varies with concentration of C₆₀ as well as temperature. Ellipsometry studies showed the annealing effect on the refractive index and thickness of C₆₀ doped polycarbonate blend on n-type Si substrate. The optical micrographs show that fullerene (C₆₀) is spherical molecule and it is blend in the form of crystallites having size of micron order.     

Electron-impact induced fragmentation of fullerene ions

The C2 fragmentation of fullerene ions C(q+)(60) (q = 1,2,3) induced by electron impact was studied for the first time. The cross sections for the loss of a C2 fragment indicate the presence of two different processes. At low electron energies the projectile electron leads to the direct excitation of the giant plasmon resonance. At electron energies larger than 100 eV the fragmentation of the fullerene ions can be described as an unsuccessful ionization. Only this second part of the cross section shows a dependence on the charge state q of the precursor ion.     

Magnetic properties of crystals of the molecular complex between fullerene C60 and an organic donor 9,9′-trans-bis(telluraxanthenyl)

The EPR and static magnetic susceptibility of the crystalline molecular complex between fullerene C60 and an organic donor 9,9′-trans-bis(telluraxanthenyl) (BTX) have been measured as functions of temperature. At temperatures T above 130 K, the samples exhibit anomalously high magnetic susceptibility exceeding the values calculated under the assumption that each molecule bears one paramagnetic spin 1/2. A very intense magnetic resonance signal is also observed in the samples in the region of high g factors (g>4.5). This allows the suggestion that the samples under study possess ferromagnetism (or superparamagnetism). The EPR signal and magnetic susceptibility sharply decay almost to zero as the temperature decreases below 100–120 K. It is supposed that electron transfer from donor molecules BTX to C60 molecules takes place at temperatures above 110 K. This electron transfer generates electron spins in the system, whereas the anomalously high magnetism is due to ferromagnetic correlations in the system of these spins.     

TR-EPR of single and double spin-labeled C60 derivatives in frozen matrices

Time-resolved electron paramagnetic resonance spectra of two single spin-labeled and two double spin-labeled C₆₀ derivatives in frozen solution are recorded with pulsed laser excitation and 100 ns time resolution. Quartet and quintet excited species are detected which arise from the electron spin coupling of the triplet excited fullerene moiety with the unpaired spin(s) of the nitroxide label(s). Despite the similar molecular structure, in both series of single and double labeled derivatives a different behavior was found, which is due to substantial difference of the energy of exchange coupling.     

ELECTRON SPIN RESONANCE CHARACTERISTICS OF NITROGEN-DOPED FULLERENE

The nitrogen-doped fullerene has been obtained by arc discharge between two high-purity graphite rods in the atmosphere of N₂ and He, The electron spin resonance(ESR) characteristics of N-doped fullerene have been investigated. The results show that the ESR spectra of N-doped fallerene axe composed of two parts, a paramagnetic signal of N-center and a paramagnetic signal of C-center, For comparing with N-doped fullerene, we have also studied ESR spectra of C₆₀ powder, C₆₀ sublimed film and H-doped C₆₀ film. For C₆₀ powder and H-doped C₆₀ film, their in situ ESR. measurements are carried out at various temperatures, and reasonable explanations are proposed.     

Structural and optical properties of solid-phase singlet oxygen photosensitizers based on fullerene aqueous suspensions

The relationship between the structural and photosensitizing properties of solid-phase particles of fullerene C₆₀ in aqueous suspensions is studied using the methods of absorption spectroscopy, electron spin resonance spectroscopy (ESR), X-ray diffraction, and spectrophotometry of solutions of singlet oxygen chemical traps—histidine in combination with p-nitrosodimethylaniline. Two new variants are proposed for obtaining aqueous suspensions of particles of solid-phase fullerene whose structures are disordered and whose degrees of amorphization are 67 and 40%, respectively. It is shown that an increase in the disorder of the structure of particles in suspensions and a decrease in their average size facilitate an increase in the formation efficiency of singlet oxygen by solid-phase fullerene presumably due to an in increase in the concentration of surface localized excitons.     

Formation of C60(2-) dianions in collisions between C60- and Na atoms

We have observed the formation of C2-60 and C2-70 in collisions between C(-)(60)/C(-)(70) and Na atoms. Cross sections for the electron transfer to the monoanion are determined to be 36+/-9 and 57+/-14 A(2) for C-60 and C-70, respectively. A simple model investigation suggests that the electron is transferred from a Na atom to a low-lying electronic state of the fullerene to form a dianion. The method leads to pico-ampere energetic beams of C60 dianions that can be used for spectroscopy and lifetime studies.     

ESR study of fullerene black

Fullerene black before and after annealing at 850°C has been studied by electron spin resonance (ESR). For initial fullerene black, the ESR line exhibits wide wings and its shape is caused by magnetic dipole-dipole interactions between radicals localized randomly on the carbon surface. Dioxygen decreases reversibly the amplitude of the ESR line without changes in its shape, width (0.19 mT) andg-factor (2.0022). This is explained by the assumption that dioxygen molecules adsorbed on the surface broaden strongly ESR lines only of neighboring radicals. For annealed fullerene black, the ESR line is Lorentzian, dioxygen reversibly broadens the line, and theg-factor decreases with the broadening of the line by dioxygen. This is explained by radical-radical and radical-dioxygen spin exchange interactions via conjugated bonds formed in the course of annealing. Flattening of curved carbon surfaces after annealing explains in a uniform way changes in parameters of ESR lines and in reactivity and catalytic activity of fullerene black.     

Resonant Electron Transfer in Collisions between Two Fullerene Ions

Fullerenes are a direct link between atoms with discrete electronic energy levels and solids with a band structure and a well-defined surface. In this Letter, we report on the first ever experiment on resonant electron transfer in collisions between two fullerene ions. Total cross sections have been measured for the reaction C+60+C2+60-->C2+60+C+60 at center-of-mass energies ranging from 27 to 69 keV. Surprisingly, within the error bars, these cross sections are identical to the respective cross sections for C+60+C60 measured by Rohmund and Campbell [J. Phys. B 30, 5293 (1997)]]. We show that the experimental data for both collision systems are very well reproduced by a quantum mechanical treatment of the reaction based on the concept of hole particles and the polarizability of the fullerene molecule.     

Neutralization of charged fullerenes during grazing scattering from a metal surface

The neutralization of C(60)(+) and C(60)(2+) fullerenes with keV energies is studied for grazing scattering from a clean and flat Al(001) surface. From the measured shifts between the angular distributions for scattered projectiles of different incident charge, we derive image-charge interaction energies, which relate to the distances of electron transfer for C(60)(+) and C(60)(2+). These neutralization distances are in accord with a classical over-the-barrier model taking into account the image-charge effects of the Al target and the polarization of the fullerene.     

Resonant electron heating and molecular phonon cooling in single C60 junctions

We study heating and heat dissipation of a single C(60) molecule in the junction of a scanning tunneling microscope by measuring the electron current required to thermally decompose the fullerene cage. The power for decomposition varies with electron energy and reflects the molecular resonance structure. When the scanning tunneling microscope tip contacts the fullerene the molecule can sustain much larger currents. Transport simulations explain these effects by molecular heating due to resonant electron-phonon coupling and molecular cooling by vibrational decay into the tip upon contact formation.     

Spin polarization in fullerene derivatives containing a nitroxide group. Observation of the intermediate photoexcited quartet state in radical triplet pair interaction

A series of C₆₀ fullerene derivatives containing a nitroxide group has been photoexcited by short LASER pulses in the microwave cavity of a cw-EPR spectrometer. Strongly spin polarized signals have been observed, in glassy matrix as well as in liquid solution, for both the ground electronic state and the excited quartet state. In the quartet state the excitation resides in the fullerene part and the molecule constitutes a triplet-radical pair with the partner covalently linked. The absorptive or emissive character of the transitions is explained in terms of the mechanism of radicaltriplet interaction producing spin polarization. Opposite initial sign and polarization patterns are observed for molecules with different spacer between nitroxide and fullerene. The time evolution of the relevant sublevel populations is fitted by a kinetic model taking into account quartet decay constants, quartet and doublet spin-lattice relaxation rates and branching ratios.     

利用不完全自锁模激光研究C60的反饱和吸收效应

本文报道首次采用色心晶体的不完全自锁模激光（１０６４ｎｍ）对Ｃ６０分子反饱和吸收效应的研究，实验结果与采用平均过程的研究方法是一致的，文中还讨论了Ｃ６０分子反饱和吸收效应产生的原因。     

Structural and electronic properties of endohedral phosphorus fullerene P@C60: an off-centre displacement of P inside the cage

Single P-doped endohedral P@C₆₀ is investigated via semiempirical and first-principles calculations. Unlike the encased N atom, which is situated on the centre of the C₆₀ cage and not covalently bound to the carbon atoms of the fullerene cage, static geometric optimization shows that the encased P atom occupies an off-centre position and is bound to the carbon atoms of the fullerene cage. The electronic ground state of the doped system is the spin quarter state, with spin density distribution significantly compressed by the cage.     

Switchable ErSc2N rotor within a C80 fullerene cage: an electron paramagnetic resonance and photoluminescence excitation study

Motivated by the possibility of observing photoluminescence and electron paramagnetic resonance from the same species located within a fullerene molecule, we initiated an EPR study of Er3+ in ErSc2N@C80. Two orientations of the ErSc2N rotor within the C80 fullerene are observed in EPR, consistent with earlier studies using photoluminescence excitation (PLE) spectroscopy. For some crystal field orientations, electron spin relaxation is driven by an Orbach process via the first excited electronic state of the 4I(15/2) multiplet. We observe a change in the relative populations of the two ErSc2N configurations upon the application of 532 nm illumination, and are thus able to switch the majority cage symmetry. This photoisomerization, observable by both EPR and PLE, is metastable, lasting many hours at 20 K.     

The sign of the exchange interaction between triplet excited fullerene and nitroxide free radicals

The sign of the exchange interactionJ in a series of radical triplet pairs (RTPs), formed by a nitroxide free radical and a triplet excited fullerene, has been determined from the spin polarization of time-resolved electron paramagnetic resonance spectra. Radical and fullerene are linked together by covalent bonds in different geometries. It is shown that the sign ofJ depends on the overlap between the orbital of nitroxide unpaired electron and the LUMO of fullerene, which is singly occupied in the excited triplet state. When the overlap does not vanish, a negative contribution toJ arises from the admixing of a charge transfer structure in the wave function of the excited doublet state D* of the RTP, which does not take place in the excited quartet state Q*. The mixing of D* and Q* states lowers the energy of the former spin state and gives antiferromagnetic coupling.     

Transmission electron microscopy imaging of individual functional groups of fullerene derivatives

Mobility and reactivity of the functionalized fullerenes with pyrrolidine (C60-C3NH7) incorporated in single-wall carbon nanotubes were examined by high-resolution transmission electron microscopy. An individual functional group attached to each fullerene cage is unambiguously visualized. This provides a direct evidence for the functionalized structure on a single-molecular basis. A rotational motion of the incorporated molecules tends to occur during the observation and, consequently, each fullerene molecule is likely to stand facing its functionalized group towards the nanotube wall. A fine structure analysis of electron energy-loss spectra for the nitrogen K(1s) edge shows a considerable change in the nitrogen chemical state and suggests a strong tube-fullerene interaction.     

Electron delocalization and dimerization in solid C59N doped C60 fullerene

Electron spin resonance and ab initio electronic structure calculations show an intricate relation between molecular rotation and chemical bonding in the dilute solid solution. The unpaired electron of C59N is delocalized over several C60 molecules above 700 K, while at lower temperatures it remains localized within short range. The data suggest that below 350 K rigid C59N-C60 heterodimers are formed in thermodynamic equilibrium with dissociated rotating molecules. The structural fluctuations between heterodimers and dissociated molecules are accompanied by simultaneous electron spin transfer between C60 and C59N molecules. The calculation confirms that in the C59N-C60 heterodimer the spin density resides mostly on the C60 moiety, while it is almost entirely on C59N in the dissociated case.     

Fullerene C60 formation in partially ionized carbon vapor

The assembling rate of a fullerene C₆₀ molecule has been theoretically studied as a function of electron concentration and temperature in partially ionized carbon vapor. For C⁶⁰ formation via one or two intermediate stages of cluster collisions, it has been shown that there is a region of plasma parameters (the temperature and electron concentration) in which fullerene C₆₀ is formed more efficiently. The C₆₀ formation rate versus temperature and electron concentration relationships have been found to correlate with the trends in the collision cross-section of carbon clusters as functions of these parameters.