Orientation effect on the electronic transport properties of C24 fullerene molecule

The transport properties of the cage-like molecule depend on its orientation between the electrodes, but the investigation on the mechanism has not been found. Using first-principle density-functional theory (DFT) and non-equilibrium Green’s function (NEGF) formalism for quantum transport calculation, we study the electronic transport properties of C₂₄ fullerene molecule with different orientations in Au–C₂₄–Au two-probe system. The effects of k-point sampling on the Brillouin zone are explored. Our results show that the negative differential resistance of C₂₄ molecule is found in such a system and can be tuned by the molecule's orientation in the two-probe system. We also proposed a mechanism for it. The I–V characteristic under bias voltage is determined. The present findings could be helpful for the application of the C₂₄ molecule in the field of single molecular devices or nanometer electronics.     

The observer-based synchronization and parameter estimation of a class of chaotic system via a single output

The conductance of a single molecule transport junction comprising anthracene molecular junction (AMJ) with fullerene as alligator clips was investigated using ab-initio density functional theory (DFT) in the Landauer–Imry regime of coherent tunnelling transport. In our previous research, we have already calculated the electrical transport properties of aromatic molecules with thiol, amine, hydroxyl and selenol end groups concluding the exceptional assistance in the formation of robust molecular junctions. In this article, we have presented the suitability of fullerene anchoring in coupling anthracene molecule with gold electrodes. AMJ with boron-20 (B-20) and C-20 alligator clips exhibited strongest conduction in contrast to nitrogen, oxygen, fluorine and neon alligator clips.     

Transport in fullerene device coupled to Cu,Ag and Au electrodes

We present an ab initio approach of the electronic transport through a single molecular junction based on C₂₀ fullerene. The electronic properties of a single molecular junction constrained within two semi-infinite metallic electrodes are largely affected by the choice of electrode material. The two-probe device formed by the mechanically control break technique has been modelled with three distinct electrode materials from group IB of the periodic table, namely copper, silver and gold. The quantum characteristics of these mechanically stable devices are obtained by utilising first-principle density functional theory together with non-equilibrium green function method. We evaluate the quantum characteristics, namely density of states, transmission spectrum, energy levels, current and conductance, which essentially determine the behaviour of a molecule linked to different electrodes. Our investigation concludes that copper, silver and gold electrode configuration in conjunction with C₂₀ fullerene behaves as metallic, non-metallic and semi-metallic in nature, respectively.     

First-principles study of the electronic transport properties of a C131 -based molecular junction

Using first-principles density functional theory and the non-equilibrium Green’s function formalism, we have studied the electronic transport properties of the dumbbell-like fullerene dimer C₁₃₁-based molecular junction. Our results show that the current-voltage curve displays an obvious negative differential resistance phenomenon in a certain bias voltage range. The negative differential resistance behavior can be understood in terms of the evolution of the transmission spectrum and the projected density of states with applied bias voltage. The present findings could be helpful for the application of the C₁₃₁ molecule in the field of single molecular devices or nanometer electronics.     

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.     

Tuning the electronic properties of the fullerene C<Subscript>20</Subscript> cage via silicon impurities

The fullerene C₂₀ represents one of the most active classes of nanostructures, and they have been widely used as active materials for important applications. In this study, we investigate and discuss the tuning of the electronic properties of the fullerene C₂₀ cage via various consternations and locations of silicon atoms. All calculations are based on the density functional theory (DFT) at the B3LYP/3-21G level through the Gaussian 09W program package. The optimized structures, density of state (DOS) analysis, total energies, dipole moments, HOMO energies, Fermi level energies, LUMO energies, energy gaps, and the work functions were performed and discussed. Our results show that the electronic properties of C₂₀ cage do not only depend on the silicon impurity concentrations, but also depend on the geometrical pattern of silicon impurities in the C₂₀ cage. The tuning of the electronic properties leads to significant changes in the charge transport and the absorption spectra for C₂₀ cage via engineering the energy gap. So, we suggest that substitutional impurities are the best viable option for enhancement of desired electronic properties of C₂₀ cage for using these structures in nanoelectronics and solar cell applications.     

One-colour resonant two-photon ionization spectrum of the 1-fluoronaphthalene dimer and ab initio calculation

The one-colour resonant two-photon ionization(R2PI) spectrum of the 1-fluoronaphthalene(1FN) dimer has been studied in the wavelength range of 304 to 322 nm by using a supersonic molecular beam and time-of-flight mass spectrometry.Compared with the original band 00(at 313.8 nm) of the S1 ← S0 transition of the 1FN monomer,a red-shifted band was observed in the 1FN dimer spectrum at about 315 nm with a relatively large linewidth,nearly 2 nm.Based on the consideration of inductive effect and ab initio calculations,this red-shifted band is assigned to the first electronic excited transition of the 1FN dimer.A possible geometric structure of the 1FN dimer is also obtained with calculations that the two 1FN molecules are combined through two hydrogen bonds which are formed between the hydrogen atom of a molecule and the fluorine atom of a neighbouring molecule.A time-dependent calculation was also carried out and the results are consistent with the experimental data.     

Direct observation of the optical anisotropy of C70 fullerene molecules in the Shpol’skii spectra

Linear optical absorption and emission spectra of C₇₀ fullerene molecules in single-crystal toluene are investigated. It is established that the lines of purely electronic S ₀-S ₁ transitions are significantly polarized. The degree of linear polarization of the spectral lines depends on the position of the fullerene molecule in the toluene matrix and can be as high as 100%. The polarization characteristics of the lines can be understood in the context of a model in which the S ₀ → S ₁ electronic transition is represented by the excitation of a planar oscillator whose axis is oriented along the principal axis of the C₇₀ molecule. The relationship between the polarization of the spectral lines and the position of the fullerene molecule in the matrix is consistent with the conclusions drawn from a theoretical analysis of different configurations possible upon the embedding of C₇₀ molecules into crystalline toluene.     

Spectroscopic and atomic force microscopy investigations of hybrid materials composed of fullerenes and 3-aminopropyltrimethoxysilane

Fullerene based materials may open a new horizon in many fields of science. In this study we fabricated thin films of the hybrid materials formed as a result of interactions between C₆₀ fullerenes and 3-aminopropyltrimethoxysilane (APTMS). The deposition technique was a combination of spin-coating and evaporation methods. Interactions within the films were investigated by means of X-ray photoelectron spectroscopy and near edge X-ray absorption fine structure spectroscopy (NEXAFS). Surface morphology was measured by atomic force microscopy (AFM). We found that there are strong chemical reactions between the nucleophilic nitrogen atoms from APTMS and electrophilic fullerene molecules. Results of NEXAFS investigations suggest that due to direct interactions between APTMS and C₆₀ the electronic structure of the fullerene molecules changes while at the same time AFM proved that the C₆₀ molecule diameter is not altered.     

First-principle study of the electronic transport properties of a new dumbbell-like carbon nanocomposite

Using a first-principle density functional theory and non-equilibrium Green's function formalism for quantum transport calculation, we have investigated the electronic transport properties of a new dumbbell-like carbon nanocomposite, in which one carbon nanotube segment is capped with two C₆₀ fullerenes. Our results show that the current–voltage curve reveals a highly nonlinear feature. A negative differential resistance (NDR) behavior is obtained at a very low bias, which is expected to be helpful for the development of low bias NDR-based molecular devices. Moreover, the carbon nanotube length and fullerene type can affect the NDR behavior strongly. The electronic transport is analyzed from the transmission spectra and the molecular projected self-consistent Hamiltonian states under different applied biases.     

Structure and electronic properties of Hn@C20 molecule

Density functional theory has been employed to optimize the structure of endohedral doped C₂₀ fullerene. We have also investigated electronic properties. We have found that C₂₀ cage can accommodate up to 8 hydrogen atoms. Some hydrogen atoms get chemisorbed on the inner surface of C₂₀ cage and form C-H bond. Structural deformation is found to increase with increase in H-atoms. From the analysis of electronic properties, we observe that due to endohedral doping of hydrogen atoms inside C₂₀, H-atoms acquire net negative charge by accepting electrons and fullerene molecules acquire positive charge by donating electrons to H-atoms. For endohedral complexes where H₃ triangular molecule formation takes place, the nature of net charge transfer changes, i.e. fractional electronic charge is transferred from H-atoms to fullerene. C₂₀ doped with odd number of H-atoms should be more reactive compared to the even number case. Most of the present results are similar to those of endohedral C₆₀.     

Na掺杂对C20H20分子的电子输运性质影响

利用第一性原理密度泛函理论和非平衡格林函数方法研究了Na@C₂₀H₂₀分子的电子输运性质. 计算结果显示它的I-V曲线在偏圧 V范围内表现出了较好的线性特性, 出现了明显的负微分电阻现象, 并得到其平衡电导为0.0101G₀. 通过与Li@C₂₀H₂₀分子对比分析, 发现掺杂Na不仅能提高C₂₀H₂₀分子的电子输运能力, 而且 关键词： 20H₂₀分子')" href="#">Na@C₂₀H₂₀分子 电子输运 负微分电阻     

Interactions of Fullerene (C60) and its Hydroxyl Derivatives with Lipid Bilayer: A Coarse-Grained Molecular Dynamics Simulation

Coarse-grained molecular dynamic simulations were employed to study the interactions of fullerene (C₆₀) and its hydroxyl derivatives (C₆₀(OH)_n, n?=?4, 5, 6, 8, 12, and 16) with a lipid bilayer composed of dipalmitoylphosphatidylcholine molecules. It was found that the C₆₀ moves towards the center of the bilayer and laid between central and peripheral regions of the bilayer. The potential mean force was calculated to estimate free energy profile when pulling the fullerene from its initial position to the center of the bilayer using an umbrella sampling method. Results showed that the hydrophobic region of the membrane acts as a barrier to transport a nonpolar C₆₀ molecule through the bilayer. This makes a deep minimum in the free energy profile between the center and head regions of membrane. Various numbers of polar functional groups (–OH) were then used to make derivatives of fullerene and change the hydrophilic of the molecule. It was found that optimal number of hydroxyl groups to facilitate the transportation of C₆₀(OH)_n through the bilayer is 4.     

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.     

Optical spectra of high-symmetry isomers 60(CH3-r 6-H)n at n=3, 6

Earlier, we found the energies of formation and the electron band structures of the fullerene molecule C₆₀ and its methylated and hydrogenated chemical derivatives with saturated r ₆ bonds of the type C₆₀(CH₃-r ₆-H)_n with n from 1 to 6. Based on the self-consistent molecular-orbital method, we found the energies of singlet and triplet excitations for each molecule by the ΔSCF technique. We compared the electron structure of the fullerene molecule with experimental data and other theoretical calculations and showed that the semiempirical quantum-chemical technique used in our work satisfactorily explains the experimental photoluminescence spectra of fullerene-containing star-shaped polystyrenes. Partial or complete removal of the dipole inhibition for the transitions in isomers that are formed upon chemical saturation of double bonds makes it possible to follow changes in the electron structure of the pπ shell of the fullerene molecule by spectroscopic techniques. Specific optical spectra of the first excited singlet states (spectra of absorption, luminescence, and excitation of luminescence) as well as phosphorescence of the first spin-triplet state are described.     

Distorted cage structures of Si36 cluster

Using full-potential linear-muffin-tin-orbital molecular-dynamics (FP-LMTO-MD) method, we have performed calculations on the fullerene cage structures and the binding energies of Si₃₆ cluster. It is found that their atomic arrangement tends towards tetrahedral geometry. The distorted structures are very stable. In addition, we have also investigated a stacked structure by tricapped trigonal prisms (TTP). The stacked structure is slightly more stable than the distorted fullerene cages. Their electronic states suggest that they present different electric properties.     

内掺氮富勒烯N_2@C_(60)的几何结构和电子性质的密度泛函计算研究

采用密度泛函理论中的广义梯度近似对内掺氮富勒烯N2@C60的几何结构和电子性质进行计算研究.发现在N2@C60中,氮倾向以分子形式存在于C60中心处.键长分析、能级图、态密度图和电荷分析表明内掺氮分子对C60几何结构和电子结构带来的影响甚微.     

Dispersion relation of dust acoustic wave in multi-wall fullerene studied by the quantum hydrodynamic model

In this letter, dispersion properties of low-frequency electrostatic waves in multi-wall fullerene (the first layer is C₆₀molecule) are investigated. It is assumed that multi-wall fullerene is charged due to the field emission, and hence the multi-wall fullerene can be regarded as charged dust spheres surrounded by degenerate electrons and ions. We obtain the dispersion relation for the low-frequency electrostatic oscillations in the multi-wall fullerene by using the quantum hydrodynamic model in conjunction with the Poisson equation.     

Fluorescence and phosphorescence from individual molecules excited by local electron tunneling

Using the highly localized current of electrons tunneling through a double barrier scanning tunneling microscope junction, we excite luminescence from a selected C60 molecule in the surface layer of fullerene nanocrystals grown on an ultrathin NaCl film on Au(111). In the observed fluorescence and phosphorescence spectra, pure electronic as well as vibronically induced transitions of an individual C60 molecule are identified, leading to unambiguous chemical recognition on the single-molecular scale.     

密度泛函理论计算内掺氢分子富勒烯H2＠C60及其二聚体的几何结构和电子结构

采用密度泛函理论中的广义梯度近似(generalized gradient approximation,简称GGA),对内掺氢分子富勒烯H₂＠C₆₀及其二聚体的几何结构和电子结构进行了计算研究.发现无论是在H₂＠C₆₀单体,还是在其二聚体中,氢倾向以分子形式存在于碳笼中心处,且在室温下氢分子可以做自由旋转.电子结构分析表明,氢分子掺入到C₆₀和C₁₂₀中,仅对距离费米能级以下-8eV至-5eV能级处有一定的贡献,其他能级的分布和能隙几乎没有变化. 关键词： 几何结构 电子结构 密度泛函