Rotation of the inner shell in a C<Subscript>20</Subscript>@C<Subscript>80</Subscript> nanoparticle

The stability of a C₂₀@C₈₀ nanoparticle and the rotation of its inner shell are studied theoretically within the tight-binding approximation. It is found that the C₂₀ skeleton in the free state is described by space group D_3d; in the case where C₂₀ is placed into the C₈₀(I _h ) fullerene field, the space group of C₂₀ is raised to I _h due to isomerization. The total energy surface of the C₂₀@C₈₀ compound is scanned over two rotation angles. Based on an analysis of the surface relief and energy isoline map, orientational melting of the nanoparticle is predicted. A nanoparticle gyroscope—C₂₀ rotating in the field of C₈₀ at a certain relative orientation and energy supply—is also predicted to exist.     

Effects of oblique-incidence evaporation on magnetic properties of Fe20Ni80/Fe70Co30 bilayer film

Evaporative deposition at oblique incidence is shown to enhance the magnetic anisotropy of an Fe₂₀Ni₈₀ magnetic film and induce magnetic anisotropy in an overlying, strongly isotropic Fe₇₀Co₃₀ film. This deposition method for the formation of an underlayer of several lattice parameters in thickness and semi-hard overlayer of a few thousands Angstroms in thickness achieves a significant change in the magnetization process and strong suppression of the coercive forces of Fe₇₀Co₃₀ in the hard magnetization direction. Soft magnetization of the Fe₇₀Co₃₀ overlayer is not achieved when one of the layers is deposited at oblique incidence. It is anticipated that shape magnetic anisotropy is responsible in part for the magnetic anisotropy induced in both in Fe₂₀Ni₈₀ under- and Fe₇₀Co₃₀ overlayer by oblique incidence evaporation.     

Electrical spin transport in a GaAs (110) channel

A homoepitaxial GaAs (110) channel gives a great interest in the field of semiconductor spintronics due to the longer spin diffusion. By utilizing optimal temperature process and V/III flux ratio control, the GaAs layer is grown without a serious defect. In a ferromagnet/semiconductor hybrid device, Tb₂₀Fe₆₂Co₁₈/Ru/Co₄₀Fe₄₀B₂₀ films are deposited on the GaAs (110) channel as a spin source to investigate the spin transport in (110)-oriented channel. To measure the Hanle signal, an in-plane magnetic field is applied to the perpendicularly polarized spins which are injected from the Tb₂₀Fe₆₂Co₁₈ layer. From the experimental results, the spin diffusion length in a GaAs (110) is longer than that in a GaAs (100) by up to 25%. The proper selection of crystalline growth direction for the spin transport channel is a viable solution for an efficient spin transport.     

A new allotropic form of carbon [C<Subscript>28</Subscript>]<Subscript>n</Subscript> based on fullerene C<Subscript>20</Subscript> and cubic cluster C<Subscript>8</Subscript> and Si and Ge analogs of this form: Computer simulation

The structure of a new allotropic form of carbon [C₂₈]_n having a simple cubic lattice and space group \(Pm \bar 3\) is proposed. The geometrical parameters of the building block of such a hypothetic crystal are preliminarily determined from DFT-PBE calculations of the cluster C₈@(C₂₀)₈ and the polyhedral hydrocarbon molecule C₈@(C₂₀H₁₃)₈, in which the centers of the cubic clusters C₈ coincide with the centers of the cluster C₈@(C₂₀)₈ and of the molecule C₈@(C₂₀H₁₃)₈, respectively, and dodecahedral C₂₀ carbon cages are located at the vertices of a cube. The energy of dissociation of the cluster C₈@(C₂₀)₈ into a cubic cluster C₈ and eight dodecahedral clusters C₂₀ is calculated to be 1482 kcal/mol, and the energy of each C₈-C₂₀ bond is equal to 74.2 kcal/mol. The structure of the [C₂₈]_n crystal is refined using the DFT-PBE96/FLAPW method and optimized geometry. Calculations show that the crystal is a dielectric with an energy gap of 3.3 eV. The lattice parameter a of the crystal is equal to 5.6 Å, and its density is 3.0 g/cm³. The possible existence of analogous allotropic forms of elements Si and Ge is discussed. A method is proposed for designing a hypothetic allotropic form [C₂₈]_n from C₂₀(CH₃)₈ molecules with T _h symmetry.     

Smallest fullerene-like clusters in two-probe device junctions: first principle study

First principle calculations based on density functional theory are realised to investigate the electron transport of the smallest fullerene-like clusters as two-probe junction devices. The junction devices are constructed by mechanically controlled break junction techniques to ensure the maximum stability of the Be₂₀, B₂₀ and N₂₀ cluster molecular junctions. We investigate the density of states, transmission spectrum, molecular orbitals, current and differential conductance characteristics at discrete bias voltages to gain insight about the various transport phenomena occurring in these nano-junctions. The results show that B₂₀ molecule when stringed to gold electrodes works as an ideal nano-device similar to the pure C₂₀ device and is more symmetric in its characteristic nature. However, in N₂₀ molecular device, the conduction is negligible due to the higher atomic interactions within N₂₀ molecule, despite the fact that it is constructed with penta-valent atoms.     

Laser induced line narrowing in three-level systems: Application to the determination of the wavenumber of the 3s2-2p4 neon line (λ = 6328 Å)

The Doppler-free absorption line narrowing technique (A.L.N.) is applied to the ²⁰Ne (3s₂-2p₄-1s₅) three-level system, using a ¹²⁷I₂ stabilized He-Ne laser (λ = 6328 Å) and a tunable single-frequency cw dye laser (λ = 5945 Å). The relative frequency positions of the ²⁰Ne 3s₂-2p₄ line and of some iodine hyperfine components are measured with an uncertainty of 1 MHz. The wavenumber of the ²⁰Ne line at low pressure (0.2 Torr) is deduced from these measurements and is found to be σ(²⁰Ne, 3s₂-2p₄) = 1579800.060 ± 0.005 m^-1. With regard to the previous results, the accuracy is increased by two orders of magnitude.     

Crystallization behaviour in a new multicomponent Ti16.6Zr16.6Hf16.6Ni20Cu20Al10 metallic glass developed by the equiatomic substitution technique

A new amorphous Ti_16.6Zr_16.6Hf_16.6Ni₂₀Cu₂₀A1₁₀ alloy has been developed using the novel equiatomic substitution technique. Melt spinning Ti_16.6Zr_16.6Hf_16.6Ni₂₀Cu₂₀A1₁₀ forms an amorphous phase with a large supercooled liquid region, ΔT=70°C. After isothermal annealing within the supercooled liquid region for 3 h at 470°C, the amorphous alloy crystallizes to form a fine-scale distribution of 2–5 nm nanocrystals, and the supercooled liquid region increases to ΔT=108°C. Atomic-scale compositional analysis of this partially crystalline material using a three-dimensional atom probe (3DAP) is unable to detect any compositional difference between the nanocrystals and the remaining amorphous phase. After annealing for 1 hr at 620°C, the amorphous alloy crystallizes to form 20–50nm equiaxed grains of a hexagonal-type C14 Laves phase with lattice parameters a = 5.2Å and c = 9.0 Å. 3DAP analysis shows that this Laves phase has a composition very close to that of the initial amorphous phase, suggesting that the alloy crystallizes via a polymorphic rather than a primary crystallization mechanism, despite the complexity of the alloy composition.     

Chemical and redox stabilities of a solid oxide fuel cell with BaCe0.8Y0.2O3−α functioning as an electrolyte and as an anode

The operation of a solid oxide fuel cell (SOFC) based on BaCe_0.8Y_0.2O_3−α (BCY20) at 800 °C was studied without using an anode material. A porous, Ce-rich phase with a fluorite structure was formed at a depth of approximately 10 μm from the BCY20 surface by heat treatment at 1700 °C. This was due to the vaporization of BaO from the BCY20 surface. This treatment improved the cell performance and chemical stability to CO₂ because the Ce-rich phase functioned as an electrically conducting and protective layer. The heat-treated BCY20 also had better chemical and redox stabilities over a Ni–Ce_0.8Sm_0.2O_1.9 (SDC) cermet anode attached to the SDC electrolyte. The cell with the heat-treated BCY20 operated well on unhumidified methane, ethane, propane, and butane without carbon deposition, while the cell with the Ni–SDC cermet anode degraded within a few hours. Moreover, the BCY20 showed higher tolerance to 10 ppm H₂S and stability over 20 times redox cycling in comparison to the Ni–SDC cermet anode.     

NANOSTRUCTURED MULTI-COMPONENT MATERIALS BY MECHANICAL ALLOYING

We have shown that nanostructured multi-component materials like TaC, Nb₇₈Ge₂₂, Mo₇₀Si₂₀B₁₀, Mo₆₀Os₂₀B₂₀, Ru₅₂Zr₆B₄₂, (NbC)₂₀Co₈₀ and (WC)₈₀-(Ti₉₀Cu₁₀)₂₀ with an effective length size reduced to atomic level (a few nanometers) can be produced by mechanical alloying of the elemental and/or alloy powders in a high-energy ball mill. All process steps and samples preparation for characterization were done under glove box conditions.     

Stability of C<Subscript>20</Subscript> fullerene chains

The stability of (C₂₀)_N metastable chains, where C₂₀ fullerenes are joined by tight covalent bonds, is analyzed by numerical simulation using a tight-binding potential. Various channels of losing the chain-cluster structure of the (C₂₀)_N complexes have been determined including the decay of the C₂₀ clusters, their coalescence, and the separation of one C₂₀ fullerene from a chain. The lifetimes of the (C₂₀)_N chains with N = 3–7 for T = 2000–3500 K are directly calculated by the molecular dynamics method. It has been shown that, although the stability of the chains decreases with an increase in N, it remains sufficiently high even for N ? 1. An interesting lateral result is the observation of new (C₂₀)_N isomers with the combination of various intercluster bonds with the maximum binding energy of fullerenes in the chain.     

Elastic properties of the premelting phases of the perfluoroalkanes C16F34 and C20F42

The elastic properties of the solid state of linear oligomers are closely related to their special intra-and inter-molecular interactions. This is proved for the perfluoroalkanes C₁₆F₃₄ and C₂₀F₄₂. The elastic tensors of both materials have been measured with Brillouin spectroscopy as a function of temperature. Both systmes show an extremely weak shear stiffnessc ₄₄, indicating the existence of a smectic-B like structure and an unexpected strong elastic anisotropy inversion in the premelting phase. Moreover a Curie-Weiss-law behavior was found for the stiffness constantc ₃₃ indicating the existence of a soft longitudinal acoustic phonon mode. The transition temperatureT _c is for C₂₀F₄₂ below the melting point. The elastic properties are purely static. The observations are tentatively attributed to an intermolecular premelting process.     

Room-temperature magnetoresistance in CoFeB/STO/CoFeB magnetic tunnel junctions

A series of Co₄₀Fe₄₀B₂₀/SrTiO₃/Co₄₀Fe₄₀B₂₀ magnetic tunnel junctions with a bottom-pinned synthetic antiferromagnet have been prepared by sputtering. Devices optimally annealed at 325 °C exhibit an exchange bias of about 65 mT, and a tunnel magnetoresistance of 2%. The smaller than predicted effect is attributed to the lack of epitaxy between the crystallized CoFeB electrodes and the SrTiO₃ (STO) barrier, due to poor crystal quality of the barrier layer. Unlike MgO, well-crystallized, oriented STO does not grow on amorphous Co₄₀Fe₄₀B₂₀.     

Hydrogen-abstraction reactions of fully hydrogenated fullerene cages with the amino radical: a density functional study

We have applied density functional theory calculations to study the reactions of NH₂ + C_nH_n (n = 20, 40, 50, 60, 70 and 80). Due to the hard curvature in C₂₀ cage, the NH₂? + C₂₀H₂₀ → NH₃ + C₂₀H₁₉? reaction is nearly thermoneutral with a high potential barrier height. For the C_nH_n fulleranes with n > 20 the transition states appear earlier on the reaction paths, as can be anticipated for exothermic reactions. Using the spherical excess parameter, we distinguished different curvatures on the surfaces of fullerane cages. The reaction enthalpies ΔH°₂₉₈ and potential barrier heights ΔE^TS of the considered reactions indicate good correlation with the values of ?_i parameter, showing an upward trend with the curvature increasing at carbon sites. We have also investigated the H-abstraction of the chemical derivatives of the C₂₀H₂₀ cage (C₂₀H₁₉–CH₃, C₂₀H₁₉–CH₂CH₃ and C₂₀H₁₉–CH₂CH₂CH₃) in comparison to the corresponding isolated alkanes (CH₄, C₂H₆ and C₃H₈). Overall, it could be inferred that the H-abstraction from the primary and secondary C–H bonds of isolated alkanes could occur more easily than fullarane derivatives.     

On the possible existence of exo-and endohedral η5-π complexes of a C20 fullerene with transition metals

The molecular and electronic structures of a number of C₂₀ fullerene complexes (CpFe-C₂₀-FeCp, CpFe-C₂₀H₁₀-FeCp, H₅C₂₀-Fe-C₂₀H₅, C₂₀H₅-Fe-H₅C₂₀, C₂₀-Fe-C₂₀, Fe@C₂₀, and Cr@C₂₀, where C_p is the C₅H₅ cyclopentadienyl radical) are simulated using the density functional theory (DFT) method in the PBE/3z.bas approximation.     

Out-of-plane coercive field of Ni80Fe20 antidot arrays

The out-of-plane magnetic anisotropy and out-of-plane magnetization reversal process of nanoscale Ni₈₀Fe₂₀ antidot arrays deposited by magnetron sputtering technique on an anodic aluminum oxide (AAO) membrane are investigated. The angular dependence of out-of-plane remanent magnetization of Ni₈₀Fe₂₀ antidot arrays shows that the maximum remanence is in-plane and the squareness of the out-of-plane hysteresis loop follow a |cos θ| dependence. The angular dependence of out-of-plane coercivity of Ni₈₀Fe₂₀ antidot arrays shows that the maximum coercivity lies on the surface of a cone with its symmetric axis normal to the sample plane, which indicates a transition of magnetic reversal from curling to coherent rotation when changing the angle between the applied magnetic field and the sample plane.     

Ti-Zr-Ni单相准晶合金的室温力学性能研究

以Ti40₄₀Zr40₄₀Ni20₂₀合金为研究对象，用铜 模吸铸法制备出直径为3mm的致密单相准晶棒，通过维氏显微硬度测定和单向压缩实验方 法研究了该合金的室温力学性能 .结果表明：Ti40₄₀Zr40₄₀Ni20₂₀准晶具有良好 的弹性变形能力，室温弹性应 变可达125%.同时，它具有相对高的室温硬度（约55GPa），是普通Ti合金的15倍.T i40_{40 关键词： 准晶 Ti-Zr-Ni合金 解理断裂}     

Non-statistical effects in the 12C(12C, α)20Ne reaction near Ec.m. = 15 MeV

The ¹²C(¹²C, α)²⁰Ne reaction is studied near E_c.m. = 15 MeV. Angular distributions for three energies and excitation functions at θ_{lab = 30°} over an energy range E_c.m. = 14.5?15.4 MeV for about 20 levels in ²⁰Ne (E_ex = 0–13 MeV) are examined. The statistical analysis yields the results that a correlated resonance is present at E_c.m. = 14.75 MeV. A nonstatistical contribution to the reaction is also apparent when energy-averaged cross sections are compared with the Hauser-Feshbach model predictions. Strong population of the 0⁺₃ band in ²⁰Ne is observed.     

Magnetic properties of lithographically defined lateral Co/Ni80Fe20 wires

A novel micro-fabrication technique has been used to create an array of lateral magnetic multilayers consisting of micron-sized sputtered Co and Ni₈₀Fe₂₀ wires. The structures were fabricated using conventional optical lithography and a combination of hard and soft lift-off methods. For the field applied parallel to the wires intrinsic easy axis, we observed two switching fields corresponding to the distinct coercive field of the Ni₈₀Fe₂₀ wires (H_c1) and Co wires (H_c2) constituting the lateral multilayer wire array. A state of anti-parallel relative alignment of magnetization was observed when the applied field is greater than the switching field of Ni₈₀Fe₂₀ wires but less than the switching field of Co wires. We found the region of anti-parallel alignment of magnetization between the Co and Ni₈₀Fe₂₀ wires to be very sensitive to the relative orientation of the applied magnetic field.     

Magnetization modification by superconductivity in Nb/Ni80Fe20/Nb trilayers

We present experimental evidences for magnetization modification by superconductivity in a series of Nb/Ni₈₀Fe₂₀/Nb trilayers. By monitoring the magnetization in a zero field as a function of temperature, we observed an irreversibility in magnetization between the cooling and warming branches just above the superconducting transition temperature T_c. These results suggest that the magnetization of the ferromagnetic Ni₈₀Fe₂₀ layer is reduced by the mutual interactions between the ferromagnet and superconductor. Moreover, this effect diminishes with increasing thickness of the Ni₈₀Fe₂₀ layer, which indicates that the interaction between the superconducting and magnetic layers occurs mainly at the vicinity of the interfaces.     

Magnetic characterization of surface-coated magnetic nanoparticles for biomedical application

The influence of the oleic acid surface coating on Fe₃O₄ and NiFe₂O₄ nanoparticles on their magnetic and calorimetric characterization was investigated. Fe₃O₄ nanoparticles (particle sizes of 15-20 and 20-30 nm) and NiFe₂O₄ nanoparticles (particle sizes of 20-30 nm) were dispersed in oleic acid. The surface coating resulted in a decrease in the dipole-dipole interaction between the particles, which in turn affected the coercivity and heat dissipation of the nanoparticles. The coercivity of the oleic-acid-coated nanoparticles was found to be lower than that of the uncoated nanoparticles. The temperature rise in the oleic-acid-coated nanoparticles was greater than that of the uncoated nanoparticles; this temperature rise was associated with the relaxation losses. The viscosity dependence on the self-heating temperature of Fe₃O₄ nanoparticles (15-20 and 20-30 nm) under an ac magnetic field was measured. The temperature rise for both the Fe₃O₄ nanoparticles (15-20 and 20-30 nm) exhibited a strong dependence on viscosity at each magnetic field frequency, and the contribution of Brownian relaxation loss to the temperature rise was revealed. Moreover, an in vitro cytotoxicity test of Fe₃O₄ and NiFe₂O₄ was performed using human cervical carcinoma cells (HeLa), and the cytotoxicity of NiFe₂O₄ nanoparticles was compared to that of Fe₃O₄ nanoparticles.