Structures and electronic properties of SimN8-m（0 〈 m 〈 8） clusters： a density functional theory study

The geometries, electronic structures and related properties of SimN8-m（0 〈 m 〈 8） clusters are studied using density functional theory （DFT） with hybrid functional B3LYP. The calculated results reveal several trends. For any stoichiometric clusters, the lowest energy isomers with an alteration of N and Si atoms are favourable in energy if the numbers of Si and N atoms are large enough to form ... Si N-Si-N... alternative chains. The bond lengths of single Si-N bonds are very close to the corresponding values of the bulk and other SiN clusters. The geometries for N-rich and Si4N4 clusters are planar structures, but three-dimensional structures are favourable in energy for Si-rich clusters. With the increase of m, the isotropic polarizability and average polarizability increase, the total binding energies generally decrease, the HOMO-LUMO gap and vertical ionization potential oscillate with increasing number of valence electrons, and their values with even valence electrons are larger than those with odd valence electrons. The atomic charges, IR and Raman properties are also reported.     

Superconductivity without dependence on valenceelectron density in Zn doped YBCO systems

This paper reports that the YBa2Cu3-xZnxO7-δ （x = 0-0.4） samples are researched by means of x-ray diffraction, calculations of binding energy, the positron experiments and variations of oxygen content. The results of simulated calculations, positron experiments and variations of oxygen content support the existence of cluster effect. Moreover, it is concluded that the cluster effect is an important factor on suppression of high-Tc cuprate superconductivity and the Tc does not depend on the density of valence electron directly.     

Calculations of state-selective differential cross sections for charge transfer in collisions between O3+ and H2

The non-dissociative charge-transfer processes in collisions between O^3＋ and H2 are investigated by using the quantum-mechanical molecular-orbital coupled-channel （QMOCC） method. The adiabatic potentials and radial coupling matrix elements utilized in the QMOCC calculations are obtained with the spin-coupled valence-bond approach. Electronic and vibrational state-selective differential cross sections are presented for projectile energies of 0.1, 1.0 and 10.0eV/u in the H2 orientation angles of 45° and 89°. The electronic and the vibrational state-selective differential cross sections show similar behaviours： they decrease as the scattering angle increases, and beyond a specific angle the oscillating structures appear. Moreover, it is also found that the vibrational state-selective differential cross sections are strongly orientation-dependent, which provides a possibility to determine the orientations of molecule H2 by identifying the vibrational state-selective differential scattering processes.     

Electron spin resonance study of the Ba-doping manganite Nd0.5Sr0.5MnO3

We have performed magnetization measurements and electron spin resonance （ESR） on polycrystalline manganites of Nd0.5Sr0.5-xBaxMnO3 （x = 0.1）. Phase separation and phase transitions are observed from the susceptibility and the ESR spectra data. Between 260 K （～ Tc） and 185 K （～ TN）, the system coexists of the paramagnetic phase and the ferromagnetic （FM） phase. Between 185 K and 140 K, the system coexists of the FM phase and the antiferromagnetic （AFM） phase. These results indicate that the system has a very complex magnetic state due to the origin of the instability stemming from manganite Nd0.5Sr0.4Ba0.1MnO3 by partially substituting the larger Ba^2＋ ions for the smaller Sr^2＋ ions.     

Low-field electron emission from pinaster-like MoO2 nanoarrays as two-stage emitters

Low-field electron emission is obtained from the pinaster-like MoO2 nanoarrays. The turn-on field of the pinasterlike MoO2 nanoarrays is found to be as low as 2.39 V/μm with the current density of 10μA/cm2. The enhancement factor is extracted to be 3590 from the Fowler-Nordheim plot. These excellent emission properties are attributed to the special structure of the pinaster-like MoO2 nanoarrays and confirmed by the calculation in the frame of the two -stage model. Our results show that the pinaster-like MoO2 nanoarrays are promising candidate in realizing field emission displays.     

Theoretical investigation on near-infrared and visible absorption spectra of nanometallic aluminium with oxide coating in nanoenergetic materials: size and shape effects

The effects of metal core dimension, oxide shell thickness and ellipsoid aspect ratio of Al-Al2O3 core-shell nanoparticles on the near-infrared and visible absorption spectra of nanocomposite Al-Al2O3/nitrocellulose（NC） film are investigated by numerical calculations. Both the size-dependent interband transitions and frequency-dependent free electron damping of the nanometallic aluminium are taken into account in the calculations. Oxidation effect of nanoaluminium is also analysed. It is shown that oxidation may enhance but may also reduce the optical absorption, depending on the excited light energy and initial dimension of nanoparticle. Metal core size and excited light energy dominate the absorption characteristic. The absorption ability of ellipsoidal nanoparticles is larger than that of spheroidal nanoparticles and increases by the square index as the aspect ratio increases. These calculations will provide some significant theoretical guidance for the preparation and laser ignition of nanoenergetic materials.     

Spontaneous magnetization and resistivity jumps in bilayered manganite （La0.8Eu0.2）4/3Sr5/3Mn2O7 single crystals

Owing to the inhomogeneous state resulting from the doping of a small number of Eu ions into Laa/3Sr5/3Mn2O7, from the resulting single crystal （La0.8Eu0.2）a/3Sr5/3Mn2O7 we have observed the magnetization jump, the resistivity jump, as well as the relaxation phenomena. For （Lao.sEuo.2）a/3Sr5/3Mn2O7, it has a very delicate ground state due to the interplays among spin, charge, orbital, lattice degrees of freedom. Consequently, the magnetization state is sensitive to temperature, magnetic field, as well as time. Meanwhile, the evolution of the magnetization with time shows a spontaneous jump when both the temperature and the magnetic field are constant. Similar step-like behaviours are also observed in resistivity. All these results suggest that Eu doping can greatly modulate the physical properties of Laa/3Sr5/3Mn2O7 and cause such interesting behaviours.     

Deceleration of a continuous-wave （CW） molecular beam with a single quasi-CW semi-Gaussian laser beam

We propose a promising scheme to decelerate a CW molecular beam by using a red-detuned quasi-cw semi-Gaussian laser beam （SGB）. We study the dynamical process of the deceleration for a CW deuterated ammonia （ND3） molecular beam by Monte-Carlo simulation method. Our study shows that we can obtain a ND3 molecular beam with a relative average kinetic energy loss of about 10% and a relative output molecular number of more than 90% by using a single quasi-cw SGB with a power of 1.5kW and a maximum optical well depth of 7.33mK.     

Accurate studies of dissociation energies and vibrational energies on alkali metals

This paper studies full vibrational spectra {Ev} and molecular dissociation energies De by using conventional least-squares （LS） fitting and an algebraic method （AM） proposed recently for 10 diatomic electronic states of ^7Li2, Na2, NaK and NaLi molecules based on some known experimental vibrational energies in a subset [Ev^expt] respectively. Studies show that： （1） although both the full AM spectrum {Ev^AM} and the LS spectrum {Ev^LS} can reproduce the known experimental energies in [Ev^expt], the {EAM} is superior to the {Ev^LS} in that the high-lying AM vibrational energies which may not be available experimentally have better or much better accuracy than those LS counterparts in {Ev^LS}, and so is the AM dissociation energy De^AM; （2） the main source of the errors in the data obtained by using the LS fitting is that the fitting which is just a pure mathematical process does not use any physical criteria that must be satisfied by the full vibrational spectrum, while the AM method does. This study suggests that when fitting or solving a physical equation using a set of source data, it is important not only to apply a proper mathematical tool, but also to use correct physical criteria which measure the physical properties of the data, kick out those data having bigger errors, and impose conditional convergence on the numerical process.     

Magnetic properties and magnetocaloric effect in NdxLa1-xFe11.5Al1.5 compounds

Effects of Nd-doping on the magnetic properties and magnetocaloric effects （MCEs） of NdxLa1-xFe11.5Al1.5 have been investigated. Substitution of Nd leads to a weakening of the antiferromagnetic （AFM） coupling and an enhancement of the ferromagnetic （FM） coupling. This in turn results in a complex magnetic behaviour for Nd0.2La0.8Fe11.5Al1.5 characterized by the occurrence of two phase transitions at ～188 K （PM AFM） and ～159 K （AFM-FM）. As a result, a table-like MCE （9 J/kg.K） is found in a wide temperature range （160-185 K） for a field change of 0-5T around the transition temperature, as evidenced by both the magnetic and calorimetric measurements. Based on the analysis of low-temperature heat capacity, it is found that the AFM-FM phase transition modifies the electron density significantly, and the major contribution to the entropy change comes from the electronic entropy change.     

Judd--Ofelt analysis of spectra and experimental evaluation of laser performance of Tm3+ doped Lu2SiO5 crystal

This paper reports that the Tm^3＋：Lu2SiO5 （Tm：LSO） crystal is grown by Czochralski technique. The roomtemperature absorption spectra of Tm：LSO crystal are measured on a b-cut sample with 4 at.% thulium. According to the obtained Judd-Ofelt intensity parameters Ω2=9.3155×10^-20 cm^2, Ω4=8.4103×10^-20 cm^2, Ω6=1.5908×10^-20 cm^2, the fluorescence lifetime is calculated to be 2.03 ms for ^3F4 → ^3H6 transition, and the integrated emission cross section is 5.81×10^-18 cm^2. Room-temperature laser action near 2μm under diode pumping is experimentally evaluated in Tm：LSO. An optical-optical conversion efficiency of 9.1% and a slope efficiency of 16.2% are obtained with continuouswave maximum output power of 0.67 W. The emission wavelengths of Tm：LSO laser are centred around 2.06μm with spectral bandwidth of -13.6 nm.     

First-principles study of interphase Ni3Sn in Sn--Ni alloy for anode of lithium ion battery

This paper investigates the mechanism of Li insertion into interphase Ni3Sn in Ni-Sn alloy for the anode of lithium ion battery by means of the first-principles plane-wave pseudopotential. Compared with other phases, it is found that the Ni3Sn has larger relative expansion ratio and lower electrochemical potential, with its specific plateaus voltage around 0.3 eV when lithium atoms are filled in all octahedral interstitial sites, and the relative expansion ratio increasing dramatically when the lithiated phase transits from octahedral interstitial sites to tetrahedral interstitial sites. So this phase is a devastating phase for whole alloy electrode materials.     

Enhanced mechanical behaviour of lead zirconate titanate piezoelectric composites incorporating zinc oxide nanowhiskers

This paper reports that the lead zirconate titanate （PZT） piezoelectric composites incorporating zinc oxide nanowhiskers （ZnOw） were prepared by the conventional solid state processing. The whisker-dispersed PZT composites （PZT/ZnOw） presented a significant enhancement in the mechanical properties such as Young＇s modulus, tensile strength and compressive strength. Especially, the compressive strength increased from 153 MPa for the PZT to 228 MPa for the PZT/ZnOw composites. The reinforcement mechanism in strength of the composites was discussed. The me- chanical quality factors of the PZT/ZnOw composites increased considerably, while the piezoelectric constants and electromechanical coupling coefficient decreased slightly. The composites with good electrical and excellent mechanical properties are promising for further applications.     

Novel vertical stack HCMOSFET with strained SiGe/Si quantum channel

A novel vertical stack heterostructure CMOSFET is investigated, which is structured by strained SiGe/Si with a hole quantum well channel in the compressively strained Si量子信道 异质结构 CMOSFET 量子论 量子阱strained SiGe/Si, quantum well channel, heterostructure CMOSFET, poly-SiGe gateProject supported by the Preresearch from National Ministries and Commissions (Grant Nos 51408061104DZ01, 51439010904DZ0101).2/2/2006 12:00:00 AM2006-01-022006-03-16A novel vertical stack heterostructure CMOSFET is investigated, which is structured by strained SiGe/Si with a hole quantum well channel in the compressively strained Sil-xGex layer for p-MOSFET and an electron quantum well channel in the tensile strained Si layer for n-MOSFET. The device possesses several advantages including： 1） the integration of electron quantum well channel with hole quantum well channel into the same vertical layer structure; 2） the gate work function modifiability due to the introduction of poly-SiGe as a gate material; 3） better transistor matching; and 4） flexibility of layout design of CMOSFET by adopting exactly the same material lays for both n-channel and p-channel. The MEDICI simulation result shows that p-MOSFET and n-MOSFET have approximately the same matching threshold voltages. Nice performances are displayed in transfer characteristic, transconductance and cut-off frequency. In addition, its operation as an inverter confirms the CMOSFET structured device to be normal and effective in function.     

Effect of Dy substitution on magnetic properties and magnetocaloric effects of Tb6Co1.67Si3 compounds

The magnetic and magnetocaloric properties of(Tb1-xDyx) 6 Co 1.67 Si 3(0 ≤ x ≤ 0.8) have been experimentally investigated.The compounds exhibit a Ce6Ni2Si3-type hexagonal structure and undergo a second-order magnetic transition.The Curie temperature decreases from ～ 187 K to 142 K as the content of Dy grows from 0 to 0.8.The maximal magnetic entropy change,for a field change of 0-5 T,varies between ～ 6.2 and ～ 7.4 J/kg.K,slightly decreasing when Dy is introduced.The substitution of Dy leads to a remarkable increase in refrigeration capacity(RC).A large RC value of ～ 626 J/kg is achieved for x = 0.4 under a field change of 0-5 T.     

Effect of the stoichiometry on the electronic structure of the Ni（111）/α-Al2O3（0001） interface： a first-principles investigation

In this paper first-principles calculations of Ni（111）/α-Al2O3（0001） interfaces have been performed, and are compared with the preceding results of the Cu （111）/α-Al2O3（0001） interface [2004 Phil. Mag. Left. 84 425]. The AI- terminated and O-terminated interfaces have quite different adhesion mechanisms, which are similar to the Cu（111）/α Al2O3（0001） interface. For the O-terminated interface, the adhesion is caused by the strong O-2p/Ni-3d orbital hybridization and ionic interactions. On the other hand, the adhesion nature of the Al-terminated interface is the image-like electrostatic and Ni-Al hybridization interactions, the latter is substantial and cannot be neglected. Charge transfer occurs from Al2O3 to Ni, which is opposite to that in the O=terminated interface. The charge transfer direction for the Al-terminated and O-terminated Ni（111）/α-A1203（0001） interfaces is similar to that in the corresponding Cu（111）/α- Al2O3（0001） interface, but there exist the larger charge transfer quantity and consequent stronger adhesion nature, respectively.     

Self-organization effect in poly（3-hexylthiophene）： methanofullerenes solar cells

This paper studies the self-organization of the polymer in solar cells based on poly（3-hexylthiophene）： [6, 6]-phenyl C61-butyric acid methyl ester by controlling the growth rate of active layer. These blend films are characterized by UV-vis absorption spectroscopy, charge-transport dark J - V curve, x-ray diffraction pattern curve, and atomic force microscopy. The results indicate that slowing down the drying process of the wet films leads to an enhanced selforganization, which causes an increased hole transport. Increased incident light absorption, higher carrier mobility, and balanced carrier transport in the active layer explain the enhancement in the device performance, the power conversion efficiency of 3.43% and fill factor up to 64.6% are achieved under Air Mass 1.5, 100 mW/cm^2.     

Effects of exchange interaction and spin-fluctuation on the magnetic and magneto-optic properties of NdF3

The exchange interaction between the electrons in the different magnetic ions and the spin-fluctuation of the magnetic ions exist in the paramagnetic media NdF3. The exchange interaction between the electrons in the different magnetic ions may be equivalent to an effective field Hin that is in direct proportion to the magnetization M. The spin-fluctuation of the magnetic ions leads the coefficient of the effective field to vary with temperature. The effective field is given as Hin = -（0.75 ＋ 0.22T） × 10^-5M in NdF3. When the secondary crystal field effect is taken into account, the magnetic susceptibility and Verdet constant are calculated for NdF3 by means of the effective field Hin and the applied field He. The calculated results are in agreement with the measured ones.     

The effect of doped ions on single-molecule magnets of the Mn12-Ac family

This paper investigates the single-molecule magnets of pure and Cr/Fe-doped Mn12-Ac. The components of the mixed crystals are identified by AC susceptibility technique. The ground-state spin and anisotropy parameters of doped Mn12-Ac are obtained： （i） MnllCr-Ac （S=19/2, D=0.62K, B=0.0009K, A=63K）, and （ii） Mn11Fe-Ac （S=21/2, D=0.39 K, B=0.001 K, △=55 K）. The single-ion origin of the magnetic anisotropy is discussed.     

First-principles investigation of BAs and BxGa1-xAs alloys

First-principles investigation of BAs and BxGa1-xAs alloys Using first-principles calculations in the generalized gradient approximation, the electronic properties of BAs and BxGa1-xAs alloys are studied. At the Brillouin-zone centre, the lowest conduction band is the three-degenerate p-like Г15c state rather than s-like Г1c state, and the conduction band minimum （CBM） is along the A line between the Г and X points-at approximately 11/14（1,0,0）2π/a. With boron content at 0%-18.75%, BxGa1-xAs alloys have a small （2.6 eV） and relatively composition-independent band-gap bowing parameter, the band-gap increases monotonically by -18meV/B% with increasing boron content. In addition, the formation enthalpies of mixing for BxGa1-xAs alloys with boron content at 6.25% and 12.5% are calculated, and the large formation enthalpies may explain the difficulty in alloying boron to GaAs.