Novel orientational ordering and reentrant metallicity in K(x)C(60) monolayers for 3 < or = x < or = 5

STM studies on K(x)C(60) monolayers reveal new behavior over a wide range of the phase diagram. As x increases from 3 to 5 K(x)C(60) monolayers undergo metal-insulator-metal reentrant phase transitions and exhibit a variety of novel orientational orderings, including a complex 7-molecule, pinwheel-like structure. The proposed driving mechanism for the orientational ordering is the lowering of electron kinetic energy by maximizing the overlap of neighboring molecular orbitals. In insulating (metallic) K(x)C(60) this gives rise to orbital versions of the superexchange (double-exchange) interaction.     

CoSb_3/C_(60)复合材料的固相反应合成和热电性能

用固相反应法和脉冲电流直接通电烧结法制备了CoSb3 C6 0 复合材料 ,其组分通过粉末x射线衍射法确定 ,SEM分析表明C6 0 颗粒是均匀地分布在CoSb3基体中 .在 30 0— 80 0K范围内测量了材料的电导率、赛贝克系数和热导率 ,研究了纳米颗粒的尺寸和分布状态对复合材料热电性能的影响 .外加的C6 0 纳米颗粒在高温时降低了复合材料的晶格热导率 ,而对电传输性能影响较小 ,从而有效地提高了复合材料的热电性能 .与CoSb3相比 ,CoSb3 6 5 4 ? 0复合材料的ZT值提高了 4 0 % .     

Disentangling surface, bulk, and space-charge-layer conductivity in Si(111)-(7 x 7)

A novel approach for extracting genuine surface conductivities is presented and illustrated using the unresolved example of Si(111)-(7 x 7). Its temperature-dependent conductivity was measured with a microscopic four point probe between room temperature and 100 K. At room temperature the measured conductance corresponds to that expected from the bulk doping level. However, as the temperatures is lowered below approximately 200 K, the conductance decreases by several orders of magnitude in a small temperature range and it saturates at a low temperature value of approximately 4 x 10(-8) Omega(-1), irrespective of bulk doping. This abrupt transition is interpreted as the switching from bulk to surface conduction, an interpretation which is supported by a numerical model for the measured four point probe conductance. The value of the surface conductance is considerably lower than that of a good metal.     

Satellite transitions in natural abundance solid-state (33)S MAS NMR of alums--sign change with zero-crossing of C(Q) in a variable temperature study

Experiences obtained from recent improvements in the performance of solid-state (14)N MAS NMR spectroscopy have been used in a natural abundance (33)S MAS NMR investigation of the satellite transitions for this interesting spin I=3/2 isotope. This study reports the first observation of manifolds of spinning sidebands for these transitions in (33)S MAS NMR as observed for the two alums XAl(SO(4))(2) x 12H(2)O with X=NH(4) and K. For the NH(4)-alum a variable temperature (33)S MAS NMR study, employing the satellite transitions, shows that the (33)S quadrupole coupling constant (C(Q)) exhibits a linear temperature dependence (in the range -35 degrees C to 70 degrees C) with a temperature gradient of 3.1 kHz/ degrees C and undergoes a sign change with zero-crossing for C(Q) at 4 degrees C (277 K). For the isostructural K-alum a quite similar increase in the magnitude of C(Q) with increasing temperature is observed, and with a temperature gradient of 2.3 kHz/ degrees C. Finally, for optimization purposes, a study on the effect of the applied pulse widths at constant rf field strength on the intensity and variation in second-order quadrupolar lineshape for the central (1/2<-->-1/2) transition of the K-alum has been performed.     

星状C60(CH3)x(PAN)x共聚物的光致发光研究

利用物理喷束淀积（ＰＪＤ）技术制备Ｃ６０（ＣＨ３）ｘ（ＰＡＮ）ｘ共聚物的薄膜。这种共聚物中,Ｃ６０分子位于星状结构的中心,聚丙烯腈（ＰＡＮ）主链修饰在Ｃ６０分子的周围。吸收及荧光光谱表明：Ｃ６０分子与聚丙烯腈（ＰＡＮ）有明显的相互作用,而且这种相互作用与ＰＡＮ的链长有关。Ｃ６０分子与ＰＡＮ间存在一定的激发传递过程,从而导致ＰＡＮ荧光的部分猝灭。     

Proton NMR T 1 Studies in Methylammonium TrichlorO Stannate(II) (CH 3 NH 3 SnCl 3 )

Proton spin lattice relaxation time ( T 1 ) measurements have been carried out in methylammonium trichloro stannate(II) (CH 3 NH 3 SnCl 3 ) as a function of temperature in the range 317-5 K at a Larmor frequency of 10 MHz. The temperature dependence of T 1 shows a phase transition around 220 K and four T 1 minima (294 K, 62 K, 32 K and 12 K). The results are discussed in terms of proton dynamics, namely, uncorrelated reorientation of NH 3 and CH 3 groups at high temperatures and tunnelling of NH 3 and CH 3 protons at low temperatures.     

Surface and bulk normal state transport properties in K(3)C(60)

The temperature dependence of the surface resistivity for a metallic K(3)C(60) ordered film in the nonsuperconducting state has been obtained by reflection electron energy loss spectroscopy. We demonstrate that the normal state electronic and transport properties of the top molecular layer of K(3)C(60) are similar to the corresponding properties measured with bulk sensitive techniques. These observations strengthen and give a general character to the experimental results obtained with surface sensitive techniques on fullerene compounds. In addition, the transport properties may deviate from the Fermi-liquid behavior above 500 K.     

锌掺杂固态电解质材料磷酸钛铝锂的制备及第一性原理研究

高安全性的固体锂离子电池是目前研究的热点之一,固态电解质是研究全固态电池的关键.磷酸钛铝锂固体电解质(LATP)具有良好的发展空间,因此采用高温固相法,制备锌掺杂LATP(LAZTP)固体电解质,通过XRD、SEM分析对比其物象和形貌特征,并对这两种材料压片进行阻抗分析,研究材料的电化学性能.基于密度泛函理论的第一性原理,研究LAZTP的能带结构和态密度与材料电化学性能的关系.结果表明:所掺杂锌的LATP材料,在球磨工艺下,与LATP相比衍射峰尖锐,材料结晶度良好,都为R-3C结构,LAZTP微观尺度下材料颗粒清晰,呈块状,孔隙均匀致密度较好,离子电导率相比较高,为1.9×10^-3S/cm,而制作的LATP的电导率为4.02x10^-4 S/cm,掺杂后的电导率明显高出一个数量级.计算得出的LATP能带带隙为0.163 eV和LAZTP能带带隙为0.05 eV,分态密度中Ti-s、Li-s、Al-s峰值尖锐,变化明显,表明掺杂锌后,材料明显提高了导电率和结构稳定性.     

Noise probe of the dynamic phase separation in La(2/3)Ca(1/3)MnO3

Giant random telegraph noise (RTN) in the resistance fluctuation of a macroscopic film of perovskite-type manganese oxide La(2/3)Ca(1/3)MnO3 has been observed at various temperatures ranging from 4 to 170 K, well below the Curie temperature ( T(C) approximately 210 K). The amplitudes of the two-level fluctuations vary from 0.01% to 0.2%. We discuss the origin of the RTN to be a dynamic mixed-phase percolative conduction process, where manganese clusters switch back and forth between two phases that differ in their conductivity and magnetization.     

Magnetic trapping and Zeeman relaxation of NH (X3Sigma-)

NH radicals are magnetically trapped and their Zeeman relaxation and energy transport collision cross sections with helium are measured. Continuous buffer-gas loading of the trap is direct from a room-temperature molecular beam. The Zeeman relaxation (inelastic) cross section of magnetically trapped electronic, vibrational, and rotational ground state NH molecules in collisions with 3He is measured to be 3.8+/-1.1 x 10(-19) cm(2) at 710 mK. The NH-He energy transport cross section is also measured, indicating a ratio of diffusive to inelastic cross sections of gamma=7 x 10(4), in agreement with recent theory [R. V. Krems, H. R. Sadeghpour, A. Dalgarno, D. Zgid, J. K?os, and G. Cha?asiński, Phys. Rev. A 68, 051401 (2003)10.1103/PhysRevA.68.051401].     

Topological Superconductivity in Cu(x)Bi(2)Se(3)

A topological superconductor (TSC) is characterized by the topologically protected gapless surface state that is essentially an Andreev bound state consisting of Majorana fermions. While a TSC has not yet been discovered, the doped topological insulator Cu(x)Bi(2)Se(3), which superconducts below ～3 K, has been predicted to possess a topological superconducting state. We report that the point-contact spectra on the cleaved surface of superconducting Cu(x)Bi(2)Se(3) present a zero-bias conductance peak (ZBCP) which signifies unconventional superconductivity. Theoretical considerations of all possible superconducting states help us conclude that this ZBCP is due to Majorana fermions and gives evidence for a topological superconductivity in Cu(x)Bi(2)Se(3). In addition, we found an unusual pseudogap that develops below ～20 K and coexists with the topological superconducting state.     

NH_x(x=1～3)在金属Ir表面吸附与解离的第一性原理研究

采用密度泛函理论,在slab模型下,研究了NH_x(x=1~3)在Ir(100)、Ir(111)和Ir(110)表面上的最稳定吸附位置、几何构型以及逐步脱氢分解过程,计算了相应的吸附能和活化能.计算结果表明,在Ir(100)、Ir(111)面上,NH_3是以C_3轴垂直吸附在顶位,在Ir(110)上,NH_3是以N-Ir键与表面成68.6°吸附在顶位,且吸附能依赖于表面的结构而不同,相比而言,NH_3更容易吸附在开放表面Ir(100)、Ir(110)面上,说明NH_3在这些表面的吸附具有结构敏感性.NH_(x(x=1~3))的分解,在Ir(100),NH_3的吸附与分解存在竞争,在Ir(110)面NH_3最容易分解,在Ir(111)面NH_3是分子性吸附,不能分解.NH_2、NH在三个表面均能够分解,在Ir(110)面活化能均较高.     

Adatom-vacancy mechanisms for the C6)/Al111-(6 x 6) reconstruction

The irreversible (6x6) reconstruction of the C(60)/Al(111) system from the (2sqrt[3]x2sqrt[3])R30 degrees phase is studied by first-principles techniques. We find that C60 binds optimally to the surface if an Al vacancy is created directly underneath. The removed Al atoms form a (6x6) array of ad-dimers in the interstices below the C60 overlayer, to which they strongly bind. This spontaneous local process, rather than the compression state of the unreconstructed C60 overlayer, explains why one molecule out of three protrudes from the surface upon reconstruction.     

Correlated electromigration of H in the switchable mirror YH(3-delta)

Electromigration of hydrogen in YH(3-delta) is studied by exploiting the H concentration dependence of the optical transmission of YH(3-delta). We find the effective valence Z* of H in YH(3-delta) to be negative. Its value is dominated by a huge wind-force-like term, i.e., Z* approximately K/rho, with K approximately -60 mOmega cm. This value is 3 orders of magnitude larger than typical for H in metals. In an Arrhenius plot, the ratio of hydrogen and electron fluxes extrapolates to unity at infinite temperature, suggesting a one-to-one correlation of hydrogen and electron hopping. We discuss our results in the light of strong electron correlation theories which predict each proton to bind two electrons in a sort of Zhang-Rice singlet.     

Ti_3(Ge_(1-x)Si_x)C_2固溶体力学和热力学性能的第一性原理研究

采用基于密度泛函理论(DFT)的第一性原理平面波超软赝势方法,系统研究了Ti_3(Ge_(1-x)Si_x)C_2(x=0, 0.5, 1)固溶体的晶体结构、弹性性质以及热力学性能.研究结果表明,Ti_3(Ge_(1-x)Si_x)C_2体系均具有力学和热力学稳定结构,并且为脆性材料;Ti_3(Ge_(1-x)Si_x)C_2固溶体的力学性能随Si含量的增加而提高;Ti_3(Ge_(1-x)Si_x)C_2固溶体在室温下具有稳定的晶格结构和较高的晶格热导率,有望用于一些需要良好散热性能电子元器件的封装材料.     

Nitridation of Si(100)-( 2x1) surface by NH3: a quantum chemical cluster model study

Based on density functional cluster model calculations, we present the first detailed mechanisms for the complete decomposition of NH3 to NHx(a) (x = 0-2) on the Si(100)-(2x1) surface. Three kinds of elementary processes, namely, N-H bond cleavage, NHx(a) insertion into the Si-Si surface dimer bond or backbond, and H2 libration, are investigated. A plausible microscopic mechanism for the nitridation of Si(100)-(2x1) surface by NH3 is proposed.     

K_3Ba_3C_(60)在不同温度下的Raman光谱研究

研究了K3Ba3C60 在不同温度下的Raman光谱 .发现Raman光谱随温度的变化发生有规律的变化 .随着温度的降低 ,所有模的线宽和强度的变化情况与纯的C60 的情况明显不同 .径向Ag(2 )模的频率在 2 0K到室温之间有一个反常大的向高频漂移 (9cm-1) ,这表明在C60 分子和掺杂离子之间存在着轨道杂化 .另外Raman光谱中Ag(1)模两个分量的相对强度随着温度的降低发生有规律的变化 .     

钙钛矿锰氧化物La0.7Sr0.3MxMn1-xO3(M=Cr,Fe)的巨磁电阻效应与磁性

研究了溶胶 -凝胶法制备氧化物巨磁电阻材料的工艺 ,制备了La0 .7Sr0 .3 CrxMn1-xO3 (x =0 ,0 .10 ,0 .15 )和La0 .7Sr0 .3 FexMn1-xO3 (x =0 .0 5 ,0 .10 ,0 .16 )两系列的单相钙钛矿锰氧化物多晶样品 ,并研究了Cr ,Fe替代La0 .7Sr0 .3 MnO3 中部分Mn后对其结构、磁性和巨磁电阻性质的影响 .观察到La0 .7Sr0 .3 Cr0 .15Mn0 .85O3 和La0 .7Sr0 .3 Fe0 .0 5Mn0 .95O3 两个样品的电阻 温度曲线都出现了双峰 .定性讨论了可能产生双峰的机制 .随Cr(或Fe)替代量的增加 ,材料的居里温度很快下降 ,铁磁性减弱 ,导电性降低 ,巨磁电阻效应增强 .但与Fe掺杂相比 ,相同数量的Cr掺杂对材料的影响要小 .     

Deuteron spin-lattice relaxation in partly and fully deuterated (NH(4))(2)PdCl(6)

Deuteron spin-lattice relaxation and spectra were studied in partially and fully deuterated (NH(4))(2)PdCl(6) in the temperature range 5-300K. The relaxation rate maximum was observed at 45K in (ND(4))(2)PdCl(6). Its value is reduced due to limited jumps by about 33% relative to the theoretical value expected for threefold reorientations. Limited jumps correspond to an N-D vector jumping between six directions on a cone around a Pd-N vector, the angle between the N-D and Pd-N vectors being denoted Delta. This motion makes a part of the quadrupole interaction ineffective in relaxation thus reducing the maximum rate at 45K. The observed reduction leads to the value Delta=21( composite function). Limited jumps are quenched to a large extent at the order-disorder phase transition and consequently a decrease is observed in the rate. Below the transition ND(4)(+) ions reorient between the tetrahedral orientations of the ordered phase, therefore the quadrupole interaction has the full relaxing efficiency. In the 10% deuterated sample the temperature of the rate maximum is shifted to 35K and below 20K the rate itself is one order of magnitude larger than in (ND(4))(2)PdCl(6). The increase is related to (1) the absence of the order-disorder phase transition and (2) to the enhanced mobility of NH(3)D(+) because of its electric dipole moment. Limited jumps are claimed to be the dominant relaxation mechanism below 20K. The relaxation in the disordered 30% deuterated sample is quite similar to that in 10% sample. The 50% and 70% deuterated samples undergo a transition to the ordered phase. The relaxation is biexponential with the characteristic rates somewhat smaller than those in (ND(4))(2)PdCl(6), but approaching them with increasing deuteration. This variation can be explained with different mobilities and varying relative numbers of the various isotopomers NH(4-n)D(n)(+), n=1-4.     

H(2)-Broadening Coefficients in the nu(4) Band of NH(3)

H(2)-broadening coefficients have been measured for 66 rovibrational lines of NH(3) at room temperature in the (P)P and (R)P branches of the nu(4) band in the range 1470-1600 cm(-1), using a high-resolution Fourier transform spectrometer. The collisional widths are obtained by fitting Voigt profiles to the measured shapes of the lines. The broadening coefficients are found to decrease on the whole as J increases and they increase with K for a given J value. The results are compared with those calculated from a semiclassical model in which the inversion vibration of NH(3) and collision-induced transitions with DeltaK = 0 and DeltaK = +/- 3 are taken into account. The intermolecular potential used includes electrostatic, induction, and dispersion energy contributions. The calculations performed by considering only DeltaK = 0 transitions provide significantly lower broadenings but with a satisfactory J and K dependence. The same trends are obtained for the broadening coefficients in inversion-rotation transitions and in the Q branch of the nu(1) parallel band of NH(3). Copyright 2001 Academic Press.