Phase Manipulation between c(4 x 2) and p(2 x 2) on the Si(100) surface at 4.2 K

Phase manipulation between c(4x2) and p(2x2) on the Si(100) surface has been demonstrated at 4.2 K for the first time using a low-temperature scanning tunneling microscope. We have discovered that it is possible to change the c(4x2) surface into the p(2x2) surface, artificially, through a flip-flop motion of the buckling dimers by using a sample bias voltage control. Also, scanning at a negative bias voltage or applying a pulse voltage can restore the c(4x2) surface. The STM images as a function of bias voltage and tunneling current reveal the interesting dynamics of the buckling dimers on the long debated surface. Our results will show that energetic tunneling electrons are most likely responsible for the observed phase transition from c(4x2) to p(2x2).     

铕(Ⅲ)-呋喃甲酸配合物的光谱表征

以硝酸铕 ,呋喃甲酸和邻菲咯啉 (phen)合成了配合物 [Eu(FA) 3·2H2 O]·NO3(4 ,4’ Hbpy) ,[Eu(FA) 3·phen]H2 O和Eu(FA) 2 ·NO3·phen。用元素分析、红外吸收光谱、紫外吸收光谱和溶液荧光光谱对配合物进行了组成确定和表征。溶液荧光光谱表明 ,配合物 [Eu(FA) 3·2H2 O]·NO3(4 ,4’ Hbpy)的发光强度比混配配合物Eu(FA) 2 ·NO3·phen和 [Eu(FA) 3·phen]H2 O的发光强度小很多 ,而且发光寿命较短 ,三元配合物 [Eu(FA) 3·phen]H2 O的发光强度比四元配合物Eu(FA) 2 ·NO3·phen的发光强度略大     

Study of the e(g) orbitals in the bilayer manganite La(2--2x)Sr(1+2x)Mn(2)O(7) by using magnetic Compton-profile measurement.

From the magnetic Compton-profile (MCP) measurement, we have directly differentiated for the first time the populations in two e(g)-type orbitals ( x(2) - y(2) and 3z(2) - r(2)) in a manganite. The experimental MCP's along the [001] direction for La(2--2x)Sr(1+2x)Mn(2)O(7) at x = 0.35 and 0.42 are fitted by the theoretical profiles obtained from the (MnO(6))(8-) ab initio calculations. The calculation confirms that the MCP clearly detects the oxygen hybridization in the e(g) orbitals. The e(g) state is dominated by the x(2) - y(2)-type orbital with almost constant population, while the population in the 3z(2) - r(2)-type orbital decreases with increasing the hole concentration x.     

2—溴甲基萘荧光和室温磷光性质研究

研究了２－溴甲基萘（２－ＢｒＭＮ）的荧光及磷光性质。２－溴甲基萘是一种优良的荧光试剂,λｅｘ／λｅｍ＝２７４／３３４ｎｍ,其浓度在１．０×１０＾－６～１．２×１０＾－４ｍｏｌ·Ｌ＾－１范围内与荧光强度呈良好的线性关系,相关系数ｒ＝０．９９９,最低检测限为４．７×１０＾－８ｍｏｌ·Ｌ＾－１。以β－环糊精（β－ＣＤ）作保护剂和１,２－二溴丙烷（ＤＢＰ）为重原子微扰剂的２－ＢｒＭＮ／β－ＣＤ／ＤＢＰ体系     

The frustrated Heisenberg antiferromagnet on the honeycomb lattice: J1-J2 model

We study the ground-state phase diagram of the frustrated spin-[Formula: see text] antiferromagnet with J(2) = xJ(1) > 0 (J(1) > 0) on the honeycomb lattice, using the coupled-cluster method. We present results for the ground-state energy, magnetic order parameter and plaquette valence-bond crystal (PVBC) susceptibility. We find a paramagnetic PVBC phase for x(c(1)) < x < x(c(2)), where x(c(1)) ≈ 0.207 ± 0.003 and x(c(2)) ≈ 0.385 ± 0.010. The transition at x(c(1)) to the Néel phase seems to be a continuous deconfined transition (although we cannot exclude a very narrow intermediate phase in the range 0.21 ? x ? 0.24), while that at x(c(2)) is of first-order type to another quasiclassical antiferromagnetic phase that occurs in the classical version of the model only at the isolated and highly degenerate critical point [Formula: see text]. The spiral phases that are present classically for all values x > 1/6 are absent for all x ? 1.     

Numerical experiment of anharmonic oscillators by using the symplectic scheme-shooting method

Symplectic scheme-shooting method (SSSM) is applied to solve the energy eigenvalues of anharmonic oscillators characterized by the potentials V(x)=λx4 and V(x)=(1/2)x2+λx2α with α=2,3,4 and doubly anharmonic oscillators characterized by the potentials V(x)=(1/2)x2+λ1x4+λ2x6, and a high order symplectic scheme tailored to the "time"-dependent Hamiltonian function is presented. The numerical results illustrate that the energy eigenvalues of anharmonic oscillators with the symplectic scheme-shooting method are in good agreement with the numerical accurate ones obtained from the non-perturbative method by using an appropriately scaled basis for the expansion of each eigenfunction; and the energy eigenvalues of doubly anharmonic oscillators with the sympolectic scheme-shooting method are in good agreement with the exact ones and are better than the results obtained from the four-term asymptotic series. Therefore, the symplectic scheme-shooting method, which is very simple and is easy to grasp, is a good numerical algorithm.     

Lithium/Silver-Doped Cu_2ZnSnS_4 with Tunable Band Gaps and Phase Structures: a First-Principles Study

Doping is an effective approach for improving the photovoltaic performance of Cu_2 ZnSnS_4(CZTS). The doping by substitution of Cu atoms in CZTS with Li and Ag atoms is investigated using density functional theory. The results show that the band gaps of Li_(2 x)Cu_(2(1-x))ZnSnS_4 and Ag_(2 x)Cu_(2(1-x))ZnSnS4 can be tuned in the ranges of 1.30-3.43 and 1.30-1.63 eV, respectively. The calculation also reveals a phase transition from kesterite to wurtzite-kesterite for Li_(2 x)Cu_(2(1-x))ZnSnS_4 as x is larger than 0.9. The tunable band gaps of Li_(2 x)Cu_(2(1-x))ZnSnS_4 and Ag_(2 x)Cu_(2(1-x)) ZnSnS_4 make them beneficial for achieving band-gap-graded solar cells.     

太阳光谱方法测量成都地区大气二氧化氮浓度

文章报道的是用太阳光谱方法测量成都地区NO2浓度的实验研究,使用CCD光学多道分析器采集成都市区和西岭雪山的太阳光谱,以大气上界太阳光谱为参考,对五个分立光谱段以最小二乘法进行数据拟合,应用差分吸收原理解谱,获得了成都市区和西岭雪山NO2浓度.成都市区NO2浓度(垂直柱体密度)在3.1×1016至5.8×1016(molecule·cm-2)之间,西岭雪山的NO2浓度在0.7×1016至1.0×1016(mole-cule·cm-2)之间.随大气温度的上升,NO2浓度有上升趋势.     

Charge and spin order on the triangular lattice: NaxCoO2 at x=0.5

The nature of electronic states due to strong correlation and geometric frustration on the triangular lattice is investigated in connection to the unconventional insulating state of NaxCoO2 at x=0.5. We study an extended Hubbard model using a spatially unrestricted Gutzwiller approximation. We find a new class of charge and spin ordered states at x=1/3 and x=0.5 where antiferromagnetic (AFM) frustration is alleviated via weak charge inhomogeneity. At x=0.5, we show that the square root of 3a x 2a off-plane Na dopant order induces weak square root of 3a x 1a charge order in the Co layer. The symmetry breaking enables successive square root of 3a x 1a AFM and 2a x 2a charge- or spin-ordering transitions at low temperatures. The Fermi surface is truncated by the 2a x 2a hexagonal zone boundary into small electron and hole pockets. We study the phase structure and compare to recent experiments.     

Unusual thermodynamic properties and nonergodicity in ferroelectric superlattices

The properties of [Pb(Zr(1-x(1))Ti(x(1)))O(3)](n)/[Pb(Zr(1-x(2))Ti(x(2)))O(3)](n) superlattices, with a 2n period, are simulated using an ab initio based approach. The x(1) and x(2) compositions are chosen to be located across the morphotropic phase boundary of the corresponding disordered alloys, while the (x(1)+x(2))/2 average composition lies inside this boundary. These superlattices exhibit an unusual thermodynamic phase transition sequence, including a triclinic ground state. They also have the kind of peculiar free-energy landscape yielding nonergodicity. The effects responsible for these anomalies are discussed.     

若干具有[（PO4）4Mo6^VO15]^12^-簇骼的化合物的光谱研究

Five novel organic-molybdenum phosphates with [(PO4)4Mo6(V)O15]12- cluster, Na x (H4TETA)3 x (H3O)5 x {Zn[(HPO4)2(PO4)2Mo6O15]2} (2), (H2en)7 x (H3O)4 x {Cu[(HPO4)2(PO4)2Mo6O15]2} x H2O (3), (H3DETA)2 x (H3O)3 x {Co0.5[(HPO4)2(PO4)2Mo6O15]} x H2O (4), [Co(H3TETA)]2{Co0.5[(HPO4)(PO4)3Mo6O15] x 3.5H2O (5) and (H3DETA) x (H3O)4 x {Co1.5 [(HPO4)2(PO4)2Mo6O15]} x 0.5H2O (6), have been synthesized. The relationship between their properties and structures was studied by using FTIR, NIR FT-Raman, UV-Vis DRS and fluorescence etc. In these compounds, every two [(PO4)4Mo6O15] clusters are coordinated by a metal atom to form a {M[(PO4)4Mo6O15]2} dimer. In compound 2, 3 and 4, {M[(PO4)4Mo6O15]2} dimers are hydrogen-bonded by the organic molecules and water molecules to form a three-dimensional expended framework, respectively. In compound 5 and 6, {Co[(PO4)4Mo6O15]2} dimers are coordinated by [Co(H3TETA)] groups and [CoO4] tetrahedra to form a network, respectively. These characteristic vibrational frequencies of the molybdenum phosphates are related to the structure of these compounds. Three characteristic bands in UV-Vis DRS spectra of these compounds have to be attributed to the absorptions of O(d) --> Mo, O(mu) --> Mo and O --> M charge transfer, respectively. These compounds exhibit strong fluorescence emission bands at about 410 nm when excited by 240 nm, which are caused by O(mu) --> Mo charge transfer.     

Role of long range interaction in oxygen superstructure formation on Cu(001) and Ni(001)

On the basis of electronic structure calculations, we show that the long range Coulomb interaction provides the driving mechanism for oxygen overlayer formation on Cu(001). We illustrate that this interaction in the precursor c(2 x 2) phase induces a missing row reconstruction of Cu(001), and leads to the (2sqrt[2] x sqrt[2])R45 degrees O structure, which has strong covalent pO-dCu coupling. For the c(2 x 2)O overlayer on Ni(001) and Cu(001), we show that pO-dNi bonding is larger than pO-dCu and serves to neutralize the perturbation of the Coulomb interaction induced by the O overlayer. Consequently, c(2 x 2)O/Ni(001)) is stable while c(2 x 2)O/Cu(001) exists only in limited environments.     

Analytic expression for the joint x and Q2 dependences of the deep-inelastic structure functions

We obtain a good analytic fit to the joint Bjorken-x and Q2 dependences of ZEUS data on the deep-inelastic structure function F(2)(p)(x,Q2). At fixed virtuality Q2, as we showed previously, our expression is an expansion in powers of ln(1/x) that satisfies the Froissart bound. Here we show that for each x, the Q2 dependence of the data is well described by an expansion in powers of lnQ2. The resulting analytic expression allows us to predict the logarithmic derivatives (partial differential(n)F(2)(p)/(partial differentiallnQ2)n)x for n=1,2 and to compare the results successfully with other data. We extrapolate the proton structure function F(2)(p)(x,Q2) to the very large Q2 and the very small x regions that are inaccessible to present-day experiments and contrast our expectations with those of conventional global fits of parton distribution functions.     

Kinetics in surface reconstructions on GaAs(001)

We have successfully controlled the surface structures of GaAs(001) by changing incident As-molecular species. Under As4 fluxes, the c(4 x 4) reconstruction with Ga-As dimers [c(4 x 4)alpha structure] is obtained, but the formation of three As-As dimer structures [c(4 x 4)beta structure] is kinetically limited. On the other hand, the structure change from the (2 x 4), through c(4 x 4)alpha, to c(4 x 4)beta phases is observed under As2 fluxes. We found that the c(4 x 4)alpha structure is energetically metastable and provides a kinetic pathway for the structure change between the (2 x 4) and c(4 x 4)beta phases under As2 fluxes.     

From stable divalent to valence-fluctuating behaviour in Eu(Rh(1-x)Ir(x))2Si2 single crystals

We have succeeded in growing high-quality single crystals of the valence-fluctuating system EuIr(2)Si(2), the divalent Eu system EuRh(2)Si(2) and the substitutional alloy Eu(Rh(1-x)Ir(x))(2)Si(2) across the range 0 < x < 1, which we characterized by means of x-ray diffraction, energy-dispersive x-ray spectroscopy, specific heat, magnetization and resistivity measurements. On increasing x, the divalent Eu ground state subsists up to x = 0.25 with a slight increase in Néel temperature, while for 0.3≤x < 0.7 a sharp hysteretic change in susceptibility and resistivity marks the first-order valence transition. For x?0.7 the broad feature observed in the physical properties is characteristic of the continuous valence evolution beyond the critical end point of the valence transition line, and the resistivity is reminiscent of Kondo-like behaviour while the Sommerfeld coefficient indicates a mass renormalization of at least a factor of 8. The resulting phase diagram is similar to those reported for polycrystalline Eu(Pd(1-x)Au(x))(2)Si(2) and EuNi(2)(Si(1-x)Ge(x))(2), confirming its generic character for Eu systems, and markedly different to those of homologue Ce and Yb systems, which present a continuous suppression of the antiferromagnetism accompanied by a very smooth evolution of the valence. We discuss these differences and suggest them to be related to the large polarization energy of the Eu half-filled 4f shell. We further argue that the changes in the rare earth valence between RRh(2)Si(2) and RIr(2)Si(2) (R = Ce, Eu, Yb) are governed by a purely electronic effect and not by a volume effect.     

Explicit Relations of Physical Potentials Through Generalized Hypervirial and Kramers' Recurrence Relations

Based on a Hamiltonian identity,we study one-dimensional generalized hypervirial theorem,Blanchardlike(non-diagonal case) and Kramers'(diagonal case) recurrence relations for arbitrary x~κ which is independent of the central potential V(x).Some significant results in diagonal case are obtained for special κ in x~κ(κ≥ 2).In particular,we find the orthogonal relation(n_1|n_2) = δ_(n_1n_2)(κ = 0),(n_1|V'(x)\n_2) =(E_(n_1)-E_(n_2))~2〈n_1x|n_2)(κ = 1),E_n =(n/V'(x)x/2|n) +(n|V(x)|n)(κ = 2) and-4E_n(n|x|n) +(n|V'(x)x~2\n〉 +4〈n|V(x)x|n〉 = 0(κ = 3).The latter two formulas can be used directly to calculate the energy levels.We present useful explicit relations for some well known physical potentials without requiring the energy spectra of quantum system.     

First-order metal-insulator transitions in manganites: are they universal?

Conductivity data for La(2-2x)Sr(1+2xMn2O7 (x = 0.6) show a first-order transition from an orbital- or charge-ordered insulator to a metal as the temperature falls below approximately 160 K. The change in conductivity is 100 times larger than that seen previously in any single-phase manganite in zero field. The metallic low-temperature state is similar to x = 0.58, but x = 0.58 shows no evidence of orbital or charge order. This result supports a conclusion that strongly coupled magnetic-conductive transitions are first order.     

Spatial and temporal resolution effects on dynamic contrast-enhanced magnetic resonance mammography

We tested the hypothesis that partial volume effects due to poor in-plane resolution and/or low temporal resolution used in clinical dynamic contrast-enhanced magnetic resonance imaging results in erroneous diagnostic information based on inaccurate estimates of tumor contrast agent extravasation and tested whether reduced encoding techniques can correct for dynamic data volume averaging. Image spatial resolution was reduced from 469 x 469 microm2 to those reported below by selecting a subset of k-space data. We then compared the top five K(trans)/V(T) "hot spots" obtained from the original data set, 469 x 469-microm in-plane spatial resolution and an 18-s temporal resolution processed by fast Fourier transform (FFT), with values obtained from data sets having in-plane spatial resolutions of 938 x 938, 1875 x 1875 and 2500 x 2500 microm2 and a temporal resolution of 18 s, or data sets with temporal resolutions of 36, 54 and 72 and a spatial resolution of 469 x 469 microm2, and found them to statistically differ from the parent data sets. We then tested four different post processing methods for improving the spatial resolution without sacrificing temporal resolution: zero-filled FFT, keyhole, reduced-encoding imaging by generalized-series reconstruction (RIGR) and two-reference RIGR (TRIGR). The top five values of K(trans)/V(T) obtained from data sets, the in-plane spatial resolutions of which were improved to 469 x 469 microm2 by zero-filling FFT, Keyhole and RIGR, statistically differed from those obtained from the original 469 x 469 microm2 FFT parent image data set. Only the 938 x 938 and 1875 x 1875 microm2 data sets reconstructed to 469 x 469 microm2 with TRIGR reconstruction method yielded values of the top five K(trans)/V(T) hot spots statistically the same as the original parent data set, 469 x 469 microm2 in-plane spatial and 18-s temporal-resolution FFT. That is, partial volume effects from data sets of different in-plane spatial resolution resulted in statistically different values of the top five K(trans)/V(T) hot spots relative to a high spatial and temporal resolution data set, and TRIGR reconstruction of these low resolution data sets to high resolution images provided statistically similar values with a savings in temporal resolution of 2 to 4 times.     

Structural and valence changes of europium hydride induced by application of high-pressure H₂

Europium hydride EuH(x), when exposed to high-pressure H?, has been found to exhibit the following structural and valence changes: Pnma(x = 2, divalent) → P6?/mmc(x = 2, 7.2-8.7 GPa) → I4/m(x > 2, 8.7-9.7 GPa) → I4/mmm(x > 2, 9.7 GPa-,trivalent). With a trivalent character and a distorted cubic fcc structure, the I4/mmm structure is the β phase commonly observed for other rare-earth metal hydrides. Our study clearly demonstrates that EuH(x) is no longer an irregular member of the rare-earth metal hydrides.