Formation of Two-Dimensional AgTe Monolayer Atomic Crystal on Ag(111) Substrate

We report on the formation of two-dimensional monolayer AgTe crystal on Ag(111) substrates. The samples are prepared in ultrahigh vacuum by deposition of Te on Ag(111) followed by annealing. Using a scanning tunneling microscope(STM) and low electron energy diffraction(LEED), we investigate the atomic structure of the samples.The STM images and the LEED pattern show that monolayer AgTe crystal is formed on Ag(111). Four kinds of atomic structures of AgTe and Ag(111) are observed:(i) flat honeycomb structure,(ii) bulked honeycomb,(iii)stripe structure,(iv) hexagonal structure. The structural analysis indicates that the formation of the different atomic structures is due to the lattice mismatch and relief of the intrinsic strain in the AgTe layer. Our results provide a simple and convenient method to produce monolayer AgTe atomic crystal on Ag(111) and a template for study of novel physical properties and for future quantum devices.

Characteristics of local photonic state density in an infinite two-dimensional photonic crystal

The local density of photonic states （LDPS） of an infinite two-dimensional （2D） photonic crystal （PC） composed of rotated square-pillars in a 2D square lattice is calculated in terms of the plane-wave expansion method in a combination with the point group theory. The calculation results show that the LDPS strongly depends on the spatial positions. The variations of the LDPS as functions of the radial coordinate and frequency exhibit “mountain chain” structures with sharp peaks. The LDPS with large value spans a finite area and falls abruptly down to small value at the position corresponding to the interfaces between two different refractive index materials. The larger/lower LDPS occurs inward the lower/larger dielectric-constant medium. This feature can be well interpreted by the continuity of electricdisplacement vector at the interface. In the frequency range of the pseudo-PBG （photonic band gap）, the LDPS keeps very low value over the whole Wiger-Seitz cell. It indicates that the spontaneous emission in 2D PCs cannot be prohibited completely, but it can be inhibited intensively when the resonate frequency falls into the pseudo-PBG.

Photonic Band Modulation in a Two-Dimensional Photonic Crystal with a One-Dimensional Periodic Dielectric Background

A two-dimensional photonic crystal with a one-dimensional periodic dielectric background is proposed. The photonic band modulation effects due to the periodic background are investigated based on the plane wave expansion method. We find that periodic modulation of the dielectric background greatly alters photonic band structures, especially for the E-polarization modes. The number, width and position of the photonic band gaps （PBGs） sensitively depend on the structure parameters （the layer thicknesses and dielectric constants） of the one-dimensional periodic background,

STUDY ON LIQUID CRYSTAL POLYMERS WITH TWO-DIMENSIONAL MESOGENIC UNITS

A series of liquid crystalline polymers with two-dimensional mesogenic units were synthesized by solution polycondensation at low temperature. All the polymers were liquid crystalline. The melting temperature T;（except that with substituent of methoxy） and the clearing temperature T;of the polymers change regularly with varying of the length of the alkyl substituent groups.

LIQUID CRYSTAL POLYMERS WITH TWO-DIMENSIONAL MESOGENIC UNITS

A series of 'liquid crystal polymers with two-dimensional mesogeuic units' were synthesized by the polycondensations of the monomer 2, 5-dihydroxybenzylidene-4-phenetidine with a diacid chloride selected from a series of α, ω-bis(4-chloroformylphenyloxy)carbonylalkues. This is the first series of polymers reported under the newly proposed concept 'liquid crystal polymers with two dimensional mesogenic units'.

Band gaps structure and semi-Dirac point of two-dimensional function photonic crystals

Two-dimensional function photonic crystals, in which the dielectric constants of medium columns are the functions of space coordinates , are proposed and studied numerically. The band gaps structures of the photonic crystals for TE and TM waves are different from the two-dimensional conventional photonic crystals. Some absolute band gaps and semiDirac points are found. When the medium column radius and the function form of the dielectric constant are modulated, the numbers, width, and position of band gaps are changed, and the semi-Dirac point can either occur or disappear. Therefore,the special band gaps structures and semi-Dirac points can be achieved through the modulation on the two-dimensional function photonic crystals. The results will provide a new design method of optical devices based on the two-dimensional function photonic crystals.

Topological aspect of disclinations in two-dimensional crystals

By using topological current theory, this paper studies the inner topological structure of disclinations during the melting of two-dimensional systems. From two-dimensional elasticity theory, it finds that there are topological currents for topological defects in homogeneous equation. The evolution of disclinations is studied, and the branch conditions for generating, annihilating, crossing, splitting and merging of disclinations are given.

The interaction of nonlinear waves in two-dimensional dust crystals

This paper investigates the collision between two nonlinear waves with different propagation directions in two- dimensional dust crystals. Using the extended Poincare-Lighthill-Kuo perturbation method, two Korteweg-de Vries equations for nonlinear waves in both the ξ and η directions are obtained, respectively, and the analytical phase shifts and trajectories after the collision of two nonlinear waves are derived. Finally, the effects of parameters of the lattice constant a, the arbitrary constant u0η, the forces f（r）, and the colliding angle θ on the phase shifts of both colliding nonlinear waves are examined.

Thermal Behavior and Crystal Transition of Biodegradable Poly(butylenes adipate)Revealed by Two-Dimensional Correlation Spectroscopy

In the present study,thermal behavior and crystal transition of pure poly(butylene adipate)(PBA)upon heating process were investigated by FTIR spectroscopy.To gain further insight into the thermal behavior alteration and the phase transition of PBA,we performed two-dimensional(2D)correlation analysis.We found thatβ-form PBA crystal undergoes not only the melting process but also crystal transition upon the heating process.

SYNTHESIS AND CHARACTERIZATION OF LIQUID CRYSTAL POLYMERS WITH T-SHAPED TWO-DIMENSIONAL MESOGENIC UNITS (Ⅱ)

A series of liquid crystalline polymers with T-shaped two-dimensional mesogenic unitswere synthesized via low temperature solution polycondensation of 2-(4'-alkoxy-phenyl)hydroquinone with various diacyl dichlorides. The polymers were found to be nematic andshown thermotropic liquid crystalline behaviors through observations using DSC, polarizedmicroscopy and X-ray diffraction. The melting temperature T_m and the isotropizationtemperature T_i of the polymers change regularly with varying of the monomer structures.

Topological Phonon Modes in a Two-Dimensional Wigner Crystal

We investigate the spin-orbit coupling effect in a two-dimensional （2D） Wigner crystal. It is shown that sufficiently strong spin-orbit coupling and an appropriate sign of g-factor could transform the Wigner crystal to a topological phonon system. We demonstrate the existence of chiral phonon edge modes in finite size samples, as well as the robustness of the modes in the topological phase. We explore the possibility of realizing the topological phonon system in 2D Wigner crystals confined in semiconductor quantum wells/heterostructure. It is found that the spin-orbit coupling is too weak for driving a topological phase transition in these systems. It is argued that one may look for topological phonon systems in correlated Wigner crystals with emergent effective spin-orbit coupling.

SYNTHESIS AND CHARACTERIZATION OF LIQUID CRYSTAL POLYESTERS WITH T-SHAPED TWO-DIMENSIONAL MESOGENIC UNITS(Ⅲ)

A new series of liquid crystal polyesters with T-shaped two-dimensional mesogenic units weresynthesized by melt polycondensation of the diacetates of 2-(4'-alkoxy -phenyl)-hydroquinones with 4,4'-alkylenedioxydibenzoic acid. The polymers were characterized by using polarized microscopy, DSC and X-ray diffraction. It was realized that all the polymers have nematic thermotropic liquid crystallinecharacteristics. The melting temperature (T_m) and isotropization temperature (T_i) of the polymers changeregularly with varying lengths of the alkoxy side group and the length of the alkylene group in the main chainin company with an even-odd effect. The mesophase temperature range also varies regularly with the polymerstructure. It is shown that the mesophase range has been widened.

SYNTHESIS AND CHARACTERIZATION OF LIQUID CRYSTAL POLYMERS WITH T-SHAPED TWO-DIMENSIONAL MESOGENIC UNITS

Two series of new liquid crystalline polymers with T-shaped two-dimensional mesogenic units were synthesized by low temperature solution polycondensations of 4-substituted N-2, 5-dihydroxybenzylidene aniline monomers with different diacyl dichlorides. The polymers were found to be nematic and shown liquid crystalline behavior. The melting temperature T-m and the clearing temperature T-i of the polymers change regularly with varying of the monomer structures.

Comment on “Band gaps structure and semi-Dirac point of two-dimensional function photonic crystals” by Si-Qi Zhang et al.

Recently, Zhang et al. （Chin. Phys. B 26 024208 （2017）） investigated the band gap structures and semi-Dirac point of two-dimensional function photonic crystals, and the equations for the plane wave expansion method were induced to obtain the band structures. That report shows the band diagrams with the effects of function coefficient k and medium column ra under TE and TM waves. The proposed results look correct at first glance, but the authors made some mistakes in their report. Thus, the calculated results in their paper are incorrect. According to our calculations, the errors in their report are corrected, and the correct band structures also are presented in this paper.

Relationship between positron bulk lifetime and lattice constants-research on NaCl-type crystals

The positron lifetimes of some compounds with NaCl-type crystal structure are calculated with the method of atomic superposition approximation （ATSUP） based on the theories of local-density-approximation （LDA） and general- gradient-approximation （GGA）. The systematical results are fitted to a curve as a function of lattice constants. The positron bulk lifetimes of some other compounds with NaCl-type crystal structure, which are deduced from the systematical results, are in agreement with the experimental results given in other literature.

C-S-H凝胶无定型纳米孔隙中NaCl蒸发结晶分子动力学分析

氯化钠(NaCl)干湿循环结晶会对水泥混凝土材料产生破坏,现有试验方法存在局限性,很难从纳米尺度对盐结晶破坏机理进行研究。因此本文采用分子动力学方法,针对水泥水化主要微观产物水化硅酸钙(C-S-H)凝胶,研究NaCl在C-S-H凝胶无定型孔隙中蒸发结晶过程和结晶破坏机理。结果表明,本文构建的C-S-H凝胶无定型模型更接近于低密度的C-S-H凝胶模型,NaCl在这个模型孔隙中蒸发结晶遵循两步成核机制,蒸发结晶后的NaCl晶体填充C-S-H凝胶纳米孔隙,会显著降低C-S-H凝胶整体抗拉变形能力,使C-S-H凝胶变脆,这一结论为解释C-S-H凝胶在蒸发结晶作用下产生破坏的现象提供了依据。

SO_2存在下NaCl沉积量对Zn大气腐蚀的影响

用石英晶体微天平研究了不同沉积量的ＮａＣｌ在ＳＯ２质量分数为１×１０－６时对Ｚｎ大气腐蚀的影响，分析了该条件下Ｚｎ初期大气腐蚀的规律.结果表明，Ｚｎ的腐蚀增重随ＮａＣｌ沉积量的增加而增加，它们之间有着较好的线性关系ＮａＣｌ沉积量较高时，暴露一段时间后，Ｚｎ的大气腐蚀有减弱的趋势建立了反映其腐蚀及影响因素的经验方程：△ｍ／Ａ＝Ｋ（ｔ／ｔｔｏｔ）ｂ．采用Ｘ射线衍射（ＸＲＤ）和显微红外技术（ＩＲ）对Ｚｎ表面腐蚀产物进行了分析．

用石英晶体微天平研究NaCl对Zn大气腐蚀的影响

用石英晶体微天平原位研究了温度为 2 5℃、相对湿度为 (80± 2 ) %时Zn表面分别沉积 5 .0 ,15 .0 ,30 .0和4 5 .0 μg/cm2 NaCl的初期大气腐蚀 .探讨了该条件下Zn的大气腐蚀规律 .结果表明 ,Zn的腐蚀增重随暴露时间的延长而加大 ,并满足指数衰减关系 .同时Zn的腐蚀增重也随NaCl沉积量的增加而增加 ,其关系可用二次函数来描述 ,在腐蚀开始较短的时间内 ,它们之间呈现近似线形关系 .