Changes in the optical properties of conducting polydiacetylene THD brought on by doping

Changes in the optical properties of conducting polydiacetylene THD (poly-1,1,6,6-tetraphenylhexadiindiamine) brought on by doping are investigated for the first time. Spectral dependences of the extinction coefficients were studied in the range 400–25 000 cm⁻¹ both for the undoped polymer (σ<10⁻⁹ S/cm) and at various doping levels (up to σ∼5×10⁻³ S/cm). The results obtained attest to the appearance of high carrier concentrations in polydiacetylene THD with conductivities σ⩾10⁻⁴ S/cm. The relatively low observed macroscopic conductivity is explained by the complex hierarchy of structural formations that are intrinsic to polymers. The results obtained are compared with the corresponding data for conducting polyacetylene. Fiz. Tverd. Tela (St. Petersburg) 40, 1162–1166 (June 1998)     

Editorial for Focus Issue on Digital and Computer Generated Holography （DCH）

This focus issue Digital and Computer Generated Holography （DCH） combines the contributions from digital holography （DH） and computer-generated holography （CGH） into a single issue. We have classified the papers into four topics： holographic microscopy, computer-generated holography,     

低维螺旋磁体纳米条带中磁场驱动的磁结构演变规律

利用蒙特卡洛方法研究了低维螺旋磁体纳米条带中磁场驱动的磁结构演变规律,以及偶极相互作用对螺旋磁体纳米条带中磁结构的影响。研究表明,螺旋磁体纳米条带中的自旋结构由自旋的面内取向平行或垂直于边界的边缘态和中间聚集态两部分构成。在一定范围内增加外磁场,条带边缘平行于边界的自旋排列将增多,最终将在条带外围形成大的磁涡旋环,该涡旋环十分稳定,即使在很强的外磁场下仍然存在。处于条带中间的聚集态随着外磁场的增大,从磁螺旋态逐步过渡到Skyrmions态,最终形成铁磁态。Skyrmions的排列状况与条带尺寸密切相关。此外,偶极相互作用对磁矩平行于边界且首尾顺次连接的排列起积极作用,在无外磁场作用下,随着偶极相互作用的增大,体系终将形成涡旋态。     

低维螺旋磁体纳米条带中磁场驱动的磁结构演变规律

利用蒙特卡洛方法研究了低维螺旋磁体纳米条带中磁场驱动的磁结构演变规律,以及偶极相互作用对螺旋磁体纳米条带中磁结构的影响.研究表明,螺旋磁体纳米条带中的自旋结构由自旋的面内取向平行或垂直于边界的边缘态和中间聚集态两部分构成.在一定范围内增加外磁场,条带边缘平行于边界的自旋排列将增多,最终将在条带外围形成大的磁涡旋环,该涡旋环十分稳定,即使在很强的外磁场下仍然存在.处于条带中间的聚集态随着外磁场的增大,从磁螺旋态逐步过渡到Skyrmions态,最终形成铁磁态.Skyrmions的排列状况与条带尺寸密切相关.此外,偶极相互作用对磁矩平行于边界且首尾顺次连接的排列起积极作用,在无外磁场作用下,随着偶极相互作用的增大,体系终将形成涡旋态.     

Competition between anchoring and reversible photo-induced alignment of a nematic liquid crystal

We investigated the alignment induced on a nematic liquid crystal (LC) by a photo-aligned polymer film with azo-dye side groups. The orientation of the LC molecules can be manipulated in a reversible manner by irradiating the film with polarized light. We analyzed the competition between the orientation induced by the main chain, through rubbing of the film and that induced by the photo-aligned polymer. Anchoring strength for the different processing conditions are reported. The changes in film morphology caused by rubbing or photo-alignment could be captured by atomic force microscopy. The reversibility of the photo-induced alignment and the competition between the two anchoring mechanisms may allow recording and erasing of information in a LC display. PACS 61.30.-v; 61.30.Gd     

Short-term reversible changes in the dielectric dispersion of a barium titanate single crystal

An effect of spontaneous fluctuation of the dispersion frequency was detected during investigations of the dielectric dispersion of a BaTiO₃ single crystal while measuring under the electric field only. A decrease in the dispersion frequency by three orders of magnitude and its subsequent return to the previous value was observed. A possible mechanism of this phenomenon is suggested, which involves the dynamics of the screening process.     

低维螺旋磁体纳米条带中磁场驱动的磁结构演变规律

利用蒙特卡洛方法研究了低维螺旋磁体纳米条带中磁场驱动的磁结构演变规律,以及偶极相互作用对螺旋磁体纳米条带中磁结构的影响。研究表明,螺旋磁体纳米条带中的自旋结构由自旋的面内取向平行或垂直于边界的边缘态和中间聚集态两部分构成。在一定范围内增加外磁场,条带边缘平行于边界的自旋排列将增多,最终将在条带外围形成大的磁涡旋环,该涡旋环十分稳定,即使在很强的外磁场下仍然存在。处于条带中间的聚集态随着外磁场的增大,从磁螺旋态逐步过渡到Skyrmions态,最终形成铁磁态。Skyrmions的排列状况与条带尺寸密切相关。此外,偶极相互作用对磁矩平行于边界且首尾顺次连接的排列起积极作用,在无外磁场作用下,随着偶极相互作用的增大,体系终将形成涡旋态。     

Energy extraction (a reversible process) from a Kerr source by tachyons

We have demonstrated through a specific example that it is possible to extract rotational energy from a Kerr source (in principle, of arbitrary size but not turned black) through a reversible process by suitably injecting tachyons.     

硫酸盐对KDP晶体质量的影响

利用“点籽晶”快速生长技术生长了掺杂硫酸钾（K2SO4）的磷酸二氢钾（KDP）晶体,并对硫酸根类杂质离子对晶体的结构及光学质量的影响进行了研究。结果表明：在掺杂相对含量为50×10-6条件下,K2SO4开始对KDP晶体产生一定影响,主要表现在不同扇形区域的结构略有改变,其原因主要在于硫酸根与KDP晶体各扇形结构有关;杂质粒子对晶体透过率、单轴性没有明显影响,但是热膨胀系数增大,光损伤阈值略有降低。     

硫酸盐对KDP晶体质量的影响

 利用“点籽晶”快速生长技术生长了掺杂硫酸钾（K₂SO₄）的磷酸二氢钾（KDP）晶体,并对硫酸根类杂质离子对晶体的结构及光学质量的影响进行了研究。结果表明：在掺杂相对含量为50×10^-6条件下,K₂SO₄开始对KDP晶体产生一定影响,主要表现在不同扇形区域的结构略有改变,其原因主要在于硫酸根与KDP晶体各扇形结构有关;杂质粒子对晶体透过率、单轴性没有明显影响,但是热膨胀系数增大,光损伤阈值略有降低。     

Effect of doping with nickel ions on the structural state of a zinc oxide crystal

The fine structure of a hexagonal zinc oxide crystal doped with nickel ions of the composition Zn_{1 − x} Ni _x O has been studied using neutron diffraction and magnetic measurements. It is established that even at very low doping levels (x = 0.0004), the crystal undergoes local distortions in basal planes of the initial hexagonal lattice. The local distortions are assumed to be sources of the formation of ferromagnetism in compounds of this class.     

P.E.HSQC: a simple experiment for simultaneous and sign-sensitive measurement of (1JCH+DCH) and (2JHH+DHH) couplings

The angular information content of residual dipolar couplings between nuclei of fixed distance makes the accurate and sign-sensitive measurement of (¹J_CH + D_CH) and (²J_HH + D_HH) couplings highly desirable. Experiments published so far are typically highly specialized for the effective measurement of a subset of couplings. The P.E.HSQC presented here, is an E.COSY based experiment which allows the simultaneous measurement of all heteronuclear and homonuclear couplings within CH, CH₂, and CH₃ groups in a single spectrum with the necessary precision and sign information. The simplicity of the approach and the absence of artefacts like phase distortions due to antiphase evolution make it ideally suited for coupling determination of organic molecules at natural abundance.     

掺杂对一维光子晶体带隙传输特性的影响

 基于传输矩阵法,数值研究了掺杂对一维光子晶体带隙特征的影响。研究表明：掺杂时,禁带中心会出现一导带,导带深度会随着掺杂位置、杂质折射率的变化而发生变化。当晶体结构给定时,总存在一个掺杂位置,使其禁带中心的导带深度达到最深;而对于给定的掺杂位置,当杂质折射率为某特定值时,禁带中心同样也会出现一个深度最深的导带,这种特性可应用于滤波器件和光学谐振腔的设计。     

An electron spin resonance study of Eu doping effect in La_(4/3)Sr_(5/3)Mn_2O_7 single crystal

The effect of Eu3+ion doping in the La sites of single-crystal La4/3Sr5/3Mn2O7was investigated. Electron spin resonance(ESR) was applied to La4/3Sr5/3Mn2O7and(La0.8Eu0.2)4/3Sr5/3Mn2O7single crystals. A phase separation and phase transitions were observed from the ESR spectra data. Between 350 K and 300 K, both paramagnetic resonance(PMR)and anisotropic ferromagnetic resonance(FMR) lines were observed in the ab plane and the c axis direction, suggesting a coexistence of the paramagnetic(PM) phase and the ferromagnetic(FM) phase. The magnetization measurement reveals a spin-glass-like behavior in single-crystal(La0.8Eu0.2)4/3Sr5/3Mn2O7below the temperature of spin freezing Tf(～ 29.5 K).     

How should one define a (weak) crystal?

We compare two proposals for the study of positional long-range order: one in terms of the spectrum of the translation operator, the other in terms of the Fourier spectrum. We point out that only the first one allows for the consideration of molecular, as opposed to atomic, (weakly) periodic structures. We illustrate this point on the Thue-Morse system.     

Light-controlled electro-optic power limiter with a Bi(12)SiO(20) crystal

An optical power limiter is a self-actuating nonlinear optical device that transmits low-intensity light and blocks high-intensity light. A light-controlled electro-optic power limiter that uses a Bi(12)SiO(20) crystal has been demonstrated. The threshold light intensity is determined by the control light and can be set to any desired level. The response time of the light-controlled electro-optic power limiter is of the order of 1 ms.     

Sign inversion of dielectric anisotropy in nematic liquid crystal by dye doping

The present paper reports sign inversion in dielectric anisotropy of a nematic liquid crystal, i.e. 5CB, as an effect of doping dye (solvent green 3) in small amount. It is the result of strong variation of the parallel component of dielectric permittivity with temperature for a dye doped sample. This behavior is attributed to the interaction taking place between the nematic liquid crystal molecule and the dye molecule. This behavior of dielectric anisotropy has been explained on the basis of interaction between the dye (guest) and the liquid crystal molecules (host).     

Phase diffraction gratings based on a Si(400) crystal

The X-ray optical properties of diffraction gratings fabricated on the basis of a Si(400) crystal with a period of D = 1 μm are studied by triple-crystal X-ray diffractometry. The diffraction gratings are manufactured both by silicon profiling during the process of plasma chemical etching and by forming a phase-shift grating on the surface of a Si crystal. The principal difference in the diffraction properties of these gratings is demonstrated. The presence of an Au phase-shift grating is shown to lead to the formation of a two-dimensional diffraction pattern, whereas Si profiling leads to the formation of only a one-dimensional diffraction pattern.     

Experimental energy band dispersions for a TiN(100) crystal

The energy band dispersions of TiN along the Γ-X symmetry line have been determined using a TiN(100) crystal and the angle-resolved photoemission technique combined with tunable synchrotron radiation. Using the direct transition model with a free-electron like final state, the dispersions are mapped out by varying the photon energy. The results are compared to an APW energy band calculation.