New method for the visualization of domain and defect structure of ferroelectrics

A new method for the visualization of domain and real structure of ferroelectric triglycine sulphate (TGS) crystals on the scale of optical microscopy by means of decoration with auramine is developed. Auramine deposits on crystal surfaces as discrete particles about 2 microns in size and as a continuous layer, thus allowing both the domains as a whole and the various electrically active elements of the domain and real TGS structure to be visualized with high resolution. Due to decoration with auramine, the domain structure of TGS detected with a very high contrast; elements of the geometrical relief-cleavage steps exhibiting different electrical properties are also revealed. Furthermore, it has been observed for the first time that the positive domains have sharp electrical boundaries, while the negative domains have erased boundaries. It has also been established that between the domains of opposite signs regions exist characterized by a very low electrical activity. Decoration of annealed TGS crystals which were rapidly cooled from the temperature of 150°C, i.e. above the Curie point (49°C) down to room temperature resulted in detection of new electrically active directions on the surface of the negative domains; these directions are likely to occur in the paraelectric state. The new method cannot only be applied to the study of the TGS crystals but can also be useful in investigation of other ferroelectrics.     

AgGaGeS_4晶体介电性能的初步探讨

利用本实验室生长的红外非线性晶体材料AgGaGeS_4(AGGS),常温下进行腐蚀实验并观察畴结构,测试了不同频率、电压下晶体的电滞回线以及同一电压下不同频率介质的电容值.腐蚀图像显示出畴结构,畴尺寸5～10 μm左右,证实AGGS为一热释电晶体.然而,室温下的电滞回线变形为一近似椭圆,介质电容与电场频率关系表现出强色散特性.本文对这一现象进行了系统分析,最后提出了进一步探索AGGS铁电性质的具体建议.     

Laser Induced Reorientation of Nematic Liquid Crystals

A significant increase of the divergence and appearance of a fringe system has been observed by illuminating of MBBA (p-n-methoxybenzilidene-p-butylaniline) and OCB (octyl-cyano-biphenyl) nematic liquid crystalline samples with a collimated beam of an argon ion laser. The dependence of this effect on laser power, beam polarization, and angle of incidence has been studied in homeopolar and planar sandwich-like cells of 50-150 μm thickness, in the nematic phase. At a homeopolar cell of MBBA (150 μm thickness), at normal incidence a threshold laser power of 45 m W was found. The phenomena can be explained as deformation of the orientation by the Fredericks effect due to light fields. The observations are in good agreement with the theoretical predictions including an estimation of the laser power threshold.     

Characterization of the Intensity Distribution in a Single Laser Spot Applied to the Annealing of Ion-Implanted Silicon

By means of the annealing events of ion-implanted p-type silicon in liquid phase epitaxy (implantation dose 2.5 × 10¹⁶ As⁺/cm²) the degree of homogeneity of a bent quartz rod diffuser for single pulses of a Q-switched Nd-glass laser (λ = 1.06 μm) is investigated using SEM-EBIC, TEM and RBS. Starting from discrete distributions of EBIC signal heights in the annealing spot the specific distribution of recrystallized monocrystalline and polycrystalline regions as well as the transition between them are proved by TEM diffraction contrast studies. The perfect recrystallization for a locally optimum laser energy density as well as the rectangular shape of the carrier concentration profile are proved by RBS measurements. At different positions of the measuring point within the annealing area RBS, too, renders it possible to point out local inhomogeneities of the energy density distribution in the case of low-quality beam diffusers.     

Nucleation in a gas‐solid state reaction

A nucleation in a reaction of a gas with a solid state where one of the products is solid (GSR‐S) has been discussed. It was pointed out that the phenomenon observed for nanopowders, i.e. nucleation in sequence of the crystallites sizes, should be valid in case of defected monocrystals. However in such a case the constituents of a monocrystal, i.e. mosaic domains separated by structural defects, should undergo phase transition in sequence of size or, in other words, the time needed for the initiation of a nucleus in the case of a small domain is shorter than in the case of big one. Finally the less defected the crystal is, the bigger domains are, and thus the longer nucleation time is needed.     

Study of LiNbO3 single crystals with a regular domain structure by piezoresponse force microscopy

Lithium niobate crystals with a regular domain structure have been studied by piezoresponse force microscopy. The period of regular domains and the domain-wall width (w = 45 nm) have been calculated for Z- and Y-cut crystals based on an analysis of two-dimensional images of the domain-structure piezoresponse. It is shown that for the Y-cut crystal, both positive and negative domain boundaries can be identified when recording the lateral component of piezoresponse.     

Investigation of domain structures in PZNT93/7 crystals by chemical etching

The domain structures in 0.93Pb (Zn_1/3Nb_2/3)O₃‐0.07PbTiO₃ (PZNT93/7) crystals were investigated by chemical etching technique. Original antiparallel 180° domains of size 20–40 μm were observed on the surface of as‐grown PZNT93/7 crystal. It was found the domain states are sensitive to the stress field induced by mechanical processing or impurities. As the composition of PZNT93/7 crystal was located near the morphotropic phase boundary, various domain configurations were observed. On the <001>‐oriented wafer, the etched a ‐ and c ‐domains revealed homogenous and island‐like patterns. The c ‐domains consist of upper and lower height regions corresponding to the tail and head of the polarization, respectively. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Study of polycrystalline diamond layers deposited from gas phase

Crystallite size in polycrystalline diamond layers with a grain size exceeding 3 μm are determined by the X-ray topography method with the use of a divergent beam from a point source. For layers with thicknesses in the range 80–700 μm deposited in SHF plasma and 1–40 μm obtained by the method of a hot filament, the size distribution of crystallites is obtained. Asterism of some spots on X-ray diffraction patterns from the diamond layers with thicknesses exceeding 100 μm showed plastic deformation of individual crystallites. The parameters of deep levels in the band gap of undoped high-resistance diamond layers and the acceptor-type defects with an activation energy higher than 1 eV are determined by the method of charge relaxation spectroscopy.     

Pseudosymmetry and some characteristics of pyroelectric properties of crystals

The relation between pseudosymmetry characteristics of the atomic structure and the values of the pyroelectric coefficients of model and real pyroelectric crystals has been studied. It is established that the electron-density projection onto the polar axis of crystals with the highest values of pyroelectric coefficients possesses the property of pseudosymmetry, i.e., that the considerable part of the electron density is invariant with respect to an additional center of symmetry.     

Cr:KNSBN晶体两波耦合及其图像存储

本文以He-Ne 632.8nm激光为写入光,在非同时读出条件下,实验研究了e偏振光写入Cr:KNSBN晶体两波耦合过程中信号光和泵浦光的透射光强随时间的变化,以及单束泵浦光的透射光强随时间的变化,实验结果表明,泵浦光损失的能量几乎全部转移到了信号光方向,基本不存在散射光;并以二值化图像作为物在晶体内进行了图像存储实验,其再现图像清晰,信噪比高,没有观察到扇形光的影响.     

Nonlinear optical properties of ZnS nanocrystals incorporated within the polyvinyl alcohole photopolymer matrices

Photoinduced nonlinear optical effects in ZnS nanocrystallites incorporated within the photopolymer polyvinyl alcohol matrices were studied. As a basic method we have used photoinduced optical second harmonic generation (SHG). The Q‐switched HF‐laser (λ = 2.64.μm; pulse duration 30‐40 ps) was used as a source of probing (fundamental) light beam and the pulsed nitrogen (λ = 337.7 nm) was applied as a source of the photoinducing pump light. With increasing photoinducing beam power, the output SHG signal (at λ = 1.32 μm) increases. The maximal second‐order non‐linear optical susceptibility corresponds to tensor component d₁₂₃ = d₁₄ = 3.8 ± 0.2 pm/V at a photoinducing power density equal to about 1.25 GW/cm². With decreasing temperature, the SHG signal increases within the temperature range 25‐30 K. Time‐dependent pump‐probe measurements of the SHG indicate an existence of the SHG maximum for a pump‐probe delaying time 20 ps. The ZnS hexagonal structural components play a crucial role in the observed photoinduced second‐order non‐linear optical effects. Large values of the non‐linear optical constants as well the good technological parameters open a possibility to enhance the non‐linear optical susceptibilities of the investigated ZnS nanocrystallites.     

不同碳源和反应温度对原位合成SiC-TiC超细粉末的影响

以碳化硅(SiC)、二氧化钛(TiO2)和不同种类碳源为初始原料,采用碳热还原法在氩气气氛下原位合成SiC-TiC超细粉末.探讨了不同碳源和不同反应温度对所合成的SiC-TiC超细粉末的物相组成和显微形貌的影响.采用X-射线衍射仪(XRD)、激光粒度分析仪、扫描电镜(SEM)等手段对所合成的SiC-TiC超细粉末进行表征.实验结果表明,以蔗糖为碳源合成SiC-TiC超细粉末的适宜条件为1450 ℃保温2 h;以炭黑或葡萄糖为碳源合成超细粉末的适宜条件为1500 ℃保温2 h.三种碳源中以炭黑为碳源时所合成的SiC-TiC超细粉末粒度最小且合成出的粉末样品分散性好,大部分球状颗粒在0.5~1.0 μm 左右.在SiC粉末中原位合成的TiC颗粒,以粒径在0.1~0.2 μm左右的不规则的多样化结构颗粒存在.     

Low energy and low dose electron irradiation of potassium–lime–silicate glass investigated by XPS. I. Surface composition

X-ray induced photoelectron spectroscopy has been used to study the influence of low-energy electron beam on the pristine potassium–lime–silicate glass surface prepared by fracturing in situ under ultrahigh vacuum. Relatively low-energy electron beam of 1600 eV with low-electron beam current density of 0.02–0.22 A/m² and low-electron dose of 29–5200 C/m² was used. The expected modified near-surface region thickness is in this case comparable with the mean sampling depth of the analytical tool. Therefore, possible changes and modifications due to electron irradiation could be recorded with high sensitivity. The freshly fractured glass surface was found to be significantly enriched with potassium, and slightly with calcium. As a consequence of the lowest electron dose irradiation used, the potassium signal substantially increased by a factor 1.24 relative to the value found for the fresh surface. For higher doses used, the potassium signal continuously increased with the dose to a maximum and decreased thereafter. This variation was accompanied with the qualitative opposite behaviour of calcium signal. The concentrations of the other elements present in the glass, oxygen and silicon, varied only slightly with the electron dose. They can be considered to be constant within experimental uncertainty. In agreement with experimental results, a model assuming mobility of only two most mobile cations, potassium and calcium, was suggested. The models assuming one layer and two layers on the bulk were developed. Their results reproduce well experimental findings: (i) the formation of a potassium-rich surface layer, and (ii) the opposite-like signal variation of calcium in comparison with potassium.     

Complex susceptibility measurements in amorphous glass-coated microwires

We have applied the measurement of the amplitude dependence of the complex AC susceptibility to study the magnetization processes in amorphous glass-coated microwires with positive, negative and vanishing magnetostriction. The features of the magnetization process (reversible domain wall movement, irreversible domain wall movement, reversible magnetization rotation or irreversible magnetization rotation) can be recognized from the shape of the amplitude dependence of complex AC susceptibility, which confirms the domain structures predicted in microwires with different magnetostriction constant.     

双温区热扩散掺杂Fe2+∶ZnSe激光晶体的制备及激光输出性能

本文以CVD ZnSe晶片为基质材料,以FeSe粉末为掺杂物,采用双温区热扩散掺杂技术获得了尺寸为Ø22 mm×4 mm的Fe²⁺∶ZnSe激光晶体。通过二次离子质谱(SIMS)测试该晶体样品表面铁离子浓度为3.43×10¹⁸ cm^-3,并通过X射线光电子能谱(XPS)分析了晶体样品中铁元素的离子价态。采用UV/Vis/NIR分光光度计和傅里叶红外光谱仪测试了Fe²⁺∶ZnSe激光晶体的透过谱图。测试结果显示,在3.0 μm处出现了明显的Fe²⁺吸收峰,峰值透过率为5.5%。以波长为2.93 μm的Cr, Er∶YAG激光器为泵浦源,温度77 K时抽运尺寸10 mm×10 mm×4 mm的 Fe²⁺∶ZnSe晶体,获得了能量为191 mJ、中心波长4.04 μm的中红外激光输出,光光转换效率13.84%。     

Numerical modeling of optical properties of a system of two zone plates for focusing hard synchrotron radiation

Results of numerical experiments on focusing of a monochromatic spherical wave by a system of two linear zone plates are reported. Calculations were performed for a photon energy of 12.3985 keV and zone plates with a radius of the first zone of 5 μm, a number of zones of 628, and an aperture of 250 μm. To calculate the Kirchhoff integrals, the double Fourier transform method was used and the fast Fourier transform procedure on a grid with a number of points 65 536 = 2¹⁶ was applied. On the basis of the calculation results, a conclusion was drawn that two zone plates operate as one with a doubled phase shift in zones with a material if the longitudinal distance between them is smaller than 1/3 of the focus depth and the transverse displacement is smaller than 1/3 of the outermost zone width (the focus size). If the distance (displacement) exceeds the focus depth (size), the two zone plates operate independently, similar to refracting lenses with a set of different focusing orders, including the zero order. The nature of the moiré pattern at a transverse displacement of the zone plates is discussed.     

Reduction of domain wall width in VTE treated near stoichiometric LiNbO3 crystals

LiNbO₃ is a ferroelectric crystal and grows with multi domains. Different domains are separated by boundaries which are known as domain boundaries. Domain walls for congruent and VTE (Vapor Transport Equilibration) treated near stoichiometric lithium niobate samples were visualised in different crystallographic directions using chemical etching technique. The sample is etched in the mixture of HF and HNO₃ (in 1:2 volume ratios) for 10 minutes at boiling temperature. Measured domain wall width was found approximately 15‐20 µm for congruent (CLN) and it reduces to 1‐3 µm for VTE treated near stoichiometric (SLN). Activation energies were also measured by two‐probe method and found to be increasing in stoichiometric sample. This activation energy is related to defect density in the crystals. Activation energy is higher for less defective crystals. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Creep characterization of alumina particulate reinforced alumino-silicate glass

Compressive creep studies on alumino-silicate glass reinforced with alumina powders of 0.2 μm particle size as a function of volume fraction showed that there was a significant increase in the creep resistance by about an order of magnitude in the 20 vol.% composite. In order to study the effect of particle size on creep resistance, composites reinforced with 20 vol.% of 1.2 and 6.5 μm alumina particle size were also characterized. It was found that the composite with 1.2 μm particle sized reinforcement gave the highest creep resistance. All the composites exhibited Newtonian viscous creep and showed no strain hardening even at strains up to 10%.     

纳米金刚石的结构、光学性能和热稳定性研究

纳米金刚石兼具纳米材料和金刚石的双重特性,呈现出与微米金刚石、块体金刚石截然不同的特点。本文以不同尺寸金刚石样品为研究对象,采用扫描电镜、X射线衍射、光谱学、热重分析技术对其结构、光学性能和热稳定性进行研究。结果显示样品尺寸分别为300 μm、30 μm和100 nm,大尺寸样品结晶质量较好,富含孤氮杂质,为Ⅰb型金刚石。纳米金刚石样品结晶较差,含有少量石墨残留,并含有H₂O、N—H和C—H键,说明其表面存在诸多有机活性基团。大尺寸金刚石样品存在中性和带负电荷的氮空位缺陷,产生较强荧光,而纳米金刚石由于存在诸多的有机基团和表面缺陷,形成非辐射中心,导致荧光猝灭。大尺寸样品在300~525 nm具有较强吸收,而纳米金刚石样品在紫外-可见-近红外整个区域均呈现出较强吸收,透过率显著较低。随着颗粒尺寸的减小,金刚石的起始氧化温度逐渐下降,氧化速率降低,因此大颗粒尺寸金刚石样品具有更好的热稳定性。