Maximizing the grain growth rate during the disorder‐to‐order transition in block copolymer melts

The factors controlling grain growth during the disorder‐to‐order transition in a polystyrene‐block‐polyisoprene copolymer melt were studied with time‐resolved depolarized light scattering. The ordered phase consisted of hexagonally packed polyisoprene cylinders, and the order–disorder‐transition temperature of the block copolymer (T_ODT) was 132 ± 1 °C. Our objective was to identify the temperature at which the grain growth rate was maximized (T_max) and compare it with theoretical predictions. We conducted seeded grain growth experiments, which comprised two steps. In the first step, which lasted for 43 min, the sample was cooled from the disordered state to 124 °C. This resulted in the formation of a small number of ordered grains or seeds. This was followed by a second step in which the sample was heated to temperatures between 124 and 132 °C and the seeds grew with time. Our objective was to study grain growth at different temperatures starting from the same initial condition. The value of T_max obtained experimentally was 128 °C. The theoretically predicted value of T_max, based entirely on the rheological properties of the disordered sample and T_ODT, was also 128 °C. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 2231–2242, 2001     

聚甲基丙烯酸乙酯的合成与性能研究

通过阴离子聚合反应合成了窄分子量分布(D=1．05-1．2)聚甲基丙烯酸乙酯CPEMA）。运用IR谱、^1HNMR和GPC等手段对合成产物进行了表征,探讨了影响甲基丙烯酸乙酯(EMA)阴离子聚合反应的因素,测定了该聚合物的玻璃化温度Tg,并研究了聚甲基丙烯酸乙酯在不同pH溶液中的降解性能。     

关于边数给定图按无符号拉普拉斯谱半径排序的注记

设$k$是正整数, $G$是一个边数给定的简单无向图, 其边数$m\ge 2k$, 最大度$\Delta(G)\le m-k$, 本文给出了图$G$的无符号拉普拉斯谱半径$q(G)$的一个上界. 对边数为$m\ge 8$的两个连通图$G_1$和$G_2$, 利用这个上界我们证明了一个排序定理: 如果$\Delta(G_1)>\Delta(G_2)+1$ 且 $\Delta(G_1)\ge \frac{m}{2}+2$, 那么$q(G_1)>q(G_2)$. 对于不含三角形的图, 我们得到两个更强的结果. 作为上述排序定理的一个应用, 我们完全刻画了无符号拉普拉斯谱半径最大的围长为$c$的$m$边图, 其中$m\ge \max\{ 2c, c+9\}$, 部分解决了陈雯雯等人在[Linear Algebra Appl. 645(2022)123-136]上提出的一个公开问题.     

Van Hove singularities,moiré-superlattices and rhombohedral stacking in exfoliated sublattices of highly oriented pyrolytic graphite

The presence of twisted sublattices in exfoliated lamellae of highly oriented-pyrolytic-graphite (HOPG) has been recently shown to induce a significant enhancement of percolative-ferromagnetic ordering at low temperature, opening new directions towards possible applications of graphitic lamellae in spintronics. Despite the significant progress, additional work is needed to elucidate possible magnetic effects arising from rhombohedral phases. In this work, we report a novel structural, electronic, and magnetic investigation. TEM allowed for the observation of multiple hexagonal moiré-superlattices and unusual staircase-like defects in those sublattices exposed by the exfoliation process. STM and STS further evidenced the appearance of multiple singularities in LDOS spectra acquired from certain sublattice-areas comprised within comparable staircase-defect features. Unusual effects involving a sharp enhancement in the density of states near the Fermi level are reported. These observations possibly imply the coexistence of both moiré superlattices and rhombohedral domains in certain twisted-sublattice regions. Further, Raman spectroscopy, through area mapping of the D, G, and D′ bands, evidenced additional signals in the proximity of ～1,800–2,100 cm^?1, attributable to electronic Raman-scattering (ERS). These effects arise locally from emerging rhombohedral domains possibly created by (1) slip-induced transformation of stacking order during tape exfoliation and (2) twisted sublattices, with θ_rot ～0.1°. T-EPR measurements also evidenced an unusual enhanced broadening and peak shift in the differential π-electron feature acquired from some of the lamellae exfoliated from the inner regions of the main HOPG.     

Spin valve with a composite dysprosium-based pinned layer as a tool for determining Dy nanolayer helimagnetism

Spin valves with nanostructure CoFe/Dy/CoFe and three-layer structures metal/Dy/metal were prepared by magnetron sputtering. The measurements of field dependences of magnetoresistance and magnetization were held at different temperatures. The changes of magnetotransport properties of spin valve containing CoFe/Dy/CoFe structure were used for getting information on the magnetic ordering in the dysprosium layer. The characteristic changes of magnetotransport properties caused by the formation of helical ordering in dysprosium layer were detected. Special attention was paid to the estimation of Neel temperature and to the investigation of microstructure of dysprosium nanolayer.     

Aqueous Chemical Solution Deposition of Functional Double Perovskite Epitaxial Thin Films

Double perovskite structure (A₂BB′O₆) oxides exhibit a breadth of multifunctional properties with a huge potential range of applications in fields as diverse as spintronics, magneto-optic devices, or catalysis, and most of these applications require the use of thin films and heterostructures. Chemical solution deposition techniques are appearing as a very promising methodology to achieve epitaxial oxide thin films combining high performance with high throughput and low cost. In addition, the physical properties of these materials are strongly dependent on the ordered arrangement of cations in the double perovskite structure. Thus, promoting spontaneous cationic ordering has become a relevant issue. In this work, our recent achievements by using polymer-assisted deposition (PAD) of environmentally friendly, water-based solutions for the growth of epitaxial ferromagnetic insulating double perovskite La₂CoMnO₆ and La₂NiMnO₆ thin films on SrTiO₃ and LaAlO₃ single-crystal substrates are presented. It is shown that the particular crystallization and growth process conditions of PAD (very slow rate, close to thermodynamic equilibrium conditions) promote high crystallinity and quality of the films, as well as favors spontaneous B-site cationic ordering.     

The crystal structures of Hf3±δNb4±δAs3 and Hf7.2Nb3.8As4: Members of a homologous series combining W-type, Mg-type and AlB2-type building blocks

Two new partially ordered compounds were synthesized in the system Hf-Nb-As by arc melting and subsequent annealing at 1400 °C and they were structurally characterized by means of single crystal X-ray diffraction. The compound Hf_3±δNb_4±δAs₃ is isostructural to Zr₃Pd₄P₃ and Hf₃Pd₄P₃ (Space group: Pnma, Pearson symbol oP40) and shows a considerable homogeneity range between the limiting compositions Hf_2.4Nb_4.6As₃ and Hf_4.1Nb_2.9As₃. Mixed occupation of Hf and Nb were found at all seven independent metal sites, with varying Hf/Nb ratios, so the compound is stabilized by differential fractional site occupation (DFSO). The compound Hf_7.2Nb_3.8As₄ is isostructural with Zr_6.45Nb_4.55P₄ (Immm, oI30) and was found to be metastable at the temperature of annealing (1400 °C). Similar to the type structure, Hf_7.2Nb_3.8As₄ is stabilized by (DFSO). Structural relations of the two compounds with Hf_1.5+δNb_1.5−δAs (Pnma, oP16) are discussed. All three compounds belong to a homologous series M_k+2l+mX_2m combining W-type, Mg-type and AlB₂-type building blocks.     

基于ZigBee技术的无线点菜系统

介绍了基于ZigBee技术的无线点菜系统的设计方案,选用集成8051内核的CC2430芯片作为网络节点。利用星型网络,简单外围电路,软件、硬件的设计,实现了无线点菜功能。在低功耗方面采用外部中断唤醒睡眠模式的工作方式,延长了终端的电池使用寿命。解决了点菜终端功耗大的问题。     

Effects of ordering quality of the pores on the photoluminescence of porous anodic alumina prepared in oxalic acid

Photoluminescence (PL) of the anodic alumina has been studied and related with quality of hexagonal ordering of the pores. The photoluminescence excitation (PLE) spectra have been successfully de-convoluted into primarily two sub-bands with peak positions at about 355 and 395 nm and maximum emission at about 450 and 500 nm, respectively; the former being assigned to F⁺ centers and the latter to the F-centers. A red shift in the PLE takes place, at a given anodizing voltage, when the quality of the hexagonal pore ordering deteriorates with an increase in number density of defects, i.e., pentagons and hexagons with missing pores. The metallic hills at these defects change the curvatures of the metal-oxide and the oxide-electrolyte interfaces that could affect the field distribution and hence the stress-state and other characteristics of the oxide at the defects. This allows a comparatively larger concentration of F centers (395 nm band), causing a red shift in the PLE with increase in defect density.