超声波提取对麦冬多糖结构和抗氧化活性的影响

研究了超声波提取法在提取麦冬多糖过程中,对麦冬多糖的结构和抗氧化活性的影响.利用气相色谱法、环境扫描电子显微镜、原子力显微镜对其进行初步结构分析,然后在体外化学模拟条件下,测定它的总还原能力、对羟基自由基的清除作用及对Fe2诱发的脂质过氧化反应的抑制作用,并与传统热水提取法提取得到的麦冬多糖进行对比.超声波提取得到的麦冬多糖(SBP)和传统热水提取法提取得到的麦冬多糖(WBP)具有相同的单糖组成,都包括阿拉伯糖、甘露糖、葡萄糖及半乳糖,环境扫描电子显微镜的结果显示经超声提取的多糖的片状结构有不同程度的变小;原子力显微镜的扫描分析显示超声波使其糖链的分子片断变小,且SBP的抗氧化活性都要高于WBP.经超声波处理不会影响多糖的单糖组成,但会改变多糖的微观结构同时提高多糖的抗氧化活性.     

丹皮多糖分子的电子显微镜观察

利用透射电镜对丹皮多糖分子（PSM2b-A）的显微结构进行了研究。观察到PSM2b-A在水溶液中呈球状或圈状的形貌,这些球状和圈状的结构可进一步连接或侧向聚集成链状或网状结构。表明在稀水溶液中,多糖分子倾向于蜷曲,且可通过氢键和其他弱作用力形成各种分子聚集形态。     

电子束控CO激光器发射特性的理论研究

对发射长脉冲（10^-4~10^-3秒）电子束控CO激光器的光谱、阈值及能量特性作了研究，该研究建立在速率方程的数值解上，这个速率方程组描述了：CO分子振动能级的粒子数；由在CO分子振动级间的跃迁引起的受激发射；及在这种气体转动-平动温度中的变化。     

左旋多巴宽频太赫兹光谱研究

利用空气等离子体太赫兹时域光谱系统,获得了0.5～14.5 THz范围内左旋多巴(L-DOPA)的特征指纹谱,并研究了吸收光谱随温度的变化效应。利用密度泛函理论计算L-DOPA的晶胞结构,并对太赫兹振动光谱进行了分析。结果表明:L-DOPA在太赫兹波段的吸收峰对应于不同的集体振动和分子局域振动,其中分子的集体振动在整个太赫兹波段分布较广,且苯环和分子侧链表现出不同的振动特点,这些结构振动特异性与分子构象以及分子间氢键的相互作用密切相关。     

多孔硅发光二极管的载流子传输特性研究

制备AI／多孔硅／c-Si／Al结构的多孔硅发光二极管，利用其I-V特性关系，以及在不同温度下其I-V特性的变化，结合多孔硅的特殊微结构及性质，分析了多孔硅发光二极管中载流子的产生和传输过程；通过比较其发光猝灭前后I-V特性的变化，解释了发光猝灭的原因。提出了如果在低电场下能够实现大量载流子在限制性Si微粒中复合．是提高多孔硅电致发光效率的一个途径。     

乙酸乙酯溶液的时间分辨荧光光谱研究

为了研究模拟白酒环境中乙酸乙酯荧光衰减的影响, 采用测得不同体积分数的乙酸乙酯乙醇水溶液的稳态及时间分辨荧光光谱结合量子化学计算的方法, 进行了实验测量和理论分析。结果表明, 乙酸乙酯的荧光峰值分别在407nm和431nm, 荧光寿命均约为1.4ns; 不同体积分数乙酸乙酯乙醇水溶液衰减过程中有两种荧光寿命, 其中短寿命成分为乙酸乙酯, 长寿命成分为乙酸乙酯和乙醇、水分子形成的多聚体结构; 多聚体结构中分子间相互作用使得乙酸乙酯的平面性提高, 这有利于辐射跃迁; 水分子通过氢键和范德华力连接乙酸乙酯和乙醇的二聚体形成层状结构, 阻碍了荧光体的运动, 从而减少非辐射跃迁, 使得荧光寿命延长。这一结果有助于丰富白酒中有机物的检测方法, 也为研究溶剂环境对分子构象及光谱特性变化提供了一定的帮助。     

海水阴离子溶液中水的激光拉曼光谱特性研究

本文对海水主要阴离子（SO42-、CO32-和HCO3-）水溶液中的水分子在温度变化下的拉曼散射特性进行了研究,探讨了水分子的振动模式随温度的变化规律和海水阴离子对水的影响。结果显示：随着温度的升高,水的伸缩振动峰逐渐向高频方向移动,拟合特征峰A1和A2强度比值呈下降趋势,表明水分子之间的氢键作用不断减弱,其数量在减少;同种阳离子溶液中不同阴离子对水拉曼峰偏移量影响的强弱顺序为：SO24-〉HCO3-〉CO23-。对探测识别海底热液口的原位物质成分具有重要的指导意义。     

对称Y型分子向列相液晶的相变

在V型双轴性向列相液晶分子的基础上构造一对称Y型分子,并将其抽象为呈"Y"状排列的三刚性分子长棒,考虑棒与棒间的简单相互作用的叠加,得到了分子间的相互作用能。利用平均场理论,得到系统的自由能与序参数之间的函数关系,并给出了在一定温度下系统从各向同性相至单轴相以及从单轴相至双轴相相变的相图。     

利用波导技术研究不同温度下铁电液晶垂直排列S_c~*相的光学特性

利用波导技术研究了在不同温度下铁电液晶(简体FLC)垂直排列的光学特性.通过计算机对与入射光角度相关的反射率理论数据与实验数据进行拟合计算,测定了一系列与FLC有关的参数,给出了在S_C相FLC分子的排列模型,讨论了在这个相中分子指向矢的扭曲角和倾斜角.     

n-GaN 基 Ti／AI／Ni／Au的欧姆接触高温特性

研究了在高温工作环境下Ti／A1／Ni／Au（15nm／220nm／40nm／50nm）四层复合金属层与n-GaN的欧姆接触的高温工作特性，退火后样品在500℃高温下工作仍能显示出良好的欧姆接触特性；接触电阻率随测量温度的增加而增大，且增加幅度与掺杂浓度有密切关系，掺杂浓度越高，其接触电阻率随测量温度的升高而增加越缓慢；重掺杂样品的Ti／A1／Ni／Au-n-GaN欧姆接触具有更佳的高温可靠性；当样品被施加500℃，1h的热应力后，其接触电阻率表现出不可恢复性增加。     

Selective growth of InP by MOCVD around dry-etched mesas having various patterns for photonic integrated circuits

We have investigated the selective growth ofpnp- InP by metalorganic chemical vapor deposition (MOCVD) around mesas. The mesas were formed by reactiveion-etching using SiO₂ masks having various patterns. The patterns include stripes along different crystallographic orientations, Y-bifurcations, and X-crossings. The behavior of the growth, and that of the mass transport before the growth, were found to depend remarkably on the crystallographic direction of the mesa stripe. The most notable mass transport, which transforms a nearly vertical mesa wall to a sloped one, was observed for a stripe misoriented by about 30° from the [011] direction. The growth was observed to proceed preferentially on the sloped planes, planarizing the crystal surface, for a mesa stripe directed between the [011] and [010] directions. However, for the stripe direction near [01-1], the growth was observed to creep up a nearly vertical plane on the mesa wall, and sloped planes are reluctant to form. Selective growth with sufficient planarity has been obtained for various waveguides including the Y-bifurcations and the X-crossings, which are used as the waveguide components in photonic integrated circuits, when the stripes are almost along the [011] direction.     

Molecular beam epitaxial regrowth of InAs/AiSb/GaSb heterostructures on patterned substrates

The molecular beam epitaxial growth of InAs/AISb/GaSb heterostructures on GaSb epilayers patterned by dry etching is investigated. Faceted growth occurs at pattern edges, depending on the adatom species, crystallographic planes and growth parameters. The morphology of the overgrown structure is determined by (111), (110), and (100) Planes near the edges of the patterned stripes, oriented in the [011], [001 ], or [0 11] direction. During the regrowth of InAs, additional (311)A planes are formed at the edges for stripe orientations in the [0 11] direction. Utilizing the faceted growth behavior at pattern edges, resonant interband tunneling diodes with a room temperature peak-to-valley current ratio of 13 have been fabricated on patterned substrates. The results indicate that this approach has the potential of realizing advanced devices with higher complexity.     

Simulation study of view angle effects on thermal infrared measurements over heterogeneous surfaces

The issue of deriving cross-scale aggregation rules has been extensively investigated over the last two decades. A widely used approach consists of formulating grid-scale surface radiances using the same equations that govern the patch-scale behavior but whose arguments are the aggregate expressions of those at the patch-scale. This approach derives the area-averaged or effective radiative surface temperature as might be observed using low spatial resolution satellite data. The problem however is that such satellite data exhibit large directional effects and no study has addressed this issue. The present work tackles this problem in the thermal infrared domain. The directional effects are studied by modeling. Thus, an infrared sensor observing a two-dimensional (2-D) heterogeneous plane surface is modeled. The 2-D heterogeneous plane surface is simulated by a grid with two homogeneous elements (vegetation-bare soil). The angular properties of the local surfaces, assumed homogeneous, are calculated by a multiple scattering model. The equivalent angular radiance of the complete heterogeneous scene is then determined by applying the aggregation method. This radiance is very sensitive to the surface heterogeneity, especially when the spatial variation of the surface temperature is significant and when the directional behavior of the surface is non-Lambertian. As a result, an angular variation of 6% on radiance was obtained on a heterogenous surface between a zenith angle of 70/spl deg/ and on-nadir measurements.     

Demonstration of Bias-Controlled Algorithmic Tuning of Quantum Dots in a Well (DWELL) MidIR Detectors

The quantum-confined Stark effect in intersublevel transitions present in quantum-dots-in-a-well (DWELL) detectors gives rise to a midIR spectral response that is dependent upon the detector's operational bias. The spectral responses resulting from different biases exhibit spectral shifts, albeit with significant spectral overlap. A postprocessing algorithm was developed by SakoĞlu that exploited this bias-dependent spectral diversity to predict the continuous and arbitrary tunability of the DWELL detector within certain limits. This paper focuses on the experimental demonstration of the DWELL-based spectral tuning algorithm. It is shown experimentally that it is possible to reconstruct the spectral content of a target electronically without using any dispersive optical elements for tuning, thereby demonstrating a DWELL-based algorithmic spectrometer. The effects of dark current, detector temperature, and bias selection on the tuning capability are also investigated experimentally.      

Critical Property in Relaxor-PbTiO(3) Single Crystals --- Shear Piezoelectric Response

The shear piezoelectric behavior in relaxor-PbTiO(3) (PT) single crystals is investigated in regard to crystal phase. High levels of shear piezoelectric activity, d(15) or d(24) >2000 pC N(-1), has been observed for single domain rhombohedral (R), orthorhombic (O) and tetragonal (T) relaxor-PT crystals. The high piezoelectric response is attributed to a flattening of the Gibbs free energy at compositions proximate to the morphotropic phase boundaries, where the polarization rotation is easy with applying perpendicular electric field. The shear piezoelectric behavior of pervoskite ferroelectric crystals was discussed with respect to ferroelectric-ferroelectric phase transitions and dc bias field using phenomenological approach. The relationship between single domain shear piezoelectric response and piezoelectric activities in domain engineered configurations were given in this paper. From an application viewpoint, the temperature and ac field drive stability for shear piezoelectric responses are investigated. A temperature independent shear piezoelectric response (d(24), in the range of -50°C to O-T phase transition temperature) is thermodynamically expected and experimentally confirmed in orthorhombic relaxor-PT crystals; relatively high ac field drive stability (5 kV cm(-1)) is obtained in manganese modified relaxor-PT crystals. For all thickness shear vibration modes, the mechanical quality factor Qs are less than 50, corresponding to the facilitated polarization rotation.     

Thermally induced crystallization behavior and film microstructure alteration of N,N,N′,N′-tetraphenylbenzidine (TPB) and N,N,N′,N′-tetra-p-tolyl-benzidine (TTB)

In this paper, the thermally induced crystallization behavior of N,N,N′,N′-tetraphenylbenzidine (TPB) and N,N,N′,N′-tetra-p-tolylbenzidine (TTB) and their microstructure changes as well as π–π aggregation mode as film state were comprehensively studied. The influence of heating rate, annealing temperature and time on the non-isothermal crystallization behavior of TPB and TTB powder was evaluated by Jeziorny method. Cold crystallization with the transition of metastable state was observed for both TPB and TTB. The thermally induced microstructure alteration and aggregation pattern of TPB and TTB films were investigated using XRD, SEM and AFM. The results revealed that both TPB and TTB could form smooth amorphous thin film and effective π–π interaction with identical edge-on orientations. TTB was prone to pack with both edge-on and face-on orientations especially after annealing, which accounts for its relatively low hole mobility. Besides, a more ordered film microstructure was formed after annealing at 70 °C for 24 h, which results in nearly four times increase of the hole mobility.     

Highly Fluorescent Mesostructured Films that consist of Oligo(phenylenevinylene)–Silica Hybrid Frameworks

Highly fluorescent and visible‐light‐responsive mesostructured organosilica films are successfully obtained by acidic sol–gel polycondensation of oligo(phenylenevinylene) (OPV)‐bridged organosilane and tetraethoxysilane precursors in the presence of a template surfactant. The OPV‐bridged organosilane precursors with different lateral alkoxy substituents, hexyloxy and 2‐ethylhexyloxy, and no substituent, are synthesized by Rh‐catalyzed silylation of corresponding aromatic iodides. From the organosilane precursors, three kinds of mesostructured OPV–silica hybrid films are prepared by spin‐casting using evaporation‐induced self‐assembly. UV‐vis absorption and fluorescence behavior of the OPV–silica hybrid films show that the optical properties and intermolecular interactions of the OPV moieties embedded within the organosilica frameworks strongly depend on the lateral alkoxy substituents in the precursors. The hexyloxy and 2‐ethylhexyloxy substituents prevent aggregation of the OPV units in the organosilica frameworks; this result leads to high fluorescence quantum yields of 0.48–0.61 and 0.63–0.66, respectively, while non‐substitution leads to lower fluorescence quantum yields of 0.25–0.34. Fluorescence decay profiles of the organosilica hybrid films also confirm a suppression of the aggregation of OPV moieties by the lateral substituents. These mesostructured organosilica films with significant optical properties in the visible‐light region are promising as a new class of phosphor materials.     

Effects of electric potential on chemical-mechanical polishing of copper

The effect of electric potential on the dissolution and polishing behavior of copper in acidic and alkaline media was investigated. The electromechanical polishing mechanism of copper is discussed based on removal rate of copper, pH of slurries, and surface morphology of polished copper. The most interesting phenomenon occurred in chemical-mechanical polishing (CMP) of copper with applied direct current (DC) voltage is the variation of pH during polishing. The dissolution experiments indicated that an acidic agent might have more hydrogen reduced with higher DC potential. The results demonstrated that the application of DC voltage is beneficial to improve planarization of copper polishing in an alkaline slurry.     

Influence of Dielectric Surface Chemistry on the Microstructure and Carrier Mobility of an n‐Type Organic Semiconductor

This paper examines the microstructure evolution of 3,4,9,10‐perylene‐tetracarboxylic bis‐benzimidazole (PTCBI) thin films resulting from conditions imposed during film deposition. Modification of the silicon dioxide interface with a hydrophobic monolayer (octadecyltrichlorosilane (OTS‐18)) alters the PTCBI growth habit by changing the unit cell contact plane. PTCBI films deposited on oxide surface have an orientation of (011), while films atop OTS‐treated oxide surface have a preferred orientation of (001). The quality of the self assembled monolayer does not appear to influence the PTCBI growth preference significantly yet it enhances the carrier mobility, suggesting that charge traps are adequately passivated due to uniform monolayer coverage. High‐quality monolayers result in n‐type carrier mobility values of 0.05 cm²V^–1s^–1 Increasing the substrate temperature during PTCBI film deposition correlates with an increase in mobility that is most significant for films deposited on OTS‐treated surface.     

Characterization study of time- and temperature-dependent mechanical behavior of polyimide materials in electronic packaging applications

The thermo-mechanical testing of the type HPP ST polyimide films with high performance, supplied by Dupont, was realized under different strain rates and temperature effects. Therefore, the rate-temperature-dependent stress-strain behavior of materials was investigated and the dependence of the Young’s modulus on temperature and strain rate was reported. In view of the uncertainty of the Young’s modulus determination, the specimens were tested with the unloading-reloading technique to verify the test results. The constant strain rate uniaxial tensile test and long-time creep test at various temperatures were performed to characterize the time-temperature-dependent mechanical property precisely. The cyclic loading test was also implemented on the specimen to investigate cyclic stress-strain behavior. In addition, the nanoindentation test was carried out at room temperature to validate the elastic modulus derived from the uniaxial tensile test. This research is expected to investigate the time-temperature-dependent mechanical behavior of the polyimide materials for different service regimes including tensile and cyclic mechanical loading under elevated temperature in a systematic manner.