438 resultados para FTIR-spektroskopia


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Tungsten wires were introduced into a plasma-enhanced chemical vapor deposition (PECVD) system as a catalyzer: we name this technique 'hot-wire-assisted PECVD' (HW-PECVD). Under constant deposition pressure (p(g)), gas flow ratio and catalyzer position, the effects of the hot wire temperature (T-f) on the structural properties of the poly-Si films have been characterized by X-ray diffraction (XRD), Raman scattering and Fourier-transform infrared (FTIR) spectroscopy. Compared with conventional PECVD, the grain size, crystalline volume fraction (X-e) and deposition rate were all enhanced when a high T-f was used. The best poly-Si film exhibits a preferential (220) orientation, with a full width at half-maximum (FWHM) of 0.2 degrees. The Si-Si TO peak of the Raman scattering spectrum is located at 519.8 cm(-1) with a FWHM of 7.1 cm(-1). The X-c is 0.93. These improvements are mainly the result of promotion of the dissociation of SiH4 and an increase in the atomic H concentration in the gas phase. (C) 2001 Elsevier Science B.V. All rights reserved.

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Hydrogen behavior in unintentionally doped GaN epilayers on sapphire substrates grown by NH3-MBE is investigated. Firstly, we find by using nuclear reaction analysis (NRA) that with increasing hydrogen concentration the background electron concentration increases, which suggests that there exists a hydrogen-related donor in undoped GaN, Secondly, Fourier transform infrared (FTIR) absorption and X-ray photoelectron spectroscopy (XPS) reveal Further that hydrogen atom is bound to nitrogen atom in GaN with a local vibrational mode at about 3211 cm(-1) Hence, it is presumed that the hydrogen-related complex Ga. . .H-N is a hydrogen-related donor candidate partly responsible for high n-type background commonly observed in GaN films. Finally, Raman spectroscopy results of the epilayers show that ill addition to the expected compressive biaxial strain, in some cases GaN films suffer from serious tensile biaxial strain. This anomalous behavior has been well interpreted in terms of interstitial hydrogen lattice dilation. (C) 2001 Elsevier Science B.V. All rights reserved.

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Tb3+-doped zinc oxide nanocrystals with a hexagonal wurzite structure were successfully prepared by reaction between Zn-O-Tb precursors and LiOH in ethanol. Good incorporation of Tb3+ in ZnO nanocrystals is proved by XRD, FTIR, PL and PLE measurements. The presence of acetate complexes to zinc atoms on particle surfaces is disclosed by FTIR results. Emission from both Tb3+ ions and surface states in ZnO matrix, as well as their correlation were observed. The luminescence mechanism is discussed. (C) 2000 Elsevier Science B.V. All rights reserved.

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Undoped hydrogenated microcrystalline silicon (mu c-Si:H) thin films were prepared at low temperature by hot wire chemical vapor deposition (HWCVD). Microstructures of the mu c-Si:H films with different H-2/SiH4 ratios and deposition pressures have been characterized by infrared spectroscopy X-ray diffraction (XRD), Raman scattering, Fourier transform (FTIR), cross-sectional transmission electron microscopy (TEM) and small angle X-ray scattering (SAX). The crystallization of silicon thin film was enhanced by hydrogen dilution and deposition pressure. The TEM result shows the columnar growth of mu c-Si:H thin films. An initial microcrystalline Si layer on the glass substrate, instead of the amorphous layer commonly observed in plasma enhanced chemical vapor deposition (PECVD), was observed from TEM and backside incident Raman spectra. The SAXS data indicate an enhancement of the mass density of mu c-Si:H films by hydrogen dilution. Finally, combining the FTIR data with the SAXS experiment suggests that the Si--H bonds in mu c-Si:H and in polycrystalline Si thin films are located at the grain boundaries. (C) 2000 Elsevier Science S.A. All rights reserved.

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Both Fourier transform infrared (FTIR) grazing incidence reflectivity and FTIR transmission methods have been used to study GaN films grown on alpha-Al2O3 (0001) substrates by atmospheric pressure metal-organic chemical vapor deposition and low pressure metal-organic chemical vapor deposition. The results show that in the frequency range from 400 to 3500 cm(-1) the signal-to-noise ratio of the FTIR grazing incidence measurement is far higher than that of the FTIR transmission measurement. Some new vibrational structures appearing in the former measurement have been discussed. The features around 1460 and 1300 cm(-1) are tentatively assigned to scissoring and wagging local vibrational modes of CH2 in GaN, respectively. (C) 1999 American Institute of Physics. [S0021-8979(99)06509-3].

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A pronounced photoluminescence enhancement on chemically oxidized porous silicon was induced by a series of organic cyano compounds including 1,2-dicyanoethylene (CE), 1,3-dicyanobenzene (1,3-CB), 1,4-dicyanobenzene (1,4-CB), 1-cyanonaphthalene (1-CN), and 9-cyanoanthracene (9-CA). Photoluminescence enhancement effects were reversible for all compounds studies in this work. A dependence of photoluminescence enhancement on the steric effect and the electronic characteristics of these compounds and the structure of the porous silicon substrates were analyzed in terms of the photoluminescence enhancing factors. Surface chemical composition examined by Fourier transform infrared (FTIR) spectra demonstrated that the surface Si-H bonds were not changed and no new luminescent compounds were formed on porous silicon surface during adsorption of cyano compounds. A mechanism based on induced surface states acting as radiative recombination centers by cyano compounds adsorption was suggested.

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The qualities of GaSb substrates commonly used for the preparation of III-V antimonide epilayers were studied before and after growing GaInAsSb multi-layers by MOCVD using PL, FTIR and DCXD together with the electrical properties and EPD value. The correlation between the substrate qualities and epilayer properties was briefly discussed. The good property epilayers of GaInAsSb and, then, the high preformance of 2.3 um photodetectors were achieved only using the good quality GaSb wafers as the substrates.

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GaN nanorods with vertebra-like morphology were synthesized by nitriding Ga2O3/ZnO films at 1000 degrees C for 20min. Ga2O3 thin films and ZnO middle layers were pre-deposited in turn on Si(111) substrates by r.f. magnetron sputtering system. In the flowing ammonia ambient, ZnO was reducted to Zn and Zu sublimated at 1000 degrees C. Ga2O3 was reducted to Ga2O and Ga2O reacted with NH3 to synthesize GaN nanorods in the help of the sublimation of Zn. The structure and morphology of the nanorods were studied by X-ray diffraction (XRD) and scanning electron microscopy (SEM), The composition of GaN nanorods was studied by energy dispersive spectroscopy (EDS) and fourier transform infrared (FTIR) system.

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A series of amorphous silicon carbide films were prepared by plasma enhanced chemical vapor deposition technique on (100) silicon wafers by using methane, silane, and hydrogen as reactive resources. A very thin (around 15 A) gold film was evaporated on the half area of the aSiC:H films to investigate the metal induced crystallization effect. Then the a-SiC:H films were annealed at 1100 degrees C for 1 hour in the nitrogen atmosphere. Fourier transform infrared spectroscopy (FTIR), X-Ray diffraction (XRD), and scanning electron microscopy (SEM) were employed to analyze the microstructure, composition and surface morphology of the films. The influences of the high temperature annealing on the microstructure of a-SiC:H film and the metal induced metallization were investigated.

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Si thin films with different structures were deposited by plasma enhanced chemical vapor deposition (PECVD), and characterized via Raman spectroscopy and Fourier transform infrared (FTIR) spectroscopy. The passivation effect of such different Si thin films on crystalline Si surface was investigated by minority carrier lifetime measurement via a method, called microwave photoconductive decay (mu PCD), for the application in HIT (heterojunction with intrinsic thin-layer) solar cells. The results show that amorphous silicon (a-Si:H) has a better passivation effect due to its relative higher H content, compared with microcrystalline (mu c-Si) silicon and nanocrystalline silicon (nc-Si). Further, it was found that H atoms in the form of Si-H bonds are more preferred than those in the form of Si-H-2 bonds to passivate the crystalline Si surface. (C) 2009 Elsevier B.V. All rights reserved.

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功能化线性低密度聚乙烯的制备、反应机理及动力学研究 学生:石强(高分子化学与物理) 导师:殷敬华 研究员 摘 要 采用反应挤出接枝方法改性聚烯烃已有近半个世纪的历史,但人们对挤出机内发生的物理变化和化学反应尚未有规律性的认识,迄今为止,尚未发现熔融反应挤出接枝反应速率常数的研究报道。本文以室温下空气中经电子束预辐照的LLDPE为接枝基底,以丙烯酸、甲基丙烯酸、甲基丙烯酸甲酯为接枝单体,首先制备了功能化LLDPE材料;随后,利用红外光谱(FTIR)、核磁光谱、电子自旋共振波谱(ESR)等实验手段,系统的研究了反应挤出接枝过程的反应机理和接枝(均聚)反应动力学;最后,使用FTIR和ESR相结合的办法,首次成功的测量了LLDPE接枝反应的链增长反应速率常数。 研究表明: 1.螺杆中的接枝(均聚)反应速度很快,大部分产物在第二捏合段之前形成;接枝(均聚)反应呈现两个阶段:线性增长阶段和近似平台增长阶段,单体浓度的变化是第一阶段向第二阶段转化的主要原因;2.接枝反应同时存在偶合终止和接枝链向聚合物链转移终止反应,单体加成到大分子自由基上是一步慢反应,起始均聚反应遵循经典的自由基聚合机理;3. 链增长速率常数基本上不随熔体粘度和起始单体浓度的改变而改变;均聚链增长反应速率常数, kp,h总是大于相应温度下接枝反应速率常数, kp,g; 4. 在起始阶段,链增长反应是化学反应控制的,用溶液聚合反应速率常数的外推值分析熔融接枝动力学行为可能是不正确的。

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近年来随着纳米材料科学、功能材料科学和超分子材料科学等学科的交叉渗透和迅猛发展,设计合成新型的多金属氧酸盐超分子变色材料和研究其结构、性质及变色机理具有重要的理论意义和应用价值。 本文以光致变色材料和热致变色材料的合成、结构与性质的研究为主线,通过水热法和溶液法制备了一系列含氮有机分子多金属氧酸盐的超分子化合物。解析了它们的晶体结构并研究了它们的光致变色与热致变色性质。采用低温固相反应法制备了具有变色特性的纳米氨基酸多金属氧酸盐。主要研究结果如下: 利用水热合成法制备了乙二胺三钼酸盐晶体,发现乙二胺三钼酸盐不仅具有光致变色性质,而且具有热致变色性质。在 365 nm 的紫外光照射下乙二胺三钼酸盐的光致变色样品呈红棕色,而热致变色样品在 180~250 ℃ 之间为蓝黑色。紫外-可见漫反射光谱被用于表征它们的变色性质。FT-IR 和 XRD 的结果确定着色后的样品其晶体结构和钼氧阴离子的骨架不改变,只是发生了轻微的畸变。一系列的光致变色样品和热致变色样品的ESR谱分别保持着各自特征,但二者有明显的差别,这反映出该化合物的热致变色机理与光致变色机理可能有所不同。这一现象是被首次发现和提出的。 利用水热法成功地合成了1, 6-己二胺三钼酸盐及四钼酸盐超分子化合物。单晶X-射线揭示出1, 6-己二胺三钼酸盐是一个新的超分子化合物,在它的晶体结构中,平行于 a 轴的新的无限链[Mo3O10]2–是由扭曲的MoO6八面体通过共边和共角连接的。质子化的己二胺阳离子占据着由无限链[Mo3O10]2–形成的隧道,它们之间以较强的氢键相互作用,形成了一维网络结构。我们发现这两种晶体均展示了新颖的光致变色与热致变色性质。我们利用FTIR、XRD、ESR和XPS对它们的变色性质进行了研究与探索。 选用4, 4'-联吡啶这种线状双基刚性配体, 利用水热法合成了两种4, 4'-联吡啶多金属钼酸盐晶体:一种是化学式为C10H12Mo7N2O23化合物, 另一种是化学式为C10H12Mo3N2O11化合物。测定了前者的晶体结构。两种晶体同样地展示了光致变色和热致变色性质,但后一种化合物有着明显比前一种化合物敏感的光热变色性质。ESR谱揭示出在UV光照射和加热的条件下,两个化合物中的Mo (Ⅵ) 原子均能被还原成Mo(Ⅴ)原子,但仅后一种化合物通过光热着色后有自由基产生。这是否是造成二者光热变色性质差别的原因,有待于今后更深入的研究和探索。 我们利用水溶液法成功地合成了氨基酸多金属氧酸盐晶体。晶体结构分析表明:组氨酸硅钨酸盐基本结构单元由一个[SiW12O40]4–多阴离子和两个质子化的[H2His]2+有机阳离子靠两个氢键相互作用组成。这个化合物展示了一个新颖的三维网络结构。脯氨酸硅钨酸盐的晶体结构正在解析中。在光照或加热后,这两个化合物的颜色由白色变为蓝色。我们利用FTIR、XRD、Raman和ESR研究了它们的光热变色性质。 将低温固相化学反应制备纳米材料的方法应用于纳米氨基酸多金属氧酸盐的制备,选取Silverton型多酸与多种氨基酸反应合成了系列纳米氨基酸-杂多酸电荷转移化合物。苏氨酸((HThr)7PMo12O42•4H2O) 磷钼多酸盐为形状不很规则的二维纳米片,酪氨酸磷钼多酸盐((HTyr)7PMo12O42•5H2O) 为一维纳米棒,丝氨酸磷钼多酸盐((HSer)7PMo12O42•5H2O)和谷氨酸磷钼多酸盐((HGlu)7PMo12O42•4H2O)为零维纳米粒子。有机给体氨基酸的结构对 Silverton 结构杂多化合物的形成起模板剂的作用,从而导致形貌的差异。在紫外光照射下,这些化合物会从白色变成蓝色,且对光比较敏感。

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聚乙二醇-聚ε-己内酯两嵌段共聚物(PEG-PCL)由于其在生物医用材料中的潜在应用而受到广泛的关注。然而,研究表明这类嵌段共聚物的许多性质,如药物渗透性,降解性能和机械性质等,都要受到它们的结晶行为与聚集态结构的显著影响。而在本课题开始之前,还没有关于PEG-PCL的结晶行为与形态的系统研究报道。因此,本文希望通过对PEG-PCL两嵌段共聚物结晶行为与形态的研究,能为这类生物降解高分子材料的工业应用提供一定的科学依据。本文使用辛酸亚锡为催化剂,甲氧基聚乙二醇(mPEG)为大分子引发剂,合成了一系列分子量分布比较窄,PCL质量百分含量为0.16-0.93的PEG-PCL两嵌段共聚物。两嵌段共聚物中的PEG段分子量固定为5000,共聚物的组成通过改变PCL链段的长度来调节。本文使用DSC,WAXD,常温或变温FTIR详细研究了PEG-PCL的结晶和熔融行为,使用偏光显微镜(POM)观察了PEG-PCL的结晶形态及结晶生长行为,利用SAXS研究了PEG-PCL的微观形态,得出了如下结果:(1)WAXD与FTIR的结果表明,两嵌段共聚物中的PEG与PCL形成微相分离的结晶微区,不存在两者的共晶或混晶。PCL含量为0.23-0.87的两嵌段共聚物中都能观察到的PEG与PCL的结晶。变温FTIR结果显示,当PCL含量低于或等于0.36,两嵌段共聚物中的PEG先从熔体中结晶;反之,当PCL含量等于或大于0.43,则熔体中PCL结晶先出现。(2)DSC结果表明,随着PEG-PCL中PCL段长度的增加,PCL段的结晶和熔融温度显著增加;相反,PEG段的结晶和熔融温度则显著降低。当PCL的质量分数由0增加至0.93,PEG的结晶度从79%降低至0,然而PCL的结晶度却不是单调变化,而是出现一个最大值。(3)在POM下观察PEG-PCL的36 oC等温熔体结晶过程,当PCL质量分数不超过0.36时,在偏光显微镜下只能观察到PEG球晶;而当PCL质量分数大于或等于0.56时,只能观察到PCL球晶;PCL含量为0.43和0.50的两种两嵌段共聚物中观察到了一种独特的同心球晶,同心球晶的中心部分形态类似于PCL球晶,而外部则类似于PEG球晶。PEG球晶与PCL球晶生长速率受PCL含量的影响显著:当PCL质量分数从0增加至0.50,PEG球晶的生长速率大大降低;然而,PCL球晶的生长速率却不是单调变化,而是在PCL质量分数为0.62时达到最大值。(4)SAXS结果表明,结晶后的PEG-PCL的微区结构是由交替的PEG与PCL的层状微区组成。共聚物的长周期在PCL质量分数为0.50时达到最大值。当PCL质量分数由0增加至0.50时,由于PCL层厚度的显著增加,共聚物的长周期显著增加;而当PCL含量由0.50继续增加至0.87,由于PEG层厚度的急剧降低,又使得共聚物的长周期迅速降低。(5)首次利用POM和微区红外光谱详细研究了PEG-PCL50/50(w/w)同心球晶的形成过程,发现同心球晶的形成是由于一种独特的结晶动力学造成的。另外,即使同心球晶的中心和外部的形态差别巨大,但是红外显微镜结果显示,两部分的组成却是相同的。

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本论文采用连续互穿网络技术,自由基的水溶液聚合,制备了一系列pH敏感的互穿网络的水凝胶膜,详细的研究了它们的性质,并探讨了其在药物输送体系潜在的应用。 用溶液聚合和化学交联方法合成了一系列PVA/PAA,PAA-co-PAMPS/PVA全互穿网络水凝胶膜,用红外光谱、DSC、SEM表征了网络的结构特征,并系统的研究了在不同介质中的溶胀性质、机械性质和吸湿性。 用水相沉淀聚合和同时采用化学交联又有物理缠结的互穿网络思想,制备了具有纳米结构、pH敏感的水凝胶膜,进一步得到了透明的PHEMA的水凝胶膜。SEM,FTIR光谱,和紫外可见光谱表征了多重互穿网络的特征。DSC分析表明这种方法使互不相容的PVA, PHEMA 和PMA具有热力学相容性。溶胀和去溶胀动力学表明由于其纳米结构使这种多重的IPN具有快速的响应;且透明的膜具有高的水含量。 本论文的创新之处是同时采用化学交联又有物理缠结的互穿网络技术制备了纳米结构的含PHEMA的水凝胶膜,解决了PHEMA与PVA、PAA、PMA不相容的问题,并进一步获得了溶胀透明的水凝胶膜,透光率最高可达93%。这种方法单体含量低,方便简单,避免了使用有机溶剂,有利于生物医学应用。

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纳米管是重要的一维纳米材料,在催化、分离、光电子材料、生物医药、超分子组装及复合材料等领域的应用前景广阔。探索新型的纳米管材料、研究它们的性质以及与高分子体系的杂化行为对该领域的发展具有重要意义。 Imogolite是一种纳米管状结构的硅铝酸盐,结构规整、具有独特的亲水性以及在水溶液中的分散性,是一种理想的纳米管研究对象。本论文采用正硅酸乙酯水解法合成了imogolite纳米管。使用光学显微镜,TEM,SEM,FTIR,WAXD,TGA等手段系统地研究了imogolite纳米管的生长机理、imogolite纳米管在液滴干燥过程中的自组装行为、imogolite纳米管与聚电解质的组装行为,以及imogolite纳米管/水溶性聚合物体系在液滴干燥过程中的组装行为。 Imogolite纳米管在液滴蒸发过程中可发生有序排列的自组装行为,这与液滴干燥过程中的毛细管流动、表面张力效应及润湿性质等有关。在空气中干燥imogolite液滴时,溶液浓度、pH、离子强度均会影响纳米管在液滴干燥斑中的聚集形态。低浓度液滴干燥后形成的取向纳米管束结构很好地验证了环状干燥斑的形成机理。而在乙醇气氛下干燥imogolite液滴时,毛细管流动被抑制,体系的表面能降低,因此可获得在基底上单根均匀分散的imogolite纳米管。 利用上述结果,首次实现了对合成imogolite纳米管聚合生长过程的直接观察。发现imogolite纳米管在生长过程中,直径尺寸均匀稳定;而长度的多分散性始终存在,且长度多分散性指数小于2。聚合反应初期,纳米管数量和长度均增长迅速;反应后期,纳米管长度和体系浓度的增大致使纳米管运动受限,反应为扩散控制,但体系内仍有大量imogolite短管生成并持续生长,使纳米管数量和长度在反应后期仍可继续增长。这表明合成imogolite纳米管是由扩散控制的硬棒状分子单元逐步聚合形成。 基于imogolite纳米管独特的表面性质,研究了imogolite与水溶性聚合物之间的组装行为。首次发现imogolite纳米管能够与聚电解质(PAA,PAH,PSS,PDDA)在水溶液中组装形成稳定的微米管结构。此类微米管是由椭球形的囊泡相互连接形成的超分子组装体。微米管结构稳定,骨架为无规的imogolite纳米管,聚电解质起粘结作用。微米管的形成不依赖于聚电解质的电荷性质或氢键作用,但聚电解质的浓度和分子量、聚电解质与imogolite的配比、温度、外力场以及pH均能够影响微米管的生长及最终形态。 聚阴离子聚电解质PAA和PSS与imogolite纳米管之间存在较强的相互作用,这阻碍了纳米管在液滴蒸发过程中的自组装行为,使其无法有序排列。Imogolite纳米管在PEO液滴干燥过程中的自组装行为与PEO浓度、分子量和端基性质有关。对于低浓度PEO体系,PEO能通过被氧化的端羟基与imogolite纳米管相互作用,吸附到imogolite纳米管外壁的PEO分子可以改变纳米管的排列间距。这表明在聚合物/imogolite体系中,通过改变聚合物分子的结构参数,可调控imogolite纳米管在液滴干燥过程中的排列方式。