SEM Observation of Nucleation and Growth of Ag Crystallites on Graphite Substrate

“In-Situ” observation of nucleation and growth of Ag crystallites on graphite substrate by vapour deposition was carried out by scanning electron microscope (SEM). Irradiation of the SEM electron beam onto the substrate surface before and during deposition enhanced Ag nucleation. The density of the Ag crystallites was 10¹⁰/cm² in room temperature condensation, but decreased to 10⁹/cm² in high temperature condensation at 140 °C. When the substrate was heated after room temperature condensation, the density of the Ag crystallites decreased prominently. This means that coalescence of the Ag crystallites takes place as a result of their migration on the substrate.     

On the Morphological Changes and Twinning of ZnS (Sphalerite) Crystallites under Hydrothermal Conditions

Morphological characteristics and twinning mechanism of ZnS crystals under hydrothermal conditions have been investigated in this paper. It was shown that under hydrothermal conditions the morphology of ZnS crystallites changes along the four‐fold axis directions, and the crystals are observed in a positive or negative tetrahedron, or in a combination of positive and negative tetrahedra depending on the growth conditions. The positive tetrahedral areas on the crystallites get larger with increase of the concentrations of OH^‐ and S^2‐ in solutions, whereas the twinned crystallites of ZnS taking an elliptic shape with (111) as composition plane are easily formed in weak basic solutions. It can be found that the morphologies of ZnS crystals are in accordance with the crystallization orientations of positive or negative coordination tetrahedra ([S‐Zn₄]⁶⁺, [Zn‐S₄]^6‐) in the crystal although, in some cases, the practical morphology could be greatly affected by growth conditions, and the twinning mechansim can be suggested based on the linkage of growth units of positive and negative coordination tetrahedra, which were formed in the solution. The present investigations further indicated that the crystal chemistry approach based on the linkage/incorporation of growth units previously proposed by us can be sucessfully applied to interpret the growth mechanisms of the crystals and to control a desirable morphology.     

水热法生长立方MgO微晶研究

以尿素与Mg(NO3)2·6H2O在不同的反应温度和不同物质的量配比条件下,制备出前驱体Mg5(OH)2(CO3)4·4H2O/MgCO3,经煅烧得到立方MgO微晶粉末.利用X射线衍射仪(XRD)和扫描电子显微镜(SEM)对所制得产物的晶相和形貌进行了表征.结果表明:当尿素和Mg(NO3)2·6H2O物质的量的比为2∶1时,在160℃的水热反应条件下,制备出立方MgO前驱体微晶,在1000℃煅烧2h后能够获得晶型完整、形貌规则、粒径约为5μm的MgO立方微晶.     

低温水热制备BaZrO3微晶及其结晶动力学研究

在碱性条件下([NaOH] =0.008 mol/mL),以氯化钡(BaCl2·2H2O)和氧氯化锆(ZrOCl2·8H2O)为原料,采用传统水热法在低温下制备了锆酸钡(BaZrO3)微晶.利用XRD和SEM分别对产物进行了物相组成及微晶形貌的测试与表征.研究了反应温度为135℃时不同反应时间对产物微观结构及形貌变化的影响.结果表明:在135℃下反应2h即可合成纯相的BaZrO3粉体,且随着水热温度的升高,产物由无定形态变为类球状结构最终变为棱角分明的菱形十二面体结构,结晶程度提高,晶粒尺寸增大.通过对其结晶动力学研究,计算得到BagrO3微晶的表观成核活化能为24.36 kJ/mol.     

SEM and TEM Observation of Carbon Nano-Fibers Prepared by Hot Filament Assisted Sputtering

Abstract

Carbon films were prepared by hot filament assisted sputtering. Pure argon was used as the sputtering gas. The substrate temperature was 600 °C and the filament temperature was about 2000 °C. Sample was inhomogeneous. Scanning electron microscope (SEM) and transmission electron microscope (TEM) images showed that some part of films consisted of carbon nano fibers (not hollow but solid). Amorphous and polycrystalline phases were also detected by these measurements. No tube structure was observed by high resolution TEM. The diameter of the fiber was 10–30 nm.     

声化学法制备FeVO4微晶及其光学性能

采用声化学法,以偏钒酸铵(NH4VO3)和九水硝酸铁(Fe(NO3)3 ·9H2O)为原料制备了FeVO4微晶.利用X射线衍射仪(XRD),扫描电子显微镜(SEM),紫外可见吸收光谱(UV-vis)和示差扫描量热分析(DSC)分别对产物的物相、形貌和光学性能等进行了表征.结果表明:所制备的FeVO4微晶为三斜型结构,超声功率由300 W增加到500 W,微晶尺寸逐渐下降,大小更为均匀.UV-vis分析表明所制备的FeVO4微晶具有较强的吸收可见光特性,且随着超声辐射的功率的增加,粒径减小,禁带宽度由2.17 eV减小到2.08 eV.     

固相合成YAG微晶粉体的XRD研究

以高纯Al_2O_3和Y_2O_3超微粉为原料,通过高能球磨和固相反应法制备了Y_3Al_5O_(12)(YAG)微晶;采用X射线衍射法(XRD)研究了球磨时间、煅烧温度、保温时间等对合成YAG微晶相组成的影响.结果表明:原料粉体的粒度随研磨时间延长而降低;随煅烧温度的提高,产物的物相由Y_4Al_2O_9和YAlO_5 逐渐向YAG相转变;延长保温时间有利于Y~(3+)和Al~(3+)的扩散以及Al_2O_3和Y_2O_3的固相反应.当Al_2O_3和Y_2O_3的摩尔比为5 ∶ 3,混合粉体经过15 h的机械球磨并于1300 ℃煅烧40 min即可得到单一物相的YAG微晶粉末.     

Growth and Characterisation of Silicon Crystallites on Laser Structured Glass

Selective growth of silicon crystallites on glass, seeded from silicon saturated metallic solution droplets is demonstrated. These droplets are deposited in micropore arrays which are generated in the glass substrate by ultrashort laser pulses. In this way, an equidistant distribution of crystallites can be achieved by preferred nucleation in the micropores. Additionally, a crystallite selection occurs corresponding to the tip geometry. The material transport is governed by the vapour-liquid-solid (VLS) mechanism. The morphological characterization of micropores and grown crystallites is performed by Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM) and Focused Ion Beam (FIB) method.     

水热法制备FeWO4微晶及其结晶动力学研究

以(NH4)2Fe(SO4)2.6H2O和Na2WO4.2H2O为起始原料,水热合成了FeWO4微晶。采用X射线衍射(XRD)以及透射电镜(TEM)对制备的微晶进行了测试和表征。结果表明,在水热温度110℃,24 h条件下即可制备出单一物相的FeWO4微晶。随着水热时间的延长和水热温度的增加,产物由针状变为粒状结构,并且产物的结晶性能有所提高,晶粒尺寸逐渐增大。动力学研究表明,FeWO4微晶粒生长符合Brook关系,计算得到晶粒生长活化能为Ea=17.36 kJ/mol。     

Ag/TiO2纳米复合材料的抑菌活性研究

用钛酸异丙酯水解的方法合成单分散性的锐钛矿型TiO2亚微球,直径约为400 nm.以TiO2球为模版,用光化学还原法在其表面沉积银,合成纳米复合材料Ag/TiO2,银粒子平均直径为11 nm.用金黄色葡萄球菌和大肠杆菌作为测试菌研究Ag/TiO2抑菌性能.结果表明,当Ag/TiO2的浓度为0.6 mg/mL时,对金黄色葡萄球菌的抑菌率为96;,对大肠杆菌为98;.由于Ag/TiO2具有高效的抑菌性能,该复合材料可以应用于生物材料,污水处理等领域.     

Understanding and Controlling the Morphology of ZnO Crystallites under Hydrothermal Conditions

The morphological features of ZnO crystallites influenced by solution basicity under hydrothermal conditions have been studied from the standpoint of the incorporation of the growth units. A crystal chemistry approach is developed to understand and thus to control a desirable morphology of the crystallites. The effects of the additive OH⁻ on the crystal morphology of ZnO crystallites are qualitatively but satisfactorily explained by a mechanism considering two aspects: (1) solution structures and the structural forms of growth units under a certain growth condition, i.e. the interactions between the solvent molecules and the growth units; and (2) the influence of the solvent molecules or additives on growth interfaces, particularly on two polar faces of ZnO crystallites in terms of the inhibition or promotion of the incorporation of various growth units depending on the solution basicity. Since the incorporation rates of the growth units are different on positive and negative polar faces, the relative growth rates of these faces are different and thus lead to the habit modifications. The approach clearly demonstrates that the hindrance of crystal growth is a consequence of surface adsorption processes.     

扫描电镜用于人工蛋白石模板中填充InP的形貌研究

扫描电子显微镜是对人工欧泊光子晶体进行形貌观察、研究的重要手段.本文利用扫描电子显微镜对人工欧泊晶体及其填充InP后的形貌进行了分析.结果发现,二氧化硅微球短程有序而在较大的区域则出现台阶、空位和失配等缺陷;在选定生长条件下,InP在SiO2球空隙间具有较高的填充率和较好的结晶质量.此项研究为制备三维InP光子晶体提供了科学依据.     

YAP晶体变色现象的研究

YAlO3(YAP)晶体具有优良的物理和化学性能,在许多方面都有广泛的应用前景.我们在对闪烁晶体Ce∶YAP的研究过程中,发现了YAP晶体的变色现象.本文利用晶体透过谱对其颜色的变化进行了研究.不同的退火气氛及不同的掺杂成份对晶体颜色有较大影响,H2气氛退火或掺杂Ce元素使晶体颜色变浅,而在空气中退火或掺杂Yb元素则使晶体颜色加深.针对这一变色现象,我们认为是在晶体生长过程由于电荷补偿的需要而产生的O-心的吸收作用导致的.不同的O-心浓度其吸收作用不同,从而使晶体在400nm附近的透过率发生变化.采用这一模型可以对晶体颜色的变化及不同退火条件和掺杂元素的影响作出合理的解释.     

原位反应合成Ag/CuO复合材料中生成立方氧化铜的研究

本文通过对原位反应合成Ag/CuO复合材料中生成立方氧化铜的可能性进行了研究,对CuO和Ag/CuO分别进行热重-差热分析实验以及反应烧结实验.结果表明:原位反应合成法制备Ag/CuO复合材料中,生成立方氧化铜有三种方式:(1)Cu与O2直接反应合成立方CuO可能性小,或者不发生;(2)以Cu与O2反应合成单斜的CuO后,在后期烧结时发生相转变生成立方CuO为立方CuO的主要形成方式.实验也说明了1048 K(即775℃)左右的温度即是单斜CuO与立方CuO转变的温度;(3)通过实验与理论分析还发现,Ag的存在对形成立方CuO的相变以及形成量有一定的影响.     

半导体单晶生长过程中的位错研究

阐述了现有的半导体单晶位错模型,即临界切应力模型和粘塑性模型的基本理论及应用状况.分析了熔体法单晶生长过程中影响位错产生、增殖的各种因素,以及抑制位错增殖的措施.与熔体不润湿、与晶体热膨胀系数相近的坩埚材料,低位错密度的籽晶可有效地抑制生长晶体的位错密度;固液界面的形状及晶体内的温度梯度是降低位错密度的关键控制因素,而两因素又受到炉膛温度梯度、长晶速率、气体和熔体对流等晶体生长工艺参数的影响.最后,对熔体单晶生长过程的位错研究进行了展望.     

煅烧温度对络合溶胶-凝胶法制备ZnGa2O4微晶形貌及光催化性能的影响

采用EDTA络合溶胶-凝胶法制备了尖晶石结构的ZnGa2O4微晶.通过XRD、SEM等分析方法对ZnGa2O4微晶进行了测试和表征.研究了不同煅烧温度对其物相组成、显微结构及光催化性能的影响.结果表明,以乙酸锌和氧化镓为反应原料,以乙二胺四乙酸为络合剂,在650～800℃能合成单一物相的ZnGa2O4微晶.在700℃时可以成功制备八面体形的ZnGa2O4微晶,在800℃时可以合成棒状的ZnGa2O4微晶;随着温度从650～800℃逐渐升高,其对罗丹明B的光催化降解性能逐渐提高.     

Study on Ag doping in congruent lithium niobate crystal

Ag doped congruent lithium niobate crystal has been demonstrated as a promising photorefractive material for holographic recording applications. In this paper, the effects of Ag doping on the lattice structure and the optical properties were investigated by XRD, Raman spectroscopy and optical absorption characterization. The Ag ion was proposed to occupy Li-sites and results in lattice deformation. The band gap became narrower and an absorption band at near 500 nm was created with Ag doping. High temperature annealing and UV irradiation were performed to further understand the Ag doping effects.     

碳量子点与银复合光催化剂的制备及其性能的研究

采用两种碳源合成的碳量子点作为光还原剂,在可见光照射下还原硝酸银(AgNO3)制备出了两种不同尺寸的银/碳量子点(Ag/CDs)复合结构.透射电镜(TEM)结果表明获得了两种尺寸不同的Ag与CDs复合结构.紫外-可见吸收光谱表明尺寸较小的复合结构在可见光区域展现出了更强的光吸收,从而导致了尺寸较小的Ag/CDs复合结构在可见光下对亚甲基兰拥有更强的光降解能力.     

第一性原理研究Ag掺杂及缺陷共存对ZnO光催化性质的影响

运用第一性原理研究了Ag掺杂及缺陷共存对ZnO光电性质的影响。计算结果表明富O条件有利于Ag的掺杂,贫O条件不利于Ag的掺杂。Ag掺杂浓度较低时有利于模型的稳定,其在富O或贫O条件下都以Ag_Zn为主要掺杂方式。当Ag掺杂浓度较高时,富O条件下以Ag_Zn-Ag_Zn为主要掺杂方式,贫O条件下Ag_Zn-Ag_i是较为有利的掺杂方式。富O条件下Ag掺杂较难引入V_Zn和O_i共存缺陷。贫O条件下优先出现的模型为V_O,V_O在一定程度上会促进Ag的掺杂。Ag掺杂降低了ZnO的带隙宽度,掺杂浓度越大模型带隙宽度越窄。V_Zn、V_O和O_i缺陷共存不同程度地增加了Ag掺杂模型的带隙宽度。Ag掺杂及V_Zn和O_i缺陷共存均使ZnO吸收边红移至可见光区,扩展了ZnO对太阳光的吸收范围,而Ag_Zn-V_O在可见光范围内依然是透明。在低能区紫外-可见光范围内,Ag_Zn-Ag_Zn表现出更高的光吸收率,但是相应形成能也高于Ag_Zn。V_Zn的引入提高了Ag_Zn-V_Zn和Ag_Zn-Ag_Zn-V_Zn对低能区紫外-可见光的吸收,V_O的引入有利于ZnO表面吸附更多的O₂进而产生更多的H₂O₂和·HO强氧化性物质,即V_Zn和V_O缺陷共存都有利于ZnO光催化性能的提高。     

Tuning of morphology of Ag nanoparticles in the Ag/polyaniline nanocomposites prepared by γ-ray irradiation

Ag/polyaniline (PANI) nanocomposites were prepared by two different methods using γ-ray irradiation. The morphology of the Ag nanoparticles in the nanocomposites was followed by transmission electron microscopy (TEM). In one of the method (Method I), Ag/PANI nanocomposites were prepared by the following sequential steps. PVP-stabilized Ag colloids were prepared by γ-irradiation, aniline was added and oxidatively polymerized. Method II involved the preparation of Ag/PANI nanocomposites by oxidative polymerization of aniline-stabilized Ag colloids prepared by γ-irradiation. The average size of PVP-stabilized Ag sphere-type nanoparticles was 13 nm. The morphology of Ag nanoparticle in Ag/PANI nanocomposites prepared by Method I was sphere-type. On the other hand, the morphology of aniline-stabilized Ag nanoparticle prepared by γ-irradiation was a hexangular-type one. Size of aniline-stabilized Ag nanoparticles was found to depend on the weight ratios of aniline-to-Ag ions used in the preparation. The paper discusses the changes in the morphology of Ag nanoparticles in the Ag/PANI nanocomposites with the method of preparation, source of protection and polymerization.