【作者】 孙宏宇；

【导师】 张湘义；

【作者基本信息】 燕山大学 ， 材料学， 2010， 博士

【摘要】 低维半导体纳米材料的控制生长是当前纳米科学与技术研究领域的前沿和热点。本文选择典型的II-VI族半导体作为研究对象,采用电化学沉积、湿化学等方法制备了一系列低维纳米结构,对所获得纳米材料的尺寸、化学成分、晶体结构以及晶体取向成功地进行了控制。采用多孔氧化铝作为模板,通过直流电沉积方法,在120 oC的低温条件下制备了高度有序的六方ZnS纳米线阵列。在电流密度I = 0.1 mAcm^-2时制备了沿[110]方向生长的六方ZnS单晶纳米线阵列;当电流密度增加时,制备的六方ZnS纳米线为多晶结构。多孔氧化铝纳米孔洞的限域作用有利于六方ZnS单晶纳米线的形成。以多孔氧化铝作为模板,通过直流电沉积方法,在110 oC条件下制得了高度有序的六方CdS纳米线阵列。结果表明,电流密度对于电沉积纳米线阵列的取向生长有重要影响:在电流密度I = 1.28 mAcm^-2时制备了六方CdS多晶纳米线阵列,当电流密度降低到I = 0.05 mAcm^-2时,获得了沿[103]方向生长的六方CdS单晶纳米线阵列。在经典的电结晶理论基础上,建立了准二维电结晶临界晶核尺寸模型,即电结晶临界晶核尺寸不仅取决于电沉积参数ηc,同时也与晶体的表面能Ehkl、沉积晶体与基体的错配关系ρ有关。利用该模型可以理解电沉积单晶纳米线的形成以及纳米线阵列的取向形成机制。通过改变阳极氧化条件,制备了直径分别为25 nm、40 nm和120 nm的多孔氧化铝模板,通过直流电沉积方法,在180 oC条件下制得了六方CdSe纳米线阵列。结果表明,纳米线直径对于电沉积纳米线阵列的取向生长有重要影响:当I = 1.28 mAcm^-2时,随着尺寸D的增加,CdSe纳米线的择优取向从[001]转变为[101]和[103]方向,且临界尺寸D0满足40 nm < D0 < 120 nm。当I = 0.06 mAcm^-2时,随着尺寸D的增加,CdSe纳米线的择优取向从[101]转变为[103]方向,且临界尺寸D0满足25 nm < D0 < 40 nm。尺寸对CdSe纳米线生长取向的影响可以从降低体系表面能的角度进行理解。通过选择电沉积CdSe纳米线阵列的生长方向,可以有效控制其光学性能。采用液相方法直接制备了高产率、壳层分布均匀的CdS/MWCNTs壳芯异质结构,制备过程简单易行,无需对CNTs进行前处理或添加有机桥分子。CdS壳层的厚度可以通过改变反应温度或反应时间进行控制。CdS壳层是由CdS纳米粒子的聚集而形成的。采用ZnO纳米针作为自牺牲模板,在90 oC条件下与TAA水热反应5 h后制备了ZnS/ZnO壳芯异质结构的纳米针;提高反应温度,在120 oC条件下反应5 h后制备了ZnS空心纳米针。ZnS/ZnO壳芯异质结构是通过原位化学反应的方式获得的,而ZnS空心纳米针则是由纳米尺度的Kirkendall效应而形成的。以所获得的空心纳米针作为初始材料可以制备新奇的纳米结构,这些结构将在纳米光电子器件中得到重要应用。更多还原

【Abstract】 The controllable growth of low dimensional semiconductor nanomaterials is the frontiers and the focus in the field of nanoscience and nanotechnology. In the present work, the typical II-VI semiconductor nanostructures have been synthesized by using electrodeposition and wet chemical methods. The size, composition, crystal structure, and growth orientation have been successfully controlled.Highly ordered wurtzite ZnS nanowire arrays have been prepared at a low temperature of T = 120 oC by employing electrochemical deposition techniques using the porous alumina membrane with 40 nm diameter pores as template. ZnS single-crystal nanowire arrays with [110] growth direction have been obtained at an extremely low current density of 0.1 mAcm^-2. At higher current densities, the deposited ZnS nanowires possess a polycrystalline structure. The nanoscale confinement is found to be favorable for the growth of wurtzite ZnS single crystals.Hexagonal CdS nanowire arrays have been prepared at a low temperature of T = 110 oC by employing electrochemical deposition techniques using the porous alumina membrane as template. It has been found that the deposition current density has important effect on the growth orientation of the deposited nanowire arrays. At higher current densities of 1.28 mAcm^-2, the deposited CdS nanowires possess a polycrystalline structure. An extremely low current density of 0.05 mAcm^-2 is favorable for the growth of single-crystal CdS nanowires along the normal direction of the intrinsic low-surface-energy （103） face. According to the classical theory of nucleation and growth for electrocrystallization, a quasi-two-dimension critical dimension model has been proposed, which shows that the critical dimension is dependent on the electrodeposition parameters, the surface energy of the formed crystal face, and the lattice misfit between the nanowires and substrate. The formation of electrodeposited single-crystal nanowires and the formation mechanism of various growth orientations can be well understood by employing the suggested model.Porous alumina templates with average diameter of ²5 nm, 40 nm, and 120 nm were obtained under selected anodizing conditions. Highly ordered hexagonal CdSe nanowire arrays have been successfully yielded by employing the electrodeposition technique using the porous alumina as templates. We demonstrate by experimental and theoretical efforts that the growth orientation of the CdSe nanowires can be effectively manipulated by varying the nanopore diameter of the templates. The preferential orientation of CdSe nanowires changes from [001] direction to the [101] and [103] directions at a critical diameter D0 in the range of 40-120 nm at the current density I = 1.28 mAcm^-2. At an extremely low current density I = 0.06 mAcm^-2, the preferential orientation of CdSe nanowires switches from [101] direction to [103] direction as D≥40 nm. The diameter-dependent orientation can be understood based on the total energy minimum principle. The electrodeposited CdSe nanowires present tunable optical properties by varying their structural characteristic and growth orientation.Multiwalled carbon nanotube （MWCNT）/CdS core/shell heterostructures have been synthesized via a simple solution-phase method. The thickness of CdS shells can be facilely tuned by either the reaction temperature or time. The CdS nanoparticles are first formed directly on the activated sites of the MWCNT surface, and then a uniform CdS sheath is yielded via orientated aggregation processes.Using the ZnO nanoneedles as self-sacrificed templates, ZnO/ZnS core/shell and ZnS hollow nanoneedles have been synthesized via a surfactant-free method. At a low temperature hydrothermal condition （90 oC）, ZnO/ZnS core/shell nanoneedles were formed through in-situ chemical reaction between the ZnO template and sulfide source. The ZnS hollow nanoneedles are yielded via nanoscale Kirkendall effect at an elevated temperature （120 oC）. If the obtained hollow nanoneedles are employed as the starting materials, fantastic nanoarchitectures could be realized by employing the Rayleigh instability. These novel nanostructures may find important application in nanodevices.更多还原