Self-catalysis: a contamination-free, substrate-free growth mechanism for single-crystal nanowire and nanotube growth by chemical vapor deposition

A unified mechanism for the growth of a wide variety of long, uniform, single-crystal nanowires and whiskers, including III-V and II-VI binary, ternary, and quaternary nanowires and whiskers, without the use of any substrate and catalyst has been presented. While elucidating the mechanism, attempts have been made to provide a kinetic and thermodynamic rationale for the growth. Various features of the growth mechanism, including the formation of liquid droplets and seeds, nucleation, and creation of products, have been discussed. Extensive studies of illustrative examples provide the validity of the proposed mechanism. The influence of various parameters such as growth temperature and chamber pressure on the growth mechanism has been studied. The advantages and disadvantages of the proposed mechanism, and its superiority to the well-known vapor-liquid-solid mechanism, have been elucidated. Means to improve the mechanism to obtain self-aligned nanowires and whiskers have been suggested. Based on these, it has been demonstrated that the present mechanism is indeed a powerful self-catalytic growth mechanism uniquely suited to the growth of a wide variety of single-crystal nanowires and whiskers. It can be very useful also for the growth of single-crystal nanotubes.     

纳米晶取向接合生长动力学研究及其在量子点发光性质调控中的应用

对晶体生长机制、动力学与微结构衍化的认识是实现纳米材料的尺寸和形貌可控制备的基础．以表面溶解沉积为特征的奥斯特瓦尔德熟化（0R）理论常用来解释传统的晶体生长过程．在该生长模式下,纳米晶体的生长呈现出小颗粒溶解而大颗粒逐渐长大的特征．在纳米材料体系,近来还发现了一种重要的新的晶体生长模式——“取向接合（OA）”机制,在该机制下,两个晶格取向一致的初级纳米颗粒可通过直接接合和结构调整,从而长成一个新的晶体．这一机制已被证实在许多纳米材料体系中广泛存在,并对所合成的纳米材料的形貌、微结构具有非常显著的影响,在构筑新型纳米结构方面具有潜在的优势．本文我们首先回顾了OA生长机制的认识历程和这一机制对材料科学的重大意义;进而,基于我们的研究工作系统介绍了OA生长动力学模型的建立与发展,进一步阐述了这一机制的微观过程及其对材料内部缺陷的特殊影响,深入地分析和讨论了表面包裹的强弱、表面作用的性质对OR机制和OA机制的抑制和调控作用;基于上述表面包裹可调控纳米材料的生长机制的认识,我们结合近期研究结果,从动力学角度分析了量子点的生长机制与其发光特性的内在关联,阐明了表面包裹调控量子点的发光性质的本质原因,为制备不同发光特征的量子点及理解其发光性质衍化规律提供了重要的理论指引．     

Evaluation of Structure,Nucleation and Growth Mechanism of Electropolymerized Polypyrrole on Highly Oriented Pyrolytic Graphite Electrode

Chronoamperometry (i–t) and atomic force microscopy (AFM) were used to study the nucleation and growth mechanism of electropolymerized polypyrrole formed on highly oriented pyrolytic graphite (HOPG) substrate surface. From i–t measurements it was found that the nucleation and growth mechanism was a 3‐D progressive after nuclei overlapping. However, before nuclei overlapping, it was not clear whether the mechanism was 2‐D instantaneous or 3‐D progressive. This ambiguity in the nucleation and growth mechanism was confirmed as 3‐D progressive from the results of AFM measurements. In addition to nucleation and growth mechanism, possible models were proposed for different structures observed on the AFM image of polypyrrole, obtained from very early stages of polymerization.     

Spatial determination of gold catalyst residue used in the production of ZnO nanowires by SIMS depth profiling analysis

In this paper we demonstrate how secondary ion mass spectrometry (SIMS) can be applied to ZnO nanowire structures for gold catalyst residue determination. Gold plays a significant role in determining the structural properties of such nanowires, with the location of the gold after growth being a strong indicator of the growth mechanism. For the material investigated here, we find that the gold remains at the substrate–nanowire interface. This was not anticipated as the usual growth mechanism associated with catalyst growth is of a vapour–liquid–solid (VLS) type. The results presented here favour a vapour–solid (VS) growth mechanism instead. Copyright © 2007 John Wiley & Sons, Ltd.     

碳纳米管的最新制备技术及生长机理

结合笔者的工作综述了碳纳米管的制备技术及生长机理的最新研究进展，重点介绍了近两年来碳纳米管制备的进展情况，包括传统制备方法的改进（电弧放电法、化学气相沉积法和激光蒸发法）、新型制备技术、特殊结构的碳纳米管制备；同时探讨了碳纳米管的各种生长机理；最后提出了碳纳米管制备技术和生长机理的发展方向。     

Controllable assembly of WO3 nanorods/nanowires into hierarchical nanostructures

The controlled synthesis of two novel h-WO3 hierarchical structures made of nanorods/nanowires has been successfully realized in a large scale via a simple hydrothermal method. It is demonstrated that the morphology of the final products is significantly influenced by adding different sulfates. The urchinlike and ribbonlike structures of WO3 can be selectively prepared by adding Rb2SO4 and K2SO4, respectively. The morphology evolvement and the growth mechanism were studied carefully. The sulfate-induced oriented attachment growth mechanism has been proposed for the possible formation mechanism of the ribbonlike sample. For urchinlike products, two growing stages are believed to be involved in the growth process. The current understanding of the growth mechanism of these nanostructures may be potentially applied for designing other oriented or hierarchical nanostructures based on 1D nanoscale building blocks through the direct solution-growth.     

Nitrate ion promoted formation of Ag nanowires in polyol processes: a new nanowire growth mechanism

In polyol processes, it was widely accepted that Ag nanowires (NWs) were formed via uniaxial growth of multiple twinned decahedral particles (MTPs) along the {111} facets. Herein, we show that the above MTP uniaxial growth mechanism for growth of nanorods (NRs) and short nanowires (NWs) is different from that for the growth of long Ag NWs. We provide experimental evidence to show that polycrystalline long Ag NWs (up to ~100 μm) could be formed in high yield (~90%) by a completely different growth mechanism via self-assembly of Ag NPs/NRs. Transmission electron microscope (TEM) measurements show that long Ag NWs are composed of crystalline Ag NPs and NRs with multiple crystal orientations, and many NRs have crystalline structures with pentagonal cross section. Solution phase in situ X-ray diffraction (XRD) measurements show that a strained face-centered tetragonal (fct) phase was gradually formed during the formation and growth of long Ag NWs, in addition to the normal face-centered cubic (fcc) phase. The strained fct phase disappears after partial etching by HAuCl(4) and Fe(NO(3))(3). The working conditions for the MTP uniaxial growth mechanism and the current nitrate-promoted self-assembly growth mechanism will be compared and discussed.     

Preparation, self-assembly, and mechanistic study of highly monodispersed nanocubes

In this paper, we describe the synthesis and growth mechanism of highly monodispersed platinum nanocubes. The platinum nanocubes are synthesized by the decomposition of a platinum precursor in a hydrogen atmosphere. The morphology and size distribution of the platinum particles formed has been studied with HRTEM. By controlling the concentration of the platinum precursor, we demonstrate that at low concentration, it is possible to grow polydispersed nanocubes with {1,0,0} facets. Increasing the concentration of the precursor changes the growth mechanism, resulting in the formation of highly monodispersed platinum nanocubes. Highly monodispersed platinum nanocubes are formed in a two-step growth mechanism with initial growth of the {1,1,1} facets followed by secondary growth filling the {1,0,0} facets. The particle monodispersity facilitates the formation of long-range arrays of nanocubes.     

Growth mechanism of amorphous carbon by liquid plasma electrolytic deposition

The growth mechanism of amorphous carbon film by the liquid deposition process is still unclear. In this study, the influence of applied voltages on the surface morphology and microstructure of amorphous carbon films was investigated as well as the bonding probability at the film/substrate interface, and a new mechanism of film growth was proposed from the electrochemistry and non‐equilibrium thermodynamics viewpoints. The results showed that growth of amorphous carbon film involved the island groove morphology; more graphitic carbons are present within the film as the applied voltage increased. A coupling model of the growth mechanism including the ionization–absorption–dehydrogenation process and the chemical volume polymerization is highlighted. Copyright © 2016 John Wiley & Sons, Ltd.     

ZnO纳米片层结构的原位生长机理及热力学函数

采用绿色水介质体系一步合成了3种不同尺寸的ZnO纳米片层结构。 通过微热量技术获取其原位生长过程的热谱曲线,从动力学和热力学角度分析其生长机理;利用电化学方法测定了不同温度下纳米ZnO与块体ZnO原电池的电势差,结合热力学基本公式求算出ZnO纳米片层结构的热力学函数值,并与生长机理关联讨论。 结果表明,ZnO纳米片层结构的生长经历了先表观吸热后表观放热,放热减慢,最后到达放热平台的热量变化阶段。 标准摩尔熵、标准摩尔生成Gibbs自由能及标准摩尔生成焓均随着尺寸减小而逐渐增大。 本文为纳米材料的原位生长机理与热力学函数的关联研究提供了新的思路和方法。     

In situ growth mechanism and the thermodynamic functions of zinc oxide nano-arrays and hierarchical structure

We report the one-step synthesis of zinc oxide nanomaterials with arrays and hierarchical structure at room temperature. The zinc oxide nanomaterials can be synthesized via a simple method without catalyst. Furthermore, we explained the growth mechanisms of the two systems. In situ growth experiment provided the information of thermodynamics and kinetics, and based on that, growth mechanism was given a further explanation via the curve of in situ growth. Moreover, the relations between thermodynamic functions and the potential difference can be established by the electrochemical method. Take bulk zinc oxide reference. The thermodynamic functions of nano zinc oxide such as standard molar entropy, standard molar Gibbs free energy of formation, and standard molar enthalpy of formation can be calculated. The change rules of thermodynamic functions at different reaction times evidenced the growth mechanism more deeply. This work may contribute to the analysis of growth mechanism for nanostructures and obtain the thermodynamic functions of nanomaterials.     

单分散铁氧体纳米颗粒的生长机制与成分偏聚的透射电子显微研究

理解纳米晶的生长机制对单分散纳米晶的可控合成至关重要。本文以热分解法制备的双金属铁氧体(钴铁氧和锰铁氧)纳米颗粒为例,利用透射电子显微镜(TEM)系统研究了铁氧体纳米晶的生长机制,揭示了由此造成的成分偏聚现象。对不同时间阶段的反应产物的分析结果表明,两步加热法(即先后在相对低的温度和相对高的温度下加热反应)是制备高质量的单分散铁氧体纳米晶的关键;通过控制低温反应阶段的时间可实现纳米晶的形核阶段和生长阶段的有效分离,从而有利于单分散纳米晶的合成。利用扫描透射电子显微镜(STEM)及电子能量损失谱(EELS)谱学成像技术分析,我们进一步发现了双金属铁氧体纳米晶中的成分偏聚现象,表明双金属铁氧体纳米晶在形核阶段主要形成富Fe的核芯,而在生长阶段则形成更富Co/Mn的双金属铁氧体壳层。这些结果对制备高质量的单分散铁氧体纳米晶具有重要的指导意义,同时也有助于正确理解热分解法制备的铁氧体纳米晶的表面成分和相关表面物理化学性质。     

Importance of Oxygen in the Metal-Free Catalytic Growth of Single-Walled Carbon Nanotubes from SiO(x) by a Vapor-Solid-Solid Mechanism

To understand in-depth the nature of the catalyst and the growth mechanism of single-walled carbon nanotubes (SWCNTs) on a newly developed silica catalyst, we performed this combined experimental and theoretical study. In situ transmission electron microscopy (TEM) observations revealed that the active catalyst for the SWCNT growth is solid and amorphous SiO(x) nanoparticles (NPs), suggesting a vapor-solid-solid growth mechanism. From in situ TEM and chemical vapor deposition growth experiments, we found that oxygen plays a crucial role in SWCNT growth in addition to the well-known catalyst size effect. Density functional theory calculations showed that oxygen atoms can enhance the capture of -CH(x) and consequently facilitate the growth of SWCNTs on oxygen-containing SiO(x) NPs.     

Nucleation and growth mechanism for the electropolymerization of aniline in trifluoroacetic acid/lithium perchlorate/propylene carbonate medium

In the present work, the nucleation and growth mechanism for the electropolymerization of aniline in propylene carbonate medium containing 0.06 M trifluoroacetic acid and 0.05 M lithium perchlorate was investigated at different potentials on highly oriented pyrolytic graphite (HOPG) by potentiostatic current-time transients (i-t) and atomic force microscopic (AFM) measurements. The electrochemical data fitted with the theoretical curves for nucleation and growth suggest that the electropolymerization of aniline consists of progressive nucleation followed by 3D growth at an early stage and layer-by-layer growth in subsequent periods. The results obtained from transient analysis were in good agreement with the results of the AFM analysis. In our previous studies with aqueous solutions, we observed only progressive nucleation followed by a 3D growth mechanism for the electropolymerization of aniline in a higher potential range, 1.5–2.0 V vs. Ag/AgCl. Hence, the results obtained from the present work indicate that the nucleation and growth mechanism depends on the medium.     

铅基复合钙钛矿型弛豫铁电单晶的生长基元与生长机理Ⅰ.PMNT单晶的表面形貌、负晶结构及生长基元的组装与拆分

铅基复合钙钛矿型弛豫铁电单晶体PMNT的生长基元为多种[BO_6]配位八面体,晶体生长过程可视为多种八面体基元与Pb~(2 )的组装过程.这些生长基元向{111}面叠合时易采取法向生长机制,向{001}面叠合时易采取层状生长机制,由此决定了晶体生长速度的各向异性与晶体的形貌.Bridgman法生长的PMNT晶体在生长过程中由内向生长机制形成规则的负晶结构;在晶体生长过程中,在其自然表面上可形成正形与负形两种形貌;在高温退火过程中,由于PbO的分解,晶体表面上可形成类似“蚀象”的构型,这些可从[BO_6]八面体生长基元的组装或拆分方面获得解释.     

铅基复合钙钛矿型弛豫铁电单晶的生长基元与生长机理1: PMNT单晶的表面形貌 、负晶结构及生长基元的组装与拆分

铅基复合钙钛矿型弛豫铁电单晶体PMNT的生长基元为多种[BO~6]配位八面体,晶体生长过程可视为多种八面体基元与Pb^2^+的组装过程。这些生长基元向{111}面叠合时易采取法向生长机制,向{001}面叠合时易采取层状生长机制,由此决定了晶体生长速度的各向异性与晶体的形貌。Bridgman法生长的PMNT晶体在生长过程中由内向生长机制形成规则的负晶结构;在晶体生长过程中,在其自然表面上可形成正形与负形两种形貌;在高温退火过程中,由于PbO的分解,晶体表面上可形成类似"蚀象"的构型,这些可从[BO~6]八面体生长基元的组装或拆分方面获得解释。     

An analytical expression for the van der Waals interaction in oriented-attachment growth: a spherical nanoparticle and a growing cylindrical nanorod

A mathematical derivation of an analytical expression is presented to evaluate the van der Waals interaction between a sphere and a cylindrical rod. This expression then is applied to study the growth of one-dimensional nanostructures, such as nanorods, using a common growth mechanism in colloidal chemistry, the oriented attachment growth mechanism. Parameters associated with the dimensions and the separation of nanoparticles and nanorods are varied in calculations to assess their influence on the magnitude of the van der Waals interaction.     

国家成长的要素、机制与格局—基于政治生态学角度的国家成长理论

在20世纪80年代以来有关“回归国家”的研究中,“国家成长”是一个新兴的主题,它意味着国家理论在方法论和理论上的双重创新。从政治生态学的角度来看,国家成长首先表现为国家要素的成长。国家成长的要素分为基本要素、组织要素和成长机制。基本要素确立国家;伴随着基本要素发育的是组织要素成长,是国家调整期的主要表现,发育成型则意味着国家进入稳定期;成长机制萌发并逐渐成为政治生活的主流,国家成长进入成熟期。在国家成长的不同时期,源动力均来自社会,所以国家−社会关系机制在国家成长中最为重要。社会形态及发展进程不同,国家与社会的结合方式也就不同,国家成长呈现出非均衡的格局。国家成长理论的提出既是对已有国家理论的挑战,同时也拓展了国家研究的逻辑、方法和场域。基于国家成长理论,国家与社会的关系需要重新审视,特别是在后国家成长时期,社会将进入到一个相互关联的共同体中,目标亦是推动构建人类命运共同体。     

Observations on clear solution silicalite-1 growth by nanoslabs

Several research groups have reported the presence of nanometer-sized particles (nanoslabs) in clear solutions, which precipitate the crystalline MFI (ZSM-5) structure. Debate about the growth mechanism for Al-free ZSM-5 (silicalite-1) has revolved around growth by small silicate units (monomers, dimers, etc.) from solution vs growth by nanoslab addition. A model developed for precipitation of uniform sized colloids by addition of sub-colloidal precursor units has been adapted for this zeolite synthesis system. Parameter values were adjusted for the simulation results to match experimental observations from work reported previously, at least to the extent possible. The model involved the simultaneous solution of up to 6000 ordinary differential equations, and required computation times of up to 24 h. The results shed light on the crystal growth mechanism, but pose questions for further investigations of the nucleation mechanism.     

Ring-disk electrode studies of the formation,growth and transformation of iodine films formed during the anodic oxidation of iodide on platinum

The kinetics and mechanism of the formation, growth and dissolution of iodine films on platinum during the electrooxidation of iodide have been investigated using rotating-disk and ring-disk techniques. The dissolution-precipitation mechanism of film formation and a linear growth law for film growth has been confirmed. The iodine film on platinum is believed to be made up of an ionically insulating barrier layer covered by a porous overlayer. The oxidation behavior of iodide and ferrous species shows that the iodine film is predominantly an iodide-ion conductor. Also, a film transformation, responsible for the transient features observed during iodide oxidation has been confirmed. This transformation changes the mechanism of iodide transport through the film from a partly “pore”-type to a Grotthus-type mechanism. The ring current maximum, which occurs at the same instant as the disk current minimum, reveals the mechanism of dissolution of iodine film during the transient period as involving complexation with iodide. Evidence for the mass-transport-controlled component of the potentiostatic transient response has been obtained from the sinusoidal hydrodynamic modulation response.