Formation of ZnSe magic-size clusters displaying optical absorption doublets from prenucleation clusters

The formation pathway of colloidal semiconductor ZnSe magic-size clusters(MSCs)in a reaction that display an optical absorption doublet remains poorly understood.The reaction of Zn(OAc)_(2)/OLA(made from zinc acetate and oleylamine)and tri-noctylphosphine selenide(SeTOP)in OLA in the presence of diphenylphosphine(HPPh_(2))is studied,in which dMSC-345 displays a doublet peaking at 328/345 nm.We suggest that the development is from the clusters that form in the initial prenucleation stage of the reaction.The clusters are the precursor compound(PC-299)of MSC-299(displaying an absorption singlet peaking at 299 nm).PC-299 transforms to PC-345 at a later stage.The presence of alcohol(such as methanol or ethylene glycol)promotes another pathway,which is the PC-299 to PC-320 transformation.PC-320 transforms to dMSC-320(with a doublet at 305/320 nm),followed by dMSC-345 via PC-345.The present study provides additional evidence that clusters(PC-299)form and transform(such as to dMSC-345 via PC-345)in the prenucleation stage of ZnSe quantum dots(QDs).

Ligand-induced,magic-size clusters enabled formation of colloidal all-inorganic II-VI nanoplatelets with controllable lateral dimensions

Achieving nanoconfinement-controlled synthesis of nanoplatelets(NPLs)via solution process under ambient condition remains a challenge.In this work,we developed a general ligand-induced strategy to synthesize colloidal stable all-inorganic semiconductor NPLs with controllable lateral dimensions.By introducing certain metal salts(cations:Zn^(2+)and In^(3+),anions:NO_(3)^(−),BF_(4)^(−),or triflate OTf−),wurtzite-structured(WZ-)CdS,CdSe,CdTe,and alloy Cd1−xZnxSe NPLs were directly synthesized in solution through the controlled diffusion of magic-size clusters(MSCs)at room temperature.Mechanism studies revealed that destabilization of MSCs and nanoconfined growth in templates facilitated the formation of NPLs.The present study not only provides a new synthetic route for the preparation of NPLs but also helps to provide insight into their probable formation mechanism and presents an important advance toward the rational design of functional nanomaterials.

Transient spectral and dynamic properties of magic-size Cd_(3)P_(2) nanoclusters in the limit of strong confinement

Both semiconductor nanocrystals and organic molecules are important photofunctional materials for an array of applications.It is interesting to examine the intermediate regime between these two families,which can be interpreted as the strong-confinement limit of the nanocrystals or alternatively as the large-size limit of molecules.Here,we choose Cd_(3)P_(2) magic-size clusters(MSCs)as a unique platform and apply time-resolved spectroscopy to investigate their spectral and dynamic properties.We find that these small clusters display molecular-like vibronic progression on their absorption and emission spectra and a large Stokes shift,which leads to well-separated transient absorption bleach and stimulated emission signals distinct from typical nanocrystals.On the other hand,such small size MSCs can still accommodate biexciton states,and the strongly enhanced Coulombic interactions lead to very fast dephasing of the biexciton resonance as well as rapid biexciton Auger annihilation(1.5 ps).Further,temperature-dependent measurements provide evidence for the transformation of band-edge excitons to localized excitons,with the localization likely driven by the softened lattice in these small-size clusters.These collective results demonstrate that strongly-confined nanoclusters indeed bridge the gap between nanocrystals and molecules,and can be a unique library to search for exotic excited state properties.

CdS magic-size clusters exhibiting one sharp ultraviolet absorption singlet peaking at 361 nm

We report,for the first time,the synthesis of CdS magic-size clusters (MSCs) which exhibit a single sharp absorption peaking at ~ 361 nm,along with sharp band edge photoemission at ~ 377 nm and broad trap emission peaking at ~ 490 nm.These MSCs are produced in a singleensemble form without the contamination of conventional quantum dots (QDs) and/or other-bandgap clusters.They are denoted as MSC-361.We present the details of several controlled syntheses done in oleylamine (OLA),using C,d(NO3)2 or C,d(OAc)2 as a C,d source and thioacetamide (TAA) or elementary sulfur (S) as a S source.A high synthetic reproducibility of the reaction of Cd(NO3)2 and TAA to single-ensemble MSC-361 is achieved,the product of which is not contaminated by other bandgap clusters and/or QDs.In some cases,the reaction product exhibits an additional absorption peak at ~ 322 nm.We demonstrate that the two peaks,at 361 and 322 nm,do not evolve synchronously.Therefore,the 322 nm peak is not a higher order electronic transition of MSC-361,but due to the presence of another ensemble,namely MSC-322.The present study suggests that there is an outstanding need for the development of a physical model to narrow the knowledge gap regarding the electronic structure in these colloidal semiconductor CdS MSCs.

Magic-sized CdSe nanoclusters for efficient visible-light-driven hydrogen evolution

Semiconductor magic-sized nanoclusters have got tremendous interests owing to their distinct chemical and photophysical properties,however,researches concerning their applications are still quite limited.Herein,we employ magic-sized CdSe nanoclusters as the light absorber for hydrogen photogeneration,which exhibits much better photocatalytic performance as compared to other conventional semiconductor quantum dots,such as CdS,CdSe,CdS/CdSe,and CdSe/CdS under identical conditions.Photoluminescence lifetime and transient absorption studies indicated that the superior activity is mainly ascribed to the longer exciton lifetime and fast electron transfer from nanoclusters to cocatalyst.Moreover,the issue of instability during reaction could be significantly inhibited by anchoring Zn2+onto the surface of nanoclusters,which gives the average efficacy of hydrogen evolution at 0.61±0.07 mL·h^(-1)·mgcatalyst^(-1),i.e.,27.3±2.9 mmol·h^(-1)·g_(catalyst)^(-1)(420 nm)with maintained 95.2%of original activity over 12 h illumination.

Synthesis and white-light emission character of CdS magic-sized nanocrystals

Family 373 and 406 of CdS magic-sized nanocrystals （MSNCs） were synthesized by a one-pot non-injection approach and white-light emission was generated from the coexistence of them. This light had excellent color characteristics, as defined by their pure white CIE （Commission International de l＇Eclairage） color coordinates （0.328, 0.343）, and it correlated with a color temperature of 5696 K. A probable thermodynamic equilibrium was proposed to explain the white-light emission behavior in this letter.

Precursor compound enabled formation of aqueous-phase CdSe magic-size clusters at room temperature

The formation pathway of aqueous-phase colloidal semiconductor magic-size clusters(MSCs)remains unrevealed.In the present work,we demonstrate,for the first time,a precursor compound(PC)-enabled formation pathway of aqueous-phase CdSe MSCs exhibiting a sharp absorption peaking at about 420 nm(MSC-420).The CdSe MSC-420 is synthesized with CdCl2 and selenourea as the respective Cd and Se sources,and with 3-mercaptopropionic acid or L-cysteine as a ligand.Absorption featureless CdSe PCs form first in the aqueous reaction batches,which transform to MSC-420 in the presence of primary amines.The coordination between primary amine and Cd^(2+)on PCs may be responsible to the PC-to-MSC transformation.Upon increasing the reactant concentrations or decreasing the CdCl_(2)-ligand feed molar ratios,the Cd precursor self-assembles into large aggregates,which may encapsulate the resulting CdSe PCs and inhibit their transformation to MSC-420.The present study sheds essential light on the syntheses and formation mechanisms of nanocrystals.

The precursor compound of two types of ZnSe magic-sized clusters

Precursor compounds(PCs)link quantum dots(QDs)and magic-sized clusters(MSCs),which is pivotal in the conversion between QDs and MSCs.Here,for the first time,we report the transformation,synthesis,and composition of a type of ZnSe PCs.ZnSe PCs can be directly transformed to two different MSCs with the assistance of octylamine and acetic acid at room temperature.The two types of MSCs exhibit sharp absorption peaks at 299 and 328 nm which are denoted as MSC-299 and MSC-328.In the preparation of ZnSe PCs,diphenylphosphine(DPP)as an additive plays a key role which not only inhibits the thermal decomposition of Zn precursor,but also acts as a reducing agent to reduce the by-products produced in the reaction.The composition was explored by X-ray photoelectron spectroscopy,energy dispersive spectrometer,matrix-assisted laser desorption/ionization time-of-flight mass spectra with ZnSe PC powder appeared as white powder after purifying by toluene(Tol)and methanol(MeOH).The results indicate that the molar ratio of Zn/Se is 2:1 with a molecular of〜3,350 Da.Therefore,we propose that the molecular formula of ZnSe PCs is Zn_(32)Se_(16).In addition,at the molecular level,the covalent bond of Zn-Se is formed in ZnSe PCs.This study offers a deeper understanding of the transformation from PCs to MSCs and for the first time proposes the composition of PCs.Meanwhile,this research provides us with a new understanding of the role of DPP in the synthesis of colloidal semiconductor nanoparticles.

Size matters:Steric hindrance of precursor molecules controlling the evolution of CdSe magic-size clusters and quantum dots

Little is known about how to precisely promote the selective production of either colloidal semiconductor metal chalcogenide(ME),magic-size clusters(MSCs),or quantum dots(QDs).Recently,a two-pathway model has been proposed to comprehend their evolution;here,we reveal for the first time that the size of precursors plays a decisive role in the selected evolution pathway of MSCs and QDs.With the reaction of cadmium myristate(Cd(MA)2)and tri-n-octylphosphine selenide(SeTOP)in 1-octadecene(ODE)as a model system,the size of Cd precursors was manipulated by the steric hindrance of carboxylic acid(RCOOH)additive.Without RCOOH,the reaction produced both CdSe MSCs and QDs(from 100 to 240℃).With RCOOH,the reaction produced MSCs or QDs when R was small(such as CH3−)or large(such as C6H5−),respectively.According to the twopathway model,the selective evolution is attributed to the promotion and suppression of the self-assembly of Cd and Se precursors,respectively.We propose that the addition of carboxylic acid may occur ligand exchange with Cd(MA)2,causing the different sizes of Cd precursor.The results suggest that the size of Cd precursors regulates the self-assemble behavior of the precursors,which dictates the directed evolution of either MSCs or QDs.The present findings bring insights into the two-pathway model,as the size of M and E precursors determine the evolution pathways of MSCs or QDs,the understanding of which is of great fundamental significance toward mechanism-enabled design and predictive synthesis of functional nanomaterials.

超细颗粒的基本特性

超细颗粒的定义域为1—100nm,乃是介于大块物质和原子间的中间物质态,在科学和枝术上有很大价值。但是,对它的基本特性研究,仅在最近的几年才有可能。本文试图对这方面工作作一评述。

一部载入史册的疗养院小说——从《魔山》看历史书记官托马斯·曼

在欧美风靡近百年的肺病疗养院也许是人类最荒诞的医学发明之一,长篇小说《魔山》则为肺病疗养院留下一幅耐人寻味的文学素描。小说不仅记录了疗养院生活的方方面面,堪称一部疗养院大全,而且对袖珍痰盂、X光体检、心理分析这类医学领域的新生事物进行了饶有兴味、别具一格的描写。托马斯·曼通过语言创造记录历史、反思历史、批判历史,实现了科学、历史、文学的三合一。

CdTe魔尺寸纳米晶的合成及其生长机理研究

不同于半导体常规纳米晶(RNCs),魔尺寸纳米晶(MSNCs)由于其精确的结构及超窄的带边荧光发射引起了广泛关注。然而MSNCs的合成常为不同种类的MSNCs和RNCs的掺杂混合,这使得高纯度、单一尺寸的MSNCs的合成往往十分困难。作者以醋酸镉和三辛基碲化膦为镉前驱体和碲前驱体,长链烷基酸为表面配体,利用高温热注的方法在1-十八烯中成功合成了两种单一尺寸的CdTe MSNCs。实验结果表明,适当链长的配体酸及相对较低的酸量是抑制RNCs生长,合成单一尺寸CdTe MSNCs的关键。反应温度很大程度上决定了生成的MSNCs的尺寸。采用TEM、EDX、XPS和XRD分析了所合成的CdTe MSNCs的形貌、组成及结构,结果显示其呈现为均一的点状形貌、且具有富镉表面的纤锌矿型结构。通过对升温处理过程中CdTe MSNCs所呈现出来的非连续生长模式进一步分析,提出一种类似Ostwald ripening的生长机制,即部分的CdTe MSNCs在高温下直接分解成单体,沉积在另一部分CdTe MSNCs上,使其"跳跃式"地生长成了尺寸更大的MSNCs。

魔幻尺寸CdSe纳米簇的连续生长与室温光学性质

以镉的脂肪酸盐和分散在三辛基膦中的硒单质分别作为镉和硒的前体,采用十二烷基硫醇做＂成核剂＂,十二烷基胺为活化剂,在非配位溶剂十八碳烯中,实现了连续尺寸高质量魔幻尺寸半导体纳米簇（CdSe）的合成。所得CdSe纳米簇的形态和光学性质分别通过透射电子显微镜、紫外可见吸收光谱、荧光激发光谱、荧光发射光谱及时间分辨的荧光光谱测试技术进行了表征和测定。该系列CdSe纳米簇具有良好的室温荧光性质,能够得到较强的以往只有低温（5~200K）下才能探测到的荧光光谱。所得发射光谱大部分为表面缺陷导致的黄光发射。部分尺寸的纳米簇能够实现白光发射,其CIE坐标为（0.339,0.340）,为白光光源的开发提供了备选材料。

魔力尺寸硒化镉纳米晶的压力稳定性研究

在极端条件下应用的耐压材料必须具有极高的结构和性能稳定性。魔力尺寸纳米晶体具有良好的结构、超小的粒子尺寸和精确的原子组成,逐渐成为研究的热点。采用胶体化学方法合成了硒化镉(CdSe)魔力尺寸纳米晶,其第一激子吸收峰位于463 nm处,相应的光致发光光谱表现出窄的半高宽,仅为13 nm。进一步利用金刚石对顶砧压机研究了所制备的CdSe魔力尺寸纳米晶在压力下的光学响应和稳定性。研究结果表明:随着压力的增大,CdSe魔力尺寸纳米晶的吸收和发光峰位保持不变,这种压力下的稳定行为与传统纳米材料在外界压力下所表现的敏感特性相反;压力卸下后,样品仍然保持CdSe魔力尺寸纳米晶的原始结构和形态。CdSe魔力尺寸纳米晶在加压过程中表现出的良好耐压性能,有助于极端压缩条件下的魔力尺寸纳米材料的研究。

磁性智能混合体MAGIC中磁性颗粒分布的研究

磁性智能混合体MAGIC(magnetic intelli-gent compounds)是一种含有磁性颗粒、磨粒以及粘结剂的可固化的磁性抛光材料,其抛光性能很大程度受其中颗粒分布的影响。MAGIC颗粒分布的研究是MAGIC抛光体制备及其抛光性能研究的基础,通过试验方法深入研究外加磁场、颗粒浓度、颗粒大小对磁性智能混合体中颗粒分布的影响。研究发现,当外加磁场强度大、磁性颗粒粒径小、磁性颗粒浓度高时,磁性颗粒容易形成交叉链和团簇链分布;而外加磁场强度小、磁性颗粒粒径大、磁性颗粒浓度低时,磁性颗粒容易形成短链分布。

在水相中通过手性配体直接合成手性魔幻尺寸团簇

尺寸小于2 nm的手性胶体半导体魔尺寸团簇(MSCs)为手性配体提供了丰富的表面结合位点,因此在手性半导体纳米材料应用方面具有巨大潜力.然而,手性MSCs的制备和光学表征却鲜有报道.本研究以手性半胱氨酸为配体,首次在室温水溶液中合成了单组合形式的手性MSCs,其中CdS MSCs在366 nm波长处有独特的尖锐吸收峰,CdSe MSCs在420 nm波长处有独特的尖锐吸收峰.通过改变手性配体的添加量,可以很容易地调节所制备的手性MSCs的光学活性.制备的手性CdS MSCs和CdSe MSCs的最大吸收不对称系数分别达到3.6×10^(−4)和5.6×10^(−4).实验结果表明,制备的MSCs的手性光学特性可能来源于配体诱导MSCs表面的原子重排.本研究不仅提供了制备手性MSCs的方法,而且为手性MSCs的研究和应用开辟了道路.

Electrospray Ionization Fourier Transform Ion Cyclotron Resonance Mass Spectrometric Study on Sodium Azide Cluster Ions

Sodium azide has rarely been studied in gas phase or in the form of cluster ions and as a model of solid ener-getic substances and inorganic azide salt was ionized by electrospray ionization (ESI) and studied by high resolution Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry (MS) systematically. This paper highlights the effects of experimental conditions on the formation of salt cluster and the collision activation dissociation path-ways of cluster ions to develop a microscopic understanding of inorganic azide salt clusters.