Single-crystal CdSe nanosaws

We report the first successful synthesis and characterization of single-crystal wurtzite CdSe nanoribbons through a simple thermal evaporation process. Asymmetric growth of the nanoribbons occurs, yielding a sawlike shape with sharp teeth on one side. This asymmetric growth is suggested to be induced by the polarization of the c-plane in the wurtzite crystal structure.     

First demonstration of CdSe as a photocatalyst for hydrogen evolution from water under UV and visible light

CdSe nanoribbons show catalytic activity for photochemical hydrogen evolution from aqueous Na2S/Na2SO3 solution under irradiation with ultraviolet and visible light.     

Lamellar assembly of cadmium selenide nanoclusters into quantum belts

Here, we elucidate a double-lamellar-template pathway for the formation of CdSe quantum belts. The lamellar templates form initially by dissolution of the CdX(2) precursors in the n-octylamine solvent. Exposure of the precursor templates to selenourea at room temperature ultimately affords (CdSe)(13) nanoclusters entrained within the double-lamellar templates. Upon heating, the nanoclusters are transformed to CdSe quantum belts having widths, lengths, and thicknesses that are predetermined by the dimensions within the templates. This template synthesis is responsible for the excellent optical properties exhibited by the quantum belts. We propose that the templated-growth pathway is responsible for the formation of the various flat, colloidal nanocrystals recently discovered, including nanoribbons, nanoplatelets, nanosheets, and nanodisks.     

In situ electrochemical organization of CdSe nanoclusters on graphene during unzipping of carbon nanotubes

In situ decoration of very small CdSe quantum dots on graphene nanoribbons (GNRs) has been achieved during the electrochemical unzipping of single walled carbon nanotubes. Critical parameters like the width of the GNRs, size distribution of quantum dots and their organization on GNRs have been shown to be strongly dependent on the electric field and time.     

High-quality ultralong Sb2Se3 and Sb2S3 nanoribbons on a large scale via a simple chemical route

Large-scale ultralong single-crystalline Sb2Se3 and Sb2S3 nanoribbons were prepared respectively by reacting SbCl3 with selenium and sulfur powders in glycol solution. Both Sb2Se3 and Sb2S3 nanoribbons are usually hundreds of microns in length, and the structures of the nanoribbons are determined to be of the orthorhombic phases. The Sb2Se3 nanoribbons are typically 100-300 nm in width and 20-60 nm in thickness and grow along the [12] direction. Sb2S3 nanoribbons are wider than Sb2Se3 nanoribbons; Sb2S3 nanoribbons are about 200-500 nm in width and grow along the [001] direction. The growth mechanism of the nanoribbons is investigated based on high-resolution transmission electron microscopy (HRTEM) observations. Optical absorption experiment reveals that Sb2Se3 and Sb2S3 nanoribbons are two semiconductors with bandwidth Eg approximately 1.15 eV and Eg approximately 1.56 eV, respectively.     

Half metallicity and electronic structures in armchair BCN-hybrid nanoribbons

We study magnetism and electronic structures of armchair BCN-hybrid nanoribbons from density functional theory. Different from armchair graphene nanoribbons, armchair BCN-hybrid nanoribbons are found to present magnetism along the edges of the nanoribbons if B and N atoms are unpaired in the nanoribbons. Intriguing spin-polarized bands, including magnetic semiconductors, half metals, and magnetic metals, are obtained in the armchair nanoribbons with both the edges composed of C and N atoms. The spin polarization in these armchair nanoribbons is ascribed to the appearance of the unsaturated electronic states in the systems. The magnetic metallicity can be tuned further to half metallicity by adsorbing O atoms at appropriate positions in the ribbons. The electronic structures of the nanoribbons without spin polarization are also analyzed. Our studies provide understanding of the magnetism mechanisms and the electronic properties and most importantly, how to achieve half metallicity in low-dimensional BCN-hybrid systems.     

Supramolecular assembly of poly(phenylene vinylene) with crown ether substituents to form nanoribbons

Poly(para-phenylene vinylene) with crown ether substituents (C-PPV) could form nanoribbons through supramolecular assembly with K(+) in dilute chloroform solution. The length of the nanoribbons increased with an increase in the standing time of the C-PPV/K(+) solution. Experimental evidence to support the interaction between K(+) and crown ether substituents was provided, and the growth mechanism of C-PPV/K(+) nanorods to nanoribbons was proposed. The influence of the length of the nanoribbons on the photophysics of C-PPV was also investigated.     

High-quality ultralong Sb2S3 nanoribbons on large scale

Large-scale, ultralong, single-crystalline Sb2S3 nanoribbons were prepared by directly reacting SbCl3 and Na2S2O3 solutions, without any organics used in the experiment. The nanoribbons were analyzed by a range of methods. The nanoribbons are usually several millimeters in length, typically 200-500 nm in width and 30-80 nm in thickness. The structure of the nanoribbons is determined to be of the orthorhombic phase. The growth mechanism of the nanoribbons was investigated based on high-resolution transmission electron microscopy observations. Optical absorption experiment shows that the nanoribbon is a semiconductor with a bandwidth Eg approximately 1.5 eV, near to the optimum for photovoltaic conversion, suggesting that Sb2S3 nanoribbons could be used in solar energy and photoelectronic applications.     

Simulation of structure and stability of carbon nanoribbons

Results of carbon nanoribbons and nanotubes simulation by means of hybrid density functional method and using empirical potentials have been compared. Energy of the nanoribbons formation and their citting from graphene sheet as well as energy of the nanotubes folding from graphene and nanoribbons have been determined. The REBO force field satisfactorily reflects the result of quantum chemical simulations; however, it cannot reproduce the formation of triple bonds between the edge atoms of the nanoribbons in the armchair conformation and thus leads to underestimated stability of the latter. Energy of the nanotubes folding from the nanoribbons is linear with the nanotube diameter.     

扶手椅型二硫化钼纳米带的电子结构与边缘修饰

采用基于密度泛函理论的第一性原理计算方法, 研究了扶手椅型二硫化钼纳米带的几何构型与电子结构, 发现其稳定性与电子性质敏感地依赖于边缘修饰. 随着边缘修饰的H原子数增加, 纳米带变得更加稳定, 并在间接带隙半导体、半金属和直接带隙半导体之间转变. 纳米带的能带结构和电子态密度显示, 其费米能级附近的能带主要由边缘态贡献. 当二硫化钼纳米带两边用不同数目的H原子修饰时, 纳米带同时具有由这两种修饰引起的边缘态并且两种边缘态的相互影响很小. 研究了三类纳米带带隙与宽度的关系, 对于每个原胞修饰0个或8个H原子的纳米带, 带隙随宽度以3为周期振荡变化; 而对于每个原胞修饰4个H原子的纳米带, 带隙振荡不再具有周期并且振荡幅度变小.     

Synthesis and optical properties of CdS nanoribbons

Rapid production of single crystalline CdS nanoribbons with hexagonal wurtzite phase has been achieved by thermal evaporation of CdS powder on Si wafers. The flow rate of the carrier (Ar) gas along with the synthesis temperature plays an important role in defining the size and shape of the CdS nanoribbons. Scanning electron and transmission electron microscopic observations revealed the nanoribbons to have a flat end as well as side surfaces which will make it ideal for optoelectronic devices such as nanolasers and light emitting diodes based on individual nanoribbons. The nanoribbons have widths within 200-400 nm and lengths approximately a few hundred micrometers. Room-temperature photoluminescence measurements show green emission centered at approximately 525 nm which may be ascribed to the near band edge emission. The Raman spectra of the CdS nanoribbons show peaks around 304, 609, 915, and 1220 cm(-1) corresponding to the first-, second-, third-, and fourth-order longitudinal optical phonon modes, respectively.     

钛酸钠一维纳米结构的构筑

以锐钛矿TiO₂为起始原料,通过水热法制备了钛酸盐纳米棒,对合成不同长度和宽度的钛酸盐纳米棒的影响和控制条件进行了研究。用X射线衍射(XRD)和扫描电子显微镜(SEM)对纳米棒的形貌和结构进行了表征。结果表明水热温度和处理时间能对纳米棒的形貌和结构进行有效的控制,得到理想的钛酸盐的结构。在更高的温度下(200 ℃),钛酸盐纳米管将更快的转化为纳米棒,而随着处理时间的延长,其形貌结构发生有规律的变化。在96 h处理时间后纳米棒束的宽度为50 nm到1 μm,长度可以达到几十微米。对后处理中酸洗对产物的形貌和晶体结构的影响也进行了对比研究,发现在酸洗之前钛酸盐纳米棒结构就已经形成,但是酸洗能使产物的晶体结构产生变化,同时使纳米棒的表面形貌更加光滑规整。最后对比研究原料和产物的紫外-可见吸收光谱,发现纳米管/棒在250至350 nm处有宽带隙吸收。     

扶手椅型缺陷硫化钼纳米带电子性质的第一性原理计算

基于密度泛函理论的第一性原理计算,研究了含空位缺陷的扶手椅型二硫化钼纳米带的电子性质.发现缺陷会导致纳米带结构稳定性降低,单空位钼缺陷和三空位缺陷使得纳米带从半导体变成金属性,而单空位硫缺陷和两种双空位缺陷仅减小纳米带的带隙;电子态密度和能带的本征态表明缺陷纳米带费米能级附近的杂质态主要是缺陷态的贡献.研究了四类半导体性质的纳米带带隙与宽度的关系,对于完整的纳米带,带隙随宽度以3为周期振荡变化;而引入空位缺陷后,纳米带的带隙振荡不再具有周期且振荡幅度变小.同时发现,当缺陷的浓度变小后,缺陷仅使纳米带的带隙减小,不会使其变为金属性.这些结果有望打开其在新型纳电子器件中的应用潜能.     

Synthesis of high-density nanocavities inside TiO2-B nanoribbons and their enhanced electrochemical lithium storage properties

Single crystalline TiO2-B nanoribbons with high-density nanocavities were successfully synthesized via a simple hydrothermal route. The as-prepared TiO2-B nanoribbons exhibited a large Brunauer, Emmett, and Teller (BET) surface area of about 305 m(2)/g because of the high-density nanocavities inside the thin nanoribbons. Electrochemical measurements indicated that the TiO2-B nanoribbons with dense nanocavities showed discharge specific capacity higher than those of TiO2-B nanotubes and nanowires. It was found that the dense nanocavities have an important influence on the electrochemical lithium intercalation properties.     

水溶性CdSe/CdS量子点的合成及其与牛血清蛋白的共轭作用

用巯基乙酸(TGA)作为稳定剂，合成了水溶性的CdSe和核壳结构的CdSe/CdS半导体量子点。吸收光谱和荧光光谱研究表明，核壳结构的CdSe/CdS半导体量子点比单一的CdSe量子点具有更优异的发光特性。用TEM、电子衍射(ED)和XPS分别表征了CdSe和CdSe/CdS纳米微粒的结构、形貌及分散性。红外光谱和核磁共振谱证实了巯基乙酸分子中的硫原子和氧原子与纳米微粒表面的金属离子发生了配位作用。在pH值为7.4的条件下，将合成的CdSe和CdSe/CdS量子点直接与牛血清白蛋白(BSA)相互作用。实验发现，两种量子点均对BSA的荧光产生较强的静态猝灭作用；而BSA对两种量子点的荧光则具有显著的荧光增敏作用，存在BSA时CdSe/CdS量子点的荧光增强是不存在BSA时体系荧光强度的3倍。     

CdSe包覆层数对水溶性CdTe/CdSe (II型)核壳量子点的光学特性和微观结构的影响

在水相合成的CdTe量子点的体系中通过分批次加入新鲜配制的NaHSe和CdCl2溶液,制备出了CdSe包覆层数不同的CdTe/CdSe核壳量子点,并着重考察了CdSe包覆层数对CdTe/CdSe核壳量子点的光学特性以及微观结构的影响.与CdTe量子点相比,CdSe单层包覆的CdTe/CdSe核壳量子点的吸收峰和荧光发射峰出现明显红移;随着CdSe包覆层数的增多,CdTe/CdSe核壳量子点吸收光谱的覆盖范围向长波方向扩展,荧光发射峰强度逐步下降,荧光寿命大幅延长,体现出Ⅱ型核壳量子点的特征.X射线衍射(XRD)分析表明,随着CdSe包覆层数的增多,CdTe/CdSe核壳量子点的粉末衍射峰由CdTe衍射峰位置逐步向CdSe衍射峰位置靠近.CdTe/CdSe核壳量子点因其延伸到近红外区域的宽吸收特性致使其在太阳电池领域具有重要的应用前景.     

Photophysical properties of biologically compatible CdSe quantum dot structures

The photophysical properties of CdSe and ZnS(CdSe) semiconductor quantum dots in nonpolar and aqueous solutions were examined with steady-state (absorption and emission) and time-resolved (time-correlated single-photon-counting) spectroscopy. The CdSe structures were prepared from a single CdSe synthesis, a portion of which were ZnS-capped, thus any differences observed in the spectral behavior between the two preparations were due to changes in the molecular shell. Quantum dots in nonpolar solvents were surrounded with a trioctylphosphine oxide (TOPO) coating from the initial synthesis solution. ZnS-capped CdSe were initially brighter than bare uncapped CdSe and had overall faster emission decays. The dynamics did not vary when the solvent was changed from hexane to dichloromethane; however, replacement of the TOPO cap by pyridine affected CdSe but not ZnS(CdSe). CdSe was then solubilized in water with mercapto-acetic acid or dihydrolipoic acid, whereas ZnS(CdSe) could be solubilized only with dihydrolipoic acid. Both solubilization agents quenched the nanocrystal emission, though with CdSe the quenching was nearly complete. Additional quenching of the remaining emission was observed when the redox-active molecule adenine was conjugated to the water-soluble CdSe but was not seen with ZnS(CdSe). The emission of aqueous CdSe could be enhanced under prolonged exposure to room light and resulted in a substantial increase of the emission lifetimes; however, the enhancement occurred concurrently with precipitation of the nanocrystals, which was possibly caused by photocatalytic destruction of the mercaptoacetic acid coating. These results are the first presented on aqueous CdSe quantum dot structures and are presented in the context of designing better, more stable biological probes.     

Metal phthalocyanine nanoribbons and nanowires

Nanoribbons and nanowires of different metal phthalocyanines (copper, nickel, iron, cobalt, and zinc), as well as copper hexadecafluorophthalocyanine (F(16)CuPc), have been grown by organic vapor-phase deposition. Their properties, as a function of substrate type, source-to-substrate distance, and substrate temperature, were studied by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and absorption measurements. The size and morphology of the nanostructures were found to be mainly determined by the substrate temperature. The crystal structure was dependent on the substrate temperature as well. At substrate temperatures below 200 degrees C, in addition to straight nanoribbons, twisted nanoribbons were found for all investigated materials except F(16)CuPc, which formed helical nanoribbons upon exposure to an electron beam. The formation of different nanostructures (nanoribbons, twisted nanoribbons, and helical nanoribbons) is discussed.     

Synthesis of core/shell nanoparticles of Au/CdSe via Au-Cd bialloy precursor

We present a novel method for the preparation of ultrasmall Au/CdSe core/shell particles. Au-Cd bialloy particles of 4.7 nm diameter were prepared as the precursor. The Cd component in the precursor reacted with the Se source at a temperature of 205 degrees C and was heated to 250 degrees C, leading to formation of a Au/CdSe core/shell structure. The sizes of Au/CdSe nanoparticles have a narrow distribution with an average size of 6.0 nm and Au core of 2.2 nm diameter. The X-ray diffraction pattern and the images of the high-resolution electron transmission microscopy show that the Au cores and the CdSe shells of Au/CdSe core/shell nanoparticles are both well crystallized, and the CdSe shells are in a cubic phase. The absorption spectrum of the Au/CdSe nanoparticles combines the absorption behaviors of the Au cores and the CdSe shells.     

水溶性的CdSe/ZnS纳米微粒的合成及表征

用L-半胱氨酸(Cys)作为稳定剂，合成了水溶性的CdSe/ZnS核壳结构的半导体纳米微粒。吸收光谱和荧光光谱表明，CdSe/ZnS纳米微粒比单一的CdSe纳米粒子具有更优异的发光特性。透射电子显微镜（TEM）、ED和XPS表征了CdSe/ZnS纳米微粒的结构、分散性及形貌。红外光谱证实半胱氨酸分子中的硫原子和氧原子参加了与纳米粒子表面的金属离子的配位作用。