ZnS/CdSe core‐shell and wire‐coil nanowire heterostructures have been synthesized by chemical vapor deposition assisted with pulsed laser ablation. Measurements from high‐resolution transmission electron microscopy and selected area electron diffraction have revealed that both ZnS/CdSe core‐shell and wire‐coil nanowires are of single‐crystalline hexagonal wurtzite structures and grow along the [0001] direction. While the lattice parameters of ZnS and CdSe in the core‐shell nanowires are nearly equal to those of bulk ZnS and CdSe, change of the lattice parameters in the CdSe‐coil is attributed to the doping of Zn into CdSe, resulting in the relaxation of compressive strain at the interface between CdSe‐coil and ZnS‐wire. Composition variation across the interfacial regions in the ZnS/CdSe nanowire heterostructures ranges only 10–15 nm despite the pronounced lattice mismatch between ZnS and CdSe by ?11%. Growth mechanisms of the ZnS/CdSe nanowire heterostructures are discussed. 相似文献
ZnO/ZnS heterostructured nanorod arrays with uniform diameter and length were synthesized from zinc substrates in a one‐pot procedure by using a simple hydrothermal method. Structural characterization by HRTEM indicated that the heterostructured nanorods were composed of parallel segments of wurtzite‐type ZnO and zinc‐blende ZnS, with a distinct interface along the axial direction, which revealed the epitaxial relationship, ZnO (10$\bar 1$ 0) and ZnS ($\bar 1$ 1$\bar 1$ ). The as‐prepared ZnO/ZnS nanorods showed only two green emissions at around 523 nm and 576 nm. We also found that the nanorods exhibited high sensitivity to ethanol at relatively low temperatures, owing to their smaller size and structure. 相似文献
Novel hierarchical heterostructures formed by wrapping ZnS nanowires with highly dense SiO(2) nanowires were successfully synthesized by a vapor-liquid-solid process. The as-synthesized products were characterized using X-ray diffraction, scanning electron microscopy and transmission electron microscopy equipped with an energy-dispersive X-ray spectrometer. Studies indicate that a typical hierarchical ZnS/SiO(2) heterostructure consists of a single-crystalline ZnS nanowire (core) with diameter gradually decreasing from several hundred nanometers to 20 nm and adjacent amorphous SiO(2) nanowires (branches) with diameters of about 20 nm. A possible growth mechanism was also proposed for the growth of the hierarchical heterostructures. 相似文献
Novel structures comprised of GaAs nanowire arrays conformally coated with conducting polymers (poly(3,4‐ethylenedioxythiophene) (PEDOT) or poly(3,4‐ethylenedioxythiophene‐co‐3‐thiophene acetic acid) display both sensitivity and selectivity to a variety of volatile organic chemicals. A key feature is room temperature operation, so that neither a heater nor the power it would consume, is required. It is a distinct difference from traditional metal oxide sensors, which typically require elevated operational temperature. The GaAs nanowires are prepared directly via self‐seeded metal–organic chemical deposition, and conducting polymers are deposited on GaAs nanowires using oxidative chemical vapor deposition (oCVD). The range of thickness for the oCVD layer is between 100 and 200 nm, which is controlled by changing the deposition time. X‐ray diffraction analysis indicates an edge‐on alignment of the crystalline structure of the PEDOT coating layer on GaAs nanowires. In addition, the positive correlation between the improvement of sensitivity and the increasing nanowire density is demonstrated. Furthermore, the effect of different oCVD coating materials is studied. The sensing mechanism is also discussed with studies considering both nanowire density and polymer types. Overall, the novel structure exhibits good sensitivity and selectivity in gas sensing, and provides a promising platform for future sensor design.
Since the conceptoffunctionally graded m aterials(FG M)is proposed[1,2],m uch attention has been paid toFG M studies.Generally,FG M s were designed with thegradientdistribution ofcom position and structure,andthe graded structure of FG M is achieved by acom position gradient from one side of m aterials to theother,resulting in gradientproperties.Itis well鄄knownthat properties of nanom eter鄄sized m aterials stronglydepend on their sizes.Such size effect offers a newconcept for the design… 相似文献
Summary: The preferential partition of silver nanowires in thin films of polystyrene/poly(vinyl pyrrolidone) (PS/PVP, with a 30/70 weight ratio) blends, that induces drastic blend morphology variation, is reported. The silver nanowires are fabricated with the anodic aluminum oxide templating method, and have a diameter of 300 nm and length of 10 µm. At a higher nanowire loading of 10 wt.‐%, the silver nanowires are entangled and selectively concentrate within the continuous PVP domain. If surface modified by thiols carrying hydrophobic tails, the silver nanowires become hydrophobic and prefer to stay within the discrete hydrophobic PS domains. At a lower nanowire loading of 5 wt.‐%, the nanowires are non‐entangled and concentrate at regions near the interfaces of the PS and PVP phases, which induces the formation of interconnected PS domains.
Preferential partition of silver nanowires in thin films of PS/PVP (30/70) blends at a casting temperature of −10 °C. 相似文献
The platina-β-diketones [Pt2{(COMe)2H}2(μ-Cl)2] (1), [PPh4][Pt{(COMe)2H}Cl2] (2) and [Pt{(COMe)2H}-(acac)] (3) were found to catalyze the hydrosilylation of alkynes (hex-1-yne, hex-2-yne, hex-3-yne) and alkenes (hex-1-ene, styrene, trimethylvinylsilane) with methyldiphenylsilane (nsilane:nsubstrate:nPt = 3000:3000:1, T = 27 °C, in C6D6). The comparison with the well-established catalysts from Speier (4) and Karstedt (5) exhibited up to twice as high activities for catalyst 1 and comparable regioselectivities. To get insight into the mechanism of the hydrosilylation, Si-H oxidative addition reactions towards the dinuclear platina-β-diketone 1 have been explored. Reactions of 1 with 2-picolyl substituted hydrosilanes of the type NSiMe2H and NSiMeHN resulted in decomposition with the formation of platinum black, only. On the other hand, the analogous reaction with the 8-quinolyl substituted silane of the type NSiMeHN was found to proceed under loss of H2 with the formation of a diacetyl(silyl)platinum(IV) complex [Pt(COMe)2Cl(NSiMeN-κ2N,N′,κSi)] (23). DFT calculations gave insight into the reason for this different reactivity and into the course of reaction. For comparison, the reaction of 1 with bis(2-picolyl)amine was performed resulting under proton shift in the sense of an oxidative addition reaction in the formation of the diacetyl(hydrido)platinum(IV) complex [Pt(COMe)2Cl(NNHN-κ3N,N′,N′′)] (25). The complexes 23 and 25 were fully characterized spectroscopically (1H, 13C, 195Pt, 29Si NMR, IR) and by single-crystal X-ray structure determinations. 相似文献
Large areas of millimeters long β-SiC nanowires with fluctuating diameters were synthesized in a polymer pyrolysis CVD (PPCVD) route. Polycarbosilane was used as the raw material. The morphology and structure of the nanowires were investigated by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The results showed that the nanowires had non-periodically fluctuating diameters in the range of 100–250 nm along the axial direction, and were composed of well crystalline β-SiC along the 〈111〉 direction. The vapor–solid (VS) mechanism was employed to interpret the nanowires growth procedure, and the diameter fluctuation was resulted from the varying concentration of the local silane fragments. 相似文献
Diacetylplatinum(II) complexes [Pt(COMe)2()] ( = bpy, 3a; 4,4′-t-Bu2-bpy, 3b), obtained by the reaction of [Pt(COMe)2X(H)()] with NaOH in CH2Cl2/H2O, were found to undergo oxidative addition reactions with halogens (Br2, I2) yielding the platinum(IV) complexes (trans, OC-6-13)/(cis, OC-6-32) [Pt(COMe)2X2()] ( = bpy, X = Br, 4a/4b; I, 4c/4d; = 4,4′-t-Bu2-bpy, X = Br, 4e/4f; I, 4g/4h). The diastereoselectivity of the reactions proved to be strongly dependent on the solvent. The oxidative addition of (SCN)2 resulted in the formation of (OC-6-13)-[Pt(COMe)2(SCN)2()] ( = bpy, 4i; 4,4′-t-Bu2-bpy, 4j). In a reaction the reverse of their formation, the diacetylplatinum(II) complexes 3 underwent oxidative addition with anhydrous HX (X = Cl, Br, I), prepared in situ from Me3SiX/H2O, yielding diacetyl(hydrido)platinum(IV) complexes [Pt(COMe)2X(H)()] ( = bpy, X = Cl, 5a; Br, 5b; I, 5c; = 4,4′-t-Bu2-bpy, X = Cl, 5d; Br, 5e; I, 5f). Furthermore, diacetyldihaloplatinum complexes 4 were found to undergo reductive elimination reactions in boiling methanol yielding acetylplatinum(II) complexes [Pt(COMe)X()] ( = bpy, X = Br, 6b; I, 6c; = 4,4′-t-Bu2-bpy, X = Br, 6e; I, 6f). All complexes were characterized by microanalysis, IR and 1H and 13C NMR spectroscopy. Additionally, the bis(thiocyanato) complex 4j was characterized by single-crystal X-ray diffraction analysis. 相似文献
The literature data on X substituent influence on the 1H, 29Si and 15N NMR chemical shifts (δ) and coupling constants (J) of Si-substituted silatranes , as well as M-N bond lengths (d) in atranes (M = C, Si, Ge, Sn, Pb) have been analyzed. It was established for the first time that the δ, J and d values depend not only on the inductive and resonance effects but also on the polarizability of X substituents. The polarizability contribution ranges from 8% to 25%. 相似文献
The chelate complexes of the types (1) and (2) have been synthesized and characterized by IR and NMR spectroscopy. The lower shift of the ν(P-Se) bands and downfield shift of the 31P-{1H}NMR signals for both P(III) and P(V) atoms in 1 and 2 compared to the corresponding free ligands indicate chelate formation through selenium donor. 1 and 2 show terminal ν(CO) bands at 1977 and 1981 cm−1, respectively, suggesting high electron density at the metal center. The molecular structure of 2 has been determined by single-crystal X-ray diffraction. The rhodium atom is at the center of a square planar geometry having the phosphorus and selenium atoms of the chelating ligand at cis-position, one carbonyl group trans- to selenium and one chlorine atom trans- to phosphorus atom. 1 and 2 undergo oxidative addition (OA) reaction with CH3I to produce acyl complexes (3) and (4), respectively. The kinetics of the OA reactions reveal that 1 undergoes faster reaction by about 4.5 times than 2. The catalytic activity of 1 and 2 in carbonylation of methanol was higher than that of the well known species [Rh(CO)2I2]− and 2 shows higher catalytic activity compared to 1. 相似文献
We report on the electrochemical synthesis of free‐standing aluminium nanowire architectures through a template‐assisted electrodeposition technique. For this purpose, nuclear track‐etched polycarbonate membranes were employed as templates. One side of the template was sputtered with a thin gold film to serve as a working electrode. Subsequently the nanowires were made in the ionic liquid 1‐ethyl‐3‐methylimidazolium chloride ([EMIm]Cl)/AlCl3 (40/60 mol %) under potentiostatic conditions. Two different electrodeposition procedures were employed to fabricate strongly adherent Al nanowire structures on an electrodeposited Al layer. In the first procedure, electrodeposition simultaneously occurs along the pores of the template and on the Au‐sputtered side of the template. In the second procedure, electrodeposition takes place in two different steps: first a thick supporting film of Al is deposited on the sputtered side of the membrane and second Al nanowires are grown within the pores. After chemical dissolution of the membrane in dichloromethane, an aluminium foil of a controlled thickness with a three‐dimensional nanowire structure on one side was obtained. Different nanowire architectures, such as free‐standing nanowires, vertically aligned tree‐shaped arrays, and bunched nanowire films, were obtained. Such nanowire architectures are of particular interest for applications in Li‐ion micro‐batteries. 相似文献
5,6,11,12-Tetrahydrodibenzo[a,e]cyclooctene derivatives with α- and β-substituents are readily accessible from [Cr(CO)3(5,6,11,12-tetrahydrodibenzo[a,e]cyclooctene)] 2 via a two-step sequence, which involves addition of a nucleophile and oxidation of the intermediate anionic cyclohexadienyl complex. Nucleophiles used included LiCMe2CN (A), LiCH2CN (B), and (C). The results show that the primary carbanion LiCH2CN and the S-stabilized carbanion give mixtures of α- and β-substituted products and in both cases α-isomers were major, whereas the opposite regioselectivity was obtained with the tertiary carbanion LiCMe2CN. 相似文献
ZnS nanoparticles were precipitated in diluted aqueous solutions of zinc and sulphide ions without capping additives at a temperature interval of 0.5–20°C. ZnS nanoparticles were arranged in large flocs that were disaggregated into smaller agglomerates with hydrodynamic sizes of 70–150 nm depending on temperature. A linear relationship between hydrodynamic radius (Ra) and temperature (T) was theoretically derived as Ra =652 - 2.11 T. The radii of 1.9–2.2 nm of individual ZnS nanoparticles were calculated on the basis of gap energies estimated from their UV absorption spectra. Low zeta potentials of these dispersions of ?5.0 mV to ?6.3 mV did not depend on temperature. Interactions between individual ZnS nanoparticles were modelled in the Material Studio environment. Water molecules were found to stabilize ZnS nanoparticles via electrostatic interactions. 相似文献
Semiconducting ZnO hierarchical nanostructure, where ZnO nanonails were grown on ZnO nanowires, has been fabricated under control experiment with a mixture of ZnO nanopowders and Sn metal powders. Sn nanoparticles are located at or close to the tips of the nanowires and the growth branches, serving as the catalyst for the vapor-liquid-solid growth mechanism. The morphology and microstructure of ZnO nanowire and nanonail were measured by scanning electron microscopy and high-resolution transmission electron microscopy. The long and straight ZnO nanowires grow along [0001] direction. ZnO nanonails are aligned radially with respect to the surface the ZnO nanowire. The long axis direction of nanonails forms an angle of ∼30° to the [0001] direction. 相似文献