ISSN:0005-9021    

DOI:10.1002/bbpc.19971011102

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1997

数据来源: WILEY

摘要:

AbstractThe electronics of colloidal nano‐particles of semiconductors and metals has been one of the fastest growing research fields in physical chemistry for the past 10 years. The historical development is briefly reviewed and a number of fundamental effects and processes are described. They include the transition from the compact material to the atom, heterogeneous photo‐catalysis, and various aspects of nano‐electrochemistry, such as the storage of excess electrons and metal deposition on nano‐particles. Preparative aspects, such as the synthesis of composite metal and semiconductor particles and of nano‐crystals of semiconductors are also

ISSN:0005-9021    

DOI:10.1002/bbpc.19971011103

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1997

数据来源: WILEY

摘要:

AbstractIn contrast to extended solids, nanometer size crystals convert from one structure to another by single nucleation events, and the transformation obey simple kinetics. Barrier heights are observed to increase in nanocrystals of larger size, but also depend on the nature of the nanocrystal surface. These results are analogous to magnetic phase transitions in nanocrystals and suggest some general rules which may be of use in the discovery of new metastable phases.

ISSN:0005-9021    

DOI:10.1002/bbpc.19971011104

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1997

数据来源: WILEY

摘要:

AbstractIn this paper we show that the use of colloidal assemblies as templates favors the control of the size and shape of nanoparticles. As expected theoretically, the change in size and shape of copper metal nanosized particles induces changes in their optical properties. Cylindrical copper metal particles having the same size and shape can be obtained in various regions of the phase diagram when the template is made of interconnected cylinders.Self‐assembly of silver and silver sulfide nanoparticles is reported. Monolayers of particles organized in a hexagonal network are formed over very large domains. Small or large aggregates can also be produced and, in these aggregates, the particles are highly organized and form pseudo‐crystals with a face‐centered cubic structure for various particle

ISSN:0005-9021    

DOI:10.1002/bbpc.19971011105

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1997

数据来源: WILEY

摘要:

AbstractA method of synthesis for cadmium selenide and cadmium telluride clusters is proposed. PhSeSiMe3reacts with [CdCl2(PPh3)2] to yield a series of cadmium selenide clusters depending on the kind of solvent used. The reaction of PhTeSiMe3with CdCl2and PEt3yields a cadmium telluride cluster. Crystalline products suitable for single‐crystal X‐ray analysis could be obtained. We describe the molecular structures of [Cd17Se4(SePh)24(PPh3)4][Cd8Se(SePh)12Cl4] (1), [Cd(DMF)6][Cd8Se(SePh)12Cl4] (2), [Cd8Se(SePh)14(PPh3)2] (3), [Cd8Se(SePh)14(DMF)3] (4) and [Cd8Te(TePh)14(PEt3)3]

ISSN:0005-9021    

DOI:10.1002/bbpc.19971011106

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1997

数据来源: WILEY

摘要:

AbstractMetal clusters exhibit unique optical properties due to the excitation of Mie plasmon resonances. It is well known since decades that measured resonances of clusters, surrounded by some adsorbate, or some solid or liquid embedding material (as e.g., in colloidal systems), are often not described quantitatively by Mie's theory. Only recently, these discrepancies were traced back to complex physical and chemical influences of the cluster‐matrix interlayer onto the optical response. They prove often to be more important than cluster size effects.These findings opened a new field of surface/interface research where deviations of measured Mie resonances from the predictions of Mie's theory are used as sensitive sensors for physical and chemical interface properties and processes in cluster‐matter.By combining optical spectroscopy experiments on free clusters in UHV and on the same clusters after embedding, this method was calibrated to separate, quantitatively, the cluster‐matrix interface effects from other cluster effects like shape and structure effects, nonlocal dielectric effects and cluster size effects.Among all metals, silver exhibits the most pronounced Mie resonances, so silver clusters were used as model systems and were embedded in a broad variety of solid and liquid embedding media, in course of the investigations reported in the present Progress Report.A theoretical description of the obtained data, based upon static and dynamic charge transfer processes of the cluster electrons into/out of adsorbate states is, however, only at its beginning. It allows to ascribe the extremely short decay times of the resonances of the order of 1 to 10 fs to phase relaxation processes; the decay times are in good correspondence with results of direct femtosecond‐expe

ISSN:0005-9021    

DOI:10.1002/bbpc.19971011107

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1997

数据来源: WILEY

摘要:

AbstractIn ten years fullerenes have gone from structural speculation to single crystals as ever more efficient preparation and separation procedures have been developed. Today fullerene solids comprise an extensive family of all‐carbon materials assembled from a large number of different ∼ 1 nm sized subunits. We discuss a number of issues related to the unique electronic and geometric structure of these molecular subun

ISSN:0005-9021    

DOI:10.1002/bbpc.19971011108

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1997

数据来源: WILEY

摘要:

AbstractTemperature‐dependent EXAFS (Extended X‐ray Absorption Fine Structure) measurements between 5 and 290 K show that structural and dynamic properties of CdS nanoparticles with 13‐120 Å diameter depend on their particle size and the way of surface stabilization. The mean Cd‐S distance of thiolcapped CdS nanoparticles (13‐40 Å) increases with decreasing particle size with respect to CdS bulk. In contrast, mean interatomic distances in polyphosphate‐stabilized particles (30‐120 Å) are slightly contracted. This demonstrates that the covalently bound thiol ligands induce the nanocluster lattice expansion. From the temperature dependence of the mean‐square relative displacement (MSRD), a slight stiffening of the Cd‐S bond can be observed with decreasing particle size. The static part of the MSRD, reflecting static disorder of the Cd‐S bond, exhibits a maximum at cluster sizes of about 30 Å. For particles larger than 30 Å diameter, the increase of the static disorder follows the change of the surface to volume ratio. This ratio also determines the size dependence of the asymmetry of the interatomic Cd‐S pair potential. Furthermore, in CdS bulk and CdS nanoparticles with the thermodynamically favored wurtzite structure this asymmetry is significantly enlarged in comparison to nanoparticles

ISSN:0005-9021    

DOI:10.1002/bbpc.19971011109

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1997

数据来源: WILEY

摘要:

AbstractColloidal gold and silver are difficult to manipulate. The surfaces are normally coated with organic acids or polymers, and conventional methods for thin metal oxide coatings normally result in clumping and heterocoagulation. We have recently developed a method to silica‐coated gold and silver particles which avoids any particle coalescence. The method can be applied to a wide range of nanoparticles [1,2]. In this report we present some results from studies into chemical reactions of nanosized coated metal particles using high resolution transmission electron microscopy. The chemical reactions were carried out on silica‐coated silver and gold nanoparticles in aqueous solution. The reaction of a single Ag@SiO2nanoparticle with I2to form AgI was monitored directly by transmission electron microscopy. As well the dissolution of Au cores by cyanide ion led to the creation of monodisperse, hollow, nanosized silica partic

ISSN:0005-9021    

DOI:10.1002/bbpc.19971011110

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1997

数据来源: WILEY

摘要:

AbstractThe structural and optical properties of heterogeneous semiconductor nanoparticles consisting of CdS and HgS are investigated by High Resolution Electron Microscopy (HRTEM) and selective spectroscopy like Hole Burning (HB) and Fluorescence Line Narrowing (FLN). The HRTEM study shows that epitaxy is possible in nanocrystals, provided the crystallites have well defined faceted shapes to begin with. From the HB‐ and FLN experiments homogeneous absorption and fluorescence spectra are calculated. It could be shown that the absorption is coupled to HgS‐like phonons (250 cm−1) whereas the emission frequency is closer to the LO phonon frequency o

ISSN:0005-9021    

DOI:10.1002/bbpc.19971011111

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1997

数据来源: WILEY