Metallic colloidal nanoparticles

HENGLEIN, A., Nanoclusters of Semiconductors and Metals. Colloidal Nanoparticles of Semiconductors and Metals. Electronic structure and Processes , Ber. Bunsenges. Phys. Chem. 1997, 101, 1562-1572. 

In the present paper, we report on observation of the pronounced enhancement of photoluminescence of semiconductor nanocrystals near nanostructured metal surfaces which is shown to depend essentially on nanocrystal-metal spacing. Unlike conventional SERS, the surface enhanced PL should exhibit non-monotonous character with distance between emitting dipole (QD) and metal surface (Au colloid). The reason is that at smallest distances when QDs and colloidal particles are in close contact, the QD emission should be damped due to resonant energy transfer (RET) from photoexcited QDs to metal colloidal nanoparticles. Enhancement of photoluminescence (PL) is possibly promoted by surface plasmons excited in the metal. So, at a certain distance the enhanced QD emission would exhibit a maximum. We use a polyelectrolyte multilayers as the most appropriate... 

Zhang JZ (1997) Ultrafast studies of electron dynamics in semiconductor and metal colloidal nanoparticles effects of size and surface. Acc Chem Res 30 423-429... 

The first SERS experiments were performed with electrochemically roughened electrodes and metal colloids, and many other types of suitable SERS substrates are known - e.g. metal island films, metal films over nanoparticles (see Fig. 4.58, below) or rough substrates, gratings, and sputter-deposited metal particles. 

Finally, the term steric stabihzation coifid be used to describe protective transition-metal colloids with traditional ligands or solvents [38]. This stabilization occurs by (i) the strong coordination of various metal nanoparticles with ligands such as phosphines [48-51], thiols [52-55], amines [54,56-58], oxazolines [59] or carbon monoxide [51] (ii) weak interactions with solvents such as tetrahydrofuran or various alcohols. Several examples are known with Ru, Ft and Rh nanoparticles [51,60-63]. In a few cases, it has been estab-hshed that a coordinated solvent such as heptanol is present at the surface and acts as a weakly coordinating ligand [61]. 

Bifunctional spacer molecules of different sizes have been used to construct nanoparticle networks formed via self-assembly of arrays of metal colloid particles prepared via reductive stabilization [88,309,310]. A combination of physical methods such as TEM, XAS, ASAXS, metastable impact electron spectroscopy (MIES), and ultraviolet photoelectron spectroscopy (UPS) has revealed that the particles are interlinked through rigid spacer molecules with proton-active functional groups to bind at the active aluminium-carbon sites in the metal-organic protecting shells [88]. 

SERS-active suspensions of elemental metal colloids or nanoparticles of various sizes can be chemically formed in solution. Silver colloids can easily... 

In materials chemistry, nanoparticles of noble metals are an original family of compounds. Well-defined in terms of their size, structure and composition, zero-valent transition-metal colloids provide considerable current interest in a variety of applications. Here, the main interest is their application in catalysis. Zerovalent nanocatalysts can be generated in various media (aqueous, organic, or mixture) from two strategic approaches according to the nature of the precursor, namely (i) mild chemical reduction of transition-metal salt solutions and (ii) metal atom... 

Finally, the development of modified nanoparticles having better stability and a longer lifetime has involved interesting results in diverse catalytic reactions. Efficient activities are obtained with these transition-metal colloids used as catalysts for the hydrogenation of various unsaturated substrates. Consequently, several recent investigations in total, partial or selective hydrogenation have received significant attention. 

There are several bottom-up methods for the preparation of nanoparticles and also colloidal nanometals. Amongst these, the salt-reduction method is one of the most powerful in obtaining monodisperse colloidal particles. Electrochemical methods, which gained prominence recently after the days of Faraday, are not used to prepare colloidal nanoparticles on a large scale [26, 46], The decomposition of lower valent transitional metal complexes is gaining momentum in recent years for the production of uniform particle size nanoparticles in multigram amounts [47,48],... 

A major obstacle in making precise structures with metal colloids has been the control of aggregation and particle size distribution. The use of micelles has allotted some success in this regard with the formation of different metal colloid geometries [30]. It is known that the nanoparticles must be stabilized by organic molecules attached to their surface [31] and in general must be embedded in a solid matrix [32], This is done to prevent agglomeration and precipitation as... 

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