Self-assembly metal nanoparticles

Self-assembled monolayers (SAMs) of organic molecules are known since decades. Self-organized metal nanoparticles have been observed for the first time only about 10 years ago. 

We analyzed the relation between absorbance spectrum of 2D self-assembled silver nanoparticle arrays and size and concentration of the nanoparticles. The high sensitivity of these parameters can be the basis for proper characterization of close-packed metal nanoparticle structures. For express optical diagnostics we provided the simple approximation for dependence of the resonance wavelength on size and surface concentration of nanoparticles. 

Although the self-assembly of nanoparticles on appropriate substrates is, without doubt, the simplest way to produce monolayers, the method suffers from several disadvantages, mainly that little or no influence can be exerted on the structure and extension of the monolayers. The formation of self assembled monolayers (SAMs) depends on experimental conditions, making reproducibflity difficult. Nevertheless, many quite impressive 2-D structures of metal nanopartides have become known during the course of the past decade. 

Self-assembly of nanoparticles with polymers is providing access in order to stabilize metal and semiconductor nanocomposites for fabrication of new materials. Characteristics of the individual building blocks mainly include the following (Skaff et al., 2008) ... 

Figure 4. Experimental design based on the new concept of self organization to obtain a hierarchic dot or stripe pattern composed of metal nanoparticles. Here polymer is used for constructing the super-layer structure with the wavelength X that is chosen by dewetting instability. The patterned polymer islands simultaneously provide the initial and boundary conditions of sub-layer, i.e., the conditions for self-assembly of nanoparticles.

We have discussed in the previous sections about the physical properties and surfactant-assisted self-assembly formations of metal nanoparticles. These assembling methods are quite beautiful and intelligent, because they are induced by the spontaneous driving force for assembling by smart choice of the conditions. In the cases of practical use, however, the methods described below are rather tend to be required (1) the method to make a desirable size, length, shape, architecture and position, etc., (2) a simple and easy method, and (3) highly stable assemblies. From these viewpoints, as a final section for a preparation of nanoparticle assembly, we introduce here the template assisted self-assemblies of nanoparticles. This section is classified to three stories corresponding to the dimension (such as ID, 2D and 3D) of the template and assembly. 

Formation of nanoparticle assemblies in solution has also been conducted. Self-assembly of nanoparticles in solution minimizes or eliminates nonspecific binding of the nanoparticles to the substrate. DNA oligonucleotides were attached to metal colloids (sizes >10 nm) bearing thiolated DNA complements based on the specific molecular recognition of the DNA sequence [1,74,91], producing analytically useful optical information. Alivisatos et al. used a similar approach to produce two-or three-dimensional assemblies of nanoparticles [92,93]. 

Self-assembly of metal nanoparticles, of course, occurs easier the smaller the difference in size and shape of the nanoparticles is. Most of the known 3D assemblies are built of ligand-protected metal nanoparticles. From... 

D self-assembly of metal nanoparticles requires special conditions since 3D growth of any kind of material is preferred. Two principal strategies to generate 2D organizations of metal nanoparticles have been developed during the last 1-2 decades true self-assembly, guided self-assembly and aimed structures. 

It should be mentioned here that Finke s group has added a whole plethora of significant contributions to the field of metal nanoclusters [295-299] including a recent study on the mechanism for the self-assembly of transition metal nanoparticles [294]. 

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]. 

Methods for the design of size- and even shape-controlled [186,190,191,370-372] metallic nanoparticles have reached a rather mature stadium thanks to the contributions of the pioneer groups of the last 25 years. Applications in a number of fields of practical Nanotechnology are now moving fast into the focus of R D [203,373]. For an overview on the potential application of metal nanoparticles in the rapidly growing fields of quantum dots, self-assembly, and electrical properties, the reader is advised to consult recently published specialist review articles, e.g.. Refs. [160,281] and book chapters (cf Chapters 2, 4, and 5 in Ref. [60]). In the following three sub-sections the authors restrict themselves to a brief summary of a few subjects of current practical interest in fields with which they are most familiar. 

On detailed electrical characteristics of a SET transistor utilizing charging effects on metal nanoclusters were reported by Sato et al. [26]. A self-assembled chain of colloidal gold nanoparticles was connected to metal electrodes, which were formed by electron-beam lithography. The cross-linking of the particles as well as their connection to the electrodes results from a linkage by bifunctional organic molecules, which present the tunnel barriers. 

Gold electrodes coated by nanostructured self-assembled monolayer of TMPP and Cl2 are used as template for in situ synthesis of metallic nanoparticles (Figure 2). 

For transition and precious metals, thiols have been successfully employed as the stabilizing reagent (capping reagent) of metal nanoparticles [6]. In such cases, various functionalities can be added to the particles and the obtained nanoparticles may be very unique. It is well known that thiols provide good self-assembled monolayers (SAM) on various metal surfaces. When this SAM technique is applied to the nanoparticle preparation, nanoparticles can be covered constantly by functionalized moieties, which are connected to the terminal of thiol compounds. 

The chapters of the book having been put forward to the reader are related to all practically important fields of interest, discussing a wide frame of points starting from application of nanoparticles in the field of manufacture, the devices for informatics and electronics and ending with self-assembly of metal nanoparticles, their characterization and relevance to biosystems. 

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