3D assemblies

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... 

Figure 16. Illustration of the formation of 3D assemblies of bare AU55 nanoclusters in an envelope of dendrimer molecules. (Reprinted from Ref. [38], 2000, with permission from Wiley-VCH.)...

Figure 4. TEM images of (A) a 2D assembly of the 11 nm Co nanoparticles, and (B) a 3D assembly of the 8 nm cobalt nanoparticles on an amorphous carbon surface.

Fig. 11 Process of the DNA-based colloidal nanoparticle assembly, a Base-pairing interactions induced assembly in ID template, b Immobilization by DNA hybridization onto 2D surface, c 3D assembly by duplex DNA interconnects...

D organization of metal nanoparticles is easy to be reached compared with 2D or even ID, since nature tends to organize itself three-, but not two- or one-dimensionally. The most convenient way to get 3D assemblies of metal nanoparticles is to let them crystallize. Usually crystallization happens with identical molecules or with oppositely charged ions. Surprisingly, nanoparticles can form 3D crystals even if they are not identical in size and shape however, it is obvious that deviations should be as small as possible. 

D assemblies of magnetic nanoparticles are formed if solntions of the corresponding particles are slowly reduced in volume or by careful destabilization of a solution by letting slowly diffuse a nonsolvent into the solution to get an oversaturation. Such procedures are in principle well known as crystallisation techniques also for nonmagnetic particles. 3D assemblies of up to several micrometers of cobalt," nickel," FePt," " or CoPtj" have been generated by one of these traditional routes. 

STED microscopy has important applications outside biology as well. For example, it currently is the only method to locally and noninvasively resolve the 3D assembly of packed nanosized colloidal particles [98,99]. In the realm of solid-state physics, STED microscopy has recently imaged densely packed fluorescent color centers in crystals, specifically charged nitrogen vacancy (NV) centers in diamonds [100]. NV centers in diamond have attracted attention, because of their potential application in quantum cryptography and... 

An example of a molecule that self-assembles to give a finite 3D assembly is triphenylmethanol.32 The alcohol has been shown to self-assemble in the solid state, via O-H-O hydrogen bonds, to form a tetramer, with the point group C3 and a structure that conforms to a molecular tetrahedron (Fig. 14). The hydrogen bonds exhibited substantial dynamic disorder in the solid. Each molecule sits at the corner of the tetrahedron with the phenyl rings in propeller-like conformations. 

Of those functional crystalline assemblies with structures that conform to polyhedra, it is the prisms that have, thus far, been most studied. In particular, Rein-houdt has described a 3D assembly with a structure that conforms to the simplest prism namely, a trigonal prism.53 Specifically, three calix[4]arenes functionalized at the upper rim with two melamine units have been shown to assemble with six barbituric acid molecules via 36 hydrogen bonds to form a nine-component assembly with a structure that approximated a trigonal prism (Fig. 31). Although the cavity of the assembly was too small to accommodate a guest, the assembly packed to produce voids that included toluene molecules as guests. 

Sinee the soft-landing bottom-up growth of polyerystalline layered ultra-thin films is not limited by the solubility or volatility of the moleeule, it is ideal for producing ultra-pure ordered architectures of giant moleeular systems with enhanced and novel functionalities. This method ean be extended to the eontrolled layer-by-layer deposition of different eomponents up to 3D assemblies. 

EXPERIMENTS RELATED TO THE DEVELOPMENT OF FLUID DYNAMICALLY DRIVEN 3D ASSEMBLY PROCESSES... 

Very available and promising square panels are tetrapyridyl porphyrins 15 and 16. In fact, 4-pyridyl-substituted porphyrin 15 has been frequently employed for infinite assemblies. In contrast, there seems to be difficulty in constructing discrete 3D assemblies from tetrapyridyl porphyrins, though there are some examples of 2D assemblies such as porphyrin squares 17 [27] and 18 [28] from dipyridyl porphyrins. 

Whereas no 3D assemblies from 4-pyridyl-substituted porphyrins have been reported, there is a successful 3D assembly from 3-pyridyl-substituted porphyrin 19. Upon treatment of 19 with the Pd(II) component 1, the porphyrin prism 20 is assembled (Scheme 7) [29]. This compound can accommodate large organic molecules in the cavity surrounded by three porphyrin panels. 

The next step is to find out the possibilities for extending the detected limits of conventional SMD assembly systems. The insufficiency of Cartesian systems lies in the possible height and angle of inclination of the MID and the fact that an unlimited length of free assembly perpendicular is required. A concept has been developed to extend these limits. A module for handling the MID in the workspace of an SMD assembling system, as well as the use of a pipette with an additional axis, make 3D assembly of component onto MID possible. 

Eigure 45 Prototypical Realization of MID Placement System for 3D assembly. (From Feldmann et al. 1998)... 

Figure 8 Pipe Laying in a 3D Assembly. (Unigraphics. Reproduced with permission of Unigraphics Solutions)...

Figure 10 2D Design of a Wiring Harness. (Pro/DIAGRAM System, PTC) and Parametric Cable Layout in the 3D Assembly. (Pro/CABLING, PTC) Reprinted by permission of PTC.

The outline of the paper is therefore as follows In section 1 we introduce the main interaction forces acting on colloidal particles, as well as the concept of nanostructured materials, in the form of 2D and 3D assemblies. We discuss the main stabilization techniques employed in the synthesis of nanoparticles in solution. Then we outline in section 2 the procedures involved in silica coating, and discuss its advantages as a general stabilization technique. Section 3 deals with the special properties of both metal and semiconductor nanoparticles, summarizing their... 

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