Nanocrystals multilayer assemblies

Multilayer assemblies using monothiols are generally fragile. Multilayer deposition of nanocrystals is best achieved by the sequential adsorption of dithiol... 

Multilayer assemblies of nanocrystals of CdSe are generally fragile and are not suited for use in functional devices. Assemblies involving alternate layers of nanocrystals and linkers are relatively robust. The method of layer-by-layer deposition has received a good deal of attention over the last few years, since it provides a convenient low-cost means to prepare ultrathin films of controlled thickness, suited for device applications. In a typical experiment, one end of a monolayer forming a bifunctional spacer, is tethered to a flat substrate such... 

Synthesis of DNA-Au hybrid nanocomposites holds promise for applications in nanotechnology. Following the pioneering work of Mirkin et al., these modified Au nanopartides can act as useful building blocks to form spatially well-defined superstructures, including nanocrystals [108], binary and multilayered nanoparticle assemblies [109,110] and also well-ordered 3D nanoclusters [111]. 

Finally, zeolite nanoparticles have been used as building blocks to construct hierarchical self-standing porous stmctures. For example, multilayers of colloidal zeolite crystals have been coated on polystyrene beads with a size of less than 10 p,m [271,272]. Also, silicalite-1 membranes with a thickness ranging from 20 to several millimeters and controlled mesoporosity [273] have been synthesized by the self-assembly of zeolite nanocrystals followed by high-pressure compression and controlled secondary crystal growth via microwave heating. These structures could be useful for separation and catalysis applications. 

Several polymer/polyelectrolyte-nanocrystal hybrid devices have been fabricated seeking to exploit the electro and photoluminescent properties of such material [179-188]. Device fabrication in all these cases is by low-cost self-assembly based techniques. These devices utilize thin films of these hybrids obtained either by multilayer deposition or drop/spin casting methods. Thus, solar cells have been made from poly(2-hexylthiophene)-CdSe nanorod multilayers, lasers from drop cast films of CdSe-titania composites and an infrared emitter from multilayers... 

As demonstrated by Heath et al., application of the LB technique in conjunction with semiconductor nanoparticies may lead to the generation of tunnel diodes [60]. These devices consist of a monolayer of 3.8 nm CdSe nanocrystals and an insulating bilayer of eicosanoic acid, sandwiched between an Au and an Al electrode. Advanced spectroscopic techniques such as attenuated low-energy photoelectron spectroscopy were also applied to LB-derived multilayered nanostructured assemblies of differently sized CdS particles [61]. Recent examples of applications of the LB technique... 

Extrusion and impregnation, electrospinning, and multilayer films are other processes applicable for reinforced nanocomposites. Thus, preparation of cellulose whiskers reinforced with polylactic acid nanocomposites (by melt extrusion carried out by pumping the suspension of nanocrystals into the polymer melt during the extrusion process), using polyvinyl alcohol as a compatibilizer for the dispersion of cellulose whiskers within the polylactic acid matrix, was reported (de Menezes et al. 2009) bacterial cellulose whiskers incorporated into poly(oxyethylene) nanofibers by electrospinn to enhance the mechanical properties of electrospun fibers (Peresin et al. 2010) or the use of the layer-by-layer assembly technique, which maximizes the interaction between cellulose whiskers and a polar polymeric matrix (Bruno et al. 2009 Aulin et al. 2010), are some examples of nanocomposites reinforced by the last three methods. 

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