Nanopartides ligand stabilization

Many nanopartide preparations lack suffident stability (above. Fig. 11.5) to allow the ordered assembly of two-dimensional or three-dimensional materials and structures, in which the particles are dosely packed, without the onset of uncontrolled aggregation (agglomeration). To overcome this problem, the partides must be rendered chemically stable, for example by ligand stabilization, also to avoid degradation processes such as partial oxidation or undesired sintering of particles [11.6]. 

The monolayers described so far have all been grown by self-assembly processes, where ligand-stabilized metal nanopartides are deposited on innocent surfaces from solution, followed by a more or less rapid evaporation of the solvent. Depending on the concentration and other experimental conditions, those procedures may occasionally also result in multilayers, or even in small 3-D microcrystals. Self-assembly processes can, however, also be supported by chemical, electrochemical, magnetic, or mechanical effects some examples of these are provided in the following subsections. 

Taken together, these results showed that SET was not only dependent on the nature of the ligands stabilizing the nanopartides, but also on the composition of the solution surrounding the function array. These points would be usefid when studying chemical signal transduction, where SET currents should be sensitive to single redox or analysis events. 

The electrical behavior of the 3-D system is also reflected in the electrical DC and AC response of compacts of ligand-stabilized nanopartides [9]. As a common feature, at high temperatures (i.e., several tens of Kelvin below room temperature), the temperature-dependent DC and AC conductivities follow a simply activated behavior according to the Arrhenius relationship ... 

Transition-metal nanopartides are of fundamental interest and technological importance because of their applications to catalysis [22,104-107]. Synthetic routes to metal nanopartides include evaporation and condensation, and chemical or electrochemical reduction of metal salts in the presence of stabilizers [104,105,108-110]. The purpose of the stabilizers, which include polymers, ligands, and surfactants, is to control particle size and prevent agglomeration. However, stabilizers also passivate cluster surfaces. For some applications, such as catalysis, it is desirable to prepare small, stable, but not-fully-passivated, particles so that substrates can access the encapsulated clusters. Another promising method for preparing clusters and colloids involves the use of templates, such as reverse micelles [111,112] and porous membranes [106,113,114]. However, even this approach results in at least partial passivation and mass transfer limitations unless the template is removed. Unfortunately, removal of the template may re-... 

Usually, nanopartides to be 3-D assembled to superlattices are covered by a shell of stabilizing ligand molecules these protect the particles from coalescence and also make them soluble in appropriate solvents. 

LB nanopartide films provide an opportunity to study interparticle sparing within a monolayer, which depends largely on the sterically stabilizing ligands. For example, Schultz and... 

---