Metal nucleation

Since the separation between the tip and the surface is such that their respective double layers do not overlap, the nanostmcturing process can be described simply through the diffusion of the ions toward the surface. Thus, the concentration profiles of the diffusing ions dehne effective Nemst potential prohles that can be employed to predict the regions where the oversaturation conditions will contribute to metal nucleation and growth. 

As far as SAM-controlled electrochemical metal deposition is concerned, substantial interest derives from microelectronics with its need to control the generation of interconnects and, thus, to understand the influence of organic layers on the metal nucleation and growth. However, the scope of this topic reaches well bqfond that, as illustrated by the substantial range of potential applications where small-scaled metal structures are of crucial importance, for example in electrochemical [31] and optical [32] sensing, molecular electronics [33], for plasmonics [34], or as metamaterials [35]. 

The local resolution of laser-induced reactions depends on primary effects, i.e., the laser light, and secondary effects induced by the system. Laser-induced metal nucleation and crystal growth and the relevant mechanisms depend mainly on the electronic properties of the substrate, but also on interfacial and electrolyte properties. Depending on the system parameters, focused laser light can influence overvoltage-dependent terms particularly by local heat formation or by local activation of the solid state/electrolyte interface. As the electric properties of the substrate material is of strong influence, the effects will briefly be discussed for metal, semiconductor and polymer substrates. 

Photoexcited hot electrons may further be emitted from metals into electrolyte solutions [6.119]. Once electrons have been emitted into the solvent, they can diffuse back to the emitter and be recaptured by the electrode, or they are scavenged by redox acceptor species within the picosecond time range. Protons appeared to be a very effective scavenger [6.120]. Particularly, subpicosecond laser-induced nonequilibrium hot electrons lead to high emission electron rates which can react with acceptors to form intermediates. This is followed by localized metal nucleation [6.121]. 

Again, photoelectron emission of semiconducting substrates can take place in metal nucleation. In addition, a complementary photoeffect, the photoemission of excited holes and oxidative decomposition of water, has to be considered in analogy to n-type semiconductors. 

The mechanism of the process is that the polymer reactive centers promote the metal nucleation and aggregation, after which the thermolysis occurs and the metal-containing substance is redistributed. The maximum amount of copper being introduced in PS through a common solvent is about 10%. At the same time, the polymer presence increases the temperature of cadmium trihydrate-oxalate decomposition [97], and the decay products increase the initial temperature of PETF intensive destruction. The copper formate thermal decomposition in the highly dispersed PETF presence allows us to produce a metallopolymeric composition (20-34% of copper) where the NP size distribution is maximal at 4nm, without any chemical interaction between the components. 

Galvanostatic reduction is another alternative for metal electrocrystallization in CPs. The metal nucleation and growth occurs at a continuously varying overpotential and therefore it is not suitable for gaining insight into the kinetics of the metal electrodeposition. Nevertheless, this approach provides a helpful opportunity to assess the involvement of CP reduction in the overall process, and to explore fine differences in the reductive behavior of CP materials synthesized under various electrochemical conditions [180-183,185,189]. 

Finally, recent investigations on mild UV-laser surface treatment of PEDOT layers [208,209] have shown that the surface chemical state of the polymer can become modified without any appreciable effect on the CP bulk properties. It was found [208] that UV-laser treatment results in activation of the surface with respect to metal nucleation and an increase in the number of dqjosited crystals by preserving a mono-disperse size distribution (Figure 7.7 c and d). 

---