Pulse Electrodeposition of Palladium Nanoparticles onto Silicon in DMSO

The deposition of palladium nanoparticles (PdNPs) on the surface of n-Si (100) substrate by pulsed electrolysis in dimethyl sulfoxide (DMSO) solutions of Pd(NO3)2 was investigated. It has been shown that nonaqueous medium (DMSO) contributes the Pd (II) recovery at high cathode potential values avoiding side processes to occur. In combination with the pulse mode, this allows the deposition of spherical PdNPs with their uniform distribution on the silicon surface. We established that the main factors influencing the geometry of PdNPs are the value of the cathode potential, the concentration of palladium ions in solution, and the number of pulse-pause cycles. It is shown that with increasing Ecathode value there is a tendency to increase the density of silicon surface filling with nanoparticles. As the concentration of Pd(NO3)2 increases from 1 to 6 mM, the density of silicon surface filling with PdNPs and their average size also increase. We found that with increasing the number of pulse-pause cycles, there is a predominant growth of nanoparticles in diameter, which causes 2D filling of the substrate surface.

Precipitation: Structures and Mechanisms

The formation of a solid, and especially an oxide, from soluble metal complexes is usually called “precipitation.” This term is a generic name that includes a set of complex and intricate phenomena. The process is governed by thermodynamic, structural, and kinetic contingencies, which should be examined in detail to understand the role of synthesis conditions and their influence on the solid obtained. The chemistry of the process involves a condensation reaction, olation or oxolation, between uncharged hydroxylated complexes. It forms particles of widely variable size over the nano- to micrometric range. These particles are portions of a solid identifiable in using techniques such as X-ray diffraction, absorption, and diffusion, electron microscopy, light-scattering, and various spectroscopies. Of course, these particles have the properties typical of the corresponding bulky solid, but they may be modulated because of the size effect, especially in the nanometric range (Chap. 1). Because of their small size, these objects have a large surface area highlighting their surface physicochemistry, such as ability to disperse in aqueous or nonaqueous medium, to aggregate, and to fix various species from solution, that allows the surface energy to be controlled to adjust the shape and size of these objects (Chap. 5). The crystal structure of polymorphic solids can also be controlled by the choice of the pathway of their formation. Thus, knowledge of the processes involved allows us to exploit the large versatility of the nanostructures synthesized in solution. This chapter has two main objectives. The first is to show that the crystalline structure of the solid may in many cases be anticipated from the characteristics of the precursor in solution, such as functionality, geometry, reactivity, and elec­tron configuration. This point concerns the structural aspect of the formation of the solid. The second objective is to understand why precipitation forms small particles, generally of nano- or micrometric size, and how the crystallization mechanism influences their morphology. These questions concern the kinetics and dynamics of the precipitation phenomenon.