Page 91 - Synthesis of Functional Nanoparticles Using an Atmospheric Pressure Microplasma Process - LiangLiang Lin

Solvent-Free Nickel Nanoparticles Synthesis and Engineering ‒Controllable Magnetic Properties
from the hcp to fcc phase. Meanwhile, the plasma power also affects the electron density and energy distribution function (EEDF), which affects precursor dissociation and particle nucleation processes, resulting in products of different size, composition and morphology. In addition to plasma power, another hypothesis is that the control over properties should be achieved by adjusting the precursor concentration, through which particle size, morphology and composition are influenced. Thus, the relationship between experimental conditions and product composition, size, morphology as well as structure is investigated to correlate with their magnetic behavior and to obtain a precise control over those parameters. Furthermore, possible mechanisms for the plasma-assisted nickelocene dissociation are discussed to provide an insight into the complex process.
5.2 Experiment Section
5.2.1 Experimental
In this research Ni nanostructures are synthesized by using nickelocene (Ni(cp)2 or Ni(C5H5)2, Acros-Organics) as the precursor. The detailed information of the plasma setup and the reactor can be referred to the Figure 2.1.
Systematic experiments were carried out to study the influence of processing parameters on the products and their magnetic properties. A detailed list of processing parameters and product properties is given in Table 5.1. Firstly, the effect of discharge power was investigated, when the plasma power was varied from 1.3 W to 3.4 W whilst keeping a constant precursor concentration (35 ppm, condition 1-4). Next the influence of precursor concentration was studied by operating the plasmas in the same power range but with half the precursor concentrations (17.5 ppm, condition 5-8). The typical procedure was as follows: a discharge was ignited in pure argon. After stabilization, Ni(cp)2 vapors were delivered into the discharge through line 1 at a fixed gas flow rate. Meanwhile, the gas flow rate of line 2 was adjusted to maintain the total gas flow at 100 sccm. After a set process time (2 hrs), line 1 was closed and the plasma was sustained for a while in pure argon to flush possible Ni(cp)2 residues, before switching off the discharge.
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