1.4 Formation and growth of dust particles in a plasma

An innovative feature of plasmas is that comprise chemically energetic species which grow the dust particles. It is true for plasma appliances that are using in the plasma processing semiconductor engineering, in which combinations of gases such as oxygen (O2), argon (Ar), and silane (SiH4) are castoff in the assembly and figments of microelectronic chips. Dust particles could also produce through sputtering, arcing, electron bombardment, etc., where the atoms or molecules from the walls of chamber or electrodes come out and immersed in the plasmatic system through a different mechanism, called plasma-material interaction [8]. Plasma processing devices are employed for the production of silicon wafers characteristically used as parallel plate electrode, in which 13.56 MHz radio frequency (rf) power is connected to the lower electrode to create the plasma. Etching process involves a reactive species such as silane along with a buffer gas like Ar. Plasmaaided gas phase chemical reactions produced silicon hydride (SiH2) by the reaction {e� + SiH4 ! (SiH4)\* ! SiH2 + 2H}. The vibrationally excited state is produced by the collisions of SiH4 with electrons which then dissociates into SiH2 [9]. The particle that grows in plasmas passes through certain phases like nucleation, coagulation, and surface growth.

the grain depends on the relative velocity between the plasma species and the grain. Electrons are repelled and the grain current will be decreased if surface potential is negative. Electrons show attraction and the grain current increases for positive

Non-Newtonian Dynamics with Heat Transport in Complex Systems

DOI: http://dx.doi.org/10.5772/intechopen.82291

In dusty plasma, the dust particles can have any shape and can be made of either dielectric or conducting materials. The size of dust particles is much larger than the size of electrons and ions of plasmas which is in microns or tens of nanometers. So, the dust particles can easily be seen without any microscope. The typical size range of dust particles is from 100 nm up to about 100 μm. For experimental studies, dust particles that are distributed into plasmas are generally plastic or glass particles (commonly used particle is melamine formaldehyde). They are spherical in shape with a very narrow distribution of diameters. For example, the diameter of a normally used particle may be 3.50 � 0.05 <sup>μ</sup>m and a mass � <sup>3</sup> � <sup>10</sup>�<sup>11</sup> kg. Such particles are named monodisperse. Fine powders, such as aluminum silicate (kaolin) with a broad size distribution ranging from the submicron to tens of microns, are used in some experiments. Such powders contain particles having

When the dust particles are immersed in the plasma, then various forces are acting on the dust particles which are significant because of their dynamics and transport characteristics. These various forces determine that where the particles are trapped or not, and these are sensitive to the position of dust particles within the

The dust particles which are under a gravitational force are proportional to the mass of dust particle, and if dust particles are under microgravity condition, then it

where "g" describes the gravitational acceleration and "ρd" represents the mass density of dust particles. Mostly, its value for solid materials is ρ<sup>d</sup> = 2000 kg/m3

For plasma having an electric field (E), the electric force acting on dust species is

This force is much larger in the bulk of the plasmas, while it is much smaller in the sheaths next to the plasma edge. For example, for characteristic radio frequency

This force can be neglected for submicron particles, but for the micron sized or larger particles, this can be considered as the dominant force that typically confines

the time during which the particle resides in the plasmas.

<sup>3</sup> <sup>π</sup>a<sup>3</sup>

ρ<sup>d</sup> g (1)

Fe ¼ QE (2)

.

Fg <sup>¼</sup> mgd <sup>¼</sup> <sup>4</sup>

potential surface.

1.5.2 Size of dust particle

laminar shapes with jagged edges.

plasmas.

1.6.1 Force of gravity (Fg)

1.6.2 The electric force (Fe)

written as:

173

must be ignored.

1.6 Forces acting on dust particles in a plasma

### 1.5 Dust particle in the plasma

Dust particles are found everywhere in the entire universe with different shapes and sizes and mostly found in the solid form but also found in the liquid and gaseous ionized form. When the dust particles coexist with the plasma, then "dusty (complex) plasma" is formed. Dust particles acquire an electric negative charge, when these dust particles are immersed in the plasma and then affected by electric and magnetic fields and plasma properties are changed. Moreover, these dust particles attain electric negative charge (typically depends on the flow of ions and electrons) very fast due to the interactions between the dust particles and the nearby plasmas.

In recent years, dusty plasmas have opened up an entirely new field of research of science and technology by investigating transport properties (thermal conductivity, shear viscosity, and diffusion coefficient) of dusty plasmas in the laboratory.

### 1.5.1 Charge on dust particle

A lot of mechanisms are adopted to produce charge on a dust particle. If all mechanisms are considered at once, then the measurement of the equilibrium charge condition on a grain becomes very difficult. For the electron temperature T<sup>e</sup> and ions temperature Ti, the flux of ions and electrons has an individual thermal velocity vte. The thermal velocity of electron is higher than that of the heavier ions which have a minute thermal velocity vti. These motions develop the charge Q on the grain and make its surface potential (ϕs) negative. The charge on a grain fluctuates continuously due to the collective current of electron and ion, i.e., dQ/dt = Ie + Ii and equilibrium of charge occurs under condition Ie + Ii = 0 or ϕ<sup>s</sup> = �2.49kT/e for an electron-ion plasma. The charge itself is associated to the surface potential by Q = Cϕs, in which C tells about the capacitance of a grain in a plasma [10]. The dust particle density differs from the density of electrons and ions because in normal plasma, neutral n<sup>0</sup> exists. If the primary electrons are very energetic, then they release subordinate electrons, which make the positive potential surface. The absorption of plasma ions also makes the positive potential surface. The transition of primary electrons and ions influenced by the surface potential of

the grain depends on the relative velocity between the plasma species and the grain. Electrons are repelled and the grain current will be decreased if surface potential is negative. Electrons show attraction and the grain current increases for positive potential surface.
