(5) The edge of substrate will gathered deposition solution to cause non-uniform films.
The dip coating process can be separated into five procedures:
(1) The substrate is immersed in the solution of the coating material at a constant speed.
(2) The substrate has remained inside the solution for a while and is started to been pulled up.
(3) The thin layer deposits itself on the substrate while it is pulled up.
The withdrawing is carried out at a constant speed to avoid any vibration. The speed plays an important role to determine the thickness of the coating layer.
(4) Excess fluid will drain from the substrate surface.
(5) The solvent of the fluid will evaporate when forming the thin film.
Evaporation starts already during the deposition and drainage steps for volatile solvents, such as alcohols.
2.4 Atmospheric pressure plasma system
2.4.1 Corona discharge
A corona is a process by which a current develops between two high-potential electrodes in air, by ionizing that fluid to create a plasma around one electrode, and by using the ions generated in plasma processes as the charge carriers to the other electrode.
It usually involves two asymmetric electrodes in corona discharge, one highly curved such as the tip of a needle or a narrow wire, and
25 corona, if the curved electrode is positive associated to the flat electrode, and vice versa. The physics of positive and negative coronas are obviously different. This asymmetry structure is a result of the great difference in mass between electrons and positively charged ions, and so only the electron having the ability to undergo a significant degree of ionizing inelastic collision at common temperature and pressures.
2.4.2 Dielectric barrier discharge (DBD)
Dielectric barrier discharges involve a specific class of high voltage, ac, gaseous discharges that typically operate in the near atmospheric pressure range. Their defining feature is the presence of dielectric layers that make it impossible for charges generated in the gas to reach the conducting electrode surfaces. The voltage applied across the gas exceeds that required for breakdown with each half cycle of the driving oscillate, and the formation of narrow discharge filaments initiates the conduction of electrons toward the more positive electrode. The voltage drop across the filament is reduced until it falls below the discharge sustaining level as charge accumulates on the dielectric layer at the end of each filament, so the discharge is quenched. The low charge mobility on the dielectric not only contributes to this self-arresting of filaments but also limits the
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lateral region over which the gap voltage is diminished, thereby allowing parallel filaments to form in close proximity to one another. Thus, the entire gas filled space between parallel electrodes can become, on average, uniformly covered by transient discharge filaments, each roughly 0.1mm in diameter and lasting only about 10ns.
The DBD’s has provided the basis for a broad range of applications and fundamental studies, because of the unique combination of non-equilibrium and quasi-continuous behavior. It has generated interest in optimizing conditions for specific chemical reactions in industrial ozone reactors. To this end, experimental DBD studies have explored different gas mixtures, electrical characteristics, and geometries. The related work has focused on maximizing the ultraviolet radiation from excimer molecules produced in DBD’s. Several researchers have designed single filament dynamics in order to account for the many reactions including electrons, ions, neutral atoms, and photons. These efforts have been moderately successful in explaining and predicting the chemical and radiative properties of different DBD systems. On another research effort, it has been seen that the transverse spatial distribution of discharge filaments in 2D, parallel plate DBD’s can take the form of stable, large scale patterns reminiscent of those associated with magnetic domains. These patterns have been modeled with some success using methods that apply generally to pattern formation in nonlinear dynamical systems. Thus, the dynamical interactions between filaments, as well as the chemical and electronic interactions within filaments have proven interesting.
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2.4.3 Atmospheric pressure plasma jet
Atmospheric pressure plasma jet is meaning that operating at
atmospheric pressure and it is non-thermal glow discharge plasma system.
The non-thermal plasma generates highly reactive ions, electrons and free radicals. The reactive species are directed onto a surface where the desired chemistry occurs. However the overall gas temperature remains quite cold, but the electrons are quite hot, typically 50-300°C.
2.4.4 Arc plasma
The operation of arc plasma is similar to an arc-welding machine, where an electrical arc is struck between two electrodes. The high energy of arc creates high temperatures ranging from 3000°C to 7000°C. The plasma is highly ionized gas which is enclosed in a chamber. The waste material is fed into the chamber and the intense heat of the plasma break down organic molecules into their elemental atoms. In the strict control of the process, these atoms recombine into harmless gases, such as carbon dioxide. Solids such as glass and metals are melted to form materials, similar to hardened lava, in which toxic metals are encapsulated. There is no burning or incineration and no formation of ash with plasma arc technology. There are two main types of plasma arc processes: plasma arc melter and plasma torch.
Plasma arc melters have very high destruction efficiency. They are very robust; they can treat any waste with minimal or no pretreatment;
and they produce a stable waste form. The arc melter uses carbon electrodes to strike an arc in a bath of molten slag. The consumable
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carbon electrodes are continuously inserted into the chamber, eliminating the need to shut down for electrode replacement or maintenance. The high temperatures produced by the arc convert the organic waste into light organics and primary elements.
Combustible gas is cleaned in the off-gas system and oxidized to CO2 and H2O in ceramic bed oxidizers. Due to the use of electrical heating in the absence of free oxygen, the potential for air pollution is low.
The inorganic portion of the waste is retained in a stable, leach-resistant slag.
In plasma torch systems, an arc is struck between a copper electrode and either a bath of molten slag or another electrode of opposite polarity.
Plasma torch systems have very high destruction efficiency with plasma arc systems; they are very robust; and they can treat any waste or medium with minimal or no pre-treatment. The inorganic portion of the waste is retained in a stable, leach-resistant slag. The air pollution control system is larger than for the plasma arc system, due to the need to stabilize torch gas.
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A
B
Figure 2-1 (a) Top Gate Structure (b) Bottom Gate Structure
(a) (b)
Figure 2-2 (a) PMOLED (b) PMOLED Control Circuit
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(a) (b)
Figure 2-3 (a) AMOLED (b) AMOLED Control Circuit
Figure 2-4. Energy band diagrams for a metal-insulator-semiconductor capacitor, assuming a unipolar n-type semiconductor under three gate bias conditions: (a) no bias, (b) negative bias, and (c) positive bias.
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Figure 2-5 Schematic illustration of magnetron sputtering [62].
Figure 2-6 Schematic illustration of a Pulsed laser deposition system [63].
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Figure 2-7 Description of the deposition process with raising the substrate temperature [64].
.
Figure 2-8 Schematic illustration of equipment for spray pyrolysis deposition [64].
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Figure 2-9 Sol-gel process
Figure 2-10 Steps of the dip coating process: dipping of the substrate into the coating solution, wet layer formation by withdrawing the substrate and gelation of the layer by solvent evaporation [65].
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Figure 2-11 Schematic the principle of corona discharge [66].
Figure 2-12 Schematic illustration of the DBD configurations [67].
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Figure 2-13 Schematic illustration of the AP plasma jet structures [68].
Figure 2-14 Schematic illustration of the arc plasma [69].
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Table 2-1 Density of charge species in the plasma discharge [70]
Source Plasma density (cm-3)
Low pressure discharge 108-1013 Arc and plasma torch 1016-1019
Corona discharge 109-1013
Dielectric barrier discharge 1012-1015 Capacitive discharge 1011-1012
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