The modification of a surface by application of a thin film, plasma enhancement, ion bombardment, self-assembly, nanomachining, chemical treatment, or other processes is called Surface engineering[a].
Surface engineering techniques are now being used in virtually every area of technology, including automotive, aerospace, missile, power, electronic, biomedical, textile, petroleum, petrochemical, chemical, steel, power, cement, machine tools, and construction industries. They are being used to develop a wide range of advanced functional properties, including physical, chemical, electrical, electronic, magnetic, mechanical, wear-resistant, and corrosion-resistant properties at the required substrate surfaces. Almost all types of materials, including metals, ceramics, polymers, and composites, can be deposited onto similar or dissimilar materials. It is also possible to form coatings of advanced materials (e.g. met glass, polymers, superlattices, photocatalysts), graded deposits, metamaterials, multicomponent deposits, etc.[]
Thin film coatings are used to modify the physical and chemical properties and morphology of a surface, which makes them a broad subset of surface engineering. A thin film can consist of one homogeneous composition, crystalline phase composition and microstructure, or have an inhomogeneous multilayer or composite structure. The structure of the multilayer can be periodic, have a set pattern or be entirely random. Examples of periodic structures are optical multilayer coatings, superlattices, and nanolaminates. Nanocomposites can be random or periodic in nature.
Thin films have distinct advantages over bulk materials. Because most processes used to deposit thin films are non-equilibrium in nature.
THIN FILM DEPOSITION PROCESSESS
Virtually every property of the thin film depends on and can be modified by the deposition process and not all processes produce materials with the same properties []. Microstructure, surface morphology, tribological, electrical, and optical properties of the thin film are all controlled by the deposition process. A single material can be used in several different applications and technologies, and the optimum properties for each application may depend on the deposition process used. Since not all deposit technologies yield the same properties or microstructures, the deposition process must be chosen to fit the required properties and application. Several publications have presented a detailed review of thin-film deposition processes;[1 Bunshah, R. F., (ed.), Deposition Technologies for Films and Coatings, Noyes Publications, NJ, (1982); Mattox, D. M., Handbook of Physical Vapor Deposition Processing, Noyes Publications, NJ (1998); Mahan, J. E., Physical Vapor Deposition of Thin Films, John Wiley & Sons, New York (2000); Elshabini-Riad, A., and Barlow, F. D., III, (ed.), Thin Film Technology Handbook, McGraw-Hill, New York (1997)] thus only brief descriptions of the thin-film deposition processes are presented in this chapter.
It is informative to list the steps in the formation of a deposit. The three basic steps are [10]:
1. Synthesis or creation of the depositing species
2. Transport from source to substrate
3. Deposition onto the substrate and subsequent film growth.
Because of the overlap in process mechanisms and the formation of hybrid deposition processes, no one scheme can accurately define and classify all coating processes. There are many different ways of depositing a thin film; the most common ones are based on deposition from a vapor of some sort. These techniques may further be subdivided into Physical Vapor Deposition (PVD) and Chemical Vapor Deposition (CVD). The difference is in the vapor: in PVD the vapor is composed of atoms and molecules that simply condense on the substrate, whereas in CVD the vapor undergoes a chemical reaction on the substrate, the product of which forms the film.
Physical Vapor Deposition Processes
PVD covers a number of deposition technologies in which materials are physically created in the vapor phase by energetic bombardment of a source (e.g. sputtering target) and subsequent ejection of material. The basic PVD processes are evaporation, sputtering and ion plating. A number of specialized PVD processes have been derived from these processes and extensively used, including reactive ion plating, reactive sputtering, unbalanced magnetron sputtering, High-Power Pulsed Magnetron Sputtering (HPPMS), and filtered cathodic arc deposition.
Evaporation is a process in which the boiling is carried out in a vacuum where there is almost no surrounding gas; the escaping vapor atom will travel in a straight line for a specified distance before it collides with structures in the vacuum chamber or residual gas atoms. Boiling is caused by thermal heating or electron beam heating of a source material.
Molecular Beam Epitaxy is an evaporation process performed in an ultra-high vacuum for the deposition of compounds of extreme regularity of layer thickness and composition from well-controlled deposition rates.
Reactive Evaporation is a process in which small traces of a reactive gas are added to the vacuum chamber; the evaporating material reacts chemically with the gas so that the compound is deposited onto the substrate.
Activated Reactive Evaporation (ARE) is the reactive evaporation process carried out in plasma which converts some of the neutral atoms into ions or energetic neutrals thus enhancing reaction probabilities and rates to deposit refractory compounds.
Biased Activated Reactive Evaporation (BARE) is the same process as ARE with the substrate held at a negative bias voltage.
Sputter Deposition is a vacuum process which uses a different physical phenomenon to produce the microscopic spray effect. When a fast ion strikes the surface of a material (target), atoms of that material are ejected by a momentum transfer process. As with evaporation, the ejected atoms or molecules can be condensed on a substrate to form a surface coating.
DC Sputtering is the simplest model in the sputtering systems. The DC sputtering system is composed of a pair of planar electrodes. One of the electrodes is a cold cathode and the other is the anode. The front surface of the cathode is covered with target materials to be deposited. The substrates are placed on the anode. The sputtering chamber is filled with sputtering gas. The glow discharge is maintained under the application of DC voltage between the electrodes. The gas ions generated in the glow discharge are accelerated at the cathode fall (sheath) and sputter the target, resulting in the deposition of the thin films on the substrates. In the DC sputtering system, the target is composed of metal since the glow discharge (current flow) is maintained between the metallic electrodes.
Radio Frequency (RF) Sputtering is sputter deposition in which RF voltage is supplied to the target. By simple substitution of an insulator for the metal target in the DC sputtering discharge system, the sputtering discharge cannot be sustained because of the immediate build up of a surface charge of positive ions on the front side of the insulator. To sustain the glow discharge with the insulator target, RF voltage is supplied to the target. This system is called RF sputtering. In the RF sputtering system, the thin films of the insulator are sputtered directly from the insulator target.
Magnetron sputtering involves a magnetic field, mainly parallel to the target surface, is superimposed to the applied electric field so that the secondary electrons (emitted by the target during its bombardment) are trapped near the target surface. Thus, one single electron can induce several argon ionizations before being lost by recombination on the chamber walls. This results in a large increase of the plasma ionization rate at the target surface and consequently a significant increase in deposition rate
Reactive Sputter Deposition is sputter deposition that involves a partial pressure of a reactive gas which reacts with the sputtered material to form a compound surface coating.
High-Power Pulsed Magnetron Sputtering (HPPMS), also known as high-power impulse magnetron sputtering (HIPIMS), utilizes extremely high-power densities of the order of kW/cm2 in short pulses (impulses) of tens of microseconds at a low duty cycle (on/off time ratio) of < 10%.
Dual Magnetron/Mid-Frequency Magnetron Sputtering process achieves both high deposition rates and improved materials utilization. Dual magnetron sputtering uses a mid-frequency (∼40-300 kHz) pulsed power source and two magnetron cathodes. In its simplest form, the power source supplies a positive pulse to one magnetron cathode during the first half of the cycle while negatively biasing the other cathode and then supplying a positive pulse to the other magnetron cathode while negatively biasing the other cathode. In this manner, one cathode acts as an anode while the other is the sputtering cathode. Sputtering only occurs during negative bias. This process is very amenable to reactive sputtering.
Ion Plating is an atomistic vacuum coating process in which the depositing film is continuously or periodically bombarded by energetic atomic-sized inert or reactive particles that can affect the growth and properties of the film. The source of depositing atoms can be from vacuum evaporation, sputtering, arc vaporization, or a chemical vapor precursor.
Reactive Ion Plating is ion plating that involves a partial pressure of a reactive gas which reacts with the sputtered material to form a compound surface coating.
Chemical Ion Plating is similar to reactive ion plating but uses stable gaseous reactants instead of a mixture of evaporated atoms and reactive gases. In most cases, the reactants are activated before they enter the plasma zone.
Ion Beam Deposition is a process in which a beam of ions generated from an ion beam source, impinge and are deposited on the substrate.
Ion Beam Assisted Deposition (IAD) - two versions are possible. In dual ion beam assisted deposition an ion beam is used to sputter a target and a second beam is used to bombard the growing film to change microstructure and properties. The other version uses an ion beam to bombard the growing film to change the structure and properties. In this case, conventional evaporation or sputtering techniques are used to generate a flux of the depositing species.
Cluster Ion Beam Deposition is ion beam deposition in which atomic clusters are formed in the vapor phase and deposited on the substrate.
Filtered and Unfiltered Cathodic Arc Deposition (FCA) processes can be considered a form of ion plating. Vacuum arc ion sources produce plasma of the source material by micro explosions at the surface of the solid cathode, in contrast to production by gaseous ionization. The vacuum arc is a discharge between two metallic electrodes in a vacuum, which is characterized by a low burning voltage (about 20 V) and a high current (35-500 A). The current transfer is made possible by the production of plasma produced at micrometer-size cathode spots on the cathode surface. Vacuum arc is an efficient way of generating plasma. Plasmas of intense energetic ions can be used to carry out high-current ion plating for material surface modification applications.
Ion Implantation is very similar to ion plating, except that now all of the depositing material is ionized, and accelerating energies are significantly higher. The depositing ions are thus able to penetrate the surface barrier of the substrate and become implanted in the substrate rather than on it.
Plasma Polymerization is a process in which organic and inorganic polymers are deposited from a monomer vapor by the use of an electron beam, ultraviolet radiation, or glow discharge. Excellent insulating films can be prepared in this manner.
Chemical Vapor Deposition Processes
Chemical vapor deposition (CVD) of thin films occurs when the reacting gas species come in contact with a heated substrate that catalyzes the reaction to produce the solid film.(2828. A. Sherman, Chemical Vapor Deposition for Microelectronics: Principles, Technology, and Applications, Noyes, Park Ridge, NJ (1987).
CVD can be classified by the method used to apply the energy necessary to activate the CVD reaction, i.e., temperature, photon, or plasma.
Thermal CVD is a form of CVD in which thermal energy is used to activate the reaction, and deposition temperatures are usually high.
Laser CVD is a form of CVD in which a laser produces a coherent, monochromatic high-energy beam of photons, which can be used effectively to activate a CVD reaction. Laser CVD occurs as a result of the thermal energy from the laser coming in contact with and heating an absorbing substrate.
Photo CVD is a form of CVD in which the chemical reaction is activated by the action of photons, specifically ultraviolet (UV) radiation, which have sufficient energy to break the chemical bonds in the reactant molecules.
Plasma-Enhanced Chemical Vapor Deposition (PECVD) is a form of CVD that involves creation of plasma of the reacting gases and subsequent deposition onto a substrate. The plasma is generally created by an RF, DC or microwave discharge between two electrodes located in the space into which the reactive gases are introduced.
Atomic Layer Deposition (ALD) is a self-limiting, sequential surface chemistry that deposits conformal thin films of materials onto substrates of varying compositions. ALD is similar in chemistry to CVD, except that the ALD reaction breaks the CVD reaction into two half-reactions, keeping the precursor materials separate during the reaction. ALD film growth is self-limited and based on surface reactions, which makes achieving atomic scale deposition control possible. By keeping the precursors separate throughout the coating process, atomic layer control of film grown can be obtained as fine as ∼0.1 °A per monolayer. ALD has unique advantages over other thin film deposition techniques, as ALD grown films are conformal, pinhole free, and chemically bonded to the substrate. With ALD it is possible to deposit coatings perfectly uniform in thickness inside deep trenches, porous media and around particles. The film thickness range is usually 1-500 nm.
Plasma-Assisted Chemical Vapor Deposition (PACVD) is a process similar to PECVD where the reaction between the precursors is stimulated or activated by creating plasma in the vapor phase using techniques such as RF, microwave or cyclotron resonance excitation.
Pyrolysis is a type of CVD which involves the thermal decomposition of volatile materials on the substrate.
Electroless Deposition is often described as a form of electrolytic decomposition which does not require a power source or electrodes. It is actually a chemical process catalyzed by the growing film, so the electroless term is somewhat of a misnomer.
Disproportionation is the decomposition of a film or crystal in a closed system by reacting the metal with a carrier gas in the hotter part of the system to form a compound, followed by dissociation of the compound in the colder section of the system to deposit the metal.
Hybrid deposition systems benefit from the possibility of combining, in one chamber, both the PECVD and PVD approaches[37]. This allows one to fabricate different coating architectures including multilayers or graded layers, or doped or nanostructured (nanocomposite) coatings with specific optical, mechanical, and other characteristics [38, 39 [37] H. Biederman, L. Martinu, Chap. 4, in: R. d'Agostino (Ed.), Plasma Deposition, Treatment and Etching of Polymers, Academic Press, Boston (1990) 269. [38] D. Dalacu, L. Martinu, J. Vac. Sci. Technol. A 17 (1999) 877. [39] J.-M. Lamarre, Z. Yu, C. Harkati, S. Roorda, L. Martinu, Thin Solid Films 479 (2005) 232.].
One of the major issues in most modern deposition technologies is the unintentional heating of substrate materials. This may cause degradation of the mechanical properties of such materials, especially upon exposure to temperatures that are much higher than the tempering temperatures [31 A.J. Perry, D.G. Teer, Surface technology for temperature-sensitive materials, Surf. Coat. Technol. 97(1-3) (1997) 244-249.]. In the case of CVD processes, because the temperatures are typically much higher, CVD may not be a good choice for heat-sensitive substrates. If a low temperature CVD is used, a postdeposition hardening heat treatment is often a must, but depending on the coating type, major problems may occur on the hard coating itself. Chief among them is severe oxidation or partial delamination of coatings from the substrate surface due to chemical reactions and thermal distortions. High-speed steels, certain intermetallics, and cemented carbides can safely be exposed to deposition temperatures as high as 450 â-¦C without major structural, chemical, or mechanical degradations. In contrast, for the deposition of nanocomposite coatings on titanium-, aluminum-, and magnesium-based engineering materials, one has to use relatively low temperatures; otherwise, major degradations or distortions may take place in such substrates. Because of their light weights, these materials are much desired for structural components in all kinds of transportation applications. There is also interest in using these materials in tribological and mechanical applications for aerospace and biomedical needs. However, mainly because of their high sensitivity to heat, extra precautions must be taken to avoid degradation in mechanical properties or loss of structural integrity of light alloy substrates. For the production of nanostructured or composite coatings, it may be necessary to combine two or more of the deposition methods mentioned earlier. Furthermore, the use of hybrid deposition system is important for producing coatings with strong bonding, dense structure, and superior mechanical properties. For example, in such systems, one can do sputtering and PECVD, sequentially, or both together.
Applications of surface engineering
Although there is significant overlap, current coating applications may be classified into the following generic areas [book]:
Optically functional: laser optics (reflective, semi-transmitting and transmitting), phase separation, telecommunication filters , architectural glazing, residential mirrors, automotive rear-view mirrors and headlamps, reflective and antireflection coatings, optically absorbing materials, low-e coatings, solar selective coatings, free-standing reflectors, transparent conductive films
Energy related: thin film battery, thin film fuel cell, thin film solar cell, thermoelectric thin films, superlattice, electrochromic coatings, s, solar absorbers, barrier coatings (oxygen and water permeation barriers), transparent solar cells, organic solar cells, photocatalytic coatings
Electrically functional: electrical conductors, electrical contacts, semiconductor films, active solid state devices, electrical insulators, photovoltaics, transparent electrical contacts
Mechanically functional: tribological coatings, lubrication films, nanocomposites, diffusion barriers, hard coatings for dies and cutting tools, wear- and erosion-resistant coatings, biomedical coatings
Chemically functional: corrosion-resistant coatings, catalytic coatings, biomedical coatings, photocatalytic coatings, thin film electrolytes, organic materials.
Materials:
Materials selection plays a crucial role in the operation and capabilities of a fabricated device. Among the material properties that must be considered: the morphology and crystal structure of each material; thermal and electrical compatibility between materials; and ability to withstand processing conditions without unacceptable degradation. Even after a material has been selected, there is the possibility that a new deposition method or material processing step could result in better device performance. This section examines the material properties of the materials synthesis in this research.
Engineered materials are the future of thin film technology. Transition metal (TM) nitrides have been the most studied and investigated compounds since the beginning of the use of hard coatings to improve the performance of mechanical components.
Aluminum Nitride (AlN)coatings:
AlN has physical properties desirable to the larger research community. An III-V semiconductor, many of its material properties are a result of its close-packed crystal structure. Under ambient conditions, the thermodynamically-stable structure of AlN is hexagonal wurtzite, although at very high pressure it can take the cubic rocksalt form [1]. The c/a ratio is 1.60 and its close-packed covalent bonds result in its very high hardness and excellent thermal conductivity, properties that it shares with the other III-V nitride semiconductors [2], [3]. AlN ceramics are found in industrial power supplies and inverters to efficiently dissipate waste heat from these devices [4]. Because of its hardness and corrosion resistance, AlN is often used as a wear- resistant and anti-corrosive coating, both in industrial and consumer applications [5 J. F. Rosenbaum, Bulk Acoustic Wave Theory and Devices. Boston: Artech House, 1988. [2] Y. Goldberg, in Properties of Advanced Semiconductor Materials: GaN, AlN, InN, BN, SiC, SiGe, L. M.E., R. S.L., and S. M.S., Eds. New York: John Wiley & Sons, 2001, pp. 31â€47. [3] M. Levnishtein, S. Rumayantsev, and M. Shur, Properties of Advanced Semiconductor Materials. New York: John Wiley & Sons, 2001. [4] Y. Tsujimura, N. Yoshino, Y. Fushii, and K. Terano, ʺDurable ceramic substrates bonded with metal circuits,ʺ Proceedings. Electronic Circuits World Convention 8. Electronics Circuits World Convention 8. 1999, pp. PO2. [5] B. Eunâ€Hyun, O. Minâ€Suk, H. Junâ€Hee, J. Jinâ€Woo, J. Jinâ€An, and K. Hanâ€Bong, ʺIndustrial applications of cathodicâ€arc and RF/DC magnetron plasma,ʺ IEEE Conference Record †Abstracts. 1995 IEEE International Conference on Plasma Science (Cat. No.95CH35796). IEEE. 1995, pp. 163.].AlN is a very chemically-resistant material. Electrically, AlN is a wide band gap semiconductor with a conduction band edge 6.2 eV above the valence band. This property has led to the use of AlN in a number of photonic applications [8 V. Siklitsky, ʺNSM Archive †Physical Properties of Semiconductors,ʺ 2003.]. AlN is a III-V semiconductor that has drawn widespread attention in the area of optical, high power and high temperature electronic devices. Aluminum nitride (AlN) is an important wide band gap semiconductor with a band gap of ∼6.2 eV. AlN also possesses a unique combination of properties, including excellent thermal conductivity, good electrical resistance, low dielectric loss, and high piezoelectric response, making the material suitable for a variety of applications in optoelectronic devices [1 [1] Benjamin M C, Wang C, Davis R F and Nemanich R 1994 Appl. Phys. Lett. 64 3288].
Silicon Nitride (Si3N4) Coatings:
The Si3N4 tool ceramics belong to materials that have a real possibility to replace steel and sintered carbides in future. Employment of these materials makes high speed machining possible with high feed rates both by turning and by milling [11 [11] L.A. Dobrza.nski, D. Pakuła, In˙zynieria materiałowa 3 (2004) 568-571]. The Si3N4 nitride ceramics demonstrates nearly the ideal properties in various applications in a wide range of temperatures. Its high strength, hardness and oxidation resistance, good thermal conductivity and resistance to thermal shocks feature its advantages.
nc-TiN/a-Si3N4 coatings:
In recent years, there has been great interest in the synthesis of thin films based on the refinement of the grain size with two or more phases present at the nano-scale. There are many types of nanostructured films, such as superlattices, nanograded, nano-scale multilayers and nanocomposite coatings [11 S. Veprek, S. Reiprich: Thin Solid Films 268, 64 (1995)]. The type of coating that has attracted the greatest amount of interest from researchers is the nanocomposite type. Nanocomposite thin films are a new class of materials that exhibit enhanced properties such as high hardness, high toughness and thermal stability. Nanocomposite coatings are composed of nanocrystalline grains of transition-metal nitride or carbide surrounded by an amorphous hard tissue. A substantial number of nanocomposite coatings have been studied [17-19]. Among them, nanocomposite coatings of TiN/Si3N4 have been studied extensively due to their high hardness and elastic modulus, improved wear resistance and high oxidation resistance [20-22[17] Holubar P, Jilek M, Sima M. Surf Coat Technol 1999;120- 121:184. [18] Veprek S, Niederhofer A, Moto K, Bolom T, Mannling HD, Nesladek P, et al. Surf Coat Technol 2000;133-134:152. [19] Niederhofer A, Nesladek P, Mannling HD, Moto K, Veprek S, Jilek M. Surf Coat Technol 1999;120-121:173. [20] Vaz F, Rebouta L, Ramos S, da Silva MF, Soares JC. Surf Coat Technol 1998;108-109:236. [21] Rebouta L, Tavares CJ, Aimo R, Wang Z, Pischow K, Alves E, et al. Surf Coat Technol 2000;133-134:234. [22] Ma S, Prochazka J, Karvankova P, Ma Q, Niu X, Wang X, et al. Surf Coat Technol 2005;194:143.].
Titanium Aluminum Nitride (TiAlN) coatings:
Thin films of transition metal nitrides have been widely used in many engineering applications especially due to their high hardness, chemical inertness and excellent wear resistance. Among them, the properties and the applications of TiN coatings have been studied extensively. The main disadvantage of TiN is its limited oxidation resistance (approximately 450-500 1C). The addition of other elements such as Al, Cr, Si, etc. increases the oxidation resistance of TiN [1-3]. TiAlN coatings have been developed for the engineering applications as an alternative to TiN since 1986 [5]. It has been reported that, the addition of aluminum to TiN, thus forming TiAlN, improves the oxidation behavior and the thermal stability of the coating, by forming a stable oxide layer on the surface of the film during oxidation [6[ [1] Vaz F, Rebouta L, Andritschky M, da Silva MF, Soares JC. J Mater Process Technol 1999;92-93:169. [2] McIntyre D, Greene JE, Hakansson G, Sundgren JE, Munz WD. J Appl Phys 1990;67:1542. [3] Otani Y, Hofmann S. Thin Solid Films 1996;287:188. [4] Wasa K, Hayakawa S. Thin Solid Films 1972;10:367. [5] Munz WD. J Vac Sci Technol A 1986;4:2717. [6] Ichimura H, Kawana A. J Mater Res 1993;8:1093.].
nc-TiAlN/a-Si3N4 coatings:
The prominent hardness of the nanocomposite TiN/Si3N4 coatings and improved thermal stability of TiAlN coatings led to the exploration of TiAlN/ Si3N4 nanocomposite coatings. Cutting tool materials with (Ti,Al)N coating have been shown to be superior to other conventional binary coatings and could be used at significantly higher cutting speed [7] since the oxidation resistance was improved [8-10 [7] T. Leyendecker, O. Lemmer, S. Esser, J. Edderink, Surf. Coat. Technol. 48 (1991) 175. [8] J.L. Huang, B.Y. Shew, J. Am. Ceram. Soc. 82 (1999) 696. [9] W.-D. Mu.nz, J. Vac. Sci. Technol., A, Vac. Surf. Films 4 (1986) 2717. [10] D. McIntyre, J.E. Greene, G. Ha°kansson, J.-E. Sundgen, W.-D. Mu.nz, J. Appl. Phys. 67 (1990) 1542.]. Silicon nitride films are useful for structural applications due to their attractive properties of hardness and chemical inertness. It was reported that an amorphous matrix, such as Si3N4, could provide a higher stability against oxidation than that of crystalline metallic nitride [1 [1] S. Veprˇek, S. Reiprich, L. Shizhi, Appl. Phys. Lett. 66 (1995) 2640.]. Therefore, nanolaminate materials consisting of nanocrystal-(Ti1 _ xAlx)Ny and amorphous-Si3N4 [designated as nc-(Ti1 _ xAlx)Ny and a-Si3N4] can be seen as future novel cutting tool coating materials.
Thesis Objectives:
At present, thin film coating processes are being rapidly advancing and are extensively applied for medical, energy and industrial technologies.
In many cases no single process can achieve films with required properties for multi layer and Nanocomposite thin films. Therefore, Hybrid coating processes are also becoming important. Plasma-enhanced chemical vapor deposition (PECVD) is combined with sputtering, sputtering is combined with electron beam evaporation, and electron beam evaporation is combined with physical vapor deposition (PVD). Plasma focus is one of the potential candidates which are used as hybrid deposition device for thin film deposition.
Plasma Focus is a compact powerful pulsed source of remarkably abundant source of multiple radiations: x-rays, neutrons, fast electrons, ions and plasma stream [1]. It generate high energy (~1-2 keV), high density (~1025- 1026 m-3), and short duration plasma column (~10-7 s) [1]. Plasma Focus device (PF) has been successfully used as a pulsed ionizing radiation source for many applications: pulsed neutron activation analysis [2-3], as a high flux X-ray source for lithography and radiography [4-8]. It has also been used as highly energetic radiation source for processing of materials in the form of surface modification, thin films coatings [9-17]. All the radiations are produced at the high-current discharge in a vacuum chamber filled with different gases. The sort of radiation depends on the type of gases inside the reactor, material of electrodes, geometry and other parameters [8]. For this reason, Plasma focus is very well fitted to a number of applications, in spite of the fact that a quite complicated picture of physical processes ruling a generation of radiation still is not understood completely.
Plasma Focus - A Potential Candidate for Surface Engineering
When compared with other plasma based thin film deposition systems, plasma processing with dense plasma focus has several attractive features.
Dense plasma focus (DPF) deposition process is a hybrid deposition process that combines key features of three existing vacuum deposition methods: the PVD sputtering process, Electron Beam evaporation and plasma-enhanced chemical vapor deposition (PECVD).
DPF provides a high deposition rate process for solid films. So, comparatively thick films can be deposited in less deposition time.
It is cost effective system compared to other deposition systems.
A simple capacitor discharge is sufficient to power the plasma focus.
DPF is a source of Intense radiation burst, Ions radiating from DPF device are more energetic (40 keV to 2 MeV).
The gas consumption is considerably small as compared to other deposition techniques.
Radiation pulse of very short duration is used to deposit thin films.
Additional substrate heating is not required during film deposition because the substrates are heated during ion beam treatment.
Plasma focus device is operated under pressure conditions which can easily be maintained.
Good adhesion between the deposited films and substrate is achieved.
The recent upsurge in demonstration of plasma focus device as a potentially suitable candidate for surface engineering motivated us to employ it in surface engineering scheme. The idea was to take advantage of the high-energy radiation from dense plasma focus to deposit and characterize
Nanocomposite coatings consisting of a nanocrystalline titanium nitride (TiN) imbedded in amorphous Silicon nitride matrix by plasma Enhanced chemical vapour deposition process.
Nanocomposite coatings consisting of a nanocrystalline titanium-aluminum-nitride by plasma Enhanced chemical vapour deposition process.
Nanocomposite coatings consisting of a nanocrystalline titanium-aluminum-nitride (TiAlN) imbedded in amorphous Silicon nitride matrix by plasma Enhanced chemical vapour deposition process.
Deposition of Silicon nitride onto Titanium by plasma Enhanced chemical vapour deposition process
Deposition of Aluminum nitride onto Titanium by plasma Enhanced chemical vapour deposition process
Layout of the Thesis
The Thesis is organized as follows:
Chapter 1 (Introduction) contains some introductory elements on plasma focus, describes the general aspects of the plasma focus device and gives an overview of the focus dynamics. It also states the aim and the objectives of this Research and illustrates the layout of this Thesis.
Chapter 2 (Literature Survey) presents previous work related to thin film deposition using plasma focus.
Chapter 3 (Experimental setup) describes the details of GCU DPF facility along with the basic diagnostics that are used to determine circuit parameters. It also includes descript ion of pulsed power driver and plasma focus tube along with pumping system respectively. Descript ion of some diagnostics, namely X-Ray diffraction (XRD) and Scanning Electron microscopy (SEM) is given.
Chapter 4 (Results and Discussion) presents the experimental findings resulting to the structural and morphological results of treated specimens are discussed. In the end, conclusions of work are given.
