Thin Films PDF

Thin films Lecture ( ) Nanomaterials:- are structures at the nanometre-scale (a nanometre is power of - of one metre), a scale, comparable to that of atoms and molecules and almost a hundred thousand times smaller than the diameter of a human head's hair ‫ ‏‬ow nan...

Thin films Lecture ( ) Nanomaterials:- are structures at the nanometre-scale (a nanometre is power of - of one metre), a scale, comparable to that of atoms and molecules and almost a hundred thousand times smaller than the diameter of a human head's hair ‫ ‏‬ow nanomaterials are classified according to the effect of Quantum H confinement Zero-dimensional ( D) structure or quantum dot: The extreme case of this process of size reduction in which all three dimensions reach the low nanometre range is called a quantum dot. Such as nanoparticle Typical dimensions: - nm ny nz nx. One-dimensional ( D) structure or quantum wire: If two dimensions are reduced in to the nanometre range and remain large the structure to as a quantum wire. such as nanorods and nano tube ( D structures) - nm range (Typical nano- scale dimension) kx nz ny. Two-dimensional ( D) structure or quantum well: Quantum confinement in nanostructure-If one dimension is confined or reduced to the nanometre ranges while other two dimensions remain large then we get a structure called quantum well. Such as thin films. Three dimensional ( D) structure or bulk structure: No quantisation of the particle motion occurs. Such as cube. What is a "thin film" Thin = less than about one micron ( Angstroms, nm) film = layer of material on a substrate (if no substrate, it is a "foil") A thin film is defined as thin layer built up on a solid support by controlled condensation of the individual atomic, molecular, or ionic species, either directly by a physical process, or via a chemical and / or electrochemical reaction. Since individual atomic, molecular, or ionic species of matter may exist either in the vapor or in the liquid phase, the techniques of the thin film deposition can be broadly classified under two main categories Others types to deposition films  Electroplating (for very high thickness films, fast process, less control on thickness)  Spin-cast  Epitaxial Thin films technique is one of the most fledged technologies that greatly contribute to developing the study of semiconductors by giving a clear indication of their chemical and physical properties. Thin films are also particularly important for their use in a great number of the optical field such as manufacturing of ordinary and thermal mirrors of high specialized filters, photo detectors and solar cells.  Investigation on the basic properties of the thin films can be grouped roughly into two categories. The first is concerned with change of the physical properties as thickness decreased, mean free path effects on the electrical conduction of thin metal films, studies of magnetization of thin films of ferromagnetic materials as function of film thickness, electron tunneling effects and effects due to the adsorption of gases are example of this category. These investigations all have the film thickness as the principle parameters. The second category of investigations is the study of the film structures. Most, optical, magnetic, chemical, electrical properties of films are of importance in an ever widening sphere of industrial, scientific and technical applications. At the same time studies of the fundamentals of film formation and of the basic reasons for differences in behavior of films and bulk materials are being pursued with increasing vigor. The structure and properties of many films are known to depend considerably on the state of the surface on which they are deposited to know exactly what kind of surface is being used for deposition of films, whether it is crystallographically oriented or not. Typical steps in making thin films  emission of particles from source ( heat, high voltage...)  transport of particles to substrate  condensation of particles on substrate  Favorable conditions are created to transfer the material from the source (target) to the destination (substrate). The nature of the film deposited depends on process parameters like substrate, deposition temperature, gaseous environment, rate of deposition etc. Special Properties of Thin Films Different from bulk materials Thin films may be:  not fully dense  small thickness  different defect structures from bulk  quasi - two dimensional (very thin films)   strongly influenced by surface and interface effects This will change electrical, magnetic, optical, thermal, and mechanical property Film composition  Grain size  Thickness  Uniformity  Adhesion  Corrosion resistance Selection of Materials for Microsystems  Mechanical properties  Elasticity (Young’s Modulus)  Chemical and electrochemical properties  Bio-compatibility issues  Electrical characteristics  Conductivity  Mobility  Thermal properties  Heat conductivity,  Expansion coeff.  Processing issues  feasibility  Optical properties  Roughness, crystalline Dr.Ghada Ayad  Thin films Lecture (2) Chemical Spray Pyrolysis Technique (CSP): Chemical spray pyrolysis is one of principle methods to produce large area and uniform coating. Spray pyrolysis has proved to be simple and inexpensive.Besides the simple experimental arrangement, high growth rate and mass production capability for large area coatings make them useful for industrial as well as solar cell applications. By using this technique one can control the film morphology and particle size in the nanometer range.The prime requisite for obtaining good quality thin film is the optimization of preparative conditions via, Substrate temperature, spray rate, concentration of solution etc. Spray pyrolysis is a processing technique used to prepare oxide films, ceramic coatings and powders. It has also been used for several years in glass industries and solar cell production. Spray pyrolysis includes a thermally stimulated chemical reaction between fine droplets of different chemical species. In this technique, a solution containing soluble salts of the constituent atoms of the compound is sprayed on a heated surface as tiny droplets by a nozzle atomizer with the help of a carrier gas.The droplets start decomposition to form a film on the substrate surface, when they reach the substrate. The hot surface maintains the required thermal energy for the decomposition and recombination. The carrier gas sometimes plays an active role in the pyrolytic process. The chemical spray pyrolysis system includes the nozzle, solution container, heater, air flow controller, liquid flow controller, airtight fiber chamber, temperature controller, thermocouple, (exhaust system, nozzle support) and substrate as shown in the following figure. 1 1. Spray Nozzle : Spray pyrolysis was fixed on a certain height by means of a holder which itself fixed on a metal rod, in such a way that the height of the apparatus above the surface of the electrical heater can be controlled. In addition to the position of the apparatus it can also be controlled because the end of the capillary tube in which the solution coming out should be in a perpendicular position on the substrate. 2. Heater: This heater is used to heat the substrate to the required temperature. The temperature controller (or the heat limit) controls the temperature with the help of special thermocouple. The temperature is registered by digital read out; the range of the heater temperature is (1-500) 0C with accuracy of ±10 0 C. 2  3. Thermocouple: The thermocouple consists of a sensitive thermal probe which is in contact with the surface of the substrate; and connected to a digital counter showing the temperature degree (in centigrade). 4. The Spray Controller Unit: This part contains the timer which controls the spray time. 5. Air Compressor: ++ Preparation of thin films : The basic steps in the process of the films preparation are: 1) The solutions must be mixed according to the films components, before starting the deposition. 2) After getting different amounts of solutions according to the ratio and volume requirement, put them in the magnetic stirrer for about 15minutes to be sure that solutions were mixed properly. 3) After cleaning the substrates, place on the flat plate heater surface, which is electrically controlled , and leave solutions for about 10 minutes so as to allow their temperature To reach a certain temperature. 4) Then the solution must be put in sprayer container. 5) After that, start the deposition process with a certain deposition time. 6) When the fine droplets arrive at the substrate, the solid compounds react to become a new chemical compound. The atomization of the solution into a spray of fine droplets is carried out by the spray nozzle, with the help of compressed air as carrier gas. 7) After the spray process is completed, the heater will be shut down and the samples are left on the surface of the hot plate to reach the room temperature, then the substrates can be raised. 8) Finally, characterize the structural, optical and electrical properties for films. Note: To measure the thickness of thin films by Weighting Method through this law 3 Advantages of Chemical Spray Pyrolysis Low cost (inexpensive apparatus). Does not require high quality targets or vacuum at any stage: a major advantage when scaled up for industrial applications. Simplicity and good productivity. Easy control of composition, deposition rate, film thickness and microstructure by changing the spray parameters. It eliminates the major problems of chemical methods such as sol-gel which produces films of limited thickness. Can produce films on less robust materials, with virtually no limitation on substrate material , dimension or the surface. Technological capability for mass production. Easy preparation of multi-layer films with composition gradient through the thickness by changing composition of the spray solution during the spray process. Offers opportunity to obtain reliable fundamental data because of well- formed film surfaces. The resulting films are quite compact, uniform without any side effects from substrate. Despite the many advantages, there are also some disadvantages to this method including: Spray nozzle might get cluttered after long usage. Film quality highly dependent on droplet size and spray nozzle. Dr.Ghada Ayad 4  Thin films Lecture (3) Sol-Gel Method Sol–gel methods are commonly employed for the synthesis of NPs by condensation and hydrolysis reaction of metal alkoxides or their precursors. The intermediates require further heat treatment in order to ensure high crystallinity of the prepared NPs. These metal alkoxides act as precursors to form oxide particles interacting through van der Waals forces or H-bonding, dispersed in a “sol” that is “gelled” by solvent evaporation or by other chemical reactions. Generally, water is a good solvent; However, the alkoxide precursors are hydrolyzed in the presence of a base or acid which either yields a colloidal gel or a polymeric gel, respectively. The properties of final products greatly rely on the rates of condensation and hydrolysis. Smaller sized NPs are obtained at slower hydrolysis rates. The major drawback of sol–gel method is the introduction of impurities from byproducts of the reaction. General mechanism A description of the sol-gel process can be formation of an oxide network through polycondensation reactions of a molecular precursor in a liquid. In general, in this process, several stages are identified, starting with a silicate solution and then forming a sol, which will then be transformed into a gel, and finally, a dry gel is obtained which is generally formed by a three-dimensional network of silica, with numerous pores of various sizes interconnected. Figure 1 presents an outline of the routes of this mechanism 1 ‫ انزٍ رسزخذو انسىائم‬Wet chemistry ‫رؼذ هزِ انطشَمخ احذي انطشق انًُجثمخ ػٍ رمُُبد انكًُُبء انشطجخ‬ ‫ انًىاد انؼضىَخ وكزنك‬colloids ‫ حُث َزى رىظُفهب فٍ اَزبج طبئفخ ػشَضخ يٍ غشوَبد‬-‫خالل انزحضُش‬ -‫ورؼزجش طشَمخ "انصىل‬. ‫وػهً االخص اكبسُذ انًىاد انفهضَخ‬, ‫انًىاد غُش انؼضىَخ الَىاع يخزهفخ يٍ انًىاد‬.‫حُث ال رزخهف ػُهب اٌ يُزجبد ضبسح ثبنجُئخ‬, ‫جم "صذَمخ نهجُئخ‬ Figure 1. Stages of the sol-gel process. Among the advantages of using the sol-gel process in the synthesis is because it can be carried out at room temperature, it allows us to produce a wide range of novel and functional materials, with potential applications in different areas; and finally, it is really attractive compared to other methods, due to its low production costs. 2 Sol-gel samples can be designed with a wide variety of morphologies, such as monoliths, films, fibers, and powders. In particular, films are the most important from the technological point of view. The process begins with the formation of a “sol,” which is a stable dispersion of colloidal particles (amorphous or crystalline) or polymers in a solvent. A “gel” is formed by a three-dimensional continuous network, which contains a liquid phase, or by the joining of polymer chains. In a colloidal gel, the network is built from agglomerates of colloidal particles. While in a polymer gel, the particles have a polymeric substructure composed of aggregates of sub-colloidal particles. Generally, van der Waals forces or hydrogen bonds dominate the interactions between the sol‟s particles. During synthesis, in most gel systems, covalent-type interactions dominate, and the gel process is irreversible. Typically, in the sol-gel chemistry, there is a reaction of an organometallic compound, which is generally an alkoxide, nitrate, or chloride under aqueous conditions to form a solid product. This product can be a dense glass monolith, a high surface area molecular filter, an aerogel to a metal oxide, a nitride coating, or nanoparticle. The process begins with reactions of hydrolysis and condensation of a precursor to form a gel followed by aging, solvent extraction, and finally drying. These reactions may be catalyzed by the addition of an acid or a base, which will produce dense or diffuse networks, respectively, by altering the hydrolysis kinetics. The selection of the precursor and catalyst depends ultimately on what you would like to make. syneresis can occur during the aging of the gel, which is the expulsion of solvent due to the contraction of the gel matrix. The process of drying the gel consists in eliminating the water from the gel system, with simultaneous collapse of the gel structure, under conditions of constant temperature, pressure, and humidity 3 Sol-gel chemistry tends to be particularly sensitive to the following parameters: pH: any colloidal chemistry that involves water is sensitive to pH. Solvent: in the polymerization process, as molecules are assembled into nanoparticles, the solvent plays two important roles; the first is that it must be able to keep the dissolved nanoparticles so that they do not precipitate out of the liquid; and second, it must play a role in helping nanoparticles connect with each other. Temperature: the chemical kinetics of the different reactions involved in the formation of nanoparticles and the assembly of the nanoparticles in a gel network are accelerated with temperature, which affects the gel time. At very low temperatures, gelation is a slow process that can take weeks or months. In contrast, at high temperatures, the reactions that bind the nanoparticles to the gel network occur so quickly that lumps form in their place and a solid precipitates out of the liquid. The gelation temperature must be controlled to optimize the reaction time. Time: depending on the type of gel to be obtained, the different steps in the gel formation process work differently at different time scales. In general, it is recommended that the formation of the gel should be slow to produce a very uniform structure, resulting in a stronger gel. Accelerating reactions through short times cause precipitates to form instead of gel network and can cause a gel to become cloudy and weak or simply not form. Catalysts: a chemical reaction can be accelerated by the presence of a catalyst. In much of the sol-gel chemistry, this is very pH sensitive. This is because both acids (H+) and bases (OH−) are catalysts but accelerate chemical reactions by different mechanisms. 4 Agitation: at this stage, the mixing of the sol during gelation should ensure that the chemical reactions in the solution are produced uniformly, allowing all molecules to receive an adequate supply of the chemicals they need for these reactions to be carried out correctly. Generally, there are microscopic and macroscopic domains of gel networks partially formed throughout the liquid, and agitation can sometimes break up the formation of these domains; and the network fragments grow back into a wider network. Irrespective of the nature of the film, the two main techniques used to apply a sol-gel coating on the surface of a metallic substrate are dip - coating and spin-coating. Applications: Applications for sol gel technology include protective coatings, catalysts, piezoelectric devices, wave-guides, lenses, high-strength ceramics, superconductors, synthesis of nanoparticles and insulating materials. ‫انزطجُمبد‬:. wave-‫رشًم رطجُمبد ركُىنىجُب( انسىل –جم ) طالء انحًبَخ وانًحفضاد واألجهضح انكهشوإجهبدَخ و‬.‫ وانؼذسبد وانسُشايُك ػبنٍ انمىح وانًىصالد انفبئمخ ورشكُت انجضَئبد انُبَىَخ وانًىاد انؼبصنخ‬guides Advantages Advantages of Sol-Gel Processes In general:  Able to get uniform & small sized powder.  Can get at low temperature high density glass, without high temperature re-crystallization. 5   Can get new compositions of glass.  New microstructure and composition.  Easy to do coating for films.  Can get objects or films with special porosity.  Can get metal (inorganic) – organic composites.  Can coat onto large area or complex shape objects.  Can get fibers.  High uniformity, multicomponent systems. ‫(يضاَب‬ :‫ ثشكم ػبو‬Sol-Gel ‫يضاَب ػًهُبد‬.‫لبدسح ػهً انحصىل ػهً يسحىق يىحذ وصغُش انحجى‬ ‫ دوٌ إػبدح رجهىس‬, ‫ًَكٍ أٌ رحصم فٍ دسجخ انحشاسح انًُخفضخ ػهً صجبج ػبنٍ انكثبفخ‬.‫ثذسجخ حشاسح ػبنُخ‬.‫ًَكٍ انحصىل ػهً رشكُجبد جذَذح يٍ انضجبج‬.‫انجُُخ انذلُمخ انجذَذح ورشكُت جذَذح‬.‫يٍ انسهم ػًم طالء االغشُخ‬.‫ًَكٍ أٌ رحصم ػهً اجضاء أو اغشُخ راد يسبيُخ خبصخ‬.‫ يشكجبد ػضىَخ‬- )ٌ‫ًَكٍ انحصىل ػهً يؼذٌ (غُش ػضى‬.‫ًَكٍ طالء ػهً يسبحخ كجُشح أو اجضاء راد شكم يؼمذ‬.‫ًَكٍ أٌ رحصم ػهً األنُبف‬ ‫ يزؼذدح انًكىَبد‬, ‫أَظًخ ػبنُخ االَزضبيُخ‬ Disadvantages: The process is not very „clean‟. As the process involves chemical reactions between several ingredients in solution, it contains undesired atoms, molecules, ions, etc., in the required material, which deteriorates the electrical as well as 6 ‫‪optical properties of the deposited material. Therefore, this technique is not‬‬ ‫‪compatible with the modern solid state device fabrication technique, which is the‬‬ ‫‪primary manufacturing process for electronic and photonic devices.‬‬ ‫‪(:‬سهجُبد‬ ‫انؼًهُخ نُسذ "َظُفخ" نهغبَخ‪َ.‬ظشًا ألٌ انؼًهُخ رزضًٍ رفبػالد كًُُبئُخ ثٍُ انؼذَذ يٍ انًكىَبد فٍ‬ ‫انًحهىل ‪ ,‬فئَهب رحزىٌ ػهً رساد وجضَئبد وأَىَبد وغُش يشغىة فُهب فٍ انًبدح انًطهىثخ ‪ ,‬يًب َؤدٌ‬ ‫إنً رذهىس انخصبئص انكهشثبئُخ وانضىئُخ نهًبدح انًشسجخ‪.‬نزنك ‪ ,‬ال رزىافك هزِ انزمُُخ يغ رمُُخ رصُُغ‬ ‫األجهضح راد انحبنخ انصهجخ انحذَثخ ‪ ,‬وانزٍ رؼذ ػًهُخ انزصُُغ األسبسُخ نألجهضح اإلنكزشوَُخ وانفىرىَُخ‪.‬‬ ‫‪Dr.Ghada Ayad‬‬ ‫‪7‬‬  Thin films Lecture (4) Spin coating Spin coating is currently the predominant technique employed to produce uniform thin films of photosensitive organic materials with thickness of the order of micrometers and nanometers. In many cases the coating material is polymeric and is applied in the form of a solution from which the solvent evaporates. Spin coating was first studied for coating of paint and pitch. This process has been widely used in the manufacture of integrated circuits optical mirrors, color television screens and magnetic disk for data storage. Centrifugal force drives the liquid radial outward. The viscous force and surface tension causes a thin residual film to be retained on the flat substrate. The film thins by the combination of outward fluid flow and evaporation.. However, at an engineering level the viscous flow effects dominate early on while the evaporation processes dominate later. Fluid flow on a flat spinning substrate is one of the most important physical processes involved in spin coating. Several processing parameters involved in the spinning process are: dispense volume, final spin speed (w), final film thickness, solution viscosity, solution concentration (c), spin time, etc. The film forming process is primarily driven by two independent parameters, viscosity and spin speed. The range of the film thickness easily achieved by spin coating is 1–200 micrometers. The Spin Coating Systems (SCS) was show in fig. (1) Fig (1): The Spin Coating Systems 1 Key stages of spin coating The physics of spin coating can be effectively modeled by dividing the whole process into four stages sketched in Figure 2, which are deposition, spin-up, spin-off and evaporation of solvents. The first three are commonly sequential, but spin-off and evaporation usually overlap. Stage 3(flow controlled) and stage 4 (evaporation controlled) are the two stages that have the most impact on final coating thickness. Clearly stage 3 and stage 4 describe the two processes that most be occurring simultaneously throughout all times (viscous flow and evaporation) Fig: (2): Key stages of spin coating process. a. Deposition During this stage, solution is allowed to fall on rotating substrates from microsyrings and the substrate is accelerated to the desired speed. Spreading of the ion takes place due to centrifugal force and height is reduced to critical height. This is the stage of delivering an excess of the liquid to be coated to the surface of the substrate a portion of which’s immediately covered or “wetted”. No matter what way is used the amount of liquid deposited through excessive is limited and this stage ends when delivery ceases. b. Spin-up The second stage is when the substrate is accelerated up to its final, desired, rotation speed. This stage is usually characterized by aggressive fluid expulsion from the wafer surface by the rotational motion. Ultimately, the wafer reaches its desired speed and the fluid is thin enough that the viscous shear drag exactly balances the rotational accelerations. 2  c. Stable fluid outflow The third stage is when the substrate is spinning at a constant rate and fluid viscous forces dominate fluid thinning behavior. This stage is characterized by gradual fluid thinning.. Mathematical treatments of the flow behavior show that if the liquid exhibits Newtonian viscosity (i.e. is linear) and if the fluid thickness is initially uniform across the wafer (albeit rather thick), then the fluid thickness profile at any following time will also be uniform. d. Evaporation When spin-off stage ends the film drying stage begins. During this stage centrifugal out flow stops and further shrinkage is due to solvent loss. This results in the formation of thin film on the substrate. The fourth stage is when the substrate is spinning at a constant rate and solvent evaporation dominates the coating thinning behavior. During the evaporation stage the suspended or dissolved solids may grow so concentrated at the liquid surface as to form a high viscosity, low diffusivity layer. Thin film(CuPcTs )preparations on Glass Spin-coating is used for the deposition of organic thin films, a small amount of a liquid is dispensed on the substrate using spin coating system works in the range of 500 rpm to 11000 rpm, then the film was left to dry in room temperature to form solid films. The thickness of the respective organic layers can be controlled by the spin speed. Compared to a drop casting, the deposited thin film by using the spin-coating technique can produce a thinner thin film. The value of rotation per minute (rpm) is inversely proportional to the thickness of the thin film. This means, that by increasing the value of rpm, the film thickness will decrease. However, CuPcTs solution did not show any adherence to the substrate when the rpm was set below 800 rpm and beyond 1500 rpm. Thus the rpm value was limited by the ability of the solution to adhere on the substrate. In this work, the spin speed was set at 1500 rpm for 1.5 min. Advantages As evidenced by its maturity, spin coating has many advantages in coating operations with its biggest advantage being the absence of coupled process variables. Film thickness is easily changed by changing spin speed, or switching to a different viscosity photoresist. But among the alternative coating techniques, many have multiple coupled parameters, making coating control more complex. Another advantage of spin coating is the ability of the film to get progressively more uniform as it thins, and if the film ever becomes completely uniform during the coating process, it will remain so for the duration of the process. It is low cost and fast operating system. 3 The maturity of spin coating implies many of the issues involved in spin coating have been studied and a lot of information exists on the subject. Disadvantages The disadvantages of spin coating are few, but they are becoming more important as substrate size increases and photoresist costs rise. Large substrates cannot be spun at a sufficiently high rate in order to allow the film to thin. The biggest disadvantage of spin coating is its lack of material efficiency. Typical spin coating processes utilize only 2–5% of the material dispensed onto the substrate, while the remaining 95–98% is fling off in to the coating bowl and disposed. Not only are the prices of the photoresist increasing substantially, but disposal costs increasing as well. Applications Spin coating has been used for several decades for the application of thin films. It is widely used in the manufacture of integrated circuits, optical mirrors, magnetic disk for data storage, device of solar cells, detectors, sensors, VLSI (very large scale integration), nano scale device (quantum dots, carbon nanotubes), DVD and CD ROM, photo resist for patterning wafers in microcircuit production, insulating layers for microcircuit fabrication such as polymers (where it can be used to create thin films with thickness below 10 nm), flat screen display coatings, antireflection coatings and conductive oxide. Dr.Ghada Ayad 4  Thin films Lecture (5) Dip-coating The dip coating method is a process used to prepare thin films on various substrates. It involves immersing a substrate into a solution or suspension of the material that will form the thin film. It is also commonly used in academic research, where many chemical and nanomaterial engineering research projects use the dip coating technique to create thin-film coatings. As a popular alternative to Spin coating, dip-coating methods are frequently employed to produce thin films from sol-gel precursors for research purposes, where it is generally used for applying films onto flat or cylindrical substrates. By this technique, the material from which the film is produced is put into solution, and then the substrate is progressively dipped into and is extracted from the solution at a controlled rate. After the solvent evaporates, a thin and homogeneous film is produced. Many factors contribute to determining the final state of the dip coating of a thin film: 1. Solution Viscosity: High solution viscosity can lead to thicker films, while low viscosity may result in thinner films. 2. Dip Speed: The speed at which the substrate is withdrawn from the solution affects film thickness. Slower withdrawal often results in thicker films. 3. Solution Concentration: The concentration of the solute in the solution impacts film thickness. Higher concentration solutions generally lead to thicker films. 1  4. Substrate Pre-treatment: The preparation and treatment of the substrate surface can affect film adhesion and quality. 5. Solvent Evaporation Rate: The rate at which the solvent evaporates during withdrawal influences film formation. 6. Temperature and Humidity: Environmental conditions can affect the drying and curing of the film. 7. Film Material Properties: The properties of the material being deposited, such as its solubility and reactivity, are critical. 8. Number of Coating Cycles: Multiple dip coating cycles can be used to build up thicker films. The dip coating technique can give uniform, high quality films even on bulky, complex shapes. Dip-coating was successfully used, for example, to prepare sol- gel-derived Al2O3 films on γ-TiAl-based alloys, porous TiO2 films and SrO-SiO2- TiO2 on NiTi, and so on. The dip-coating process can be separated into several stages. This process involves several key steps: 1. Surface Cleaning: The substrate's surface is thoroughly cleaned to ensure good adhesion between the thin film and the surface. 2. Solution Preparation: A solution containing the materials that will form the thin film is prepared. These materials may be dissolved in a solvent or suspended in a liquid. 3. Immersion: The substrate is immersed in the solution of the coating material at a constant speed. 4. Start-up: The substrate has remained inside the solution for a while and is starting to be pulled up. 2  5. Deposition: 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 jitters. The speed determines the thickness of the coating. 6. Drainage: Excess liquid will drain from the surface. 7. Evaporation: The solvent evaporates from the liquid, forming the thin layer. For volatile solvents, such as alcohols, evaporation starts already during the deposition and drainage steps. In the continuous process, the steps are carried out directly after each other. Figure 1. Schematics of a dip-coating process. Applications the Dip coatings in research include: 1. Dip coating is used in the production of thin films for electronic devices, such as display screens and solar panels. 2. Dip coating can be used to apply protective coatings to surfaces to protect them from corrosion and contamination. 3. Dip coating is used in the chemical industry for the production of chemical materials such as coatings and protective films 3  4. Dip coating is used in chemical analysis to extract important compounds from solutions. 5. Dip coating can be used in the manufacture of medical and biological devices. 6. Multilayer sensor coatings. 7. Dip coating is allows the application of a variety of oxide and inorganic- organic hybrid materials on both large area and complex shaped substrates. 8. Sol-Gel nanoparticle coatings. 9. Layer-by-layer nanoparticle assemblies. 10. It’s used in the production of automotive rear mirrors. The Advantages of Dip Coating 1. Uniform Thickness: Dip coating allows for the creation of thin films with very uniform thickness, making it suitable for various applications requiring precise control. 2. Simple Process: It's a relatively simple and cost-effective process, requiring minimal equipment and expertise. 3. Wide Range of Materials: Dip coating can be used with a wide range of materials, including polymers, ceramics, and metals. 4. Large Substrate Compatibility: It can be applied to various substrate shapes and sizes, including complex geometries. 5. Scalability: The process is easily scalable to mass production, making it suitable for industrial applications. 6. Same coating on both sides. 7. the excellent homogeneity of dip coated layers. 8. Dip coating provides a protective shield that resists corrosion. 4  9. Insulates against heat, cold, stress and electrical currents. 10.Durable and UV resistant. 11.Dip coatings are hard and scratch resistant and very durable against environmental influences. The disadvantages of Dip Coating 1. Clean room is required. 2. Dip coating is primarily used for thin films. It may not be suitable for very thick coatings. 3. The dip coating process can be relatively slow, which may not be ideal for high-volume production. 4. Handling solvents can be a safety and environmental concern. Proper disposal and ventilation are needed. 5. Typically, dip coating produces single-layer films. Multilayer structures may require additional processes. 6. Achieving consistent quality can be challenging, and variations in environmental conditions can affect the process. 7. Overall, dip coating is a versatile method for producing thin films with precise control, but it may not be suitable for all coating thicknesses or high- speed production needs. 8. Metal films are extremely difficult to produce. Asst. Prof.Dr.Ghada A. Kdhim 5  Thin films Lecture (6)  Electrochemical polymerization Electrochemical polymerization in the preparation of thin films is the process of forming a thin layer of polymeric materials on an electrically charged surface using chemical reactions. The process involves the polymerization induced by the electric influence, encompassing both electrical current and voltage, to stimulate these chemical reactions. Electrochemical polymerization of polymers such as polypyrrole, polythiophene, polyfuran, etc. have greatly dominated the field of conducting and semiconducting polymers where advancements in polymerization techniques have led to the development of a field interfacing polymer science and electrochemistry. All electrochemical polymerizations were carried out by using an electrochemical cell, which is formed by three electrodes, working electrode (WE), reference electrode (RE) and counter-electrode (CE) In the working electrode takes place the polymerization (oxidation of monomer), thus, it is considered one of the most important electrodes in the polymerization process, as shown fig.A. The WE can be made of different materials, such as stainless steel, indium-tin oxide (ITO) coated glass. Or consist from two electrodes (a-ITO was used as a substrate (Reference Electrode) (RE, to determine the working electrode potential according to the potential of reference electrode.b-Working Electrode (WE) consist of high purity titanium metal. In this technique, electrolysis is used to initiate the process with the monomer being polymerized in situ to a conducting surface,as shown fig.B. For this reason, the process is often referred to as electro-initiated polymerization). It uses monomers of low molecular weight that have higher 1 solubility in the media, as well as more favorable viscosity and mobility. Polymerization initiation can be directly controlled by electrolytic means. It also provides a possible method to control the propagation and termination processes. It is possible for the formed polymer to have a controlled molecular weight and molecular weight distribution and a predetermined yield. Electropolymerization usually involves some specific interaction between the monomer and the electrode surface which leads to better coating adhesion. Electropolymerization is a relatively new technique involving aspects of electrochemical engineering, polymer science, organic chemistry and coating/plating technology. (A) (B) 2 Factors influencing the preparation of thin films through electrochemical polymerization include:  Polymeric Material Type: The choice of polymeric material is crucial, considering its properties and suitability for electrochemical reactions.  Polymer Solution Concentration: The quantity and concentration of polymeric materials in the solution affect the quality and thickness of the thin layer.  Current and Voltage Intensity: The amount of electricity used influences the speed and distribution of polymerization on the surface.  Reaction Time: The duration of the process is critical in controlling the thickness and quality of the polymer layer.  Cathode and Anode Type: The characteristics of the cathode and anode play a role in influencing the polymer growth. Advantage of electrochemical polymerization  Precision Control: Precise control over the thickness and properties of the polymer layer.  Formation Ease: Ability to tune the formation of the polymer layer by adjusting electrochemical conditions.  Time Efficiency: Faster deposition of thin films compared to some traditional methods. Disadvantages of electrochemical polymerization:  Difficult to remove film from electrode surface.  Equipment Cost: The equipment used in electrochemical polymerization can be expensive. 3   Sensitivity to Conditions: Sensitivity to changes in electrochemical and environmental conditions affecting the quality of the polymer layer.  Limitation on Material Types: Some materials may not be suitable for this method. Asst. Prof. Dr.Ghada Ayad Kadhim 4  Thin films Lecture (7)  Electrolytic Anodization: Electrolytic anodization is a process of forming a thin layer of a specific compound on the surface of a metal through electrochemical oxidation. The metal piece is immersed in a solution containing the target compound and connected to a power source to stimulate the oxidation reaction, leading to the formation of a thin layer on its surface. This method is employed in areas such as the preparation of thin films and enhancement of the surface properties of metals. Nanoporous and well adhering oxides can be formed on aluminum, tantalum, niobium, titanium, zirconium, and silicon. The most important applications are corrosion protective films and decorative coatings with dyes on aluminum and its alloys, and layers for electrical insulation for electrolyte capacitors on aluminum and tantalum. Steps to prepared thin films by Electrolytic anodization: 1- solution Preparation: Prepare an electrolyte solution containing a compound that can form a thin film. The solution may include an acid, such as sulfuric acid, and the target compound. 1  2- Anode Preparation: Prepare a metallic piece, such as aluminum, to be the anode. Clean the surface of the anode carefully to ensure good electrical conductivity. 3- Anode Immersion: Immerse the anode in the electrolyte solution, allowing the oxide thin film to form on its surface. 4- Cathode Connection: Connect the anode and another metallic piece (cathode) to the power source. The anode is connected to the positive pole, while the cathode is connected to the negative pole. 5- Electric Current Activation: When the electric current is activated, oxidation of the metal on the anode's surface begins, releasing metal ions into the solution. 6- thin film Formation: The ions deposit on the anode's surface, forming a thin film of the targeted metal oxide compound. The thickness of the thin film can be controlled by adjusting the duration of the electric current. 7- Rinsing and Drying: After formation is complete, rinse the thin film carefully to remove residues, then dry to obtain the final thin film. The thin film formation in electrolytic anodization is influenced by several factors, including: 1- Metal Type: The type of metal used in the anode affects the thin film properties, as the choice of metal can lead to the formation of a thin film with specific characteristics. 2- Solution Concentration: The concentration of the electrolyte solution affects the thickness and quality of the thin film, and it should be carefully adjusted to achieve the desired results. 3- Temperature: The temperature of the solution may play a role in influencing the rate of thin film formation, and precise temperature control may be required. 2  4- Electric Current Density: The electric current density influences the rate of thin film formation, and it can be adjusted to control the thickness of the thin film. Advantages of Electrolytic Anodization in Thin Film Preparation:  Precise Control: Precise control over process conditions, such as solution concentration and current density, allows for accurate adjustment of the thin film thickness.  Uniform Layer Formation: The process enables the formation of a thin and uniform layer on the anode's surface, improving the quality of the resulting thin film.  Time and Cost Efficiency: Electrolytic anodization is a time and cost- efficient process, especially when compared to some other methods of thin film preparation.  Preparation of Tailored thin film: The choice of metal type and process conditions can be tailored to obtain thin films with specific properties, increasing the varity of applications. Disadvantages of Electrolytic Anodization in Thin Film Preparation:  Impurity Impact: The quality of the thin film may be affected by impurities in the solution, necessitating additional purification processes.  Limitations on Metal Types: Not all metal types are suitable for electrolytic anodization, which can impact material availability and cost.  Temperature Sensitivity: The thin film thickness may be sensitive to temperature changes, requiring careful monitoring of these factors.  Limited Compatibility with Some Materials: There may be limitations regarding the compatibility of electrolytic anodization with certain materials or chemical compositions. Asst.Prof.Dr.Ghada A.Kadhim 3  Thin films Lecture (8) Chemical bath deposition (CBD) Chemical bath deposition (CBD) is a method for preparing thin films by immersing a substrate in a solution containing chemical compounds. Chemical reactions occur between the compounds in the solution and the immersed surface, leading to the formation of a thin layer of the desired material. Such as the fig.1 fig.1. show Chemical bath deposition (CBD) is a method Factors Affecting Chemical Bath Deposition of Thin Films:  Chemical Composition: The composition of the solution and its chemical compounds affects the thin film formation.  Solution Concentration: The concentration of compounds influences the thickness and quality of the thin film.  Bath Temperature: The temperature can influence the rate of chemical reactions and thin film formation.  Immersion Time: The duration of immersion plays a role in thin film formation and thickness.  Surface Preparation: The condition and cleanliness of the substrate surface impact the uniformity and adherence of the thin film. 1   Reaction Monitoring: Precise control of reaction processes contributes to obtaining a homogeneous thin film. Steps of Chemical Bath Deposition:  Solution Preparation: A solution containing chemical compounds relevant to the desired material is prepared.  Submersion: The target surface is placed in the solution, exposing it to react with the chemical compounds.  Chemical Reaction: Chemical reactions take place between the compounds in the solution and the substrate surface, resulting in the formation of a thin layer.  Rinsing and Drying: The surface is rinsed to remove any excess materials, and the thin layer is dried to obtain the final film. Advantages of Chemical Bath Deposition:  Chemical bath deposition is a straightforward process that can be easily controlled.  The required chemicals for deposition are often readily available at low costs.  Achieving an even distribution of the thin film on the target surface is possible. Disadvantage of Chemical Bath Deposition:  Surface distortions or irregularities in the thin film may occur due to factors like temperature and immersion time.  There might be limitations in choosing materials that can be prepared using this method.  The method may be sensitive to temperature changes, affecting the quality of the thin film. Applications of Chemical Bath Deposition :  Used for preparing thin films of semiconductors in the manufacturing of thin-film electronic devices like liquid crystal displays.  Applied in preparing thin films of photoactive materials used in the manufacturing of solar cells. 2   Utilized to produce thin films of nanomaterials for applications in nanotechnology.  Can be used to prepare thin films in the manufacturing of sensing devices for a wide range of applications.  Employed in forming thin protective films on surfaces to guard against corrosion and damage. Asst. Prof.Dr.Ghada Ayad Kadhim 3  Thin films Lecture (9) Drop coating Drop coating is a method used in the preparation of thin films, involving the controlled deposition of small droplets of a solution onto a flat substrate. This can be achieved by filling a dropper with the solution and releasing one drop at a time consistently onto the target surface. The aim is to achieve an even distribution of the solution on the surface, resulting in the formation of a thin layer after solvent evaporation. Parameters influencing drop-coated thin films include:  Solution Concentration: The amount of solute in the solution affects the thickness and properties of the thin layer.  Drop Deposition Speed: How the droplets are released onto the surface and its impact on uniform distribution.  Solvent Quality: The choice of solvent influences evaporation rate and the final structure of the thin film.  Surface Properties: The condition of the target surface and its preparation impact the final formation of the thin layer.  Temperature and Humidity: Environmental conditions play a role in the drying process of the droplets and affect the ultimate performance of the membrane. The steps for preparing thin film by drop coating include:  Solution Preparation: Prepare a solution containing the substances that will form the thin film.  Surface Preparation: Ready the receiving surface for drop deposition to ensure proper accumulation of the solution.  Drop Deposition: Sequential and even dropping of the solution onto the receiving surface using a suitable tool such as a dropper.  Drying: Allow the thin film to naturally dry, enabling the solvent to evaporate and leave behind the thin film. 1   Adjustment if Needed: Fine-tune conditions or undertake additional steps if necessary to achieve the desired properties of the thin film Figure1 show the drop coating fig.1. show drop coating method Advantages of drop coating in thin film:  A simple and easily applicable method for thin film preparation.  Relatively economical compared to some other methods.  Good control over the thickness of the thin layer. Disadvantage of drop coating in thin film:  The distribution may not be entirely uniform, especially at high deposition speeds.  Environmental conditions may affect the drying process and film formation.  High evaporation rates due to faster deposition speed may influence crystalline structure and final properties of the thin film. Applications of drop coating:  Sensors: Thin films can be used in sensor devices for detecting specific compounds.  Display Devices: In electronics, enhancing the performance of electronic display screens. 2   Solar Cells: Improving conversion efficiency in solar cells.  Optical Technologies: In designing optical devices and technologies related to light and lasers.  Chemical Sensing Applications: For detecting chemicals and gases. Asst. Prof.Dr.Ghada Ayad Kadhim 3