Electrochemical method (corrosion) · Electrochemical method (corrosion) Porous Anodic Alumina...
Transcript of Electrochemical method (corrosion) · Electrochemical method (corrosion) Porous Anodic Alumina...
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University of Technology Department of Materials Engineering
3rd Grad Nanotechnology (Lec. 7+8+9) By: Dr. Mayyadah S. Abed
2014-2015
Electrochemical method (corrosion)
Porous Anodic Alumina (PAA) can be prepared by two-step anodization on
both sides of an aluminium foil. The anodization carried out at anodizing
temperature 17oC using oxalic acid as an anodizing electrolyte. The average pore
diameter may found to be (75) nm. The average interpore distance of (PAA)
prepared are (99) nm. The thickness of (PAA) is approxilatelly (59.5) µm.
The overall reaction is thus oxide film growth and hydrogen gas formation,
equation below.
2Al3+ + 3H2O → Al2O3 + 6H+ …………….. (1)
2Al + 3O2- → Al2O3 + 6e- …………….. (2)
6H+ + 6e- → 3H2 ……………..(3)
2Al + 3H2O → Al2O3 +3H2 …………….(4)
Structure of Porous Anodic Alumina. (A) Idealized
structure of porous anodic alumina and (B) a cross-
sectional view of the anodized layer.
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University of Technology Department of Materials Engineering
3rd Grad Nanotechnology (Lec. 7+8+9) By: Dr. Mayyadah S. Abed
2014-2015
Anodizing mechanism
SEM image of PAA after second anodizing at 17ºC.
Application: filtration for different material like water filtration, air filtration, petroleum and medical applications.
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University of Technology Department of Materials Engineering
3rd Grad Nanotechnology (Lec. 7+8+9) By: Dr. Mayyadah S. Abed
2014-2015
Chemical Vapor Deposition CVD And
Physical Vapor Deposition PVD
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University of Technology Department of Materials Engineering
3rd Grad Nanotechnology (Lec. 7+8+9) By: Dr. Mayyadah S. Abed
2014-2015
Thin films: are thin material layers ranging from fractions of a nanometers (monolayer) to several micrometers in thickness. Electronic semiconductor devices and optical coatings are the main applications benefiting from thin film construction.
A familiar application of thin films is the household mirror which typically has a thin metal coating on the back of a sheet of glass to form a reflective interface. The process of silvering was once commonly used to produce mirrors. A very thin film coating (less than a nanometer) is used to produce two-way mirrors.
Work is being done with ferromagnetic thin films for use as computer memory. It is also being applied to pharmaceuticals, via thin film drug delivery. Thin-films are used to produce thin-film batteries.
Chemical vapor deposition (CVD) Chemical vapor deposition (CVD) is a chemical process used to produce
high-purity, high-performance solid materials. The process is often used in the semiconductor industry to produce thin films. In a typical CVD process, the wafer (substrate) is exposed to one or more volatile precursors, which react and/or decompose on the substrate surface to produce the desired deposit. Frequently, volatile by-products are also produced, which are removed by gas flow through the reaction chamber. The two major industrial sectors are: (a) microelectronics which currently accounts for approximately 80% of the market, and (b) surface coatings applications (surface hardness enhancement, corrosion inhibition, and medical) which accounts for the remaining 20% of the market.
Nanofabrication processes widely use CVD to deposit materials in various forms, including: monocrystalline, polycrystalline, amorphous, and epitaxial. These materials include: silicon, carbon fiber, carbon nanofibers, filaments, carbon nanotubes, SiO2, silicon-germanium, tungsten, silicon carbide, silicon nitride, silicon oxynitride, titanium nitride, and various high-k dielectrics. The CVD process is also used to produce synthetic diamonds.
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University of Technology Department of Materials Engineering
3rd Grad Nanotechnology (Lec. 7+8+9) By: Dr. Mayyadah S. Abed
2014-2015
Chemical deposition is further categorized by the phase of the precursor:
Chemical vapor deposition (CVD) generally uses a gas-phase precursor, often a halide or hydride of the element to be deposited. In the other case, an organometallic gas is used. Commercial techniques often use very low pressures of precursor gas.
Types of chemical vapor deposition
A number of forms of CVD are in wide use and are frequently referenced in the literature. These processes differ in the means by which chemical reactions are initiated (e.g., activation process) and process conditions.
Classified by operating pressure
[1] Atmospheric pressure CVD (APCVD) - CVD processes at atmospheric pressure.
[2] Low-pressure CVD (LPCVD) - CVD processes at subatmospheric pressures. Reduced pressures tend to reduce unwanted gas-phase reactions and improve film uniformity across the wafer. Most modern CVD processes are either LPCVD or UHVCVD.
[3] Ultrahigh vacuum CVD (UHVCVD) - CVD processes at a very low pressure, typically below 10-6 Pa (~10-8 torr). Note that in other fields, a lower division between high and ultra-high vacuum is common, often 10-7 Pa.
Classified by physical characteristics of vapor
[1] Aerosol assisted CVD (AACVD) - A CVD process in which the precursors are transported to the substrate by means of a liquid/gas aerosol, which can be generated ultrasonically. This technique is suitable for use with non-volatile precursors.
[2] Direct liquid injection CVD (DLICVD) - A CVD process in which the precursors are in liquid form (liquid or solid dissolved in a convenient solvent). Liquid solutions are injected in a vaporization chamber towards injectors (typically car injectors). Then the precursor vapors are transported
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University of Technology Department of Materials Engineering
3rd Grad Nanotechnology (Lec. 7+8+9) By: Dr. Mayyadah S. Abed
2014-2015
to the substrate as in classical CVD process. This technique is suitable for use on liquid or solid precursors. High growth rates can be reached using this technique.
Plasma methods [1] Microwave plasma-assisted CVD (MPCVD) [2] Plasma-Enhanced CVD (PECVD) - CVD processes that utilize plasma to
enhance chemical reaction rates of the precursors. PECVD processing allows deposition at lower temperatures, which is often critical in the manufacture of semiconductors.
[3] Remote plasma-enhanced CVD (RPECVD) - Similar to PECVD except that the wafer substrate is not directly in the plasma discharge region. Removing the wafer from the plasma region allows processing temperatures down to room temperature.
Hot-wall thermal CVD (batch operation type)
Plasma assisted CVD
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University of Technology Department of Materials Engineering
3rd Grad Nanotechnology (Lec. 7+8+9) By: Dr. Mayyadah S. Abed
2014-2015
Physical Vapor Deposition PVD Physical Vapor Deposition PVD uses mechanical or thermodynamic means
to produce a thin film of solid. An everyday example is the formation of frost. Since most engineering materials are held together by relatively high energies, and chemical reactions are not used to store these energies, commercial physical deposition systems tend to require a low-pressure vapor environment to function properly; most can be classified as physical vapor deposition (PVD).
Examples of physical deposition include:
[1] Evaporative deposition: In which the material to be deposited is heated to a high vapor pressure by electrically resistive heating in "low" vacuum.
[2] Electron beam physical vapor deposition: In which the material to be deposited is heated to a high vapor pressure by electron bombardment in "high" vacuum.
[3] Sputter deposition: In which a glow plasma discharge (usually localized around the "target" by a magnet) bombards the material sputtering some away as a vapor.
[4] Cathodic Arc Deposition: In which a high power arc directed at the target material blasts away some into a vapor.
[5] Pulsed laser deposition: In which a high power laser ablates material from the target into a vapor.
PVD is used in the manufacture of items including semiconductor devices, aluminized PET film for balloons and snack bags, and coated cutting tools for metalworking. Besides PVD tools for fabrication special smaller tools mainly for scientific purposes have been developed. They mainly serve the purpose of extreme thin films like atomic layers and are used mostly for small substrates.
A good example are mini e-beam evaporators which can deposit monolayers of virtually all materials with melting points up to 3500°C.
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University of Technology Department of Materials Engineering
3rd Grad Nanotechnology (Lec. 7+8+9) By: Dr. Mayyadah S. Abed
2014-2015
PVD/CVD Tool Coatings Enhance Stamping & Forming of Stainless Steels
For several reasons, stainless steel materials are more challenging to successfully
stamp and form compared to carbon steels. The combination of high forming
pressures and surface friction results in significantly higher tool wear rates than
those used to form carbon steels. This causes significant increases in tool
maintenance, downtime and production costs. As a result, PVD and CVD coatings
often are applied to improve tool performance and increase tool life.
Properties of traditional PVD and CVD coatings of steel.
COATING
HARDNESS
VHN (50GF)
COEFF. OF
FRICTION
OXIDATION
TEMP.
CORROSION
RESISTANCE
TiN PVD 2900 0.65 500º C Good
AITiN PVD 4500 0.42 800° C Good
CrN PVD 2500 0.55 700º C Excellent
TiC CVD 3200 0.60 350º C Good
TiC/TiN CVD 3000 0.65 500º C Good
TiCN PVD 4000 0.45 400º C Good
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University of Technology Department of Materials Engineering
3rd Grad Nanotechnology (Lec. 7+8+9) By: Dr. Mayyadah S. Abed
2014-2015
Spark erosion (discharge)
Plasma is the ionized state of matter, it's conformed by neutral gas composed of charged and neutral particles, which exhibit a collective behavior; plasma is the most abundant form of matter in the universe. It is formed whenever ordinary matter is heated over 5,000 ºC, which results in electrically charged gases or fluids. They are profoundly influenced by the electrical interactions of the ions and electrons by the presence of a magnetic field.
An electric arc, or arc discharge, is an electrical breakdown of a gas that produces an ongoing plasma discharge, resulting from a current through normally nonconductive media such as air.
The principle of this method is: that arc discharge or electric arc occurs between
two electrodes when direct current DC is passed through them. The gap between
electrodes (air or any gas like hydrogen or argon) acts as dielectric, so the electron
pass throw the gas between the electrodes as arc. Due to high induced temperature,
the anode (+) evaporate to plasma which deposit on cooled cathode (-) as anode
material forms like amorphous, fibers, and or nanotubes depending on conditions.
Spark or arc discharge system
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University of Technology Department of Materials Engineering
3rd Grad Nanotechnology (Lec. 7+8+9) By: Dr. Mayyadah S. Abed
2014-2015
Application: Carbon nanotube synthesis, thin film deposition, nanoparticles synthesis.
Spark or arc discharge mechanism
Nanoparticles synthesis by plasma condensation
Evaporation of solid by plasam
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University of Technology Department of Materials Engineering
3rd Grad Nanotechnology (Lec. 7+8+9) By: Dr. Mayyadah S. Abed
2014-2015
Laser Ablation (Pulse Laser Deposition PLD)
Pulsed laser deposition (PLD) is a thin-film deposition method, which uses
short and intensive laser pulses to evaporate target material. The ablated particles
escape from the target and condense on the substrate as shown schematically in
Figure (1). The deposition process occurs in vacuum chamber or inert gas to
minimize the scattering of the particles. The thin film formation process in PLD
generally can be divided into the following four stages (see Figure 2)
1- The interaction of the laser beam with the target resulting in melting and
then evaporation of the surface layers.
2- The interaction of the laser beam with the evaporation materials causing the
formation of isothermal expanding plasma.
3- The expansion of the laser induced plasma with a rapid transfer of thermal
energy of the species in plasma into kinetic energy.
4- Thin film growth to the desired thickness depending on conditions.
Applications of laser Ablation
Laser machining and drilling, thin film deposition, teeth enameling, carbon nanotubes synthesis, cleaning surface and others are the main ones.
Figure (1): Schematic diagram of Laser ablation process.
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University of Technology Department of Materials Engineering
3rd Grad Nanotechnology (Lec. 7+8+9) By: Dr. Mayyadah S. Abed
2014-2015
Figure (2): Laser ablation stages.
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University of Technology Department of Materials Engineering
3rd Grad Nanotechnology (Lec. 7+8+9) By: Dr. Mayyadah S. Abed
2014-2015
Laser Ablation Deposition Actual Plum
Laser Ablation Deposition Stages
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University of Technology Department of Materials Engineering
3rd Grad Nanotechnology (Lec. 7+8+9) By: Dr. Mayyadah S. Abed
2014-2015
Sputtering Technique Sputtering is a process whereby atoms are ejected from a solid target material
due to bombardment of the target by energetic particles. It only happens when the
kinetic energy of the incoming particles is much higher than conventional thermal
energies (≫ 1 eV). This process can lead, during prolonged ion or plasma
bombardment of a material, to significant erosion of materials, and can thus be
harmful. On the other hand, it is commonly utilized for thin-film deposition,
etching and analytical techniques.
Sputtering relies on a plasma (usually a noble gas, such as argon) to knock
material from a "target" a few atoms at a time. The target can be kept at a relatively
low temperature, since the process is not one of evaporation, making this one of
the most flexible deposition techniques. It is especially useful for compounds or
mixtures, where different components would otherwise tend to evaporate at
different rates. Note, sputtering's step coverage is more or less conformal. It is also
widely used in the optical media. The manufacturing of all formats of CD, DVD,
and BD are basically done with the help of this technique. It is a fast technique and
also it provides a good thickness control. Now a days in sputtering, Nitrogen and
Oxygen gases are also being used.
Applications
• Film deposition • Etching • For analysis • In space
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University of Technology Department of Materials Engineering
3rd Grad Nanotechnology (Lec. 7+8+9) By: Dr. Mayyadah S. Abed
2014-2015
Mechanism of Sputtering
Rotated
Target
Sputtering system
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University of Technology Department of Materials Engineering
3rd Grad Nanotechnology (Lec. 7+8+9) By: Dr. Mayyadah S. Abed
2014-2015
Evaporative deposition In which the material to be deposited is heated to a high vapor pressure by
electrically resistive heating in "low" vacuum.
Evaporation is a common method of thin-film deposition. The source material
is evaporated in a vacuum. The vacuum allows vapor particles to travel directly to
the target object (substrate), where they condense back to a solid state. Evaporation
is used inmicrofabrication, and to make macro-scale products such
as metallized plastic film.
Evaporation involves two basic processes: a hot source
material evaporates and condenses on the substrate. It resembles the familiar
process by which liquid water appears on the lid of a boiling pot. However, the
gaseous environment and heat source (see "Equipment" below) are different.
Thermal Evaporation system
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University of Technology Department of Materials Engineering
3rd Grad Nanotechnology (Lec. 7+8+9) By: Dr. Mayyadah S. Abed
2014-2015
Electron Beam Physical Vapor Deposition (EBPVD) It is a form of physical vapor deposition in which a target anode is bombarded with an electron beam given off by a charged tungsten filament under high vacuum. The electron beam causes atoms from the target to transform into the gaseous phase. These atoms then precipitate into solid form, coating everything in the vacuum chamber (within line of sight) with a thin layer of the anode material as shown schematically in Figure below.
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University of Technology Department of Materials Engineering
3rd Grad Nanotechnology (Lec. 7+8+9) By: Dr. Mayyadah S. Abed
2014-2015
Carbon nanotubes synthesis
Carbon nanotubes were first discovered by Japanese scientist Sumio Iijima in 1991. Carbon nanotubes are large pure self-assemble crystalline carbon molecules with sp2 hybridization with long thin cylinder structure of one atom thick sheet of carbon (graphene). Each carbon atom in graphene sheet bonds covalently with three another carbon atoms forming honey-comb hexagon network. If carbon nanotube grows from one atom thick sheet, it will form single wall carbon nano tube SWCNT, but if it grows from many layers of graphene separated by Vander Waals forces, it will form multi wall carbon nanotube MWCNT. Carbon nanotube is one member of fullerenes family with elongated mid.
Synthesis:
Carbon nanotubes have been produced using methods such as plasma arc discharge, pulsed laser vaporization (PLV), Chemical vapor deposition (CVD),) and hydrocarbon flame synthesis. Schematic representation of these synthesis processes is shown in figure below.
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University of Technology Department of Materials Engineering
3rd Grad Nanotechnology (Lec. 7+8+9) By: Dr. Mayyadah S. Abed
2014-2015
Arc Discharge Method:
Iijima (Iijima, 1991) used the arc discharge method for production of CNTs.
The process involved condensation of carbon atoms generated from evaporation of
a solid carbon source. In this method, high electric current (~50 - 120 A) is passed
through graphite electrodes placed at a distance of approximately 1 mm in the
synthesis chamber that causes material from the cathode to sublimate and the
nanotubes to form on the anode. The arc discharge process is difficult to control
because of the very high temperature (~3200 K) in the electrode gap. The method
is also cost and energy intensive and unwanted byproducts such as polyhedron
graphite particles contaminate the relatively low yield of CNTs.
Pulsed laser vaporization PLD or laser ablation method LA
In the pulsed laser vaporization or laser ablation method, a high energy laser
is directed to ablate a carbon target that contains some nickel and cobalt in a tube
furnace, at the temperature of ~ 1400 K. A flow of inert gas is passed through the
chamber to carry the CNTs downstream, to a collector surface. Single walled
carbon nanotubes, mostly in the form of ropes, at a 1- 10nm scale have been
formed by this method. The CNTs formed by the laser ablation method are of a
higher quality than those produced by the arc discharge method. However, the
production rate is low, and the pulsed laser vaporization or laser ablation method is
both capital and energy intensive.
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University of Technology Department of Materials Engineering
3rd Grad Nanotechnology (Lec. 7+8+9) By: Dr. Mayyadah S. Abed
2014-2015
Chemical deposition method (CVD)
The chemical deposition method (CVD) is an alternative method in which
CNTs are grown using catalysis. This method involves decomposition of a
hydrocarbon gas over a transition metal catalyst and initiation of CNT synthesis by
some of the resulting carbon atoms. CVD growth mechanism generally involves
the dissociation of hydrocarbon molecules and saturation of carbon atoms in the
catalyst metal nano-particles. The precipitation of carbon from the saturated metal
particles leads to the formation of carbon nanotubes. Use of catalysis reduces the
need for high temperatures. Hydrogen from the decomposition process, and
supplemented by that carried with the bulk phase, contributes to the activation and
reactivation of the catalytic surface. The CVD method has a better CNT yield and
is potentially scalable to commercial manufacturing.
Hydrocarbon Flames Method
Hydrocarbon flames provide a unique combination of the chemical and
catalytic factors that are conducive to initiation and growth of carbon nanotubes.
Gases (CO, CH4, C2H2, C2H4 and C2H6) present in the post flame environment
form a diverse source of gaseous carbon. The chemical energy released in the form
of heat in the flame supports the endothermic carbon deposition reactions.
Catalysts in appropriate form (substrate or aerosol) provide the reaction sites for
deposition of solid carbon. Growth mechanisms similar to those observed in the
CVD process govern the growth of nanotubes in flames.
The geometry and characteristics of the catalysts play an important role in
the structural properties of the carbon nanotubes. Flames are scalable and are
commercially used for the production of solid carbon forms such carbon black and
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University of Technology Department of Materials Engineering
3rd Grad Nanotechnology (Lec. 7+8+9) By: Dr. Mayyadah S. Abed
2014-2015
printing ink. Appropriately tailored flame conditions may provide an ideal
environment for growth of CNTs on a large commercial scale. Mechanism of carbon nanotube formation in a catalytic synthesis process
Catalytic nano-particles from transitional metal/metal alloys (e.g. Fe, Ni, and
Co) are assumed to be spherical or pear-shaped and are either floating or deposited on a substrate like by sputtering. The catalytic decomposition of the carbon precursor molecules (e.g. CO, CH4, C2H2, C2H4 and C2H6) is conjectured to occur on one half of the nano-particle surfaces (the lower curvature side for the pear shaped particles). The released carbon atoms diffuse into the catalyst nano-particles along the concentration gradients until carbon super-saturation at the particle temperature occurs. Post super saturation of the catalyst particle, carbon atoms precipitate in solid carbon form on the opposite half of the catalyst particle around and below the bisecting diameter. This description is similar to the Vapor- Liquid-Solid (VLS) process. As per this process, the solid carbon nanotube grows from a super-saturated molten liquid catalyst droplet. Decomposition of the gas phase hydrocarbon molecules provides the carbon necessary for saturation of the molten catalyst.
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University of Technology Department of Materials Engineering
3rd Grad Nanotechnology (Lec. 7+8+9) By: Dr. Mayyadah S. Abed
2014-2015
**** You can see the you tube video in the link below https://www.youtube.com/watch?v=B099DRAX_X4 or type the address: (Electron-Microscopy-growth-CNTs.avi) in you tube search field.
Scanning Electron
Microscopic Image for MWCNT
Transmission Electron Microscopic Image for MWCNT
Transmission Electron Microscopic Image for SWCNT