1

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

14

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