basic of Nanotechnology for ug students.pptx

made for ug students specially for itnu students

1. Introduction to Nanotechnology In 1959, Prof. Richard Feynman presented an idea of building materials atom by atom and this idea evolve into a new branch of science called nanoscience. In 1974, Prof. Norio Taniguchi coined the term Nanotechnology to describe semiconductor processes like thin film deposition and ion beam milling exhibiting characteristic control on the order of a nanometer. The invention of the Scanning Tunneling Microscope (STM) in 1981, followed by the Atomic Force Microscope (AFM) in 1982 marked the beginning of nanotechnology, as it enabled scientists to observe atoms for the 1 st time. Nanotechnology is defined as the technology of manipulating materials at the atomic and molecular scale to produce innovative functionalities and exotic properties of the material.

2. Introduction to Nanotechnology One of the first notable successes in nanotechnology has been in manipulating the magnetic and electrical properties of atoms to store vast amounts of data , paving the way for iPods and other storage devices. Dr. Fert and Dr. Grunberg discovered even smaller and denser types of memory storage using spintronics (for which they received Nobel prizes) where the data is stored by manipulating the spins of electrons. Nanoparticles of iron compounds can be used to clean up waste sites and break down hazardous organic compounds such as PCBs, dry cleaning fluids and neutralizing poisons such as lead and arsenic.

3. Introduction to Nanotechnology Study of materials and their properties at the scale of few nanometers is called nanoscience , and to do so, we required some tools and techniques used to synthesize and characterize the nanomaterials, as well as the use of nanomaterial properties in various applications is called nanotechnology. The prefix “nano” comes from the Greek word for “dwarf” and it means one billionth. The materials having grain size of the order of nanometer (10 -9 m) scale are known as nanoscale. The dimensions are in the range of 0.1 to 100 nm.

4. What is the need for Nanotechnology? Nanotechnology offers a variety of new opportunities to tackle a number of problems and enable research that was not thought to be possible earlier. The impact of nanotechnology is being observed in diverse fields as Electronics, Health care & Medicine, Energy, Agriculture & Food, Materials science, and many more. Nanotechnology is revolutionary owing to following primary reasons: Novel properties : Since a material's properties at the nanoscale differ drastically from the material's macroscale properties, we have novel properties to exploit in research. Opportunities of Scale : The fact that the scale is so small which allows novel approaches and applications that weren't thought possible in the past.

5. Novel Properties Breaking a piece of gold or silver into smaller and smaller pieces, each piece will still have the same color, melting & boiling points, density, electrical conductivity, and ability to catalyze chemical reactions as the original. However at the nanoscale, both gold and silver exhibits different colors throughout the nanoscale size range and other different properties except the size dependent catalytic properties of gold until 5 nm.

6. Novel Properties Material Bulk Nanoscale Gold Non magnetic Ferromagnetic Gold Yellow Red/Orange Graphite Conductor Semiconductor (Armchair) Graphite Opaque Transparent Hexagonal Boron nitride Insulator Conductor /Semiconductor

7. Opportunities of Scale Synthesizing a nanoparticle to target specific cells . e.g. In photothermal therapy, the nanoparticles embedded within tumors are exposed to tissue-penetrating near-infrared light, which causes the nanoparticles to produce enough heat to damage adjacent cancer cells.

8. Opportunities of Scale

9. Why materials behave differently at nanoscale? At nanoscale, the different properties of the materials changes. There are two principal factors owing to which the properties of the material changes and hence the materials behave differently at the nanoscale. Higher Surface to Volume ratio Consider a sphere of radius r as shown in figure. The surface area of the sphere is and, The volume of the sphere is The surface area to volume ratio (S/V) will be = It is evident from the above relation that (S/V) ratio varies inversely with radius r. This signifies that as the size of particle is small, the S/V ratio will be higher.  

10. Why materials behave differently at nanoscale? Quantum confinement effect : When the diamensions of the material is equal to the de-Broglie wavelength of electron or mean free path of electrons , the energy of electron changes. This effect is known as quantum confinement. If only one dimension of any material is constrained to the nanoscale, we obtain a layered structure known as two-dimensional (2D) material . If two dimensions are constrained to the nanoscale, we obtain a wired/rod/tube shape structure called one-dimensional (1D) material. if all three dimensions are limited to the nanoscale, we acquire a sphere-shaped structure called zero-dimensional (0D) materials.

11. Schematic of 0D, 1D and 2D

12. Synthesis of nanomaterials There are two different approaches available to synthesize the nanomaterials namely Top-down Approach and Bottom-up Approach. Top-down Approach It is a physical process wherein a large scale object is progressively reduced in dimensions to get nanomaterials. Bottom-up Approach It is a chemical process wherein atomic and molecular component assembles themselves (atom by atom/ molecule by molecule) to produce nanomaterials.

13. Synthesis of nanomaterials There are two different approaches available to synthesize the nanomaterials namely Top-down Approach and Bottom-up Approach.

14. Synthesis of nanomaterials

15. Synthesis of nanomaterials (Physics Methods) Mechanical Method (High energy ball milling) It is one of the simplest ways of making nanoparticles in the form of powder. Many types of mills such as planetary, vibratory, rod, tumbler etc. are being used for the preparation of nanoparticles. Usually one or more containers are used at a time to make large quantities of fine particles . Size of container, of course, depends upon the quantity of interest. In this case we have considered a planetary mill .

16. Synthesis of nanomaterials (Physics Methods) Mechanical Method (High energy ball milling) Container consist of Hardened steel or tungsten carbide balls along with powder or flakes (< 50 of a material of interest. Usually 2:1 mass ratio of balls to material is advisable. Container is closed with tight lids and can have two different movements, 1) About its own axis 2) About particular central axis If the container is more than half filled , the efficiency of milling is reduced.  

17. Synthesis of nanomaterials (Physics Methods) Mechanical Method (High energy ball milling) When the containers starts rotating around the central axis as well as their own axis at more than 100 rpm speed , the collision between steel balls and materials takes place. The material is also forced to the walls and is pressed against the walls . Hence, the temperature rise i n the range of 100–1100 . Cryo-cooling is used sometimes to dissipate the heat generated. Heavy milling produce smaller grain size but larger defects in the particles. The process, however, may add some impurities from balls.  

18. Synthesis of nanomaterials (Physics Methods) Mechanical Method (High energy ball milling) Advantages: This technique is simple and does not require any complex set up. It is very cheap and easy process. It produces nano powder of 2-20 nm in size. This technique is effective for synthesizing metal-ceramic composite powder. It is possible to produce large quanta of nanoparticles by this method.

19. Synthesis of nanomaterials (Physics Methods) Mechanical Method (High energy ball milling) Disadvantages: It is not sophisticated process therefore shape of the nano material is irregular. There is a possibility of contamination from milling media and atmosphere. This method produces crystalline defects. This process is very restrictive for the production of non-oxide materials. The milling should take place in an inert atmosphere

20. Synthesis of nanomaterials (Physics Methods) Laser Ablation Laser ablation method has been extensively used for the preparation of nanoparticles and thin films. It is the process of removing material from a solid surface by irradiating it with a laser beam. In this technique, a highly intense pulsed laser beam is allowed to strike the target surface. For instance, Pulsed laser beam Nd:YAG . The target is placed in an evacuated chamber at a pressure of 10 -6 Torr. Nd:YAG Laser

21. Synthesis of nanomaterials (Physics Methods) Laser Ablation When a Nd:YAG laser beam strikes the target surface, it evaporates the target material. This evaporated material forms the ablation plume. This plume is nothing but the molecular fragment of target materials (atoms, ions and molecule) which are going to be removed from the surface which will result in a situation like plasma. The inert gas carries the plume to the surface of the substrate on which the nanomaterial is deposited. Nd:YAG Laser

22. Synthesis of nanomaterials (Physics Methods) Precautions to be taken care of The ablation site should be cleared very often by a pressurized inert gas, such as nitrogen or argon for the sake of cleanliness. Pulse duration must be short to maximize peak power and to minimize thermal conduction to the surrounding work material If the pulse repetition rate is too low, all of the energy which was not used for ablation will leave the ablation zone which cooling down the system Nd:YAG Laser

23. Synthesis of nanomaterials (Physics Methods)

24. Synthesis of nanomaterials (Physics Methods) Sputtering Sputtering is a physical vapor deposition process used for depositing a thin-film onto a substrate, by ejecting atoms from target materials and condensing the ejected atoms onto a substrate in a high vacuum environment. The ejection of atoms from the target materials is to be done by bombarding the high energetic ions , typically inert gas ions such as Ar + . In this process, the substrate and target material are first placed on the anode and cathode, respectively, inside a vacuum chamber.

25. Synthesis of nanomaterials (Physics Methods) Sputtering Electrically-neutral argon atoms are introduced into a vacuum chamber at a pressure of 1-10 mTorr . A DC voltage is then applied between the target and substrate which ionizes argon atoms and creates a plasma, hot gas‐like phase consisting of ions and electrons in the chamber. These argon ions are accelerated towards the cathode target. Upon collision with the target, atoms from the target are ejected and travel to the substrate, where they begin to condense.

26. Synthesis of nanomaterials (Physics Methods) Sputtering As atoms accumulate on the substrate, they interact at the molecular level, forming a strongly bonded atomic layer. By controlling the sputtering time, one or more layers of these atoms can be created, enabling the production of precise layered thin-film structures. Electrons released during Argon ionization are accelerated to the anode substrate, subsequently colliding with additional Argon atoms, creating more ions and free electrons in the process, continuing the cycle.

27. Synthesis of nanomaterials (Chemical Methods) Chemical Vapor Deposition (CVD) Chemical Vapor Deposition (CVD) is a thin film deposition technique that uses chemical reactions to deposit high quality layers of a designated material. In this technique, the predefined mix of reactive gases are introduced at the specified flow rate into the reaction chamber at ambient temperature.

28. Synthesis of nanomaterials (Chemical Methods) Chemical Vapor Deposition (CVD) This gas moves towards the heated substrate and the reacting gas adsorbed on the surface of the substrate and undergo chemical reactions there. As a result of this chemical reaction, a thin film is formed on the surface of the substrate.

29. Synthesis of nanomaterials (Chemical Methods) Chemical Vapor Deposition (CVD) During this chemical reaction, some byproducts are going to form which will desorbed and evacuated from the reaction chamber by means of carrier gas flow. To avoid undesired chemical reactions, the substrate surface temperature, deposition time, pressure and type of surface is carefully selected.

30. Synthesis of nanomaterials (Chemical Methods) Chemical Vapor Deposition (CVD)

31. Synthesis of nanomaterials (Chemical Methods) Advantages of Chemical Vapor Deposition (CVD) Uniform thickness of the film Flexibility of using wide range of chemical precursors Require Low deposition temperature Ability to control crystal structure Deposition rate can easily be adjusted It can be adapted to many process variations

32. Synthesis of nanomaterials (Chemical Methods) Disadvantages of Chemical Vapor Deposition (CVD) Safety and health hazards as precursor gases are toxic, corrosive, flammable. Require numerous test runs to determine and reach suitable growth parameters

33. Synthesis of nanomaterials (Chemical Methods) Types of CVD processes APCVD-Atmospheric Pressure CVD MOCVD-Metal Organic CVD PECVD-Plasma Enhanced CVD LPCVD-Low pressure CVD PCVD-Photochemical Vapour Deposition CVI-Chemical Vapour Infiltration CBE-Chemical Beam Epitaxy

34. Synthesis of nanomaterials (Chemical Methods) Sol-Gel method Sol-Gel method is an example of wet chemical synthesis of nanomaterials. It is based on inorganic polymerization reaction. It is generally carried out at room temperature and includes four steps: Hydrolysis, polycondensation, drying and thermal decomposition. This method is widely used to synthesize oxide particles and as the name suggests Sol-Gel involves two types of materials or components namely, ‘Sol’ and ‘Gel’.

35. Synthesis of nanomaterials (Chemical Methods) Sol-Gel method Sol is a liquid solution with solid particles suspended in it. Gel is nothing but a continuous network of a solid particles with pores filled with liquid. The reactions and steps involved in the sol-gel process can be described as follows:

36. Synthesis of nanomaterials (Chemical Methods) Sol-Gel method A stable solution of the alkoxide or solvated metal precursor (the sol) is formed. An oxide- or alcohol- bridged network (the gel) forms by a polycondensation reaction. The polycondensation reactions continue until the gel transforms into a solid mass. Drying of the gel by thermal evaporation or supercritical condition resulting into the product xerogel/aerogel.

37. Synthesis of nanomaterials (Chemical Methods) Advantages of Sol-Gel method It is used to synthesize nano materials of very high purity. It is economically cheap. Moderate temperatures are sufficient for drying or calcination of the sample. It is suitable to produce extremely homogeneous nano composites. One material can be coated on other during the sol-gel process. Disadvantages of Sol-Gel method It is qualitative approach ; therefore, the output of the product is very less.

38. Characterization of Nanomaterials Scanning Electron Microscope (SEM) Scanning Electron Microscope (SEM) is used to study the surface topography of material. An electron gun made up of Tungsten Filament or Lanthanum Hexaboride crystal is used as a source of electron. This emitted electrons are accelerated to an energy between 1-30 keV by means of anode and directed towards magnetic lens (condenser lens). The electron beam then passes through the magnetic lens and get focus into a small region of size 40-50 Angstrom.

39. Characterization of Nanomaterials Scanning Electron Microscope (SEM) Scanning Coil provides movement to the electron beam in both the x and y directions over the material. This type of scanning is known as Raster Scanning. The electron beam then passes through an objective lens and is focused onto the surface of the material, resulting in the generation of Backscattered electrons, Secondary electrons and X-rays. They then analyzed and an enlarged version is displayed on the monitor.

40. Characterization of Nanomaterials Scanning Electron Microscope (SEM)

41. Characterization of Nanomaterials Transmission Electron Microscope (SEM) Principle: Electrons of very high energy typically >50 keV are made to pass through the specimen and the image is formed on the fluorescent screen, either by using the transmitted beam or by using the diffracted beam. Construction: It consists of an electron gun to produce electrons. Magnetic condensing lens is used to condense the electrons and to adjust the size of the electron.

42. Characterization of Nanomaterials Transmission Electron Microscope (SEM) The specimen is placed in between the condensing lens and the objective lens as shown. The magnetic objective lens is used to block the high angle diffracted beam and the aperture is used to eliminate the diffracted beam (if any) and in turn increases the contrast of the image. The magnetic projector lens is placed above the fluorescent screen in order to achieve higher magnification. The image can be recorded by using a fluorescent (Phosphor) screen.

43. Characterization of Nanomaterials Transmission Electron Microscope (TEM) Working: Stream of electrons are produced by the electron gun and is made to fall over the specimen using the magnetic condensing lens. Based on the angle of incidence the beam is partially transmitted and partially diffracted. Both these beams are recombined at the E- wald sphere to form the image. The combined image is called the phase contrast image.

44. Characterization of Nanomaterials

45. Characterization of Nanomaterials X-ray Diffraction (XRD) and Bragg’s Law Incident beam Incident beam

46. Characterization of Nanomaterials Single Crystal Method for XRD In this method, monochromatic X-rays are incident on a crystal rotating about an axis. A single crystal of about 1 mm in size is placed on a rotating shaft. When the crystal is rotated, angle 𝝷 for different plane changes continuously. Whenever a set of 𝝺, 𝝷 and d satisfy Bragg’s condition Bragg peak (spot) appears. A cylindrical photographic film is used to record the diffracted beams.

47. Characterization of Nanomaterials Single Crystal Method for XRD This process can be performed in 2-ways. Method of Complete Rotation: In this method, the crystal is uniformly rotated through 360 . In a complete rotation, some of the planes are repeated and thus overlapping of spots occurs. Oscillating Crystal Method: To reduce the overlapping of spots, the crystal is oscillated through some angle. Spot pattern is not symmetric.

48. Characterization of Nanomaterials Powder Method for XRD In this method, instead of a single crystal the specimen is used in the form of powders of different particle size. The powder is filled in a narrow, needle shaped glass tube and a monochromatic beam of X-ray is going to incident on the powder specimen. The specimen is not rotated as different microcrystals have already different oriented planes in them. A strip shaped photographic film encircles the powder specimen inside of the cylindrical drum.

49. Characterization of Nanomaterials Powder Method for XRD When a monochromatic beam of X-ray is allowed to fall on the powder sample, Bragg’s condition is satisfied by many planes in differently oriented microcrystals and a diffracted beams of conical shape emerging out. This diffracted beams are going to record by a photographic film and produce a pattern as shown in figure. This method is used to determine lattice constants. Since lattice constants are unique for a material, this method is used for the identification of materials.

50. Nanostructures As discussed in the beginning of the session, nanostructures are those materials which are having their dimensions in the nanometer scale. Following are the well-known nanostructure Graphene: It is a single atom thick layer of carbon atom where in the carbon atoms are tightly packed in a hexagonal lattice. Carbon nanotubes: is a cylindrical rolled up sheet of graphene. Fullerenes: It is the form of carbon having a large spheroidal molecule consisting of a hollow cage of sixty atoms.

51. Carbon Nanotubes In 1991, Sumio Ijima discovered Carbon Nano Tubes (CNT). They are allotropes of carbon atoms with a cylindrical nanostructure. CNTs are large molecules of pure carbon that are long and thin shape like tubes having diameter of 1-3 nm.

52. Carbon Nanotubes SINGLE WALLED CNT: A single graphene tube (Graphite layer) having diameter of 2 nm and length of 100 μm is called single walled CNT (SWCNT). MULTI WALLED CNT: Two or more than two graphene tubes (Graphite layers) having diameter in few nanometers is called multi walled CNT. (MWCNT)

53. Carbon Nanotubes CHIRAL VECTOR (CH): The structure of nanotube can be specified by a vector Ch, which is given by Ch = na 1 +ma 2 in an infinite graphene sheet. where n & m are the unit vector of graphite in real space. Translational Vector (T): The angle which is normal to chiral vector, is known as translational vector. Chiral Tube: A tube obtained by folding the sheet along chiral angle is called chiral tube. Chiral Angle ( ϴ) : The angle (ϴ) between X axis and chiral vector (Ch) is known as chiral angle. It is also used to denote the folding types. The angle between 0° < ϴ < 30° are sufficient to uniquely define different types of nanotubes.

54. Carbon Nanotubes Sr. No. Various Parameters Armchair Zigzag Chiral / Helical 1. Definition CNTs having value of chiral angle equal to 30° and T is parallel to C-C bond of carbon hexagons are known as armchair CNTs. CNTs having value of chiral angle equal to 0° and T isn’t parallel to C-C bond of carbon hexagons are known as zigzag CNTs. CNTs having value of chiral angle in between 0° – 30° and T isn’t parallel to C-C bond of carbon hexagons are known as Helical CNTs. 2. Chiral Vector (Ch) Ch = (n, m) where n=m Ch = (n, 0) where, m=0 Ch = (n, m) where, n, m≠0, n≠m. 3. Chiral Angle (ϴ) 30° 0° 0° < ϴ < 30° 4. Chirality Achiral Achiral Chiral   5.   Types   Metallic   Semiconducting Metallic or Semiconducting depending upon chirality

55. Carbon Nanotubes Characteristics of Carbon Nanotubes (CNTs): CNTs have high electrical and thermal conductivity. CNTs are very elastic. CNTs have high tensile strength. CNTs are highly flexible. CNTs have low thermal expansion. CNTs are good electron field emitter.

56. For Your Time Thank you