Nanotechnologyqfwgwjwfsdwwywuwfwy-1.pptx

It is about the nanotechnology

1.   UNIT-4 Nanotechnology 36 Introduction to Nano technology and Nano scale   37 Quantum confinement & Surface to Volume ratio   38 Numerical problems   39 Bottom-Up fabrication: Sol Gel   40 Precipitation method   41 Combustion method   42 Top-down Fabrication; Ball Milling and Physical Vapor Deposition (PVD)   43 Chemical Vapor Deposition (CVD)   44 Characteristics techniques: Basic principles of XRD (X-Ray Diffraction), SEM (Scanning Electron Microscope  

2. Synthesis routes:- There are two types of approaches for synthesis of nano materials and fabrication of nano structures. ➢ 1. Top-Down method ➢ 2. Bottom-up method Top-Down method :- This approach for the synthesis of nanomaterials is the one in which the bulk material is broken down to smaller dimensions by different means and then restructured. Bottom-Up method:- The formation of a material via atom-by-atom, molecules-by-molecules and cluster-by cluster deposition is called a bottom up approach. Bottom-up approaches are generally based on chemical growth process techniques.

3. Top–Down Methods :-   Ball milling Method :- I ncludes mechanical breakdown of large substances into smaller one. It is used in producing metallic as well as ceramic nanomaterials. B all mill is a grinder in which a powder mixture is subjected to high-energy collision from the balls. The working of a ball mill is based on impact and attrition

4. It includes a hollow cylindrical shell which is rotated about its own axis. The axis of the shell is either horizontal or slightly inclined. The shell is partially filled with balls. The balls form the grinding medium balls are made up of ceramic, flint pebbles, iron, hardened steel, silicon carbide, tungsten carbide or hard rubber. The inner wall of the shell generally contains a coating of abrasion resistant material, e.g., manganese steel or rubber.

5. The powder of a material is taken inside the steel container. When the shell is rotated, the balls lift upwards on the rising side of the mill and falls after reaching near the top causing an impact on the particles trapped between these balls and the shell surface. This impact reduced the size of these particles. A magnet is placed outside the container to provide the pulling force to increase the milling energy. The ball to material mass ratio is normally maintained at 2 ratio1. This process of ball milling is done approximately 100 to 150 hrs to get uniform fine powder

6. Advantages of ball milling process: 1. Nanopowders of 2 to 20 nm in size can be produced. 2. It is an inexpensive and easy process. Disadvantages: 1. The shape of the nanomaterial is irregular. 2. There may be contaminants inserted from ball and milling additives. 3. This method produces crystal defects.

7. Chemical Vapour Deposition :- CVD is popular to produce 1-D nanostructures. In CVD a solid material is deposited from a vapor by chemical reaction. The solid material is obtained as a coating, a powder, or as single crystals. By varying experimental conditions, substrate material, substrate temperature, pressure, etc., different structures can be grown.

8. Basic components of CVD: Precursors Delivery Systems Controlled delivery of the precursor(Liquid, solid or gas) into the reaction chamber. Consists of flow meter or mass flow controller which can control the flow rate of the precursor. Reaction Chamber or Reactor A reaction tube or reactor, in which the CVD reactions take place to form the desired material. It consists of the following parts. A alumina or quartz tube Couplings to hold the pressure and maintain environment isolation. Inlet & Outlet for the flow of gas into the chamber.  

9. Energy Source Include resistance heating, radiant heating, electric induction heating, laser heating, magnetic induction heating CVD, etc. Vacuum System A vacuum system is usually used in CVD to provide continuous and uniform pressure throughout the CVD process. Exhaust Gas Handling Systems To remove the byproduct gases created from reaction process.

10. Advantages :- Uniform and harder films on topographically complex substrate. Any element or compound can be deposited. High purity can be obtained. High density – nearly 100% of theoretical value. Economical in production.

11. Physical vapor deposition  ( PVD ) :- Physical vapor deposition  ( PVD ) is an environment friendly vacuum deposition technique c to produce thin films and coatings. It c onsisting of three fundamental steps: 1) Vaporization of the material from a solid source. 2) Transportation of the vaporized material. 3) Condensation on the substrate to generate thin films and nanoparticles.

12. The two most common PVD processes are: Thermal evaporation sputtering Thermal evaporation  uses the heating of a material to form a vapour which condenses on a substrate to form the coating. Heating is achieved by various methods including resistive heating, electron or laser beam etc.

13. Hot resistance Substrate Vaccum chamber Metal Vapour Vaccum system

14. Pulsed Laser Deposition  (PLD) A focused pulsed laser strike the target material and vaporizes or ablates the surface. V aporized materials deposited on the substrate as  thin film .

15. Sputtering technique :-   Sputtering is a PVD process to develop thin films. The atoms are ejected from a solid target by bombarding with energetic particles like argon ions. The energetic ions are generated by the ionization of gas using DC, AC or RF input signal between the two electrodes - the cathode (target) and anode (substrate) of the system.

16. Sputtering Process

17. The sputtering process stages: ionization of sputtering gas, usually an inert gas such as argon acceleration of ions towards the target collision between ions and atoms on the surface of target material ejection of atoms from target and deposition of sputtered atoms onto the substrate.

18.   PVD has several advantages including:   Improved properties compared to the  substrate material ; all types of inorganic materials can be used; E nvironmentally friendly. However, PVD has also some disadvantages including: Problems with coating complex shapes; High process cost and low output; Complexity of the process.

19. Characterization techniques X-Ray Diffraction (XRD) :- X-rays are the electromagnetic radiation with a very short wavelength about 1Å (λ ≈ 1 Å) which is comparable to the atomic size and interplanar spacing in solids. XRD patterns(graphs) are used to calculate the variety of crystalline parameters like lattice parameter (a), inter-planner spacing (d), phase purity, crystallite sizes (D), etc.

20. Experimental setup to draw the XRD patterns for powder samples: XRD instrument consist of four main components: X-ray source, specimen holder, receiving optics and X-ray detector. The source and detector lie on the circumference of focusing circle and the sample stage at the centre of the circle. The angle between the projection of X-ray and the detector is 2θ, where ‘θ’ is the Bragg’s angle. F ine powder samples are mounted on the sample holder. When a beam of X-ray is incident on the sample, X-rays are scattered by each atom in the sample. When the X-rays scattered from a particular set of crystal plane are in phase, they interfere constructively and gets the intensity maximum at that particular angle.

21. Experimental setup to draw the XRD patterns for powder samples:

22. The distance between the crystal planes are calculated using Bragg’s equation. 2 d sin θ = n λ Where, λ is the incident X-rays wavelength , n is an integer , d is inter-planar separation, and θ is Bragg angle or diffraction angle

23. Particle size or grain size: Using Scherrer equation, particle size of nano particles can be found from XRD patterns using Scherrer equation. The  Scherrer equation , in  XRD , is a formula that relates the size of the particle(D) in a solid in powder form to the broadening of a peak in a diffraction pattern.

24. K is a dimensionless  shape factor , with a value close to unity( ∿ 0.9) and depends on the shape of the crystallite. λ  is the  X-ray   wavelength β is the line broadening at half the maximum  intensity  ( FWHM ).

25. Fig: Schematic Block diagram of SEM SEM provides topographical and elemental information of the sample at magnifications of 10 times to 300000 times.

26. A collimated electron beam impinges on the thin surface layer of a specimen. Backscattered electrons of high energy, secondary electrons of low energy and characteristic X- rays are generated . These signals are detected by suitable detectors and sent to the computer screen. The backscattered electrons produce the image of the sample. The characteristic X-rays generated are used for the identification and estimation of different elements present in the specimen by EDS. In order to avoid the oxidation and contamination of filament (tungsten tip) as well as to reduce the collisions between air molecules and electron, filament and sample will be placed in a vacuum chamber.

27. Silver Shelled Gold Nanoparticles

28. TEM studies provide information regarding the crystal structure, crystal quality, and grain size , particle shapes as well as their size and degree of agglomeration

29. A field emission gun at the top of the microscope produces a stream of electrons. This stream of electrons is condensed by the initial condenser lens. The next condenser lens produces electrons into a narrow coherent beam. The condenser aperture further eliminates high angle electrons. The accelerated electron beam hits the test sample, and some portion of it is transmitted.  

30. The transmitted portion of electron beam is focused by an objective lens arrangement into an image. The objective aperture improves the contrast by blocking out high angle diffracted electrons. Selected area aperture facilitates the observer to examine the diffraction by an ordered arrangement of atoms in the specimen. Intermediate and projector lenses magnify the image. The beam strikes the phosphor screen to form an image. The brighter areas of the image represent thinner or lesser dense sample areas since these areas transmit more electrons. The darker area of the image represents thicker or denser sample areas since these are transmitted few electrons.

31. TEM of Gold Nanoparticles

32. Applications of Nanomaterials Material Technology Cutting tools made of nanosrystalline tungsten carbide, Titanium carbide are more wear resistant. Nano scale intermediate layers for wear and scratch resistant hard coating Ceramic materials with small grain size are ductile Nanocrystalline silicon carbide ceramics with good chemical and HT properties used in automobiles and furnaces Carbon nanoparticles fillers used in car tyres and bumpers Titanium dioxide nanocoating is highly hydrophobic and anti bacterial Nanocrystalline yettrium samarium and cobalt magnets with high coercivity used in motors and MRI Nanoengineered membranes used in water purification process(RO) Metal nanoparticles are used in degradation of harmful pollutatnts in soil and ground water (Photocatalytic property) Controlled porocity at nanoscale leads to breathable, water proof and strain resistant fabrics Nano TiO2 and ZnO used in sunsceens Nanospheres of inorganic materials used in lubricants

33. IT: Nano fabricated magnetic materials have increased data storage capacity Thin films of nanoscale used in optoelectronic devices Nano crystalline lead tellurite has good photo phosphorescence property used in flat panel displays Quantum electronic devices are replacing commercial devices Biomedical: Nano crystalline zinconium oxide is hard, wear reistant and biocompatible used for implants Nano crystalline silicon carbide used for artificial heart valves Biosensitive nano particles used for tagging of DNA and DNA chips Nnao porous polymers are used in controlled drug delivery Nanostructral ceramics used in bone implants ENERGY STORAGE: Nano ceramics used as additive to diesel Nanoengineered memberances used as fuel cells Aerogel nanomaterials are used as separators in batteries Magnetic refrigeration Fabrication of ionic batteries Ni-Pt nanoparticles are used in Hydrogen storage devices.