Material science project presentation...

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1. Synthesizing techniques Top Down Approach Breaking down matter into small basic building blocks Bottom Up Approach Building complex systems by combining simple atomic level components.

2. Top Down and Bottom Up Approach

3. Top Down Approach Sol- Gel Method Bottom Down Approach CVD PVD PLVD

4. Sol gel technique This sol gel process is a wet chemical technique usually used for the fabrication of ceramic materials. A sol is a stable dispersion of colloidal particles in a solvent. A gel is a semi rigid mass that forms when the solvent from the sol begins to evaporate and the ions or particles left behind join together in a continuous network. This method basically involves the conversion of monomer into a colloidal solution (sol) that acts as the precursor for an integrated network (gel) of either discrete particles or network polymers. The precursor sol can be either deposited on substrate to form a film, or cast into a suitable container with a desired shape or used to synthesize powders . The sol gel approach is interesting in that it is cheap and low temperature technique that allows for the fine control on the product’s chemical composition.

5. One Example on Experimental procedure The formula of synthesised rare earth doped cobalt nickel ferrite is given as Ni 0.5 Co 0.5 R y Fe 2-y O 4 (where R = Sm, Nd, Dy, Yb and y = 0.05, 0.1 ). The glycine, cobalt nitrate, rare earth nitrate, and ferric nitrate are used to synthesise powders. The mixture is then dissolved in a minimum amount of double-distilled water to get a clear solution. The mixture is stirred continuously using magnetic stirrer for one hour at 25°C and then for half an hour at 80°C. The mixed solution is then kept on a hot plate with continuous stirring at 150°C-200 C. Ammonium solution is added until pH reaches 6.5 and the viscosity increases. During evaporation, the solution becomes viscous and finally forms viscous brown gel. Formula used for calculating the number of grams required : stochiometric coefficient × M Wt. × Volume of distilled water

6. Continue on Experimental procedure After a few minutes, the gel automatically gets ignited and burnt with glowing flints. The auto-ignition gets completed within one minute, and results in the formation very light and short fibres. Then the as burnt ferrite powder is crushed using a mortar and pestle. The powder, after complete grinding, is first pre-sintered at 700 o C in a furnace for 5 hours, followed by furnace cooling. Approximately 3-5 wt% Polyvinyl alcohol is added to the obtained powder, which helps in the granulation/binding of powder particles. Then pre sintered samples are then uniaxially pressed into pellets under a pressure of 7 tons using hydraulic KBr press. Finally pellets are sintered at 950°C for about 7 hours in order to remove the organic binders and obtain the proper density.

7. Experimental procedure . Fig: Stirrer and gel formation Fig: auto combustion and combustion product Fig: Hydraulic press Fig: Pellets formed after pressing

8. Experimental procedure Sol-Gel Technique Fig. Schematic flow chart for sol gel synthesis Fig. Gel formation Fig. powdered sample S M Chavan , Journal of Alloys and Compounds, 2010, 507(1) 21–25

9. Experimental procedure: Sol-Gel Technique S M Chavan , Journal of Alloys and Compounds, 2010, 507(1) 21–25 3. Ashes 4. Final product 1. Nitrate mixture 2. Combustion

10. Important

11. T hin film growth techniques There are many thin film growth techniques to synthesis high-quality thin film samples with the designs required for the application purposes. P ulsed laser deposition (PLD). RF magnetron sputtering. C hemical vapor deposition (CVD). M etal-organic CVD (MOCVD). C hemical solution deposition. M olecular beam epitaxy (MBE)

12. Department of Physics, Central University of Kashmir

13. Pulsed Lased Deposition(PLD) Pulse Laser Deposition (PLD) is a versatile technique used for depositing thin films of various materials onto substrates. It involves the use of a high-energy pulsed laser to ablate material from a target, which then condenses onto a substrate to form a thin film.

14. Basic Theory The Pulsed laser deposition Technique can be described in following steps. Each Step has importance in determining the crystallinity, uniformity and stoichiometry. 1. 2. 3. 4. 5. 6. Laser ablation of the target material from pellet Formation of plasma Dynamic of Plasma Deposition of the target material on substrate Nucleation and growth of the film Department of Physics, Central University of Kashmir Preparation of the target material

15. Pulsed Laser Deposition Target Substrate Temperature Pressure Plasma Laser Department of Physics, Central University of Kashmir Breakthrough came in 1987 when Dijkkamp et al. were able to deposit thin film of YBa 2 Cu 3 O 7, which was of superior quality than the films deposited with other alternative techniques .

16. Preparation of Target PLD begins with the preparation of the target material. The target is typically a high-purity solid material in the form of a single crystal, polycrystalline, or amorphous structure. The composition and quality of the target material directly influence the properties of the deposited film.

17. Setup The target is placed inside a vacuum chamber along with the substrate, which is positioned facing the target. The entire setup is maintained under a controlled atmosphere to prevent contamination and oxidation during the deposition process. The vacuum environment also facilitates the control of film growth parameters.

18. A high-energy pulsed laser is directed onto the surface of the target material. The laser pulses have very short durations (typically in the nanosecond to femtosecond range) and high peak powers. When the laser beam strikes the target surface, it rapidly heats a small volume of the target material, causing it to undergo a phase transition from solid to vapor (ablation). The atoms are removed from the target/bulk through vaporization of bulk at surface in a state of non-equilibrium Pulse of Laser beam is incident on the surface of bulk and penetrates into it within the depth depending on wavelength of laser and nature of material. Electric field is generated that is sufficient to knock out electrons from the penetrated volume. The free electrons oscillate within the electromagnetic field of laser light thereby colliding with atoms of bulk and transferring some energy to lattice of target material within the surface region. The surface gets heated and material is vaporized Laser ablation of the target material from pellet

19. Plume Formation/ Dynamic of Plasma The ablated material forms a plasma plume above the target surface. This plume consists of neutral atoms, ions, and electrons, which rapidly expand away from the target due to the high kinetic energy imparted by the laser ablation process. The plume contains the vaporized target material along with any contaminants or gas species present in the vacuum chamber. Expansion of material in the form of plasma in a direction perpendicular to the target surface due to coulomb repulsion and recoil from target surface. Background pressure inside the chamber determines the shape of plume. Vacuum causes the much narrowness and forwardly directed plume. No scattering with background gases. High pressure cause diffusion like expansion of ablated material. The scattering depend on the mass of background gas. Department of Physics, Central University of Kashmir

20. Deposition of the target material on substrate An equilibrium is established between incoming and re-evaporating species. The collision region serve as source for condensation of particles. The crystalline film growth depends on the surface diffusion of the atoms. Normally the atom will diffuse through several atomic distances before sticking to a stable position within the newly formed film. High temperature results in defect free crystal growth, while low temperature may result in disordered structure. Three types of growth modes are possible: Step-flow growth, Layer-by-Layer growth, and 3D growth. Department of Physics, Central University of Kashmir

21. Experimental Setup and Methodology Department of Physics, Central University of Kashmir

22. Department of Physics, Central University of Kashmir

23. Example and Illustration Synthesis Conditions Before deposition, chamber was cleaned and Base Pressure was maintained at 1 10 -5 Torr Wavelength of laser= 248 nm Repetition rate= 10 Hz Temperature = 750 C Distance between target and substrate = 5 cm Laser energy=220 mJ BULK Thin Film Pulsed Laser Deposition Time of deposition = 15 minutes Cooling rate after deposition= 20 /min Partial pressure of 330 mTorr Optimized Parameters Ablation carried out in oxygen at a partial pressure of 330 mTorr Department of Physics, Central University of Kashmir

24. Conclusion The PLD technique has been used to deposit high-quality complex oxide films for more than a decade. The technique uses high power laser pulses to melt, evaporate and ionize material from the surface of a target. This ablation event produces a transient, highly luminous plasma plume that expands rapidly away from the target surface. The ablated material is collected on an appropriately placed substrate upon which it condenses and the thin film grows. The target material which is evaporated by the laser is normally found as a rotating disc attached to a support. This process can occur in an ultra high vacuum or in the presence of a background gas, such as oxygen which is commonly used for oxide materials. Thin film growth kinematics by PLD depends on several growth parameters such as laser energy; laser fluence (Joule/cm 2 ) and ionization degree of the ablated material. The surface temperature of the substrate has an influence on the nucleation density. The s ubstrate surface is the most important parameter for the thin film formation and the l attice mismatch between the target and substrate and also the roughness of the substrate effects the nucleation and growth of the film. In case of oxide deposition, proper oxygen pressure in the deposition chamber is needed to ensure stoichiometric transfer from the target to the film. The d istance between the target and substrate and repetition rate also have to optimize to get a high-quality thin film.