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Growth of Metallic Carbide Nano Structures Employing Laser Assisted Plasma Based Ion’s Source 2 5/5/2017 11:17:06 PM Contents Objective Introduction Experimentation Results and Discussion Conclusions Applications References Objective • To implant the metallic ions to grow nano hillocks on the surface of graphite Laser Material Excitation Temperature Rise Thermal + Non Thermal Excitation Volume Changes Stresses Defects Ablation Plasma Formation Direct bond Breaking 5 Ion Generation Process 5/5/2017 11:17:06 PM Target irradiation: Focused laser beam irradiated on target surface induces plasma. a Schematic of generation of Plasma b Controlling Parameters Laser energy, fluence, pulse width and focal spot • influence the characteristics of the plasma. 7 5/5/2017 11:17:06 PM Steps to Perform Experiment Production of ions Energy Measurement of Ions Ion Implantation Electrochemical Etching 8 5/5/2017 11:17:06 PM Step – 1 and 2 Production of Ions and Energy Measurements Nd: YAG laser (1064 nm, 10 mJ, 12 ns, 1.1 MW) Target (W, Al, Cu) IR focussing lens (to focus laser beam) Vacuum ( ~ 10-4 torr ) Potential Applied (2KV) 9 5/5/2017 11:17:06 PM Ions Electrons Region of fast ions and slow electrons Region of fast electrons Region of slow ions Direction of the self generated electric field Figure : Block diagram of laser generated ion emission process (M. Shahid Rafique, M. Khaleeq ur Rahman, M. Shahbaz Anwar, Faryaal Mahmood, Afshan Ashfaq & Khurram Siraj, “Angular Distribution & Forward Peaking in Laser Produced Plasma Ions”, Laser & Particle Beams,23, 131-135, 2005). • The laser beam was focused on Al target to generate plasma. • An external electric field was applied to these ions by using an acceleration assembly. • This assembly (Fig.) comprised of an extraction box/chamber (EB) and ground electrode. • The target (placed inside EB) was kept at positive potential with respect to the ground electrodes. Step 2. Ion Energy Measurements • Thomson parabola technique, the associated parameters are shown. • For ion energy measurements E = e2B2R2/2 (M J) • where, R2 = a[x + (x2+ 1)1/2] • is the radius of curvature of ion trajectory in magnetic field and x = L/d. 12 5/5/2017 11:17:06 PM Step - 3 Ion Implantation Nd: YAG laser Target IR convex Lens Substrate Substrate size Vacuum (1064 nm, 10 mJ, 12 ns, 1.1 MW) (W, Al, Cu) (to focus laser beam) (Graphite) (1 cm2) ( ~ 10-4 torr ) Fig. A schematic of ion implantation setup. Table 1: Energy measurement Ions 15 5/5/2017 11:17:06 PM Mass Value of Value of Value of (amu) X (cm) R (cm) Energy T(keV ) Aluminu 26.982 0.0493 273.85 85.722 Copper 63.546 0.0637 211.93 21.8 Tungsten 183.85 0.0543 248.6 10.368 m I. II. M. Shahid Rafique, M. Khaleeq ur Rahman, Aziz ul Rehman, Khurram Siraj & M. Fiaz Khan, “Laser produced copper ion energy spectrum employing Thomson Parabola Technique” Journal Laser Physics (Russia), 17, 3, 282 – 285, (2007). M. S. Rafique, M. Khaleeq-ur-Rahman, Shakoor Munazza, K. A. Bhati, “Characteristics of Ions Emitted from Laser-Induced Silver Plasma”, Plasma Science and Technology,10,4, (2008). Results Taken from TRIM (a) Aluminum Ions 16 5/5/2017 11:17:06 PM (b) Copper Ions Figure : Penetration depth of ions into the Graphite substrate (a) For Aluminum ions (b) For Copper Ions 17 Results Taken from TRIM 5/5/2017 11:17:06 PM (a) Tungsten ions Table 2: Penetration depth of ions into the graphite substrate Ions Figure : (c) Penetration depth of ions into Graphite for Tungsten Ions Value of Energy Penetration Depth T(keV) (Ǻ) Aluminum 85.722 1225 Copper 21.8 278 Tungsten 10.368 98 Ion matter interaction • When ions are bombarded on a substrate, they collide with the surface atoms transferring large amount of energy to the surface. • An energetic ion can collide with several atoms before coming to rest. • In this process, the atoms in the path of an ion are displaced and energized resulting in a cascade collisional process, which is responsible for the sputtering of the substrate atoms hence creating damage. Nuclear (elastic) collision • In a nuclear (elastic) collision, the incident ion interacts with the nuclei of the substrate atom. • This interaction results in the deflection of ion and it can displace the lattice atom. • The outcome of this interaction depends on the energy of ion. • The displaced atom (primary recoil) can then initiate cascade collisions. • The cascades and sub-cascades can result in a thermal spike. • This could generate heat and cause melting and evaporation in substrates. • Phonons can also be generated if the atom does not possess enough energy to move away from its lattice site and hops back into its original position. Electronic (inelastic) collision • In an electronic (inelastic) collision or ionization, the incident ion interacts with the electrons of substrate atoms. • The electrons gaining energy from this collision leave the atom and possess enough energy to induce electron phonon interaction. • It results in heat production and it can also lead to thermal spike. • The intense ionization along the path of ions can also lead to coulomb explosion. Stopping of ions in matter • Energetic ions impinging a solid slow down by transferring their energy by elastic or in elastic collisions, ions loose energy until they reach the thermal energy of the substrate. • At this point, the ion is considered to be stopped. • This ion can either become an interstitial or replacement atom. • The interstitials induce mechanical tangential stresses in the substrate. • By ion irradiations, material can be plastically deformed resulting in observable change in surface structure • A vacancy is produced if the ion displaces an atom and still possesses the energy greater than the lattice energy of the substrate. • Energetic ions can generate micro voids in the substrate, which can also produce stresses. Electronic stopping of ions • Electronic stopping is often termed as ionization. • If the ion velocity is lower than the Fermi velocity, which is of the same order as Bohr velocity vo = 2.19×108 cm/s, target electrons induce friction like force on the incoming ion. • The electronic stopping cross section is thus predicted to be proportional to the velocity of incoming ion. • High velocity or energy of ions would result in more electronic friction hence more electronic stopping Se. • There is another model, the Firsov’s model, according to which, during interaction of ion and atoms, electron clouds penetrate each other as shown in Fig. where, 1 is denoting the ion and 2 is the substrate atom. • The electrons transverse the intersecting plane and accommodate their kinetic energy (for both the ion and atom moving) to dynamic electronic configuration of the inter-atomic system. • Kinetic energy of ions can be transferred to the electrons of atoms. • With very low ion energy or velocity, the substrate atom will have enough time to be scattered early in the collision, due to potential development between the atom and the approaching ion. • The energy transfer would be small. • For moderate ion energy, the ion and atom would be able to achieve the smallest possible distance before scattering. • In which case, the nuclear energy transfer will be maximized. • If ion energy further increases, there will be no time for potential development between ion and substrate atom and ion will transfer its energy to the screening electron hence exciting the substrate atom. • Therefore, for very high energy ions, the interaction times become the limiting factor for nuclear stopping resulting into dominating electronic stopping. 32 Step-3 Electrochemical Etching 5/5/2017 11:17:07 PM KCl-Saturated Calomel ( Reference Electrode) Graphite (Counter Electrode) Ions implanted substrate (Working Electrode) A potential of 1.8 V was applied to the sample for 30 min in a 0.1 M NaOH aqueous solution at room temperature. 33 5/5/2017 11:17:07 PM 1.8 V Ions Implanted Substrate (OH)- Kcl saturated Calomel (Na)+ 0.1 M NaOH eq. Graphit e Figure : Schematic of Electrochemical Etching 34 Adsorption and intercalation of hydroxide ions (OH-): 5/5/2017 11:17:07 PM C(s) + OH- C(s)OH(ads’ int) + e4C(s)OH(ads’ int) 4C+ 2H2O + O2 where C(s)OH(ads,int) represents the carbon on the substrate with OH- chemisorbed or intercalated, while {C} indicates detached carbon atoms. S. Kato, T. Yamaki, S. Yamamoto, T. Hakoda, K. Kawaguchi, T. Kobayashi, A. Suzuki and T. Terai. “Preparation of tungsten carbide nanoparticles by ion implantation and electrochemical etching”. Nuclear Instruments and Methods in Physics Research B 314, 149–152, (2013). 35 5/5/2017 11:17:07 PM Characterization Techniques SEM A F M XRD EDX • Figure shows a schematic of the ion irradiation setup. • The substrates were kept 2 cm away from the ground electrodes to irradiate a well collimated beam at the surface. • Five hundred laser shots were used to generate ions at 2 kV, 4 kV, 6 kV, 8 kV, and 10 kV acceleration potentials. Fig. A schematic of ion irradiation setup. Aluminum Carbide Nanoparticles 39 5/5/2017 11:17:07 PM X-Z dimension profile for 1 1 2 X-Z dimension profile for 2 Figure: AFM Image of Aluminum Carbide nanoparticles (b),(c) diameter profile for different particles Aluminum Carbide Nanoparticles 40 5/5/2017 11:17:07 PM C C C C C C 00-035-0799 “Rhombohedral” structure having Grain sizes, 6.72, 6.89, 7.08, 7.46, 7.9 and 7.29 nm respectively was observed. Figure : XRD Spectrum of Aluminum Carbide nanoparticles I. Natl. Bur. Stand. (U.S.) Monogr. 25, 21, 128 (1984). II. Davey, Phys. Rev., 25, 753 (1925). III. Jeffrey, G., Wu, V. , Acta Crystallogr., 20, 538, (1966). Aluminum Carbide Nanoparticles 41 5/5/2017 11:17:07 PM Figure : EDX Profile of Aluminum Carbide nanoparticles 42 Copper Carbide Nanoparticles 5/5/2017 11:17:08 PM X-Z dimension profile for 1 2 1 X-Z dimension profile for 2 Figure : (a) AFM Image of Copper Carbide nanoparticles (b), (c) diameter profile for different particles 43 Copper Carbide Nanoparticles 5/5/2017 11:17:08 PM C C C C C C C 00-051-0626 “Hexagonal” structure having average Grain sizes 5.5 nm was observed. Figure : (a) XRD Spectrum of Copper Carbide nanoparticles Braga, D., Ripamonti, A., Savoia, D., Trombini, C., Umani-Ronchi, A., J. Chem. Soc., Dalton Trans. (1979), 2026. 44 Copper Carbide Nanoparticles 5/5/2017 11:17:08 PM Figure 8.5: EDX Profile of Copper Carbide nanoparticles 45 Tungsten Carbide Nanoparticles 5/5/2017 11:17:08 PM X-Z dimension profile for 1 2 1 X-Z dimension profile for 2 Figure : (a) AFM Image of Tungsten Carbide nanoparticles (b), (c) diameter profile for different particles Tungsten Carbide Nanoparticles 46 5/5/2017 11:17:08 PM C C C C 00-035-0776 “Hexagonal” structure having average Grain sizes 7.41 nm was observed. C Figure : XRD Spectrum of Tungsten Carbide nanoparticles I. II. Natl. Bur. Stand. (U.S.) Monogr. 25, 21, 128, (1984). Rudy, E., Windisch, S., J. Am. Ceram. Soc., 50, 272, (1967). Tungsten Carbide Nanoparticles 5/5/2017 11:17:08 PM Figure 8.8: EDX Profile of Tungsten Carbide nanoparticles 47 Conclusions 51 5/5/2017 11:17:08 PM Metallic carbide nanoparticles have been fabricated by implanting the laser induced ions on the graphite substrates. The diameter range of the nanoparticles was 5-80 nm. The crystal structure for aluminum carbide nanoparticles was rhombohedral while for nanoparticles it was hexagonal. tungsten and copper carbide 52 5/5/2017 11:17:08 PM Applications • Metallic carbides are being used…… Dye sensitized solar cells Artificial leaf In methanol fuel cells Ultrafine cutting tools