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Nanoscale Electrodeposition Rob Snyder July 2102

Nanoscale Electrodeposition Rob Snyder July 2102. Teapots can be electroplated with a thin layer of silver on a more rigid metal to give them an attractive and durable finish . http://encarta.msn.com/media_461526422/Electroplating.html. Why choose electrodeposition to make very thin films?.

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Nanoscale Electrodeposition Rob Snyder July 2102

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  1. Nanoscale Electrodeposition Rob Snyder July 2102

  2. Teapots can be electroplated with a thin layer of silver on a more rigid metal to give them an attractive and durable finish. http://encarta.msn.com/media_461526422/Electroplating.html

  3. Why choose electrodeposition to make very thin films? The process is relatively easy to manage and only needs simple equipment. It is relatively easy to control the deposition rate by manipulating voltage, current, and solution concentrations.

  4. These are the components of an electrodeposition circuit that you will use today

  5. A Schematic Diagram of the Circuit Zn2+ and SO4-2 ions in solution Neutral Zno and Cuo atoms

  6. There are a variety of learning goals for this activity.Students can learn how: • Electrical energy can drive an electrodeposition process. • A masking process can produce specific patterns of electrodeposition. • To apply the concepts of oxidation and reduction to a description of the electrodeposition process. • Use electric current, time and atomic radii data to calculate the depth of a layer of metal that has been deposited on an electrode.

  7. Water is not a good conductor of electricity. A small amount of Zinc Nitrate is dissolved in water to provide some ions so that the solution conducts electricity. ZnNO3 dissociates in water NO3-1 NO3-- Zn+2 Zn+2

  8. Copper and Zinc Electrodes are put into the solution.A battery provides a source of electric potential difference (voltage). ← e- I → V Zinc anode Copper cathode Zn+2 Zn+2 NO3-- NO3-1 Zn+2 Zn+2 Zinc ions in solution migrate in the direction of the copper electrode. More zinc ions are produced at the zinc anode.

  9. oxidation Zn(0) –> Zn2+ + 2e- Neutral Zno atoms in the anode are oxidized and become Zn+2 ions.Zn+2 ions are reduced at a copper cathode and become neutral Zno atoms. ← e- I → V Zinc anode Copper cathode ZnSO4 dissociates in water NO3-1 NO3-- Zn+2 reduction Zn2+ + 2e- –> Zn(0)

  10. Assemble an electrodeposition circuit with a switch in the off position. Clean copper and zinc electrodes. Carefully install the electrodes on the bracket as you lower them into a solution of zinc nitrate. Turn the switch on to start the electrodeposition process. You can turn the copper electrode around at some point so that both sides are electrodeposited somewhat evenly. Stop electrodeposition when the copper electrode seems to be covered with zinc. Carefully put the electrodes on a paper towel to dry before making measurements of the length and width of the electroplated zinc metal. A document describes a procedure for electrodepositing a thin film of Zn atoms onto a copper electrode.

  11. You can use painters tape to mask a portion of a copper electrode and do a second electrodeposition. After the masking electrodeposition, we will discuss how to calculate the thickness of the layer of zinc atoms on the copper strip.

  12. It is important to understand what an ammeter in the electrodeposition circuit measured.

  13. An ammeter measured the number of electrons lost by Zn atoms during oxidation at the Zn anode. That was equal to the number of electrons gained by Zn+2 ions during reduction at the copper cathode. A coulomb is equal to 6.24 x 1018 elementary charges (electrons) . One Ampere = 6.24 x 1018 electrons lost and gained at the electrodes each second.

  14. Milliamperes Using a 1.5 volt D Cell battery may result in milliampere (mA) ammeter reading. An example would be a current reading of 17 milliamperes. 17 mA x 1 ampere = 0.017 amperes 1000 mA

  15. Mathematical operations using scientific notation becomes very useful as students determine if they have actually created a nanoscale structure!

  16. Time of Trial: 5 minutes = 3.0 x 102 seconds Width of copper electrode in the solution 2 cm = 2.0 x 10-2 meters Length of electrode in the solution 5 cm = 5.0 x 10-2 meters Average ammeter reading 17 milliamperes Average ammeter reading 0.017 ampere = 1.7 x 10-2Coulomb/sec Sample Data

  17. Step One. Calculate the number of electrons that zinc ions gains in 5 minutes. (1.7 x 10-2 C/s)(6.24 x 1018 e/C)(3.0 x 102 s) = 3.18 x 1019e Step Two. Calculate the number of zinc atoms that formed. 3.18 x 1019 e = 1.59 x 1019 atoms of Zn formed 2 electrons for each Zn ion A sample calculation of the number of Zinc Ions reduced at the copper cathode.

  18. Step 3: Calculate the number of atoms of zinc in a row across the width of the copper electrode. Note: Distances are measured in meters (m). ____2.0 x 10-2 m = 7.72 x 107 atoms in a row 2.59 x 10-10 m/atom Step 4: Calculate the number of atoms in a column along the length of the electrode that was in the solution. ___5.0 x 10-2 m = 1.93 x 108 atoms in a column 2.59 x 10-10 m/atom Step 5: Calculate the number of atoms in one rectangular layer on one side of the copper electrode. (7.72 x 107 atoms in a row) x (1.93 x 108 atoms in a column) = 1.49 x 1016 atoms A zinc atom has a diameter of 2.59 x 10-10 meters

  19. Zinc atoms were electrodeposited on both sides of the Copper Electrode. Step 6: Calculate the number of atoms that formed a single layer on both sides of the copper electrode. 2 x 1.49 x 1016 atoms = 2.98 x 1016 atoms Students will probably observe that more zinc atoms were deposited on the side of the copper electrode facing the zinc electrode.

  20. Step 7: Calculate the average number of layers of zinc atoms. __1.59 x 1019 atoms of zinc__ = 5.34 x 102 layers of atoms 2.98 x 1016 atoms / layer Step 8: Calculate the average thickness of the layer of zinc. 5.34 x 102 layers x 2.48 x 10-10 m/layer = 13.24 x 10-8 m Is the thin layer of Zinc a Nanoscale Structure?

  21. The calculation of the thickness of the was based on an assumption that there were an equal number of zinc atoms in each later. If electrodeposition is managed very carefully, zinc atoms will form a hexagonal close-packed structure. http://www.geo.ucalgary.ca/~tmenard/crystal/metalstatic.html

  22. ∆G = ∆H - T ∆S The Gibbs Free Energy equation indicates if a chemical change is exergonic (when ∆G < 0) or endergonic (when ∆G > 0). The battery was a source internal energy. ∆H (Enthalpy) had a positive value. and Zinc ions moving somewhat randomly in solution become more ordered on the copper electrode. ∆S (Entropy) had a negative value. The process occurred at a relatively low temperature. As a result, ∆G > 0 The Gibbs Free Energy Equationcan be used to describe electrodeposition.

  23. Another possible electrodeposition trial.

  24. How many “big ideas” of nanoscale self-assembly were a part of this activity? • Mobile structural components • Target is low energy equilibrium state • Ordered structures • Assembly through attraction or repulsion forces between the components • Environment selected to induce designed interaction • Components retain physical identity through and after • Reversible by controlling the environment Whitesides & Boncheva (2002)

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