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Electrochemical Electrochemical Deposition of Cobalt Deposition of Cobalt

NanoparticlesNanoparticles

PREPARED BY: Louis Wong

INTRODUCTIONINTRODUCTION

Experimental Objective.Experimental Objective.Experimental Setup.Experimental Setup.

Electrochemical Deposition.Electrochemical Deposition.SEM Image / ESCASEM Image / ESCA

Results and Discussions.Results and Discussions.Varying Cobalt Solution Concentration.Varying Cobalt Solution Concentration.Varying Voltage, Charge.Varying Voltage, Charge.Varying pH.Varying pH.

Experiment ObjectivesExperiment Objectives

To deposit nanoTo deposit nano--sized cobalt films by sized cobalt films by electrochemical deposition.electrochemical deposition.To determine the effects of charge, pH and To determine the effects of charge, pH and cobalt solution concentration on film deposition.cobalt solution concentration on film deposition.Master the operation of SEM, AFM by Master the operation of SEM, AFM by integrating these techniques into my research integrating these techniques into my research procedures. procedures.

Electrochemical StationElectrochemical StationSTEP 1: Hydrogen Termination of 2.5mm X 13mm Si Wafer:

1. Ultrasonic pre-cut wafers in HPLC Grade Acetone.

2. Rinse wafers with alcohol followed by millipore water.

3. Immerse wafers in 5:1:1 H2O, NH4OH and H2O2 at 70oC for 20 minutes.

4. Immerse wafers in 5:1:1 H2O, HCl and H2O2 at RT for 10 minutes.

5. Immerse wafers in 2% HF solution at RT for 10 minutes.

Electrochemical StationElectrochemical Station

Working Electrode

Reference Electrode

Counter Electrode

VA

Stored in 3M KCl Solution

Hydrogen Terminated Si

Computer Display Output

Electrochemical Control Module

Electrochemical StationElectrochemical Station

Cobalt Solution bubbled with N2 for 1 hr

prior to deposition

Counter Electrode

flamed for 30 second before

deposition

Cobalt NanoparticlesCobalt NanoparticlesDifferent types of particles observedDifferent types of particles observed

Hexagonal Single Crystal Oxide Flowers Oxide Flower with Fibrous Base

Stacked Hex Crystals Wedge Crystals Crystal with Fibrous Base

Oswald RipeningOswald Ripening

For a curved surface (For a curved surface (egeg. Surface of the . Surface of the deposited particle), the pressure at the concave deposited particle), the pressure at the concave side > the pressure at the convex side. side > the pressure at the convex side.

increase in curvature will decrease the increase in curvature will decrease the stability of the particle and increase the solubility.stability of the particle and increase the solubility.

Smaller particles have higher curvature at its surfaces.Smaller particles have higher curvature at its surfaces.Less stable.Less stable.

Larger particles have less curvature at its surfaces.Larger particles have less curvature at its surfaces.More favoured. More favoured.

Oswald RipeningOswald Ripening

Smaller particles cluster together to form larger particles thusforming irregular shaped larger particles.

CV CurveCV Curve

Used to identify the Used to identify the deposition potential of deposition potential of material.material.Cycling the voltage Cycling the voltage within the given range within the given range for a given number of for a given number of times while monitoring times while monitoring currentcurrent

Deposition potential = -0.8V

CV CurveCV CurveDifferent concentration Different concentration of CoSOof CoSO44 solution have solution have different deposition different deposition potential. potential.

Concentration DependenceConcentration Dependence0.001 M

200nm

0.01 M

0.1 M

200nm

0.5 M

pH DependencepH DependenceCobalt sulfate solution cannot be titrated to pH Cobalt sulfate solution cannot be titrated to pH > 7 since Co(OH)> 7 since Co(OH)22 will precipitate out. will precipitate out.

Normal pH = ~3.25 pH = ~6 pH = ~7+NaOH +NaOH

-pH does not influence the deposition of Cobalt film in any significant way between the pH range of 1~6

Voltage DependenceVoltage Dependence-0.3 V

-1.0 V~20nm

~50nm

-0.8 V

~25nm -1.2 V

~200nm

Voltage DependenceVoltage Dependence

With very high concentration the following With very high concentration the following reaction will occur at the wafer surface:reaction will occur at the wafer surface:

2H2H++(aq) + 2e(aq) + 2e-- HH22 (g)(g)

This will cause an increase in pH at the wafer This will cause an increase in pH at the wafer surface surface precipitation of Co(OH)precipitation of Co(OH)22 occurs. occurs.

Film DistributionFilm DistributionThe deposited cobalt film have some unique distribution The deposited cobalt film have some unique distribution of particles.of particles.

MENISCUS – large aggregates of crystals.

Area with less deposits.

Area with normal deposits with occasional uniformity.

Diffusion LayerDiffusion Layere-

CEWE

Co2+

Co2+

Co2+

Co2+Co2+

Co2+

Co2+

Co2+

Diffusion LayerDiffusion Layer

Surface AnalysisSurface AnalysisCo 2pCo2p

x 103

6

8

10

12

14

16

18

20

CPS

820 810 800 790 780 770 760Binding Energy (eV)

ORIGINAL SAMPLECo2p

x 103

4

6

8

10

12

14

16

18

20

CPS

820 810 800 790 780 770 760Binding Energy (eV)

10 SECOND SPUTTERING

Surface AnalysisSurface AnalysisCo2p

x 103

4

6

8

10

12

14

16

18

20

22

24

CPS

820 810 800 790 780 770 760Binding Energy (eV)

Co2p

x 103

5

10

15

20

25

30

CPS

820 810 800 790 780 770 760Binding Energy (eV)

Surface AnalysisSurface AnalysisCOMPLICATION! COMPLICATION!

Ag3d

x 101

300

310

320

330

340

350

CPS

382 380 378 376 374 372 370 368 366 364 362Binding Energy (eV)

Above is a “cobalt deposit” that appear to be silver under ESCA.

Silver has a much lower deposition potential (~ -0.2V) than Cobalt.

Surface AnalysisSurface Analysis

- Indicate that silver particles are present in all of the deposited cobalt films.

- LEFT: SEM image of the depth profile ESCA sample.

ConclusionConclusion

The optimal electrochemical deposition The optimal electrochemical deposition condition at room temperature is with the condition at room temperature is with the following:following:

Amperimetric iAmperimetric i--t Curve Techniquet Curve Technique0.1M CoSO0.1M CoSO44 solutionsolution--0.8V initial applied voltage0.8V initial applied voltage6 second deposition time6 second deposition time

Future ResearchesFuture ResearchesInvestigate the properties of the deposited Investigate the properties of the deposited nanoparticles. nanoparticles. EgEg. MFM, AFM. MFM, AFM

Future ResearchesFuture Researches

To solve the silver contamination problem by:To solve the silver contamination problem by:Using different RE such as Mercury Sulfate, Mercury Using different RE such as Mercury Sulfate, Mercury chloride electrodes.chloride electrodes.

Investigate the influence of external magnetic Investigate the influence of external magnetic field on the deposition of the film. field on the deposition of the film.

Scanning Electron MicroscopyScanning Electron Microscopy

Atomic Force MicroscopyAtomic Force Microscopy

XX--Ray Photoelectron SpectroscopyRay Photoelectron Spectroscopy

AcknowledgementAcknowledgement

I would like to thank everybody in WATLabs I would like to thank everybody in WATLabs for your help and support! It is my pleasure to for your help and support! It is my pleasure to be apart of this tremendous group!be apart of this tremendous group!

Reaction from First AudienceReaction from First Audience

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