uci c h e m i s t r y p e n n e r g r o u p nanowire "thinning" by kinetically controlled...

UCI C h e m i s t r yP e n n e r G r o u p

Nanowire "Thinning" by Kinetically Controlled Electrochemical Stripping: A New Route to Ultra

Small Metal Nanowires

2005 IM-SURE Symposium

Mike Thompson, R.M. Penner. Department of Chemistry. UC Irvine

Fig 2: At left is an SEM image of antimony wires with no stripping. At right is an image of the same sample that has been set at a potential of 0.01V for 60s. The diameter of the wire and the number of particles on the terraces have been greatly reduced by the stripping, while still retaining the morphology of the original wires.


1. Electrochemical Step Edge Decoration (ESED) as a method for making metal nanowires.

2. My mission: Make smaller Sb and Au nanowires

3. Smaller nanowires: Results and discussion

outline


Electrochemical Step Edge Decoration:


Our electrochemical setup…


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500

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Scan 1

Scan 2

Scan 3

Potential (mV vs. SCE)

Cu

rre

nt

(A

)

EoxEnuc

Egrow

Three steps : oxidation, nucleation, and growth

Sb3+ + 3 e- Sb0

Sb0 Sb3+ + 3 e-


0

200

400

600

800

1000

0 5 10 15

Wire

Dia

met

er,

nm.

Time1/2,s1/2

-0.75 V, 1.0 mM Na2MoO

4-0.90 V, 0.16 mM Na

2MoO

4

4 s 16 s

256 s128 s

64 s32 s

ESED allows for size selective growth (MoO2 wires pictured):





outline


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Scan 1

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Cu

rre

nt

de

ns

ity

(A

cm

-2)

Egrow, 75 sEox, 5sEnucl, 40 ms

A case study using antimony nanowires… 5 mM SbCl3, 0.1 M Tartaric Acid, 0.1 M Nitric Acid


122 nm


THESE WIRES ARE TOO BIG! Antimony nanowires with diameters larger than 40 nm have no interesting properties, and thus are useless.

How can we reduce the minimum size of these wires (from 120 nm to 40 nm)?

The answer is simple: Use electrochemistry to slowly etch them away.


Sb CV(vs. SCE)

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Potential (mV)C

urr

ent

(μA

)

Using kinetically-controlled anodic etching to make the wires smaller...


Cu

rrent (

A)

Sb3+ + 3 e- Sb0

Sb0 Sb3+ + 3 e-


Penner, JPC-B 106 (2002) 3339.

Walter et al. ChemPhysChem 4 (2003) 131.

nanowire smoothing is predicted by the growth law...

nFL

Vt2iR(t) mdepdep

R= nanowire radius

idep=constant deposition current

Vm=molar volume

n=moles of e-

F= the Faraday

L= nanowire length


nF

t2jVR(t) stripm

kinetically controlled stripping causes a constant anodic current density, thus...

Thompson, Menke, Penner. in preparation





outline


Sb CV(vs. SCE)

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Scan 1

Scan 2

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0

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Potential (mV)C

urr

ent

(μA

)

Choosing the right stripping potential…


Cu

rrent (

A)

Sb3+ + 3 e- Sb0

Sb0 Sb3+ + 3 e-


-0.060 V

-0.025 V

Stripping is extremely sensitive to the applied potential…


0

5

10

15

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140

Sb no stripping

Count

Wire Diameter (nm)

No stripping122 nm


0

5

10

15

20

0 10 20 30 40 50 60 70 80 90 100110120130140

250 s @ -0.060 V vs. SCE

Count

Nanowire Diameter (nm)

73 nm

250 s stripping


0

5

10

15

20

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140

500 s -0.060 V vs. SCE

Count


33 nm 500 s stripping


33 nm


Nanowire Diameter vs. Etching Time

y = -0.1717x + 117.64

R2 = 0.987

0

20

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0 100 200 300 400 500 600

Etching Time (s)

Nan

ow

ire

Dia

met

er (n

m)

nF

t2jVR(t) stripm


Gold nanowires are interesting and difficult to make small…try stripping!

Au CV 7-15-05

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Cu

rre

nt

(uA

)

Scan 1

Scan 2

Scan 3

Oxidation: 5s @ 0.8V

Nucleation:

100ms @ -1.0 V

Growth:

30 s @ 0.45 V


158 nm145 nm


0

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12

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16

0 10 20 30 40 50 60 70 80 90100110120130140150160170180

Au no stripping

Count


No stripping145 nm

158 nm


0

2

4

6

8

10

0 10 20 30 40 50 60 70 80 90100110120130140150160170180

600 s @ 0.810 V vs. SCE

B

Count


0

2

4

6

8

10

12

0 10 20 30 40 50 60 70 80 90100110120130140150160170180

1200 s @ 0.810 V vs. SCE

Count

Nanowire DIameter (nm)

600 s

1200 s

109 nm

66 nm


Gold @ 0.810 V vs. SCE

y = -0.0707x + 144.4

R2 = 0.9909

0

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Stripping Time

Nan

ow

ire

Dia

met

er

Series1

Linear (Series1)

nF

t2jVR(t) stripm


THANK YOU!

Thanks also to:

Prof. Reg Penner

Erik Menke

Ben Murray

Said Shokair and UROP staff

Konstantin Arutyunov

Funding provided by:

NSF

UROP

EU Commission ULTRA 1-D project for the HOPG

uci c h e m i s t r y p e n n e r g r o u p nanowire "thinning" by kinetically controlled...

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