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IMPROVEMENT OF HEIGHT UNIFORMITY OF ZnO NANOWIRE ARRAYS BY USING ELECTROPOLISHING METHOD

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IMPROVEMENT OF HEIGHT UNIFORMITY OF ZnO NANOWIRE ARRAYS BY USING ELECTROPOLISHING METHOD - PowerPoint PPT Presentation


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Zinc solution. Hot plate. DC Power supply. Motivation & Purpose. Results. +. -. A. V. N.W cation. anion. +. -. Ir. cathode. Anode. electrolyte. stirrer. Synthesis of ZnO nanowire. Roughness measurement. Hydrothermal Method. Experimental. Principle of Electropolishing.

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Presentation Transcript
slide1

Zinc solution

Hot plate

DC Power supply

Motivation & Purpose

Results

+

-

A

V

N.W cation

anion

+

-

Ir

cathode

Anode

electrolyte

stirrer

Synthesis of ZnO nanowire

Roughness measurement

Hydrothermal Method

Experimental

Principle of Electropolishing

Summary & Future work

Reference

Additives

IMPROVEMENT OF HEIGHT UNIFORMITY OF ZnO NANOWIRE ARRAYS BY USING

ELECTROPOLISHING METHOD

Mee Na Park 1,*, Ee-Le Shim1, Joonho Bae 3, C. J. Kang1,2, and Young Jin Choi 1 ,2**

1 Department of Physics, MyongJi University, Yongin, 449-728, Korea

2 Dept. of Nanoscience & engineering , MyongJi University, Yongin, 449-728, Korea

3 School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, GA 30332-0245, USA

◎ Applications of ZnO nanostructures

- solar cells , chemical sensors , field emitters and nanogenerators.

◎ In order to be successfully incorporated into nanodeives,

the nanowires have to be grown with a high degree of control in

uniformity.

Before E.P

  • * Main experimental parameters
    • pH value of the acid
    • applied voltage
    • current
    • reaction time

After E.P

To control and improve the uniformity

of heights of ZnO nanowire arrays

Electropolishing method

An aqueous solution of phosphoric acid is used as the electrolyte to planarize the top surfaces of ZnO nanowire arrays.

Applied voltage ranged from 7 to 15 V in phosphoric acid (pH 5.0).

Apparent planarizationof protruded ZnO nanowires

. Zinc solution :

Zinc nitrate hexahydrate + Hexamethylenetetramine + Deionized water

. Concentration of solution : 7.5 mM

. Temperature : 70~90℃

. Synthesis time : 6h

planarization

(CH2)6N4 + 6 H2O ↔ 4 NH3 + 6 HCHO , (1) NH3 + H2O ↔ NH3 ·H2O, (2) NH3·H2O ↔ NH4+ + OH− , (3) Zn2+ + 2 OH−↔ Zn(OH)2 , (4) Zn(OH)2→ ZnO + H2O . (5)

(a) As-grown ZnO

nanowire arrays

Same position

(b) After EP

7V , 1h , pH 5.0

※ To directly observe the morphology change when nanowires were electropolished, patterned ZnO nanowire arrays were fabricated on Si substrate, and the same regions of nanowire arrays were compared before and after the EP process.

※ SEM image of patterned

ZnO nanowire arrays

Before E.P

After E.P

(b) Line profile

E.P condition ; 15 V , 1min , pH 5.0

(a) Typical AFM image of as-grown ZnO nanowire arrays

Bulk concentration additive species

Diffusion layer

Before E.P

∆ up

∆ down

After E.P

The height variation of nanowires was reduced after EP had been performed.

In order to optimize EP conditions for the planarization of nanowire arrays, the statistical analysis of the roughness change is in progress.

Electropolishing(EP) has been conventionally used to remove a thin layer of material on the surface of a metal part.

The basic mechanism of EP is based on the differential rates of metal removal in an aqueous solution of acid. Areas of metal with high current densities are rapidly dissolved, resulting in the smoothing of metal surfaces .

EP is the electrolytic removal of metal in a highly ionic solution by means of an electrical potential and current.

[1] M.Al-Ajlouni and A.Al-Hamdan, J. Applied Sci. 8(10), pp.1912-1918 (2008).

[2] Shih-Chieh Chang, Jia-Min Shieh, Electrochemical and Solid-State Letters. 6(5), G72-G74 (2003).

[3] Sheng Xu, Yaguang Wei, Zhong Lin Wang*, J. Am. Chem. Soc. 130,pp.14958–14959(2008).

[4] M. Law, L. E. Greene, P. D. Yang, Nature Materials 4, pp. 455 , (2005).

Nano-Scale Measurement & AnaLysis Lab.

http://n-small.mju.ac.kr

[email protected]

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