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TitleLuminescence Properties of ZnO Nanostructures and Their Implementation as White Light Emitting ...
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Table of Contents
                            Chapter 1
	Introduction and motivation
		2.2 The basic physical parameters for ZnO
Chapter 3
	Device applications of ZnO nanostructures
	Synthesis of ZnO nanostructures and fabrication of LEDs
		4.2.2 Synthesis of nanostructures by the aqueous chemical growth (ACG) method
		4.2.2.1 Synthesis of ZnO nanorods
		4.2.2.2 Growth of ZnO nanotubes
		4.2.2.3 Growth of ZnO nanowalls
		4.2.2.4 Growth of ZnO nanoflowers
			4.2.3 Growth of ZnO nanorods by sol-gel method
			4.2.4 Synthesis of ZnO nanorods by the electro-chemical deposition (ECD)
		References
Chapter 6
	Results
Chapter 7
	Conclusion and outlook
		References
		Abstract
		Introduction
		Results and discussions
                        
Document Text Contents
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Linköping Studies in Science and Technology

Dissertation No. 1378

Luminescence Properties of ZnO
Nanostructures and Their Implementation as

White Light Emitting Diodes (LEDs)





Naveed ul Hassan Alvi













Physical Electronics and Nanotechnology Division

Department of Science and Technology (ITN)

Campus Norrköping, Linköping University

SE-60174 Norrköping Sweden



Linköping 2011

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II










Copyright © 2011 by Naveed ul Hassan Alvi

[email protected]

[email protected]





ISBN: 978-91-7393-139-7

ISSN 0345-7524


Printed by LiU-Tryck, Linköping University,

Linköping, Sweden

June, 2011


























mailto:[email protected]
mailto:[email protected]

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4.2.2 Synthesis of nanostructures by the aqueous chemical growth (ACG)

method

4.2.2.1 Synthesis of ZnO nanorods
The aqueous chemical growth (ACG) is the most common and simple method

for the growth of ZnO nanorods and it was described by Vayssieres et al. [35]. It is a low

temperature (<100 oC) growth technique. In this method zinc nitrate (Zn(NO3)2 6H2O) is

mixed with hexa-methylene-tetramine (HMT, C6H12N4). An equimolar concentration of HMT

and zinc nitrate (0.010- 0.075 mM) is usually used for growth. The substrate is placed in the

solution with the growth face of the substrate down towards the bottom of the solution

container and the solution container is placed in an oven at 50- 95 ºC for 2-5 hours. The

growth of ZnO nanorods proceeds through the following reactions [36]. At f irst the HMT

reacts with water and produces ammonia according to the following reaction:

(CH2)6 N4 + 6H2O → 6HCHO + 4NH3

The ammonia produced in the above reaction reacts with water and disassociates

into ammonium and hydroxide ions under the following reaction:

NH3 + H2O → NH4+ + OH-

The hydroxide ions produced in the above reaction react with zinc ions to grow

solid ZnO nanorods on the substrate according to the following reaction:

2OH- + Zn+2 → ZnO (s) + H2O

After the growth, the samples were cleaned with deionized water and dried in

air. The ZnO nanorods grown by the above method have less density and alignment. To

improve the quality of the grown ZnO nanostructures, the growth method is combined with

substrate preparation technique developed by Greene et al. [37]. In this method, ZnO seed

layer is usually spun coated on substrates to form a thin and uniform seed layer. The seed

solution can be prepared by two methods. In the first method 5 mM zinc acetate dihydrate is

diluted in pure ethanol. The ethanol needs to be at least 99% pure otherwise growth will not

lead to well aligned nanorods. The solution is shaken well until all of the zinc acetate crystals

are dissolved. The solution should look transparent; if it is not transparent then it needs more

pure ethanol. The second seed solution is introduced by Womelsdof et al. [38]. Using this

method, we mix 0.01M zinc acetate dihydrate in methanol. The solution should also be

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transparent. This solution is heated to 60 oC under continuous stirring and we mix 0.03 M

KOH in methanol. We shake the solution until it looks transparent. We add the KOH

solution drop wise to the zinc acetate solution, still under stirring. The resulting solution

should be kept at 60 oC for 2h under stirring. The seed solution is applied to the substrate by

spin coating. In this way we cover the sample with the seed solution and spin it at 5000 rpm.

This process was repeated at least three times to get a uniform layer. Then the substrate is

heated in air at 250 ºC for 20 minutes. By using this treatment, well aligned ZnO nanorods

can be grown. The growth temperature, molar concentration of the HMT and the zinc nitrate,

and growth time affect the length, diameter and density of the grown ZnO nanorods. ZnO

nanorods with different diameters were grown by changing some growth parameters. SEM

images of ZnO nanorods with different diameters ~ 440, 200, 150 and 35 nm are shown in

figure 4.5 (a-d), respectively.

(a)

(d)(c)

(b)



Figure 4.5: Shows the SEM images of ZnO nanorods with different diameters, (a) ~440 nm,

(b) ~200 nm, (c) ~150 nm, and (d) ~35 nm.

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