Study on coalescent properties of ZnO nanoclusters using molecular dynamics simulation and experiment

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Study on coalescent properties of ZnO nanoclusters using molecular

dynamics simulation and experiment

Te-Hua Fang

a

, Win-Jin Chang

b,

*, Jun-Wei Chiu

c

a_{Institute of Mechanical and Electromechanical Engineering, National Formosa University, Yunlin 632, Taiwan, ROC} b_{Department of Mechanical Engineering, Kun-Shan University, Tainan 710, Taiwan, ROC}

c_{Department of Mechanical Engineering, Southern Taiwan University of Technology, Tainan 710, Taiwan, ROC}

Received 1 September 2005; accepted 18 December 2005 Available online 21 February 2006

Abstract

The coalescent properties of ZnO clusters were studied through experiment and molecular dynamics simulation in combination with the tight-binding potential and ZnO potential. The results from the simulation show that the linearly relationship between the melting temperature and the function of atom numbers of NK1/3was obtainable. Extrapolating the result yield at a melting point of 2130 K for N/N (i.e. NK1/3/0) was slightly lower than the bulk value of 2248 K. In addition, the neck diameter of two ZnO clusters was a function of temperature during coalescence. The contact length was influenced by the coalescence temperature and time, when a cluster was simulated being deposited onto a substrate. The experimental results showed that the grain size increased when the coalescence temperature and sintering time were increased.

Keywords: Molecular dynamics; Tight-binding potential; Coalescent properties; ZnO clusters

1. Introduction

Nanoclusters and its coalescence properties are currently attracting lots of attention due to their unique characteristics

[1–5]. In the past years, many researchers studied the

coalescence properties of metal clusters using molecular dynamic simulation. Lewis et al. [6] developed a molecular-dynamics simulation using the embedded-atom method to study the melting, freezing, and coalescence of gold nanoclusters. Qi et al.[7]investigated the melting and freezing of Ni nanoclusters using molecular dynamics with the many-body force field. Zhao et al.[8]studied the coalescence of three identical size nanoclusters through molecular dynamics simulation with an analytic embedded-atom potential. Shim et al. [9] studied the thermal stability of gold nanoparticles, using molecular dynamics simulation in combination with the modified embedded-atom-method potential.

Recently, Bilalbegovic [10] studied aggregates of gold clusters by molecular dynamics simulation. Ding et al. [11] utilized molecular dynamics simulation to show that the

coalescence of iron nanoclusters occurs at temperatures lower than the cluster melting point, and that the difference between coalescence and melting temperatures increased as the cluster size decreased. Arcidiacono et al. [12] investigated the coalescence process of two gold nanoparticles using a host of initial temperatures and measuring the starting radii in a vacuum with the help of molecular dynamics simulation.

Zinc oxide (ZnO) has a wide band gap and good piezoelectric properties. It will have an important application in the field of nanodevices [13–16]. However, very little literature studies coalescent properties of ZnO clusters. In this paper, the effect of the temperature and the structure on the coalescent properties of ZnO nanoclusters was studied using molecular dynamics simulation with the tight-binding poten-tial, ZnO potential and an experimental method.

2. Simulation procedure

The interaction forces between ZnO nanocluster zinc atoms, oxygen atoms and zinc atom to oxygen atom were complicated. The many-body tight-binding potential [17] is adopted to simulate the interatomic energy between zinc atoms and expressed as: EcZK X i ðEbiCE i rÞ (1) Microelectronics Journal 37 (2006) 722–727 www.elsevier.com/locate/mejo

* Corresponding author.

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to green to brown when the coalescence temperature was increased from 700 to 1300 8C.

5. Conclusions

In this paper, the effect of the temperature and the structure on the coalescent properties of ZnO clusters was studied using molecular dynamics simulation and experimental method. The following results were obtained:

(1) The melting point of the ZnO clusters decreased linearly as the simulated atom increased due to a function of NK1/3of the curvature effect.

(2) The neck diameter rate of increase of two simulated ZnO clusters increased as the temperature during coalescence was increased.

(3) The contact length between a simulated ZnO cluster and ZnO substrate increased as the coalescence temperature and time were increased.

(4) The grain size obtained from the experiment increased when increasing the coalescence time.

(5) The grain size rapidly increased while increasing the coalescence temperature.

Acknowledgments

This work was partially supported by the National Science Council of Taiwan, under Grant No. NSC 94-2218-E-150-045, NSC 94-2212-E-168-004.

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