Abstract

We report the growth mechanism of metal oxide nanostructures synthesized by electron beam evaporation. The condensed electron beam can easily decompose metal oxide sources that have a high melting point, thereby creating a self-catalytic metal nanodot for the vapor-liquid-solid process. The metal oxide nanostructures can be grown at a temperature just above the melting point of the self-catalyst by dissolving oxygen. The morphology of nanostructures, such as density and uniformity, strongly depends on the surface energy and surface migration energy of the substrate. The density of the self-catalytic metal nanodots increased with decreasing surface energies of the substrate due to the perfect wetting phenomenon of the catalytic materials on the high surface energy substrate. However, the surfaces with extremely low surface energy had difficulty producing the high density of self-catalyst nanodot, due to positive line tension, which increases the contact angle to >180°. Moreover, substrates with low surface migration energy, such as single layer graphene, make nanodots agglomerate to produce a less-uniform distribution compared to those produced on multi-layer graphene with high surface migration energy.

Highlights

  • Division of Advanced Materials Science and Department of Materials Science and Engineering, Pohang University of Science and Technology (POSTECH), Pohang, 790-784, Korea

  • We report the growth mechanism of metal oxide nanostructures synthesized by electron beam evaporation

  • Most metal oxides can be decomposed by the condensed electron-beam, and sufficient metal flux for the self-catalyst of the VLS process can be formed under a low oxygen www.nature.com/scientificreports partial pressure

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Summary

Introduction

Most metal oxides can be decomposed by the condensed electron-beam, and sufficient metal flux for the self-catalyst of the VLS process can be formed under a low oxygen www.nature.com/scientificreports partial pressure We focused on the group 13 elements in the periodic table (Al, Ga, and In) that have high decomposition temperatures for their metal oxides, but, low melting points of metals themselves, as shown in Fig. 2a (Refer to supplementary information S1 for the growth of MgO nanowire by electron beam evaporation using MgO pellet as a source material without use of a catalyst). The effect of surface migration energy on the nucleation of the self-catalytic nanodots for the VLS process was studied using an n-graphene layer as the substrate, because the surface energy of n-graphene is independent of n, whereas the surface migration energy is strongly dependent on it[22,23,24]

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