Microstructure of ZnO shell on Zn nanoparticles
- PDF / 1,290,693 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 91 Downloads / 217 Views
When exposed to air at room temperature, Zn nanoparticles oxidize gradually to form crystalline ZnO shells with a thickness of a few nanometers. Electron diffraction and high-resolution lattice imaging revealed that the ZnO layer on the Zn {0001} surface is composed of many epitaxial domains with small rotation angles relative to the lattice of the Zn core. The oxidized Zn particle bends when irradiated by the electron beam in a transmission electron microscope. This is due to the increase of internal stress in the ZnO layer as a result of the realignment of adjacent domains under electron beam irradiation. Corrosion of Zn nanoparticles was observed and the scaling and spalling start to occur on the {101¯0} prismatic faces.
I. INTRODUCTION
As the size of modern devices approaches the nanometer scale, the formation mechanism and structural and chemical stability of nano-sized materials become very important. The oxidation of Zn is of particular interest due to the fact that ZnO is a very important semiconductor material with many applications in optical and electronic devices. Other than ZnO thin film, amazingly diverse forms of ZnO nanostructures, such as wires,1 belts,2 tetrapods,3 tubes,4 nails,5 and rings,6 etc., have been prepared recently. Formation of these nanostructures is closely related to the oxidation behavior of Zn under various conditions. Classical theories have long been established to understand the oxidation of Zn.7,8 Generally, after oxidation, a protective oxide layer will form on the Zn surface, and the Zn nanoparticle will be encapsulated by a thin ZnO shell.9,10 This oxide shell plays a key role in the oxidation of Zn nanoparticles as well as the formation of ZnO tetrapod structures.3,9,10 The one-dimensional core/shell structure, called Zn/ZnO nanocable, was also reported recently.4 It was found that, unlike the formation of an amorphous layer around aluminium nanoclusters,11 the ZnO shell is an epitaxial crystalline layer.4 In this paper, we report a transmission electron microscopy (TEM) study of Zn nanoparticles with a semiconductor ZnO shell. Electron diffraction and highresolution lattice imaging revealed that the ZnO layer grows epitaxially on Zn (0001) surface and is composed
a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2004.0402 3062
http://journals.cambridge.org
J. Mater. Res., Vol. 19, No. 10, Oct 2004 Downloaded: 13 Mar 2015
of many rotational domains. Electron beam irradiation can increase the internal stress of the ZnO layer and cause a bending of Zn nanoparticles. Corrosion of the Zn particles will occur in an ambient environment by scaling and spalling from the {101¯0} faces.
II. EXPERIEMENTAL
The Zn particles were prepared by a vacuum sputtering method that was described elsewhere in detail.12 Briefly, a pencil-core was fixed between two electrodes in a vacuum chamber and then an alternating voltage was gradually applied to the electrode to increase currents until the pencil-core broke. Nanoparticles that were sputtered out fr
Data Loading...
