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ApplPhysLett_91_031914

ApplPhysLett_91_031914
ApplPhysLett_91_031914

1.Abstract:

The authors employ density functional theory within the generalized-gradient approximation to investigate in?nitely long (0001)ZnO nanowires.

The authors report on atomic relaxations, formation energies, and electronic structure of bare and hydrogen passivated ZnO wires with triangular cross sections.

The authors ?nd that surface reconstruction plays an important role in stabilizing the nanowires.

The authors have shown that the band gap can be tuned by changing the wire diameter and by passivating with hydrogen.

While bare and completely passivated wires are semiconducting, wires with intermediate hydrogen passivation exhibit metallic behavior.

作者采用的纳米线结构是:界面是三角格子的。他们发现了表面重构对纳米线的稳定起很重要的作用。而且他们还用H来钝化纳米线,发现吸附H以后的纳米线是金属性的。

思考:

这样,金属性的导电能力是很强的。如果在TP结构中,在散射区采用吸附H的纳米线了做导体,比较没有吸附H的,我们就可以比较他们导电性的好坏,说不定

就是什么开关效应什么之类的。注意,是完全钝化的纳米线是半导体的,而部分钝

化是金属的。所以,可以通过调节H的多少来控制导电能力;

为什么H会吸附在上面?那么H能否在ZnO纳米线中以杂质的形式存在,如果,存在的话,又会有什么的结果。是不是有金属到半导体的转换,还是是否有磁性的

出现。

2.Introduction: 写得非常漂亮!逻辑关系明了,简单实在!

ZnO has attracted great interested in the past few years, since it is regarded as an important functional material. 这句话提出ZnO很重要

It has a direct wide band gap of 3.4 eV and a strong excitonic binding energy of 60 meV at room temperature making it promising for high-ef?ciency light-emitting devices,

including blue light emitting diodes and nanoscale ultraviolet lasers. 1 指出ZnO为什

么重要,因为他的Gap以及强的激子结合能(?)

Since the discovery of carbon nanotubes,2 several one-dimensional nanostructures have become the focus of intensive research owing to their unique physical and chemical

properties. 这句话过度提出CNT的发现,1D体系的独特物理及化学性质而受到关

注。

ZnO exhibits a wide range of unique structures, including nanowires, 3 nanorings, 4 nanobelts,5 and nanobridges. 6,7 指出ZnO存在各种结构形态,包括纳米线等。这也

是在过度到自己的研究目的上来。

Being able to control the direction of growth means that it is possible to tune various physical properties of the material, such as band gap, index of refraction, thermal and

electrical conductivity, and piezoelectric polarization. 提出能够控制生长方向就意味

着可以调节材料的各种物理性质,比如能隙什么。这种说法确实如此,生长方向不

一样,当然其物理性质不一样,比如电导什么之类的。这可以为自己的Au nanowire

准备。

ZnO nanowires usually grow along the (0001) direction, having a hexagonal cross section. 指明ZnO纳米线一般是沿着(0001)方向生长,而且是六角的截面。

ZnO nanowires with a triangular cross section have been recently grown.8 作者提出,三角界面的纳米线也已经生长出来了,所以要研究…….,这样很自然的将内容归

结到自己的研究上来。

This particular shape can exhibit very interesting properties as it has been found for GaN nanowires. 9 进一步指明这种结构的纳米线具有与已经发现的GaN纳米线象类似

的性质

Therefore, an understanding of the structural and electronic properties of these wires is of great interest. 所以,这种结构的纳米线的…值得研究。

思考:

做工作,要来源于实验,作者的工作就是来源于不久前的Chem. Phys. Lett. 424, 86;

所以ZnO纳米线的掺入C杂质的实验背景是什么?不过,可以参考本文中为什么

要掺杂H,还可以搜索ZnO纳米线掺杂的实验或者理论文章,比如那些掺杂Cu

的文章;

ZnO纳米线的生长,到目前为止我知道有两种方式一种就是文中提到的沿着(0001)方向生长的界面为六角格子的纳米线,另一种就是沿着(0001)方向生长的界面是三

角格子的纳米线。最近,是否还有其他生长的方式?

自己的工作是可以考虑这两种的方式的纳米线都可以做的。

https://www.sodocs.net/doc/2a15513053.html,putation Method and Model: 注意作者没有优化C方向的单胞长度这实际上是有不

足的。因为For such a small diameter wire, the spacing c is not the same as bulk;

Code: V ASP

Parameters:

(1)GGA, An energy cutoff of 500 eV

(2)For the charge density integration we have used a (1x1x8) k-point Monkhorst-Pack

mesh.

(3)All atoms were allowed to relax until the forces were smaller than 0.001 eV/?.

Object: the triangular-shaped ZnO nanowires with diameters of 7.7 and 11.3 ?.

Nanowires have in?nite length along the (0001) direction (c axis) and are enclosed by

(10(-1)0)surfaces

Properties concerned: the structure and electronic properties 我们实际上关注输运性质。

Model:

(1)The triangular-shaped ZnO nanowires with diameters of 7.7 and 11.3 ?.

(2)Nanowires have in?nite length along the (0001) direction (c axis) and are enclosed

by (10(-1)0) surfaces.

(3)The wires are separated by a vacuum region of 15 ? in the x and y directions.

(4)ZnO crystallizes in the wurtzite structure in which the cations have tetrahedral

coordination with the anions. 这里指出ZnO块体的结构

(5)测试以及作者采用的初始晶格常数大小:To construct the nanowires, we have

used our optimized lattice parameters for ZnO bulk: a=3.291 ?, c=5.272 ?, and

u=0.381, which are in very good agreement with the experimental values, a=3.258

?, c=5.220 ?, and u=0.382.

(6)We investigated wires with 26 (small) and 44 (large) atoms. Those wires have layers

with different numbers of atoms: 6 and 7 atoms in the small wire, and 10 and 12

atoms in the large wire. 作者做了两种大小的纳米线,一种6767排列的纳米线

(26个原子),另一种是10-12-10-12排列,即44个原子。在C方向,反正是一

个周期。

结果发现:小纳米线和大纳米线follow the same trends,所以作者focus on the relaxations for the small wire only.

4.为什么要做H-doped ZnO nanowire:

The interaction between hydrogen and ZnO nanowires is of great concern, since exposure to hydrogen can strongly affect the ZnO electrical properties.

参考文献ApplPhysLett_85_5601,Nanotechnology 16, 913,Phys. Rev.

Lett. 85, 1012

考察方法:

One expects that hydrogen will passivate both O and Zn dangling bonds under

adsorption. We have therefore investigated hydrogen passivation of ZnO

nanowires for the followin g con?gurations:

passivation of (i) O atoms and (ii) passivation of both Zn and O atoms.

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