二维材料的表面修饰与性能调控

论文总字数：29444字

摘 要

随着近年来科技的飞速发展，人们对高性能电子产品的需求日益增长，尤其是小型电子器件越来越受到人们的青睐。而由于硅基半导体材料的体积不能无限缩小，导致电子器件的性能发展受到限制，人们对材料性能的研究也遇到困难。2004年，单层石墨烯被成功制备引起轰动，这给材料研究人员带来了新的研究方向，也让二维材料因为其优异的性能成为了新世纪最热门和最有潜力的材料。

许多二维材料虽然自身拥有良好的物理化学性质，但也不可避免地存在致命缺点，因此研究者们通过表面吸附、掺杂、引入缺陷等方法来进行表面改性，希望通过这种手段来克服这些缺陷并调控其物理化学性质。同时得益于近年来计算机技术的快速发展，可以通过计算机模拟计算来研究二维材料的表面改性带来的影响。

本文选用层状二维黑磷为基础，通过VASP第一性原理模拟计算，研究以下两个方面的内容：

第一部分主要研究二维黑磷氧化中吸附氧形成P-O-P桥键的情况。寻找最稳定为氧原子吸附位置，得到了一种在单层黑磷晶体上表面或下表面两个磷原子中间形成桥键的稳定结构。然后通过改变氧的吸附比例来研究氧化物结构与原先结构的变化。结果发现桥键氧化使得黑磷结构在上下表面层间方向膨胀，P-P键被拉伸。然后研究了在这些不同比例下氧化物结构的电子性质，发现吸附氧会使黑磷从直接带隙变为间接带隙，并且能够改变其带隙宽度，随着吸附比例的增大带隙宽度不断缩减。这说明表面吸附可以有效调控黑磷的带隙，对研究黑磷在光学尤其是光催化领域有很大帮助。

第二部分主要研究二维黑磷的OH吸附，研究步骤与上一部分类似，首先找到了一个OH的稳定吸附位点，发现吸附后黑磷中上下两个表面的磷原子结构收缩，使得两表面间的结构发生拉扯，上下表面间的P-P键断裂，表面间距增大。随后以此为基础改变吸附OH的比例，发现随着吸附比例的降低，整体结构的拉扯逐渐减弱，体系形变程度变小。最后研究这些吸附比例下体系的能带结构，发现无论哪种比例的吸附均使得费米面下移，导带穿过费米面，这说明吸附OH使黑磷从半导体变为金属导体。这为表面吸附改变二维材料导电性质提供了思路。

关键词：二维黑磷，表面吸附，稳定结构，带隙调控

ABSTRACT

With the development of science and technology in recent years, people’s demand for high-performance electronic products is steadily increasing, especially small electronic devices are more and more popular. However, because the volume of silicon-based semiconductor materials can’t be reduced infinitely, the development of electronic devices is limited, and the research of material properties is also difficult. In 2004, the successful preparation of s monolayer graphene aroused much attention, which brought new research directions to materials researchers, and made two-dimensional materials become the most popular and potential materials in the new century because of their excellent properties.

Although many two-dimensional materials have exceptional physical and chemical properties, they unavoidably have fatal shortcomings. Therefore, researchers hope to overcome these shortcomings and regulate their physicochemical properties by means of surface adsorption, doping and introducing defects or other methods of surface modification. At the same time, thanks to the rapid development of computer technology in recent years, the influence of surface modification of two-dimensional materials can be studied by computer simulation calculation.

Based on the layered two-dimensional black phosphorus and the first-principles calculation simulation of VASP, this paper studied the following two aspects:

The first part mainly studies the formation of P-O-P bridge bond by adsorbing oxygen in two-dimensional black phosphorus oxidation. In order to find the most stable adsorption site for oxygen atoms, a stable structure of bridging bond between two phosphorus atoms on the upper or lower surface of single-layer black phosphorus crystal was obtained. Then the change of oxide structure and original structure was studied by changing the adsorption ratio of oxygen. The results show that the oxidation of bridge bond makes the black phosphorus structure expand in the direction between the upper and lower surface layers, and the P-P bond is stretched. Then the electronic properties of oxide structures at these different ratios were studied. It was found that adsorption of oxygen can change the band gap width of black phosphorus from direct to indirect, and can change its band gap width. With the increase of adsorption ratio, the band gap width decreases continuously. This indicates that surface adsorption can effectively regulate the band gap of black phosphorus, which is very helpful to the study of black phosphorus in the field of optics, especially in photocatalysis.

The second part mainly studies the OH adsorption of two-dimensional black phosphorus. The research steps are similar to the previous part. Firstly, a stable adsorption site of OH is found. It is found that the structure of phosphorus atoms on the upper and lower surfaces of black phosphorus shrinks after adsorption, resulting in the pulling of the structure between the two surfaces, the breaking of P-P bonds between the upper and lower surfaces, and the increase of surface spacing. Subsequently, the proportion of OH adsorbed on this basis was changed. It was found that with the decrease of the adsorption ratio, the pull of the whole structure gradually weakened, and the degree of deformation of the system became smaller. At last, the band structure of the system under these adsorption ratios was studied. It was found that the Fermi surface was moved down and the conduction band passed through the Fermi surface, which indicated that the adsorption of OH changed black phosphorus from semiconductor to metal conductor. This provides an idea for surface adsorption to change the conductivity of two-dimensional materials.

Keywords: Two-dimensional black phosphorus, surface adsorption, stable structure, bandgap control

目 录

摘要…………………………………………………………………………………..Ⅰ

Abstract………………………………………………………………………………Ⅲ

1. 绪论…………………………………………………………………………1

1.1材料科学的兴起与发展…………………………………………………………..1

1.2二维材料研究背景………………………………………………………………..1

1.3Ⅴ族二维材料……………………………………………………………………...2

1.4本文研究内容……………………………………………………………………..5

1. 计算方法……………………………………………………………………7

2.1密度泛函理论……………………………………………………………………..7

2.1.1 Born-Oppenheimer近似…………………………………………………...7

2.1.2 Hartree-Fock (HF) 近似……………………………………………….......8

2.1.3 Hohenberg-Kohn (HK) 理论………………………………………………9

2.1.4 Kohn-Sham (KS) 方程……………………………………………..……...9

2.1.5交换关联泛函…………………………………………………..………...10

2.1.6赝势方法………………………………………………………………….12

2.2 VASP软件包介绍………………………………………………………………..12

第三章 二维黑磷吸附氧的桥键结构的研究…………………………..…………13

3.1桥键中氧原子最稳定的吸附位置和晶体结构…………………………………13

3.2不同比例氧吸附形成桥键的晶体结构…………………………………………15

3.3不同比例桥键氧化结构的能带结构和电子态密度……………………………16

3.4 本章小结………………………………………………………………………...17

第四章 二维黑磷吸附OH的结构的研究……………………………………..….18

4.1 OH最稳定的吸附位置和晶体结构……………………………………………..18

4.2 不同比例OH吸附的晶体结构…………………………………………………20

4.3 不同比例OH吸附的能带结构和电子态密度…………………………………22

4.4 本章小结………………………………………………………………………...23

第五章 总结与展望………………………………………………………………..24

参考文献……………………………………………………………………………..27

致谢…………………………………………………………………………………..29

1. 绪论

1.1材料科学的兴起与发展

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