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物联网-智慧传输-基于石墨烯的甲烷气体传感机理的分析模拟研究.pdf
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物联网-智慧传输-基于石墨烯的甲烷气体传感机理的分析模拟研究.pdf
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Abstract
II
Abstract
At present, the sensor is widely used and its types are varied, such as biosensor, gas
sensor, chemical sensor, humidity sensor, optics sensor, pressure sensor, etc. However, many
defects of gas sensors remain to be optimized in many aspects such as conductivity, stability
and adsorption capacity, so we study the gas sensor. The graphene has been attracted popular
attention all over the world, because the two-dimensional crystal structure of graphene has a
good mechanical, electrical properties etc. The graphene also has a great specific surface area,
so it has a well adsorption capacity. The graphene is a zero-n gap semiconductor with no
magnetism, however, the graphene will be magnetic if it adsorbed or doped with other
materials even the band gap is opened. Therefore, the graphene has a promising future in nano
electronic devices such as gas sensor.
We compared the electronic structures and the magnetism between the pristine graphene
and the gas molecule-adsorbed graphene through the first principle calculation. We have
found that the different types of graphene have different band structures. Most of the
molecules adsorption on graphene can be weakly charged took as donor or acceptor. We
discovered that the band gap and the adsorption energy is different when the gas molecules
adsorped on the graphene with different structure. Finally, we use Materials Studio software
to calculation the different structure graphene in this paper.
We choose the structure of the multilayer graphene, the structure of defect graphene and
the doped graphene based on the different structure of the gas sensor’ materials to calculation
their the structure of the energy band structure, the density of States and the charge transfer
data. First of all, we find that the adsorption energies are dependent on the number of the
graphene layers. In light of the band structures, density of states and the charge densities, the
electronic structures of graphenes with different numbers of layers exhibit no apparent
changes before and after the CH
4
adsorption. Besides, the graphene with monovacancy defect
presents the best adsorption performance over the CH
4
gas molecules because it has the
largest adsorption energy together with the most stable adsorption configuration. Finally, we
introduce element dopants to the above two graphene structures and find that the the Al-doped
ones show the largest adsorption energies upon CH
4
with the most appreciable effects on the
electronic structures, the adsorption of CH
4
can largely enhance the conductivity of these
graphene.
In summary, we believed that the Al-doped graphene with single vacancy defect is a
万方数据
Abstract
III
promising candidate material for the CH
4
gas sensors.
Key words: graphene; the first principle; the gas sensor; band structure; Materials Studio
万方数据
目 录
IV
目 录
摘 要........................................................................................................................................... I
Abstract...................................................................................................................................... II
第一章 绪论...............................................................................................................................1
§1.1 课题的研究背景和意义.....................................................................................................1
§1.2
气体传感器的简介
.............................................................................................................2
§1.2.1
气体传感器的性能
...................................................................................................2
§1.2.2
气体传感器的分类
...................................................................................................3
§1.2.3
气体传感器的发展趋势
...........................................................................................5
§1.3 石墨烯气体传感器的研究进展.........................................................................................6
§1.3.1
石墨烯简介
...............................................................................................................6
§1.3.2
石墨烯在传感材料方面的应用
...............................................................................8
§1.4 本文的主要研究内容.........................................................................................................9
第二章 仿真软件的基本理论和计算方法
.............................................................................11
§2.1 第一性原理简介...............................................................................................................11
§2.1.1 Born-Opeenheimer..................................................................................................11
§2.1.2 Hartree-Fock
近似
.................................................................................................. 12
§2.2 密度泛函理论...................................................................................................................13
§2.2.1 Hohenberg-Kohn 定理............................................................................................13
§2.2.2 Kohn-Sham 方程.................................................................................................... 14
§2.2.3 交换关联能泛函.....................................................................................................14
§2.2.3.1
局域密度近似
.............................................................................................14
§2.2.3.2 广义梯度近似.............................................................................................15
§2.3 计算软件介绍...................................................................................................................16
§2.4
本章小结
...........................................................................................................................16
第三章 石墨烯层数的研究.....................................................................................................18
§3.1 计算模型与研究方法.......................................................................................................18
§3.2
吸附体系的结构和性能研究
...........................................................................................19
§3.2.1
模型的体系能量分析
.............................................................................................20
§3.2.2
吸附后模型的体系能量分析
.................................................................................21
§3.2.3
吸附能
.....................................................................................................................22
§3.2.4
电荷转移
.................................................................................................................23
§3.3 本章小结...........................................................................................................................24
第四章 缺陷石墨烯的研究.....................................................................................................25
§4.1
缺陷石墨烯的分类
...........................................................................................................25
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目 录
V
§4.1.1
拓扑缺陷
.................................................................................................................25
§4.1.2
单空位(
SV
)缺陷
............................................................................................... 25
§4.1.3
复合空位(
DV
)缺陷
...........................................................................................26
§4.2 计算模型与研究方法.......................................................................................................27
§4.3
计算结果分析
...................................................................................................................28
§4.3.1
模型的体系能量分析
.............................................................................................28
§4.3.2
吸附后模型的体系能量分析
.................................................................................30
§4.4 本章小结...........................................................................................................................33
第五章 元素掺杂石墨烯的研究.............................................................................................34
§5.1
石墨烯的掺杂研究
...........................................................................................................34
§5.2 计算模型与研究方法.......................................................................................................34
§5.3 多层石墨烯的掺杂研究...................................................................................................35
§5.4
缺陷石墨烯的掺杂研究
...................................................................................................38
§5.4.1
模型的体系能量分析
.............................................................................................38
§5.4.2
吸附后模型的体系能量分析
.................................................................................40
§5.5 本章小结...........................................................................................................................43
第六章 总结与展望.................................................................................................................44
§6.1
本文总结
...........................................................................................................................44
§6.2 本文的不足及未来研究展望...........................................................................................44
§6.2.1
本文的不足
.............................................................................................................44
§6.2.2
未来研究展望
.........................................................................................................45
参考文献...................................................................................................................................46
作者在攻读硕士期间的主要成果
...........................................................................................52
万方数据
第一章 绪论
1
第一章 绪论
§1.1 课题的研究背景和意义
甲烷,化学式
CH
4
[1]
,一种主要由稻田和湿地释放出来的温室气体。甲烷在我们的
生活中随处可见,它是天然气、油田和沼气等主要成分,也是含碳量最小的烃。甲烷是
一种无味、透明色、可燃性的气体,甲烷的密度约比空气的密度轻一半左右。甲烷燃烧
的时候会产生蓝色且明亮的火焰,也有 的时候是偏绿色,因为在化学实验室中,甲烷
放在玻璃导管中燃烧,玻璃种含有钠元素,所以有可能会呈现黄颜色的火焰,甲烷烧起
来是蓝颜色,所以在试管中混合燃烧在一起看的时候其燃烧颜色就会成为绿色。甲烷的
沸点:-161.5℃,熔点:-182.5℃,相对密度(水=1),蒸气压:53.32kPa/-168.8℃,
燃烧热:0.55,890.31KJ/mol。甲烷的化学性质比较稳定,甲烷对人虽然无毒,但是浓
度过高的话,会使空气中的氧浓度降低,使人窒息死亡。
随着现在科技的日益发达,人民的生活水平越来越好。古人云:“眼见为实,耳听
为虚”,但是现在我们看见的已经不一定就是真实的了,也不能满足现代人的要求了,
眼睛的视觉、鼻子的嗅觉、舌头的味觉都不能分辨现在的一些东西了。我们必须得依靠
一些高科技来区分、辨别。上文说的甲烷气体,我们仅靠鼻子的嗅觉就没办法区分,因
为它是无色无味的,一旦等你吸入体内再发觉就为时已晚了,有可能就出现了生病危险。
所以我们需要依靠高科技手段,比如气体传感器来检测空气中的有害气体,不仅仅是针
对甲烷气体,也有其他的气体传感器去检测其他的有害气体,比如一氧化碳、二氧化硫
和监测空气好坏指标的气体传感器等等。所以我们选择去研究检测甲烷气体,结合现在
性能各方面比较优秀的材料去制作气体传感器。由于近几年石墨烯材料作为新型材料特
别的火热,它的性能在各方面也特别的优秀,如它有着较大的比表面积(2630m
2
·g
-1
),
较高的本征迁移率(2.0×10
5
cm
2
·v
-1
·s
-1
)
[2, 3]
、较高的杨氏模量(1.0~1.2TPa)
[4]
、较高
的热导电性(~5000W·m
-1
·K
-1
)
[5]
、较高的光学透视率(~97.7%)和较高的电导性
[6, 7]
,所
以我们选择用石墨烯这样的一种二维材料作为气体传感器的材料去研究。由于实验室的
限制,我们选择用仿真软件去研究关于石墨烯气体传感器吸附甲烷气体的情况。本文用
Materials Studio 中的 DMol
3
软件对其石墨烯吸附甲烷气体的体系研究,软件中采用的是
第一性原理来得出结果。第一性原理现在被越来越多的科学家结合实践一起运用,主要
是对实验的结果做一个预判和为实验理论做解释。
本文主要研究了以下几个方面的研究工作:
石墨烯气体传感器发展得主要问题在于高精度,高可靠性以及低成本。因此本文建
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