共查询到19条相似文献,搜索用时 171 毫秒
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运用第一性原理研究了闭口硼氮纳米管(BNNT)顶层掺碳体系(C@BNNT)的电子场发射性能.结果表明:随外电场增强,C@BNNT电子结构变化显著,态密度(DOS)向低能方向移动;碳原子的局域态密度(LDOS)在费米能级附近明显增大;赝能隙、最高占据分子轨道(HOMO)/最低未占据分子轨道(LUMO)能隙减小;体系电荷移向帽端.DOS,HOMO/LUMO及Mulliken电荷分析一致表明,与BNNT相比,C@BNNT电子场发射性能显著改善,且C@BNmoreNT性能更优.
关键词:
碳掺杂
硼氮纳米管
电子场发射
第一性原理 相似文献
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基于第一性原理的密度泛函理论,计算并分析了铝氮共掺杂小半径碳纳米管的电子结构.结果表明,铝氮共掺杂的情况下,更容易形成相邻的铝氮对.在掺杂的七种位置中,电子性质都发生了很大的变化,原来的金属性碳纳米管转变为半导体性质.为了更好的理解其电子性质的变化,我们分析其能带结构和态密度. 相似文献
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利用脉冲激光沉积,分别制备了一系列不同Si掺杂浓度的铝镓氮(AlGaN)薄膜.对此薄膜进行场致电子发射测试表明,Si掺杂浓度为1%的AlGaN薄膜具有最好的场发射特性.相对于非掺杂样品,其场发射电流明显增加,场发射开启电场显著降低.掺杂带来载流子浓度的提升,为场发射提供足够的电子源,使样品的场发射性能提升.但掺杂浓度的进一步提高,薄膜缺陷增加,电子迁移率降低,其薄膜内部电子输运能力降低大于电子浓度的增加对场电子发射的贡献,导致场发射性能开始变差. 相似文献
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采用基于密度泛函理论(DFT)的第一性原理的平面波超软赝势方法,对闪锌矿结构CdS晶体及CdS:M(M=Mg, Cu)的几何结构、能带结构、电子态密度、集聚数和电荷密度分布进行了研究.对掺杂后体系的几何结构进行了优化计算,发现Mg和Cu原子掺入CdS后晶格常量均减少,晶格发生畸变.在此基础上研究了掺杂对体系电子结构的影响.结果表明,Mg,Cu掺入CdS都能提供较多空穴态,形成p型电导,并且Cu较Mg是更好的p型掺杂剂.
关键词:
密度泛函理论
电子结构
p型掺杂 相似文献
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石墨烯负载的单个金属原子体系(M-gra)具有高的结构稳定性,显正电性的金属原子可作为活性位用在气敏器件和催化材料.本文采用基于密度泛函理论的第一性原理方法研究单个有毒气体小分子(NO和CO)在M-gra表面的吸附特性.研究结果表明:单个NO分子吸附的稳定性高于CO分子,由于其能够从反应衬底获得更多的转移电荷,因此,M-gra衬底对NO分子表现出高的灵敏度.此外,不同小分子吸附能够改变M-gra体系的电荷密度和自旋电荷分布,进而使得气体分子吸附体系表现出不同大小的磁矩.通过对比气体分子吸附前后M-gra体系的磁矩变化,能够有效判断吸附分子和反应衬底的类型. 相似文献
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采用密度泛函理论结合投影缀加波方法,对掺杂Cd导致ZnO禁带宽度下降的机理进行了研究. 通过对掺杂前后电子能带结构,态密度以及分态密度的计算和比较,发现CdxZn1-xO价带顶端(VBM)始终由O-2p占据;而导带顶端(CBM)则由Cd-5s与Zn-4s杂化轨道控制. 随着掺杂浓度的增加,决定带隙宽度的CBM的位置下降,同时VBM的位置上升,从而导致了带隙的变窄,出现了红移现象. 此外,Cd掺杂会使晶胞发生膨胀,这种张应变也是导致Cd
关键词:
密度泛函理论
电子结构
Cd掺杂ZnO 相似文献
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采用密度泛函理论结合投影缀加波方法,对掺杂Cd导致ZnO禁带宽度下降的机理进行了研究. 通过对掺杂前后电子能带结构,态密度以及分态密度的计算和比较,发现CdxZn1-xO价带顶端(VBM)始终由O-2p占据;而导带顶端(CBM)则由Cd-5s与Zn-4s杂化轨道控制. 随着掺杂浓度的增加,决定带隙宽度的CBM的位置下降,同时VBM的位置上升,从而导致了带隙的变窄,出现了红移现象. 此外,Cd掺杂会使晶胞发生膨胀,这种张应变也是导致Cd 相似文献
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采用密度泛函理论结合投影缀加波方法,对Be掺杂导致ZnO禁带宽度增加的机理进行了研究.通过对掺杂前后电子能带结构、总态密度以及分态密度的计算和比较,发现导带底(CBM)是由Be 2s电子与Zn 4s电子共同控制;而BexZn1-xO价带顶 (VBM)始终由O 2p电子占据.随着掺杂量的增加,决定带隙宽度的CBM的位置上升,同时VBM的位置下降,从而导致了带隙的变宽,出现了蓝移现象.此外,Be掺杂会使晶胞发生压缩,这种压应变也是导致Be
关键词:
密度泛函理论
电子结构
Be掺杂ZnO 相似文献
11.
Interference fringes are obtained in a field-emission microscopy
(FEM) study of a multi-walled carbon nanotube (MWCNT) with two
open-ended branches. The FEM pattern, which is composed of three
parallel streaks, can be interpreted by using classical Young's
double-slit interference with the ends of the two MWCNT branches
treated as two secondary sources of the electron wave. The origin of
the coherency of the electron beams from the two branches is
discussed on the basis of the quantitative analysis of the FEM
pattern. The result suggests a new approach to obtaining a coherent
electron source. 相似文献
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运用第一性原理研究了不同锥角和结构的碳纳米锥 (CNC) 电子场发射性能.结果表明:随外电场 (Eadd) 增强,CNC电子结构变化显著,费米能级 (Ef) 处态密度 (DOS) 明显增大;赝能隙减小;体系电荷移向尖端.DOS,HOMO/LUMO及Mulliken电荷分析表明:CNC的电子场发射性能除依赖于尖端结构外,很大程度上还取决于锥角大小,特别顶层6个原子的CNC3和CNC4场发射性能
关键词:
碳纳米锥
电子场发射
第一性原理 相似文献
13.
Field electron emission (FE) is a quantum tunneling process in which electrons are injected from materials (usually metals)
into a vacuum under the influence of an applied electric field. In order to obtain usable electron current, the conventional
way is to increase the local field at the surface of an emitter. For a plane metal emitter with a typical work function of
5 eV, an applied field of over 1 000 V/μm is needed to obtain a significant current. The high working field (and/or the voltage
between the electrodes) has been the bottleneck for many applications of the FE technique. Since the 1960s, enormous effort
has been devoted to reduce the working macroscopic field (voltage). A widely adopted idea is to sharpen the emitters to get
a large surface field enhancement. The materials of emitters should have good electronic conductivity, high melting points,
good chemical inertness, and high mechanical stiffness. Carbon nanotubes (CNTs) are built with such needed properties. As
a quasi-one-dimensional material, the CNT is expected to have a large surface field enhancement factor. The experiments have
proved the excellent FE performance of CNTs. The turn-on field (the macroscopic field for obtaining a density of 10 μA/cm2) of CNT based emitters can be as low as 1 V/μm. However, this turn-on field is too good to be explained by conventional theory.
There are other observations, such as the non-linear Fowler-Nordheim plot and multi-peaks field emission energy distribution
spectra, indicating that the field enhancement is not the only story in the FE of CNTs. Since the discovery of CNTs, people
have employed more serious quantum mechanical methods, including the electronic band theory, tight-binding theory, scattering
theory and density function theory, to investigate FE of CNTs. A few theoretical models have been developed at the same time.
The multi-walled carbon nanotubes (MWCNTs) should be assembled with a sharp metal needle of nano-scale radius, for which the
FE mechanism is more or less clear. Although MWCNTs are more common in present FE applications, the single-walled carbon nanotubes
(SWCNTs) are more interesting in the theoretical point of view since the SWCNTs have unique atomic structures and electronic
properties. It would be very interesting if people can predict the behavior of the well-defined SWCNTs quantitatively (for
MWCNTs, this is currently impossible). The FE as a tunneling process is sensitive to the apex-vacuum potential barrier of
CNTs. On the other hand, the barrier could be significantly altered by the redistribution of excessive charges in the micrometer
long SWCNTs, which have only one layer of carbon atoms. Therefore, the conventional theories based upon the hypothesis of
fixed potential (work function) would not be valid in this quasi-one-dimensional system. In this review, we shall focus on
the mechanism that would be responsible for the superior field emission characteristics of CNTs. We shall introduce a multi-scale
simulation algorithm that deals with the entire carbon nanotube as well as the substrate as a whole. The simulation for (5,
5) capped SWCNTs with lengths in the order of micrometers is given as an example. The results show that the field dependence
of the apex-vacuum electron potential barrier of a long carbon nanotube is a more pronounced effect, besides the local field
enhancement phenomenon. 相似文献
14.
Shanawer Niaz Hamed Abbasian Manzoor Ahmad Badar M. Anwar-ul-Haq Arzu Karayel 《Molecular physics》2017,115(20):2515-2520
We present ab initio study using dispersion-corrected density functional theory calculations to investigate the hydrogen interaction with Ti-coated, one end closed, single-walled carbon nanotube (SWCNT). Our results demonstrate that a single Ti atom binds up to five hydrogen molecules on SWCNT cap top, whereas adsorption of four hydrogen molecules is energetically more favourable. The analyses from adsorption energy profile, highest occupied molecular orbital–lowest unoccupied molecular orbital gap and Mulliken charge distribution show contrast in first hydrogen molecule adsorption compared with the rest of four configurations. This is clearly due to the strongly different bonding nature of first hydrogen adsorption among others, between hydrogen molecules and Ti-coated SWCNT. These results not only support our understanding of adsorption nature of hydrogen in Ti-coated SWCNTs but also suggest new directions for smart storage techniques. 相似文献
15.
运用密度泛函理论研究了锥顶碳纳米管的结构稳定性与电子场致发射性能.结果表明:在外电场作用下,该体系的结构稳定性明显优于碳纳米锥体、C30半球封口的碳纳米管,且电子发射性能与锥角大小、锥顶构型密切相关,特别是锥角38.9°及棱脊型顶部的cone1@(6,6)综合性能最优,用其作为场致发射源的阴极时可显著提高发射电流密度并延长器件的使用寿命.
关键词:
锥顶碳纳米管
电子场致发射
结构稳定性
密度泛函理论 相似文献
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Structural, curvature and electronic properties of Rh adsorption on armchair single-walled carbon nanotube 下载免费PDF全文
This paper systematically studies the rolling effects of the (n, n) single-wall carbon nanotubes (SWCNT) with different curvatures on Rh adsorption behaviours by using density functional theory. The outside charge densities of SWCNTs are found to be higher than those inside, and the differences decrease with the increase of the tube radius. This electronic property led to the discovery that the outside adsorption energies are higher than the inside ones, and that the differences are reduced with the increase of the tube radius. Partial density of states and charge density difference indicate that these strong interactions induce electron transfer between Rh atoms and SWCNTs. 相似文献
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Adsorption of hydrogen molecules on an Ni-doped (8,0) single-walled
carbon nanotube (SWNT) is investigated by using first-principles
density functional calculations. The result shows that a single
Ni atom adsorbed on the bridge site of the tube could cannot
dissociate the H2, however it can chemisorb three H2 at
most, with the average binding energy per H2 suitable
for the hydrogen storage at the room temperature. More H2 would
physisorb around an Ni atom weakly. As for the SWNT with an Ni dimer
adsorbed, we find that when the H2 approaches the Ni--Ni bond,
it dissociates without overcoming any barrier and makes bonds
with Ni atom. 相似文献
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Initiation of vacuum breakdown and failure mechanism of the carbon nanotube during thermal field emission 下载免费PDF全文
The carbon nanotube(CNT)-based materials can be used as vacuum device cathodes. Owing to the excellent field emission properties of CNT, it has great potentials in the applications of an explosive field emission cathode. The falling off of CNT from the substrate, which frequently appears in experiments, restricts its application. In addition, the onset time of vacuum breakdown limits the performance of the high-power explosive-emission-cathode-based diode. In this paper, the characteristics of the CNT, electric field strength, contact resistance and the kind of substrate material are varied to study the parameter effects on the onset time of vacuum breakdown and failure mechanism of the CNT by using the finite element method. 相似文献