arXivDaily arXiv每日学术速递 周一至周五更新
arXiv 2006.11344cond-mat.mes-hall
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基于感生电子密度的碳纳米管场发射增强因子模型

Modeling the Field Emission Enhancement Factor for Capped Carbon Nanotubes using the Induced Electron Density

Caio P. de Castro, Thiago A. de Assis, Roberto Rivelino, Fernando de B. Mota, Caio M. C. de Castilho, Richard G. Forbes

摘要:

在单壁碳纳米管(SWCNT)的许多场电子发射实验中,SWCNT位于两个分开的平行平板之一上,在它们之间施加宏观场FM。对于SWCNT表面上的任何给定位置“L”,场增强因子(FEF)被定义为$F_{\rm{L}}$ / $F_{\rm{M}}$,其中$F_{\rm{L}}$是在“L”处定义的局部场。来自小半径封端的SWCNT的最佳发射测量表现出恒定的特征FEF(即,独立于$F_{\rm{M}}$)。本文讨论了如何在量子力学(而不是经典的静电)计算中恢复这一结果。利用密度泛函理论(DFT)分析了两种两端封端的短的、浮动的SWCNT的性质,即(6,6)和(10,0)结构。两者实际上具有相同的高度($\sim 5.46$ nm)和半径($\sim 0.42$ nm)。结果发现,两个单壁碳纳米管的局部诱导FEF的峰值是相似的,是独立的$F_{\rm{M}}$,并从经典导体模型中发现的FEF值相似。有人建议,这些诱导的FEF值与单壁碳纳米管的纵向系统的极化率,这是假定相似。DFT计算还产生了“真实的”,而不是"诱导的”,两个SWCNT的势能(PE)势垒,FM值从3 V/ $μ$ m到2 V/nm。沿着单壁碳纳米管轴和沿着平行的"观察线”通过最上面的原子之一的PE分布是相似的。在低宏观领域的障碍形状的细节不同的两个单壁碳纳米管类型。即使对于$F_{\rm{M}}=0$,在发射极顶点处也存在不同的PE结构(对于两个SWCNT不同);这表明存在结构特异性化学诱导的电荷转移和相关的贴片场分布。

英文摘要:

In many field electron emission experiments on single-walled carbon nanotubes (SWCNTs), the SWCNT stands on one of two well-separated parallel plane plates, with a macroscopic field FM applied between them. For any given location "L" on the SWCNT surface, a field enhancement factor (FEF) is defined as $F_{\rm{L}}$/$F_{\rm{M}}$, where $F_{\rm{L}}$ is a local field defined at "L". The best emission measurements from small-radii capped SWCNTs exhibit characteristic FEFs that are constant (i.e., independent of $F_{\rm{M}}$). This paper discusses how to retrieve this result in quantum-mechanical (as opposed to classical electrostatic) calculations. Density functional theory (DFT) is used to analyze the properties of two short, floating SWCNTS, capped at both ends, namely a (6,6) and a (10,0) structure. Both have effectively the same height ($\sim 5.46$ nm) and radius ($\sim 0.42$ nm). It is found that apex values of local induced FEF are similar for the two SWCNTs, are independent of $F_{\rm{M}}$, and are similar to FEF-values found from classical conductor models. It is suggested that these induced-FEF values relate to the SWCNT longitudinal system polarizabilities, which are presumed similar. The DFT calculations also generate "real", as opposed to ``induced", potential-energy (PE) barriers for the two SWCNTs, for FM-values from 3 V/$μ$m to 2 V/nm. PE profiles along the SWCNT axis and along a parallel ``observation line" through one of the topmost atoms are similar. At low macroscopic fields the details of barrier shape differ for the two SWCNT types. Even for $F_{\rm{M}}=0$, there are distinct PE structures present at the emitter apex (different for the two SWCNTs); this suggests the presence of structure-specific chemically induced charge transfers and related patch-field distributions.

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