Jiang Zhuoling, Yam Kah-Meng, Guo Na, Zhang Lishu, Shen Lei, Zhang Chun
Department of Physics, National University of Singapore, 2 Science Drive 3, 117551, Singapore.
Department of Chemistry, National University of Singapore, 3 Science Drive 3, 117543, Singapore.
Nanoscale Horiz. 2021 Sep 27;6(10):801-808. doi: 10.1039/d1nh00293g.
The standard density functional theory (DFT) based first-principles approach has been widely used for modeling nanoscale electronic devices. A recent experiment, however, reported surprising transport properties of thiol-terminated silane junctions that cannot be understood using the standard DFT approach, presenting a severe challenge for the current computational understanding of electron transport at the nanoscale. Using the recently proposed steady-state DFT (SS-DFT) for nonequilibrium quantum systems, we found that in silane junctions, underlying the puzzling experimental observations is a novel type of intriguing nonequilibrium effect that is beyond the framework of the standard DFT approach. Our calculations show that the standard DFT approach is a good approximation of SS-DFT when silane junctions are near equilibrium, but the aforementioned nonequilibrium effects could drive the thiol-terminated silanes far away from equilibrium even at low biases of around 0.2 V. Further analysis suggests that these nonequilibrium effects could generally exist in nanoscale devices in which there are conducting channels mainly residing at the source contact and close to the bias window. These findings significantly broaden our fundamental understanding of electron transport at the nanoscale.
基于标准密度泛函理论（DFT）的第一性原理方法已被广泛用于纳米级电子器件的建模。然而，最近的一项实验报告了硫醇封端的硅烷结令人惊讶的输运特性，而使用标准DFT方法无法理解这些特性，这对当前纳米级电子输运的计算理解提出了严峻挑战。使用最近针对非平衡量子系统提出的稳态DFT（SS-DFT），我们发现在硅烷结中，令人困惑的实验观察结果背后是一种新型的有趣非平衡效应，它超出了标准DFT方法的框架。我们的计算表明，当硅烷结接近平衡时，标准DFT方法是SS-DFT的良好近似，但即使在约0.2 V的低偏压下，上述非平衡效应也可能使硫醇封端的硅烷远离平衡。进一步分析表明，这些非平衡效应通常可能存在于纳米级器件中，其中导电通道主要位于源极接触处且靠近偏压窗口。这些发现显著拓宽了我们对纳米级电子输运的基本理解。
