二维材料电子器件辐照失效机制探索

Electronic device is of crucial importance in exploring unknown spaces like the universe. However, it poses a huge challenge that the degradation and failure may frequently happen for the devices under extremely conditions, e.g. highly level radiation, which has been a critical issue for decades. Recently, several novel electronic materials and devise do emerge. Their behavior and durability under beam irradiation are yet to be revealed. As people learned in the past decades, it is very difficult to reveal the detailed mechanism experimentally, however, theoretical modelling shows its potential to more suitably investigating the failure and degradation processes at the atomic scale. In this proposal, We first consider the interaction between the irradiation and the atoms/electrons of the device materials by calculating the variation of electronic and geometric structures under the excitations from elastic and inelastic ions/electrons and periodically modulated temperature. Then, we simulate the dynamics process of atomic structures in a few materials or nanostrucutres under excitations, by which we could reveal a few representative defect configurations that being input into electron transport calculations. All these results allow us to build the relationship among excitation strength/type, irradiation/thermal damage, electric performance degradation and device failure. A likely proposal may be offered to overcome this issue and a few emerging materials will be examined for their robustness under electronic and thermal excitations. Particularly, we employ density functional theory calculation to model the systems, with the projector augmented wave method to manipulate the core electrons and simulate an effect ionic state. A semi-classic scattering formalism is used to compute the scattering cross-section and estimate the total amount of transferred momentum to the studied atom/ion. We keep the ionic state in molecular dynamic simulations, which gives us a few configurations under the ionic state. Non-equilibrium Green function method helps use to assess the transport properties change with those defects. We aim to publish 15-20 peer reviewed papers during the whole project and contend for a team/network grant at higher levels.

人类探索宇宙等未知空间的活动强烈依赖于电子器件，但其在射线辐照等极端条件下的服役失效是困扰世界各国多年的重要问题。随着电子器件的发展，新材料、新器件层出不穷。虽然这些新兴材料和器件的辐照失效问题十分重要，但其实验研究难度大，我国尚未开展这方面研究工作。项目拟从射线辐照与器件材料原子和电子的基本相互作用出发，采用第一性原理电子结构计算中的缀加投影平面波方法对芯能级电子进行调控模拟电子激发态，采用电子（质子）散射公式估算散射界面并得到动量转移，考虑弹性和非弹性散射激发对器件材料电子和原子几何结构的影响；利用激发态分子动力学模拟电子激发态下的材料原子结构弛豫动力学演化过程，找到几种特征的缺陷或损伤结构，并使用非平衡格林函数方法预测这些构型对器件电子输运性质的影响。通过这些结果建立辐照种类—辐照损伤—电学性质退化—服役失效这四者之间的关联，揭露器件失效机制，提出可能的解决方案，探索可能的替代材料。

在强射线辐照下的电子器件服役稳定性是一个广为关注的问题。在射线辐照下，电子态的激发和弛豫通常是可逆的，但这些激发（包含弹性和非弹性的）可以诱导不可逆的原子位置激发和弛豫，从而改变器件材料的具体原子材料，导致其物性变化甚至失效。项目研究了黑磷等新兴二维沟道材料在电子辐照下的结构稳定性和动力学问题，在辐照下的一维线结构构筑和物性，关注了黑磷在辐照下的缺陷形成机制，以及黑磷、碲等在电子辐照下的结构相变等。提出了一种模拟高能电子束轰击二维材料过程的理论方案，为高能电子束在二维材料上的刻蚀实验提供了详细的理论指导。讨论了六种无限长磷原子链的几何稳定性和他们之间可能发生的相变，并预测 单原子锯齿形链是一种狄拉克半金属。此外，研究还发现在有基底支撑有限长链中，锯齿形链依然具有最好的稳定的性，而扶手椅链只能在大致基底[110]的方向上存在。在MoSe2单一材料中实现了多种未曾被发现的低对称性、单一、大面积的不同堆叠的晶畴。结合STS测量与DF T计算，研究进一步发现各种堆叠的价态对应了不同的带隙与带尾能态(band tail states)。发现电荷掺杂的方法可以调控Te不同相的相互转变，在相变的同时能够实现从1.17eV到0.33eV的能隙调 控，乃至于半导体向金属的转变。研究发现由于MoS2和MoSe2的晶格常数不同，发生取代之后在材料整体产生了长程的应力，进而改变了不同位置的取代势垒。发现WSe2本征的带隙中的缺陷能级难以被实验观测到，主要是由于其波函数在z方向缺乏分布。而K原子修饰成功调控了缺陷能级及波函数的形状，使得以前被隐藏的缺陷能级得以被扫描隧道谱观测到。同时计算显示K原子贡献的未成对电子会导致局域磁矩的出现，而外加电场导致的奇偶数电子填充可以对 应不同的局域磁矩开关态。实现了多种人工二维晶格物性调控：在黑磷上实现了具有面内压应力的C60分子单层薄膜，发现了由孤立的分子轨道形成了分子间能带导致的分子间离域电子态，有望本质改善C60单层薄膜的电荷输运性质。