基于电磁激励的电子摩擦机理研究

Micro- and nano-electromechanical systems (M/NEMS) show promising capabilities in the current and future technological advancement. One of the biggest challenges in the miniaturization of these systems is overcoming the nanotribological issues, which prevent M/NEMS devices with sliding interfaces from being marketed. At the micro/nano scale, the energy from contacting bodies with relative motion may dissipate not only due to adhesive/cohesive interactions between asperities and phonon but also due to triboelectricity. Semiconductors, principally silicon (Si), have become main construction materials in M/NEMS devices. These systems with sliding interfaces in rotary and linear motion are therefore often in patterned with semiconductor substrates and require a friction control system. Therefore, this study aims at proposing a novel route to assess the electronic contributions to friction, which is applicable principally to Si. This new introduced technique uses different spectra of electromagnetic disturbance to elicit the electronic friction. The proposed method will exhibit the capability to electronically tune friction in semiconductors-M/NEMS and will bring an answer for a more fundamental quantification of the electronic friction on semiconductors. For the purpose of this study, experiments will be performed using an atomic force microscopy for the friction force measurements, and associated with a laser setup to assure the electronic excitations. The electronic friction will be further numerically studied by means of ab-initio molecular dynamics calculations. .This investigation will elucidate the complex energy dissipation mechanisms pertaining to electronic friction and on how they affect semiconductors-M/NEMS. Moreover, in line to the different phononic friction reduction techniques proposed in literature, this novel method would help to establish different procedures to control the electronic friction.

微/纳机电系统展现出了广阔的应用前景，而系统微型化所面临的最大挑战之一就是解决纳米尺度下的摩擦问题。在纳米尺度下，两相对滑动界面之间的能量耗散不仅来自于粘附作用和声子耗散，电子耗散也是其重要的组成部分。由于半导体，特别是硅，是构成微/纳器件的主要材料，因此控制存在相对转动或滑动的半导体界面处的摩擦力显得尤为重要。本项目针对硅材料提出了一个独特的方法来评估电子耗散。新方法利用电磁干扰来诱发电子摩擦并通过激发不同数量的电子来调节摩擦力，从而达到量化电子耗散的目的。首先，对原子力显微镜进行改造，用激光照射半导体表面以确保电子被激发并测量摩擦力；其次，采用第一性原理分子动力学建模完成数值研究。.本项目旨在揭示电子摩擦机理和量化电子摩擦对半导体微器件的影响并根据所得结果制定控制电子摩擦的解决方案。

微纳机电系统具有广阔的应用前景，如何厘清纳尺度下摩擦的内在机制，进而调控摩擦耗能是系统微型化所面临的最大挑战之一。本项目基于分子动力学和量子力学等理论，结合原子力显微镜等实验仪器，揭示了纳米摩擦耗能机理。具体如下：1）采用分子动力学和PT模型研究了垂直于滑动方向的侧向超声激励对纳米摩擦的影响。发现施加侧向激励会减小摩擦力，甚至可实现超滑；对于任意的激励幅值，当激励频率等于共振频率时，平均摩擦力最小；2）通过建立金刚石探针-单晶硅基底的单粗糙峰接触摩擦模型，研究了不同法向载荷下摩擦过程中硅基底的变形行为。结果表明随着法向载荷的增大，基底经历了弹性变形、塑性变形以及磨损三个阶段；3）采用雷诺方程、超弹性变形和粗糙接触的数值模型，描述了O形密封圈的弹流润滑以及密封泄露问题。结果表明，随着连接器使用深度的增大，密封圈两侧的压力增大，连接器插拔过程中的O形圈摩擦力减小，且摩擦力小于常规液压装置中O形圈的摩擦力；4）利用原子力显微镜研究了温度对黏附力的影响。结果表明，黏附力随温度的升高逐渐降低。5）基于声子寿命阐释了石墨烯层间的摩擦力随滑动速度呈非单调变化的现象。当速度较低时，声子的散射时间随速度的增大而减小，造成更高的摩擦耗能；而当速度超过临界值时，声子的散射时间远高于探针跨过单晶格的周期，此时界面处的声子没有充足的时间被耗散掉，导致摩擦耗能随速度的增大逐渐下降。该项目的研究成果将对实现摩擦润滑的主动控制提供理论指导。