Controlled Movements in Superlubric MEMS

结构超滑微机电系统的受控运动

瞿苍宇¹,向小健¹,马明^2,3,郑泉水^1,2,3,4,*

(1.深圳清华大学 研究院超滑技术研究所,广东 深圳 518057;

2.清华大学 微纳米力学与多学科交叉创新研究中心,北京 100084;

3.清华大学 摩擦学国家重点实验室&清华大学机械工程学院,北京 100084;

4.清华大学 工程力学系,北京 100084)

中文说明：

结构超滑是指两个固体表面接触摩擦近乎为零、磨损为零的状态,为发明极低能耗和极高寿命的微机械或微机电系统提供了基础。但要实现这些应用,则需要能够有效控制或限制滑移运动按希望或规定的路线进行,同时不破坏超滑。如何实现这类控制或限制,至今还是一个有待于解决的挑战。本文研究表明,通过对滑块和滑床的几何形状,或滑块和隐藏在滑床表面下面的电极的形状的恰当设计,就可以借助于界面能或电容势能的极小化来实现动态控制或限制。通过恰当设计,滑移接触界面的界面能可对滑块提供回复力与约束力,而电极不仅可提供回复力与约束力,还可提供驱动力,且这些力均可调控。作为以上原理的示例,本文设计一种超滑谐振器,其侧向振动模态具有确定的固有频率,而其他自由度上的运动可被有效约束。本文提出的原理具有一定的通用性,有助于引导未来超滑机械或微机电系统的发明。

关键词：结构超滑,微机电系统（MEMS）,谐振器,受控运动

     

Hydrogen-Enhanced Catalytic Conversion of Amorphous Carbon to Graphene for Achieving Superlubricity

The solid-state conversion of amorphous carbon into graphene is extremely difficult, but it can be achieved in the friction experiments that induce macroscale superlubricity. However, the underlying conversion mechanisms remain elusive. Here, the friction experiments with Cu nanoparticles and (non-hydrogen (H) or H) a-C in vacuum, show the H-induced conversion of mechanical to chemical wear, resulting in the a-C's tribosoftening and nanofragmentating that produce hydrocarbon nanoclusters or molecules. It is such exactly hydrocarbon species that yield graphene at hydrogen-rich a-C friction interface, through reaction of them with Cu nanoparticles. In comparison, graphene isn't formed at Cu/non-H a-C friction interface. Atomistic simulations reveal the hydrogen-enhanced tribochemical decomposition of a-C and demonstrate the energetically favorable graphitization transformation of hydrocarbons on Cu substrates. The findings are of importance to achieve solid-state transformation between different carbon allotropes and provide a good strategy to synthesize other graphitic encapsulated catalysts with doped elements.