Theoretical Modeling of Tribochemical Reaction on Pt and Au Contacts: Mechanical Load and Catalysis

TL;DR

This study uses density functional theory to analyze how mechanical load and catalysis contribute to tribopolymer formation on Pt and Au contacts, impacting MEMS/NEMS device conductivity.

Contribution

It provides a detailed mechanistic understanding of tribopolymer formation involving mechanical stress and catalytic effects, guiding strategies to prevent it.

Findings

Tribopolymer formation is driven by mechanical load and catalysis.

Pt acts as a catalyst, facilitating dehydrogenation of benzene.

Electrochemical effects enhance catalytic activity and polymer formation.

Abstract

Micro-electro-mechanical system and nano-electro-mechanical system (MEMS and NEMS) transistors are considered promising for size-reducing and power-maximizing electronic devices. However, the tribopolymer which forms due to the mechanical load to the surface contacts affects the conductivity between the contacts dramatically. This is one of the challenging problems that prevent widespread practical use of these otherwise promising devices. Here, we use density functional theory (DFT) to investigate the mechanisms of tribopolymer formation, including normal mechanical loading, the catalytic effect, as well as the electrochemical effect of the metal contacts. We select benzene select as the background gas, because it is one of the most common and severe hydrocarbon contaminants. Two adsorption cases are considered: one is benzene on the reactive metal surface, Pt(111), and the other is benzene on the noble metal, Au(111). We demonstrate that the formation of tribopolymer is induced both by the mechanical load and by the catalytic effect of the contact. First, benzene molecules are adsorbed on the Pt surfaces. Then, due to the closure of the Pt contacts, stress is applied to the adsorbates, making the C-H bonds more fragile. As the stress increases further, H atoms are pressed close to the Pt substrate and begin to bond with Pt atoms. Thus Pt acts as a catalyst, accelerating the dehydrogenation process. When there is voltage applied across the contacts, the catalytic effect is enhanced by electrochemistry. Finally, due to the loss of H atoms, C atoms become more reactive and link together or pile up to form tribopolymer. By understanding these mechanisms, we provide guidance on design strategies for suppressing tribopolymer formation.