Tin, The Enabler-Hydrogen Diffusion into Ruthenium.

Chidozie Onwudinanti,Ionuţ Tranca,Shuxia Tao,Thomas Morgan

doi:10.3390/nano9010129

Chidozie Onwudinanti, Ionuţ Tranca + Show 2 more

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https://doi.org/10.3390/nano9010129

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Abstract

Hydrogen interaction with ruthenium is of particular importance for the ruthenium-capped multilayer reflectors used in extreme ultraviolet (EUV) lithography. Hydrogen causes blistering, which leads to a loss of reflectivity. This problem is aggravated by tin. This study aims to uncover the mechanism via which tin affects the hydrogen uptake, with a view to mitigation. We report here the results of a study of hydrogen interaction with the ruthenium surface in the presence of tin using Density Functional Theory and charge density analyses. Our calculations show a significant drop in the energy barrier to hydrogen penetration when a tin atom or a tin hydride molecule (SnHx) is adsorbed on the ruthenium surface; the barrier has been found to drop in all tested cases with tin, from 1.06 eV to as low as 0.28 eV in the case of stannane (SnH4). Analyses show that, due to charge transfer from the less electronegative tin to hydrogen and ruthenium, charge accumulates around the diffusing hydrogen atom and near the ruthenium surface atoms. The reduced atomic volume of hydrogen, together with the effect of electron–electron repulsion from the ruthenium surface charge, facilitates subsurface penetration. Understanding the nature of tin’s influence on hydrogen penetration will guide efforts to mitigate blistering damage of EUV optics. It also holds great interest for applications where hydrogen penetration is desirable, such as hydrogen storage.

Highlights

Hydrogen interacts with metal surfaces in many varied and important technological applications
We have investigated hydrogen penetration of the Ru(0001) surface in the presence and absence of tin, by means of Density Functional Theory (DFT) computations, chemical bonding, and charge density analysis
We showed that hydrogen faces a significant barrier to subsurface penetration in the absence of tin

Summary

Introduction

Hydrogen interacts with metal surfaces in many varied and important technological applications. The ability of the small atom to permeate metals and change their properties gives hydrogen–metal systems added significance; for instance, embrittlement of metals remains an obstacle to the transport and storage of hydrogen [7,8]. In this case, as in separation and purification, diffusion into the subsurface and bulk of the metal is quite important [9]. The addition of a second metal creates a so-called bimetallic surface This often introduces significant changes to the electronic structure and characteristics of that surface relative to the single metal [14,15,16,17], with consequences for its technological applications

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