Abstract
A major obstacle in the utilization of Mo thin films in flexible electronics is their brittle fracture behavior. Within this study, alloying with Re is explored as a potential strategy to improve the resistance to fracture. The sputter-deposited Mo1−xRex films (with 0 ≤ x ≤ 0.31) were characterized in terms of structural and mechanical properties, residual stresses as well as electrical resistivity. Their deformation behavior was assessed by straining 50 nm thin films on polyimide substrates in uniaxial tension, while monitoring crack initiation and propagation in situ by optical microscopy and electrical resistance measurements. A significant toughness enhancement occurs with increasing Re content for all body-centered cubic solid solution films (x ≤ 0.23). However, at higher Re concentrations (x > 0.23) the positive effect of Re is inhibited due to the formation of dual-phase films with the additional close packed A15 Mo3Re phase. The mechanisms responsible for the observed toughness behavior are discussed based on experimental observations and electronic structure calculations. Re gives rise to both increased plasticity and bond strengthening in these Mo-Re solid solutions.
Highlights
A major obstacle in the utilization of Mo thin films in flexible electronics is their brittle fracture behavior
The influence of Re on the fracture behavior of Mo was further investigated by density functional theory (DFT) calculations, which were used to determine the theoretical fracture toughness of Mo-Re alloys and to rationalize the change in electronic structure and bonding upon Re incorporation
We demonstrated in a previous publication[9] that crack onset strain (COS) can be significantly increased by inducing compressive residual stress in the film
Summary
A major obstacle in the utilization of Mo thin films in flexible electronics is their brittle fracture behavior. The sputter-deposited Mo1−xRex films (with 0 ≤ x ≤ 0.31) were characterized in terms of structural and mechanical properties, residual stresses as well as electrical resistivity Their deformation behavior was assessed by straining 50 nm thin films on polyimide substrates in uniaxial tension, while monitoring crack initiation and propagation in situ by optical microscopy and electrical resistance measurements. Mo films are often the primary choice in many electronic applications due to their attractive combination of functional properties They serve as back electrode materials in flexible CuInGaSe2-based solar cells due to their good chemical stability and low contact resistance[3, 4]. The influence of Re on the fracture behavior of Mo was further investigated by density functional theory (DFT) calculations, which were used to determine the theoretical fracture toughness of Mo-Re alloys and to rationalize the change in electronic structure and bonding upon Re incorporation
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