Exceptional fracture resistance of ultrathin metallic glass films due to an intrinsic size effect

Abstract

Metallic glasses typically fail in a brittle manner through shear band propagation but can exhibit significant ductility when the sample size is reduced below a few hundreds of nanometers. To date the size effect was mainly demonstrated for free-standing samples and the role of extrinsic setup parameters on the observed behavior is still under debate. Therefore, in the present work we investigated the mechanical properties of polymer-supported sputtered amorphous Pd 82 Si 18 thin films with various thicknesses. We show that the films exhibit brittle fracture for thicknesses far below 100 nm. A pronounced size effect resulting in extended crack-free deformation up to 6% strain was observed only in films as thin as 7 nm – a thickness which is lower than the typical shear band thickness. This size effect results in exceptional cyclic reliability of ultrathin metallic glass films which can sustain cyclic strains of 3% up to at least 30,000 cycles without any indication of fatigue damage or electrical conductivity degradation. Since the enhancement of mechanical properties is observed at ambient conditions using inexpensive substrates and an industrially scalable sputter deposition technique, a new research avenue for utilization of ultrathin metallic glasses in microelectronics, flexible electronics or nanoelectromechanical devices is opened up.

Au-Based Thin-Film Metallic Glasses for Propagating Surface Plasmon Resonance-Based Sensor Applications

“…Thin-film metallic glasses (TFMGs) are a new group of MGs which have been commonly fabricated by physical vapor deposition (PVD). − With the process of vapor-to-solid by PVD, TFMGs are subjected to a much faster cooling rate compared to the process of liquid-to-solid by casting for bulk MGs. As a result, TFMGs not only possess the unique properties of MGs but also have a better glass-forming ability with a wider composition range. , Moreover, TFMGs can exhibit higher fracture resistance compared with their bulk MG counterparts because of the size effect. , Previously, we have confirmed the Au-based TFMGs as a plasmonic material, used nanoimprint to fabricate periodic nanostructures by taking advantage of the viscous flow behavior of TFMGs in the supercooled liquid region, and proved the feasibility of using Au-based TFMGs as LSPR-based sensor . In addition, we have studied the effects of crystallinity of Au-based TFMGs on SERS recently .…”

“… 36 , 37 Moreover, TFMGs can exhibit higher fracture resistance compared with their bulk MG counterparts because of the size effect. 37 , 38 Previously, we have confirmed the Au-based TFMGs as a plasmonic material, used nanoimprint to fabricate periodic nanostructures by taking advantage of the viscous flow behavior of TFMGs in the supercooled liquid region, and proved the feasibility of using Au-based TFMGs as LSPR-based sensor. 39 In addition, we have studied the effects of crystallinity of Au-based TFMGs on SERS recently.…”

Electrical and Optical Properties of Co75Si15B10 Metallic Glass Nanometric Thin Films

“…This prompted us to check the transmittance spectra of light through the thinner TFMGs (i.e., those of thicknesses of 5, 10, and 20 nm). It was found that the TFMG gained optical transparency for thicknesses less than 5 nm, unlike the Pd-based TFMG [ 18 ].…”

“…Binary Zr-Cu based TFMGs have been reported to exhibit conductivity 1.4 and 8 times as large as that for the pure Zr and Cu films, respectively [ 17 ]. Meanwhile, it was demonstrated that Pd-based TFMGs were optically transparent at thickness less than 10 nm while being mechanically flexible [ 18 ]. Furthermore, Zr-Cu-Al-based TFMG was also reported to produce enhanced transmittance at near-infrared wavelengths by the addition of Si [ 19 ].…”

Small-Scale Mechanical Testing

“…In compositionally homogeneous laminated FeP amorphous crystalline nanolaminates (213), extensive crack deflection at interfaces contributes to the highest strength and ductility values at an intermediate layer spacing of 40 nm. Size effects in fracture strength due to shear band inhibition in metallic glass thin films subject to 3% tensile strain occurred below 10 nm in PdSi films on polyimide, as assessed through the use of electrical resistance to detect the nucleation and growth of channeling cracks (214). This finding suggests that such films could be used in cycling applications.…”