Abstract
While one might assume that the force to break a chemical bond gives a measure of the bond strength, this intuition is misleading. If the force is loaded slowly, thermal fluctuations may break the bond before it is maximally stretched, and the breaking force will be less than the bond can sustain. Conversely, if the force is loaded rapidly it is more likely that the maximum breaking force is measured. Paradoxically, no clear differences in breaking force were observed in experiments on gold nanowires, despite being conducted under very different conditions. Here we explore the breaking behaviour of a single Au–Au bond and show that the breaking force is dependent on the loading rate. We probe the temperature and structural dependencies of breaking and suggest that the paradox can be explained by fast breaking of atomic wires and slow breaking of point contacts giving very similar breaking forces.
Highlights
While one might assume that the force to break a chemical bond gives a measure of the bond strength, this intuition is misleading
Returning to the apparent paradox from the literature, that the breaking force observed for the spontaneous regime at room temperature seemed to be the same as the breaking force observed for the activationless regime at cryogenic temperatures, we can see a resolution
The paradox exists if we assume that it is the same types of structures breaking in all cases, but it is certainly likely that a 1G0 structure at room temperature is, on average, more point-contact-like, while a 1G0 structure at cryogenic temperatures is more linear-chain-like
Summary
While one might assume that the force to break a chemical bond gives a measure of the bond strength, this intuition is misleading. If an applied force is loaded slowly, the structure may break spontaneously due to thermal fluctuations before any significant force is applied to the system; if the force is loaded rapidly it is more likely that we measure the maximum force required to break the physical/chemical bond. Prior experiments breaking gold nanowires did not observe any clear differences in the breaking force, with all measurements reporting a breaking force of 1.2–1.8 nN (refs 4–10), despite being conducted under very different conditions. The activationless regime corresponds to our intuition from the macroscopic world: the breaking force is constant as the forceloading rate is always fast enough to ensure that environmental fluctuations play no role in the breaking process. Through a combination of experiment and theory, we show that the force required to break gold nanowires is dependent on the force-loading rate
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