The distinction between hard and soft materials is most frequently described at the microscopic level as a difference in the nature of the bonding and molecular assembly, but concepts of “soft” and “hard” are more intuitively associated with macroscopic mechanical properties, such as stiffness or hardness. The behavior of a hard material may resemble that of a soft material in many aspects when a structural dimension is reduced to the nanoscale, even if elastic constants and moduli do not change. When semiconductor crystals, strongly covalently bonded and brittle, are made into membranes as thin as a few nanometres, they can behave like traditional soft matter, while maintaining their single-crystal structure without defects even after substantial deformation. This review presents single-crystal Si in a new fashion, i.e., as a form of soft matter, if fabricated as flexible nanomembranes, and suggests a plethora of interesting science and many applications that may benefit from the use of Si in this “soft matter” form. We suggest that the nanomembrane form gives Si an additional, new life as a soft material.
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