Curving Nanostructures Using Extrinsic Stress

Many thin films develop high residual stress during deposition. These stresses develop due to grain boundaries, dislocations, voids, and impurities within the film itself, or interfacial factors such as a lattice mismatch, difference in thermal expansion, or adsorption.[1–4] It is known that these intrinsic stresses can cause the spontaneous curving of substrates on which they are deposited.[5] If the substrate is much thicker than the stressed thin film, the substrate curves with a large radius of curvature. [6] In contrast, when the stressed thin film is deposited atop or below another thin film and the films are released from the substrate, it will spontaneously curve with a micro or nanoscale radii of curvature. [7–13] However, it is challenging to get the high intrinsic stress magnitudes needed to enable assembly with small nanoscale radii of curvature; typically, heteroepitaxial deposition at elevated temperatures is required, [11–13] which limits the types of devices and structures that can be assembled.

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