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Science  23 Jun 2006:
Vol. 312, Issue 5781, pp. 1719
DOI: 10.1126/science.312.5781.1719c

Nanohelices can be used in micro- and nano-electromechanical systems as resonators, mech-anical components, or sensors. One route for the controlled fabrication of nanohelices is to grow strained heterofilms on a substrate and to etch and release the films, which then form coiled structures attached to the substrate at one end.

Previously, Zhang et al. developed such a method for SiGe and SiGe/Cr films on single-crystalline Si(100) substrates that was limited to helical angles of 45° or more (the maximum orientation mismatch). They now report that as the width of the stripes is decreased below 1 μm, edge effects lead to tighter pitches and cause the handedness of the helices to reverse (from right to left, through a disordered transition regime); even concentric multiwall rings can be fabricated. Although the Cr layers are isotropic, they change the edge stresses and cause the onset of anomalous coiling (deviation from the preferred <100> scrolling direction) to occur at larger stripe widths. The authors map out the conditions for controlling helical angles to less than 10° and model the relaxation behavior of these films with finite-element simulations. — PDS

Nano Lett. 6, 10.1021/nl053240u (2006).

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