Significant new mechanical and electronic phenomena can arise in single-crystal semiconductors when their thickness reaches nanometer dimensions, where the two surfaces of the crystal are physically close enough to each other that what happens at one surface influences what happens at the other. We show experimentally that, in silicon nanomembranes, through-membrane elastic interactions cause the double-sided ordering of epitaxially grown nanostressors that locally and periodically highly strains the membrane, leading to a strain lattice. Because strain influences band structure, we create a periodic band gap modulation, up to 20% of the band gap, effectively an electronic superlattice. Our calculations demonstrate that discrete minibands can form in the potential wells of an electronic superlattice generated by Ge nanostressors on a sufficiently thin Si(001) nanomembrane at the temperature of 77 K. We predict that it is possible to observe discrete minibands in Si nanoribbons at room temperature if nanostressors of a different material are grown.

The influence of in-plane biaxial strain on the conduction bands of Si is explored using elastically strained Si(001) nanomembranes and high-resolution x-ray absorption measurements with electron yield detection. The strain-induced splitting of the conduction band minimum and the energy shifts of two higher conduction bands near L1 and L3 are clearly resolved. The linear increase of the splitting of the conduction band minimum with increasing strain and the nonlinear shift of the L1 point toward the conduction band minimum agree quantitatively with current theories.

Freestanding, ultracompliant crystalline-sheet substrates provide a new opportunity to control the growth of strained epitaxial films. Three-dimensional SiGe islands grown on thin silicon nanomembranes self-order as the strain field induced by initial island growth guides nucleation of subsequent islands on the opposite surface. A mechanics analysis explains this unique growth mode, possible only on ultracompliant substrates. The ordering can be tailored by manipulating the thickness and elastic properties of the membrane.

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The flexibility of single-crystal Si nanomembranes allows strain to be applied elastically without introducing dislocations in the fabrication process, resulting in uniform strain. It is also relatively easier to apply different types and orientations of strain to Si using elastic-strain sharing than by the traditional graded-strained-layer approach. We use X-ray absorption spectroscopy to measure the effect of uniform biaxial strain on several features of the conduction band structure of Si with ͑001͒ and ͑110͒ orientations. By also measuring the Si 2p photoelectric threshold, we are able to determine the absolute positions of features of the Si conduction band and their change with strain.

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Abstract:Integrated freestanding single-crystal silicon nanowires with typical dimension of 100 nm × 100 nm × 5 μm are fabricated by conventional 1:1 optical lithography and wet chemical silicon etching. The fabrication procedure can lead to wafer-scale integration of silicon nanowires in arrays. The measured electrical transport characteristics of the silicon nanowires covered with/without SiO2 support a model of Fermi level pinning near the conduction band. The I-V curves of the nanowires reveal a current carrier polarity reversal depending on Si-SiO2 and Si-H bonds on the nanowire surfaces.

On page 722, in the first paragraph under Results and Discussion, we wrote "The QDs on each surface are aligned in rows along the ͗100͘ elastically soft crystallographic directions of Si, but those on one surface are offset in the ͗100͘ direction from those on the other surface." The latter "͗100͘" should be "͗110͘". This correction does not affect the results or conclusions in this article.