Submitted for the MAR09 Meeting of The American Physical Society Mechano-electronic Superlattices in Silicon Nanoribbons1 M. HUANG, C.S. RITZ, B. NOVAKOVIC, F. FLACK, D.E. SAVAGE, P.G. EVANS, I. KNEZEVIC, University of Wisconsin-Madison, D. YU, Y. ZHANG, F. LIU, University of Utah, M.G. LAGALLY, University of Wisconsin-Madison — Single-crystal silicon nanomembranes (SiNMs) have the mechanical compliance fundamentally different from bulk materials or supported thin films that can produce unique structural and electronic effects. The growth of nanostressors on SiNMs utilizes this mechanical compliance to create a “strain lattice” consisting of tiny regions of local curvature in the SiNMs, the order occurring because the locally bending SiNMs provides a strong feedback for self-organization of the nanostressors. We demonstrate that a high degree of order occurs when Ge or SiGe nanostressors are grown on both sides of free-standing but end-tethered Si nanoribbons. Our calculations prove that the strain lattice in the Si produces a modulation in the electronic band structure, and thus an electronic superlattice. Our calculations also demonstrate that discrete minibands can be observable in such an electronic superlattice at 77K. It is expected that an electric conductivity will be increased in the superlattice. We predict that it is possible to observe discrete minibands at room temperature if other nanostressors are used. 1This work was supported by DOE, AFOSR, and NSF. Ming-Huang Huang University of Wisconsin-Madison Date submitted: 19 Nov 2008 Electronic form version 1.4

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 SiO(2) 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-SiO(2) and Si-H bonds on the nanowire surfaces.

Epitaxial growth of self-assembled quantum dots (QDs) on single-crystal nanomembranes yields organized arrays of QDs via a growth mode mediated by QD-induced strains in the membrane. A crucial aspect of this effect arises because epitaxial growth on thin Si sheets and nanostructures derived from them can occur simultaneously on two surfaces separated only by the 10-nm-scale thickness of the membrane. A QD on one surface of a free-standing membrane causes the nucleation of QDs in specific positions on the opposite surface. Control experiments using molecular beam epitaxy to deposit QDs on a single surface do not yield long-range order. Through-membrane elastic interactions consistent with predictions from finite-element-based mechanics models are observed using synchrotron x-ray microdiffraction. The role of crystallographic anisotropy is evident in finite-element predictions of the strains that bias the nucleation events. The scaling of the dot spacing with membrane thickness is consistent with the spacing of nucleation sites predicted using the mechanical model.

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 (001) and (110) 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.

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.

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.

ADVERTISEMENT RETURN TO ISSUEPREVAddition/CorrectionORIGINAL ARTICLEThis notice is a correctionMechano-electronic Superlattices in Silicon NanoribbonsMinghuang Huang, Clark S. Ritz, Bozidar Novakovic, Decai Yu, Yu Zhang, Frank Flack, Donald E. Savage, Paul G. Evans, Irena Knezevic, Feng Liu, and Max G. Lagally*Cite this: ACS Nano 2009, 3, 5, 1305Publication Date (Web):May 8, 2009Publication History Published online8 May 2009Published inissue 26 May 2009https://pubs.acs.org/doi/10.1021/nn900396rhttps://doi.org/10.1021/nn900396rcorrectionACS PublicationsCopyright © 2009 American Chemical Society. This publication is available under these Terms of Use. Request reuse permissions This publication is free to access through this site. Learn MoreArticle Views767Altmetric-Citations1LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail PDF (46 KB) Get e-AlertscloseSUBJECTS:Crystallography,Lattices,Quantum dots,Silicon,Two dimensional materials Get e-Alerts

We present both experimental results and a compact model on nanoscale thermal transport in the vicinity of a hot spot in silicon. Effective-local-temperature measurements on the nanoscale are influenced by localized heating effect and a thermal interface resistance, as well as by the spreading resistance in silicon. Ballistic phonon transport is observed for nanoheaters where the interface thermal resistance contribution can be minimized. Thermoelectricity in silicon nanostructures is investigated as a possible route to convert thermal energy into electricity.

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.

This paper reports the first demonstration of both n- and p-type thin-film transistors (TFTs) on flexible plastic substrate using single-crystal Si (110) surface-oriented nanomembrane as active layer. The Si (110) nanomembrane of 190-nm thickness is derived from UNIBOND® silicon-on-insulator (SOI) fabricated by hybrid orientation technology (HOT) and transferred to flexible plastic substrate followed by a low-temperature (< 120 ºC) device process. Good device performance has been achieved under so far not-perfected device processing conditions, which includes field-effect mobility of around 95 and 45 cm2/V-sec on the linear region for the n- and p-type Si (110) TFTs, respectively, and device current ON/OFF ratio better than 10000 for both types of TFTs.

Undercut or fully released silicon template layers of ultrathin silicon-on-insulator are structurally compliant and allow long- range mechanical interactions that are impossible on supported SOI, thick SOI, or on bulk surfaces. SiGe quantum dots create and respond to strain in these freestanding Si substrates. We show that elastic effects lead to long-range order in the positions of quantum dots grown on both sides of a free- standing thin SOI substrate. A statistical analysis of the distribution of quantum dots shows that the ordered lattice of dots is coherent over distances of at least several hundred of nanometers. X-ray microdiffraction probes the structure of the SOI and finds that curvature in the Si lattice is consistent with the proposed deformation of the substrate by quantum dots.

Nanomembranes composed of single-crystal, tensilely strained Si( 110) and compressively strained SiGe( 110) layers have been fabricated from silicon- on-insulator (SOI) substrates. Elastic strain sharing is demonstrated for a trilayer structure consisting of a 12 nm Si) 80 nm Si0.91Ge0.09 film epitaxially grown on a 12 nm thick ( 110) oriented Si template layer that is subsequently released from its handle substrate. X-ray diffraction on the as-grown and released structures confirms a virtually dislocation-free membrane with a tensile strain of 0(23 +/- 0.02% in the Si(110) layers after release. Lower growth temperatures in molecular beam epitaxy allow for smoother growth fronts than are possible using chemical vapour deposition.