The combination of piezoelectric ceramics with silicon nanomembranes can provide a unique combination of electronic and mechanical functionality. For example, an integrated remotely accessible sensor/actuator can serve as a sound transducer to be placed on the tympanic membrane of the human ear. Such an implant would enable direct sound transmission in the kHz range via down-conversion of a modulated carrier signal at radio frequency. The viability of this concept is demonstrated via a specific design of the nanomembrane bonded over a hole in the piezoelectric chip as well as driving this chip to create a strong nonlinear mechanical response in the nanomembrane. The response in the audible-frequency range and the result is demonstrated by modulating the piezoelectric chip with a C-major audible tune-the tone ladder-and retrieving this sound by an optical readout method are centered. Finally, to prove the possibility of remote actuation of the nanomembrane, an antenna on the chip is integrated and the wide-band transmission from a mobile source is simulated. It is concluded that a remotely actuated invisible hearing aid is possible. Conceptualization of the combination of silicon nanomembranes (SiNM) and lead-zirconia-titanate (PZT) device placed in contact with the tympanic membrane in the ear. The system is designed for use as an implantable sound transducer enabling direct sound transmission in the kHz range. The figure shows the integration of an antenna for remote actuation as an invisible, remotely actuated hearing aid. image

A rolling-based printing approach for transferring arrays of patterned micro- and nano-structures directly from rigid fabrication substrates onto flexible substrates is presented. Transfer-printing experiments show that the new process can achieve high-yield and high-fidelity transfer of silicon nanomembrane components with diverse architectures to polyethylene terephthalate substrates over chip-scale areas (>1 × 1 cm2) in <0.3 s. The underlying mechanics of the process are investigated through finite element simulations of the contact and transfer process. These mechanics models provide guidance for controlling the contact area and strain in the flexible substrate during transfer, both of which are key for achieving reproducible and controlled component transfer over large areas.

Submitted for the MAR13 Meeting of The American Physical Society Nanostressor growth on Silicon Nanomembranes1 FRANK FLACK, BENJAMIN TREML, DONALD SAVAGE, MAX LAGALLY, University of Wisconsin Madison — Single-crystal semiconductor nanomembranes (NMs) have great potential for microelectronic materials heterointegration. In particular, they allow for the fabrication of custom-strained, dislocation-free growth interfaces. However, thin substrates are extremely compliant and it is, therefore, crucial to understand the added effects of residual processing strain and substrate bonding. We study the strain distributions on silicon NMs transferred to patterned Si substrates such that some NM regions are bonded and others freestanding. As the critical thickness for Stranski-Krastanow growth of quantum dots (QDs) is very strain dependent, we decorate the surface with Ge quantum dots (QDs) and use the resulting distribution as an easily visible indicator of strain. We see dramatic differences between QD distributions on the bound and freestanding regions, and also between the bound regions and the bulk Si substrate, suggesting that the buried interface may influence nanostressor growth.

Coherently strained CdSe quantum structures are fabricated under varying dynamical growth conditions during the epitaxy of cubic CdSe on (100) ZnSe. Reflection high energy electron diffraction (RHEED) is employed to monitor the growth mode (2D vs. 3D). Conventional photoluminescence (PL) shows that both growth modes yield quantum structures with high PL efficiencies in which excitons are strongly localized by interface fluctuations at varying length scales. Spatially-resolved, near-field PL from quantum structures formed during 3D growth reveals reproducible fine structure in the PL spectrum attributed to emission from excitons laterally confined to quantum dot-like regions. Transmission electron microscopy (TEM) studies suggest that these observations result from a combination of island growth and strain-driven interdiffusion.

Electrical conductivity of silicon nanomembranes (SiNMs) was measured by van der Pauw method under two surface modifications: hydrofluoric acid (HF) treatment and vacuum-hydrogenated(VH) treatment, which create hydrogen-terminated surface; and one interface modification: forming gas (5% H2 in N2) anneal, which causes hydrogen passivated interfaces. The results show that thinner SiNMs are more sensitive to the surface modifications, and HF treatment can cause larger drop of sheet resistance than that caused by VH treatment probably because of Fluorine (F). Forming gas anneal can also improve the conductivity depending on the interface trap density.

We demonstrate the use of holographic optical tweezers for trapping and manipulating silicon nanomembranes. These macroscopic free-standing sheets of single-crystalline silicon are attractive for use in next-generation flexible electronics. We achieve three-dimensional control by attaching a functionalized silica bead to the silicon surface, enabling non-contact trapping and manipulation of planar structures with high aspect ratios (high lateral size to thickness). Using as few as one trap and trapping powers as low as several hundred milliwatts, silicon nanomembranes can be rotated and translated in a solution over large distances.

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.

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 progress in manipulating silicon nanomembranes using holographic optical tweezers. The holographic optical tweezers technique provides a non-contact means of directly controlling the nanomembranes. Silicon nanomembranes are macroscopic free-standing sheets of single-crystal silicon which can be as thin as 10 nm or less. The thinness of the membranes imparts unique electronic, optical and mechanical properties. This characteristic, combined with the ability to precisely engineer their dimensions, makes silicon nanomembranes ideal candidates for use in new electronic and photonic devices. The nanomembranes utilized for this work have controlled thicknesses of 220 nm and areas reaching up to 200x200 microns. Novel all optically actuated methods for directing membranes in microfluidic flow environments, controllable membrane flexing and as well as vertical reorientation and positioning are outlined.

A method to fabricate single-crystal Si∕SiO2 multilayer heterostructures is presented. Heterostructures are fabricated by repeated transfer of single crystal silicon nanomembranes alternating with deposition of spin-on-glass. Nanomembrane transfer produces multilayers with low surface roughness and smooth interfaces. To demonstrate interface quality, the specular reflectivities of one-, two-, and three-membrane heterostructures are measured. Comparison of the measured reflectivity with theoretical calculations shows good agreement. Nanomembrane stacking allows for the preprocessing of individual membranes with a high thermal budget before the low thermal budget assembly of the stack, suggesting a new avenue for the three dimensional integration of integrated circuits.

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.

Multiple-layer SOI, in which there are multiple device layers per unit area, is of great interest because it potentially enables fully 3D integration. It also offers the prospect of more complete integration between optics and microelectronics than is possible with purely 2D structures. Here we present a technique for transfer and stacking of multiple single crystal Si nanomembranes with intervening oxide layers, enabling fabrication of multiple-layer SOI. We explain how to overcome transfer challenges, the most important of which is unintentional bonding of nanomembranes to their host substrate during lift-off. We examine the surface roughness of the membranes using atomic force microscopy (AFM). Intriguingly, the intermediate spin-on-glass layers used in this work are rougher than the silicon layers above and below, indicating that membrane transfer can ameliorate roughness introduced by such layers. We have used this process to create multilayer Si/SiO2 heterostructures, i.e., multiple-layer SOI. These structures naturally function as Bragg reflectors, and thus their optical reflectivity can be used as a measure of structure quality. The reflectivity of one, two, and three membrane structures has been measured, and reflectivity above 99% has been achieved for three-layer samples.

The lattice-mismatch-induced strain in growth of Ge on Si produces a host of exciting scientific and technological consequences, both in 3D nanostructure formation and, when silicon-on-insulator (SOI) is used as a substrate, in 2D membrane fabrication. One can use the ideas of strain sharing and critical thickness, combined with the ability to release the top layers of SOI, to create freestanding, dislocation-free, elastically strain relieved flexible Si/Ge membranes with nanometer scale thickness, which we call NanoFLEXSi or Si nanomembranes (SiNMs). The membranes can be transferred to new substrates, producing the potential for novel heterogeneous integration. The very interesting, and in some cases surprising, structural and electronic properties of these very thin membranes have been revealed using STM, X-ray diffraction, and electronic transport measurements. For example, STM shows that conduction in very thin Si layers on SOI with bulk-Si mobilities is possible even though the membrane is bulk depleted. Using the effect of elastic strain, we have fabricated two-dimensional electron gases (2DEGs) in membrane structures; we support the transport measurements with calculations suggesting that we are observing a single bound state in the well. We have fabricated thin-film transistors (TFTs) that we have transferred to flexible-polymer hosts that show a very high saturation current and transconductance. Thus very highspeed flexible electronics over large areas become possible.

The strain driven self-assembly of faceted Ge nanocrystals during epitaxy on Si(001) to form quantum dots (QDs) is by now well known. We have also recently provided an understanding of the thermodynamic driving force for directed assembly of QDs on bulk Si (extendable to other QD systems) based on local chemical potential and curvature of the surface. Silicon-on-insulator (SOI) produces unique new phenomena. The essential thermodynamic instability of the very thin crystalline layer (called the template layer) resting on an oxide can cause this layer, under appropriate conditions, to dewet, agglomerate, and self-organize into an array of Si nanocrystals. Using low-energy electron microscopy (LEEM), we observe this process and, with the help of first-principles total-energy calculations, we provide a quantitative understanding of this pattern formation. The Si nanocrystal pattern formation can be controlled by lithographic patterning of the SOI prior to the dewetting process. The resulting patterns of electrically isolated Si nanocrystals can in turn be used as a template for growth of nanostructures, such as carbon nanotubes (CNTs). Finally we show that this growth may be controlled by the flow dynamics of the feed gas across the substrate.