arXiv subjects

Luis Guillermo Villanueva

Publications and source records attributed to Luis Guillermo Villanueva.

22 records · Page 2Linked to original sources

arXiv2015

Size Effects on Mechanical Properties of Micro/Nano Structures

Experiments on Micro- and Nano-mechanical systems (M/NEMS) have shown that their behavior upon bending loads departs in many cases from the classical predictions using Euler-Bernoulli theory and Hooke law. This anomalous response has usually been seen as a dependence of the material properties with the size of the structure, in particular thickness. A theoretical model that allows for quantitative understanding and prediction of this size effect is important for the design of M/NEMS. In this paper, we summarize and analyze the five theories that can be found in the literature: Grain Boundary Theory (GBT), Surface Stress Theory (SST), Residual Stress Theory (RST), Couple Stress Theory (CST) and Surface Elasticity Theory (SET). By comparing these theories with experimental data we propose a simplified model combination of CST and SET that properly fits all considered cases, therefore delivering a simple (two parameters) model that can be used to predict the mechanical properties at the nanoscale.

cond-mat.mes-hall↗

arXiv2014

Evidence of surface loss as ubiquitous limiting damping mechanism in SiN micro- and nanomechanical resonators

Silicon nitride (SiN) micro- and nanomechanical resonators have attracted a lot of attention in various research fields due to their exceptionally high quality factors ($Q$s). Despite their popularity, the origin of the limiting loss mechanisms in these structures has remained controversial. In this paper we propose an analytical model combining acoustic radiation loss with intrinsic loss. The model accurately predicts the resulting mode-dependent $Q$s of a low-stress silicon-rich and a high-stress stoichiometric SiN membrane. The large acoustic mismatch of the low-stress membrane to the substrate seems to minimize radiation loss and $Q$s of higher modes ($n \wedge m \geq 3$) are limited by intrinsic losses. The study of these intrinsic losses in low-stress membranes with varying lengths $L$ and thicknesses $h$ reveals an inverse linear dependence of the intrinsic loss with $h$ for thin resonators independent of $L$. This finding was confirmed by comparing the intrinsic dissipation of arbitrary (membranes, strings, and cantilevers) SiN resonators extracted from literature, suggesting surface loss as ubiquitous damping mechanism in thin SiN resonators with $Q_{surf} = β\cdot h$ and $β= 6\times10^{10} \pm4\times 10^{10}$~m$^{-1}$. Based on the intrinsic loss the maximal achievable $Q$s and $Q\cdot f$ products for SiN membranes and strings are outlined.

cond-mat.mes-hall↗

arXiv2013

Demonstration of suppressed phonon tunneling losses in phononic bandgap shielded membrane resonators for high-Q optomechanics

Dielectric membranes with exceptional mechanical and optical properties present one of the most promising platforms in quantum opto-mechanics. The performance of stressed silicon nitride nanomembranes as mechanical resonators notoriously depends on how their frame is clamped to the sample mount, which in practice usually necessitates delicate, and difficult-to-reproduce mounting solutions. Here, we demonstrate that a phononic bandgap shield integrated in the membrane's silicon frame eliminates this dependence, by suppressing dissipation through phonon tunneling. We dry-etch the membrane's frame so that it assumes the form of a $\mathrm{cm}$-sized bridge featuring a 1-dimensional periodic pattern, whose phononic density of states is tailored to exhibit one, or several, full band gaps around the membrane's high-$Q$ modes in the MHz-range. We quantify the effectiveness of this phononic bandgap shield by optical interferometry measuring both the suppressed transmission of vibrations, as well as the influence of frame clamping conditions on the membrane modes. We find suppressions up to $40~\mathrm{dB}$ and, for three different realized phononic structures, consistently observe significant suppression of the dependence of the membrane's modes on sample clamping - if the mode's frequency lies in the bandgap. As a result, we achieve membrane mode quality factors of $5\times 10^{6}$ with samples that are tightly bolted to the $8~\mathrm{K}$-cold finger of a cryostat. $Q\times f$-products of $6\times 10^{12}~\mathrm{Hz}$ at $300~\mathrm{K}$ and $14\times 10^{12}~\mathrm{Hz}$ at $8~\mathrm{K}$ are observed, satisfying one of the main requirements for optical cooling of mechanical vibrations to their quantum ground-state.

cond-mat.mes-hall↗

arXiv2013

Graphene on silicon nitride for optoelectromechanical micromembrane resonators

Due to their exceptional mechanical and optical properties, dielectric silicon nitride (SiN) micromembrane resonators have become the centerpiece of many optomechanical experiments. Efficient capacitive coupling of the membrane to an electrical system would facilitate exciting hybrid optoelectromechanical devices. However, capacitive coupling of such dielectric membranes is rather weak. Here we add a single layer of graphene on SiN micromembranes and compare electromechanical coupling and mechanical properties to bare dielectric membranes and to membranes metallized with an aluminium layer. The electrostatic coupling of graphene coated membranes is found to be equal to a perfectly conductive membrane. Our results show that a single layer of graphene substantially enhances the electromechanical capacitive coupling without significantly adding mass, decreasing the superior mechanical quality factor or affecting the optical properties of SiN micromembrane resonators.

cond-mat.mes-hall↗