High-stress silicon nitride nanostrings are a promising system for sensing applications because of their ultrahigh mechanical quality factors (Qs). By performing thermomechanical calibration across multiple vibrational modes, we are able to assess the roles of the various dissipation mechanisms in these devices. Specifically, we possess a set of nanostrings in which all measured modes fall upon a single curve of peak displacement versus frequency. This allows us to rule out bulk bending and intrinsic loss mechanisms as dominant sources of dissipation and to conclude that the most significant contribution to dissipation in high-stress nanostrings occurs at the anchor points.The extremely high values of mechanical Q that have been reported in silicon nitride nanostrings 1-3 have generated a great deal of excitement in the nanomechanics community. 4 These devices are ideal for use in mass sensing, 5 temperature sensing, 6 and optomechanics 7-9 and have proved to be an invaluable platform for research into the quantum properties of nanoscale resonators. 10,11 Nanostrings possess all the desired properties for these endeavors, including small mass, high frequency, and high Q, with correspondingly large displacement amplitudes. This combination makes them sensitive to external perturbation yet still within the limits of current detection techniques. 12 In this manuscript, we demonstrate thermomechanically limited detection of up to six mechanical nanostring modes. Furthermore, we present a set of devices in which all harmonics fall upon a single curve of calibrated peak displacement versus frequency. As we discuss below, we are able to infer that the mechanical Q is limited by dissipation processes operating in the vicinity of the anchor points-thus suggesting ways to further engineer the mechanical Q.Silicon nitride nanostrings are devices under extremely high tensile stress (σ = 0.8 GPa for our devices). The accepted understanding is that the tension along their length results in large stored elastic energy and a correspondingly large mechanical Q. 3 Experiments have confirmed that Q increases with mechanical tensioning of non-prestressed (low tension, non-stoichiometric silicon nitride) devices, 13,14 corroborating the tension's central role.In addition to causing the high Q, the tension compels the devices to behave like strings rather than doubly clamped beams, as one would usually expect for this geometry. The harmonics are at integer multiples of the fundamental frequency, 15 ν n = nν 1 , where ν 1 is the fundamental mode frequency and n indicates the mode number; the mode frequency depends only on the length of the string (not on the width or thickness). These features are in contrast to the more complicated harmonics of doubly clamped beams, 16 which are realized in low-stress silicon nitride devices of the same geometry. 17 Furthermore, it has now been shown that very high mechanical Qs exist for nanostrings under tension in a variety of other materials, including the polymer SU-8, 18 aluminum, 6,19 and AuPd...

Low-mass, high-Q, silicon nitride nanostrings are at the cutting edge of nanomechanical devices for sensing applications. Here we show that the addition of a chemically functionalizable gold overlayer does not adversely affect the Q of the fundamental out-of-plane mode. Instead the device retains its mechanical responsiveness while gaining sensitivity to molecular bonding. Furthermore, differences in thermal expansion within the bilayer give rise to internal stresses that can be electrically controlled. In particular, an alternating current (AC) excites resonant motion of the nanostring. This AC thermoelastic actuation is simple, robust, and provides an integrated approach to sensor actuation. V C 2012 American Institute of Physics. [http://dx.

The union of quantum fluids research with nanoscience is rich with opportunities for new physics. The relevant length scales in quantum fluids, 3He in particular, are comparable to those possible using microfluidic and nanofluidic devices. In this article, we will briefly review how the physics of quantum fluids depends strongly on confinement on the microscale and nanoscale. Then we present devices fabricated specifically for quantum fluids research, with cavity sizes ranging from 30 nm to 11 microns deep, and the characterization of these devices for low temperature quantum fluids experiments.Comment: 12 pages, 3 figures, Accepted to Journal of Low Temperature Physic

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We study high-Q nanostrings that are joined end-to-end to form coupled linear arrays. Whereas isolated individual resonators exhibit sinusoidal vibrational modes with an almost perfectly harmonic spectrum, the modes of the interacting strings are substantially hybridized. Even far-separated strings can show significantly correlated displacement. This remote coupling property is exploited to quantify the deposition of femtogram-scale masses with string-by-string positional discrimination based on measurements of one string only.