7 research outputs found
Clamp-tapering increases the quality factor of stressed nanobeams
Stressed nanomechanical resonators are known to have exceptionally high
quality factors () due to the dilution of intrinsic dissipation by stress.
Typically, the amount of dissipation dilution and thus the resonator is
limited by the high mode curvature region near the clamps. Here we study the
effect of clamp geometry on the of nanobeams made of high-stress
. We find that tapering the beam near the clamp - and locally
increasing the stress - leads to increased of MHz-frequency low order modes
due to enhanced dissipation dilution. Contrary to recent studies of
tethered-membrane resonators, we find that widening the clamps leads to
decreased despite increased stress in the beam bulk. The tapered-clamping
approach has practical advantages compared to the recently developed
"soft-clamping" technique. Tapered-clamping enhances the of the fundamental
mode and can be implemented without increasing the device size
Hierarchical tensile structures with ultralow mechanical dissipation
Structural hierarchy is found in myriad biological systems and has improved
man-made structures ranging from the Eiffel tower to optical cavities.
Hierarchical metamaterials utilize structure at multiple size scales to realize
new and highly desirable properties which can be strikingly different from
those of the constituent materials. In mechanical resonators whose rigidity is
provided by static tension, structural hierarchy can reduce the dissipation of
the fundamental mode to ultralow levels due to an unconventional form of soft
clamping. Here, we apply hierarchical design to silicon nitride nanomechanical
resonators and realize binary tree-shaped resonators with quality factors as
high as at 107 kHz frequency, reaching the parameter regime of levitated
particles. The resonators' thermal-noise-limited force sensitivities reach
at room temperature and $\mathrm{90\
zN/\sqrt{Hz}}$ at 6 K, surpassing state-of-the-art cantilevers currently used
for force microscopy. We also find that the self-similar structure of binary
tree resonators results in fractional spectral dimensions, which is
characteristic of fractal geometries. Moreover, we show that the hierarchical
design principles can be extended to 2D trampoline membranes, and we fabricate
ultralow dissipation membranes suitable for interferometric position
measurements in Fabry-P\'erot cavities. Hierarchical nanomechanical resonators
open new avenues in force sensing, signal transduction and quantum
optomechanics, where low dissipation is paramount and operation with the
fundamental mode is often advantageous.Comment: 19 pages, 11 figures. Fixed link to Zenodo repositor
Generalized dissipation dilution in strained mechanical resonators
Mechanical resonators with high quality factors are of relevance in precision
experiments, ranging from gravitational wave detection and force sensing to
quantum optomechanics. Beams and membranes are well known to exhibit flexural
modes with enhanced quality factors when subjected to tensile stress. The
mechanism for this enhancement has been a subject of debate, but is typically
attributed to elastic energy being "diluted" by a lossless potential. Here we
clarify the origin of the lossless potential to be the combination of tension
and geometric nonlinearity of strain. We present a general theory of
dissipation dilution that is applicable to arbitrary resonator geometries and
discuss why this effect is particularly strong for flexural modes of
nanomechanical structures with high aspect ratios. Applying the theory to a
non-uniform doubly clamped beam, we show analytically how dissipation dilution
can be enhanced by modifying the beam shape to implement "soft clamping", thin
clamping and geometric strain engineering, and derive the ultimate limit for
dissipation dilution
Elastic strain engineering for ultralow mechanical dissipation
Extreme stresses can be produced in nanoscale structures, a feature which has been used to realize enhanced materials properties, such as the high mobility of silicon in modern transistors. Here we show how nanoscale stress can be used to realize exceptionally low mechanical dissipation, when combined with "soft-clamping" - a form of phononic engineering. Specifically, using a non-uniform phononic crystal pattern, we colocalize the strain and flexural motion of a freestanding Si3N4 nanobeam. Ringdown measurements at room temperature reveal string-like modes with quality (Q) factors as high as 800 million and Q x frequency exceeding 10(15) Hz
Ultralow Dissipation Mechanical Resonators for Quantum Optomechanics
We demonstrate dissipation dilution engineering techniques for ultralow dissipation mechanical resonators. The Si3N4 nanobeams show quality factors (Q) as high as 800 million and Q x f exceeding 10(15) Hz-both records at room temperature. (C) 2019 The Author(s