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Giant, Voltage Tuned, Q-factors of Single Wall Carbon Nanotubes and Graphene at Room Temperature
摘要： Mastering dissipation in graphene based nanostructures is still the major challenge in most fundamental and technological exploitations of these ultimate mechanical nanoresonators. Although high quality factors have been measured for carbon nanotubes (> 106) and graphene (> 105) at cryogenic temperatures, room temperature values are orders of magnitude lower ((cid:39) 102). We present here a controlled quality factor increase of up to ×103 for these basic carbon nanostructures when externally stressed like a guitar string. Quantitative agreement is found with theory attributing this decrease in dissipation to the decrease in viscoelastic losses inside the material, an effect enhanced by tunable "soft clamping". Quality factors exceeding 25,000 for SWCNTs and 5000 for graphene were obtained on several samples, reaching the limits of the graphene material itself. The combination of ultra-low size and mass with high quality factors opens new perspectives for atomically localized force sensing and quantum computing as the coherence time exceeds state of the art cryogenic devices.
关键词： Q factor,graphene,carbon nanotube,NEMS,nanomechanics
更新于2025-09-19 17:15:36
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Quantum Dot Optomechanics in Suspended Nanophononic Strings
摘要： The optomechanical coupling of quantum dots and flexural mechanical modes is studied in suspended nanophononic strings. The investigated devices are designed and monolithically fabricated on an (Al)GaAs heterostructure. Radio frequency elastic waves with frequencies ranging between f = 250 and 400 MHz are generated as Rayleigh surface acoustic waves on the unpatterned substrate and injected as Lamb waves in the nanophononic string. Quantum dots inside the nanophononic string exhibit a 15-fold enhanced optomechanical modulation compared to those dynamically strained by the Rayleigh surface acoustic wave. Detailed finite element simulations of the phononic mode spectrum of the nanophononic string confirm that the observed modulation arises from valence band deformation potential coupling via shear strain. The corresponding optomechanical coupling parameter is quantified to 0.15 meV nm?1. This value exceeds that reported for vibrating nanorods by approximately one order of magnitude at 100 times higher frequencies. Using this value, a derived vertical displacement in the range of 10 nm is deduced from the experimentally observed modulation. The results represent an important step toward the creation of large scale optomechanical circuits interfacing single optically active quantum dots with optical and mechanical waves.
关键词： nanomechanics,optomechanics,quantum dots,Lamb waves,hybrid quantum systems
更新于2025-09-11 14:15:04
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[IEEE 2018 Conference on Precision Electromagnetic Measurements (CPEM 2018) - Paris, France (2018.7.8-2018.7.13)] 2018 Conference on Precision Electromagnetic Measurements (CPEM 2018) - Coherent Dynamics of Nanowire Force Sensors
摘要： We describe the use of grown nanowires as scanning directional force sensors. Two orthogonal flexural modes are used to demonstrate vectorial sensing of electric and magnetic fields. Furthermore, we show that the modes can be strongly coupled by demonstrating Rabi oscillations. These results open the way to implement coherent control and frequency stabilization in nanomechanical force and mass sensors.
关键词： Scanning probe microscopy,nanomechanics,quantum sensing,nanowires,frequency fluctuations
更新于2025-09-10 09:29:36
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[IEEE 2018 International Conference on Optical MEMS and Nanophotonics (OMN) - Lausanne (2018.7.29-2018.8.2)] 2018 International Conference on Optical MEMS and Nanophotonics (OMN) - Elastic Strain Engineering for Ultralow Mechanical Dissipation
摘要： 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 free-standing Si3N4 nanobeam. Ringdown measurements at room temperature reveal string-like modes with quality (Q) factors as high as 800 million and Q × frequency exceeding 1015 Hz.
关键词： optomechanics,strain engineering,nanomechanics
更新于2025-09-09 09:28:46
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Combined Raman- and AFM-based detection of biochemical and nanomechanical features of endothelial dysfunction in aorta isolated from ApoE/LDLR?/? mice
摘要： Endothelial dysfunction is recognized as a critical condition in the development of cardiovascular disorders. This multifactorial process involves changes in the biochemical and mechanical properties of endothelial cells leading to disturbed release of vasoprotective mediators. Hypercholesterolemia and increased stiffness of the endothelial cortex are independently shown to result in reduced release of nitric oxide and thus endothelial dysfunction. However, direct evidence linking these parameters to each other is missing. Here, a novel method combining Raman spectroscopy for biochemical analysis and Atomic Force Microscopy (AFM) for analysing the endothelial nanomechanics was established. Using this dual approach, the same areas of native ex vivo aortas were investigated, either derived from mice with endothelial dysfunction (ApoE/LDLR-/-) or wild type mice. In particular an increased intracellular lipid content and elevated cortical stiffness/elasticity was shown in ApoE/LDLR-/- aortas, demonstrating a direct link between endothelial dysfunction, the biochemical composition and the nanomechanical properties of endothelial cells.
关键词： Atomic Force Microscopy,Endothelial dysfunction,hypercholesterolemia,endothelial nanomechanics,Raman spectroscopy
更新于2025-09-04 15:30:14