High frequency mechanical excitation of a silicon nanostring with piezoelectric aluminum nitride layers

A strong trend for quantum based technologies and applications follows the avenue of combining different platforms to exploit their complementary technological and functional advantages. Micro and nano-mechanical devices are particularly suitable for hybrid integration due to the easiness of fabrication at multi-scales and their pervasive coupling with electrons and photons. Here, we report on a nanomechanical technological platform where a silicon chip is combined with an aluminum nitride layer. Exploiting the AlN piezoelectricity, Surface Acoustic Waves are injected in the Si layer where the material has been localy patterned and etched to form a suspended nanostring. Characterizing the nanostring vertical displacement induced by the SAW, we found an external excitation peak efficiency in excess of 500 pm/V at 1 GHz mechanical frequency. Exploiting the long term expertise in silicon photonic and electronic devices as well as the SAW robustness and versatility, our technological platform represents a strong candidate for hybrid quantum systems

Broadband Dynamic Polarization Conversion in Optomechanical Metasurfaces

Artificial photonic materials, nanofabricated through wavelength-scale engineering, have shown astounding and promising results in harnessing, tuning, and shaping photonic beams. Metamaterials have proven to be often outperforming the natural materials they take inspiration from. In particular, metallic chiral metasurfaces have demonstrated large circular and linear dichroism of light which can be used, for example, for probing different enantiomers of biological molecules. Moreover, the precise control, through designs on demand, of the output polarization state of light impinging on a metasurface, makes this kind of structures particularly relevant for polarization-based telecommunication protocols. The reduced scale of the metasurfaces makes them also appealing for integration with nanomechanical elements, adding new dynamical features to their otherwise static or quasi-static polarization properties. To this end we designed, fabricated and characterized an all-dielectric metasurface on a suspended nanomembrane. Actuating the membrane mechanical motion, we show how the metasurface reflectance response can be modified, according to the spectral region of operation, with a corresponding intensity modulation or polarization conversion. The broad mechanical resonance at atmospheric pressure, centered at about 400 kHz, makes the metasurfaces structure suitable for high-frequency operation, mainly limited by the piezo-actuator controlling the mechanical displacement, which in our experiment reached modulation frequencies exceeding 1.3 MHz

Ferromagnetic resonance assisted optomechanical magnetometer

The resonant enhancement of mechanical and optical interaction in optomechanical cavities enables their use as extremely sensitive displacement and force detectors. In this work we demonstrate a hybrid magnetometer that exploits the coupling between the resonant excitation of spin waves in a ferromagnetic insulator and the resonant excitation of the breathing mechanical modes of a glass microsphere deposited on top. The interaction is mediated by magnetostriction in the ferromagnetic material and the consequent mechanical driving of the microsphere. The magnetometer response thus relies on the spectral overlap between the ferromagnetic resonance and the mechanical modes of the sphere, leading to a peak sensitivity better than 900 pT Hz$^{-1/2}$ at 206 MHz when the overlap is maximized. By externally tuning the ferromagnetic resonance frequency with a static magnetic field we demonstrate sensitivity values at resonance around a few nT Hz$^{-1/2}$ up to the GHz range. Our results show that our hybrid system can be used to build high-speed sensor of oscillating magnetic fields

Contactless characterization of the elastic properties of glass microspheres

Glass microspheres are of great interest for numerous industrial, biomedical, or standalone applications, but it remains challenging to evaluate their elastic and optical properties in a non-destructive way. In this work, we address this issue by using two complementary contactless techniques to obtain elastic and optical constants of glass microspheres with diameters ranging from 10 to 60 µm. The first technique we employ is Brillouin Light Scattering, which yields scattering with longitudinal acoustic phonons, the frequency of which is found to be 5% lower than that measured in the bulk material. The second technique involves exciting the optical whispering gallery modes of the microspheres, which allows us to transduce some of their vibrational modes. The combined data allow for extracting the refractive index and the elastic constants of the material. Our findings indicate that the values of those properties are reduced with respect to their bulk material counterpart due to an effective decrease of the density, resulting from the fabrication process. We propose the use of this combined method to extract elastic and optical parameters of glass materials in microsphere geometries and compare them with the values of the pristine material from which they are formed

Injection locking in an optomechanical coherent phonon source

[EN] Spontaneous locking of the phase of a coherent phonon source to an external reference is demonstrated in a deeply sideband-unresolved optomechanical system. The high-amplitude mechanical oscillations are driven by the anharmonic modulation of the radiation pressure force that result from an absorption-mediated free-carrier/temperature limit cycle, i.e., self-pulsing. Synchronization is observed when the pump laser driving the mechanical oscillator to a self-sustained state is modulated by a radiofrequency tone. We employ a pump-probe phonon detection scheme based on an independent optical cavity to observe only the mechanical oscillator dynamics. The lock range of the oscillation frequency, i.e., the Arnold tongue, is experimentally determined over a range of external reference strengths, evidencing the possibility to tune the oscillator frequency for a range up to 350 kHz. The stability of the coherent phonon source is evaluated via its phase noise, with a maximum achieved suppression of 44 dBc/Hz at 1 kHz offset for a 100 MHz mechanical resonator. Introducing a weak modulation in the excitation laser reveals as a further knob to trigger, control and stabilize the dynamical solutions of self-pulsing based optomechanical oscillators, thus enhancing their potential as acoustic wave sources in a single-layer silicon platform.This research was funded by EU FET Open project PHENOMEN (GA: 713450). ICN2 is supported by the Severo Ochoa program from the Spanish Research Agency (AEI, grant no. SEV-2017-0706) and by the CERCA Programme/Generalitat de Catalunya. G. A. and C. M. S.-T. acknowledge the support from the Spanish MICINN project SIP (PGC2018-101743-B-I00). D. N. U., G. A. and M. F. C. gratefully acknowledge the support of a Ramon y Cajal postdoctoral fellowship (RYC-2014-15392), a BIST studentship, and a Severo Ochoa studentship, respectively. D. N. U. acknowledges the funding through the Ministry of Science, Innovation and Universities (PGC2018-094490-B-C22).Arregui, G.; Colombano, MF.; Maire, J.; Pitanti, A.; Capuj, NE.; Griol Barres, A.; Martínez, A.... (2021). Injection locking in an optomechanical coherent phonon source. Nanophotonics. 10(4):1319-1327. https://doi.org/10.1515/nanoph-2020-05921319132710

Properties of Nanocrystalline Silicon Probed by Optomechanics

Nanocrystalline materials exhibit properties that can differ substantially from those of their single crystal counterparts. As such, they provide ways to enhance and optimize their functionality for devices and applications. Here, we report on the optical, mechanical and thermal properties of nanocrystalline silicon probed by means of optomechanical nanobeams to extract information of the dynamics of optical absorption, mechanical losses, heat generation and dissipation. The optomechanical nanobeams are fabricated using nanocrystalline films prepared by annealing amorphous silicon layers at different temperatures. The resulting crystallite sizes and the stress in the films can be controlled by the annealing temperature and time and, consequently, the properties of the films can be tuned relatively freely, as demonstrated here by means of electron microscopy and Raman scattering. We show that the nanocrystallite size and the volume fraction of the grain boundaries play a key role in the dissipation rates through nonlinear optical and thermal processes. Promising optical (13,000) and mechanical (1700) quality factors were found in the optomechanical cavity realized in the nanocrystalline Si resulting from annealing at 950°C. The enhanced absorption and recombination rates via the intragap states and the reduced thermal conductivity boost the potential to exploit these nonlinear effects in applications including Nanoelectromechanical systems (NEMS), phonon lasing and chaos-based devices

The NAMPT inhibitor FK866 reverts the damage in spinal cord injury

<p>Abstract</p> <p>Background</p> <p>Emerging data implicate nicotinamide phosphoribosyl transferase (NAMPT) in the pathogenesis of cancer and inflammation. NAMPT inhibitors have proven beneficial in inflammatory animal models of arthritis and endotoxic shock as well as in autoimmune encephalitis. Given the role of inflammatory responses in spinal cord injury (SCI), the effect of NAMPT inhibitors was examined in this setting.</p> <p>Methods</p> <p>We investigated the effects of the NAMPT inhibitor FK866 in an experimental compression model of SCI.</p> <p>Results</p> <p>Twenty-four hr following induction of SCI, a significant functional deficit accompanied widespread edema, demyelination, neuron loss and a substantial increase in TNF-α, IL-1β, PAR, NAMPT, Bax, MPO activity, NF-κB activation, astrogliosis and microglial activation was observed. Meanwhile, the expression of neurotrophins BDNF, GDNF, NT3 and anti-apoptotic Bcl-2 decreased significantly. Treatment with FK866 (10 mg/kg), the best known and characterized NAMPT inhibitor, at 1 h and 6 h after SCI rescued motor function, preserved perilesional gray and white matter, restored anti-apoptotic and neurotrophic factors, prevented the activation of neutrophils, microglia and astrocytes and inhibited the elevation of NAMPT, PAR, TNF-α, IL-1β, Bax expression and NF-κB activity.</p> <p>We show for the first time that FK866, a specific inhibitor of NAMPT, administered after SCI, is capable of reducing the secondary inflammatory injury and partly reduce permanent damage. We also show that NAMPT protein levels are increased upon SCI in the perilesional area which can be corrected by administration of FK866.</p> <p>Conclusions</p> <p>Our findings suggest that the inflammatory component associated to SCI is the primary target of these inhibitors.</p

Optomechanical crystals for spatial sensing of submicron sized analytes

Optomechanical crystal cavities have rich perspectives for detecting and indirectly analysing biological particles, such as proteins, bacteria and viruses. In this work we demonstrate the working principle of an optomechanical crystal cavity operating under ambient conditions as a sensor of submicrometer analytes by optically monitoring the frequency shift of thermally activated mechanical modes. The resonator has been specifically designed so that the cavity region supports a particular family of low modal-volume mechanical modes, commonly known as -pinch modes-. These involve the oscillation of only a couple of adjacent cavity cells that are relatively insensitive to perturbations in other parts of the resonator. The eigenfrequency of these modes decreases as the deformation is localized closer to the centre of the resonator. Thus, by identifying specific modes that undergo a frequency shift that amply exceeds the mechanical linewidth, it is possible to infer if there are particles deposited on the resonator, how many are there and their approximate position within the cavity region.Comment: 15 pages, 3 figures, Supplementary Info (10 pages, 9 figures