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Under the terms of the Creative Commons Attribution (CC BY) license to their work.-- et al., We report on the optomechanical properties of a breathing mechanical mode oscillating at 5.5 GHz in a 1D corrugated Si nanobeam. This mode has an experimental single-particle optomechanical coupling rate of |g o, OM | = 1.8 MHz (|g o, OM |/2π = 0.3 MHz) and shows strong dynamical back-action effects at room temperature. The geometrical flexibility of the unit-cell would lend itself to further engineering of the cavity region to localize the mode within the full phononic band-gap present at 4 GHz while keeping high g o, OM values. This would lead to longer lifetimes at cryogenic temperatures, due to the suppression of acoustic leakage., This work was supported by the EU through the FP7 project TAILPHOX (ICT-FP7-233883) and the ERC Advanced Grant SOULMAN (ERC-FP7-321122) and the Spanish projects TAPHOR (MAT2012-31392). D.N-U and J.G-B acknowledge support in the form of postdoctoral fellowships from the Catalan (Beatriu de Pinòs) and the Spanish (Juan de la Cierva) governments, respectively.

Optical forces can set tiny objects in states of mechanical self-sustained oscillation, spontaneously generating periodic signals by extracting power from steady sources. Miniaturized self-sustained coherent phonon sources are interesting for applications such as mass-force sensing, intra-chip metrology and intra-chip time-keeping among others. In this paper, we review several mechanisms and techniques that can drive a mechanical mode into the lasing regime by exploiting the radiation pressure force in optomechanical cavities, namely stimulated emission, dynamical back-action, forward stimulated Brillouin scattering and self-pulsing., This work was supported by the European Comission project TAILPHOX (ICT-FP7-233883), the Spanish Severo Ochoa Excellence program and the MINECO project PHENTOM (FIS2015-70862-P). DNU and MFC gratefully acknowledge the support of a Ramón y Cajal postdoctoral fellowship and a Severo Ochoa studentship, respectivelyn.

We present and validate a reformulated Akhieser model that takes into account the reduction of thermal conductivity due to the impact of boundary scattering on the thermal phonons' lifetime. We consider silicon nanomembranes with mechanical mode frequencies in the GHz range as textbook examples of nanoresonators. The model successfully accounts for the measured shortening of the mechanical mode lifetime. Moreover, the thermal conductivity is extracted from the measured lifetime of the mechanical modes in the high-frequency regime, thereby demonstrating that the Q-factor can be used as an indication of the thermal conductivity and/or diffusivity of a mechanical resonator., The authors acknowledge the financial support from the FP7 project MERGING (grant no. 309150), as well as from the Spanish MINECO projects nanoTHERM (grant no. CSD2010-0044) and TAPHOR (MAT2012-31392). E.C.A. gratefully acknowledges the Becas Chile 2010 CONICYT fellowship from the Chilean government.

Under the terms of the Creative Commons Attribution (CC BY) license to their work., We report on the modification of the optical and mechanical properties of a silicon 1D optomechanical crystal cavity due to thermo-optic effects in a high phonon/photon population regime. The cavity heats up due to light absorption in a way that shifts the optical modes towards longer wavelengths and the mechanical modes to lower frequencies. By combining the experimental optical results with finite-difference time-domain simulations, we establish a direct relation between the observed wavelength drift and the actual effective temperature increase of the cavity. By assuming that the Young's modulus decreases accordingly to the temperature increase, we find a good agreement between the mechanical mode drift predicted using a finite element method and the experimental one., This work was supported by the EU through the project TAILPHOX (ICT-FP7-233883) and the ERC Advanced Grant SOULMAN (ERC-FP7-321122) and the Spanish projects TAPHOR (MAT2012-31392).