Optically driven ultra-stable nanomechanical rotor

Nanomechanical devices have attracted the interest of a growing interdisciplinary research community, since they can be used as highly sensitive transducers for various physical quantities. Exquisite control over these systems facilitates experiments on the foundations of physics. Here, we demonstrate that an optically trapped silicon nanorod, set into rotation at MHz frequencies, can be locked to an external clock, transducing the properties of the time standard to the rod's motion with the remarkable frequency stability $f_{\rm r}/\Delta f_{\rm r}$ of $7.7 \times 10^{11}$. While the dynamics of this periodically driven rotor generally can be chaotic, we derive and verify that stable limit cycles exist over a surprisingly wide parameter range. This robustness should enable, in principle, measurements of external torques with sensitivities better than 0.25zNm, even at room temperature. We show that in a dilute gas, real-time phase measurements on the locked nanorod transduce pressure values with a sensitivity of 0.3%.Comment: 5 pages, 4 figure

Cavity-assisted manipulation of freely rotating silicon nanorods in high vacuum

Optical control of nanoscale objects has recently developed into a thriving field of research with far-reaching promises for precision measurements, fundamental quantum physics and studies on single-particle thermodynamics. Here, we demonstrate the optical manipulation of silicon nanorods in high vacuum. Initially, we sculpture these particles into a silicon substrate with a tailored geometry to facilitate their launch into high vacuum by laser-induced mechanical cleavage. We manipulate and trace their center-of-mass and rotational motion through the interaction with an intense intra-cavity field. Our experiments show optical forces on nanorotors three times stronger than on silicon nanospheres of the same mass. The optical torque experienced by the spinning rods will enable cooling of the rotational motion and torsional opto-mechanics in a dissipation-free environment.Comment: 8 page

Full rotational control of levitated silicon nanorods

We study a nanofabricated silicon rod levitated in an optical trap. By manipulating the polarization of the light we gain full control over the ro-translational dynamics of the rod. We are able to trap both its centre-of-mass and align it along the linear polarization of the laser field. The rod can be set into rotation at a tuned frequency by exploiting the radiation pressure exerted by elliptically polarized light. The rotational motion of the rod dynamically modifies the optical potential, which allows tuning of the rotational frequency over hundreds of Kilohertz. This ability to trap and control the motion and alignment of nanoparticles opens up the field of rotational optomechanics, rotational ground state cooling and the study of rotational thermodynamics in the underdamped regime.Comment: 5 pages, 4 figures, 4 Supplementary pages, 4 Supplementary figure

Universal Approach to Direct Spatiotemporal Dynamic in-situ Optical Visualization of On-Catalyst Water Splitting Electrochemical Processes

Electrochemical reactions are the unrivaled backbone of next generation energy storage, energy conversion and healthcare devices. However, the in-situ real-time visualization of electrochemical reactions, which can shed light on various critical unknown insights on the electrochemical processes, still remains the bottleneck for fully exploiting their intrinsic potential. In this work, for the first time, a universal approach to the direct spatiotemporal-dynamic in-situ optical visualization of pH based as well as specific byproduct based electrochemical reactions is performed. As a highly relevant and impactful example, the in-operando optical visualization of on-catalyst water splitting processes is performed under neutral water/seawater conditions. pH based visualization are performed using a water-soluble fluorescent pH probe HPTS (8-hydroxypyrene-1,3,6-trisulfonicacid), known for its exceptional optical capability of detecting even the tiniest environment pH changes, thus allowing the unprecedented “spatiotemporal” real-time visualization at the cathode and anode. The successful experimental investigations embarked here, allowed us to reach several yet unveiled deeper insights into the spatiotemporal water splitting processes and their practical modulation for potentially improving the applicability and efficiency of water splitting devices. As a result, we were able to unprecedentedly reveal that at a critical cathode-to-anode distance, a continuous bulk-electrolyte “self-neutralization” phenomenon can be achieved during the water splitting process, leading to the practical realization of enhanced additive-free neutral water splitting. Furthermore, we experimentally unveiled that at increasing electrolyte flow rates, a swift and severe inhibition of the concomitantly forming acidic and basic ‘fronts’, developed at anode and cathode compartments is observed, thus acting as a continuous on-catalysts “buffering” mechanism that allows for a remarkably enhanced water splitting process. Furthermore, to demonstrate the universal applicability of this elegant strategy which is not limited to pH changes, the technique was extended to visualization of specific electrochemical process by the use of reaction product-specific fluorophore. For the purpose, N-(4-butanoic acid) dansylsulfonamide (BADS) fluorophore was successfully explored to in-situ visualize the formation of hypochlorite/ chlorine at the anode during electrolysis of sea water. Thus, a unique experimental tool that allow real-time spatiotemporal visualization and simultaneous mechanistic investigation of complex electrochemical processes in developed that can be universally extended to various fields of research