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Register a new userSelective high frequency mechanical actuation driven by the VO2 electronic instability
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Micro- and nano-electromechanical resonators are a fundamental building block of modern technology, used in environmental monitoring, robotics, medical tools as well as fundamental science. These devices rely on dedicated electronics to generate their driving signal, resulting in an increased complexity and size. Here, we present a new paradigm to achieve high-frequency mechanical actuation based on the metal-insulator transition of VO$mathrm{_2}$, where the steep variation of its electronic properties enables to realize high-frequency electrical oscillations. The dual nature of this phase change, which is both electronic and structural, turns the electrical oscillations into an intrinsic actuation mechanism, powered by a small DC voltage and capable to selectively excite the different mechanical modes of a microstructure. Our results pave the way towards the realization of micro- and nano-electro-mechanical systems with autonomous actuation from integrated DC power sources such as solar cells or micro-batteries.
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Realizing optical manipulation of microscopic objects is crucial in the research fields of life science, condensed matter physics and physical chemistry. In non-liquid environments, this task is commonly regarded as difficult due to strong adhesive surface force ($simmurm N$) between solid interfaces that makes tiny optical driven force ($simrm pN$) insignificant. Here, by recognizing the microscopic interaction mechanism between friction force -- the parallel component of surface force on the contact surface -- and thermoelastic waves induced by pulsed optical absorption, we establish a general principle enabling the actuation of micro-objects on dry frictional surfaces based on the opto-thermo-mechanical effects. Theoretically, we predict that nanosecond pulsed optical absorption with mW-scale peak power is sufficient to tame $murm N$-scale friction force. Experimentally, we demonstrate that two-dimensional spiral motion of gold plates on micro-fibers driven by a nanosecond pulsed laser, and reveal the specific rules of motion control. Our results pave the way for future development of micro-scale actuators in nonliquid environments.
We propose a frequency selective light trapping scheme that enables the creation of more visually-transparent and yet simultaneously more efficient semitransparent solar cells. A nanoparticle scattering layer and photonic stack back reflector create a selective trapping effect by total internal reflection within a medium, increasing absorption of IR light. We propose a strong frequency selective scattering layer using spherical TiO2 nanoparticles with radius of 255 nm and area density of 1.1% in a medium with index of refraction of 1.5. Using detailed numerical simulations for this configuration, we find that it is possible to create a semitransparent silicon solar cell that has a Shockley Queisser efficiency of 12.0%pm0.4% with a visible transparency of 60.2%pm1.3%, 13.3%pm1.3 more visibly-transparent than a bare silicon cell at the same efficiency.
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.
Low frequency communication systems offer significant potential in portable electronics and internet of things (IoT) applications due to the low propagation loss and long transmission range. However, because the dimension of electrical antenna is comparable to one quarter wavelength of the electromagnetic wave that it transmits and receives, currently a gap exists between LF communication systems and IoT, as IoT generally implement miniaturized electrical antennas with a small wavelength at a high frequency while traditional LF electrical antennas are too bulky. In this paper, we present an LF magnetoelectric mechanical transmitting and receiving antenna pair to significantly miniaturize the dimension of LF antennas. As the operation principle of the magnetoelectric mechanical antenna pair is based on mechanical resonance, its dimension is reduced by four orders of magnitude compared with an electrical antenna counterpart. The transmitting and receiving antennas are the same in structure and dimensions: they are both composed of magnetostrictive Terfenol-D and piezoelectric PZT laminate, and their dimensions are both 38x12x8.2mm3. Both the transmitting and receiving antennas are integrated with DC magnetic bias to improve its performance. Antenna pair performance measurement demonstrates that a maximum operation distance of 9m is demonstrated with DC magnetic bias, while maximum operation distance without DC magnetic bias is 4m, which is reduced by 56%. The LF magnetoelectric mechanical antenna pair may be a promising candidate for the portable electronics and IoT applications.
With important application prospects, eutectic high entropy alloys have received extensive attention for their excellent strength and ductility in a large temperature range. The excellent casting characteristics of eutectic high entropy alloys make it possible to achieve well manufacturability of selective laser melting. For the first time, we have achieved crack-free eutectic high entropy alloy fabricated by selective laser melting, which has excellent mechanical properties in a wide temperature range of -196 degrees Celsius~760 degrees Celsius due to ultra-fine eutectic lamellar spacing of 150 ~ 200nm and lamellar colony of 2 ~ 6 {mu}m. Specifically, the room temperature tensile strength exceeds 1400MPa and the elongation is more than 20%, significantly improved compared with those manufactured by other techniques with lower cooling rate.
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