Inducing micromechanical motion by optical excitation of a single quantum dot

Engineering the Impact of Phonon Dephasing on the Coherence of a WSe_{2} Single-Photon Source via Cavity Quantum Electrodynamics

Emitter dephasing is one of the key issues in the performance of solid-state single-photon sources. Among the various sources of dephasing, acoustic phonons play a central role in adding decoherence to the single-photon emission. Here, we demonstrate that it is possible to tune and engineer the coherence of photons emitted from a single WSe_{2} monolayer quantum dot via selectively coupling it to a spectral cavity resonance. We utilize an open cavity to demonstrate spectral enhancement, leveling, and suppression of the highly asymmetric phonon sideband, finding excellent agreement with a microscopic description of the exciton-phonon dephasing in a truly two-dimensional system. Moreover, the impact of cavity tuning on the dephasing is directly assessed via optical interferometry, which points out the capability to utilize light-matter coupling to steer and design dephasing and coherence of quantum emitters in atomically thin crystals.

Transduction of Single Nanomechanical Pillar Resonators by Scattering of Surface Acoustic Waves

One of the challenges of nanoelectromechanical systems (NEMS) is the effective transduction of the tiny resonators. Vertical structures, such as nanomechanical pillar resonators, which are exploited in optomechanics, acoustic metamaterials, and nanomechanical sensing, are particularly challenging to transduce. Existing electromechanical transduction methods are ill-suited as they put constraints on the pillars' material and do not enable a transduction of freestanding pillars. Here, we present an electromechanical transduction method for single nanomechanical pillar resonators based on surface acoustic waves (SAWs). We demonstrate the transduction of freestanding nanomechanical platinum-carbon pillars in the first-order bending and compression mode. Since the principle of the transduction method is based on resonant scattering of a SAW by a nanomechanical resonator, our transduction method is independent of the pillar's material and not limited to pillar-shaped geometries. It represents a general method to transduce vertical mechanical resonators with nanoscale lateral dimensions.

On-Chip Electrostatic Actuation of a Photonic Wire Antenna Embedding Quantum Dots

A photonic wire antenna embedding individual quantum dots (QDs) constitutes a promising platform for both quantum photonics and hybrid nanomechanics. We demonstrate here an integrated device in which on-chip electrodes can apply a static or oscillating bending force to the upper part of the wire. In the static regime, we achieve control over the bending direction and apply at will tensile or compressive mechanical stress on any QD. This results in a blue shift or red shift of their emission, with direct application to the realization of broadly tunable sources of quantum light. As a first illustration of operation in the dynamic regime, we excite the wire fundamental flexural mode and use the QD emission to detect the mechanical vibration. With an estimated operation bandwidth in the GHz range, electrostatic actuation opens appealing perspectives for the exploration of QD-nanowire hybrid mechanics with high-frequency vibrational modes.

Nanomechanical Resonators: Toward Atomic Scale

The quest for realizing and manipulating ever smaller man-made movable structures and dynamical machines has spurred tremendous endeavors, led to important discoveries, and inspired researchers to venture to previously unexplored grounds. Scientific feats and technological milestones of miniaturization of mechanical structures have been widely accomplished by advances in machining and sculpturing ever shrinking features out of bulk materials such as silicon. With the flourishing multidisciplinary field of low-dimensional nanomaterials, including one-dimensional (1D) nanowires/nanotubes and two-dimensional (2D) atomic layers such as graphene/phosphorene, growing interests and sustained effort have been devoted to creating mechanical devices toward the ultimate limit of miniaturization─genuinely down to the molecular or even atomic scale. These ultrasmall movable structures, particularly nanomechanical resonators that exploit the vibratory motion in these 1D and 2D nano-to-atomic-scale structures, offer exceptional device-level attributes, such as ultralow mass, ultrawide frequency tuning range, broad dynamic range, and ultralow power consumption, thus holding strong promises for both fundamental studies and engineering applications. In this Review, we offer a comprehensive overview and summary of this vibrant field, present the state-of-the-art devices and evaluate their specifications and performance, outline important achievements, and postulate future directions for studying these miniscule yet intriguing molecular-scale machines.

General heterostructure strategy of photothermal materials for scalable solar-heating hydrogen production without the consumption of artificial energy

Solar-heating catalysis has the potential to realize zero artificial energy consumption, which is restricted by the low ambient solar heating temperatures of photothermal materials. Here, we propose the concept of using heterostructures of black photothermal materials (such as Bi₂Te₃) and infrared insulating materials (Cu) to elevate solar heating temperatures. Consequently, the heterostructure of Bi₂Te₃ and Cu (Bi₂Te₃/Cu) increases the 1 sun-heating temperature of Bi₂Te₃ from 93 °C to 317 °C by achieving the synergy of 89% solar absorption and 5% infrared radiation. This strategy is applicable for various black photothermal materials to raise the 1 sun-heating temperatures of Ti₂O₃, Cu₂Se, and Cu₂S to 295 °C, 271 °C, and 248 °C, respectively. The Bi₂Te₃/Cu-based device is able to heat CuO_x/ZnO/Al₂O₃ nanosheets to 305 °C under 1 sun irradiation, and this system shows a 1 sun-driven hydrogen production rate of 310 mmol g^-1 h^-1 from methanol and water, at least 6 times greater than that of all solar-driven systems to date, with 30.1% solar-to-hydrogen efficiency and 20-day operating stability. Furthermore, this system is enlarged to 6 m² to generate 23.27 m³/day of hydrogen under outdoor sunlight irradiation in the spring, revealing its potential for industrial manufacture.

Inferring the energy sensitivity and band gap of electronic transport in a network of carbon nanotubes

Since the industrialization of single-phase nanomaterial-based devices is still challenging, intensive research focus has been given to complex materials consisting of multiple nanoscale entities, including networks and matrices of nanowires, nanotubes, nanoribbons, or other large molecules; among these complex materials, networks of carbon nanotubes are a typical example. Detailed knowledge of the energy sensitivity and band gap of electronic transport in such a material system is difficult to detect, despite its importance in electronic, energetic and sensing applications. Here, we propose a new methodology to obtain these quantities using the measured Seebeck coefficient at a certain temperature but different Fermi levels. We discover that the network consisting of semiconducting (11,10)-carbon nanotubes actually exhibits metallic transport at room temperature. It is also interesting to verify that intrananotube ballistic transport is dominant over diffusive scattering by long-range disorder, as well as the quantum hopping resistance at the contact points. The transport asymmetry ratio between the holes and electrons (1.75) is similar to the value observed in pristine graphene samples (1.50).