We introduce the photoinduced electrochemiluminescence (P-ECL) of the model ECL system involving the simultaneous oxidation of [Ru­(bpy)3]2+ and tri-n-propylamine (TPrA). This system classically requires highly anodic potentials of greater than +1 V vs SCE for ECL generation. In the reported approach, the ECL emission is triggered by holes (h+) photogenerated in an n-type semiconductor (SC) electrode, which is normally highly challenging because of competing photocorrosion occurring on SC electrodes in aqueous electrolytes. We employ here Si-based tunnel electrodes protected by few-nanometer-thick SiO x and Ni stabilizing thin films and demonstrate that this construct allows generation of P-ECL in water. This system is based on an upconversion process where light absorption at 810 nm induces ECL emission (635 nm) at a record low electrochemical potential of 0.5 V vs SCE. Neither this excitation wavelength nor this low applied potential is able to stimulate ECL light if applied alone, but their synergetic action leads to stable and intense ECL emission in water. This P-ECL strategy can be extended to other luminophores and is promising for ultrasensitive detection and light-addressable and imaging devices.

The combination of electrochemiluminescence and semiconductor gives rise to a rich field at the interface of photoelectrochemistry, materials and analytical chemistry. It offers interesting possibilities for ultrasensitive (bio)detection, imaging and light conversion.

Photoinduced electrochemiluminescence (PECL) allows the electrochemically assisted conversion of low-energy photons into high-energy photons at an electrode surface. This concept is expected to have important implications, however, it is dramatically limited by the stability of the surface, impeding future developments. Here, a series of metal-insulator-semiconductor (MIS) junctions, using photoactive n-type Si (n-Si) as a light absorber covered by a few-nanometerthick protective SiO x /metal (SiO x /M, with M = Ru, Pt, and Ir) overlayers are investigated for upconversion PECL of the model co-reactant system involving the simultaneous oxidation of tris(bipyridine)ruthenium(II) and tri-n-propylamine. We show that n-Si/SiO x /Pt and n-Si/SiO x /Ir exhibit high photovoltages and record stabilities in operation (35 h for n-Si/SiO x /Ir) for the generation of intense PECL with an anti-Stokes shift of 218 nm. We also demonstrate that these surfaces can be employed for spatially localized PECL. These unprecedented performances are extremely promising for future applications of PECL.

The ability to program highly modulated morphology upon silicon nanowires (SiNWs) has been fundamental to explore new phononic and electronic functionalities. We here exploit a nanoscale locomotion of metal droplets to demonstrate a large and readily controllable morphology engineering of crystalline SiNWs, from straight ones into continuous or discrete island-chains, at temperature <350 °C. This has been accomplished via a tin (Sn) droplet mediated in-plane growth where amorphous Si thin film is consumed as precursor to produce crystalline SiNWs. Thanks to a significant interface-stretching effect, a periodic Plateau-Rayleigh instability oscillation can be stimulated in the liquid Sn droplet, and the temporal oscillation of the Sn droplets is translated faithfully, via the deformable liquid/solid deposition interface, into regular spatial modulation upon the SiNWs. Combined with a unique self-alignment and positioning capability, this new strategy could enable a rational design and single-run fabrication of a wide variety of nanowire-based optoelectronic devices.

Line-shape engineering is a key strategy to endow extra stretchability to 1D silicon nanowires (SiNWs) grown with self-assembly processes. We here demonstrate a deterministic line-shape programming of in-plane SiNWs into extremely stretchable springs or arbitrary 2D patterns with the aid of indium droplets that absorb amorphous Si precursor thin film to produce ultralong c-Si NWs along programmed step edges. A reliable and faithful single run growth of c-SiNWs over turning tracks with different local curvatures has been established, while high resolution transmission electron microscopy analysis reveals a high quality monolike crystallinity in the line-shaped engineered SiNW springs. Excitingly, in situ scanning electron microscopy stretching and current-voltage characterizations also demonstrate a superelastic and robust electric transport carried by the SiNW springs even under large stretching of more than 200%. We suggest that this highly reliable line-shape programming approach holds a strong promise to extend the mature c-Si technology into the development of a new generation of high performance biofriendly and stretchable electronics.

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Photogenerated nonequilibrium hot carriers play a key role in graphene's intriguing optoelectronic properties. Compared to conventional photoexcitation, plasmon excitation can be engineered to enhance and control the generation and dynamics of hot carriers. Here, we report an unusual negative differential photoresponse of plasmoninduced "ultrahot" electrons in a graphene−boron nitride− graphene tunneling junction. We demonstrate nanocrescent gold plasmonic nanostructures that substantially enhance the absorption of long-wavelength photons whose energy is greatly below the tunneling barrier and significantly boost the electron thermalization in graphene. We further analyze the generation and transfer of ultrahot electrons under different bias and power conditions. We find that the competition among thermionic emission, the carrier-cooling effect, and the field effect results in a hitherto unusual negative differential photoresponse in the photocurrent−bias plot. Our results not only exemplify a promising platform for detecting low-energy photons, enhancing the photoresponse, and reducing the dark current but also reveal the critically coupled pathways for harvesting ultrahot carriers.

Dual-comb sources with equally spaced and low phase noise frequency lines are of great importance for high resolution spectroscopy and metrology. In the terahertz frequency range, electrically pumped semiconductor quantum cascade lasers (QCLs) are suitable candidates for frequency comb and dual-comb operation. Although free running terahertz QCLs can be operated as frequency combs and dual-comb sources, the phase noise originated from the carrier frequency and repetition rate instabilities are relatively high, which hinders the high precision applications. The locking techniques that have been used for a single laser comb can be, in principle, applied to a dual-comb laser source. However, the complete locking of dual-comb lines considerably complicates the implementation of such a system. Here, a method is proposed to stabilize a terahertz QCL dual-comb source by phase locking one dual-comb line. Although only one dual-comb line is locked, it is shown that the phase noise of other dual-comb lines close to the phase locked line is significantly reduced. Finally, it is demonstrated that the terahertz QCL comb without a control of the repetition rate can produce pulsed-type waveforms. The demonstrated approach provides a convenient method to actively stabilize terahertz dual-comb laser sources, which can be further utilized for fast gas sensing and spectroscopy.