Search

Silicon (Si) is generally considered as a poor photon emitter, and various scenarios have been proposed to improve the photon emission efficiency of Si. Here, we report the observation of a burst of the hot electron luminescence from Si nanoparticles with diameters of 150-250 nm, which is triggered by the exponential increase of the carrier density at high temperatures. We show that the stable white light emission above the threshold can be realized by resonantly exciting either the mirror-image-induced magnetic dipole resonance of a Si nanoparticle placed on a thin silver film or the surface lattice resonance of a regular array of Si nanopillars with femtosecond laser pulses of only a few picojoules, where significant enhancements in two- and three-photon-induced absorption can be achieved. Our findings indicate the possibility of realizing all-Si-based nanolasers with manipulated emission wavelength, which can be easily incorporated into future integrated optical circuits.

Many sensors exhibit nonlinear characteristics [1]–[5] and are deployed in noisy environments [1]–[7]. In terms of device design and forming standards, this is a challenging area. However, it also presents opportunities for non-conventional signal processing methods based on stochastic resonance that have been shown to be of benefit for individual nonlinear sensors [1]–[7], sensor arrays [3]–[10], sensor networks [3], [8], [11], and even portable devices for people with reduced sensory capacity [12]–[14]. The most fascinating property of stochastic resonance is that nonlinear sensors connected in parallel or in a network yield improved performance over that achieved by using individual sensors [1]–[10]. Studies in stochastic resonance have led to evidence of noise-enhanced signal transmission and processing in nonlinear sensors, and noise can be exploited in the design of engineered devices [2]–[7], [10] and biological systems [1], [11]–[13]. This paper studies noise-enhanced signal transmission and processing in nonlinear sensors and also exploits the positive role of noise in the design of engineered devices that enhance the sensitivity of hand movements.

Random lasing (RL) from self-constructed localized cavities based on micropits scatters in a single GaN microwire (MW) was investigated. The spectra and spatial resolution of RL exhibits that the lasing modes originated from different regions in the MW. Temperature-dependent lasing measurement of GaN RL shows an excellent characteristic temperature of about 52 K. In addition, the dependence of spatial localized cavities’ dimension on the pumping intensity profile and temperature was studied by fast Fourier transform spectroscopy. For GaN RL, the optical feedback was supported by localized paths through the scattering effect of micropits in the MW. The scattering feedback mechanism for RL can avoid the enormous difficulty in fabricating artificial cavity structures for GaN. Hence, the results in this paper represent a low-cost technique to realize GaN-based ultraviolet laser diodes without the fabrication difficulty of cavity facets.

In this paper, the generalized energy (GE) detector is investigated for detecting weak random signals via vibrational resonance (VR). By artificially injecting the high-frequency sinusoidal interferences into an array of GE statistics formed for the detector, we show that the normalized asymptotic efficacy can be maximized when the interference intensity takes an appropriate non-zero value. It is demonstrated that the normalized asymptotic efficacy of the dead-zone-limiter detector, aided by the VR mechanism, outperforms that of the GE detector without the help of high-frequency interferences. Moreover, the maximum normalized asymptotic efficacy of dead-zone-limiter detectors can approach a quarter of the second-order Fisher information for a wide range of non-Gaussian noise types.

Nonlinear multiphoton absorption technology is crucial for developing novel optoelectronic devices and nanophotonics. The large enhancement of two-photon absorption (TPA) photoresponse by a high Q-factor whispering gallery mode (WGM) resonance based on a single-microwire (MW) self-formed hexagonal cavity was investigated comprehensively in this paper. The typical quadratic relationship of photocurrent as a function of incident power indicated that excited carriers resulted from a third-order nonlinear mechanism. Moreover, the photocurrent response had a dramatic dependence on the spatial location of the focus spot of the incident photons. It was demonstrated that the TPA photocurrent response in the resonant WGM mode was one-order of magnitude larger than the response in the Fabry-Perot mode. Furthermore, the photoresponse characteristics of TPA detection exhibited sensitive dependence on the incident laser polarization direction.

Semiconductor micro/nanowire is an attractive candidate for light-emitting devices (LED), especially laser diodes, due to its ideal geometric shape, excellent optical performance, and electrical transport properties. However, the realization of single micro/nanostructure semiconductor LED or lasers is still a challenge topic. In this Letter, we demonstrated a feasible route to fabricate electrically injection single microwire (MW) light-emitting devices. First, the excellent optical properties of single MW were investigated comprehensively, especially for the self-formed high-Q whisper gallery mode lasing. By properly engineering the band alignment of n-ZnO MW/p-GaN heterojunction using a dielectric MgO interlayer, the effective carrier injection and excitonic-type recombination electroluminescence was realized in the single MW active media. Our results present a significant step toward future fabrication of single micro/nanowire LED and laser diode.

Etoposide is one of the most used first-line chemotherapeutic drugs. However, its application is still limited by its side effects. Herein, we designed a novel H2O2 sensitive prodrug 6YT for selectively releasing the anti-cancer drug etoposide in cancer cells. In this paper, etoposide and a hydrogen peroxide (H2O2) sensitive aryl borate ester group were linked by a fluorescent coumarin and finally the prodrug 6YT was generated. The fluorescence of coumarin was quenched before the connected aryl borate ester group was cleaved by H2O2. However, in the high level H2O2 environment of the tumor, the fluorescence could be activated simultaneously with the release of etoposide, and the drug release state of the prodrug was monitored real-time. With the support of 6YT, we obtained direct and visual evidence of etoposide release in a high H2O2 environment both in cells and zebrafish. The prodrug 6YT was also verified with comparable activity and improved safety with etoposide both in cells and in a mouse model. As a safe and effective prodrug, 6YT is expected to be one of the promising candidates in chemotherapy against cancer.

Rock-ice avalanches pose serious risks to humans and infrastructures due to their extremely large volumes and high mobility in glacierized mountain regions. The mobility of rock-ice avalanches is supposed to be influenced by water, while the solid-liquid interactions induced by minor wetting remain an open issue. A series of flume tests was performed to investigate the influence of a small amount of water (no more than 4% of the gravel weight) on the behavior and mobility of gravel-ice mixtures. The test results show that intergranular refreezing bonds were created with a preliminary addition of water. The breakup of some weak refreezing bonds during particle rearrangement likely dissipated some kinetic energy, and thus, the mixture mobility was reduced. As the water content increased, the thermal conductivity could likely not remain efficient enough to refreeze all the trapped water and thus allowed unfrozen water to lubricate particle corners, which enhanced mixture mobility. With a further increase in the water content, suction-induced cohesion cemented particles as clusters and reduced mixture mobility. However, a high ice content resulted in mobility enhancement with increasing water content because more gravel was refrozen into the ice matrix, and thus, the basal friction was lowered by the occupation of ice cubes at the bottom. The redistribution pattern of trapped water during mass propagation changed at a characteristic water content. When the water content was lower than the characteristic content, superficially cohered water detached from the surface asperity of one particle and transferred to another during particle rearrangement, i.e., local redistribution of trapped water. When the water content was higher than the characteristic content, the downward transfer of a considerable amount of trapped water was triggered by particle rearrangement under the influence of gravity, i.e., bulk redistribution of trapped water. The water experiencing bulk redistribution influenced the mixture mobility by exerting intergranular drag force via the build-up and break-up of liquid bridges, while locally redistributed water influenced mixture mobility by altering the surface properties of particles. This study is expected to be helpful in better understanding the propagation mechanisms of water-poor rock-ice avalanches and in improving relevant hazard assessments.

Compared with conventional lasers, the random laser is realized through strong multiple scatterings in disordered gain system. In this paper, random lasing (RL) in one-dimensional metal surface plasmon (SP) waveguide with gold-plated self-formed silicon pyramids was investigated comprehensively. Consequently, the emission intensity of RL was enhanced dramatically and the RL threshold was reduced significantly through Au-coated Si spiky tips. Meanwhile, one-dimensional metal SP channel waveguides confined the emitting light in a certain direction with a small divergence angle. Using FDTD simulations, it was found that the enhancement effect for RL is likely attributed to the localized surface plasmon (LSP) field. In addition, the LSP field nearby the spiky tips can enhance field-molecule interaction, which was benefit for lasing in small scale. The results in this letter supplied a feasible method to realize the application of RL in subwavelength optical elements.

This paper investigates noise benefits to the statistics with sign function in robust estimation problems. Sign function, as the score function of a robust M-estimator in location estimation, composes a median estimator. We show that, the mean-square error (MSE) of this statistic can be effectively decreased both under the background of the symmetric and asymmetric contamination noise by adding additive noise. Furthermore, the noise-enhanced effect observed in the linear regression estimation demonstrates that the conclusions in the location parameter estimation can be extended to multidimensional parameter estimation tasks.

Rock-ice avalanches in cold high-mountain regions have extremely high mobility and enormous destructive potential. As a special material component, ice is supposed to play a crucial role in enhancing the mobility of rock-ice avalanches. A series of small flume tests was performed to quantify the influence of the ice content, initial arrangement, and released mass on the behavior and mobility of gravel-ice mixtures, and to provide insights into the propagation mechanisms of rock-ice avalanches in their initial phase. Test results show that the run-out distance and abrupt-stopping distance increased significantly when the ice content reached 30%. This implies that a certain amount of ice was helpful in enhancing the mobility of rock-ice avalanches. With an ice content higher than 80%, the run-out distances decreased slightly. The run-out distance in the well-mixed case was greater than that in the layered-arrangement cases. Segregation, the phenomenon of ice cubes to tend toward the surface and front of the deposit, was vital for the mobility of gravel-ice mixtures. Segmentation was much more evident with an increase in ice content, which indicates that the deposit was highly dispersed and spreading. This was a key difference in the deposition morphology between cases of gravel-ice mixture and cases of pure gravel or pure ice. Although little meltwater was generated in this study, the development of intergranular water film and suction-induced cohesion caused the particles to pack more closely together and to act as clusters rather than individual particles. This study provides insights into the propagation mechanisms and deposition characteristics of rock-ice avalanches.

Single microbelt (MB) photodetectors with metal–semiconductor-metal structure have been demonstrated and characterized comprehensively. For single-photon absorption, the maximum responsivity of ZnO-MB photodetector can reach as high as 1.4 × 105 A W−1 at 20 V bias. The results about photoresponse of MB-detector reveals that two relaxation mechanisms contribute to the carrier decay time. Moreover, the two-photon absorption upconversion photoresponsivity in the single-MB detector has also been realized, which is the first report about the two-photon absorption detector to the best of our knowledge. The excellent two-photon absorption photoresponsivity characteristic of the MB device can be available not only for detector but also for solar cell and biomedical imaging. The above results present a significant step towards future fabrication of single micro/nano-structure based multiphoton excitation optoelectronic devices.