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We report a coupling structure to realize tunable sound transmission in various frequency ranges. The structure, consisting of a flexible Helmholtz resonator and a waveguide, excites three main coupling modes that generate bandpass and bandstop filter effects. Importantly, the coupling modes are controlled by membrane tension or the device structure. These properties show that a tunable filter can be realized simply by regulating the coupling vibration states by changing the membrane tension with different electromagnetic forces. In applications, the flexible Helmholtz resonator operating at its multiple resonances can be fabricated on the sub-wavelength scale, making it easy to achieve acoustic devices with small size for noise suppression or sound control at low frequencies. [ABSTRACT FROM AUTHOR]

Due to the limitation of the hole injection, p-type doping is essential to improve the performance of InGaN/GaN multiple quantum well light-emitting diodes (LEDs). In this work, we propose and show a depletion-region Mg-doping method. Here we systematically analyze the effectiveness of different Mg-doping profiles ranging from the electron blocking layer to the active region. Numerical computations show that the Mg-doping decreases the valence band barrier for holes and thus enhances the hole transportation. The proposed depletion-region Mg-doping approach also increases the barrier height for electrons, which leads to a reduced electron overflow, while increasing the hole concentration in the p-GaN layer. Experimentally measured external quantum efficiency indicates that Mg-doping position is vitally important. The doping in or adjacent to the quantum well degrades the LED performance due to Mg diffusion, increasing the corresponding nonradiative recombination, which is well supported by the measured carrier lifetimes. The experimental results are well numerically reproduced by modifying the nonradiative recombination lifetimes, which further validate the effectiveness of our approach. [ABSTRACT FROM AUTHOR]

In this work, we systematically conduct parametric studies revealing the sensitivity of the hole injection on the hole accelerator (a hole accelerator is made of the polarization mismatched p-electron blocking layer (EBL)/p-GaN/p-AlxGa1-xN heterojunction) with different designs, including the AlN composition in the p-AlxGa1-xN layer, and the thickness for the p-GaN layer and the p-AlxGa1-xN layer. According to our findings, the energy that the holes obtain does not monotonically increase as the AlN incorporation in the p-AlxGa1-xN layer increases. Meanwhile, with p-GaN layer or p-AlxGa1-xN layer thickening, the energy that the holes gain increases and then reaches a saturation level. Thus, the hole injection efficiency and the device efficiency are very sensitive to the p-EBL/p-GaN/p-AlxGa1-xN design, and the hole accelerator can effectively increase the hole injection if properly designed. [ABSTRACT FROM AUTHOR]

In this work, we propose a charge inverter that substantially increases the hole injection efficiency for InGaN/GaN light-emitting diodes (LEDs). The charge inverter consists of a metal/electrode, an insulator, and a semiconductor, making an Electrode-Insulator-Semiconductor (EIS) structure, which is formed by depositing an extremely thin SiO2 insulator layer on the p+-GaN surface of a LED structure before growing the p-electrode. When the LED is forward-biased, a weak inversion layer can be obtained at the interface between the p+-GaN and SiO2 insulator. The weak inversion region can shorten the carrier tunnel distance. Meanwhile, the smaller dielectric constant of the thin SiO2 layer increases the local electric field within the tunnel region, and this is effective in promoting the hole transport from the p-electrode into the p+-GaN layer. Due to the improved hole injection, the external quantum efficiency is increased by 20% at 20 mA for the 350 × 350 μm2 LED chip. Thus, the proposed EIS holds great promise for high efficiency LEDs. [ABSTRACT FROM AUTHOR]

Both Raman spectroscopy and the photoluminescence (PL) spectroscopy are intensively used in studying the characteristics of monolayer MoS2. However, the substrate-related interference effect will influence the optical signal intensities collected from monolayer MoS2. In this work, we investigated the influence of multilayer film interference on the optical signal intensity of monolayer MoS2 on SiO2/Si substrate. Based on our results, the most commonly used substrate for monolayer MoS2, SiO2/Si with SiO2 thickness around 280-300 nm, is not the optimized choice. By considering the interference effect caused by the Air-MoS2-SiO2 multilayers, we can now enhance the optical signal intensity of monolayer MoS2 greatly by selecting proper SiO2 thickness for any chosen incident light wavelength. [ABSTRACT FROM AUTHOR]

The low p-type doping efficiency of the p-GaN layer has severely limited the performance of InGaN/GaN light-emitting diodes (LEDs) due to the ineffective hole injection into the InGaN/GaN multiple quantum well (MQW) active region. The essence of improving the hole injection efficiency is to increase the hole concentration in the p-GaN layer. Therefore, in this work, we have proposed a hole modulator and studied it both theoretically and experimentally. In the hole modulator, the holes in a remote p-type doped layer are depleted by the built-in electric field and stored in the p-GaN layer. By this means, the overall hole concentration in the p-GaN layer can be enhanced. Furthermore, the hole modulator is adopted in the InGaN/GaN LEDs, which reduces the effective valance band barrier height for the p-type electron blocking layer from ~332 meV to ~294 meV at 80 A/cm² and demonstrates an improved optical performance, thanks to the increased hole concentration in the p-GaN layer and thus the improved hole injection into the MQWs. [ABSTRACT FROM AUTHOR]

The quantum efficiency of InGaN/GaN light-emitting diodes (LEDs) has been significantly limited by the insufficient hole injection, and this is caused by the inefficient p-type doping and the low hole mobility. The low hole mobility makes the holes less energetic, which hinders the hole injection into the multiple quantum wells (MQWs) especially when a p-type AlGaN electron blocking layer (EBL) is adopted. In this work, we report a hole accelerator to accelerate the holes so that the holes can obtain adequate kinetic energy, travel across the p-type EBL, and then enter the MQWs more efficiently and smoothly. In addition to the numerical study, the effectiveness of the hole accelerator is experimentally shown through achieving improved optical output power and reduced efficiency droop for the proposed InGaN/GaN LED. [ABSTRACT FROM AUTHOR]

We report an acoustic dual filter to realize the sound regulation in the audio frequency range, in which resonant vibrations of two membrane-air and metal-elastomer systems generate two sound transmission peaks and a sound blocking below 3000 Hz. The local vibrational profiles manifest that the transmission peak at lower frequency is mainly dependent on the resonant vibration of the membrane-air system, and the coupling vibrations of two systems generate the blocking frequency and transmission peak at higher frequency. Importantly, two transmission peaks can be controlled independently. It is feasible to realize the acoustic device in sound shield and dual filters. [ABSTRACT FROM AUTHOR]

In conventional InGaN/GaN light-emitting diodes (LEDs), thin InGaN quantum wells are usually adopted to mitigate the quantum confined Stark effect (QCSE), caused due to strong polarization induced electric field, through spatially confining electrons and holes in small recombination volumes. However, this inevitably increases the carrier density in quantum wells, which in turn aggravates the Auger recombination, since the Auger recombination scales with the third power of the carrier density. As a result, the efficiency droop of the Auger recombination severely limits the LED performance. Here, we proposed and showed wide InGaN quantum wells with the InN composition linearly grading along the growth orientation in LED structures suppressing the Auger recombination and the QCSE simultaneously. Theoretically, the physical mechanisms behind the Auger recombination suppression are also revealed. The proposed LED structure has experimentally demonstrated significant improvement in optical output power and efficiency droop, proving to be an effective solution to this important problem of Auger recombination. [ABSTRACT FROM AUTHOR]

The coupling acoustic matching is investigated to realize acoustic sensors with a microfluidic channel, in which two overlap layers couple three local quarter-wavelength transmission elements. Provided that the reflecting waves from both sides of each overlap layer satisfy destructive interferences, most acoustic energy can be transmitted. Especially, the microfluidic channel is sensitive to realize a function of the acoustic matching, which could induce effects of an approximate halfwavelength transmission and much acoustic dissipation. With an optimized design, the detections of liquid properties with a high quality factor 300 in liquid environment, and a mass sensitivity of 95 kHz mm2/ng are obtained. [ABSTRACT FROM AUTHOR]

InGaN/GaN light-emitting diodes (LEDs) grown along the [0001] orientation inherit very strong polarization induced electric fields. This results in a reduced effective conduction band barrier height for the p-type AlGaN electron blocking layer (EBL) and makes the electron blocking effect relatively ineffective and the electron injection efficiency drops. Here, we show the concept of polarization self-screening for improving the electron injection efficiency. In this work, the proposed polarization self-screening effect was studied and proven through growing a p-type EBL with AlN composition partially graded along the [0001] orientation, which induces the bulk polarization charges. These bulk polarization charges are utilized to effectively self-screen the positive polarization induced interface charges located at the interface between the EBL and the last quantum barrier when designed properly. Using this approach, the electron leakage is suppressed and the LED performance is enhanced significantly. [ABSTRACT FROM AUTHOR]

InGaN/GaN light-emitting diodes (LEDs) grown along the polar orientations significantly suffer from the quantum confined Stark effect (QCSE) caused by the strong polarization induced electric field in the quantum wells, which is a fundamental problem intrinsic to the III-nitrides. Here, we show that the QCSE is self-screened by the polarization induced bulk charges enabled by designing quantum barriers. The InN composition of the InGaN quantum barrier graded along the growth orientation opportunely generates the polarization induced bulk charges in the quantum barrier, which well compensate the polarization induced interface charges, thus avoiding the electric field in the quantum wells. Consequently, the optical output power and the external quantum efficiency are substantially improved for the LEDs. The ability to self-screen the QCSE using polarization induced bulk charges opens up new possibilities for device engineering of III-nitrides not only in LEDs but also in other optoelectronic devices. [ABSTRACT FROM AUTHOR]

A three-step graded undoped-InGaN layers embedded between the GaN last quantum barrier layer and the p-AlGaN electron blocking layer was proposed and its effect on the performance of InGaN/GaN light-emitting diodes was investigated both experimentally and theoretically. In the proposed structure, the electron leakage is found to be effectively reduced, while the hole injection efficiency is simultaneously increased significantly, hence enabling a greatly enhanced radiative recombination rate within the active region. As a result, improvements of 12.25% in the optical output power and 11.98% in the external quantum efficiency are obtained from the proposed device with the respect to the reference device. [ABSTRACT FROM AUTHOR]

We demonstrate the possibility of forming long-range ordered self-assembled arrays of 5-nmdiameter nanodots with pitch of 10×7.5 nm² using guide line templates and low molecular weight (MW) (4700-1200 g/mol) poly(styrene)-poly(dimethylsiloxane) (PS-PDMS) for application in ultrahigh density patterned magnetic recording media. We propose a three-dimensional control which involves control of the height of the guide lines, the thickness of the PS-PDMS films, and the gap between the guide lines in order to produce 5-nm-diameter, sub-10 nm pitched nanodots with long-range order along the guide lines. Adopting a 13-nm-thick PS-PDMS film and 14-nm-high resist guide lines, the 5-nm-diameter and 10×7.5 nm²-pitched self-assembled nanodots were ordered in 4-7 dot arrays with long-range order. The experimental results demonstrate that the method is suitable for the production of patterned media with magnetic recording densities of 8.6 Tbit/in². using low MW PS-PDMS and slim guide lines. [ABSTRACT FROM AUTHOR]

In this work, the origin of electron blocking effect of n-type Al0.25Ga0.75N electron blocking layer (EBL) for c+ InGaN/GaN light-emitting diodes has been investigated through dual-wavelength emission method. It is found that the strong polarization induced electric field within the n-EBL reduces the thermal velocity and correspondingly the mean free path of the hot electrons. As a result, the electron capture efficiency of the multiple quantum wells is enhanced, which significantly reduces the electron overflow from the active region and increases the radiative recombination rate with holes. [ABSTRACT FROM AUTHOR]

In this letter, on the basis of Stoner-Wohlfarth model, the changes in magnetization of Tb0.3Dy0.7Fe2 alloy have been calculated with a compressive stress along the [111] and [112] axes. The results have shown that the significant change in magnetization for Tb0.3Dy0.7Fe2 alloy can be induced by the compressive stress. A feasible application of power generation floor which can convert the energy from the vibration created by a walking person on it into electric energy has been proposed, and its structure and performance also have been revealed. [ABSTRACT FROM AUTHOR]

Based on the analysis of the photocurrent behavior of Pt sandwiched Pb(Zr0.2Ti0.8)O3 (PZT) films, the experimental evidence of top Pt/PZT interface layer thickness effect on the photocurrent is reported. It was well established before that the photocurrent of metal/ferroelectric film is attributed to the height of Schottky contact barrier. However, our results suggest that the photocurrent of Pt/PZT interface contact is determined not only by the barrier height but also by the interface layer thickness, namely, by the built-in electrical field at the interface layer. The mechanism behind such photocurrent phenomenon is proposed. [ABSTRACT FROM AUTHOR]

We report a simple and robust magnetomechanical system for direct visual observation of the DNA packaging behavior of the bacteriophage phi29 in real time. The system comprises a micron-sized magnetic bead attached to the free end of the viral DNA, a magnet and a bright-field microscope. We show that the phi29 DNA packaging activity can be observed and dynamically analyzed at the single molecular level in bright field with a relatively simple system. With this system we also visually demonstrate the phi29 motor transporting a cargo 10 000 times the viral size. [ABSTRACT FROM AUTHOR]

We fabricated dark-bright-dark plasmon resonators, investigated enhanced-transmission induced by plasmon transfer from the bright mode to the dark modes. Furthermore, we demonstrated interferences between dark plasmons excited by the near-field bright plasmons and directly excited by slantwise incident light, which leads to selective storage of excited energy in one of the two dark plasmon cells in the resonators by adjusting the phase between signal and control sources. This could find the applications in all-optical modulations. [ABSTRACT FROM AUTHOR]

We propose an ultra-thin plasmonic color filtering device based on subwavelength metal grating engraved on a dielectric membrane waveguide without substrate. As experiments demonstrate, the fabricated free-standing plasmonic color filters have more than 70% transmission efficiency at different resonant wavelengths in the visible spectral region and are capable of generating arbitrary colors. Experimental results are in good agreement with the theoretical calculations. These artificial nanostructured color filtering devices may find potential applications in high resolution color imaging and sensing systems. [ABSTRACT FROM AUTHOR]

An acoustic metamaterial is designed based on a simple and compact structure of one string of side pipes arranged along a waveguide, in which diverse group velocities are achieved. Owing to Fabry-Perot resonance of the side pipes, a negative phase time is achieved, and thus, acoustic waves transmitting with negative group velocities are produced near the resonant frequency. In addition, both fast and slow acoustic waves are also observed in the vicinity of the resonance frequency. The extraordinary group velocities can be explained based on spectral rephasing induced by anomalous dispersion on the analogy of Lorentz dispersion in electromagnetic waves. [ABSTRACT FROM AUTHOR]

Insulating against low-frequency sound (below 500 Hz) remains challenging despite the progress that has been achieved in sound insulation and absorption. In this work, an acoustic metamaterial based on membrane-coated perforated plates is presented for achieving sound insulation in a low-frequency range, even covering the lower audio frequency limit, 20 Hz. Theoretical analysis and finite element simulations demonstrate that this metamaterial can effectively block acoustic waves over a wide lowfrequency band regardless of incident angles. Two mechanisms, non-resonance and monopolar resonance, operate in the metamaterial, resulting in a more powerful sound insulation ability than that achieved using periodically arranged multi-layer solid plates. [ABSTRACT FROM AUTHOR]

Physical phenomena induced by nonlinear effects in an acoustic metamaterial with double-negativity based on two types of scatterers, side holes and membrane, located along a pipe are theoretically and experimentally studied. We find that the pass and forbidden bands related to double-negativity and single-negativity effects in the metamaterial vary with the input acoustic intensities because of the nonlinearities of both types of scatterers. The nonlinearities can disrupt the unique features associated with these characteristic frequency bands of the metamaterial; however, the nonlinear effects may also lead to applications as automatically triggered acoustic isolators, tunable acoustic metamaterials, and so on. [ABSTRACT FROM AUTHOR]

The characteristics of electroluminescence (EL) and photoluminescence (PL) emission from GaN light-emitting diodes (LEDs) grown on (1122) semipolar plane and (0001) polar plane have been comparatively investigated. Through different bias-dependent shifting trends observed from the PL and time-resolved PL spectra (TRPL) for the two types of LEDs, the carrier dynamics within the multiple quantum wells (MQWs) region is systematically analyzed and the distinct field-dependent emission kinetics are revealed. Moreover, the polarization induced internal electric field has been deduced for each of the LEDs. The relatively stable emission behavior observed in the semipolar LED is attributed to the smaller polarization induced internal electric field. The study provides meaningful insight for the design of quantum well (QW) structures with high radiative recombination rates. [ABSTRACT FROM AUTHOR]

Laser wakefield acceleration of electrons well beyond 1 GeV and optical guiding of ultraintense laser pulses of peak powers up to 160 TW over a 4-cm long ablative capillary discharge plasma channel were experimentally demonstrated. Electron beams, with energies up to 1.8 GeV, were generated by using the 130 TW, 55 fs driving laser pulses. A comparison of oxygen-containing acrylic resin (C:O:H = 4:2:7) capillary and no oxygen-containing polyethylene (C:O:H = 1:0:2) capillary measurements suggests that the injection of electron into the laser wakefield is assisted by the ionization of oxygen K-shell electrons. [ABSTRACT FROM AUTHOR]

Anomalous subharmonics named as quasisubharmonics (QSHs) in plates excited by intensive ultrasonic pulses are first observed, in which the QSH frequencies are incommensurable with the fundamental frequency. The experimental results show that the low (such as 1/3) order subharmonics appear in the transient process of the ultrasonic excitation, and then several QSHs successively appear as the ultrasonic power increases and approaches steady state, in which the first QSH appears near the system eigenfrequency. A phenomenological model is presented and the theoretical simulations indicate that the QSHs are produced by the intermittent contacts between the transducer horn and the plate. [ABSTRACT FROM AUTHOR]