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Jiaxin Zhu, Jinyan Xiong, Gang Cheng, Weijie Li, Shixue Dou
Developing a highly efficient photocatalysis system based on a photocatalyst-cocatalyst host for the hydrogen evolution reaction has potential but is still challenging. Herein, we report enhanced splitting of water achieved by loading copper metal particles on mesoporous TiO2 microrods through involving of dual ligand agents into the reaction system. The composition, structure, and surface characteristics of the TiO2 -Cu hybrid were analyzed by X-ray diffraction, X-ray photoelectron spectroscopy, scanning and transmission electron microscopy, and nitrogen adsorption...
March 6, 2019: Journal of Colloid and Interface Science
M Gębski, J A Lott, T Czyszanowski
We achieve the continuous-wave (CW) lasing of electrically-injected, first-of-their-kind vertical-cavity surface-emitting lasers (VCSELs) that use a subwavelength monolithic high-refractive-index-contrast grating (MHCG) mirror. The MHCG, unlike the well-known high-refractive-index-contrast grating (HCG) is neither a membrane suspended in the air nor a structure that requires a cladding layer. The MHCG is patterned in a semiconductor material atop the VCSEL cavity creating an all-semiconductor laser. Static measurements show CW operation of the VCSELs from room temperature up to 75 °C...
March 4, 2019: Optics Express
Xin Zhang, Jilin Zheng, Tao Pu, Yunshan Zhang, Yuechun Shi, Jin Li, Yuandong Li, Huatao Zhu, Xiangfei Chen
A novel approach to realizing an optoelectronic oscillator (OEO) based on an integrated multi-section (IMS) distributed feedback (DFB) laser is proposed and experimentally demonstrated. Our scheme adopts the method of direct modulation and a built-in microwave photonic filter (MPF), making the structure simpler and more flexible than an external modulator and electrical bandpass filter (EBPF). The IMS-DFB laser, which can overcome the drawbacks of using discrete lasers, is the key device in the scheme. Further, the two DFB sections, which are fabricated by Reconstruction Equivalent Chirp (REC) technique, are injected mutually...
March 4, 2019: Optics Express
Jon Mariñelarena, Haritz Iribas, Javier Urricelqui, Alayn Loayssa
We demonstrate a technique to compensate the nonlocal effects that appear in Brillouin optical time-domain analysis sensors when pump pulses with limited extinction ratio are deployed. These recently discovered nonlocal effects are originated in the interaction between the probe wave and the pulse pedestal. Hence, their compensation method is based on deploying a modulation (dithering) of the optical frequency of the probe and pulse pedestal waves that provides a reduction of the effective interaction length between them...
March 4, 2019: Optics Express
T Ostatnický
We derive a simple, semi-classical formula for the calculation of the linear electron conductivity spectrum of semiconductor nanocrystals in the THz spectral range from the general quantum-mechanical model. We show that the reliability and range of applicability of the formula significantly exceed the scope of both the Drude-Smith model and the recently developed modified Drude-Smith model.
March 4, 2019: Optics Express
B H Le, X Liu, N H Tran, S Zhao, Z Mi
We report on the demonstration of an electrically injected AlGaN nanowire photonic crystal laser that can operate in the ultraviolet spectral range. The nanowire heterostructures were grown on sapphire substrate using a site-controlled selective area growth process. By exploiting the topological high-Q resonance of a defect-free nanowire photonic crystal, we have demonstrated electrically pumped lasers that can operate at 369.5 nm with a relatively low threshold current density of ~2.1 kA/cm2 under continuous wave operation at room-temperature...
February 18, 2019: Optics Express
Arifur Rahaman, Aravinda Kar, Xiaoming Yu
Ultrafast lasers have been used for high-precision processing of a wide range of materials, including dielectrics, semiconductors, metals and polymer composites, enabling numerous applications ranging from micromachining to photonics and life sciences. To make ultrafast laser materials processing compatible with the scale and throughput needed for industrial use, it is a common practice to run the laser at a high repetition rate and hence high average power. However, heat accumulation under such processing conditions will deteriorate the processing quality, especially for polymers, which typically have a low melting temperature...
February 18, 2019: Optics Express
Pijie Ma, Anjin Liu, Fengxin Dong, Mingjin Wang, Wanhua Zheng
The output characteristics, modal properties, far-field profiles, and dynamic modulation responses of semiconductor lasers with surface higher-order gratings fabricated by the standard photolithography are presented. Single-mode semiconductor lasers with 20th - and 37th -order gratings for the 1.55 µm wavelength range are realized. The single-mode semiconductor lasers with 20th -order gratings have lower threshold currents and higher slope efficiencies than those with 37th -order gratings. The surface higher-order grating placed closed to the output facet can deteriorate the vertical far-field profile of the semiconductor laser...
February 18, 2019: Optics Express
I Kilen, J Hader, S W Koch, J V Moloney
Microscopic many-body theory coupled with Maxwell's equation is used to study dual-wavelength operation in vertical external-cavity surface-emitting lasers. The intrinsically dynamic nature of coexisting emission wavelengths in semiconductor lasers is associated with characteristic non-equilibrium carrier dynamics, which causes significant deformations of the quasi-equilibrium gain and carrier inversion. Extended numerical simulations are employed to efficiently investigate the parameter space to identify the regime for dual-wavelength operation...
February 18, 2019: Optics Express
Chenpeng Xue, Songkun Ji, Yanhua Hong, Ning Jiang, Hongqiang Li, Kun Qiu
Enhanced photonic microwave generation by using a filtered optical feedback in an optically injected semiconductor laser operating at period-one (P1) dynamics is numerically demonstrated. In the simulation, the frequency tunability of the generated narrow-linewidth photonic microwave with the filtered optical feedback has been investigated. The results show that the frequency of the narrow-linewidth photonic microwave can be widely tuned by adjusting the injection parameters only or adjusting both the injection parameters and the center frequency of the filter...
February 18, 2019: Optics Express
Kevin M W Boyd, Rafael N Kleiman
We present self-induced absorption, a pump/probe-like modulation technique that uses a single monochromatic laser acting simultaneously as both a pump and a probe. The technique is applicable to any system where the phenomenon that us being excited simultaneously induces additional absorption in the beam through a secondary process, leading to a non-linear power component in the beam transmission. The technique is demonstrated on a silicon wafer, where the non-linear transmission is due to free-carrier absorption, and provides information about the recombination lifetime of the semiconductor...
February 18, 2019: Optics Express
R Joseph Weiblen, Igor Vurgaftman
Integrated microresonator-based mid-infrared frequency combs based on III-V semiconductors exhibit pronounced higher-order group velocity dispersion that can make it difficult to achieve stable output. One way to stabilize multiple solitons and their repetition rate is to pump simultaneously at two nearby comb lines. Two-color (or bichromatic) pumping also promises to boost the relatively low conversion efficiencies of single-soliton combs. We present simulations showing that, for a realistic InGaAs/InP ridge waveguide, the stabilization effect occurs over only a limited range of pump power and detuning parameters...
February 18, 2019: Optics Express
Rodolphe Vaillon, Jean-Philippe Pérez, Christophe Lucchesi, Dilek Cakiroglu, Pierre-Olivier Chapuis, Thierry Taliercio, Eric Tournié
Simulations of near-field thermophotovoltaic devices predict promising performance, but experimental observations remain challenging. Having the lowest bandgap among III-V semiconductors, indium antimonide (InSb) is an attractive choice for the photovoltaic cell, provided it is cooled to a low temperature, typically around 77 K. Here, by taking into account fabrication and operating constraints, radiation transfer and low-injection charge transport simulations are made to find the optimum architecture for the photovoltaic cell...
February 18, 2019: Optics Express
Tien Van Nguyen, Khoa Van Pham, Kyeong-Sik Min
As a software framework, Hierarchical Temporal Memory (HTM) has been developed to perform the brain's neocortical functions, such as spatial and temporal pooling. However, it should be realized with hardware not software not only to mimic the neocortical function but also to exploit its architectural benefit. To do so, we propose a new memristor-CMOS (Complementary Metal-Oxide-Semiconductor) hybrid circuit of temporal-pooling here, which is composed of the input-layer and output-layer neurons mimicking the neocortex...
March 15, 2019: Materials
Minas M Stylianakis, Temur Maksudov, Apostolos Panagiotopoulos, George Kakavelakis, Konstantinos Petridis
Inorganic and organic-inorganic (hybrid) perovskite semiconductor materials have attracted worldwide scientific attention and research effort as the new wonder semiconductor material in optoelectronics. Their excellent physical and electronic properties have been exploited to boost the solar cells efficiency beyond 23% and captivate their potential as competitors to the dominant silicon solar cells technology. However, the fundamental principles in Physics, dictate that an excellent direct band gap material for photovoltaic applications must be also an excellent light emitter candidate...
March 14, 2019: Materials
Kisung Chae, Young-Woo Son
To accelerate development of innovative materials, their modelings and predictions with useful functionalities are of vital importance. Here, based on a recently developed crystal structure prediction method, we find a new family of stable two-dimensional crystals with an open-channel tetrahedral bonding network, rendering a potential for electronic and energy applications. The proposed structural prototype with a space group of Cmme hosts at least thirteen different freestanding T3 X compounds with group IV (T=C, Si, Ge, Sn) and VI (X=O, S, Se, Te) elements...
March 15, 2019: Nano Letters
Songcan Wang, Gang Liu, Lianzhou Wang
Photoelectrochemical (PEC) water splitting is a promising approach for solar-driven hydrogen production with zero emissions, and it has been intensively studied over the past decades. However, the solar-to-hydrogen (STH) efficiencies of the current PEC systems are still far from the 10% target needed for practical application. The development of efficient photoelectrodes in PEC systems holds the key to achieving high STH efficiencies. In recent years, crystal facet engineering has emerged as an important strategy in designing efficient photoelectrodes for PEC water splitting, which has yet to be comprehensively reviewed and is the main focus of this article...
March 15, 2019: Chemical Reviews
Wei Zhao, Sheng Bi, Cheng Zhang, Philip D Rack, Guang Feng
Most studies of ionic liquid (IL) gated field effect transistors (FETs) focus on the extremely large electric field and capacitance induced in liquid/solid interfaces and correspondingly the significantly enhanced carrier density in semiconductors, which can appreciably improve the gating performance. However, how to boost the switching speed, another key property of gating performance of FETs, has been rarely explored. In this work, the gating performance of molybdenum disulfide (MoS2) FETs, gated by the mixtures of IL/organic solvent (1-butyl-3-methylimidazolium tetrafluoroborate/acetonitrile, [Bmim][BF4]/ACN) at different ion concentrations, is investigated for both dynamic and static properties by a combination of molecular dynamics simulation and resistance network analysis...
March 15, 2019: ACS Applied Materials & Interfaces
Zirui Liu, Xiaoyong Liu, Xinxin Gu, Renqing Guo, Wenwu Zhong
The rapid recombination of electron-hole pairs in BiVO4 has limited its performance as a photocatalysis. In this paper, BiVO4 is combined with Cu2-x Se semiconductor to slow down the recombination process, and thus improve its photocatalytic activity. This is enabled by careful band structure design. The work function of Cu2-x Se is larger than that of BiVO4 . Therefore, electrons flow to Cu2-x Se from BiVO4 after the composition. Accordingly, an inner field could be built, which facilitates the separation of electrons and holes...
March 14, 2019: Nanoscale Research Letters
Xiji Shao, Lin Li, Xingqiang Shi, Yaping Ma, Xuefeng Wu, Kedong Wang
The strong interaction between transition metal (TM) atoms and semiconductor surface atoms may diminish the magnetic moments of the TM atoms and prevent them from being used as single atom spin-based devices. A carbon cage that can encapsulate TM atoms and isolate them from interacting with surface atoms is considered to protect the magnetic moments of the TM atoms. We have studied the magnetic moments of Fe, Co, and Ni atoms adsorbed inside the corner hole of Si(111)-(7 × 7) by using first-principles calculations based on the density functional theory...
March 15, 2019: Nanoscale
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