The bandgaps of monolayer and bulk molybdenum sulfide (MoS2 ) result in that they are far from suitable for application as a saturable absorption device. In this paper, the operation of a broadband MoS2 saturable absorber is demonstrated by the introduction of suitable defects. It is believed that the results provide some inspiration in the investigation of two-dimensional optoelectronic materials.

Photodetectors with excellent detecting properties over a broad spectral range have advantages for the application in many optoelectronic devices. Introducing imperfections to the atomic lattices in semiconductors is a significant way for tuning the bandgap and achieving broadband response, but the imperfection may renovate their intrinsic properties far from the desire. Here, by controlling the deviation from the perfection of the atomic lattice, ultrabroadband multilayer MoS photodetectors are originally designed and realized with the detection range over 2000 nm from 445 nm (blue) to 2717 nm (mid-infrared). Associated with the narrow but nonzero bandgap and large photoresponsivity, the optimized deviation from the perfection of MoS samples is theoretically found and experimentally achieved aiming at the ultrabroadband photoresponse. By the photodetection characterization, the responsivity and detectivity of the present photodetectors are investigated in the wavelength range from 445 to 2717 nm with the maximum values of 50.7 mA W and 1.55 × 10 Jones, respectively, which represent the most broadband MoS photodetectors. Based on the easy manipulation, low cost, large scale, and broadband photoresponse, this present detector has significant potential for the applications in optoelectronics and electronics in the future.

No abstract

An endstation with two high-efficiency soft x-ray spectrographs was developed at Beamline 8.0.1 of the Advanced Light Source, Lawrence Berkeley National Laboratory. The endstation is capable of performing soft x-ray absorption spectroscopy, emission spectroscopy, and, in particular, resonant inelastic soft x-ray scattering (RIXS). Two slit-less variable line-spacing grating spectrographs are installed at different detection geometries. The endstation covers the photon energy range from 80 to 1500 eV. For studying transition-metal oxides, the large detection energy window allows a simultaneous collection of x-ray emission spectra with energies ranging from the O K-edge to the Ni L-edge without moving any mechanical components. The record-high efficiency enables the recording of comprehensive two-dimensional RIXS maps with good statistics within a short acquisition time. By virtue of the large energy window and high throughput of the spectrographs, partial fluorescence yield and inverse partial fluorescence yield signals could be obtained for all transition metal L-edges including Mn. Moreover, the different geometries of these two spectrographs (parallel and perpendicular to the horizontal polarization of the beamline) provide contrasts in RIXS features with two different momentum transfers.

Photodetectors that capture light and convert it into electricity have been used in many applications, such as imaging systems, environmental surveillance, communications, and biological sensing. [1][2][3] UV detectors play an important role in practical applications, many devices have been prepared with wide bandgap semiconductors, such as ZnO, NiO, and TiO 2 etc. [4][5][6][7][8][9] However, these heterojunction self-powered detectors often exhibit low responsivity and slow response times.

Large-area vertical rutile TiO2 nanorod arrays (TNAs) were grown on F/SnO2 conductive glass using a hydrothermal method at low temperature. A self-powered ultraviolet (UV) photodetector based on TiO2 nanorod/water solid–liquid heterojunction is designed and fabricated. These nanorods offer an enlarged TiO2/water contact area and a direct pathway for electron transport simultaneously. By connecting this UV photodetector to an ammeter, the intensity of UV light can be quantified using the output short-circuit photocurrent without a power source. A photosensitivity of 0.025 A/W and a quick response time were observed. At the same time, a high photosensitivity in a wide range of wavelength was also demonstrated. This TNA/water UV detector can be a particularly suitable candidate for practical applications for its high photosensitivity, fast response, excellent spectral selectivity, uncomplicated low-cost fabrication process, and environment-friendly feature.

space. By selecting and arranging these components, the electronic structuresincluding the bandgap and the density of states (DOS) dispersion relation-can be tailored, and desirable effects, such as the photovoltaic effect, [1] quantum Hall effect, [2] and Anderson localization, [3] can be generated and optimized. The detection of light in optoelectronic semiconductors, which exploits the photoelectric effect and involves the conversion of light into an electrical signal, has become indispensable to optoelectronic devices that are used in an array of applications today, such as safety monitoring, biological sensors, remote optical communication, and so on. [4,5] The possible photodetection range is determined by the bandgap of the semiconductor. For UV, visible, and near-IR regimes, photodetectors are typically made from commercial semiconductors with relatively large bandgaps such as silicon, [6] gallium nitride, [7] and indium phosphide. [8,9] However, the fabrication of high-performance mid-IR (3-8 µm) and far-IR (>8 µm) photodetectors remains a major challenge as a result of the intrinsic competition between narrow bandgaps, which give rise to broad wavelength responsivity, and small dark currents, which correspond to highly responsive capacity and large shot noise. [10][11][12][13] This conditions above undoubtedly constrain the development of modern technologies and systems associated with broadband photodetection including the safety monitoring, multiwavelength photodetection, remote optical communication, etc.Generally, the intensity of the dark current depends on the temperature-dependent Fermi-Dirac distribution function, [14] , where E − E F is the energy position, k is the Boltzmann constant), as well as the electronic state density, N c , of the conduction band. The primary calculation shows the f E at 150 K (low temperature) is three orders of magnitude smaller than that at room temperature (RT) when the energy levels correspond to mid-IR region (3-8 µm) corresponding to the narrow bandgap of semiconductors (≈0.4-0.15 eV). To date, researchers have focused mainly on suppressing the dark current by lowering the operating temperature of narrow-bandgap semiconductors which reduces the population of the Fermi-Dirac distribution. [15,16] For instance, state-of-the-art mid-IR photodetectors in the market based on HgCdTe demand the operating temperature as low as about 70 K [15] besides its Photodetection using semiconductors is critical for capture, identification, and processing of optical information. Nowadays, broadband photodetection is limited by the underdeveloped mid-IR photodetection at room temperature (RT), primarily as a result of the large dark currents unavoidably generated by the Fermi-Dirac distribution in narrow-bandgap semiconductors, which constrains the development of some modern technologies and systems. Here, an electronic-structure strategy is proposed for designing ultrabroadband covering mid-and even far-IR photodetection materials operating at RT and a layered MoS 2 is manifested ...

For van der Waals (vdW) heterostructures, optical and electrical properties (e.g., saturable absorption and carrier dynamics) are strongly modulated by interlayer coupling, which may be due to effective charge transfer and band structure recombination. General theoretical studies have shown that the complementary properties of graphene and MoS 2 enable the graphene/MoS 2 (G/MoS 2 ) heterostructure to be used as an important building block for various optoelectronic devices. Here, density functional theory was used to calculate the work function values of G/MoS 2 with different thicknesses of MoS 2 , and its relaxation dynamic mechanism was illustrated. The results reveal that the G/MoS 2 heterostructure interlayer coupling can be tuned by changing the thickness of MoS 2 , furthering the understanding of the fundamental charge-transfer mechanism in few-layer G/MoS 2 heterostructures. The tunable carrier dynamics and saturable absorption were investigated by pump−probe spectroscopy and open-aperture Z-scan technique, respectively. In the experiments, we compared the performances of Q-switched lasers based on G/MoS 2 heterostructures with different MoS 2 layers. Taking advantage of ultrafast recovery time and good saturable absorption properties, a femtosecond solid-state laser at 1.0 μm with G/MoS 2 heterostructure saturable absorber was successfully achieved. This study on interlayer coupling in G/MoS 2 may allow various vdW heterostructures with controllable stacking to be fabricated and shows the promising applications of vdW heterostructures for ultrafast photonic devices. KEYWORDS: G/MoS 2 heterostructure, nonlinear optical response, femtosecond solid-state bulk laser, saturable absorption, charge-transfer process