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Intrinsic linear polarized optics discovered in anisotropic two-dimensional (2D) materials has attracted intense interest for polarization-sensitive optical and optoelectronic applications, such as black phosphorous, ReSe2, etc. However, the lack of matured method to synthesize high-quality, large-scale and air-stable 2D materials with anisotropic properties, is still an obstacle for practical applications. Monolayer molybdenum disulfide (MoS2), which exhibits strong direct-band-gap light-harvesting properties, can be grown maturely. But unfortunately, MoS2 does not show linear dichroism owing to its in-plane isotropic crystalline symmetry. We, herein, for the first time, report on an artificial control of extrinsic linear polarized photoelectric effect in monolayer MoS2, by successfully controlling its anisotropic degree of in-plane crystal symmetry via artificially induced uniaxial tensile strain. Strong linear polarization-sensitive photodetection from visible to near-infrared range is realized for monolayer MoS2-based device, and the polarization anisotropic ratio can reach up over 2.0 under 4.5% strain. The observation is supported by combination of experiment-theory study on polarized Raman spectrum and optical absorption under gradually applied strains. Our results have demonstrated that the artificial-controlled symmetry reducing of MoS2 is a promising strategy to achieve high performance polarization photodetection. This method can also be extended to other 2D materials, which potentially opens up a new field to endow isotropic 2D materials with anisotropic functionalities by artificial structure engineering.

The van der Waals integration of atomically thin two-dimensional (2D) materials can enable a new generation of tunable optoelectronic devices, in which the photocarrier generation, separation and extraction can be modulated by an external gate potential. However, studies to date only show a limited modulation due to non-ideal band alignment and the lack independent modulation of distinct 2D layers in the van der Waals heterojunction. Here report the construction of a WSe2/GeSe heterojunction photodiode with type-II band alignment, in which the value of the conduction band and valence band edge in WSe2 is approximately equal to that of GeSe. What's more, the Fermi level of GeSe remains relative stationary and that of WSe2 can be modulated across the entire band gap by an external gate-voltage, thus rendering widely tunable open-circuit voltages from positive (+ 0.7 V) to negative (− 0.1 V). We further show the photoresponsivity can be modulated by the gate-voltage with a factor of 105, which is similar to the current switching ratio in traditional field-effect transistors, opening up exciting potential for photonic logic circuits.

The terahertz (THz) technique is still confronted with challenges partly due to lack of an efficient method to achieve sensitive detection at room temperature. Gapless graphene is highly sought-after as a potential candidate for active material in photo-detection across the whole electromagnetic spectrum. However, the efficient photo-to-electric conversions within THz range are not well-developed at present. Here we report the hot carrier-assisted photoconduction being triggered by a sub-THz electromagnetic wave in homogeneous graphene, which is beyond the conventional interband mechanism and can be potentially extended to the higher THz band. The photoconductive effect here is attributed to the additional carriers replenished from the electrode following the potential disturbance of the hot carrier diffusion, which depletes or increases the sheet density in the channel depending on the carrier-polarity in the channel. The biased photoconductive device shows sensitivity over 400 V/W (4 × 103 V/W) at room temperature and noise-equivalent power less than 0.5 nW/Hz0.5 (20 pW/Hz0.5) in reference to the incident (absorbed) power. The reported figures of merit represent the benchmark for further performance improvement via several different methods such as shortening the channel, using a matched antenna or material with improved mobility. All results presented open up the feasibility of achieving a photoconductive device for sensitive room temperature detection at terahertz frequencies.

In this paper, we demonstrate the effect of polarization conversion in a plasmonic metasurface structure, in which each unit cell consists of a metal bar and four metal split-ring resonators (SRRs). Such effect is attributed to the fact that the dark plasmon mode of SRRs (bar), which radiates cross-polarized component, is induced by the bright plasmon mode of bar (SRRs) due to the electromagnetic near-field coupling between bar and SRRs. We find that there are two ways to achieve a large cross-polarized component in our proposed metasurface structure. The first way is realized when the dark plasmon mode of bar (SRRs) is in resonance, while at this time the bright plasmon mode of SRRs (bar) is not at resonant state. The second way is realized when the bright plasmon mode of SRRs (bar) is resonantly excited, while the dark plasmon mode of bar (SRRs) is at nonresonant state. It is also found that the linearly polarized light can be rotated by 56.5 0 after propagation through the metasurface structure. Furthermore, our proposed metasurface structure exhibits an asymmetric transmission for circularly polarized light. Our findings take a further step in developing integrated metasurface-based photonics devices for polarization manipulation and modulation.

The ability to use infrared imaging systems with multicolor capabilities, high photoresponsivity and polarization sensitivity, is central to practical photodetectors and has been demonstrated with conventional devices based on Ⅲ-Ⅴ or Ⅱ-Ⅵ semiconductors. However, the photodetectors working at room temperature with high responsivity for polarized infrared light detection remains elusive. Here, we first demonstrate a broadband photodetector using a vertical photogate heterostructure of BP-on-WSe 2 (black phosphorus-on-tungsten diselenide) in which BP serves as the photogate and WSe 2 as the conductive channel. Ultrahigh visible and infrared photoresponsivity at room temperature can reach up to ~10 3 A/W and ~5×10 −1 A/W, respectively, and ultrasensitive visible and infrared specific detectivity is obtained up to ~10 14 and ~10 10 Jones respectively at room temperature. Moreover, the high sensitivity to infrared polarization is about 40 mA/W with incident light polarized along the horizontal axis (defined as 0° polarization). This performance is due to the strong intrinsic linear dichroism of BP and the device design which can sufficiently collect the photoinduced carriers isotropically, as well as the influence from the orientation of the edge of the BP-on-WSe 2 overlapped area which is the same for all polarizations. The high responsivity, good sensitive detectivity and highly polarization-sensitive infrared photoresponse suggest that the photodetectors based on photogate structure afford new opportunities for infrared detecting or imaging at room temperature by using two-dimensional materials.

We report the tunable enhanced transmission of light through a hybrid metal–graphene structure, in which a graphene ribbon array is situated over a metallic grating. The graphene ribbon is employed to make the graphene–insulator–metal waveguide of finite length as a Fabry–Perot (F–P) cavity. When the slit of metallic grating is opened at the position with a maximal magnetic field in F–P resonant cavity, the transmission of light through metallic grating is greatly enhanced since the strongly localized magnetic field is effectively coupled to the slit. The transmission spectrum and the enhancement factor can be adjusted by changing geometrical parameters including the width and the length of slit, the width of graphene ribbon and the period of metallic grating. The transmission peaks exhibit a broad tuning range with a small change in the Fermi energy level of graphene. Moreover, the enhancement factor of transmission peak can be manipulated by the Fermi energy level and the carrier mobility of graphene, and an enhancement factor of 154 is obtained. The findings expand our understanding of hybrid metal–graphene plasmons and have potential applications in building active plasmonic devices.

The self-sharpening vitrified-metal bond diamond wheels added with a 3 wt.% brittle Na2O-B2O3-SiO2-Al2O3-Li2O vitrified bond were fabricated by hot pressed sintering technique. Using the methods of scan-electroscope, energy spectrum analysis, X-diffraction analysis, XPS analysis, Rockwell hardness test and three-point bending test, the effects of hot pressing temperature on the microstructure, hardness and the transverse rupture strength (TRS) of vitrified-metal bond were investigated. Then the grinding performance of cylinder of the diamond wheels was also studied. The results showed that, when the hot pressing temperature was 850 °C, a thin FeAl2O4 transition layer formed, which enhanced the interfacial bending strength between metal and glass phase, and the TRS of vitrified-metal bond reached the maximum value 826.54 MPa. Comparing with metal bond diamond wheel's, the average value of the roundness and straightness of the 50 cylinders ground by the vitrified-metal diamond wheel reduced from 3.1 μm and 2.5 μm to 2.7 μm and 2.1 μm.

Resistance–voltage ( R – V ) curves of arsenic doped long-wavelength infrared (LWIR) Mercury Cadmium Telluride (HgCdTe) photodiodes were measured in the temperature range of 59–92 K. The dark current characteristics of HgCdTe junction diode are presented by using a simultaneous-mode nonlinear fitting method. The observed R – V characteristics have been shown in agreement with the theoretical calculation by taking into account the contributions: (i) diffusion mechanism ( R diff ), (ii) generation–recombination mechanism ( R gr ) in the depletion region, (iii) trap-assisted tunneling mechanism ( R tat ), and (iv) band-to-band tunneling mechanism ( R bbt ). Six characteristic parameters as function of temperature are extracted from the measured current–voltage ( I – V ) curves by considering the dominant current mechanisms under different bias levels. The fitted current components under different temperatures show that, as the temperature rises, the contribution to the dominant dark current component around maximum dynamic resistance range is changed from the trap-assisted tunneling and diffusion currents to the generation recombination effect. This change indicates that the dark current component may mainly be caused by the generation recombination current, which limits the performance of arsenic doped LWIR HgCdTe detectors.

The metallic periodic bowtie structure is systematically investigated using a three-dimensional finite difference time domain (FDTD) method. The oscillating dipoles picture is proposed to explain the novel enhancement of localized near-field. It is indicated that the shift and the intensity change of notable resonant dips in the transmission spectrum result from the variation of localized surface plasmon resonance (LSPR) conditions due to the different geometrical sizes of the structure and the array periodicity. The results are helpful for guiding the bowtie structures to the application of the near-field imaging and sensing in the subwavelength optics.

The diamond abrasive particles were coated with the TiO 2 /Al 2 O 3 film by the sol–gel technique. Compared with the uncoated diamonds, the TiO 2 /Al 2 O 3 film was excellent material for the protection of the diamonds. The results showed that the incipient oxidation temperature of the TiO 2 /Al 2 O 3 film coated diamonds in air atmosphere was 775 °C, which was higher 175 °C than that of the uncoated diamonds. And the coated diamonds also had better the diamond's single particle compressive strength and the impact toughness than that of uncoated diamonds after sintering at 750 °C. For the vitrified bond grinding wheels, replacing the uncoated diamonds with the TiO 2 /Al 2 O 3 film coated diamonds, the volume expansion of the grinding wheels decreased from 6.2% to 3.4%, the porosity decreased from 35.7% to 25.7%, the hardness increased from 61.2 H RC to 66.5 H RC and the grinding ratio of the vitrified bond grinding wheels to carbide alloy (YG8) increased from 11.5 to 19.1.

This paper simulates a kind of new sub-50 nm n-type double gate MOS nanotransistors by solving coupled Poisson–Schrodinger equations in a self-consistent manner with a finite element method, and presents a systematic simulation-based study on quantum-mechanical effects, gate leakage current of FinFETs. The simulation results indicate that the deviation from the classical model becomes more important as the gate oxide, gate length and Fin channel width becomes thinner and the Fin channel doping increases. Gate tunneling current density reduces with the body thickness decreasing. Excessive scaling increases the gate current below Fin thickness of 5 nm. The gate current can be dramatically reduced beyond 1017 cm−3 with the Fin body doping increasing. In order to understand the influence of electron confinement, quantum mechanical simulation results are also compared with the results from the classical approach. Our simulation results indicate that quantum mechanical simulation is essential for the realistic optimization of the FinFET structure.

A metallodielectric photonic crystal with photonic band gaps in near infrared regime has been constructed using layer-by-layer stacking of two-dimensional micro-size metal-coated dielectric spheres array. In transmission spectra two photonic band gaps are observed at 1.38 μm and 2.46 μm, which are in agreement with theoretical calculations. Experimental results show that the photonic band gaps can be realized with about ten layers. The structure with metallic microspheres provides us a novel way for fabrication of near infrared metallic photonic crystals.