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Material sputtering and erosion are key issue in fusion science. In the steady state, tungsten sputtering can be maintained at a low level. However, tungsten is seriously sputtered by the hot plasma from edge localized mode (ELM) bursts. The time evolution and spatial distribution of sputtering on the divertor gap are still not clear. This unclearness influences the understanding of ELM-induced sputtering and the explanation of experimental phenomenon. In this study, the evolution of tungsten flux generated by ELM burst is obtained via hybrid multiscale simulation and a double-peak of tungsten flux is found. The first peak is produced by the ELM electrons, which provides great sheath potential, and the second peak is generated by the energetic ions from ELM. The castellated divertor gap (CDG) can influence the tungsten sputtering distribution due to the change of the impacting angle. The sputtering and erosion on CDG are more serious than that on the mono-block top, but the tungsten source from the gap is very insignificant because the gap size is small. The simulation results are compared with EAST experiments and a qualitative consistency is obtained.

In our previous study, we introduced a machine learning technique, namely Cosmic Microwave Background Foreground Subtraction with Convolutional Neural Networks ( CMBFSCNN ), for the removal of foreground contamination in cosmic microwave background (CMB) polarization data. This method was successfully employed on actual observational data from the Planck mission. In this study, we extend our investigation by considering the CMB lensing effect in simulated data and utilizing the CMBFSCNN approach to recover the CMB lensing B-mode power spectrum from multifrequency observational maps. Our method is first applied to simulated data with the performance of the CMB-S4 experiment. We achieve reliable recovery of the noisy CMB Q (or U ) maps with a mean absolute difference of 0.016 ± 0.008 μ K (or 0.021 ± 0.002 μ K) for the CMB-S4 experiment. To address the residual instrumental noise in the foreground-cleaned map, we employ a “half-split maps” approach, where the entire data set is divided into two segments sharing the same sky signal but having uncorrelated noise. Using cross-correlation techniques between two recovered half-split maps, we effectively reduce instrumental noise effects at the power spectrum level. As a result, we achieve precise recovery of the CMB EE and lensing B-mode power spectra. Furthermore, we also extend our pipeline to full-sky simulated data with the performance of the LiteBIRD experiment. As expected, various foregrounds are cleanly removed from the foregrounds contamination observational maps, and recovered EE and lensing B-mode power spectra exhibit excellent agreement with the true results. Finally, we discuss the dependency of our method on the foreground models.

Edge-localized modes (ELMs) produce an intense transient heat flux on castellated divertor mono-blocks (MBs). The parallel transport of electrons and ions from the ELM burst varies due to their different velocities, which significantly influences the power load on the MBs. This study shows that two heat load phases are caused by an ELM burst. In the first phase, the horizontal surface withstands the intense heat flux because the faster electrons generate a high sheath potential drop. The leading edge of the MBs suffers a great power load from energetic ions in the second phase. This study applies a multiscale hybrid numerical approach to investigate the temporal evolution of heat flux on the poloidal gap from the ELM source in the scrape-off layer to the castellated divertor surface. Our results indicate that the power load on both the MB surface and the leading edge should be considered in the future design of castellated divertors.

In previous works, we proposed to estimate cosmological parameters with an artificial neural network (ANN) and a mixture density network (MDN). In this work, we propose an improved method called a mixture neural network (MNN) to achieve parameter estimation by combining ANN and MDN, which can overcome shortcomings of the ANN and MDN methods. Besides, we propose sampling parameters in a hyperellipsoid for the generation of the training set, which makes the parameter estimation more efficient. A high-fidelity posterior distribution can be obtained using ${ \mathcal O }({10}^{2})$ forward simulation samples. In addition, we develop a code named CoLFI for parameter estimation, which incorporates the advantages of MNN, ANN, and MDN, and is suitable for any parameter estimation of complicated models in a wide range of scientific fields. CoLFI provides a more efficient way for parameter estimation, especially for cases where the likelihood function is intractable or cosmological models are complex and resource-consuming. It can learn the conditional probability density p ( θ ∣ d ) using samples generated by models, and the posterior distribution p ( θ ∣ d _0 ) can be obtained for a given observational data d _0 . We tested the MNN using power spectra of the cosmic microwave background and Type Ia supernovae and obtained almost the same result as the Markov Chain Monte Carlo method. The numerical difference only exists at the level of ${ \mathcal O }({10}^{-2}\sigma )$ . The method can be extended to higher-dimensional data.

The lensing effect of the cosmic microwave background (CMB) is a powerful tool for our study of the distribution of matter in the universe. The quadratic estimator (QE) method, which is widely used to reconstruct lensing potential, has been known to be suboptimal for the low noise level polarization data from next-generation CMB experiments. To improve the performance of the reconstruction, other methods, such as the maximum-likelihood estimator and machine-learning algorithms, have been developed. In this work, we present a deep convolutional neural network model named the Residual Dense Local Feature U-net (RDLFUnet) for reconstructing the CMB lensing convergence field. By simulating lensed CMB data with different noise levels to train and test network models, we find that for noise levels less than 5 μ K-arcmin, RDLFUnet can recover the input gravitational potential with a higher signal-to-noise ratio than the previous deep-learning and traditional QE methods at almost the entire observation scale.

Primordial B -mode detection is one of the main goals of next-generation cosmic microwave background (CMB) experiments. Primordial B -modes are a unique signature of primordial gravitational waves (PGWs). However, the gravitational interaction of CMB photons with large-scale structures will distort the primordial E modes, adding a lensing B -mode component to the primordial B -mode signal. Removing the lensing effect (“delensing”) from observed CMB polarization maps will be necessary to improve the constraint of PGWs and obtain a primordial E -mode signal. Here, we introduce a deep convolutional neural network model named multi-input multi-output U-net (MIMO-UNet) to perform CMB delensing. The networks are trained on simulated CMB maps with size 20° × 20°. We first use MIMO-UNet to reconstruct the unlensing CMB polarization ( Q and U ) maps from observed CMB maps. The recovered E -mode power spectrum exhibits excellent agreement with the primordial EE power spectrum. The recovery of the primordial B -mode power spectrum for noise levels of 0, 1, and 2 μ K-arcmin is greater than 98% at the angular scale of ℓ < 150. We additionally reconstruct the lensing B map from observed CMB maps. The recovery of the lensing B -mode power spectrum is greater than roughly 99% at the scales of ℓ > 200. We delens the observed B -mode power spectrum by subtracting the reconstructed lensing B -mode spectrum. The recovery of tensor B -mode power spectrum for noise levels of 0, 1, and 2 μ K-arcmin is greater than 98% at the angular scales of ℓ < 120. Even at ℓ = 160, the recovery of tensor B -mode power spectrum is still around 71%.

Primordial B-mode detection is one of the main goals of current and future cosmic microwave background (CMB) experiments. However, the weak B-mode signal is overshadowed by several Galactic polarized emissions, such as thermal dust emission and synchrotron radiation. Subtracting foreground components from CMB observations is one of the key challenges in searching for the primordial B-mode signal. Here, we construct a deep convolutional neural network (CNN) model, called CMBFSCNN (Cosmic Microwave Background Foreground Subtraction with CNN), which can cleanly remove various foreground components from simulated CMB observational maps at the sensitivity of the CMB-S4 experiment. Noisy CMB Q (or U) maps are recovered with a mean absolute difference of 0.018 ± 0.023 μ K (or 0.021 ± 0.028 μ K). To remove the residual instrumental noise from the foreground-cleaned map, inspired by the needlet internal linear combination method, we divide the whole data set into two “half-split maps,” which share the same sky signal, but have uncorrelated noise, and perform a cross-correlation technique to reduce the instrumental noise effects at the power spectrum level. We find that the CMB EE and BB power spectra can be precisely recovered with significantly reduced noise effects. Finally, we apply this pipeline to current Planck observations. As expected, various foregrounds are cleanly removed from the Planck observational maps, with the recovered EE and BB power spectra being in good agreement with the official Planck results.

The lensing effect of the cosmic microwave background (CMB) is a powerful tool for our study of the distribution of matter in the universe. The quadratic estimator (QE) method, which is widely used to reconstruct lensing potential, has been known to be suboptimal for the low noise level polarization data from next-generation CMB experiments. To improve the performance of the reconstruction, other methods, such as the maximum-likelihood estimator and machine-learning algorithms, have been developed. In this work, we present a deep convolutional neural network model named the Residual Dense Local Feature U-net (RDLFUnet) for reconstructing the CMB lensing convergence field. By simulating lensed CMB data with different noise levels to train and test network models, we find that for noise levels less than 5 μ K-arcmin, RDLFUnet can recover the input gravitational potential with a higher signal-to-noise ratio than the previous deep-learning and traditional QE methods at almost the entire observation scale. [ABSTRACT FROM AUTHOR]

Global warming is often associated with changes in abiotic factors and the community composition across alpine ecosystems. However, the way that an altered community dynamics affects the ecosystem carbon (C) balance remains unclear. A warming experiment was initiated in 2010 to assess the potential impacts of warming-induced changes in the community composition and how these changes affect the C balance in mountain meadows located in the permafrost region of the Qinghai–Tibet Plateau (China). Under warming conditions, we found an increased importance value (IV) of forbs and grasses of 4.9%, in contrast to the IV of sedges, which decreased by 4.4%. For forbs and grasses, the IV showed positive exponential relationships with gross ecosystem production and ecosystem respiration, while negative correlations were found for sedges. These results indicate that a slight change in the IVs of sedges, grasses and forbs favors C sequestration. Moreover, the warming treatment significantly increased the mean height of sedges, grasses and forbs, and the net ecosystem exchange increase was positively correlated with the increase in the mean height of grasses and forbs. In summary, the warming-induced shift toward forb and grass species and the increase in plant height strengthen the C uptake capacity of alpine meadow ecosystems.

The weakly bound nucleus 29F locates near the neutron drip line. Experiments have confirmed that it is the heaviest two-neutron halo nucleus discovered up to now. To understand the halo structure in 29F, we explore the weakly bound and resonant levels close to the Fermi surface with the complex momentum representation method. Not only the narrow resonances and the broad resonances. Since the broad resonance 2 p 3/2 is disclosed, the p âˆ' f inversion and N = 20 shell gap quenching are found. The last valence neutron can occupy the weakly bound level 1/2[310], composed mainly of p 3/2â€"component, or the 1/2[211], composed mainly of s 1/2â€"component. Since the wavefunctions of p and s â€"components extend to a large range in the coordinate space, which results in the density distributions of the levels 1/2[310] and 1/2[211] being considerably diffuse. This is the most likely cause of halo formation in 29F and the halo may be formed by the p â€"component, s â€"component, or their mixtures by pairing correlations. [ABSTRACT FROM AUTHOR]

Two-dimensional electron gas (2DEG) with high electron mobility is highly desired to study the emergent properties and to enhance future device performance. Here we report the formation of 2DEG with high mobility at the interface between rock-salt BaO and perovskite SrTiO3. The interface consists of the ionically compensated BaO1 â€" δ layer and the electronically compensated TiO2 layer, which is demonstrated as a perfect interface without lattice mismatch. The so-formed interface features metallic conductivity with ultralow square resistance of 7.3 Ă— 10âˆ'4 Ω/â—» at 2 K and high residual resistance ratios R 300 K/ R 2 K up to 4200. The electron mobility reaches 69000 cm2â‹...Vâˆ'1â‹...sâˆ'1 at 2 K, leading to Shubnikovâ€"de Haas oscillations of resistance. Density functional theory calculations reveal that the effective charge transfers from BaO to the Ti 3 dxy orbital occur at the interface, leading to the conducting TiO2 layer. Our work unravels that BaO can adapt itself by removing oxygen to minimize the lattice mismatch and to provide substantial carriers to SrTiO3, which is the key to forming 2DEGs with high mobility at the interfaces. [ABSTRACT FROM AUTHOR]

An ultra-wideband 2-bit coding metasurface is designed for radar cross-section (RCS) reduction. The design process is presented in detail, in which a polarization conversion metasurface (PCM) is first proposed. The proposed PCM can realize ultra-wideband circular polarization (CP) maintaining reflection. Moreover, Pancharatnam-Berry (PB) phase will be generated in the co-polarized reflection coefficient by rotating the metallic patches in its unit cells. Thus, based on the PCM, the four coding elements of a 2-bit coding metasurface are constructed using PB phase, and an ultra-wideband PB 2-bit coding metasurface is proposed according to an appropriate coding sequence. The simulated and experimental results show that the coding metasurface has obvious advantages of wideband and polarization-insensitivity. Compared to a metallic plate of the same size, it can achieve more than 10 dB RCS reduction in the frequency band from 9.8 GHz to 42.6 GHz with a relative bandwidth of 125.2% under normal incidence with arbitrary polarizations. [ABSTRACT FROM AUTHOR]

In the framework of nonlinear wave optics, we report the evolution process of a dipole breathing wave in lossy nonlocal nonlinear media based on the nonlocal nonlinear Schrödinger equation. The analytical expression of the dipole breathing wave in such a nonlinear system is obtained by using the variational method. Taking advantage of the analytical expression, we analyze the influences of various physical parameters on the breathing wave propagation, including the propagation loss and the input power on the beam width, the beam intensity, and the wavefront curvature. Also, the corresponding analytical solutions are obtained. The validity of the analysis results is verified by numerical simulation. This study provides some new insights for investigating beam propagation in lossy nonlinear media [ABSTRACT FROM AUTHOR]

Small-scale magnetic fields are not only the fundamental element of the solar magnetism but also closely related to the structure of the solar atmosphere. The observations have shown that there is a ubiquitous tangled small-scale magnetic field with a strength of 60–130 G in the canopy-forming layer of the quiet solar photosphere. On the other hand, the multidimensional MHD simulations show that the convective overshooting expels the magnetic field to form the magnetic canopies at a height of about 500 km in the upper photosphere. However, the distribution of such small-scale "canopies" in the solar photosphere cannot be rigorously constrained by either observations or numerical simulations. Based on stellar standard models, we identify that these magnetic canopies can act as a global magnetic arch splicing layer, and we find that the reflections of the solar p-mode oscillations at this magnetic arch splicing layer result in significant improvement on the discrepancy between the observed and calculated p-mode frequencies. The location of the magnetic arch splicing layer is determined at a height of about 630 km, and the inferred strength of the magnetic field is about 90 G. These features of the magnetic arch splicing layer derived independently in the present study are quantitatively in agreement with the presence of small-scale magnetic canopies such as those obtained by the observations and 3D MHD simulations. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) van der Waals material is a focus of research for its widespread application in optoelectronics, memories, and spintronics. The ternary compound Nb2SiTe4 is a van der Waals semiconductor with excellent air stability and small cleavage energy, which is suitable for preparing a few layers counterpart to explore novel properties. Here, properties of bulk Nb2SiTe4 with large in-plane electrical anisotropy are demonstrated. It is found that hole carriers dominate at a temperature above 45 K with a carrier active energy of 31.3 meV. The carrier mobility measured at 100 K is about 213 cm2⋅V−1⋅s−1 in bulk Nb2SiTe4, higher than the reported results. In a thin flake Nb2SiTe4, the resistivity ratio between the crystalline axes of a and b is reaching about 47.3 at 2.5 K, indicating that there exists a large anisotropic transport behavior in their basal plane. These novel transport properties provide accurate information for modulating or utilizing Nb2SiTe4 for electronic device applications. [ABSTRACT FROM AUTHOR]

We investigate the structural variation and physical properties of layered La2M5As3O2 (M = Cu, Ni) compound upon Co doping. It is found that the substitution of Co ion just induces the monotonous change of lattice constants without observing the anomalous kink in superconducting La2(Cu1–xNix)5As3O2 solid-solutions. Meanwhile, this doping barely changes As–As bond length in [M5As3]2– subunit (±2%), being significantly smaller than 7% shrinkage of that in La2(Cu1–xNix)5As3O2. Therefore, the doping dependence of crystal structure exhibits similar trend with Ba1–xKxFe2As2 without the interference of As1–As2 bonding, implying that the Co substitution for Cu/Ni is hole-doped. In terms of physical property, La2(Cu1–xCox)5As3O2 turns into itinerant ferromagnetic metal, while La2(Ni1–xCox)5As3O2 shows paramagnetism and suppressed structural phase transition upon Co-doping. The distinct structural variation and absence of superconductivity provide important clues to understand the effect of As–As bond in [M5As3]2– subunit. [ABSTRACT FROM AUTHOR]

We demonstrate a broadband optical parametric oscillation, using a sheet cavity, via cavity phase-matching. A 21.2 THz broad comb-like spectrum is achieved, with a uniform line spacing of 133.0 GHz, despite a relatively large dispersion of 275.4 fs2/mm around 1064 nm. With 22.6% high slope efficiency, and 14.9 kW peak power handling, this sheet optical parametric oscillator can be further developed for χ(2) comb. [ABSTRACT FROM AUTHOR]

We present the superconducting (SC) property and high-robustness of structural stability of kagome CsV3Sb5 under in situ high pressures. For the initial SC-I phase, its Tc is quickly enhanced from 3.5 K to 7.6 K and then totally suppressed at P ∼ 10 GPa. With further increasing pressure, an SC-II phase emerges at P ∼ 15 GPa and persists up to 100 GPa. The Tc rapidly increases to the maximal value of 5.2 K at P = 53.6 GPa and slowly decreases to 4.7 K at P = 100 GPa. A two-dome-like variation of Tc in CsV3Sb5 is concluded here. The Raman measurements demonstrate that weakening of E2g mode and strengthening of E1g mode occur without phase transition in the SC-II phase, which is supported by the results of phonon spectra calculations. Electronic structure calculations reveal that exertion of pressure may bridge the gap of topological surface nontrivial states near EF, i.e., disappearance of Z2 invariant. Meanwhile, the Fermi surface enlarges significantly, consistent with the increased carrier density. The findings here suggest that the change of electronic structure and strengthened electron-phonon coupling should be responsible for the pressure-induced reentrant SC. [ABSTRACT FROM AUTHOR]

ZnGa2O4 films with different nitrogen impurity concentrations were deposited using radio frequency magnetron sputtering in an ammonia (NH3)/Ar gas mixture and were post-annealed at different temperatures, ranging from 600 °C to 900 °C, in NH3 atmosphere. The influence of ammonia partial pressure ratio and nitridation temperature on the microstructure, surface morphology, nitrogen doping profile, and optical properties has been investigated. The optical band gap of ZnGa2O4, under in-situ nitrogen-doping, decreases from 4.6 to 4.1 eV but the primitive ZnGa2O4 crystalline structure does not change. On nitridation, the optical band gap gradually decreases from 4.6 to 2.1 eV and the ZnGa2O4 changes into a zinc gallium oxynitride quaternary alloy structure. Secondary ion mass spectrometry analysis revealed that nitrogen atoms were uniformly distributed in the film. The narrowing, by more than 40%, of the optical band gap is attributed to the hybridization of Zn3d and N2p orbits promote p-d repulsion in the top of the valence band, and the formation of hexagonal wurtzite phase. [ABSTRACT FROM AUTHOR]

RT spin injection and optical polarization in nitride-based spin-LEDs are investigated. By employing CoFeB/MgO as the spin injector, the spin relaxation time and diffusion length in n-type GaN film are revealed to be 54.9 ps and 214.4 nm, respectively, through the three-terminal Hanle measurement. As the spin injector structure is applied to blue spin-LED, a maximal circular polarization of 3.3% is detected in electroluminescence, with the surface-emitting geometry and under a vertical magnetic field. UV spin-LED with n-Al0.05Ga0.95N transport layer is also fabricated, whose optical polarization is relatively smaller due to the larger spin–orbit coupling in Al atoms. [ABSTRACT FROM AUTHOR]

An ultra-wideband and high-efficiency reflective linear-to-circular polarization conversion metasurface is proposed. The proposed metasurface is composed of a square array of a corner-truncated square patch printed on grounded dielectric substrate and covered with a dielectric layer, which is an orthotropic anisotropic structure with a pair of mutually perpendicular symmetric axes u and v along the directions with the tilt angles of ±45° with respect to the vertical y axis. When the u- and v-polarized waves are incident on the proposed metasurface, the phase difference between the two reflection coefficients is close to –90° in an ultra-wide frequency band, so it can realize high-efficiency and ultra-wideband LTC polarization conversion under both x- and y-polarized incidences in this band. The proposed polarization conversion metasurface is simulated and measured. Both the simulated and measured results show that the axial ratio (AR) of the reflected wave is kept below 3 dB in the ultra-wide frequency band of 5.87 GHz–21.13 GHz, which is corresponding to a relative bandwidth of 113%; moreover, the polarization conversion rate (PCR) can be kept larger than 99% in a frequency range of 8.08 GHz–20.92 GHz. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) materials received large amount of studies because of the enormous potential in basic science and industrial applications. Monolayer Pd2Se3 is a fascinating 2D material that was predicted to possess excellent thermoelectric, electronic, transport, and optical properties. However, the fabrication of large-scale and high-quality monolayer Pd2Se3 is still challenging. Here, we report the synthesis of large-scale and high-quality monolayer Pd2Se3 on graphene-SiC (0001) by a two-step epitaxial growth. The atomic structure of Pd2Se3 was investigated by scanning tunneling microscope (STM) and confirmed by non-contact atomic force microscope (nc-AFM). Two subgroups of Se atoms have been identified by nc-AFM image in agreement with the theoretically predicted atomic structure. Scanning tunneling spectroscopy (STS) reveals a bandgap of 1.2 eV, suggesting that monolayer Pd2Se3 can be a candidate for photoelectronic applications. The atomic structure and defect levels of a single Se vacancy were also investigated. The spatial distribution of STS near the Se vacancy reveals a highly anisotropic electronic behavior. The two-step epitaxial synthesis and characterization of Pd2Se3 provide a promising platform for future investigations and applications. [ABSTRACT FROM AUTHOR]

The study of exotic nuclei is one of the most interesting topics in nuclear physics. 34Na has attracted additional attentions for an odd–odd nucleus with special structure. Here, we combine the complex momentum representation (CMR) and Green's function (GF) to establish the CMR-GF method for the exploration of exotic structure, such as halo, skin, the level inversion and so on, in 34Na. The available density distributions, the configuration occupations, and the root mean square radius for the orbit occupied by the last valence neutron suggest a p-wave single-neutron halo or skin structure in 34Na. [ABSTRACT FROM AUTHOR]

Using the first principle method, we investigate the influence of Sr/Ti ratio on the atomic structure and dislocation behavior of Srn+1TiO3n+1 (Ruddlesden-Popper phase) and SrnTin+1O3n+2 (Magnéli phase). A linear lattice expansion versus the Sr/Ti ratio exhibits in the Ruddlesden-Popper and Magnéli phases. The Ruddlesden-Popper phase has lower formation energy and superior structural stability than the Magnéli phase. The two phases show different dislocation behaviors and it is found that a possibly preferred slip system (110) {110} emerges in the two phases, and the dislocations are more likely to dissociate into partial dislocations in Magnéli phases. [ABSTRACT FROM AUTHOR]

The time evolution of populations of the ground state hyperfine Zeeman levels of 87Rb atoms is analyzed using the Runge-Kutta method for the case that a rubidium beam is optically pumped, under different conditions of polarization, with a weak monochromatic laser and an 87Rb lamp. On the base of the results above, the least estimated laser and 87Rb lamp power for the best population inversion is obtained, aiding further investigations. [ABSTRACT FROM AUTHOR]

We investigate the controllable group velocity of a microwave probe field in a superconductive quantum circuit (SQC) pumped by microwave fields, and the use of such a SQC function as an artificial Λ-type three-level atom. The exchange between the subluminal and the superluminal states of the probe field can be realized simply by sweeping the pumping intensity, and the superluminal state is usually realized with a lower absorption. This work is one of the efforts to extend the study of electromagnetically induced transparency and its related properties from the lightwave band to the microwave band. [ABSTRACT FROM AUTHOR]

We study two families of two-dimensional bright lattice solitons in photovoltaic-photorefractive crystals. It is shown that self-focusing and self-defocusing lattice solitons are possible only when their power level exceeds a critical threshold. It is found that self-focusing lattice solitons exist not only in the semi-infinite band gap, but also in the first band gap, whereas self-defocusing lattice solitons exist only in the first band gap. The structures of these lattice solitons are also analyzed. Our results indicate that a self-focusing lattice soliton in the semiinfinite band gap is more confined than in the first band gap so its tails in the first band gap occupy many lattice sites; when a self-defocusing lattice soliton is close to the second band, the self-defocusing lattice soliton is more confined so its tails occupy a few lattice sites [ABSTRACT FROM AUTHOR]

Bi4Si3O12 (BSO) is an excellent scintillation crystal, and is becoming the desirable candidate for dual-readout calorimeters in high-energy physics. In this work, high quality BSO crystals are successfully grown by the modified Bridgman method. For the first time, its mechanical and thermal properties are investigated and compared with those of the famous scintillation crystal Bi4Ge3O12 (BGO). The Vickers hardness and fracture toughness of BSO crystal are higher than those of BGO crystal. Its specific heat, thermal diffusivity and thermal conductivity are measured to be 0.319 J·g-1K-1, 1.54mm2·s-1 and 3.29W·m-1K-1 at 298 K, respectively. The average thermal expansion coefficient is calculated to be 7.07×10-6 K-1 from 300 to 1173 K. Compared with BGO crystal, BSO crystal possesses larger specific heat, thermal conductivity and smaller thermal expansion. These results indicate that BSO crystals possess better mechanical and thermal properties, which will benefit its practical applications. [ABSTRACT FROM AUTHOR]

We report the dc and rf performance of graphene rf field-effect transistors, where the graphene films are grown on copper by using the chemical vapour deposition (CVD) method and transferred to SiO2/Si substrates. Composite materials, benzocyclobutene and atomic layer deposition Al2O3 are used as the gate dielectrics. The observation of n- and p-type transitions verifies the ambipolar characteristics in the graphene layers. While the intrinsic carrier mobility of CVD graphene is extracted to be 1200 cm2/V·s, the parasitic series resistances are demonstrated to have a serious impact on device performance. With a gate length of 1 µm and an extrinsic transconductance of 72 mS/mm, a cutoff frequency of 6.6 GHz and a maximum oscillation frequency of 8.8 GHz are measured for the transistors, illustrating the potential of the CVD graphene for rf applications. [ABSTRACT FROM AUTHOR]

Wafer-scale graphene field-effect transistors are fabricated using benzocyclobutene and atomic layer deposition Al2O3 as the top-gate dielectric. The epitaxial-graphene layer is formed by graphitization of a 2-inch-diameter Si-face semi-insulating 6H-SiC substrate. The graphene on the silicon carbide substrate is heavily n-doped and current saturation is not found. For the intrinsic characteristic of this particular channel material, the devices cannot be switched off. The cut-off frequencies of these graphene field-effect transistors, which have a gate length of 1 μm, are larger than 800 MHz. The largest one can reach 1.24 GHz. There are greater than 95% active devices that can be successfully applied. We thus succeed in fabricating wafer-scale gigahertz graphene field-effect transistors, which paves the way for high-performance graphene devices and circuits. [ABSTRACT FROM AUTHOR]

This paper compares the properties of silicon oxide and nitride as host matrices for Er ions. Erbium-doped silicon nitride films were deposited by a plasma-enhanced chemical-vapour deposition system. After deposition, the films were implanted with Er3+ at different doses. Er-doped thermal grown silicon oxide films were prepared at the same time as references. Photoluminescence features of Er3+ were inspected systematically. It is found that silicon nitride films are suitable for high concentration doping and the thermal quenching effect is not severe. However, a very high annealing temperature up to 1200 degC is needed to optically activate Er3+, which may be the main obstacle to impede the application of Er-doped silicon nitride. [ABSTRACT FROM AUTHOR]

We have studied the optical matching layers (OMLs) and external quantum efficiency in the evanescent coupling photodiodes (ECPDs) integrating a diluted waveguide as a fibre-to-waveguide coupler, by using the semi-vectorial beam propagation method (BPM). The physical basis of OML has been identified, thereby a general designing rule of OML is developed in such a kind of photodiode. In addition, the external quantum efficiency and the polarization sensitivity versus the absorption and coupling length are analysed. With an optical matching layer, the absorption medium with a length of 30 mm could absorb 90% of the incident light at 1.55 mm wavelength, thus the total absorption increases more than 7 times over that of the photodiode without any optical matching layer. [ABSTRACT FROM AUTHOR]

This paper critically analyses and simulates the circuit configuration of the integral gated mode single photon detector which is proposed for eliminating the transient spikes problem of conventional gated mode single photon detector. The relationship between the values of the circuit elements and the effect of transient spikes cancellation has been obtained. With particular emphasis, the bias voltage of the avalanche photodiode and the output signal voltage of the integrator have been calculated. The obtained analysis results indicate that the output signal voltage of the integrator only relates to the total quantity of electricity of the avalanche charges by choosing the correct values of the circuit elements and integral time interval. These results can be used to optimize the performance of single photon detectors and provide guides for the design of single photon detectors. [ABSTRACT FROM AUTHOR]