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We investigate the formations of wurtzite (WZ) SiC nano polytypes in zinc blende (ZB) SiC nanofilms hetero-grown on Si-(100) substrates via low pressure chemical vapor deposition (LPCVD) by adjusting the Si/C ratio of the introduced precursors. Through SEM, TEM, and Raman characterizations, we find that the nanofilms consist of discrete WZ SiC nano polytypes and ZB SiC polytypes composed of WZ polytypes (WZ + ZB) and disordered ZB SiC polytypes, respectively, according to Si/C ratios of 0.5, 1.5, and 3. We attribute the WZ polytype formation to being due to a kinetic mechanism based on the Si/C surface saturation control. [ABSTRACT FROM AUTHOR]

The high-resolution photoassociation spectrum of the ultracold cesium molecular 0u+ state below the 6S1/2 + 6P1/2 limit is presented in this paper. The saturation of the photoassociation scattering probability is observed from the dependence of the trap-loss probability on the photoassociation laser intensity. The corresponding resonant line width is also demonstrated to increase linearly with increasing photoassociation laser intensity. Our experimental data have good consistency with the theoretical saturation model of Bohn and Julienne [Bohn J L and Julienne P S 1999 Phys. Rev. A60 1]. [ABSTRACT FROM AUTHOR]

The infrared reflectance spectra of both 4H-SiC substrates and epilayers are measured in a wave number range from 400 cm-1 to 4000 cm-1 using a Fourier-transform spectrometer. The thicknesses of the 4H-SiC epilayers and the electrical properties, including the free-carrier concentrations and the mobilities of both the 4H-SiC substrates and the epilayers, are characterized through full line-shape fitting analyses. The correlations of the theoretical spectral profiles with the 4H-SiC electrical properties in the 30 cm-1-4000 cm-1 and 400 cm-1-4000 cm-1 spectral regions are established by introducing a parameter defined as error quadratic sum. It is indicated that their correlations become stronger at a higher carrier concentration and in a wider spectral region (30 cm-1-4000 cm-1). These results suggest that the infrared reflectance technique can be used to accurately determine the thicknesses of the epilayers and the carrier concentrations, and the mobilities of both lightly and heavily doped 4H-SiC wafers. [ABSTRACT FROM AUTHOR]

Evidences show that electric fields (EFs) induced by the magnetic stimulation could modulates brain activities by regulating the excitability of GABAergic interneuron. However, it is still unclear how and why the EF-induced polarization affects the interneuron response as the interneuron receives NMDA synaptic inputs. Considering the key role of NMDA receptor-mediated supralinear dendritic integration in neuronal computations, we suppose that the applied EFs could functionally modulate interneurons' response via regulating dendritic integration. At first, we build a simplified multi-dendritic circuit model with inhomogeneous extracellular potentials, which characterizes the relationship among EF-induced spatial polarizations, dendritic integration, and somatic output. By performing model-based singular perturbation analysis, it is found that the equilibrium point of fast subsystem can be used to asymptotically depict the subthreshold input–output (sI/O) relationship of dendritic integration. It predicted that EF-induced strong depolarizations on the distal dendrites reduce the dendritic saturation output by reducing driving force of synaptic input, and it shifts the steep change of sI/O curve left by reducing stimulation threshold of triggering NMDA spike. Also, the EF modulation prefers the global dendritic integration with asymmetric scatter distribution of NMDA synapses. Furthermore, we identify the respective contribution of EF-regulated dendritic integration and EF-induced somatic polarization to an action potential generation and find that they have an antagonistic effect on AP generation due to the varied NMDA spike threshold under EF stimulation. [ABSTRACT FROM AUTHOR]

Based on the nonlinear Schrödinger equation (NLSE) with damping, detuning, and driving terms describing the evolution of signals in a Kerr microresonator, we apply periodic nonlinear Fourier transform (NFT) to the study of signals during the generation of the Kerr optical frequency combs (OFCs). We find that the signals in different states, including the Turing pattern, the chaos, the single soliton state, and the multi-solitons state, can be distinguished according to different distributions of the eigenvalue spectrum. Specially, the eigenvalue spectrum of the single soliton pulse is composed of a pair of conjugate symmetric discrete eigenvalues and the quasi-continuous eigenvalue spectrum with eye-like structure. Moreover, we have successfully demonstrated that the number of discrete eigenvalue pairs in the eigenvalue spectrum corresponds to the number of solitons formed in a round-trip time inside the Kerr microresonator. This work shows that some characteristics of the time-domain signal can be well reflected in the nonlinear domain. [ABSTRACT FROM AUTHOR]

Carbon nanotubes (CNTs) have long been expected to be excellent nanochannels for use in desalination membranes and other bio-inspired human-made channels owing to their experimentally confirmed ultrafast water flow and theoretically predicted ion rejection. The correct classical force field potential for the interactions between cations and CNTs plays a crucial role in understanding the transport behaviors of ions near and inside the CNT, which is key to these expectations. Here, using density functional theory calculations, we provide classical force field potentials for the interactions of Na+/hydrated Na+ with (7,7), (8,8), (9,9), and (10,10)-type CNTs. These potentials can be directly used in current popular classical software such as nanoscale molecular dynamics (NAMD) by employing the tclBC interface. By incorporating the potential of hydrated cation-π interactions to classical all-atom force fields, we show that the ions will move inside the CNT and accumulate, which will block the water flow in wide CNTs. This blockage of water flow in wide CNTs is consistent with recent experimental observations. These results will be helpful for the understanding and design of desalination membranes, new types of nanofluidic channels, nanosensors, and nanoreactors based on CNT platforms. [ABSTRACT FROM AUTHOR]

We report a robust method of directly stabilizing a grating feedback diode laser to an arbitrary frequency in a large range. The error signal, induced from the difference between the frequency measured by a wavelength meter and the preset target frequency, is fed back to the piezoelectric transducer module of the diode laser via a sound card in the computer. A visual Labview procedure is developed to realize a feedback system. In our experiment the frequency drift of the diode laser is reduced to 8 MHz within 25 min. The robust scheme can be adapted to realize the arbitrary frequency stabilization for many other kinds of lasers. [ABSTRACT FROM AUTHOR]

Large-scale topography, such as a seamount, substantially impacts low-frequency sound propagation in an ocean waveguide, limiting the application of low-frequency acoustic detecting techniques. A three-dimensional (3D) coupled-mode model is developed to calculate the acoustic field in an ocean waveguide with seamount topography and analyze the 3D effect. In this model, a correction is introduced in the bottom boundary, theoretically making the acoustic field satisfy the energy conservation. Furthermore, a large azimuth angle calculation range is obtained by using the operator theory and higher-order Padé approximation. Additionally, the model has advantages related to the coupling mode and parabolic equation theory. The couplings corresponding to the effects of range-dependent environment are fully considered, and the numerical implementation is kept feasible. After verifying the accuracy and reliability of the model, low-frequency sound propagation characteristics in the seamount environment are analyzed. The results indicate lateral variability in bathymetry can lead to out-of-plane effects such as the horizontal refraction phenomenon, while the coupling effect tends to restore the abnormal sound field and produces acoustic field diffraction behind the seamount. This model effectively considers the effects of the horizontal refraction and coupling, which are proportional to the scale of the seamount. [ABSTRACT FROM AUTHOR]

4H-SiC junction barrier Schottky (JBS) diodes with a high-temperature annealed resistive termination extension (HARTE) are designed, fabricated and characterized in this work. The differential specific on-state resistance of the device is as low as 3.64 mΩ·cm2 with a total active area of 2.46 × 10−3 cm2. Ti is the Schottky contact metal with a Schottky barrier height of 1.08 V and a low onset voltage of 0.7 V. The ideality factor is calculated to be 1.06. Al implantation annealing is performed at 1250°C in Ar, while good reverse characteristics are achieved. The maximum breakdown voltage is 1000 V with a leakage current of 9 × 10−5 A on chip level. These experimental results show good consistence with the simulation results and demonstrate that high-performance 4H-SiC JBS diodes can be obtained based on the double HARTE structure. [ABSTRACT FROM AUTHOR]

10-kV 4H–SiC p-channel insulated gate bipolar transistors (IGBTs) are designed, fabricated, and characterized in this paper. The IGBTs have an active area of 2.25 mm2 with a die size of 3 mm × 3 mm. A step space modulated junction termination extension (SSM-JTE) structure is introduced and fabricated to improve the blocking performance of the IGBTs. The SiC p-channel IGBTs with SSM-JTE termination exhibit a leakage current of only 50 nA at −10 kV. To improve the on-state characteristics of SiC IGBTs, the hexagonal cell (H-cell) structure is designed and compared with the conventional interdigital cell (I-cell) structure. At an on-state current of 50 A/cm2, the voltage drops of I-cell IGBT and H-cell IGBT are 10.1 V and 8.3 V respectively. Meanwhile, on the assumption that the package power density is 300 W/cm2, the maximum permissible current densities of the I-cell IGBT and H-cell IGBT are determined to be 34.2 A/cm2 and 38.9 A/cm2 with forward voltage drops of 8.8 V and 7.8 V, respectively. The differential specific on-resistance of I-cell structure and H-cell structure IGBT are and , respectively. These results demonstrate that H-cell structure silicon carbide IGBT with SSM-JTE is a promising candidate for high power applications. [ABSTRACT FROM AUTHOR]

The sheet size of a graphene oxide (GO) can greatly influence its electrical, optical, mechanical, electrochemical and catalytic property. It is a key challenge to how to control the sheet size during its preparation in different application fields. According to our previous theoretical calculations of the effect of temperature on the oxidation process of graphene, we use Hummers method to prepare GOs with different sheet sizes by simply controlling the temperature condition in the process of the oxidation reaction of potassium permanganate (KMnO4) with graphene and the dilution process with deionized water. The results detected by transmission electron microscopy (TEM) and atomic force microscopy (AFM) show that the average sizes of GO sheets prepared at different temperatures are about 1 μm and 7 μm respectively. The ultraviolet–visible spectroscopy (UV-vis) shows that lower temperature can lead to smaller oxidation degrees of GO and less oxygen functional groups on the surface. In addition, we prepare GO membranes to test their mechanical strengths by ultrasonic waves, and we find that the strengths of the GO membranes prepared under low temperatures are considerably higher than those prepared under high temperatures, showing the high mechanical strengths of larger GO sheets. Our experimental results testify our previous theoretical calculations. Compared with the traditional centrifugal separation and chemical cutting method, the preparation process of GO by temperature control is simple and low-cost and also enables large-size synthesis. These findings develop a new method to control GO sheet sizes for large-scale potential applications. [ABSTRACT FROM AUTHOR]

The interface properties and electrical characteristics of the n-type 4H–SiC planar and trench metal–oxide–semiconductor (MOS) capacitors are investigated by measuring the capacitance voltage and current voltage. The flat-band voltage and interface state density are evaluated by the quasi-static method. It is not effective on further improving the interface properties annealing at 1250°C in NO ambient for above 1 h due to the increasing interface shallow and fast states. These shallow states reduce the effective positive fixed charge density in the oxide. For the vertical MOS capacitors on the () and () faces, the interface state density can be reduced by approximately one order of magnitude, in comparison to the result of the planar MOS capacitors on the (0001) face under the same NO annealing condition. In addition, it is found that Fowler–Nordheim tunneling current occurs at an oxide electric field of 7 MV/cm for the planar MOS device. However, Poole–Frenkel conduction current occurs at a lower electric field of 4 MV/cm for the trench MOS capacitor. This is due to the local field crowded at the trench corner severely causing the electrons to be early captured at or emitted from the SiO2/SiC interface. These results provide a reference for an in-depth understanding of the mobility-limiting factors and long term reliability of the trench and planar SiO2/SiC interfaces. [ABSTRACT FROM AUTHOR]

Annealing effects on structural and compositional performances of Al2O3 thin films on 4H–SiC substrates are studied comprehensively. The Al2O3 films are grown by atomic layer deposition through using trimethylaluminum and H2O as precursors at 300 °C, and annealed at various temperatures in ambient N2 for 1 min. The Al2O3 film transits from amorphous phase to crystalline phase as annealing temperature increases from 750 °C to 768 °C. The refractive index increases with annealing temperature rising, which indicates that densification occurs during annealing. The densification and grain formation of the film upon annealing are due to crystallization which is relative with second-nearest-neighbor coordination variation according to the x-ray photoelectron spectroscopy (XPS). Although the binding energies of Al 2p and O 1s increase together during crystallization, separations between Al 2p and O 1s are identical between as-deposited and annealed sample, which suggests that the nearest-neighbour coordination is similar. [ABSTRACT FROM AUTHOR]