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We report on the fabrication and characterization of synthesized multiwall MoS2 nanotube (NT) and nanoribbon (NR) field-effect transistors (FETs). The MoS2 NTs and NRs were grown by chemical transport, using iodine as a transport agent. Raman spectroscopy confirms the material as unambiguously MoS2 in NT, NR, and flake forms. Transmission electron microscopy was used to observe cross sections of the devices after electrical measurements and these were used in the interpretation of the electrical measurements, allowing the estimation of the current density. The NT and NR FETs demonstrate n-type behavior, with ON/OFF current ratios exceeding 10³, and with current densities of 1.02 μA/μm and 0.79 μA/μm at VDS = 0.3 V and VBG = 1V, respectively. Photocurrent measurements conducted on a MoS2 NT FET revealed short-circuit photocurrent of tens of nanoamps under an excitation optical power of 78 μW and 488 nm wavelength, which corresponds to a responsivity of 460 μA/W. A long channel transistor model was used to model the common-source characteristics of MoS2 NT and NR FETs and was shown to be consistent with the measured data. [ABSTRACT FROM AUTHOR]

The properties of multilayer exfoliated MoTe2 field-effect transistors (FETs) on SiO2 were investigated for channel thicknesses from 6 to 44 monolayers (MLs). All transistors showed p-type conductivity at zero back-gate bias. For channel thicknesses of 8 ML or less, the transistors exhibited ambipolar characteristics. ON/OFF current ratio was greatest, 1 × 105, for the transistor with the thinnest channel, 6 ML. Devices showed a clear photoresponse to wavelengths between 510 and 1080 nm at room temperature. Temperature-dependent current-voltage measurements were performed on a FET with 30 layers of MoTe2 . When the channel is turned-on and p-type, the temperature dependence is barrier-limited by the Au/Ti/MoTe2 contact with a hole activation energy of 0.13 eV. A long channel transistor model with Schottky barrier contacts is shown to be consistent with the common-source characteristics. [ABSTRACT FROM AUTHOR]

The spectral method is considered in solving boundary integral equations. By subtracting known solutions from the Helmholtz integral equation, the singularities of the Helmholtz integral equation are removed. Therefore, any order of basis functions, used in spectral methods, that times nonsingular kernels in the modified Helmholtz integral equation can be integrated easily and efficiently. Instead of solving the variables at collocation points using conventional methods, the generalized Fourier coefficients are solved by the spectral method which reduces the number of unknowns and the storage of matrix elements in computation. Scattering and radiation problems from a sphere are used to illustrate the technique in the present paper. © 1997 Acoustical Society of America. [ABSTRACT FROM AUTHOR]

A bounded form of the hypersingular Helmholtz integral equation for 3-D acoustic problems is developed in this paper. All integrals with singular kernels are regularized within each regular surface element, in the sense of Kellogg, with twice continuous differentiability. The standard Gaussian quadrature formula is applied without any special treatment for all the computational points. The collocation points are chosen to be the Gauss-Legendre nodes and no interpolation function is assumed for acoustic variables. © 1997 Acoustical Society of America. [ABSTRACT FROM AUTHOR]

In this article, a computational method is proposed for computing the Helmholtz integral equation for acoustic radiation and scattering problems with a three-dimensional body shape. Unlike the previous boundary element method, the integration of acoustic properties is based on the global body surface instead of local elements. The approximation function of body geometry and the weighting function of numerical integration are independently chosen. When the singular kernels of Helmholtz equation are regularized as bounded, discontinuous functions, the order of integration polynomials for acoustic properties can be arbitrarily chosen, therefore, the accuracy and efficiency of computation can be increased. © 1997 Acoustical Society of America. [ABSTRACT FROM AUTHOR]