325,516 research outputs found

    An improved method for determining the inversion layer mobility of electrons in trench MOSFETs

    Get PDF
    For the first time trench sidewall effective electron mobility (/spl mu//sub eff/) values were determined by using the split capacitance-voltage (CV) method for a large range of transversal effective field (E/sub eff/) from 0.1 up to 1.4 MV/cm. The influences of crystal orientation, doping concentration and, for the first time, temperature were investigated. In conclusion, the results show that (1) the split CV method is an accurate method for determining /spl mu//sub eff/(E/sub eff/) data in trench MOSFETs, (2) the {100} /spl mu//sub eff/ data approach published data of planar MOSFETs for high E/sub eff/ and (3) the mobility behavior can be explained with generally accepted scattering models for the entire range of E/sub eff/. The results are important for the optimization of trench power devices

    Microscopic theory of refractive index applied to metamaterials: Effective current response tensor corresponding to standard relation n2=εeffμeffn^2 = \varepsilon_{\mathrm{eff}} \mu_{\mathrm{eff}}

    Full text link
    In this article, we first derive the wavevector- and frequency-dependent, microscopic current response tensor which corresponds to the "macroscopic" ansatz D=ε0εeffE\vec D = \varepsilon_0 \varepsilon_{\mathrm{eff}} \vec E and B=μ0μeffH\vec B = \mu_0 \mu_{\mathrm{eff}} \vec H with wavevector- and frequency-independent, "effective" material constants εeff\varepsilon_{\mathrm{eff}} and μeff\mu_{\mathrm{eff}}. We then deduce the electromagnetic and optical properties of this effective material model by employing exact, microscopic response relations. In particular, we argue that for recovering the standard relation n2=εeffμeffn^2 = \varepsilon_{\mathrm{eff}} \mu_{\mathrm{eff}} between the refractive index and the effective material constants, it is imperative to start from the microscopic wave equation in terms of the transverse dielectric function, εT(k,ω)=0\varepsilon_{\mathrm{T}}(\vec k, \omega) = 0. On the phenomenological side, our result is especially relevant for metamaterials research, which draws directly on the standard relation for the refractive index in terms of effective material constants. Since for a wide class of materials the current response tensor can be calculated from first principles and compared to the model expression derived here, this work also paves the way for a systematic search for new metamaterials.Comment: minor correction

    Fluctuation tension and shape transition of vesicles: renormalisation calculations and Monte Carlo simulations

    Full text link
    It has been known for long that the fluctuation surface tension of membranes rr, computed from the height fluctuation spectrum, is not equal to the bare surface tension σ\sigma introduced in the Helfrich theory. In this work we relate these two surface tensions both analytically and numerically and compare them to the Laplace tension γ\gamma, and the mechanical frame tension τ\tau. Using one-loop renormalisation calculations, we obtain, in addition to the effective bending modulus κeff\kappa_{\rm eff}, a new expression for the effective surface tension σeff=σϵkBT/(2ap)\sigma_{\rm eff}=\sigma - \epsilon k_{\rm B}T/(2a_p) where apa_p the projected cut-off area, and ϵ=3\epsilon=3 or 1 according to the allowed configurations. Moreover we show that the crumpling transition for an infinite planar membrane occurs for σeff=0\sigma_{\rm eff}=0, and also that it coincides with vanishing Laplace and frame tensions. Using extensive Monte Carlo (MC) simulations, triangulated membranes of vesicles made of N=1002500N=100-2500 vertices are simulated. No local constraint is applied. It is shown that the numerical rr is equal to σeff\sigma_{\rm eff} both with radial MC moves (ϵ=3\epsilon=3) and with corrected MC moves locally normal to the fluctuating membrane (ϵ=1\epsilon=1). For finite vesicles of typical size RR, two different regimes are defined: a tension regime for σ^eff=σeffR2/κeff>0\hat \sigma_{\rm eff}=\sigma_{\rm eff}R^2/\kappa_{\rm eff}>0 and a bending one for 1<σ^eff<0-1<\hat \sigma_{\rm eff}<0. A shape transition from a quasi-spherical shape imposed by the large surface energy, to more deformed shapes only controlled by the bending energy, is observed numerically at σ^eff0\hat \sigma_{\rm eff}\simeq 0. We propose that the buckling transition, observed for planar supported membranes in the literature, occurs for σ^eff1\hat \sigma_{\rm eff}\simeq-1, the associated negative frame tension playing the role of a compressive force.Comment: to be published in Soft Matte
    corecore