325,516 research outputs found
An improved method for determining the inversion layer mobility of electrons in trench MOSFETs
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
In this article, we first derive the wavevector- and frequency-dependent,
microscopic current response tensor which corresponds to the "macroscopic"
ansatz and with wavevector- and frequency-independent,
"effective" material constants and
. 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
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,
. 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
It has been known for long that the fluctuation surface tension of membranes
, computed from the height fluctuation spectrum, is not equal to the bare
surface tension 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 , and the mechanical frame tension .
Using one-loop renormalisation calculations, we obtain, in addition to the
effective bending modulus , a new expression for the
effective surface tension where the projected cut-off area, and or 1
according to the allowed configurations. Moreover we show that the crumpling
transition for an infinite planar membrane occurs for , and
also that it coincides with vanishing Laplace and frame tensions. Using
extensive Monte Carlo (MC) simulations, triangulated membranes of vesicles made
of vertices are simulated. No local constraint is applied. It is
shown that the numerical is equal to both with radial MC
moves () and with corrected MC moves locally normal to the
fluctuating membrane (). For finite vesicles of typical size ,
two different regimes are defined: a tension regime for and a bending one for . 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 . We
propose that the buckling transition, observed for planar supported membranes
in the literature, occurs for , the associated
negative frame tension playing the role of a compressive force.Comment: to be published in Soft Matte
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