251 research outputs found
Temperature dependent metallic conductance above the mobility edge of a silicon inversion layer
The temperature dependence of the conductance of an n-type inversion layer on a (100) silicon surface has been examined between 1.4K and 4.2K at electron densities at which the Fermi level is close above the mobility edge of the lowest sub-band. It can be explained by assuming a separate band of localised bound states from which electrons are thermally excited into the extended states of the sub-band. The absence of any noticeable change in the conductivity mobility demonstrates that the nature of the electron transport is preserved when the conductivity is lowered from 8*10-5mho to 2*10-5mho
Thermally activated conductance of a silicon inversion layer by electrons excited above the mobility edge
The thermally activated conductivity sigma of an n-type inversion layer on a (100) oriented silicon surface and its derivative d sigma /dT were measured in the temperature range 1.4K-4.2K. Above T approximately=2.5K both the temperature dependence of (T/ sigma ) (d sigma /dT) and the relation between this quantity and sigma cannot be reconciled with a universal pre-exponential factor, i.e. the minimum metallic conductivity, but are shown to be satisfactorily described by a prefactor which is proportional to the temperature. The experimental results presented are consistent with activation of the number of mobile electrons above a mobility edge in the lowest sub-band, and indicate a mobility which is independent of both temperature and electron density
Detecting Casimir Forces through a Tunneling Electromechanical Transducer
We propose the use of a tunneling electromechanical transducer to dynamically
detect Casimir forces between two conducting surfaces. The maximum distance for
which Casimir forces should be detectable with our method is around m,
while the lower limit is given by the ability to approach the surfaces. This
technique should permit to study gravitational forces on the same range of
distances, as well as the vacuum friction provided that very low dissipation
mechanical resonators are used.Comment: 10 pages, revtex, 4 figures (not included
Reflectometric study of surface states and oxygen adsorption on clean Si(100) and (110) surfaces
External differential reflection measurements were carried out on clean Si(100) and (110) surfaces in the photon energy range of 1.0 to 3.0 eV at 300 and 80 K. The results for Si(100) at 300 K showed two peaks in the joint density of states curve, which sharpened at 80 K. One peak at 3.0 ± 0.2 eV can be attributed to optical transitions from a filled surface states band near the top of the valence band to empty bulk conduction band levels. The other peak at 1.60 ± 0.05 eV may be attributed to transitions to an empty surface states band in the energy gap. This result favours the asymmetric dimer model for the Si(100) surface. For the (110) surface at 300 K only one peak was found at 3.0 ± 0.2 eV. At 80 K the peak height diminished by a factor of two. Oxygen adsorption in the submonolayer region on the clean Si(100) surface appeared to proceed in a similar way as on the Si(111) 7 × 7 surface. For the Si(110) surface the kinetics of the adsorption process at 80 K deviated clearly. The binding state of oxygen on this surface at 80 K appeared to be different from that on the same surface at 300 K
A new "polarized version" of the Casimir Effect is measurable
We argue that the exactly computable, angle dependent, Casimir force between
parallel plates with different directions of conductivity can be measured.Comment: One Figure, 11 page
Casimir Energy of a Relativistic Perfect Fluid Confined to a D-dimensional Hypercube
Compact formulas are obtained for the Casimir energy of a relativistic
perfect fluid confined to a -dimensional hypercube with von Neumann or
Dirichlet boundary conditions. The formulas are conveniently expressed as a
finite sum of the well-known gamma and Riemann zeta functions. Emphasis is
placed on the mathematical technique used to extract the Casimir energy from a
-dimensional infinite sum regularized with an exponential cut-off. Numerical
calculations show that initially the Dirichlet energy decreases rapidly in
magnitude and oscillates in sign, being positive for even and negative for
odd . This oscillating pattern stops abruptly at the critical dimension of
D=36 after which the energy remains negative and the magnitude increases. We
show that numerical calculations performed with 16-digit precision are
inaccurate at higher values of .Comment: 20 pages, 4 figure
The electromagnetic field near a dielectric half-space
We compute the expectations of the squares of the electric and magnetic
fields in the vacuum region outside a half-space filled with a uniform
non-dispersive dielectric. This gives predictions for the Casimir-Polder force
on an atom in the `retarded' regime near a dielectric. We also find a positive
energy density due to the electromagnetic field. This would lead, in the case
of two parallel dielectric half-spaces, to a positive, separation-independent
contribution to the energy density, besides the negative, separation-dependent
Casimir energy. Rough estimates suggest that for a very wide range of cases,
perhaps including all realizable ones, the total energy density between the
half-spaces is positive.Comment: Latex2e, IOP macros, 15 pages, 2 eps figure
On the importance of testing gravity at distances less than 1cm
If the mechanism responsible for the smallness of the vacuum energy is
consistent with local quantum field theory, general arguments suggest the
existence of at least one unobserved scalar particle with Compton wavelength
bounded from below by one tenth of a millimeter. We show that this bound is
saturated if vacuum energy is a substantial component of the energy density of
the universe. Therefore, the success of cosmological models with a significant
vacuum energy component suggests the existence of new macroscopic forces with
range in the sub-millimeter region. There are virtually no experimental
constraints on the existence of quanta with this range of interaction.Comment: 9 pages TeX, 2 eps figures, uses mtexsis.tex and epsf.tex. Entry in
1996 Gravity Research Foundation essay competition. To be published in the
Journal of General Relativity and Gravitatio
Spectral representation of the Casimir Force Between a Sphere and a Substrate
We calculate the Casimir force in the non-retarded limit between a spherical
nanoparticle and a substrate, and we found that high-multipolar contributions
are very important when the sphere is very close to the substrate. We show that
the highly inhomegenous electromagnetic field induced by the presence of the
substrate, can enhance the Casimir force by orders of magnitude, compared with
the classical dipolar approximation.Comment: 5 page + 4 figures. Submitted to Phys. Rev. Let
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