6,690 research outputs found
Formation and stability of self-assembled coherent islands in highly mismatched heteroepitaxy
We study the energetics of island formation in Stranski-Krastanow growth
within a parameter-free approach. It is shown that an optimum island size
exists for a given coverage and island density if changes in the wetting layer
morphology after the 3D transition are properly taken into account. Our
approach reproduces well the experimental island size dependence on coverage,
and indicates that the critical layer thickness depends on growth conditions.
The present study provides a new explanation for the (frequently found) rather
narrow size distribution of self-assembled coherent islands.Comment: 4 pages, 5 figures, In print, Phys. Rev. Lett. Other related
publications can be found at http://www.fhi-berlin.mpg.de/th/paper.htm
Limits on Interactions between Weakly Interacting Massive Particles and Nucleons Obtained with NaI(Tl) crystal Detectors
Limits on the cross section for weakly interacting massive particles (WIMPs)
scattering off nucleons in the NaI(Tl) detectors at the Yangyang Underground
Laboratory are obtained with a 2967.4 kg*day data exposure. Nuclei recoiling
are identified by the pulse shape of scintillating photon signals. Data are
consistent with no nuclear recoil hypothesis, and 90% confidence level upper
limits are set. These limits partially exclude the DAMA/LIBRA region of
WIMP-sodium interaction with the same NaI(Tl) target detector. This 90%
confidence level upper limit on WIMP-nucleon spin-independent cross section is
3.26*10^-4 pb for a WIMP mass at 10 GeV/c^2
Pulse-shape discrimination between electron and nuclear recoils in a NaI(Tl) crystal
We report on the response of a high light-output NaI(Tl) crystal to nuclear
recoils induced by neutrons from an Am-Be source and compare the results with
the response to electron recoils produced by Compton scattered 662 keV
-rays from a Cs source. The measured pulse-shape discrimination
(PSD) power of the NaI(Tl) crystal is found to be significantly improved
because of the high light output of the NaI(Tl) detector. We quantify the PSD
power with a quality factor and estimate the sensitivity to the interaction
rate for weakly interacting massive particles (WIMPs) with nucleons, and the
result is compared with the annual modulation amplitude observed by the
DAMA/LIBRA experiment. The sensitivity to spin-independent WIMP-nucleon
interactions based on 100 kgyear of data from NaI detectors is estimated
with simulated experiments, using the standard halo model.Comment: 11page
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