9,484 research outputs found
Ultra-dense phosphorus in germanium delta-doped layers
Phosphorus (P) in germanium (Ge) delta-doped layers are fabricated in
ultra-high vacuum by adsorption of phosphine molecules onto an atomically flat
clean Ge(001) surface followed by thermal incorporation of P into the lattice
and epitaxial Ge overgrowth by molecular beam epitaxy. Structural and
electrical characterizations show that P atoms are confined, with minimal
diffusion, into an ultra-narrow 2-nm-wide layer with an electrically-active
sheet carrier concentration of 4x10^13 cm-2 at 4.2 K. These results open up the
possibility of ultra-narrow source/drain regions with unprecedented carrier
densities for Ge n-channel field effect transistors
Spontaneous breaking of time reversal symmetry in strongly interacting two dimensional electron layers in silicon and germanium
We report experimental evidence of a remarkable spontaneous time reversal
symmetry breaking in two dimensional electron systems formed by atomically
confined doping of phosphorus (P) atoms inside bulk crystalline silicon (Si)
and germanium (Ge). Weak localization corrections to the conductivity and the
universal conductance fluctuations were both found to decrease rapidly with
decreasing doping in the Si:P and Ge:P layers, suggesting an effect
driven by Coulomb interactions. In-plane magnetotransport measurements indicate
the presence of intrinsic local spin fluctuations at low doping, providing a
microscopic mechanism for spontaneous lifting of the time reversal symmetry.
Our experiments suggest the emergence of a new many-body quantum state when two
dimensional electrons are confined to narrow half-filled impurity bands
A program to develop a high-energy density primary battery with a minimum of 200 watt hours per pound of total battery weight Seventh quarterly report, Jan. 1 - Mar. 31, 1966
Cathodic materials for high energy density storage batter
Free-space quantum key distribution
A working free-space quantum key distribution (QKD) system has been developed
and tested over a 205-m indoor optical path at Los Alamos National Laboratory
under fluorescent lighting conditions. Results show that free-space QKD can
provide secure real-time key distribution between parties who have a need to
communicate secretly.Comment: 5 pages, 2 figures, 2 tables. To be published in Physical review A on
or about 1 April 199
Combinatorial Bounds and Characterizations of Splitting Authentication Codes
We present several generalizations of results for splitting authentication
codes by studying the aspect of multi-fold security. As the two primary
results, we prove a combinatorial lower bound on the number of encoding rules
and a combinatorial characterization of optimal splitting authentication codes
that are multi-fold secure against spoofing attacks. The characterization is
based on a new type of combinatorial designs, which we introduce and for which
basic necessary conditions are given regarding their existence.Comment: 13 pages; to appear in "Cryptography and Communications
Current-driven ferromagnetic resonance, mechanical torques and rotary motion in magnetic nanostructures
We study theoretically the detection and possible utilization of electric
current-induced mechanical torques in ferromagnetic-normal metal
heterostructures that are generated by spin-flip scattering or the absorption
of transverse spin currents by a ferromagnet. To this end, we analyze the DC
voltage signals over a spin valve that is driven by an AC current. In agreement
with recent studies, this "rectification", measured as a function of AC
frequency and applied magnetic field, contains important information on the
magnetostatics and --dynamics. Subsequently, we show that the vibrations
excited by spin-transfer to the lattice can be detected as a splitting of the
DC voltage resonance. Finally, we propose a concept for a spin-transfer-driven
electric nanomotor based on integrating metallic nanowires with carbon
nanotubes, in which the current-induced torques generate a rotary motion.Comment: This resubmission corrects typos in Appendix A 26 pages, 7 figure
Maximizing phonon thermal conductance for ballistic membranes
At low temperatures, phonon scattering can become so weak that phonon
transport becomes ballistic. We calculate the ballistic phonon conductance G
for membranes using elasticity theory, considering the transition from three to
two dimensions. We discuss the temperature and thickness dependence and
especially concentrate on the issue of material parameters. For all membrane
thicknesses, the best conductors have, counter-intuitively, the lowest speed of
sound.Comment: 4 pages, 4 figures, proceedings to phonons 2007 conferenc
A program to develop a high-energy density primary battery with a minimum of 200 watt hours per pound of total battery weight Eighth quarterly report, 1 Apr. - 30 Jun. 1966
Electrochemical characteristics of lithium in various electrolytes and magnesium in aluminum chloride-acetonitrile studied by voltammetric sweep metho
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