1,085 research outputs found
Microstructure, magneto-transport and magnetic properties of Gd-doped magnetron-sputtered amorphous carbon
The magnetic rare earth element gadolinium (Gd) was doped into thin films of
amorphous carbon (hydrogenated \textit{a}-C:H, or hydrogen-free \textit{a}-C)
using magnetron co-sputtering. The Gd acted as a magnetic as well as an
electrical dopant, resulting in an enormous negative magnetoresistance below a
temperature (). Hydrogen was introduced to control the amorphous carbon
bonding structure. High-resolution electron microscopy, ion-beam analysis and
Raman spectroscopy were used to characterize the influence of Gd doping on the
\textit{a-}GdC(:H) film morphology, composition, density and
bonding. The films were largely amorphous and homogeneous up to =22.0 at.%.
As the Gd doping increased, the -bonded carbon atoms evolved from
carbon chains to 6-member graphitic rings. Incorporation of H opened up the
graphitic rings and stabilized a -rich carbon-chain random network. The
transport properties not only depended on Gd doping, but were also very
sensitive to the ordering. Magnetic properties, such as the spin-glass
freezing temperature and susceptibility, scaled with the Gd concentration.Comment: 9 figure
Effect of Native Defects on Optical Properties of InxGa1-xN Alloys
The energy position of the optical absorption edge and the free carrier
populations in InxGa1-xN ternary alloys can be controlled using high energy
4He+ irradiation. The blue shift of the absorption edge after irradiation in
In-rich material (x > 0.34) is attributed to the band-filling effect
(Burstein-Moss shift) due to the native donors introduced by the irradiation.
In Ga-rich material, optical absorption measurements show that the
irradiation-introduced native defects are inside the bandgap, where they are
incorporated as acceptors. The observed irradiation-produced changes in the
optical absorption edge and the carrier populations in InxGa1-xN are in
excellent agreement with the predictions of the amphoteric defect model
The efficacy of low vision devices for students in specialized schools for students who are blind in Kathmandu Valley, Nepal
In Nepal, children with low vision attend specialized schools for students who are totally blind and are treated as if they were totally blind. This study identified children with low vision and provided low vision devices to them. Of the 22% of the students in the school who had low vision, 78.5% benefited from the devices. Proper devices and counseling improved the quality of life of a significant number of these students. ©2008 AFB, All Rights Reserved
Formation of diluted IIIâV nitride thin films by N ion implantation
iluted IIIâNââVâËâ alloys were successfully synthesized by nitrogen implantation into GaAs,InP, and AlyGa1âyAs. In all three cases the fundamental band-gap energy for the ion beam synthesized IIIâNââVâËâ alloys was found to decrease with increasing N implantation dose in a manner similar to that observed in epitaxially grownGaNâAs1âx and InNâPâËâalloys. In GaNâAsâËâ the highest value of x (fraction of âactiveâ substitutional N on As sublattice) achieved was 0.006. It was observed that NAs is thermally unstable at temperatures higher than 850â°C. The highest value of x achieved in InNâPâËâ was higher, 0.012, and the NP was found to be stable to at least 850â°C. In addition, the N activation efficiency in implantedInNâPâËâ was at least a factor of 2 higher than that in GaNâAsâËâ under similar processing conditions. AlyGa1âyNâAsâËâ had not been made previously by epitaxial techniques. N implantation was successful in producing AlyGa1âyNâAsâËâalloys. Notably, the band gap of these alloys remains direct, even above the value of y (y>0.44) where the band gap of the host material is indirect.This work was supported by the ââPhotovoltaic Materials
Focus Areaââ in the DOE Center of Excellence for the Synthesis
and Processing of Advanced Materials, Office of Science,
Office of Basic Energy Sciences, Division of Materials
Sciences under U.S. Department of Energy Contract No. DE-ACO3-76SF00098. The work at UCSD was partially supported
by Midwest Research Institute under subcontractor
No. AAD-9-18668-7 from NREL
Line Broadening and Decoherence of Electron Spins in Phosphorus-Doped Silicon Due to Environmental 29^Si Nuclear Spins
Phosphorus-doped silicon single crystals with 0.19 % <= f <= 99.2 %, where f
is the concentration of 29^Si isotopes, are measured at 8 K using a pulsed
electron spin resonance technique, thereby the effect of environmental 29^Si
nuclear spins on the donor electron spin is systematically studied. The
linewidth as a function of f shows a good agreement with theoretical analysis.
We also report the phase memory time T_M of the donor electron spin dependent
on both f and the crystal axis relative to the external magnetic field.Comment: 5 pages, 4 figure
High fidelity quantum memory via dynamical decoupling: theory and experiment
Quantum information processing requires overcoming decoherence---the loss of
"quantumness" due to the inevitable interaction between the quantum system and
its environment. One approach towards a solution is quantum dynamical
decoupling---a method employing strong and frequent pulses applied to the
qubits. Here we report on the first experimental test of the concatenated
dynamical decoupling (CDD) scheme, which invokes recursively constructed pulse
sequences. Using nuclear magnetic resonance, we demonstrate a near order of
magnitude improvement in the decay time of stored quantum states. In
conjunction with recent results on high fidelity quantum gates using CDD, our
results suggest that quantum dynamical decoupling should be used as a first
layer of defense against decoherence in quantum information processing
implementations, and can be a stand-alone solution in the right parameter
regime.Comment: 6 pages, 3 figures. Published version. This paper was initially
entitled "Quantum gates via concatenated dynamical decoupling: theory and
experiment", by Jacob R. West, Daniel A. Lidar, Bryan H. Fong, Mark F. Gyure,
Xinhua Peng, and Dieter Suter. That original version split into two papers:
http://arxiv.org/abs/1012.3433 (theory only) and the current pape
Host isotope mass effects on the hyperfine interaction of group-V donors in silicon
The effects of host isotope mass on the hyperfine interaction of group-V
donors in silicon are revealed by pulsed electron nuclear double resonance
(ENDOR) spectroscopy of isotopically engineered Si single crystals. Each of the
hyperfine-split P-31, As-75, Sb-121, Sb-123, and Bi-209 ENDOR lines splits
further into multiple components, whose relative intensities accurately match
the statistical likelihood of the nine possible average Si masses in the four
nearest-neighbor sites due to random occupation by the three stable isotopes
Si-28, Si-29, and Si-30. Further investigation with P-31 donors shows that the
resolved ENDOR components shift linearly with the bulk-averaged Si mass.Comment: 5 pages, 4 figures, 1 tabl
Application of Pulsed Field Gel Electrophoresis to Determine Îł-ray-induced Double-strand Breaks in Yeast Chromosomal Molecules
The frequency of DNA double-strand breaks (dsb) was determined in yeast cells exposed to Îł-rays under anoxic conditions. Genomic DNA of treated cells was separated by pulsed field gel electrophoresis, and two different approaches for the evaluation of the gels were employed: (1) The DNA mass distribution profile obtained by electrophoresis was compared to computed profiles, and the number of DSB per unit length was then derived in terms of a fitting procedure; (2) hybridization of selected chromosomes was performed, and a comparison of the hybridization signals in treated and untreated samples was then used to derive the frequency of dsb
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