112,092 research outputs found
Zeeman splittings of the 5D0–7F2 transitions of Eu3+ ions implanted into GaN
We report the magnetic field splittings of emission lines assigned to the 5D0–7F2 transitions of Eu3+ centres in GaN. The application of a magnetic field in the c-axis direction (B||c) leads to a splitting of the major lines at 621 nm, 622 nm and 622.8 nm into two components. The Zeeman splitting is linear with magnetic field up to 5 Tesla for each line. In contrast, a magnetic field applied in the growth plane (B┴c) does not influence the photoluminescence spectra. The estimated g-factors vary slightly from sample to sample with mean values of g|| ~2.8, ~1.5 and ~2.0 for the emission lines at 621 nm, 622 nm and 622.8 nm respectively
New measurement of via neutron capture on hydrogen at Daya Bay
This article reports an improved independent measurement of neutrino mixing
angle at the Daya Bay Reactor Neutrino Experiment. Electron
antineutrinos were identified by inverse -decays with the emitted
neutron captured by hydrogen, yielding a data-set with principally distinct
uncertainties from that with neutrons captured by gadolinium. With the final
two of eight antineutrino detectors installed, this study used 621 days of data
including the previously reported 217-day data set with six detectors. The
dominant statistical uncertainty was reduced by 49%. Intensive studies of the
cosmogenic muon-induced Li and fast neutron backgrounds and the
neutron-capture energy selection efficiency, resulted in a reduction of the
systematic uncertainty by 26%. The deficit in the detected number of
antineutrinos at the far detectors relative to the expected number based on the
near detectors yielded in the
three-neutrino-oscillation framework. The combination of this result with the
gadolinium-capture result is also reported.Comment: 26 pages, 23 figure
Anharmonicity changes the solid solubility of an alloy at high temperatures
We have developed a method to accurately and efficiently determine the
vibrational free energy as a function of temperature and volume for
substitutional alloys from first principles. Taking TiAlN alloy as
a model system, we calculate the isostructural phase diagram by finding the
global minimum of the free energy, corresponding to the true equilibrium state
of the system. We demonstrate that the anharmonic contribution and temperature
dependence of the mixing enthalpy have a decisive impact on the calculated
phase diagram of a TiAlN alloy, lowering the maximum temperature
for the miscibility gap from 6560 K to 2860 K. Our local chemical composition
measurements on thermally aged TiAlN alloys agree with the
calculated phase diagram.Comment: 4 pages, 5 figures, supplementary materia
Polarisation Observations of HO 620.701 GHz Maser Emission with Herschel/HIFI in Orion KL
Context. The high intensities and narrow bandwidths exhibited by some
astronomical masers make them ideal tools for studying star-forming giant
molecular clouds. The water maser transition at
620.701 GHz can only be observed from above Earth's strongly absorbing
atmosphere; its emission has recently been detected from space. Aims. We sought
to further characterize the star-forming environment of Orion KL by
investigating the linear polarisation of a source emitting a narrow 620.701 GHz
maser feature with the heterodyne spectrometer HIFI on board the Herschel Space
Observatory. Methods. High-resolution spectral datasets were collected over a
thirteen month period beginning in 2011 March, to establish not only the linear
polarisation but also the temporal variability of the source. Results. Within a
uncertainty, no polarisation was detected to an upper limit of
approximately 2%. These results are compared with coeval linear polarisation
measurements of the 22.235 GHz maser line from
the Effelsberg 100-m radio telescope, typically a much stronger maser
transition. Although strongly polarised emission is observed for one component
of the 22.235 GHz maser at 7.2 km s, a weaker component at the same
velocity as the 620.701 GHz maser at 11.7 km s is much less polarised.Comment: Accepted for publication in A&
Europium doping of zincblende GaN by ion implantation
Eu was implanted into high quality cubic (zincblende) GaN (ZB-GaN) layers grown by molecular beam epitaxy. Detailed structural characterization before and after implantation was performed by x-ray diffraction (XRD) and Rutherford backscattering/channeling spectrometry. A low concentration ( direction, while a Ga substitutional site is observed for W-GaN:Eu. The implantation damage in ZB-GaN:Eu could partly be removed by thermal annealing, but an increase in the wurtzite phase fraction was observed at the same time. Cathodoluminescence, photoluminescence (PL), and PL excitation spectroscopy revealed several emission lines which can be attributed to distinct Eu-related optical centers in ZB-GaN and W-GaN inclusions
Alternative glues for the production of ATLAS silicon strip modules for the Phase-II upgrade of the ATLAS Inner Detector
The Phase-II upgrade of the ATLAS detector for the High Luminosity Large
Hadron Collider (HL-LHC) includes the replacement of the current Inner Detector
with an all-silicon tracker consisting of pixel and strip detectors. The
current Phase-II detector layout requires the construction of 20,000 strip
detector modules consisting of sensor, circuit boards and readout chips, which
are connected mechanically using adhesives. The adhesive between readout chips
and circuit board is a silver epoxy glue as was used in the current ATLAS
SemiConductor Tracker (SCT). This glue has several disadvantages, which
motivated the search for an alternative.
This paper presents a study concerning the use of six ultra-violet (UV) cure
glues and a glue pad for use in the assembly of silicon strip detector modules
for the ATLAS upgrade. Trials were carried out to determine the ease of use,
the thermal conduction and shear strength, thermal cycling, radiation hardness,
corrosion resistance and shear strength tests. These investigations led to the
exclusion of three UV cure glues as well as the glue pad.
Three UV cure glues were found to be possible better alternatives. Results
from electrical tests of first prototype modules constructed using these glues
are presented.Comment: 23 pages, to be published in Journal of Instrumentatio
Absorption resonance and large negative delay in Rb vapor with buffer gas
We observe a narrow, isolated, two-photon absorption resonance in Rb for
large one-photon detuning in the presence of a buffer gas. In the absence of
buffer gas, a standard Lambda configuration of two laser frequencies gives rise
to electromagnetically induced transparency (EIT) for all values of one-photon
detuning throughout the inhomogeneously (Doppler) broadened line. However, when
a buffer gas is added and the one-photon detuning is comparable to or greater
than the Doppler width, an absorption resonance appears instead of the usual
EIT resonance. We also observe large negative group delay (~ -300 us for a
Gaussian pulse propagating through the media with respect to a reference pulse
not affected by the media), corresponding to a superluminal group velocity v_g=
-c/(3.6x10^6)=-84 m/s.Comment: 4 pages, 5 figure
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