218 research outputs found
Demonstration of fine pitch FCOB (Flip Chip on Board) assembly based on solder bumps at Fermilab
Bump bonding is a superior assembly alternative compared to conventional wire
bond techniques. It offers a highly reliable connection with greatly reduced
parasitic properties. The Flip Chip on Board (FCOB) procedure is an especially
attractive packaging method for applications requiring a large number of
connections at moderate pitch. This paper reports on the successful
demonstration of FCOB assembly based on solder bumps down to 250um pitch using
a SUESS MA8 flip chip bonder at Fermilab. The assembly procedure will be
described, microscopic cross sections of the connections are shown, and first
measurements on the contact resistance are presented.Comment: 4 pages, 8 figure
Performance of prototype BTeV silicon pixel detectors in a high energy pion beam
The silicon pixel vertex detector is a key element of the BTeV spectrometer.
Sensors bump-bonded to prototype front-end devices were tested in a high energy
pion beam at Fermilab. The spatial resolution and occupancies as a function of
the pion incident angle were measured for various sensor-readout combinations.
The data are compared with predictions from our Monte Carlo simulation and very
good agreement is found.Comment: 24 pages, 20 figure
Beam Test of BTeV Pixel Detectors
The silicon pixel vertex detector is one of the key elements of the BTeV
spectrometer. Detector prototypes were tested in a beam at Fermilab. We report
here on the measured spatial resolution as a function of the incident angles
for different sensor-readout electronics combinations. We compare the results
with predictions from our Monte Carlo simulation.Comment: 7 pages, 5 figures, Invited talk given by J.C. Wang at "Vertex 2000,
9th International Workshop on Vertex Detectors", Michigan, Sept 10-15, 2000.
To be published in NIM
Search for flavor-changing neutral currents and lepton-family-number violation in two-body D0 decays
Results of a search for the three neutral charm decays, D0 -> mu e, D0 -> mu
mu, and D0 -> e e, are presented. This study was based on data collected in
Experiment 789 at the Fermi National Accelerator Laboratory using 800 GeV/c
proton-Au and proton-Be interactions. No evidence is found for any of the
decays. Upper limits on the branching ratios, at the 90% confidence level, are
obtained.Comment: 28 pages, 18 figures. Submitted to Physical Review
Beam Test Results of the BTeV Silicon Pixel Detector
The results of the BTeV silicon pixel detector beam test carried out at
Fermilab in 1999-2000 are reported. The pixel detector spatial resolution has
been studied as a function of track inclination, sensor bias, and readout
threshold.Comment: 8 pages of text, 8 figures, Proceedings paper of Pixel 2000:
International Workshop on Semiconductor Pixel Detectors for Particles and
X-Rays, Genova, June 5-8, 200
Hybrid electron spin resonance and whispering gallery mode resonance spectroscopy of Fe3+ in sapphire
The development of a new era of quantum devices requires an understanding of how paramagnetic dopants or impurity spins behave in crystal hosts. Here, we describe a spectroscopic technique which uses traditional electron spin resonance (ESR) combined with the measurement of a large population of electromagnetic whispering gallery modes. This allows the characterization of the physical parameters of paramagnetic impurity ions in the crystal at low temperatures. We present measurements of two ultrahigh-purity sapphires cooled to 20 mK in temperature, and determine the concentration of Fe3 ions and their frequency sensitivity to a dc magnetic field. Our method is different from ESR in that it is possible to track the resonant frequency of the ion from zero applied magnetic field to any arbitrary value, allowing excellent measurement precision. This high precision reveals anisotropic behavior of the Zeeman splitting. In both crystals, each Zeeman component demonstrates a different g factor
Crystal Phase Transitions in the Shell of PbS CdS Core Shell Nanocrystals Influences Photoluminescence Intensity
ABSTRACT We reveal the existence of two different crystalline phases, i.e., the metastable rock salt and the equilibrium zinc blende phase within the CdS shell of PbS CdS core shell nanocrystals formed by cationic exchange. The chemical composition profile of the core shell nanocrystals with different dimensions is determined by means of anomalous small angle X ray scattering with subnanometer resolution and is compared to X ray diffraction analysis. We demonstrate that the photoluminescence emission of PbS nanocrystals can be drastically enhanced by the formation of a CdS shell. Especially, the ratio of the two crystalline phases in the shell significantly influences the photoluminescence enhancement. The highest emission was achieved for chemically pure CdS shells below 1 nm thickness with a dominant metastable rock salt phase fraction matching the crystal structure of the PbS core. The metastable phase fraction decreases with increasing shell thickness and increasing Exchange times. The photoluminescence intensity depicts a constant decrease with decreasing metastable rock salt phase fraction but Shows an abrupt drop for shells above 1.3 nm thickness. We relate this effect to two different transition mechanisms for changing from the metastable rock salt phase to the equilibrium zinc blende phase depending on the shell thicknes
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