12 research outputs found
The upgrade of the ALICE TPC with GEMs and continuous readout
The upgrade of the ALICE TPC will allow the experiment to cope with the high interaction rates foreseen for the forthcoming Run 3 and Run 4 at the CERN LHC. In this article, we describe the design of new readout chambers and front-end electronics, which are driven by the goals of the experiment. Gas Electron Multiplier (GEM) detectors arranged in stacks containing four GEMs each, and continuous readout electronics based on the SAMPA chip, an ALICE development, are replacing the previous elements. The construction of these new elements, together with their associated quality control procedures, is explained in detail. Finally, the readout chamber and front-end electronics cards replacement, together with the commissioning of the detector prior to installation in the experimental cavern, are presented. After a nine-year period of R&D, construction, and assembly, the upgrade of the TPC was completed in 2020.publishedVersio
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Calculated angular distribution of fragment ions from polyatomic-ion collisions
The angular distribution of ion fragments from dissociation collisions of ions with molecular ions is discussed, and results are given for the fragments of nitromethane molecular ion. (WHK
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MEMS sensors and wireless telemetry for distributed systems
Selectively coated cantilevers are being developed at ORNL for chemical and biological sensing. The sensitivity can exceed that of other electro-mechanical devices as parts-per-trillion detection can be demonstrated for certain species. The authors are now proceeding to develop systems that employ electrically readable microcantilevers in a standard MEMS process and standard CMOS processes. One of their primary areas of interest is chemical sensing for environmental applications. Towards this end, they are presently developing electronic readout of a mercury-sensitive coated cantilever. In order to field arrays of distributed sensors, a wireless network for data reporting is needed. For this, the authors are developing on-chip spread-spectrum encoding and modulation circuitry to improve the robustness and security of sensor data in typical interference- and multipath-impaired environments. They have also provided for a selection of distinct spreading codes to serve groups of sensors in a common environment by the application of code-division multiple-access techniques. Most of the RF circuitry they have designed and fabricated in 0.5 {micro}m CMOS has been tested and verified operational to above 1 GHz. The initial intended operation is for use in the 915 MHz Industrial, Scientific, and Medical (ISM) band. This paper presents measured data on the microcantilever-based mercury detector. They also present design data and measurements of the RF telemetry chip
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New insights into the kinetics of the stress-driven 2D to 3D transition
The authors have systematically investigated the morphological evolution of Ge{sub 0.5}Si{sub 0.5} strained films during post-growth annealing. The changes of the surface structure are found to follow the kinetic route of strain relaxation at different stages. A number of interesting features are revealed, which include the existence of an energy barrier to the 2D/3D transition, and a self-limiting effect in the growth kinetics of strained 3D islands. They demonstrate that the annealing approach provides a new way to grow coherent islands with uniform size
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Triangular step instability and 2D/3D transition during the growth of strained Ge films on Si(100)
We show that an activation energy barrier exists to the formation of wavy step edges due to stress-driven 2D instability. The barrier height and the barrier width depend sensitively on the surface stress anisotropy and step free energy. The large misfit strain of Ge films significantly reduces the barrier by lowering the S{sub B} step energy, inducing S{sub A} steps to undergo a triangular instability even during low temperature growth of Ge on Si(100). The step instability results in a novel arrangement of stress domains, and the interaction between the domains causes a spatial variation of surface strain with a surprisingly large influence on the energy barrier for island nucleation. Calculations indicate a dramatic enhancement in the nucleation of 3D islands at the apex regions of triangular steps, in good agreement with our experimental measurements
Au/Si(111) and the formation of silicides at the interface examined by spin-resolved photoemission
Vogt B, Stoppmanns P, Schmiedeskamp B, Heinzmann U. Au/Si(111) and the formation of silicides at the interface examined by spin-resolved photoemission. Applied Physics A: Materials Science and Processing. 1991;52(5):323-327
The upgrade of the ALICE TPC with GEMs and continuous readout
The upgrade of the ALICE TPC will allow the experiment to cope with the high interaction rates foreseen for the forthcoming Run 3 and Run 4 at the CERN LHC. In this article, we describe the design of new readout chambers and front-end electronics, which are driven by the goals of the experiment. Gas Electron Multiplier (GEM) detectors arranged in stacks containing four GEMs each, and continuous readout electronics based on the SAMPA chip, an ALICE development, are replacing the previous elements. The construction of these new elements, together with their associated quality control procedures, is explained in detail. Finally, the readout chamber and front-end electronics cards replacement, together with the commissioning of the detector prior to installation in the experimental cavern, are presented. After a nine-year period of R&D, construction, and assembly, the upgrade of the TPC was completed in 2020