120 research outputs found
Resonant Electron Attachment to Oxygen Impurities in Dense Neon Gas
No full textMeasurements of resonant electron attachment to
O2 impurities in dense Ne gas at moderately low temperature
T=80 K are here reported. The density-normalized attachment
frequency shows a peak at a specific density. The present data
are compared to previous results obtained in dense He gas at
similar temperatures. Similarly to the He case, the present data
are explained by assuming that the dense environment affects the
energetics of the quasi-free electrons
Resonant low-energy electron attachment to O2 impurities in dense neon gas
No full textWe report measurements of resonant low-energy electron attachment to O2 molecular impurities in neon gas in the temperature range 46.5 K T 101 K. The reduced attachment frequency shows a well defined peak as a function of the gas density N when the electron energy is resonant with the 4th vibrational level of O_2-. For 46.5K T8.4K a second peak has been detected at a much higher density, which is due to the formation of ions in the 5th vibrational level. The temperature dependence of the first peak position can be explained within an ionic bubble model by computing the electron excess free energy as a function of T and N. The peak shape is rationalized by taking into account the density dependent shift of the electron energy distribution function and the density of states of excess electrons in a disordered medium, and by assuming that electrons sample the gas density over a region of the order of the ionic bubble radius
Accurate electron drift mobility measurements in moderately dense helium gas at several temperatures
No full textWe report new accurate measurements of the drift mobility μ of quasifree electrons in moderately dense helium gas in the temperature range 26K ≤ T ≤ 300K for densities lower than those at which states of electrons localized in bubbles appear. By heuristically including multiple-scattering effects into classical kinetic formulas, as previously done for neon and argon, an excellent description of the field E, density N, and temperature T dependence of μ is obtained. Moreover, the experimental evidence suggests that the strong decrease of the zero-field density-normalized mobility μ0N with increasing N from the low up to intermediate density regime is mainly due to weak localization of electrons caused by the intrinsic disorder of the system, whereas the further decrease of μ0N for even larger N is due to electron self-trapping in cavities. We suggest that a distinction between weakly localized and electron bubble states can be done by inspecting the behavior of μ0N as a function of N at intermediate densities
Infrared and visible scintillation of Ho3+-doped YAG and YLF crystals
No full textIn our effort to develop a new kind of detector for low-energy, low-rate energy deposition events we have investigated the cathodo- and radioluminescence of Ho:YAG and Ho:YLF single crystals in an extended wavelength range from 200 nm to 2200 nm. The emission spectra of both crystals show a much more intense emission in the infrared range than in the visible one. We estimate an infrared light yield of several tens of photons/keV when exciting the crystals with X-rays of energy ≈ 30 keV. The main reason of this high value is due to the Ho3+ ions energy levels scheme that allows efficient cross relaxation processes to occur even at low dopant concentration
Undercut in a CF4-Based High-Pressure Poly-Si Plasma Etch
No full textThe behaviour of the plasma etching of polycrystalline Si (P-doped and undoped) in a CF4-based high-pressure glow discharge is studied as a function of the power density, of the exposed poly-Si surface area (the so called loading effect), of the flow rate of CF3Cl and of the flow rate of N2O and O2 as additive gases.
Partially in contrast with the current results reported in the literature, the experimental data here presented show that P-doped poly-Si is etched slower than undoped poly-Si in the mixture CF4+CF3Cl+N2O as well as in the mixture CF4+CF3Cl+O2, probably as a result of the different interaction mechanisms between substrate and gaseous reactants, which could be established at such high pressure and flowrate as in our experiment.
Furthermore, our data reveal that the lateral etch rate (or undercut) is critically determined by the effective concentration of atomic F.
Finally, we observed that CF3Cl has a clear anisotropic mechanism of etch
INFLUENCE OF THE DEMAGNETIZATION ON THE POLARIZATION OF THE THERMAL RDIATION EMITTED BY HOT COBALT WIRES
No full textThe polarization P of thermal radiation emitted by a hot cobalt wire in the temperature range from T � 400. K up to melting is studied for the first time. The radiation is linearly polarized perpendicularly to the wire. P decreases from 30 %. just above room temperature down to 6:5 % near melting and is continuous across the martensitic hcp fcc transition at Tm � 700 K and across the Curie point at Tc � 1400K. However, P shows a rapid decrease for T≳1000K and, contrary to previous measurements with tungsten wires, it hysteretically behaves if the temperature change is reversed. This behavior is rationalized by accounting for the thermal demagnetization of the wire with magnetic domain size change
Ions and electrons in liquid helium
No full textElectrons and ions have been used for over 40 years as probes to investigate the fascinating properties of helium liquids. The study of the transport properties of microscopic charge carriers sheds light on superfluidity, on quantum hydrodynamics, and on the interactions with collective excitations in quantum liquids. The structure of the probes themselves depends on their coupling with the liquid environment in a way that gives further insight into the microscopic behavior of the liquid in different thermodynamic conditions, such as in the superfluid phase, in the normal phase, or near the liquid-vapor critical point.
This book provides a comprehensive review of the experiments and theories of transport properties of charge carriers in liquid helium. It is a subject about which no other monograph exists to date. The book is intended for graduate and postgraduate students and for condensed matter physicists who will benefit from its completeness and accuracy
Cathodo- and radioluminescence of Tm3+: YAG and Nd3+: YAG in an extended wavelength range
No full textWe have studied the cathodo- and radioluminescence of Nd:YAG and of Tm:YAG single crystals in an extended wavelength range up to ≈5μm in view of developing a new kind of detector for low-energy, low-rate energy deposition events. Whereas the light yield in the visible range is as large as ≈104photons/MeV, in good agreement with literature results, in the infrared range we have found a light yield ≈5×104photons/MeV, thereby proving that ionizing radiation is particularly efficient in populating the low lying levels of rare earth doped crystals
Phase Difference-to-voltage Converter
No full textA phase difference‐to‐voltage converter has been developed in order to measure and to monitor the phase angle φ between the rotating magnetic field and the disk magnetization in the recently developed rotating magnetic disk viscometer. The circuit described here shows a very good linearity (the nonlinearity has been experimentally found to be well ≤50 p.p.m.), high resolution (fractional phase changes as low as Δφ/φ≊10−4 can be detected), very high short‐term stability (1/VφΔVφ/ΔT ≤10 p.p.m./°C), very good long‐term stability (ΔVφ/Vφ ≤50 p.p.m. over several months), and a rapid response even at the low frequencies (0.5–30 Hz) used in the viscometer
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