Biscari P.,Polytechnic of Milan |
Urbano M.F.,SAES Getters |
Zanzottera A.,Polytechnic of Milan |
Zanzotto G.,University of Padua
Journal of Elasticity | Year: 2016
We develop a nonlinear, three-dimensional phase field model for crystal plasticity which accounts for the infinite and discrete symmetry group G of the underlying periodic lattice. This generates a complex energy landscape with countably-many G-related wells in strain space, whereon the material evolves by energy minimization under the loading through spontaneous slip processes inducing the creation and motion of dislocations without the need of auxiliary hypotheses. Multiple slips may be activated simultaneously, in domains separated by a priori unknown free boundaries. The wells visited by the strain at each position and time, are tracked by the evolution of a G-valued discrete plastic map, whose non-compatible discontinuities identify lattice dislocations. The main effects in the plasticity of crystalline materials at microscopic scales emerge in this framework, including the long-range elastic fields of possibly interacting dislocations, lattice friction, hardening, band-like vs. complex spatial distributions of dislocations. The main results concern the scale-free intermittency of the flow, with power-law exponents for the slip avalanche statistics which are significantly affected by the symmetry and the compatibility properties of the activated fundamental shears. © 2015, Springer Science+Business Media Dordrecht.
Hasegawa M.,CNRS Femto ST Institute |
Chutani R.K.,CNRS Femto ST Institute |
Gorecki C.,CNRS Femto ST Institute |
Boudot R.,CNRS Femto ST Institute |
And 4 more authors.
Sensors and Actuators, A: Physical | Year: 2011
This paper reports on the Si-glass anodic bonding process to fill micro Cs vapor cells with a buffer gas (Ar or Ne) at a controlled pressure (up to 20 kPa), which is one of the technological key steps to fabricate Cs vapor cells for miniature atomic clocks. In the atmosphere of these gases, the applicable bonding voltage was not high enough to achieve strong bonding because of the electrical breakdown caused by ionization of the gas. To improve the bonding quality, an original two-step anodic bonding method was proposed. The first step of the anodic bonding, which intends to pre-seal the gas in microcells, is carried out in the presence of a buffer gas by applying a voltage lower than the breakdown voltage. Subsequently, the second bonding is performed in air at sufficiently high voltages to improve the sealing quality. By employing optical spectroscopy, it was demonstrated that the cells maintain the buffer gas at an appropriate pressure for atomic clock operation. The accelerated aging tests show that Cs vapor as well as the buffer gas remained in the cells without any significant change in the pressure, which allow us to estimate the lifetime of the cells to be at least 3 years. Further CPT experiments revealed that the buffer-gas pressure change is less than 6.13 × 10-4 kPa throughout the aging test at 125 °C for more than 3 weeks. These results show that these microcells are appropriate for applications to atomic frequency references. © 2011 Elsevier B.V. All rights reserved.
Hasegawa M.,FEMTO ST Institute |
Chutani R.K.,FEMTO ST Institute |
Boudot R.,FEMTO ST Institute |
Mauri L.,SAES Getters |
And 3 more authors.
Journal of Micromechanics and Microengineering | Year: 2013
The wafer-level integration technique of PageWafer® (SAES Getters' solution for getter film integration into wafer to wafer bonded devices) has been tested in hermetically sealed miniature glass-Si-glass cells filled with Cs and Ne, e.g. for microelectromechanical systems (MEMS) atomic clock applications. Getter effects on the cell atmosphere are analyzed by quadruple mass spectroscopy and coherent population trapping (CPT) spectroscopy. The quadruple mass spectroscopy revealed that the residual gases (H2, O2, N2 and CO2) that are attributed to anodic bonding process are drastically reduced by the getter films while desirable gases such as Ne seem to remain unaffected. The impurity pressure in the getter-integrated cells was measured to be less than 4 × 10-2 mbar, i.e. pressure 50 times lower than the one measured in the cells without getter (2 mbar). Consequently, the atmosphere of the getter-integrated cells is much more pure than that of the getter-free cells. CPT signals obtained from the getter-integrated cells are stable and are, in addition, similar to each other within a cell batch, suggesting the strong potential of applications of this getter film and especially for its wafer-level integration to MEMS atomic clocks and magnetometers. © 2013 IOP Publishing Ltd.
Saes Getters | Date: 1997-08-12
Saes Getters | Date: 1996-10-15
non-melting, non-evaporating chemical getter materials for use in sorbing gasses.