5,114 research outputs found
Characterization of arsenic-rich waste slurries generated during gallium arsenide wafer lapping and polishing
The toxicology of gallium arsenide is well established; it is classified by the state of California as a known carcinogen. Consequently, environmental aspects of GaAs wafer manufacture are coming under greater scrutiny, with the cost of waste disposal becoming an economic issue for fabs operating under this jurisdiction. It is estimated that 85% of a GaAs boule is lost during manufacturing and device packaging, which usually ends up land filled as hazardous waste. This percentage is likely to increase as final wafer thickness is reduced to improve thermal dissipation. GaAs wafer backthinning and polishing generates waste slurries that are contaminated by arsenic and must be disposed of as hazardous waste. Although GaAs is largely insoluble in H2O, it is readily oxidized to soluble oxides and hydroxides, especially during chemo-mechanical polishing. Further, the valency state of the arsenic species determines the toxicity of effluent. Waste slurries from three sources were studied by ICP-MS and ICP-OES analysis to determine the amount of arsenic in the supernate and the form of the arsenic species. This data was related to mechanical lapping processes, such as the size distribution of particles in the slurry, and to the oxidation chemistry of the polishing processes. The analytical results provide guidance as to the most effective strategy to minimize the environmental impact of slurries produced during wafer thinning and polishing
Electron impact excitation rates for transitions in Mg V
Energy levels, radiative rates (A-values) and lifetimes, calculated with the
GRASP code, are reported for an astrophysically important O-like ion Mg~V.
Results are presented for transitions among the lowest 86 levels belonging to
the 2s2p, 2s2p, 2p, and 2s2p3 configurations.
There is satisfactory agreement with earlier data for most levels/transitions,
but scope remains for improvement. Collision strengths are also calculated,
with the DARC code, and the results obtained are comparable for most
transitions (at energies above thresholds) with earlier work using the DW code.
In thresholds region, resonances have been resolved in a fine energy mesh to
determine values of effective collision strengths () as accurately as
possible. Results are reported for all transitions at temperatures up to
10~K, which should be sufficient for most astrophysical applications.
However, a comparison with earlier data reveals discrepancies of up to two
orders of magnitude for over 60\% of transitions, at all temperatures. The
reasons for these discrepancies are discussed in detail.Comment: 11p of Text, 6 Tables and 6 Figures will appear in Canadian J.
Physics (2017
Radiative rates for E1, E2, M1, and M2 transitions in S-like to F-like tungsten ions (W LIX to W LXVI)
Calculations of energy levels, radiative rates and lifetimes are reported for
eight ions of tungsten, i.e. S-like (W LIX) to F-like (W LXVI). A large number
of levels has been considered for each ion and extensive configuration
interaction has been included among a range of configurations. For the
calculations, the general-purpose relativistic atomic structure package (GRASP)
has been adopted, and radiative rates (as well as oscillator strengths and line
strengths) are listed for all E1, E2, M1, and M2 transitions of the ions.
Comparisons have been made with earlier available experimental and theoretical
energies, although these are limited to only a few levels for most ions.
Therefore for additional accuracy assessments, particularly for energy levels,
analogous calculations have been performed with the flexible atomic code (FAC).Comment: 12 pages of Text + Tables A to Q and 1 to 16, will appear in ADNDT
(2016
Comment on "Multiconfiguration Dirac-Fock energy levels and radiative rates for Br-like tungsten" by S. Aggarwal, A.K.S. Jha, and M. Mohan [Can . J. Phys. 91 (2013) 394]
We report calculations of energy levels and oscillator strengths for
transitions in W XL, undertaken with the general-purpose relativistic atomic
structure package ({\sc grasp}) and flexible atomic code ({\sc fac}).
Comparisons are made with existing results and the accuracy of the data is
assessed. Discrepancies with the most recent results of S. Aggarwal et al.
[Can. J. Phys. {\bf 91} (2013) 394] are up to 0.4 Ryd and up to two orders of
magnitude for energy levels and oscillator strengths, respectively.
Discrepancies for lifetimes are even larger, up to four orders of magnitude for
some levels. Our energy levels are estimated to be accurate to better than 0.5%
(i.e. 0.2 Ryd), whereas results for oscillator strengths and lifetimes should
be accurate to better than 20%.Comment: Text 7p, Tables 4, will appear in Canadian Journal of Physics (2013
Radiative rates for E1, E2, M1, and M2 transitions in Br-like ions with 43 Z 50
Energies and lifetimes are reported for the eight Br-like ions with 43
Z 50, namely Tc ~IX, Ru~X, Rh~XI, Pd~XII, Ag~XIII, Cd~XIV, In~XV, and
Sn~XVI. Results are listed for the lowest 375 levels, which mostly belong to
the 4s4p, 4s4p4, 4s4p, 4s4p5,
4s4p4d, 4s4p4, and 4s4p5 configurations.
Extensive configuration interaction among 39 configurations (generating 3990
levels) has been considered and the general-purpose relativistic atomic
structure package ({\sc grasp}) has been adopted for the calculations.
Radiative rates are listed for all E1, E2, M1, and M2 transitions involving the
lowest 375 levels. Previous experimental and theoretical energies are available
for only a few levels of three, namely Ru~X, Rh~XI and Pd~XII. Differences with
the measured energies are up to 4\% but the present results are an improvement
(by up to 0.3 Ryd) in comparison to other recently reported theoretical data.
Similarly for radiative rates and lifetimes, prior results are limited to those
involving only 31 levels of the 4s4p, 4s4p4d, and
4s4pconfigurations for the last four ions. Moreover, there are generally no
discrepancies with our results, although the larger calculations reported here
differ by up to two orders of magnitude for a few transitions.Comment: Complete Tables 1-16 will soon appear in ADNDT. arXiv admin note:
substantial text overlap with arXiv:1504.0033
Radiative rates for E1, E2, M1, and M2 transitions in the Br-like ions Sr IV, Y V, Zr VI, Nb VII, and Mo VIII
Energies and lifetimes are reported for the lowest 375 levels of five Br-like
ions, namely Sr~IV, Y~V, Zr~VI, Nb~VII, and Mo~VIII, mostly belonging to the
4s4p, 4s4p4, 4s4p, 4s4p5,
4s4p4d, 4s4p4, and 4s4p5 configurations.
Extensive configuration interaction has been included and the general-purpose
relativistic atomic structure package ({\sc grasp}) has been adopted for the
calculations. Additionally, radiative rates are listed among these levels for
all E1, E2, M1, and M2 transitions. From a comparison with the measurements,
the majority of our energy levels are assessed to be accurate to better than
2\%, although discrepancies between theory and experiment for a few are up to
6\%. An accuracy assessment of the calculated radiative rates (and lifetimes)
is more difficult, because no prior results exist for these ions.Comment: 112 pages including 10 Tables, will appear in ADND
Energy levels, radiative rates, and lifetimes for transitions in W LVIII
Energy levels and radiative rates are reported for transitions in Cl-like W
LVIII. Configuration interaction (CI) has been included among 44 configurations
(generating 4978 levels) over a wide energy range up to 363 Ryd, and the
general-purpose relativistic atomic structure package ({\sc grasp}) adopted for
the calculations. Since no other results of comparable complexity are
available, calculations have also been performed with the flexible atomic code
({\sc fac}), which help in assessing the accuracy of our results. Energies are
listed for the lowest 400 levels (with energies up to 98 Ryd), which
mainly belong to the 3s3p, 3s3p, 3s3p3d,
3s3p3d, 3s3p3d, 3s3p3d, and 3p3d
configurations, and radiative rates are provided for four types of transitions,
i.e. E1, E2, M1, and M2. Our energy levels are assessed to be accurate to
better than 0.5%, whereas radiative rates (and lifetimes) should be accurate to
better than 20% for a majority of the strong transitions.Comment: About 12p of Text and 3 Tables which will be published in ADNDT
(2014
Radiative rates for E1, E2, M1, and M2 transitions among the 3s3p, 3s3p, and 3s3p3d configurations of Cl-like W LVIII
We report calculations of energy levels, radiative decay rates, and lifetimes
for transitions among the 3s3p, 3s3p, and 3s3p3d
configurations of Cl-like W LVIII. The general-purpose relativistic atomic
structure package (GRASP) has been adopted for our calculations. Comparisons
are made with the most recent results of Mohan et al. [Can. J. Phys. {\bf 92}
(2014) xxx] and discrepancies in lifetimes are noted, up to four orders of
magnitude in some instances. Our energy levels are estimated to be accurate to
better than 0.5\%, whereas results for radiative rates and lifetimes should be
accurate to better than 20\%.Comment: Will appear in Can J. Phys. 92 (2014) xxx. Text 21 pages including 5
Table
Electron impact excitation of N IV: calculations with the DARC code and a comparison with ICFT results
There have been discussions in the recent literature regarding the accuracy
of the available electron impact excitation rates (equivalently effective
collision strengths ) for transitions in Be-like ions. In the present
paper we demonstrate, once again, that earlier results for are
indeed overestimated (by up to four orders of magnitude), for over 40\% of
transitions and over a wide range of temperatures. To do this we have performed
two sets of calculations for N~IV, with two different model sizes consisting of
166 and 238 fine-structure energy levels. As in our previous work, for the
determination of atomic structure the GRASP (General-purpose Relativistic
Atomic Structure Package) is adopted and for the scattering calculations (the
standard and parallelised versions of) the Dirac Atomic R-matrix Code ({\sc
darc}) are employed. Calculations for collision strengths and effective
collision strengths have been performed over a wide range of energy (up to
45~Ryd) and temperature (up to 2.010~K), useful for applications in
a variety of plasmas. Corresponding results for energy levels, lifetimes and
A-values for all E1, E2, M1 and M2 transitions among 238 levels of N~IV are
also reported.Comment: This paper with 5 Figs. and 8 Tables will appear in MNRAS (2016
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