International Coordination of A+M Data Efforts
R.K. Janev (Panel Chair)1, K.H. Becker2,
R.E.H. Clark3,
G. Lister4, K. Niemax5
1International Atomic Energy Agency, Vienna, Austria
2Physics Department, Stevens Institute of Technology, Hoboken,
USA
3Los Alamos National Laboratory, Los Alamos, USA
4OSRAM Sylvania Inc., Beverly, USA
5Institute of Spectroscopy and Applied Spectroscopy, Dortmund,
Germany
Reproduced with permission from Atomic and Molecular Data and
Their Applications
edited by P.J. Mohr and W.L. Wiese
© 1998 American Institute of Physics, New York, Conference Proceeding #434
INTRODUCTION
A summary of the discussions at the ICAMDATA panel on international
coordination of atomic and molecular (A+M) data efforts is presented. The
status of databases and the needs for coordination of data generation,
compilation and assessment efforts in the areas of
spectrochemistry, low-temperature plasma applications, plasma processing
of materials, lighting industry and fusion energy research are specifically
addressed.
PANEL DISCUSSION
The progress in many scientific and technological areas in which atomic and
molecular processes play an important role depends on the availability of
accurate quantitative information on the collisional properties of these
processes and spectroscopic characteristics of interacting species. The
understanding of various astrophysical, atmospheric and biophysical
phenomena, or the development and optimization of various technological
processes and industrial devices relies on the knowledge of underlying physical
and chemical mechanisms and on a detailed modeling of the corresponding atomic
and molecular kinetics. The amount of required spectroscopic and collisional
information for complete understanding and successful description of
properties and behaviour of the gaseous and plasma media in natural or
industrial systems may be extremely large. The generation of this information,
either through compilation and critical assessment of the available literature
data or through new experimental measurements and theoretical calculations,
frequently appears to be an effort which is well beyond the capacity of a
scientific or industrial laboratory, group of such laboratories, or even a
nation. Astrophysics, fusion energy research, aeronomy and various
low-temperature industrial plasma applications (such as plasma processing
of materials, lighting devices, analytic spectrochemistry, etc) provide
examples of research and technological development areas in which the
establishment of required atomic and molecular databases needs coordination
of the corresponding efforts on a transnational level. The international
coordination of database establishment efforts in certain scientific or
applied research field accelerates the process of database establishment,
ensures the required scientific expertise for critical data assessment (and,
thereby, the high quality of the data), and considerably reduces the required
resources. Such collaborative efforts are advantageous also from technical
point of view (e.g., unification of data presentation formats and data
dissemination). Examples of very successful international database
establishment efforts can be found in astrophysics (the OPACITY and the IRON
projects), in magnetic fusion research (the AMDIS/ALADDIN and the ADAS
databases) and in the atmospheric research (earth atmosphere photochemistry).
The ICAMDATA panel discussions on the international coordination of A+M data
efforts focussed on the analysis of A+M data status and needs for coordination
in the fields of spectrochemistry, low-temperature plasma applications, plasma
processing of materials, lighting devices and controlled thermonuclear fusion.
The highlights and conclusions of these discussions are summarized below.
SPECTROCHEMICAL APPLICATIONS
Element analysis in spectrochemistry includes a wide range of measurement
techniques, such as optical emission spectrosmetry, atomic absorption
spectrometry, X-ray fluorescence, all of which involve a significant amount
of spectroscopic data information. In recent years, the optical spectrometer
in the techniques based on an inductively coupled plasma is more and more
frequently replaced by a mass spectrometer in order to lower the element
detection limits. Time-of-flight techniques have recently been also employed
in this field because they allow for a simultaneous elements analysis. Further,
the laser induced breakdown spectrometry, where a sample material is ablated by a
pulsed laser and the transient spectra of the laser produced plasma are
measured with intensified diode arrays or CCD - cameras attached to the
spectrometers, is currently considered as a very promising analytical
technique.
The spectroscopic data information associated with the application of the
above (and other, less standard) spectrochemical techniques is to a large
extent already available (mainly due to the activity of NIST/NBS data centres)
and includes: wavelengths and (source dependent) intensities of spectral
lines, energy levels, transition probabilities and lifetimes of atomic states,
hyperfine structure, isotope shifts and spectral line broadening and shifts
parameters. However, the spectroscopic data information for spectrochemical
applications is far from being complete. Wavelength and spectral line
intensity data are needed for metals and non-metals in the spectral range
150-800 nm (particularly for the weak lines which interfere with the strong
ones). Atomic state energy and transition probability data are still needed
for the species present in the analytical plasmas (for determining the plasma
parameters) and for the laser spectrometry.
International collaboration in completing the spectroscopic data information
required for advancing the spectrochemical analysis methods, as well as for
other applications, would certainly be very useful for meeting the needs in
a timely fashion. Such collaborations already exist on a bilateral level
(e.g., between NIST and JAERI), but a wider coordination of the data efforts
conducted in various national centres could be much more effective.
LOW-TEMPERATURE PLASMA TECHNOLOGIES
The use of non-equilibrium, low-temperature plasmas for materials processing
is the key to the advancement of many rapidly developing technologies. The
selective and highly anisotropic etching of materials and the controlled
deposition of thin films in the fabrication of microelectronic structures are
among the most important methods of plasma-assisted materials processing,
plasma polymerization and plasma-assisted surface modification. Plasma-based
processes are used in about 40 percent of the steps in the manufacture of
semiconductor chips and the more sophisticated the chip, the larger the number
of steps relying on plasma technology.
A low-temperature plasma is a system far from thermodynamic equilibrium. The
electron temperature is much higher than the gas temperature and can drive
"high-temperature" chemistry (without any adverse effects on the processed
materials). The high-energy tail of the electron energy distribution function
induces collisional break-up of the parent feedstock molecules which further
leads to formation of chemically active neutral and ionic radicals and to a
complex reaction kinetics. For modeling the behaviour and properties of such
chemically active plasmas, a detailed quantitative
information is required for the most important collisional and
radiative processes taking place both in the gas phase and on the surfaces.
The available data information depends on the specific technological plasma,
and in the case of plasma deposition applications (where Si-organic and
metal-organic compounds are used) the existing databases are particularly
scarce. The collisional and spectroscopic databases for most technological
plasma applications are inadequate for a full understanding of the corresponding plasma chemistry dynamics and full exploitation of the optimization potential
of these reactive plasmas. A coordinated international effort to improve the
current status of the A+M databases relevant to low-temperature plasmas used
in plasma processing applications would be extremely useful for advancement
of the corresponding technological development. The coordination effort
should include data generation (experimental and theoretical), data collection
and assessment, data distribution, as well as stronger interaction with the
relevant industrial partners and national funding agencies. Establishment
of an international data collection, evaluation and dissemination centre,
entrusted also with a coordinating role, would be an attractive organizational
form for such an effort.
LOW-TEMPERATURE PLASMA APPLICATIONS IN LIGHTING INDUSTRY
Lighting devices are one of the traditional and still a vigorously developing
field of low-temperature plasma applications. The gas discharges used in
lighting devices (fluorescent lamps, HID, barrier discharge lamps, flat
panel displays, etc) cover a wide range of plasma parameters, with electron
temperatures in the range 0.1 - 2 eV, electron densities around
10;i:;sup:11;/sup:;/i:-10;i:;sup:13;/sup:;/i: cm;i:;sup:-3;/sup:;/i: and gas pressures from about 3 torr (in the
fluorescent lamps) up to a few atmospheres (in HID lamps). The understanding
of the chemistry, dynamics and radiative properties of these plasmas,
required to optimize the device parameters (the most important of which are
the lamp efficiency and lifetime), relies on the knowledge of collisional
and spectroscopic characteristics of all relevant plasma constituents. This
understanding and the way to device optimization is achieved by detailed
plasma behaviour modeling and, in particular, calculation of level populations
of active gas atoms. Besides the knowledge of collisional and radiative
characteristics of plasma constituents, the plasma modeling requires also
knowledge of the electron energy distribution function, which in some cases
may not be Maxwellian (e.g., in barrier discharge lamps). Existence of a
high-energy tail in the electron energy distribution function requires
inclusion in the atomic database collisional and radiative processes
involving highly excited states, which results in a drastic increase of the
size of the database and the kinetic model calculations.
The recent developments in low pressure discharge technology for the lighting
industry (electrodeless devices, small diameter cold cathode discharges)
have led to new extensions of operating parameters of lighting devices with
involvement of new important collisional and radiative processes and new
working gas species (e.g., in the mercury free lamps). These developments
have further expanded the diversity and quantity of the required collisional and
spectroscopic information.
Despite the long and distinguished history of lighting research community
to establish the required atomic databases, the present status is still
unsatisfactory, particularly in view of new technology developments. A
broad scale and well coordinated joint effort of the A+M and lighting
research communities on establishing the required databases would be
highly desirable for the further development of light sources. The
establishment of such joint efforts, however, meets certain difficulties in
the area of the intellectual property rights.
FUSION ENERGY RESEARCH
The atomic and molecular collisional and radiative processes play an
important role in magnetic fusion devices as they influence the energy
balance of the confined plasma, the plasma transport and radiation
properties and are used as the basis for many plasma diagnostic methods.
The design and operation of some vital fusion device systems, such as
the neutral beam heating, the impurity control and the thermal power and
particle exhaust systems, require large amounts of atomic and molecular
collisional and radiative data. The overall A+M data information needed in
fusion energy research is enormous and the need for coordination of the
A+M data acquisition efforts on an international level has become evident
already at the beginning of seventies. In response to this need, the
International Atomic Energy Agency (IAEA) has established (1975) an activity
on compilation, evaluation and dissemination of A+M bibliographic and
numerical data for fusion and was charged (by the International Fusion
Research Council) to coordinate the national A+M data efforts for fusion.
Soon after, an international A+M Data Centre Network was established (with
participating data centres from USA, UK, Russia, Japan and France) which
presently includes about 15 data centres. Apart from coordinating the
activities of this Data Centre Network on the establishment of evaluated
and/or recommended international A+M
databases for fusion, the IAEA organizes and
supports additional international coordinated research programmes for
enhancing the A+M data generation for fusion. More than 40 laboratories and
theoretical groups are currently involved in the data generation (and
critical data assessment) effort. The results of the IAEA coordinated A+M
data activities for fusion are contained in the IAEA Atomic and Molecular
Data Information System (AMDIS), the databases of which are online accessible
(via Internet and WWW).
The establishment of the international A+M database for fusion is an example
(among many others) which illustrates the usefulness of the coordination of
A+M data efforts for creating a comprehensive database for certain field of
scientific or technological research. This example also reveals the
necessary conditions for a successful coordination of the A+M data efforts
on establishing a database for a research field (or a specific research
subject): (i) clear identification of the needs for such data (the users
community), (ii) identification of the research groups, laboratories or data
centres which jointly have the potential to provide (compile, evaluate and/or
generate) the required data, (iii) establishment of an effective mechanism
for work coordination, (iv) availability of adequate funds (normally
provided by the data users or national funding agencies) and (v) resolved
situation regarding the intellectual property rights.
GENERAL CONCLUSIONS
Although limited in the scope (due to the time constrains), the panel
discussions have shown that the A+M collisional and radiative processes play
an essential role in many modern science and technology areas and that the
quantitative information about these processes is instrumental for the further
progress in these areas. The research and development fields analysed
at the panel (spectrochemistry, industrial and technology plasma applications,
fusion energy research) have demonstrated that there are urgent needs for
establishing comprehensive and reliable A+M databases for the advancement
of these fields. Coordination of world-wide efforts on establishing such
databases is found to be advantageous for rapid and efficient achievement of
the development goals (as has been demonstrated in the case of fusion energy
research). The coordination of database establishment efforts in the areas
of industrial and technology plasma applications requires fulfillment of
certain conditions (see the last part of the previous section), the most
critical of which are those related to the funding and
intellectual properties rights.
The interaction and constructive dialogue of all factors involved in a
database establishment process may help in removing these difficulties.
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