Atomic Physics Division
- The strategy of the Atomic Physics Division is to develop and apply
atomic physics research methods, and particulary the interaction between atoms
and electromagnetic fields, to achieve fundamental advances in measurement
science--some at the quantum limit--relevant to industry and the technical
community, and to produce and critically compile physical reference
data.
|
GOAL: To determine
atomic properties and
investigate fundamental
quantum interactions |
Strategic Focus Are: |
| |
First |
Light-Matter Interactions and
Atom Optics - to advance the physics of
electromagnetic-matter interactions and to explore new applications for laser
cooled and trapped atoms, to study exotic states of matter, and to study
and control many-body quantum systems. |
Second |
Nanoscale and Quantum Metrology - to advance measurement science at the
atomic and nanometer scale, focusing on ultraprecise length-displacement measurements, x-ray and gamma-ray precision metrology, and nanooptics and
nanosystems modeling. |
Third |
Critically Evaluated Atomic Data - to
produce reference data on atomic structure, to critically compile
reference data for scientific and technological applications, and to
develop techniques to apply the data to further the understanding of
important plasma devices. |
to produce reference
data on atomic structure, to critically compile reference
data for scientific and technological applications, and to
develop techniques to apply the data to further the
understanding of important plasma devices.
INTENDED OUTCOME AND
BACKGROUND
The objective of this strategic element
is to critically compile fundamental
constants and atomic spectroscopy data
from the far infrared to the x-ray spectral
regions. We disseminate these reference
data on the Physics Laboratory
website, produce high-quality data for
urgent scientific or technological needs,
and resolve discrepancies in the body
of the data. When reliable data do not
exist for high-priority needs, specific
measurements or calculations are undertaken to produce them.
The NIST databases for atomic spectra
and fundamental constants are recognized
throughout the world. The
Atomic Spectra Database on our website
now dispenses about 100,000 downloads
(answers) per month, up from
80,000 only two years ago. The
principal users are plasma physicists,
crystallographers, astronomers, lighting
engineers, and spectrochemists.
The newest version of the Atomic
Spectra Database significantly reduces
internal inconsistencies between atomic
energy levels and atomic transition frequencies
by merging older databases and
resolving and removing inconsistencies.
However, the databases remain far from
complete, and the quality of the data
available in the literature from which
the databases are built is still uneven.
The current versions of our databases
are not sufficiently reliable for some
fields of science and technology, and
needs for such reference data are continuously
growing. Our scientists focus
their resources on the most urgent needs
of the user communities.
Accomplishments
-
New Generation of Atomic
Spectra Database
Version 3.0 of the NIST Atomic Spectra
Database has been released, which contains
many new data and interface
improvements. Information is given for
the wavelengths, energy levels, transition
probabilities, Lande g-factors, and
ionization energies of many atoms and
ions. The Database now contains evaluated
data for over 100,000 spectral lines
and over 70,000 energy levels.
This new version is based on a relational
database management system, which
assures a high level of consistency and
integration of the data, as, for example,
for the information on the lines and levels
of a particular atom. New interface
features include instant access to bibliographic
references, dynamic transition
(Grotrian) diagrams, online generated
plots for spectral line identification, and
online generated plots for Saha/LTE
plasma emission spectra for arbitrary
electron temperature and density.
-
2002 CODATA
Recommended Fundamental
Constants
Based on work of the Fundamental
Constants Data Center of the Division,
the Committee on Data for Science
and Technology (CODATA) has recommended
for international use a new set
of values of the fundamental physical
constants and energy-related conversion factors.
The new set of values, termed the 2002 CODATA recommended
values, became available to the public
on December 8, 2003 at http://physics.nist.gov/constants.
A detailed paper on the data selection
and methodology of the adjustment is
due to be published in the Reviews of Modern Physics.
This review of the fundamental constants
provides recommended values and
their associated uncertainties, updating
the last review of 1998. Since then, new
methods have become competitive for
the determination of the Planck constant
h, the fine-structure constant α,
and the relative atomic mass of the electron
me; and there has been a dramatic
improvement in the measurement of the
Newtonian constant of gravitation G.
Two noteworthy additions in the 2002 adjustment are recommended
values for the bound-state RMS charge radii of the proton and deuteron,
and tests of the exactness of the Josephson and quantum-Hall-effect
relations KJ = 2e/h and
RK = h/e2,
where KJ and RK are the
Josephson and von Klitzing constants, respectively,
and e is the elementary charge.
This work has met with immediate acceptance by the scientific community.
The new values were published in the online August 2004 Physics Today
Buyer's Guide and in the 85th edition of
the CRC Handbook of Chemistry and Physics for 2004-2005.
Precision Measurement of
Reference Wavelengths for 193 nm Lithography
| |
Figure 7. High-resolution spectrum of iron,
germanium, and platinum, showing lines
measured as wavelength standards for lithography at 193 nm.
|
Some of the newest tools for microlithography
are based on the ArF excimer
laser, which emits radiation that can be
tuned over a narrow band near 193 nm.
In order to design systems that focus the
laser light onto substrate surfaces, lens
designers must know the index of refraction
of the optical materials to a high
degree of accuracy. Since the index of
refraction varies rapidly in this spectral
region, it is essential that the ArF laser
be stabilized at an accurately known wavelength.
In one method used to determine the
laser wavelength, the laser is observed
along with reference spectra of iron,
germanium, and platinum, excited in
hollow cathode discharge lamps. The
ArF laser wavelength is determined by
interpolation among the reference lines.
However, until now the wavelengths of
the reference lines were not known
sufficiently well to obtain the desired
accuracy for the laser wavelength.
By using a Fourier transform spectrometer
optimized for use in this region of
the ultraviolet, we have made precise
wavelength measurements for seven lines
of iron, germanium, and platinum that
span the tuning range of the ArF laser.
(See Fig. 7.) An overall relative uncertainty
of 3 × 10-8 was achieved. These
results will serve to determine the ArF
laser wavelength to the required accuracy.
The experiment was conducted in
collaboration with an excimer laser
manufacturer that supplies lasers for
microlithography applications, and the
results have been incorporated in a commercial laser system.
X-Ray Probes of Metal-Halide
Discharge Lamps
| |
Figure 8. X-ray mapping of plasma properties in
a metal-halide lamp. a) Temperature distribution
from x-ray absorption imaging. b) Spatial distribution
of atoms capable of emitting light from
x-ray induced fluorescence.
|
There are about one billion plasma light
sources in service in the United States,
consuming an estimated 2 exajoules
(600 billion kilowatt hours) of electrical
energy annually. These sources are principally
fluorescent lamps and metalhalide
discharge lamps. In the past,
metal-halide lamps were used mainly for
high-intensity lighting of large spaces.
Now, because of their high brightness
and energy efficiency, they are also being
developed for interior lighting. As a
result, there is growing interest in better
understanding the processes that govern
the operation of metal-halide lamps.
Advances in understanding can lead to
improved design rules, advanced production
methods, and eventually, more energy-efficient lighting.
We are developing new, noninvasive
techniques to map the temperature and
the spatial distribution of atomic and
molecular constituents in metal-halide
lamps. In experiments using the
Advanced Photon Source (APS) at the
Argonne National Laboratory, one of
the world's most brilliant sources of
x rays, we have observed x-ray absorption
and x-ray induced fluorescence in
operating lamps. (See Fig. 8.) The use
of x rays rather than light allows investigation
of advanced lamp designs having
high-temperature ceramic envelopes that
are translucent, in contrast to transparent quartz envelopes.
Some of these same techniques are now
being developed on a smaller scale at
NIST using a laboratory x-ray source.
This will make these new techniques
more accessible to the lighting industry.
Comprehensive Atomic
Spectral Data on Xenon and its Ions
Reliable spectroscopic data for xenon
and its ions are needed in order to
understand processes taking place in
many different types of electrical discharges,
such as those used for EUV microlithography and
the plasmas in new types of tokamaks. Although there
are numerous data for xenon in the
literature, they are scattered in a large
number of publications and can be difficult to locate.
A critical compilation was assembled for
the energy levels, spectral lines, and ionization
energies of the xenon atom and
all of its ions. This 157-page volume
includes 1600 energy levels and 4800
observed lines. The critical compilation
process collects the data, validates them
by using various comparisons and theoretical
calculations, and provides them
in a form that is available in print as
well as on the World Wide Web.
This compilation work was complemented
by an experiment that revealed,
for the first time, the detailed nature of
the spectrum of ten-times ionized xenon
at 13 nm, the region of prime interest
for EUV lithography. In this experiment,
xenon gas was puffed into a high
voltage spark, and the spectrum was
observed with a high-resolution spectrograph.
From Nanometers to
Megaparsecs: EBIT Data Applied to Disciplines
Spanning 30 Orders of Magnitude
With the recent addition of new measurement
capabilities, the EBIT facility
is attracting a wide range of customers
who need atomic data from HCIs. At
one extreme are the astrophysicists who
are trying to resolve puzzles associated
with observed line ratios in neon-like Fe
(Fe XVII). X-ray lines from this ion are
among the strongest to appear in many
spectra from space observatories such as
Chandra and XMM, but their utility as
remote diagnostics is being hampered
by inconsistencies across data sets.
Benchmark Fe XVII
data from our EBIT, previously reported in an
Astrophysical Journal Letter, has been
referenced several dozen times and has
stimulated a number of independent
experimental and theoretical studies
elsewhere. In the meantime, we have
installed a new x-ray microcalorimeter,
currently the best in the world by several
measures, to address new issues raised
by the recent theoretical work.
In a very different application, Intel and
International SEMATECH have asked
us to provide benchmark data on ten-times
ionized xenon, the initial ion of
choice for EUV lithography radiation
sources. (See Fig. 9.) This work was
stimulated by the needs of plasma modelers
who are being employed by the
semiconductor industry to ascertain
fundamental limits on output power
and to help achieve them. In connection
with this work, the leader of the Plasma
Radiation Group was appointed Chair
of the International SEMATECH
Fundamental Data Working Group and
co-chair (with Intel) of the 1st EUV
Source Modeling Workshop.
| |
Figure 9. EUV spectra of xenon, taken on the NIST EBIT.
The variation of spectral features as a function of the electron
beam energy provides valuable data for benchmarking models of the
atomic processes. |
First strategic focus |
Second strategic focus |
Third strategic focus
"Technical Activities 2004" - Table of Contents |
|
