Composition
and reactions of
atmospheric aerosol particles
Microscopic aerosol particles in the
atmosphere contain carbonaceous components from mineral dust
and combustion emissions released from around the world. How
long these tiny particles remain in the atmosphere can have
a huge impact on the global climate. Measurements based on
high-resolution scanning transmission x-ray images obtained
at the ALS have revealed chemical reactions on and in atmospheric
aerosol particles that caused particle growth while changing
organic composition by 13 to 24% per day, an oxidation rate
significantly slower than is currently used in atmospheric
models. Since oxidation has a strong effect on particle lifetime
in the atmosphere, these results will help climate scientists
refine the computer models used to predict climate change.
Full
story.
Publication about this research: S.F.
Maria, L.M. Russell, M.K. Gilles, and S.C.B. Myneni, "Organic
aerosol growth mechanisms and their climate forcing implications,"
Science 306, 1921 (2004).
Contact: Lynn Russell, lmrussell@ucsd.edu
A hollow-ion
resonance of
unprecedented strength
A so-called hollow ion is formed when
core electrons are removed or excited to higher energy levels,
leaving an empty inner shell. Such states can be produced
in He–, a fundamental three-electron system
and prototypical negative ion. The nuclear Coulomb attraction
is efficiently screened in negative ions, greatly enhancing
the effects that the electrons have on each other and providing
an ideal opportunity to verify and further motivate theoretical
models of electron correlation. Our understanding of these
basic interactions can elucidate processes of importance in
many fields, from the interpretation of cosmic spectra to
x-ray lasing efforts using inner-shell ionization and hollow-ion
formation. At the Ion-Photon Beamline at the ALS, researchers
have detected in negative helium ions a resonant simultaneous
double-Auger decay of unprecedented strength, evidence of
a triply excited hollow-ion state that has eluded observation
for 25 years. Full
story.
Publication about this research: R.C.
Bilodeau, J.D. Bozek, A. Aguilar, G.D. Ackerman, G. Turri,
and N. Berrah, "Photoexcitation of He–
hollow-ion resonances: Observation of the 2s2p2
4P state," Phys. Rev. Lett. 93,
193001 (2004).
Contact: Rene C. Bilodeau, RCBilodeau@lbl.gov
Flame chemistry
discovery makes
cover of Science Magazine
 Work
done using the flame chamber at Chemical Dynamics Beamline
9.0.2 was featured on the cover of the June 24 issue of Science
Magazine. An international team of researchers was surprised
to detect, for the first time, a type of organic compound
called enols among the hundreds of intermediate chemical species
that form when various types of hydrocarbon fuel is burned.
The detection of enols hinges on the ability to distinguish
between different isomers—molecules with identical composition
but different structure. Enols are less-stable isomers of
carbonyl (keto) compounds, which are well-known combustion
intermediates. The technique used at Beamline 9.0.2 capitalizes
on the fact that different isomers have different ionization
energies. Tunable VUV light is used to ionize the molecules
emitted by a laminar "flat flame" burner. The photoions
are then collected and analyzed using time-of-flight mass
spectrometry. The results indicate a rich and previously unsuspected
enol chemistry in a wide range of combustion systems. The
discovery will have considerable impact on prevailing models
of hydrocarbon oxidation and could someday lead to cleaner-burning
fuels, more efficient engines, and enhanced modeling of planetary
atmospheres and interstellar chemistry.
C.A. Taatjes, N. Hansen, A. McIlroy,
J.A. Miller, J.P. Senosiain, S.J. Klippenstein, F. Qi, L.
Sheng, Y. Zhang, T.A. Cool, J. Wang, P.R. Westmoreland, M.E.
Law, T. Kasper, and K. Kohse-Hoinghaus, "Enols are common
intermediates in hydrocarbon oxidation," Science
308, 1887 (2005).
Contact: Craig Taatjes, cataatj@sandia.gov
ALS Colloquium:
Modern photoemission—
its potential and challenges
by Art Robinson
 Valence-band
angle-resolved photoelectron spectroscopy (ARPES) with high
energy and momentum resolution has become one of the premier
spectroscopic tools at synchrotron light sources in general
and the ALS in particular for working at the frontier of condensed
matter physics. In the latest of an occasional series of ALS
Colloquia, Z.-X. Shen of Stanford University explained why
ARPES is such an effective technique, illustrated with recent
examples what ARPES can do, and looked at the challenges to
be overcome in order to bring this technique to the next level,
possibly leading to new paradigms of physics.
A co-developer and frequent user of the
condensed-matter branch of Beamline 10.0.1, Shen's credentials
include serving as the leader of a Stanford group that has
authored several widely cited publications based on ARPES
studies of high-temperature superconductors and other advanced
materials and as the mentor of a dozen or so students and
postdocs who have moved onto faculty positions at other universities
to continue their own ARPES research.
Beginning with theory, Shen called attention
to this centennial year of Albert Einstein's Nobel-Prize-winning
discovery of the theory underlying the photoelectric effect,
which is the basis of ARPES. The ability of ARPES to decipher
electronic structure in solids stems from the Fermi liquid
model of many-particle systems that was developed by the late
theoretical physicist Lev Landau in the former Soviet Union,
who also received a Nobel Prize for this work in 1962. For
the purposes of ARPES, the Fermi liquid model dramatically
simplifies the problem of a system with 1023 particles
and makes it possible to isolate the energy states near the
Fermi level of a solid, which are the most important for physical
properties. The "self-energy," which can be extracted
from ARPES spectra (photoemission intensity as a function
of photoelectron energy and angle of emission relative to
the surface) carries information about the strong interactions
of electrons with each other and other entities, such as lattice
vibrations and magnetic excitations, that are at the heart
of forefront problems in condensed-matter physics.
William Spicer pioneered valence-band
photoemission of solids. Stanford University News Service. |
On the experiment side, modern-day ARPES
to study the electronic structure of solids began with the
valence-band photoemission studies of the late William Spicer,
first at RCA Laboratories in Princeton and later at Stanford,
where his many students included Shen. The addition of angular
resolution to map electronic structure throughout the Brillouin
zone was pioneered by Neville Smith (now ALS Division Deputy
for Science but then at Bell Laboratories and before that
a postdoc under Spicer at Stanford). A hemispherical electron
energy analyzer with an angle-resolved capability owes its
start to David Shirley, former director of Berkeley Lab and
father of the ALS, while the modern version of the type now
widely used with high energy and angular resolution stems
from the work of Kai Siegbahn at Uppsala University, a Nobel
Prize winner for his earlier work on electron spectroscopy.
Shen illustrated the value of ARPES with
several recent examples made possible by ever-increasing energy
and momentum resolution and throughput (spectra per hour).
For example, a key feature of high-temperature superconductors,
the anisotropic nature of the superconducting gap (gap is
dependent on direction in momentum space), was demonstrated
in 1993. In 2001, a kink in the slope of the energy–momentum
curve near the Fermi level (change in velocity) was observed,
interpreted as a possible a sign of phonon coupling. This
year it has been possible to resolve fine structure in the
self-energy that matches four known modes in the phonon density
of states. Other advances discussed included resolution of
spin–charge separation in one-dimensional systems and
orientation-dependent electronic structure in carbon-60 clusters
on substrates.
Looking to the future, Shen discussed
the recently demonstrated use of lasers for ultrahigh-resolution
studies (possible if one knows in advance the photon energy
needed), attainment of bulk rather than surface sensitivity
in certain materials, and spatial resolution to study inhomogeneous
materials and small crystals. Now that ARPES has become such
an exciting field with so many activities, a major challenge
will be finding beam time at synchrotron sources for the growing
number of researchers in the field.
Contact: Zhi-Xun Shen, zxshen@stanford.edu
Deadline for
General User Proposals
Extended to July 5
 The
User Services Office is still accepting general user proposals
from scientists who wish to conduct research in the general
sciences at the ALS during the running period from January
through June 2006. The deadline for submissions has been extended
through the close of business on Tuesday, July 5, 2005. (This
deadline does not apply to protein crystallography proposals,
which have a separate process and schedule.) To submit a new
proposal, go to the online ALS
General User Proposal and Request for Beamtime form.
Existing proposals can be renewed for
up to three six-month cycles following their initial submission.
Scientists with proposals that are eligible for renewal have
been sent instructions on how to submit an online Proposal
Renewal Form. Send email to alsproposals@lbl.gov
if you believe you are eligible for renewal but have not received
renewal instructions. If your proposal is designated ALS-01186
or lower, then you must submit a new proposal. The following
resources are available for further information:
ALS
User Services Administrator
General
user proposals
ALS online forms
Beamline
information
Proposal
scores for July–December 2005
Contact: alsproposals@lbl.gov
DOE Office of
Science Director
Ray Orbach visits ALS
Dr. Ray Orbach, Director of the Office
of Science for the Department of Energy, made his annual visit
to Berkeley Lab on Friday, June 24, for meetings, tours, and
program updates. Accompanied by Berkeley Lab Director Steve
Chu, Dr. Orbach toured the ALS with Acting ALS Director Janos
Kirz. The group stopped at Beamline 7.0.1, where Beamline
Scientist Eli Rotenberg discussed recent results obtained
with the Electronic Structure Factory.
Eli Rotenberg (left) and Janos Kirz
(right) discuss
recent work done at Beamline 7.0.1 with Ray Orbach.
The tour then moved on to Building 10,
built in 1944 and recently rated "very poor" from
a seismic standpoint. It is currently being used for a variety
of ALS activities, but would be replaced by a new User Support
Building with additional staging and office space if funding
can be secured. Dr. Orbach then spent the lunch hour in discussions
with members of the ALS Users' Executive Committee. During
this visit, Dr. Orbach also helped to dedicate a new metropolitan
area network at the Oakland Scientific Facility, toured the
new Potter Street biosciences center in West Berkeley, talked
with scientists about optical accelerators, and met with the
Lab's safety committees.
2005 ALS Users'
Meeting update:
Workshops announced
 General
information, meeting deadlines, and online registration for
this year's ALS Users' Meeting, to be held at Berkeley Lab
October 20–22, will soon be available on the Users'
Meeting Web site. The deadline for abstract submission
is August 15, and the early registration deadline is October
1. Jinghua Guo and Simon Morton are the program committee
co-chairs. This year, 11 focused workshops will follow the
end of the formal Users' Meeting program. The workshop topics
and their organizers are as follows:
Forefront AMO Science: Clusters,
Ions, Dressed States...
John Bozek and Nora Berrah
Frontiers of Synchrotron-Based
X-Ray Microdiffraction
Nobumichi Tamura and B.W. Batterman
Macromolecular Crystallography
I: Advanced Experimental Techniques for Getting the Best Data
from Difficult Samples
Christine Trame
Macromolecular Crystallography
II: New Strategies for Data Processing with Automated Software
Tools
James Holton
New Visions in Bandmapping
Eli Rotenberg, Alexei Fedorov, and Zahid Hussain
Novel Approaches to Soft X-Ray
Spectroscopy: Scanning Transmission X-Ray Microscopy and Ambient-Pressure
X-Ray Photoelectron Spectroscopy
Hendrik Bluhm, Mary Gilles, Simon Mun, and Tolek Tyliszczak
Soft and Hard X-Ray Tomography
at the ALS
Alastair MacDowell and Gerry McDermott
Soft X-Ray Photon-In and Photon-Out
Spectroscopy: New Frontiers
Jinghua Guo and Zahid Hasan
THz Science and Technology Network:
Opportunities and Organization
Michael C. Martin
Ultrafast X-Ray Science at the
ALS
Bob Schoenlein and Peter Fischer
XANES and NEXAFS Spectroscopy
of Materials and Biological Samples: Expanding the Range of
Applications at Beamline 9.3.1
Robert Szilagyi and Heinz Frei
Interested participants are encouraged
to contact the workshop leaders directly for more detailed
information about workshop agendas and speakers.
Contact: alsum@lbl.gov
SXR/EUV lectures
to be
Webcast live this fall
"Soft X-Rays and Extreme Ultraviolet
Radiation," a course taught by David Attwood at UC Berkeley,
will be Webcast live over the Internet on Tuesdays and Thursdays,
2:00–3:30 p.m. (Pacific time), beginning on August 30,
2005. The course
Web page includes links to the Webcasts, handouts, and
homework problems. All lectures and materials are free—just
log on.
 The
course explores modern developments in the physics and applications
of soft x rays and extreme ultraviolet radiation. Following
a brief review of atomic physics and relevant absorption edges,
the lectures consider electromagnetic radiation at short wavelengths,
including dipole radiation, scattering, and refractive index
using a semiclassical atomic model. Subject matter includes
the generation of x rays with synchrotron radiation (bending-magnet,
undulator, and wiggler radiation), laser-plasma sources, high-harmonic
generation, x-ray/EUV lasers, and black-body radiation. Concepts
of spatial and temporal coherence are described, along with
applications to interferometry, scattering, and imaging. Topics
in x-ray optics include total external reflection, multilayer
coatings, Kirkpatrick-Baez focusing, zone-plate (diffractive)
lenses, microscopes, and EUV telescopes. Applications include
high-resolution (15-nm) soft x-ray microscopy and examples
in the life and physical sciences, generally with elemental
and chemical sensitivity. Recent progress with three-dimensional
imaging of biological samples using high-resolution nanotomography
will be presented, as well as studies of magnetic nanostructures
and operational electronic devices. EUV lithography for future
(2009) 19-GHz nanoelectronic devices with features smaller
than 20 nm will also be discussed. Prerequisites: Knowledge
of Maxwell's equations, undergraduate modern physics, vector
calculus.
Contact: David Attwood, attwood@eecs.berkeley.edu
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