Water spectroscopy
makes the top ten
Over the last two years, soft x-ray core-excitation
spectroscopy techniques at the ALS and elsewhere have become
sensitive and effective tools for probing the electronic structure
of hydrogen bonds in liquid water. These relatively "loose"
bonds based on attractions between positive and negative electrical
charges on different parts of the water molecule are responsible
for many of water's unusual properties and its essential role
as a solvent in chemistry and biology. We are pleased to note
that Science magazine, in its December 17 issue featuring
the "Breakthrough of the Year," has recognized this
development as one of its top ten breakthroughs of 2004. Specifically,
it cites a publication by a group of researchers, led by Anders
Nilsson of the Stanford Synchrotron Radiation Laboratory (SSRL),
who used the ALS and the Advanced Photon Source (APS) to obtain
detailed information about the nearest-neighbor coordination
geometry of liquid water: P.H. Wernet et al., "The Structure
of the First Coordination Shell in Liquid Water," Science
304, 995 (May 2004).
Structure of first coordination shell
in liquid water
(illustration courtesy of H. Ogasawara,
Stanford Synchrotron Radiation Laboratory).
Said Science in its citation:
"After a century of intense scientific study, water still
gives researchers much to scratch their heads about. This
year, a flurry of papers on the structure and chemical behavior
of this familiar substance revealed results that, if they
hold up, could reshape fields from chemistry to atmospheric
sciences.
"First and most controversial, a
team of researchers from the United States, Germany, Sweden,
and the Netherlands reported that the 100-year-old picture
of the structure of liquid water might be wrong. Theorists
thought slight charge differences between oxygen and hydrogen
atoms pulled liquid water into an extended network, with each
water molecule bound to four others in a tetrahedral pattern.
But the team's synchrotron x-ray results suggest that many
water molecules are, in fact, bound to only two neighbors.
Don't rewrite the chemistry textbooks just yet: More-recent
x-ray data back up the original structure, and debate will
likely rage through 2005."
Polaron behavior
in
CMR manganites
by Bruce Balfour
Spintronic devices manipulate electron
spin to sense magnetic fields, store information, or perform
logical operations. Colossal magnetoresistive (CMR) manganites
are a class of materials under study for future spintronic
applications such as nonvolatile magnetic computer memory
(MRAM). Researchers have recently used several soft x-ray
spectroscopies at the ALS to study a prototypical CMR manganite
as it was heated past its Curie temperature—the point
at which the material ceases to be magnetic. They were able
to observe the formation of polarons: electrons whose interaction
with the lattice creates a deformation (energy well) that
traps the electron, as a pocket on a pool table traps a billiard
ball. For the first time, this provided a direct look inside
polaron formation in a CMR material, indicating that electron
localization as polarons is a defining characteristic of all
CMR materials. Full
story.
Publication about this research: N. Mannella,
A. Rosenhahn, C.H. Booth, S. Marchesini, B.S. Mun, S.-H. Yang,
K. Ibrahim, Y. Tomioka, and C.S. Fadley, "Direct Observation
of High-Temperature Polaronic Behavior in Colossal Magnetoresistive
Manganites, " Phys. Rev. Lett. 92,
166401 (2004).
Contact: Norman Mannella, NMannella@lbl.gov
Nanoparticle/VUV
interactions
at Beamline 9.0.2
 Nanoscience
in the 21st century is thriving—nanoparticles are being
studied in unprecedented detail across a broad spectrum of
disciplines. Applications for the particles have been found
in fields varying from medicine to computers, and the particles
themselves are integral to studies ranging from spectral emissions
in interstellar space to climate changes in our own environment.
Systematic studies with vacuum ultraviolet light (VUV) can
contribute to the study of nanoparticle chemistry and physics
in new and important ways. In a seminar last week, Musa Ahmed
of Berkeley Lab's Chemical Sciences Division described recent
developments in the study of nanoparticles at the Chemical
Dynamics Beamline 9.0.2. The work encompasses novel studies
of production, detection, size measurement and selection,
and chemical interactions of nanoparticles. The combination
of size-selected intense particle beams and tunable VUV light
affords the opportunity to study the optical and electronic
properties of substrate-free ultrafine particles in regimes
not previously accessible.
Beamline 9.0.2 is dedicated to the study
of the chemical and physical properties of matter using VUV
light. To address issues involving particle formation, aging,
and morphology, the beamline combines commercial equipment
for size-selective aerosol nanoparticle generation (scanning
mobility particle sizer, differential mobility analyzer, electrospray,
atomizer) with a state-of-the-art custom endstation. Coupled
to the beamline's intense VUV light, the system provides new
opportunities for nanometer-sized aerosol measurements. In
his talk, Ahmed focused on four areas: light scattering, photoelectron
imaging, time-of-flight mass spectrometry, and future directions.
While light scattering is a proven technology
for noninvasive monitoring of micron-sized particles, it becomes
difficult to study particles smaller than 200 nm using visible
light. VUV light, however, is more sensitive to smaller size;
the cross sections for scattering increase enormously in the
VUV range. Initial experiments have shown that it is possible
to measure the angular dependence of the scattered light and
thus to obtain refractive indices. Better detection techniques
should enable the study of fluorescence versus scattering,
and plans are underway to use time-of-flight analysis for
single-particle coincidence detection of ablated and desorbed
particles.
A technique that images photoelectron
position and energy from beams of free nanoparticles allows
for detailed investigations of the ionization and relaxation
dynamics in nanoparticles without the influence of a surrounding
substrate medium. A proof-of-principle experiment on size-selected
nanoparticles has shown a remarkable size-dependent asymmetry
in the angular distributions of the released photoelectrons.
This phenomenon (measuring photoemission electron escape probabilities
as a function of particle size) offers a means for novel particle
sizing and measuring surface-specific chemical properties.
Asymmetry in photoelectron intensity
as
particle size increases (left to right).
The technique of aerosol particle generation
has also been used to produce intense beams of biomolecules
such as amino acids. The beams transport the fragile molecules
to the interaction region of a time-of-flight mass spectrometer,
where gas-phase studies of the photoionization dynamics of
the biomolecules can be performed. This has resulted in the
measurement, for the first time, of the ionization energies
and fragmentation patterns of several fragile biological molecules.
Future experiments on the drawing board for this beamline
include reactions on aerosol surfaces, new particle formation,
and soot kinetics. For more information on Beamline 9.0.2,
see the Chemical
Dynamics Web site.
Contact: Musa Ahmed, MAhmed@lbl.gov
Basic Energy
Sciences review
to begin next week
The ALS has been gearing up over the
past few months for an important triennial program review
required by the Department of Energy (DOE) Office of Basic
Energy Sciences (BES). The review, to be held at the ALS on
February 2–4, 2005, is one of a series focusing on the
four DOE synchrotron light sources. Open sessions will be
held in ALS Conference Room 6-2202 starting at 1:00 on Wednesday
afternoon. Pier Oddone, Berkeley Lab's Deputy Director for
Scientific Programs, will begin the proceedings with a welcome
message, followed by Acting ALS Director Janos Kirz with an
overview of the ALS strategic plan. ALS Deputies Ben Feinberg,
Neville Smith, and Jim Krupnick will address Safety and Operations,
User Access Evolution, and Finance and Staffing, respectively.
Scientific highlight topics to be covered
include the electronic structure of strongly correlated systems
(Alessandra Lanzara), soft x-ray spectroscopy of volatile
liquids and their surfaces (Richard Saykally), phase-transition
dynamics viewed with femtosecond x-ray diffraction and absorption
(Andrea Cavalleri), magnetic materials (Yves Idzerda), atomic
and molecular physics (Nora Berrah), ultrafast nanomagnetism
(Andreas Scholl), microscopy of polymers (Harald Ade), x-ray
tomography of cells (Carolyn Larabell), and the Molecular
Foundry (Paul Alivisatos). The reviewers' agenda also includes
time for extensive beamline visits, meetings with ALS staff,
and lunch with members of the Users' Executive Committee.
Contact: Neville Smith, NVSmith@lbl.gov
Town hall meeting
focuses on safety
The ALS community convened in a town
hall meeting on January 18 to discuss a variety of issues,
including the upcoming BES review, safety concerns, the switch
to top-off mode, and questions concerning the UC's DOE contract
bid.
 After
Acting Director Janos Kirz briefed the group regarding preparations
for the BES review (see item above), the floor was handed
over to Deputy Director for Operations Ben Feinberg, who described
the circumstances surrounding a recent accident that occurred
at the Stanford Linear Accelerator Center (SLAC). The accident
severely injured an electrician and shut down all accelerators
at the Lab, including our sister facility, SSRL. SSRL is now
beginning to restart operations, over three months after the
accident. The SLAC linac is still shut down. Ben stressed
the importance of looking at what happened at SLAC with an
eye toward examining our own actions here at the ALS. According
to the DOE accident report, there were many opportunities
to avoid the accident—either by those who were doing
the work or those who requested the work—but no one
took advantage of them. All members of the ALS community are
urged to take a look at the full DOE
accident report and Ben's brief
summary presented at the town meeting. The stated ALS
mission is "To support users in doing outstanding science
in a safe environment." All members of the ALS community—users
as well as staff—must pay careful attention to their
safety and to that of those working around them. The bottom
line: "Stay Vigilant."
Ben next described a few changes in beamline
construction and modification procedures expected in anticipation
of the switch to top-off injection mode. A review of the top-off
upgrade was completed in November and BES has approved funding
to commence work starting this year. The ALS is expecting
to receive written permission shortly to begin initial testing.
Major activity for this upgrade is expected to continue over
the next couple of years.
Finally, Randy Scott, head of Berkeley
Lab's Human Resources Department, reported that the UC's proposal
for the Berkeley Lab management contract is in the final stages
of preparation and review. Proposals are to be submitted to
DOE by February 9, and announcement of the winner is expected
on April 1, with a 60-day transition period during which there
will be a smooth and orderly transition from the old to the
new contract without interruption of Berkeley Lab programs.
Fielding questions from the audience, Randy reported that
there are no other known competitors for the contract, that
no changes are expected in retirement and benefits programs,
and that the terms of the contract are for five years, renewable
for up to 20 years, contingent upon performance.
Contact: Ben Feinberg, B_Feinberg@lbl.gov
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