ALS Spectrum

Advanced Light Source : : Facility Report : : 2007 PUBLISHED BY THE ADVANCED LIGHT SOURCE COMMUNICATIONS GROUP The ALS Graphene Scene Although derived from What’s graphite, the form of car- Like an “unrolled” car- layer of carbon atoms bon in pencils, these two- Inside: bon nanotube, graphene is arranged in a hexagonal dimensional graphene a densely packed single pattern like a honeycomb. sheets may hold the prom- ise of a new generation of faster, smaller, cheaper, and 2 more durable computer SCIENCE ROUNDUP chips than today's silicon- A selection of ten ALS based devices. Conse- research highlights published quently, interest in the elec- in 2007 tronic properties of this form of carbon has surged worldwide. At the ALS, two 5 research groups, led by AROUND THE RING Alessandra Lanzara of UC Scientific and technical Berkeley and Eli Rotenberg reports from ALS staff and of the ALS, continue to be user groups very active in this field. In 2007, the groups separately published two high-profile 11 papers exploring graphene's PEOPLE AND EVENTS fundamentally interesting BES review, UEC update, and potentially valuable high-profile visitors, awards, The atomic arrangement of graphene (background) is a properties. new faces, etc. honeycomb lattice of carbon atoms arranged in a two-di- Before graphene can be mensional plane. Its electronic band structure consists of engineered into transistors two bands (yellow) that intersect only at a few points at or other electronic devices, 16 the corners of a hexagonal Brillouin zone (red). continued on page 4 FACILITY UPDATES Beam delivery, user demo- graphics, construction proj- Top-Off Gets a Boost mately every minute to re- ects, and new initiatives plenish lost electrons, as The ALS took a big step aspects, culminating in a opposed to every eight towards the successful successful outside review hours, doubling the average completion of the top-off of the radiation safety track- beam current, allowing a upgrade late in 2007. The ing studies and controls. reduction in vertical beam recommissioning of the in- The transition to top-off size, and eliminating the jector complex was suc- mode is motivated by the large swings in temperature cessfully completed and possibility of increasing that can adversely affect user operation was moved brightness and improving storage-ring and beamline from injection at 1.5 GeV to thermal stability, keeping components. The plan is full-energy injection at 1.9 the ALS competitive with before the end of 2008 to GeV. Furthermore, there newer light sources for the operate with top-off injec- was further steady progress next decade. In top-off tion at 500 mA, which will over the last year in studying mode, beam is injected into result in brightness gains all relevant radiation safety the storage ring approxi- continued on page 19 2 Science Roundup Breaking H2 Symmetry gether) skews the distribution by that coherence-driven transitions Pt/C catalysts used in existing Martín et al., Science 315, 629 breaking the molecular symmetry. are a generic controlling factor PEM fuel cells. This new varia- (2007) for novel quantum phenomena in tion of the platinum–nickel alloy http://www-als.lbl.gov/als/science/ Coherently Condensing doped transition-metal oxides. is the most active oxygen-reduc- sci_archive/150symmetry-break.html Polarons ing catalyst ever reported. A single hydrogen (or deuterium) Mannella et al., Phys. Rev. B 76, Pt3 Revs Up Fuel Cells molecule consists of only two pro- 233102 (2007) Stamenkovic et al., Science 315, Detangling DNA tons (deuterons) and two elec- http://www-als.lbl.gov/als/science/ 493 (2007) Dong and Berger, Nature 450, trons and is perfectly symmetric. sci_archive/169manganites.html http://www-als.lbl.gov/als/science/ 1201 (2007) Linearly polarized photons are Novel quantum phenomena, such sci_archive/139cathode.html http://www-als.lbl.gov/als/science/ similarly symmetric. So one might as high-temperature supercon- Two out of three of the kinetic sci_archive/160topoII.html think that the angular distribution ductivity (HTSC) and colossal barriers to the practical use of The veil has finally been lifted on an of photoelectrons resulting from magnetoresistance (CMR), arise polymer electrolyte membrane enzyme that is critical to the photoionization of the molecule in certain materials where the in- (PEM) hydrogen fuel cells in au- process of DNA transcription and by the photon accompanied by teractions between electrons are tomobiles have been breached: replication and is a prime target of dissociation into a hydrogen very strong, but the mechanism the impractically high amount of antibacterial and anticancer drugs. atom and a hydrogen ion would driving their appearance remains extra energy needed for the oxi- Researchers at Berkeley Lab and itself be symmetric. However, an a major puzzle. Now, angle-re- dation reduction reaction (ORR) the University of California, Berkeley, international team of researchers solved photoemission findings on the catalyst and the loss of have produced the first three-di- from Germany, Spain, and the from an international team led by catalytic surface areas available mensional structural images of a U.S. has now shown that this researchers from Stanford Uni- for ORR. Using a combination of DNA-bound type II topoisomerase need not be the case. When there versity and the ALS provide the probes and calculations, a group (topo II) that is responsible for are multiple quantum paths for first direct spectroscopic evidence of scientists has demonstrated untangling coiled strands of the the process, interference be- that the transition from insulator that the Pt3Ni(111) alloy is ten chromosome during cell division. tween waves in the coherent su- to metal in CMR manganese ox- times more active for ORR than Preventing topo II from disentan- perposition of electron states ides (manganites) results from the corresponding Pt(111) sur- gling a cell's DNA is fatal to the (which exists when the molecular coherent “polaron condensation.” face and ninety times more active cell, which is why drugs that target fragments are still close to- The new findings also suggest than the current state-of-the-art topo II serve as agents against bac- 0 (eV) F –0.1 Energy, E–E Energy, –0.2 With Ni (gray) in the subsurface Sample plot of electron angular layers, the topmost Pt atoms (yel- distribution for ionization of deu- low) have a modified electronic terium. The molecule axis is indi- 0.3 0.4 structure, which alters different ad- –1 cated by the blue and green circles. Wavevector, k (Å ) sorption properties of Pt. Conse- High-resolution three-dimensional The curves represent theory (solid quently, interaction between OH– crystallography images of the bind- red line), experiment (circles), and ARPES data plots photoelectron ions (blue/white) and the Pt skin is ing and cleavage core of type II fit of the experimental data (dotted intensity variation with energy (rel- weakened, leaving more Pt sites topoisomerase (topo II) as it inter- line). The three-dimensional plots ative to the Fermi level) and momen- active for adsorption of O2 (blue). acts with DNA. are also theoretical results. tum in the nodal direction. Color represents photoelectron intensity. continued on page 3 3 Read more about these and other science highlights at http://www-als.lbl.gov/als/science/ terial infections and some forms of size the larger diamondoid mole- can be magnetic at room temper- scope XM-1 at the ALS to demon- cancer. This first ever structural cules, but to no avail. This situa- ature, attempts to prove that pure strate that magnetic domain walls image of topo II should help in the tion was finally changed in2003 carbon can be magnetized have in curved permalloy nanowires development of future antibacterial when significant quantities of remained unconvincing. However, can be moved at high speed by and anticancer drugs that are even higher diamondoids were found in using a proton beam and an ad- injecting nanosecond pulses of more effective and carry fewer petroleum by researchers in Mo- vanced x-ray microscope at the spin-polarized currents into the potential side effects. lecular Diamond Technologies. Advanced Light Source, a multi- wires, but the motion is largely Now, scientists from Berkeley Lab, national team of researchers from stochastic. This result will have Diamondoids Display Stanford University,Lawrence Liv- the SSRL, the University of Leipzig, an impact on the current devel- Potential ermore National Laboratory, and and the ALS finally put to rest opment of magnetic storage de- Yang et al., Science 316, 1460 Germany have used photoelec- doubts about the existence of vices in which data is moved (2007) tron spectroscopy at the ALS to magnetic carbon. electronically rather than mechan- http://www-als.lbl.gov/als/science/ reveal an intriguing feature: mono- ically as in computer disk drives. sci_archive/155diamondoids.html chromatized electron emission Pushing the Wall Diamondoids are nanometer-sized from a self-assembled monolayer Meier et al., Phys. Rev. Lett. 98, Nano Gold molecules that feature diamond- of diamondoids. This has caught 187202 (2007) Jadzinsky et al., Science 318, crystal cage structures. Adaman- the attention of people who are http://www-als.lbl.gov/als/science/ 430 (2007) tane, the smallest member in the searching for materials for next- sci_archive/153domainwall.html http://www-als.lbl.gov/als/science/ family, consists of one cage struc- generation electron emitters. The quest to increase both com- sci_archive/164gold.html ture, diamantane two, triamantane puter data-storage density and For the first time, a team of sci- three, tetramantane four, and so Magnetic Carbon the speed at which one can read entists led by Roger Kornberg on. On all of these, the dangling Ohldag et al., Phys. Rev. Lett. and write the information remains has synthesized thiol-covered gold bonds on the outer surfaces are 98, 187204 (2007) unconsummated.

Load more