1. POLYMERS IN CONFINED GEOMETRIES
Contact: harald_ade@ncsu.edu

Some details of the behavior of thin films of polymer mixtures are difficult to study with conventional characterization techniques because many of these methods are unable to chemically differentiate materials with good spatial resolution and without damage, staining, or preferential solvent washing. In order to achieve direct and quantitative chemical characterization, researchers from several institutions are collaborating to use near-edge x-ray absorption fine structure (NEXAFS) microscopy to investigate the surface and bulk properties of polymer thin films.

Confining polymer molecules to geometries that are smaller than a few times the molecules' size influences properties such as viscosity and morphology. A polymer thin film on a substrate, where the substrate surface provides a rigid interface and the transition to air a flexible interface, is one of the simplest confined geometries. The interaction of a polymer with the substrate determines, for example, if the polymer film is stable, or if the film has a tendency to dewet the substrate. The dewetting process of a polymer is similar to a water film breaking up into water droplets on a car windshield or a dinner plate. The wetting characteristics of polymers are commercially important for the effective production of various coatings and films, including dielectric layers, photographic materials, and paints.

Films of polymer blends often exhibit more desirable characteristics than individual homopolymers; however, most blend components are also highly incompatible and will undergo demixing and phase separation. The degree of phase separation in polymer blends can have adverse effects on the properties of the resulting film, owing to changes in morphology. Conversely, a phase-separated film with controlled morphology might exhibit superior characteristics. The controlled thin-film morphologies might be used as selective membranes or sensors, or they could be used to produce controlled nanostructures that might have interesting optical or magnetic properties.

The team of researchers used the photoemission electron microscope (PEEM) at the ALS for NEXAFS microscopy of surfaces, and scanning transmission x-ray microscopes (STXMs) at the ALS and the National Synchrotron Light Source for NEXAFS microcopy of the interior. They investigated a variety of confined-polymer behaviors, including the thickness dependence of the dewetting characteristics of annealed bilayers comprising brominated polystyrene (PBrS) on top of polystyrene (PS) on a silicon substrate. A highlight showing some of their results is available on the Web at http://www-als.lbl.gov/als/science/sci_archive/polymer.html.

The researchers observed that the PBrS dewets the PS layer upon annealing. The PS even encapsulates the PBrS during the advanced stages of dewetting as the system approaches its thermodynamic equilibrium. The encapsulation process proceeds more slowly as the PS layer thickness is reduced, a direct result of the increased viscosity of thinner films due to spatial confinement. The researchers observed no encapsulation or only partial encapsulation once the PS layer thickness approached the radius of gyration (a measure of the PS molecule's size). The decreased encapsulation occurs because the PS is being pinned to the silicon surface, thereby trapping the system in a state far from thermodynamic equilibrium.

This type of research provides the information needed to investigate the pathways leading to reproducible fabrication of polymer nanostructures and to study the morphological characteristics and dynamics of such nanostructures.

Research conducted by H. Ade, D.A. Winesett, and A.P. Smith (North Carolina State University); S. Anders, T. Stammler, and C. Heske (Berkeley Lab); D. Slep (Hilord Chemical Corp.); J. Asselta, M.H. Rafailovich, and J. Sokolov (State University of New York at Stony Brook); and J. Stohr (IBM), using Beamlines 7.0.1 and 8.0.1. Some work was also conducted on Beamline X-1 at the National Synchrotron Light Source.

Funding: National Science Foundation (Young Investigator Award) and U.S. Department of Energy, Office of Basic Energy Sciences.

Publications about this experiment: H. Ade et al., Appl. Phys. Lett. 73, 3775 (1998).

2. DEADLINE FOR PHYSICAL SCIENCES
INDEPENDENT INVESTIGATOR PROPOSALS: JUNE 1, 1999
Contact: GFKrebs@lbl.gov

June 1, 1999, is the deadline for independent investigator (II) proposals in the physical sciences for the next running period, which will last from October 1999 to May 2000. This transitional running period will be eight months long instead of the usual six because the ALS will be shifting its running periods by two months, so that they start in June and December rather than in April and October. (This schedule does not apply to protein crystallography proposals, which have a separate process and schedule.)

Other important changes in the II proposal process for the physical sciences include the following. First, starting with the current proposal cycle, all II proposals will have the option to remain active for two years (i.e., four six-month cycles) with the submission of a one-page Experiment Report/Beamtime Request every six months. Second, for the current proposal cycle only, investigators may request to have a previous proposal considered by notifying the User Services Office by the June 1, 1999, deadline (such resubmissions will also begin their two years of eligibility with the current proposal cycle). Third, the numeric rating for each II proposal will be communicated to the investigator along with comments from the Proposal Study Panel (PSP); investigators can then check the Web for the cut-off rating for each beamline. For details about these changes, see ALSNews Vol. 126 (http://www-als.lbl.gov/als/als_news/news_archive/vol.126_042899.html).

The proposal form for independent investigators is available on the Web at http://www-als.lbl.gov/als/quickguide/independinvest.html. Data sheets describing the capabilities of the beamlines at the ALS are also on the Web at http://www-als.lbl.gov/als/als_users_bl/datasheets.html.

To request a proposal form by mail, contact:
Ruth Pepe, ALS User Administrator
Tel: (510) 486-5268
Fax: (510) 486-4773
Email: alsuser@lbl.gov

3. ENDSTATION FOR XAS OF BIOLOGICAL SAMPLES INSTALLED
Contacts: MPKlein@lbl.gov, HMFrei@lbl.gov (endstation); FSSchlachter@lbl.gov, WCStolte@lbl.gov (beamline)

A new endstation designed for x-ray absorption spectroscopy (XAS) studies of biological samples has been installed at Beamline 9.3.1 and is ready to undergo initial testing. Karen McFarlane, of Berkeley Lab's Physical BioSciences Division, oversaw the endstation's design and construction. XAS is an element-specific technique with widespread applications in structural biology. Most notably, it has been used in the hard x-ray region to probe metal centers in metalloproteins. The new endstation will utilize 2- to 5-keV photons for XAS studies of lower-Z atoms (such as sulfur, chlorine, and calcium) in proteins or other biological samples. Samples may be solid or liquid and can be studied at various temperatures (down to 10 K) and pressures (in vacuum or in an atmosphere of the user's choice). The sample and exchange gas are housed in an inner sample chamber with minimally attenuating windows. The sample surface can be positioned at a selectable angle, and the illumination spot size can be varied by changing the focus of the photon beam. While the endstation was designed for the study of protein samples, modifications are being planned to allow materials science applications as well.

The chamber was built by Mel Klein and Vittal Yachandra of Berkeley Lab's Physical BioSciences Division using Laboratory Directed Research and Development (LDRD) funds. Zahid Hussain (ALS) and Neil Hartman (Engineering) were instrumental during endstation planning and design. Engineering was provided by Matt Swanson (ALS) and Jason Akre (Engineering) with assembly completed by Noel Kellogg (Technical Services). Fred Schlachter and Wayne Stolte (ALS) assisted and ensured the compatibility of the endstation with the beamline. Modifications to the chamber for the materials science applications are being completed by Heinz Frei (Physical BioSciences) using LDRD funds.

4. BEAMLINE SCHEDULES AVAILABLE ON WEB
Contact: AMGreiner@lbl.gov

Schedules for individual ALS beamlines are now available on the World Wide Web at http://www-als.lbl.gov/als/schedules/beamlinesch.html. You can also reach this page via the "Individual Beamline Schedules" link on the Operating Schedules page (http://www-als.lbl.gov/als/accelinfo.html). Long-term schedules have been kindly provided by the beamline scientists, and weekly schedules are available for some beamlines as well. Most of these are available as downloadable, printable PDF files. Instructions for obtaining the Acrobat Reader software (required for viewing and printing PDF files) are included.

5. NEW STAFF MEMBERS JOIN THE USER SERVICES GROUP

The Beamline Coordination Section of the User Services Group has grown by two. Kelly Gonzalez, from the Administrative Support Division, and Tony Marquez, from Facilities, will work under the supervision of Donna Hamamoto to develop the user stock room; assist with shipping, receiving, and ordering; and help users out on the floor. Please join us in welcoming Kelly and Tony to the ALS.

6. WHO'S IN TOWN: A SAMPLING OF ALS USERS

To highlight the richness of our user community and help introduce recent arrivals, we offer this listing of some of the experimenters who will be collecting data during the next two weeks at the ALS.

Beamline 1.4.3: Ted Raab (Univ. of Colorado at Boulder) will continue studies of rhizosphere root/soil interactions by using IR spectromicroscopy. Hoi-Ying Holman (Berkeley Lab) will continue FTIR spectromicroscopy studies of individual human cells.

Beamline 7.3.1.1: Zi Qiang Qiu (Univ. of California, Berkeley) will study local magnetization in thin films and multilayers. Adam Hitchcock (McMaster Univ.) will investigate radiation damage in polymers.eley Lab) will be performing biological crystallography experiments.

Beamline 8.0.1: Jeff Kortright (Berkeley Lab, with collaborators from the Univ. of California, San Diego; IBM; and Argonne National Laboratory), will utilize the field- and temperature-dependent x-ray magnetooptical Kerr effect to study exchange interactions at buried interfaces in layered films.

Beamline 9.3.1: Mel Klein and Karen McFarlane (Berkeley Lab) will be performing x-ray absorption spectroscopy studies of proteins near the sulfur K edge.

Beamline 10.0.1: Scott Kellar (Berkeley Lab) and coworkers from Z.X. Shen's group (Stanford University) will be performing high-momentum-resolution studies of the high-Tc superconductor Bi2212, to explore the nature of the superconducting gap. Aaron Covington and Ron Phaneuf (Univ. of Nevada, Reno) will begin comissioning the ion accelerator and beamline to study photoionization of ions.

7. OPERATIONS UPDATE
Contact: RMMiller@lbl.gov

Beam reliability for user shifts during the last two weeks (April 26-May 9) was 99.6%. There were no significant outages.

Long-term and weekly operations schedules are available on the Web (http://www-als.lbl.gov/als/accelinfo.html). Weekly operations scheduling meetings are held on Fridays at 3:30 p.m. in the Building 6 conference room. The Accelerator Status Hotline at (510) 486-6766 (ext. 6766 from Lab phones) features a recorded message giving up-to-date information on the operational status of the accelerator.