Signaling inside neurons takes some new twists. At cold spring harbot laboratory's annual symposium on quantitative biology, devoted this year to neuroscience, neurobiologists basked in long island sunshine while discussing their recent work. Among the freshest new results were two that add surprising new twists to the stories of how certain neurons respond to incoming signals. /*---------------------------------------------------------------------*/ New Solar Cells seem to have power at the fright price. Efficiency versus cost. It's a trade off that bedevils makers of solar cells, frustrating their efforts to harness the sun. Cells made from wafers of crystalline silicon are rather good at absorbing photons and converting them to electricity. But they cost a lot to make. In contrast, noncrystalline cells made with an ultrathin film, amorphous silicon, are much cheaper. New thin film materials are showing signs that they can be both inexpensive and efficient, and have created "a sense of tremendous excitement in the technological side of the field." A mixture of copper,indium, gallium and selenium (CIGS) has been made into prototypes cells that convert 18% of incoming sunlight. to electricity. Ken Zweibel thin film solar cell research at National Renewable Energy Lab (NREL) Golden, Colorado. Hans Schock thin film solar cell expert at U of Stuttgart in Germany says this result and others on display at the meeting "really give us a chance to bring the cost down" Crystalline solar cells can be built for manufacturing costs of $3.50 to $4 per watt generated. Many researchers expect the new thin films CIGS and one other, a blend of cadmium and tellurium (cdTe) to do better. If researchers can overcome nagging manufacturing and marketing problems. new devices could produce power for less than $0.50/watt. Making the cost of PV generated electricity competitive with gas generators says Zweibel. CIGS is difficult to deposit over large areas, and PV panels are window pane-sized; and anything made with cadmium a toxic heavy metal, could face resistance from consumers. To convert sunlight to electricity, all PVs rely on layers of semiconducting materials at their core. Electrons in these materials exist at discrete energy levels known as bands. When the material absorbs photons, the extra energy boosts electrons up to a high conduction band, leaving behind positively charged holes. Additional semiconductor layers above and below the absorbing layer then channel the electrons and holes in opposite directions, creating an electric current. Conventional crystalline silicon PVs good at this charged particle steering, hence their efficiency. They are not so good at kicking electrons up to the conduction band; the photons need an extra energy boost from vibrations in the crystalline lattice , or phonons, to get the electrons to move. So solar-cell makers use large crystalline wafers up to 200 micrometers thick to give photons more opportunity to encounter phonons in the material. And the thickness of the material drives up the cost of the PVs. Amorphous silicon, in contrast, is a direct bandgap material, meaning its electrons don't need extra phonon help to jump bands. Manufacturers need to lay down layers only a few micrometers thick. And because the material, being amorphous, doesn't have a regular crystal structure, it can essentially be sprayed onto large panels at relatively low cost. But the amorphous nature of the material also comes with a drawback: defects. These defects - silicon atoms with an unfilled bond- trap the moving electrons and holes, preventing the charges from traveling to their destinations. This limits the efficiency of the best existing devices to about 11%. CdTe and CIS (without gallium) were originally explored as possible thin films back in the 1970's because they are direct bandgap materials well suited to absorbing photons from the sun The materials - now being investigated by dozens of groups world-wide also tend to have fewer charge trapping defects than amorphous silicon does, in part because they're actually made up of thousands of tiny crystallites: The charged particles flow relatively unimpeded within each crystalline grain. The charges do however, run into trouble at the grain boundaries, which are harder to jump. In an effort to convert CIGS and its predecessor into efficient solar cells, scientists have reduced the number of boundaries in films of the material by slightly increasing the crystallite size, says John Tuttle, a physicist and solar cell expert at NREL whose team holds the current CIGS efficiency record. They have done so by varying the concentration of copper as the film is deposited. Because copper and selenium trigger a temporary liquid phase in the material, making it easier for atoms to arrange themselves into larger, trap free groups, a copper rich layer at the bottom produces slightly larger crystalline grains when the film is complete. But the biggest boost, says tuttle has come from gallium. The recent addition of gallium to the CIS mix, graded so that its gratest concentration is near the bottom of the film, has produced two benefits. First, it increases the bandgap of the alloy to a point that more closely matches the energy of most photons in sunlight, improving light- to-electricity conversion. Second the graded gallium content causes the bandgap to vary throughout the CIGS layer, from a largest bandgap at the base to a smaller one on top, creating a kind of sloper for electrons to flow along. Electron energies follow bandgap size, so those kicked into the conduction band at the bottom of the film can easily give up a little energy as heat to occupy lower bandgap sites closer to the front, while the lower energy electronics can't move the opposite way. This gives extra force driving electrons to the top contat. Says Alan Delahoy who heads research at Energy Photovoltaics (EPV) a princeton New jersy based PV company. Thanks to these and other improvements, Tuttle and his colleagues were able to unveil their latest record holder in april at the materials research society metting in San Francisco: a 17.7% efficient test cell 0.4cm^2 in area. And the arlington meeting, Schock and his colleagues also showed that they could produce a CIGS cell more than 100 times that size that was 13.9% efficient. But even shock's cell measured just 10cm on a side, a fraction of the size of real world PVs. And larger CIGS cells are out of reach for the moment, says Vijay Kapur, President of International Solar Energy Technology (ISET) Ion Inglewood, California. The complicated evaporation techniques used to produce small CIGS cells are not amenable to large scale production he says for they cannot maintain constant film thickness over much larger surfaces. But companies are working on improvements. According to Delahoy, EPV has already developed a machines capable of depositing CIGS films on areas roughly 1m x 0.5m And ISET has come up with a nonvacuum method capable to making large-area films, albeit with poorer efficiency. CdTe Films, by contrast, don't face the same scale-up problems. CdTe can be manufactured by 4 or 5 technologies that all produce fairly high efficiency devices. Over large areas, says Chris Ferekides, a CdTe solar cell researcher at the University of south florida in Tampa. Working with lab-scale machines, Ferekides and his group have produced small cells that achieve nearly 16% efficiency. To get these record breaking results, Ferekides and his colleagues needed a couple of tricks of their own to overcome a drawback that has limited the efficiently of CdTE solar cells in the past : Their light blocking out layers. In order to operate CdTE PV require that a layer of photon absorbing cadmium sulfide (cdS) be grown atop the CdTE; the CdS draws electrons from the CdTe toward the top electrode. To minimize unwanted photon absorption by CdS the group used a special liquid based technique to grow a thinner than normal - and there force more transparent CdS layer in the device The florida group also topped off its device with a special ultratransparent glass. Full-scale CdTe panels have yet to reproduce these results. Nevertheless, because CdTe is more easily produced than CIGS, at least two companies - Golden Photon in Golden, Colorado, and Solar Cells Inc (SCI) in Toledo, Ohio are already building pilot scale facilities to manufacture CdTE Panels. Early full scale prototypes currently being tested by these and other companies has reached 7-9% efficiency. They hope to reach Ferekides's level. CdTE may lag slightly behind CIGS in the lab, "but it seems ready for the market", says David Carlson, a physicist at Solarex in Newtown Pennsylvania, who invented the amorphous silicon solar cell. The question is whether the market is ready for CdTe, or at least Cadmium , Concern over consumer resistance to product containing toxic metal has already prompted companies like EPV to bet on the competition. We considered going to CdTe but was became convinced that public perception of cadmium would create tremendous difficulties in marketing (says delahoy). SCI VP of operations, Dan Sandwisch, maintains that the Cd problem can easily be managed by setting up a recycling program to recover the solar panels at the end of their lives. Until such panels and programs are rolled out, solar-cell makers anticipating consumer reactions will be working in the dark. /*---------------------------------------------------------------------*/ Ion-Induced Morphological changes in crew cut aggregates of amphiphilic block copolymers. The addition of ions in micromolar 9caCl2 or HCl) or millimolar (NaCl) concentrations can change the morphology of crew cut aggregates of amphiphilic block copolymers in dilute solutions. In addition to spherical, rodlike, and univesicular or lamellar aggregates, an unusual large compound vesicle morphology can be obtained from a single block copolymer. Some features of the spontaneously formed large compound vesicles may make them especially useful as vehicles for delivering drugs and as models of biological cells. Gelation of dilute spherical micelle solution can also be induced by ions as the result of the formation of a cross-linked "pearl necklace " morphology. /*---------------------------------------------------------------------*/ Nanoscale Magnetic Domains in Mesoscopic Magnets The basic magnetic properties of 3D nanostructured materials can be drastically different from those of continuous film. High resolution magnetic force microscopy studies of magnetic submicrometer sized cobalt dots with geometrical dimensions comparable to the width of magnetic domains reveal a variety of intricate domain patterns controlled by the details of the dot geometry. By changing the thickness of the dots, the width of the geometrically constrained magnetic domains can be tuned. Concentric rings and spirals with vortex configurations have been stabilized, with particular incidence in the magnetization reversal process as observed in the ensemble-averaged hysteresis loops. /*---------------------------------------------------------------------*/