NEWS OF THE WEEK NANOTECHNOLOGY
SINGLE-MOLECULE SPIN VALVE DEBUTS Device opens new possibilities for nanoscale computing and data storage
T
H E REALMS O F MOLECULAR
electronics and spin-based e l e c t r o n i c s (spintronics) have been merged in a new device —a single-molecule spin valve. Jan Hendrik Schon, the physicist who created the device at Lucent Technologies' Bell Laboratories in Murray Hill, N.J., says that "it opens up a lot of possibilities" for making new types of molecular-scale devices and exploiting new physical effects at the nanometer scale. T h e new variant on the spin valve is the first to involve a single organic molecule. A conventional spin valve in its most basic form is a thin layer of a nonmagnetic metal sandwiched between two ferromagnetic layers. In one of the ferromagnetic layers, the aligned electron spins have been "pinned" and c a n n o t be easily changed. In the other, "free" magnetic layer, the orientation of the spins can be changed by applying a relatively small magnetic field. W h e n t h e spins in t h e t w o
magnetic layers are aligned, a current of electrons with the same spin can pass through the sandwich easily But when the spins in the magnetic layers are opposed, the electrical resistance of the device is higher, impeding the flow of current. Such a spin valve, built into a read head, can sense the magnetism of data bits on a computer hard drive. In Schon's device, the magnetic layers are two nickel electrodes that sandwich a 1-nm-thick selfassembled monolayer [Science, published online April 18, http:/Avww sciencemag.org/cgi/content/ab stract/1070563vl}. T h e monolayer is thought to have about one molecule of benzene- 1,4-dithiolate, which can conduct electrons, in an insulating "carpet" of roughly 10 5 molecules of 1-pentanethiol. W h e n the spins in both nickel electrodes point in the same direction, current flows through the dithiolate molecule. But when the electrodes' spin orientations are opposite, the resistivity of the de-
vice jumps by 3 0 % at S P I N VALVE room temperature. Schon's molecular Theoretical moddevice eling by Schon's coauthors at other institutions —Eldon G. Emberly and George Kirczenow— agrees with the experimental results. "This work is very interesting from the scientific standpoint SiOo since it shows t h a t the electron spin diSi rection is preserved when the spin-poA single dithiolate molecule larized electron cur(red) provides a conduit for rent is transported electrons passing from one through a single ornickel electrode to the other. ganic molecule," says Stuart A. Wolf, a program manager for spintronics at the D e fense Advanced Research P r o jects Agency "This portends very well for organic s p i n t r o n i c s , " which is perhaps 10 years away " W h e n devices and circuits reach the nano scale (1-5 nm), spin will be the preferred method for storing and transporting information in the solid state," W)lf believes. "Thus, although this device relies on metallic ferromagSchon n e t i c c o n t a c t s , it m e a n s t h a t when we develop molecular ferromagnets at room temperature, we will have most of the building b l o c k s for a n e w p a r a d i g m of spintronics."—RON DAGANI
BUSINESS
Biotech Leaders Ally In Manufacturing Pact
G
enentech will produce Immunex' antirheumatoid arthritis drug Enbrel under a manufacturing agreement signed last week. Sales of the drug have been limited by a supply shortage caused by strong demand and lack of manufacturing capacity. Immunex, which is in the process of being acquired by Amgen, expects sales of Enbrel, among the top-selling biopharmaceuticals, to hit $1 billion this year, up from $762 million in 2001. Immunex has already acquired from Wyeth a facility in Rhode Island dedicated to Enbrel production. Wyeth also markets the drug through its pharmaceuticals division. Immunex expects to obtain FDA approval for the plant in the second half of 2002. The Genentech agreement is a longer term solution to the capacity problem. FDA approval for production by Genentech is not
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expected until 2004, when its facility in South San Francisco will become a licensed manufacturing plant for the drug. Peggy V. Phillips, executive vice president and chief operating officer at Immunex, says, "This Genentech agreement adds flexibility and depth to our plans to expand the production capacity of Enbrel to the multi-billion-dollar level." Immunex' latest move underscores a point made in a study of biological manufacturing capacity by analysts at U.S. Bancorp Piper Jaffray. They found that, given current investments, there will be ample capacity for biologies manufacturing as new plants become functional over the next five years. But some biotech companies will face capacity shortfalls in the intervening years as they struggle to match supply with industry demand.—WILLIAM STORCK
C & E N / A P R I L 22, 2002
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