Nerve gases

H3C-

•

0 H 3 C X | |

^p-s-CH3CH2CT

Mustard gas CICH2CH2

0 II - ρ — ο ­ι 1 F

Sarin (GB)

CH2CH2

VX

CH3

CH 1 CH3

/ CH(CH 3 ) 2 — Ν

XCH(CH3)2

S CH2CH2CI HD

Williams finds the NRC committee's report "encouraging because it shows we're on our way to deployment of alter­native approaches at several sites previ­ously slated for incineration systems." Even before the NRC report, four sites

were nearly certain to use alterna­tive disposal systems. The Army is gearing up to use hydrolysis at storage depots in Aberdeen, Md., and Newport, Ind., where bulk agents are stored in 1-ton contain­ers. And an alternative method to destroy the variety of assembled weapons at the Pueblo, Colo., and Richmond, Ky., sites is likely be­cause Congress has essentially prohibited incineration facilities at these sites.

Given the technical challeng­es remaining, the committee concludes that absent an excep­tional commitment of resources, none of the seven alternatives is likely to be able to meet the 2007

deadline. And a 1998 Arthur Anderson report, cited by the committee, claims the Army's preferred incineration sys­tem is also unlikely to meet that deadline.

Lois Ember

Probe for Si devices doesn't ruin them

Destroying chemical arms: No easy task A just-released National Research Coun­cil (NRC) report assessing alternative technologies to incineration for destroy­ing the U.S. stockpile of chemical weap­ons offers the Army little succor.

By U.S. law and international treaty, the Army has to destroy the stockpile by April 2007. Its method of choice—incin­eration—is widely opposed by citizen and activist groups, and Congress has required that the Army "coordinate" with NRC to come up with at least two alternative systems.

All seven alternatives chosen by the Army "can destroy the chemical agents [the nerve gases sarin (GB) and VX and mustard gas] to 99.9999%," says Robert A Beaudet, chairman of the NRC committee that issued the report and professor of chemistry at the University of Southern California, Los Angeles. But there is a key hurdle that must be overcome, he adds. That is "reducing the by-products to environmentally acceptable materials."

The technologies "are complex collec­tions of operations that have not yet been interfaced and tested as a complete sys­tem," Beaudet explains, "so additional de­velopment is required." This is especially true for technology to safely process and deactivate the energetics—the propel-lants and explosives—in the assembled mortar and artillery shells, rockets, and land mines making up the stockpile.

All seven alternatives, even the four primary ones—hydrolysis, electrochemi­cal oxidation using silver ions in nitric acid, plasma arc, and solvated electron technology—are fairly immature. Al­though more advanced than lab bench, they have not been tested at the pilot-plant level. And, Beaudet warns, "scaling up the processes can lead to problems."

The problems inherent in scaling up to operational level are well illustrated by the history of the only two currently oper­ating U.S. weapons destruction facili­ties—Johnston Island in the Pacific Ocean and Tooele, Utah. "After 12 years of full-scale operational experience," says Craig Williams, director of the Chemical Weapons Working Group (Berea, Ky.), "there have been major engineering changes and major subsystems have been aborted." The throughput projec­tion for processing rockets is 40 rockets per day. 'Tooele is averaging two rockets per day," says Williams, whose group op­poses incineration.

Manufacturers of microelectronic devic­es may have a new tool for measuring dopant profiles quickly, inexpensively, and without destroying their samples, thanks to a new atomic force microsco­py method developed at Colorado State University, Fort Collins.

As semiconductor-based devices continue to shrink, makers of computer memory chips and other items with mi­croscopic circuits need finer and finer probes to pinpoint the locations of dop­ants—charge-carrying impurities such as arsenic or boron ions that are deliber­ately implanted in silicon wafers to cus­tomize a product's electronic properties. Precise dopant placement is one of the keys to good device performance.

Unlike some methods currently used

for quality control or failure analysis— such as secondary-ion mass spectrome­try, a technique in which energetic ions blast away the topmost layers of a sam­ple for analysis—the Colorado State process leaves specimens intact as it charts the whereabouts of positive (p) and negative (n) charge carriers.

The new procedure was developed by chemistry professor Bruce A. Parkin­son, graduate students Mark W. Nelson and Paul G. Schroeder, and postdoctor­al associate Rudy Schlaf, who is now as­sistant professor of physics at State Uni­versity of New York, Binghamton.

'The group has shown a simple way to do nondestructive characterization of dopant location in semiconductors," re­marks Neal R. Armstrong, professor of

Closely spaced regions of p-type and η-type doping on a random access memory (RAM) circuit are readily distinguished as dark or light areas by using an atomic force microscopy procedure developed at Colorado State. Changing a potential applied between probe tip and sample changes image contrast Reversing the applied potential reverses the contrast

AUGUST 30,1999 C&EN 11