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July/August 2001

The Laboratory
in the News

Commentary by
C. Bruce Tarter

Annual Certification Takes a Snapshot of Stockpile Stewardship

Sensing for Danger

It's the Pits in the Weapons Stockpile

Looking into the Shadow World






Lewis A. Glenn
Pressure Enhanced Penetration with Shaped Charge Perforators
U.S. Patent No.6,223,656 B1
May 1, 2001
A downhole tool, adapted to retain a shaped charge surrounded by a super, atmospherically pressurized light gas, is employed in a method for perforating a casing and penetrating reservoir rock around a wellbore. Penetration of a shaped-charge jet can be enhanced by at least 40 percent by imploding a liner in the high-pressure, light-gas atmosphere. The gas pressure helps confine the jet on the axis of penetration in the later stages of formation. The light gas, such as helium or hydrogen, is employed to keep the gas density low enough so as not to inhibit liner collapse.

Laurence R. Brewer, Joseph Kimbrough, Joseph Balch, J. Courtney Davidson
System and Method for Optically Locating Microchannel Positions
U.S. Patent No. 6,225,635 B1
May 1, 2001
A system and method is disclosed for optically locating a microchannel position. A laser source generates a primary laser beam that is directed at a microchannel plate, whose microchannels are variously located. A back-reflectance beam detector receives a back-reflected beam from the plate, generated when the primary laser beam reflects off the plate. When the back-reflected beam exceeds a predetermined threshold, which indicates the presence of a microchannel, a photodiode circuit generates a trigger signal. The method of this invention includes the steps of generating a primary beam and generating a trigger signal in the presence of a microchannel.

Russell M. Hudyma
Reflective Optical Imaging Systems with Balanced Distortion
U.S. Patent No.6,226,346 B1
May 1, 2001
Optical systems compatible with extreme ultraviolet radiation, comprising four reflective elements for projecting a mask image onto a substrate, are described. The four optical elements are, in order from object to image, convex, concave, convex, and concave mirrors. The optical systems are particularly suited for step and scan lithography methods. The invention enables the use of larger slit dimensions associated with ring-field scanning optics, improves wafer throughput, and allows higher semiconductor device density. The inventive optical systems are characterized by reduced dynamic distortion because the static distortion is balanced across the slit width.

Sasa C. Bajt, Mark A. Wall
MoRu/Be Multilayers for Extreme Ultraviolet Applications
U.S. Patent No. 6,228,512 B1
May 8, 2001
High-reflectance, low-intrinsic-roughness, and low-stress multilayer systems for extreme ultraviolet (EUV) lithography consist of amorphous molybdenum ruthenium (MoRu) and crystalline beryllium (Be) layers. Reflectance greater than 70 percent has been demonstrated for MoRu/Be multilayers with 50 bilayer pairs. Optical throughput of MoRu/Be multilayers can be 30 to 40 percent higher than that of Mo/Be multilayer coatings. The throughput can be improved using a diffusion barrier to make sharper interfaces. A capping layer on the top surface of the multilayer improves the long-term reflectance and EUV radiation stability of the multilayer by forming a very thin native oxide that is water resistant.

Jackson C. Koo
Paper Area Density Measurement from Forward Transmitted Scattered Light
U.S. Patent No.6,229,612 B1
May 8, 2001
A method whereby the average paper fiber area density (weight per unit area) can be directly calculated from the intensity of transmitted, scattered light at two different wavelengths, one being a nonabsorption wavelength. The method also makes it possible to derive the water percentage per fiber area density from a two-wavelength measurement. In an example of this measurement technique, the optical transmitted intensity at a 2.1-micrometer cellulose absorption line is measured and compared with another scattered, optical transmitted intensity from a nearby spectrum region, such as 1.68 micrometers, where there is no absorption. From the ratio of these two intensities, one can calculate the scattering absorption coefficient at 2.1 micrometers. The absorption coefficient at this wavelength is then experimentally correlated to the paper fiber area density.

Sasa Bajt, Troy W. Barbee, Jr.
High Reflectance and Low Stress Mo2C/Be Multilayers
U.S. Patent No. 6,229,652 B1
May 8, 2001
A material for extreme ultraviolet (EUV) multilayers that will reflect at about 11.3 nanometers, have a high reflectance, low stress, and high thermal and radiation stability. The material consists of alternating layers of molybdenum carbide (Mo2C) and beryllium (Be) deposited by direct current magnetron sputtering on a substrate such as silicon. In one example, a Mo2C/Be multilayer gave 65.2 percent reflectance at 11.25 nanometers measured at 5 degrees off normal incidence angle; it consisted of 70 bilayers with a deposition period of 5.78 nanometers and was deposited at 0.83 millitorr argon (Ar) sputtering pressure, with the first and last layers being Be. The stress of the multilayer is tensile and only +88 megapascals, compared with +330 megapascals for Mo/Be multilayers of the same thickness. The Mo2C/Be multilayer was capped with carbon that produced an increase in reflectivity of about 7 percent over a similar multilayer with no carbon-capping material, thus raising the reflectivity from 58.3 percent to over 65 percent. The multilayers were formed using either Mo2C or Be as the first and last layers. Initial testing has shown the formation of beryllium carbide at the interfaces between the layers, which both stabilizes and has a smoothing effect, and appears to be smoother than the interfaces in Mo/Be multilayers.

Abraham P. Lee, Jonathan N. Simon, Charles F. McConaghy
Micromachined Low Frequency Rocking Accelerometer with Capacitive Pickoff
U.S. Patent No.6,230,566 B1
May 15, 2001
A microelectromechanical sensor that uses capacitive readout electronics. The sensor involves a micromachined, low-frequency rocking accelerometer with capacitive pickoff fabricated by deep reactive ion etching. The accelerometer includes a central silicon proof mass, is suspended by a thin polysilicon tether, and has a moving electrode (capacitor plate or interdigitated fingers) located at each end of the proof mass. During movement (acceleration), the tethered mass moves relative to the surrounding packaging. This defection is measured by a plate capacitor or interdigitated finger capacitor, with the cooperating fixed electrode (capacitor plate or interdigitated fingers) positioned on the packaging, for example. The micromachined rocking accelerometer has a low frequency (lesser than 500 hertz), high sensitivity (microgauss), and uses minimal power. The capacitors are connected to a power supply (battery) and to sensor interface electronics, which may include an analog-to-digital converter, logic, radiofrequency communication link, and antenna. The sensor (accelerometer) may be packaged along with the interface electronics and a communication system in a 5- by 5- by 5-centimeter cube. The proof mass may be asymmetric or symmetric. Additional actuating capacitive plates may be used for feedback control, which gives a greater dynamic range.

Waleed S. Haddad, James E. Trebes, Dennis L. Matthews
Microwave Hematoma Detector
U.S. Patent No. 6,233,479 B1
May 15, 2001
The microwave hematoma detector is a noninvasive device used to detect and localize blood pooling and clots near the outer surface of the body. Although geared toward finding subdural and epidural hematomas, the device can be used to detect blood pooling anywhere near the surface of the body. Modified versions of the device can also detect pneumothorax, organ hemorrhage, and atherosclerotic plaque in the carotid arteries; evaluate perfusion (blood flow) at or near the body surface, and body tissue damage at or near the surface (especially for burn assessment); and be used in a number of nondestructive evaluation applications. The device is based on low-power-pulsed microwave technology combined with a special antenna, signal processing/recognition algorithms, and a disposable cap worn by the patient that will facilitate accurate mapping of the brain and proper functioning of the instrument.

Long N. Dinh, William McLean II, Mehdi Balooch, Edward J. Fehring, Jr., Marcus A. Schildbach
Generation of Low Work Function, Stable Compound Thin Films by Laser Ablation
U.S. Patent No. 6,235,615 B1
May 22, 2001
Generation of low-work-function, stable-compound thin films by laser ablation. Compound thin films with low work function can be synthesized by simultaneously laser ablating silicon, for example, and thermal evaporating an alkali metal into an oxygen environment. For example, the compound thin film may be composed of silicon, cesium, and oxygen. The work functions of the thin films can be varied by changing the ratios of silicon, alkali, metal, and oxygen. The low work functions of the compound thin films deposited on silicon substrates were confirmed by ultraviolet photoelectron spectroscopy. The compound thin films are stable up to 500°C as measured by x-ray photoelectron spectroscopy. Tests have established that for certain chemical compositions and annealing temperatures of the compound thin films, negative electron affinity was detected. The low-work-function, stable-compound thin films can be used in solar cells, field emission flat panel displays, electron guns, and cold-cathode electron guns.




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