bluuebunny/crossref_metadata_2025 huggingface dataset:
Deposition and subsequent removal of single Si atoms on the Si(111)-7×7 surface by a scanning tunneling microscope
Authors: Huang Dehuan , Uchida Hironaga , Aono Masakazu
Published: July 2002

Single Si atoms can be deposited onto a Si(111)-7×7 sample surface from the tip of a scanning tunneling microscope, the Si atoms to be deposited being previously picked up by the tip from another place on the sample surface. The crystallographic position of these deposited Si atoms changes as their density increases. The deposited Si atoms can be re-removed by picking them up again with the tip, the substrate atomic arrangement remaining unperturbed. It is also possible to fill Si atom vacancies on the sample surface with a Si atom deposited from the tip.
Nanoscale scanning tunneling microscope patterning of silicon dioxide thin films by catalyzed HF vapor etching
Authors: Whidden Thomas K. , Allgair John , Jenkins-Gray Angela , Kozicki Michael N.
Published: July 2002

We report on the use of electron beam and scanning tunneling microscope (STM) patterns of ambient hydrocarbon residues on silicon dioxide as chemical initiators for the localized high-temperature HF vapor etching of oxide thin films. The treated films, when subjected to HF vapor etching at 115 °C, are patterned in the areas that have been exposed to an electron beam in either a scanning electron microscope or STM. The technique has been combined with reactive ion etching or metallization to yield nanometer scale patterns and nanoscale metal silicide lines on silicon. Nonaqueous Bronsted bases have been shown to be retained on the oxide surface at temperatures of up to 125 °C and to function as HF etch initiators. Such species show promise as monolayer resists for the patterning of silicon dioxide using the HF vapor etch process.
Micromorphology of Ge and Si1−xGex layers grown on Si(001) by solution epitaxy and the negative-differential conductivity on the Ge layer
Authors: Müssig H.-J. , Krüger D. , Hinrich S. , Hansson P. O.
Published: July 2002

The micromorphology and the electronic structure of heteroepitaxial Ge and Si1−xGex layers grown pseudomorphically by solution epitaxy on Si(001) has been investigated by Auger electron spectroscopy as well as scanning tunneling microscopy (STM) and scanning tunneling spectroscopy. A pure Ge film of 4–5 monolayer thickness typically repeats the structure of the Si substrate surface. A significant decrease of tunneling current at a sample voltage of 1.5 V is observed in areas of 0.5 nm diameter between Ge dimer rows. This decrease is due to a negative-differential conductivity at a tunnel diode configuration consisting of a surface defect structure of the Ge layer and the STM tungsten tip. On Si1−xGex films a strong Ge enrichment was found due to segregation during growth. The high Ge surface concentration on Si1−xGex results in additional surface strain fields and trench formation in the uppermost monolayer.
Simulation of electromigration in thin-film diffusion barriers by the transmission line matrix method
Authors: Gui Xiang , Dew Steven K. , Brett Michael J.
Published: July 2002

A phenomenological model of grain-boundary diffusion and electromigration in thin-film diffusion barriers for microelectronic device metallizations is developed by using the transmission line matrix method. Both diffusion and drift effects are included in the numerical analysis with a multidimensional variable mesh structure. Special attention is paid to the ‘‘vertical’’ electromigration effect and a comparison of the two-dimensional (2D) and three-dimensional (3D) simulation results. Two fundamental driving forces for impurity grain-boundary diffusion, the concentration gradient across a diffusion barrier, and the current flow perpendicular to the deposited metal films can reinforce each other, leading to an enhanced impurity diffusion and a reduced barrier efficiency. Such material transport through the diffusion barrier is quantified with a 2D model of parallel planar grain boundaries and a 3D model of rectangular columnar microstructures. Concentration profiles along all directions are visualized in graphs for the cases with and without the electromigration driving force. Average atom penetration as a function of time and the underestimation by the 2D model are also illustrated.
High-temperature structural stability of MoSi2-based nanolayer composites
Authors: Kung H. , Jervis T. R. , Hirvonen J.-P. , Mitchell T. E. , Nastasi M.
Published: July 2002

A systematic study of the high-temperature structural stability is reported for the following three nanolayered composites: (1) MoSi2–MoSi2Nx, (2) Mo–MoSi2Nx, and (3) Mo–MoSi2Nx–MoSi2, where x∼3–4. The alternating layers with layer thickness varying from 1 to 50 nm were synthesized by sputtering techniques. The structural evolution in these composites has been studied by cross-sectional transmission electron microscopy as a function of annealing temperature. As-deposited Mo layers exhibit nanocrystalline structure, while the other types of layers are amorphous in structure. With increasing annealing temperature, MoSi2 crystallizes to form a metastable C40 phase at ∼500 °C and then transforms to the stable C11b phase at ∼900 °C, while MoSi2Nx remains amorphous up to temperature as high as 1000 °C. No difference in crystallization behavior was observed for the constituents in either single phase or multilayered form. One way to improve the toughness of MoSi2 is through the addition of a ductile phase, e.g., Mo. However, the Mo and MoSi2 layers react and the layer structure deteriorates. Previous study has shown that the compound, MoSi2Nx, stays amorphous at 1000 °C. This suggests that it could function either as a stable second-phase reinforcement or as a diffusion barrier between Mo and MoSi2. The MoSi2–MoSi2Nx, Mo–MoSi2Nx, and Mo–MoSi2–MoSi2Nx nanolayers are found to remain stable up to 900 °C (highest temperature tested).
Scanning tunneling microscope for magneto-optical imaging
Authors: Prins M. W. J. , Groeneveld R. H. M. , Abraham D. L. , Schad R. , van Kempen H. , van Kesteren H. W.
Published: July 2002

Images of magnetic bits written in a Pt/Co multilayer are presented. Using photosensitive semiconducting tips in a scanning tunneling microscope the surface topography as well as the polarization-dependent optical transmission are measured. Magnetic contrast is achieved by detection of the Faraday effect. Magneto-optical lateral resolution of 250 nm is demonstrated.
Epitaxial growth, structure, and composition of Fe films on GaAs(001)-2×4
Authors: Kneedler E. , Thibado P. M. , Jonker B. T. , Bennett B. R. , Shanabrook B. V. , Wagner R. J. , Whitman L. J.
Published: July 2002

The structure and composition of Fe films grown on As-terminated GaAs(001)-2×4 surfaces at 175 °C has been studied in situ with scanning tunneling microscopy (STM), photoelectron diffraction (PED), and x-ray photoelectron spectroscopy (XPS). The GaAs surfaces were prepared by molecular beam epitaxy (MBE) and exhibited large atomically well-ordered terraces. We find that the 2×4 reconstruction has a significant impact on the Fe nucleation and growth, with initial nucleation occurring at As-dimer sites. STM reveals that the first half-monolayer of Fe forms small two-dimensional islands along the As-dimer rows before growing onto the adjacent Ga-rich rows, with no evidence of substrate disruption. PED indicates that the growth is predominantly layer by layer, with the growth front for the nth deposited layer limited to the (n+1)th layer. XPS spectra show that the Fe films include a concentration gradient of Ga and As out-diffused from the interface, with some of the As segregating to the Fe surface, similar to previous results obtained for growth on non-MBE prepared GaAs surfaces. Possible mechanisms for the film growth and the origins of the intermixing are discussed.
Interfacial reactions and ohmic contact formation in the Ni/Al–6H SiC system
Authors: Marinova Ts. , Yakimova R. , Krastev V. , Hallin C. , Janzén E.
Published: July 2002

The interface chemistry and the electrical properties of annealed Ni/Al–6H SiC Ohmic contacts are studied by using x-ray photoemission spectroscopy, current–voltage characteristics, and contact resistance measurements employing a four-point method. All depositions and analysis were performed on the Si face of nitrogen doped, n-type (1×1018 cm−3) wafers of 6H SiC (0001). The chemical reactions at the interface are revealed. Al at the SiC interface acts by reducing the SiOx and forming Al2O3. At elevated temperatures, SiC in the presence of Al dissociates with formation of Al4C3 which is a stable compound. At about 1000 °C the Si atoms at the interface bond to Al and Ni either in ternary compounds with different stoichiometry or in NiSi. In the subsurface region carbon is present in the graphite state of ∼5 at. %. The Ohmic behavior of the contact is related to the formation of the NiSi while the weak contact resistivity degradation is due to the low graphite precipitation. The improved temperature stability may also be due to the presence of Al2O3 on the top of the contact structure.
Kinetics of field-induced oxidation of hydrogen-terminated Si(111)
Authors: Ley L. , Teuschler T. , Mahr K. , Miyazaki S. , Hundhausen M.
Published: July 2002

Using an atomic force microscope (AFM) with a highly doped Si tip (0.01–0.02 Ω cm) we induced the oxidation of hydrogen-terminated Si(111) surfaces by scanning the surface with an applied bias Uox between sample tip (negative) and substrate (positive) in air of 60% relative humidity. The resulting oxide height was measured relative to the unoxidized substrate immediately afterwards using the same setup in the AFM mode. Typical oxide thicknesses of some nm were achieved. p-type as well as n-type samples were investigated and the oxidation time at each point was varied by varying the scan speed of the tip during oxidation. Some of the salient results are as follows: (i) There is a definite threshold voltage Uth such that no oxidation takes place below Uth; (ii) Uth depends on doping and is lowest (2.7 V) for n+- and highest (5.4 V) for p+-type material; (iii) Uth is independent of scan speed and thus oxidation time for speeds between 0.25 and 7 μm/s. Assuming that the oxidation time is inversely proportional to the tip scan speed during oxidation we tried to fit the data to current models of oxide growth (parabolic growth law, linear-quadratic growth law, and Mott–Cabrera mechanism). None of them fits the experimental data. Instead, we find that the results are well described by a power law of the form Z=(Uox−Uth) α0 (tox/t0)γ where Z and t are the oxide thickness and the oxidation time, respectively, and α0 is a factor that depends on experimental conditions such as doping, tip shape, and humidity. The exponent γ has a value of 1/4 to within experimental uncertainty.
Metal–insulator–semiconductor structure on GaAs using a pseudomorphic Si/GaP interlayer
Authors: Park Dae-Gyu , Mohammad S. Noor , Chen Zhi , Morkoç Hadis
Published: July 2002

We report on a novel GaAs metal–insulator–semiconductor (MIS) structure exhibiting the interface state densities in the 9.2×1010 eV−1 cm−2 with a Si (10 Å)/GaP (12 Å) layer on GaAs. The structure was grown by a combination of molecular beam epitaxy and chemical vapor deposition. The hysteresis and frequency dispersion of the MIS capacitor were lower than 100 mV, some of them as low as 70 mV under a field swing of about ±1.4 MV/cm. Ex situ solid phase annealing around 500–550 °C in N2 using rapid thermal annealing was high enough to recrystallize the as-deposited Si interlayer at low temperature (∼300 °C). The 100 kHz frequency response at 77 K suggests that the interface pinning levels are close to the conduction band edge of GaAs. This article reports the first application of a pseudomorphic Si/GaP interlayer to ideal GaAs MIS diodes and exhibits a favorable interface stability with high temperature annealing.
Study of the copper reflow process using the GROFILMS simulator
Authors: Friedrich L. J. , Gardner D. S. , Dew S. K. , Brett M. J. , Smy T.
Published: July 2002

Copper has been proposed as a possible replacement for aluminum as the primary microelectronics metallization material. As the feature sizes of ultralarge scale integration (ULSI) technologies reach sub-0.25 μm in dimension, new metallization processes must be developed to properly fill the extreme topographies. This article uses GROFILMS (a thin film process simulator) to study the Cu reflow process. Comparison of simulation with experimental scanning and transmission electron micrographs show excellent agreement with regards to profile evolution and internal structure. GROFILMS is further used to study material dependent properties such as the underlayer wetting characteristics of Cu. Results show that during both the deposition and the anneal procedures, Cu’s ability to wet the underlayer can determine success or failure of the reflow process. Further, the effects of the film microstructure such as grain boundary grooving and facetting are simulated, observed in real films, and discussed in terms of process development. On the scale of ULSI features, the film texture is shown to be a significant factor in determining the success of copper reflow.
Tunneling spectroscopy on semiconductors with a low surface state density
Authors: Sommerhalter Ch. , Matthes Th. W. , Boneberg J. , Leiderer P. , Lux-Steiner M. Ch.
Published: July 2002

A detailed study of tunneling spectroscopy concerning semiconductors with a low surface state density is presented. For this purpose, I–V curves under dark conditions and under illumination were measured on the (0001) van der Waals surface of a p-type WS2 single crystal, which is known to be free of intrinsic surface states. The measurements are interpreted by an analytical one-dimensional metal-insulator-semiconductor model, which shows that the presence of the finite tunneling current has to be considered in the calculation of the tip-induced bandbending. Rectification of the dark I–V curves is explained by the absence of an inversion layer at the semiconductor surface. In contrast, the I–V curves measured for different light intensities and tip-sample separations indicate the existence of an optically induced inversion layer. Since no surface recombination needs to be considered to model these spectra, we conclude that bulk recombination, diffusion and direct tunneling of photogenerated minority charge carriers are the dominant processes for semiconductors with a low density of surface states. In contrast to the standard interpretation of tunneling spectroscopy, which can be applied to semiconductors with a high surface state density, our results clearly show that in this case the normalized differential conductivity (dI/dU)/(I/U) cannot be used to determine the energetic distribution of the local surface state density.
Dielectric breakdown of silicon oxide studied by scanning probe microscopy
Authors: Yasue Takao , Yoshida Yoshiko , Koyama Hiroshi , Kato Tadao , Nishioka Tadashi
Published: July 2002

The applicability of scanning probe microscopy in the dielectric breakdown characteristics of silicon oxide has been demonstrated. Our study demonstrates that the measurement on the oxide is free from the effect of trapped charge created by Fowler–Nordheim tunneling when a sufficient distance is maintained between the measuring points. In this condition, for a 13-nm-thick oxide, the dielectric breakdown voltages were found to be so uniform as to fluctuate only 1%. We applied this method to oxides on the wafers from two different vendors, and found that the dielectric breakdown strength of the oxide depends on the difference on the Si substrates. We also applied this method to a square oxide pattern surrounded by a field oxide, and the result was that the dielectric breakdown strength of the oxide on the edge is lower than the one in the center.
Fabrication and characterization of silicon field emitter arrays by spin-on-glass etch-back process
Authors: Lee Jin Ho , Kang Sung Weon , Song Yoon-Ho , Cho Kyoung Ik , Lee Sang Yun , Yoo Hyung Joun
Published: July 2002

Silicon field emitter arrays have been fabricated by a novel method employing a two-step tip etch and spin-on-glass etch-back process using double layered thermal/tetraethylorthosilicate oxides as a gate dielectric. Partial etching was performed by low viscosity photoresist coating and O2 plasma ashing in order to form the double layered gate dielectric. A small gate aperture with low gate leakage current was obtained by the novel process. The height and the radius of the fabricated emitter was about 1.1 μm and less than 100 Å, respectively. The anode emission current from a 256 tip array was 23 μA (i.e., 90 nA/tip) at a gate voltage of 60 V. The turn-on gate voltage was 40 V. The gate current was less than 0.1% of the total current (i.e., gate current and anode current).
Consideration of in-line qualification for ultrashallow junction implantation
Authors: Boyd Wendell , Lee Mark , Wagner Dennis , Romig Terry , Bennett Joe , Larson Lawrence , Johnson Walt , Zhou Li
Published: July 2002

The electrical characteristics of shallow junction devices are often dependent on tightly controlled ion implants for their performance and yield. However, concerns exist over the ability of existing in-line metrology tools to accurately verify low energy implants, and therefore, determine whether the ion implanter is in control before committing product to it. This article will explore the capabilities of the Therma-Probe TP500, the Tencor OmniMap RS75, and secondary-ion-mass spectroscopy to measure low energy ion implants done on an Applied Materials xR-LEAP with energies 10 keV and below, doses of 1.0E15–3.0E15 cm−2, and both boron and arsenic species.
Field emission properties of the polycrystalline diamond film prepared by microwave-assisted plasma chemical vapor deposition
Authors: Kwon Sang Jik , Hwa Shin Young , Aslam Dean M. , Lee Jong Duk
Published: July 2002

Field emission characteristics for the diamond films grown using a gas mixture of different methane concentration in hydrogen were investigated. Measured by using the field emitter with diode structure, the turn-on voltage (field) for emitting 0.1 mA/cm2 current density and the critical electric field for 10 mA/cm2 were 5 V (3.0 V/μm) and 9 V (5.5 V/μm), respectively, for the diamond emitter of a little poor quality grown in 1.5% methane concentration. While, for the good quality diamond emitter grown in 0.5% methane concentration, the values were shown as 10 V (6.1 V/μm) and 21 V (12.7 V/μm), respectively. It is suggested that this phenomenon can be related with the field enhancement effect due to protruding small crystallites and the energy bands induced by internal stress or defects, depending on the film quality.
Surface composition and morphology of chemical beam epitaxy grown GaN thin films
Authors: Kim Esther , Berishev I. , Bensaoula A. , Lee S. , Perry S. S. , Waters K. , Schultz J. A.
Published: July 2002

In this article, we present our results on gallium nitride (GaN) films grown by chemical beam epitaxy (CBE) using triethyl gallium (TEG) and ammonia (NH3), on Al2O3(0001) substrates. In situ characterization of the GaN surface was performed by reflection high energy electron diffraction and time-of-flight mass spectroscopy of recoil ions. In order to initiate the growth, a 200 Å thick buffer layer was grown using electron cyclotron resonance plasma activated nitrogen and TEG. During CBE growth of GaN, growth rates were in the range of 1000–4000 Å/h limited only by the pumping capacity of the growth reactor. It is only in a narrow temperature window of 800–825 °C that two-dimensional smooth single crystal layers are obtained. A clear correlation between crystal quality and surface carbon was observed. GaN films grown at 800 °C consist of hexagonal hillocks less than 1 μm in size with surface root mean square roughness of 40 Å/1 μm.
Intersubband absorption and photoluminescence in Si-doped self-organized InAs/Ga(Al)As quantum dots
Authors: Phillips J. , Kamath K. , Zhou X. , Chervela N. , Bhattacharya P.
Published: July 2002

We report on far-infrared absorption in directly and modulation doped self-organized InAs quantum dots. Photoluminescence spectra demonstrate a blue shift in peak intensity for increasing doping in the quantum dots. Band to band transitions from InAs wetting layer, and InAs ground and excited states are observed from photovoltage spectroscopy. Far infrared absorption measurements using a Fourier transform infrared spectrometer show absorption in the range of 6–18 μm for InAs quantum dots using a waveguide (45°) geometry and under normal incidence.
In situ ultraviolet illumination of porous silicon during scanning tunneling microscopy
Authors: Schwall D. , Otter F. A. , Galligan J. M.
Published: July 2002

Studies of porous silicon before and during ultraviolet excitation were performed using scanning tunneling microscopy. Images taken during ultraviolet excitation compared with images taken immediately prior to ultraviolet excitation show changes in the size of selective surface features. There is an increase in feature height and a decrease in feature width between the images of nonluminescing and luminescing porous silicon. These drastic effects are a consequence of an increase in available charge carriers in porous silicon, namely, in the quantum wires.
Very high-resolution focused ion beam nanolithography improvement: A new three-dimensional patterning capability
Authors: Gierak J. , Cambril E. , Schneider M. , David C. , Mailly D. , Flicstein J. , Schmid G.
Published: July 2002

We detail a novel three dimensional (3D) patterning capability for focused ion beam technology which uses, as a resist, a gold cluster compound Au55(PPh3)12Cl6. The high-resolution 3D morphology of the patterned structures is examined and electrical characterization analyses are carried out. Patterns having minimal lateral dimension about 30 nm and vertical resolution below 10 nm, are displayed using this method. Direct writing speeds up to 3.6 103 μm/s were reached.
Effects of phase and thickness of cobalt silicide on field emission properties of silicon emitters
Authors: Yoon Young Joon , Kim Gi Bum , Baik Hong Koo
Published: July 2002

For solving the drawbacks of silicon emitters, emitters coated with cobalt silicide were developed in this study. The cobalt silicide emitters showed enhanced emission properties including I–V characteristics and long-term current stability compared to bare silicon emitters. This was mainly caused by a reduction of the effective work function and the formation of a chemically stable surface. However, the electron emission characteristics differed according to the phase and thickness of the cobalt silicide. Detailed results about the effect of the phase and thickness of cobalt silicide on electron emission are discussed.
Between the Sheets: Why Do Protein Strands Line Up?
Authors: Service Robert F.
Published: July 2002

To understand how protein chains fold into their complex structures and mimic them in new drugs and materials, protein chemists want to know how their basic structural elements--coils, bends, and sheets--take shape. The toughest to understand are the so-called beta sheets, in which two or more segments of the protein chain lie parallel to each other, like pencils placed side by side. But by making their own small beta sheets or disrupting natural ones, biochemists are learning the key factors that hold them together.
All-in-One Detectors for the Faintest Objects
Authors: Nadis Steve
Published: July 2002

By separating two thin layers of superconductor with an insulating barrier, scientists at the European Space Agency have created an optical detector that can detect a signal as faint as a single photon and determine its wavelength. That combination of abilities is far beyond current astronomical detectors, and laboratories are now vying to fabricate large arrays of these devices, called superconducting tunnel junctions (STJs), which could capture complete images. If these efforts succeed--cooling the devices and taming their electronic noise may be stumbling blocks--STJs could revolutionize the search for faint galaxies, planets around other stars, and pulsars.
Going Dutch: Mainstreaming Alternatives
Authors: Roush Wade
Published: July 2002

The Netherlands has taken the lead on alternatives to animal testing and has slashed the number of animals used by some 60% since 1978. Dutch law requires classes in animal welfare and consideration of alternative methods, which researchers say can be time-consuming but don't unduly impede research.
Could Transgenic Supercrops One Day Breed Superweeds?
Authors: Kling James
Published: July 2002

Seattle--In the United States, government officials are approving more and more transgenic crops for widespread field testing. But based on new data on the frequency of gene transfer, some ecologists fear that advantageous genes, such as those that confer virus resistance, could escape from the crops into wild plants and create a hardier race of weeds.
Some Biologists See Holes in Gap Analysis
Authors: Schmidt Karen
Published: July 2002

To target the best places for protection, conservation biologists often overlay maps of the ranges of different species in a technique called “gap analysis.” The method has been valuable in pinpointing unprotected sites, but some critics charge that the range maps themselves are unreliable.
Martian Rocks Tell Divergent Stories
Authors: Kerr Richard A.
Published: July 2002

New developments continue in the life on Mars story, as a British team announced strong new isotopic evidence for ancient life in a Martian meteorite—while an American researcher suggested that such meteorites are marked by earthly contamination instead.
The R&D Portfolio: A Concept for Allocating Science and Technology Funds
Authors: McGeary Michael , Smith Philip M.
Published: July 2002

A research and development (R&D) portfolio concept is proposed to allocate federal funds for science and technology. The portfolio approach, analogous to that used by financial investors to ensure returns under conditions of great uncertainty and risk, would help ensure that national investment in R&D is productive during a period of great change and severe fiscal stringency. It could be adapted to the decentralized structure of the American R&D enterprise and rely on the informed advice of scientists and engineers on priorities and funding needs at each level of the policy-making decision process.
Unscrambling Time in the Fossil Record
Authors: Kerr Richard A.
Published: July 2002

Geochronologist Glenn Goodfriend and paleontologist Stephen Jay Gould report on
page 1894
how they used a combination of two dating techniques to extract a 15,000-year-long record of one campaign in a land snail's long and ultimately successful battle to win the Bahamian island of Great Inagua from a native species. This fossil record revealed a surprisingly prolonged intermingling of an invading species and its eventual victim.
Baltimore to Head New Vaccine Panel
Authors: Cohen Jon
Published: July 2002

In an effort to jump-start stalled efforts to develop an AIDS vaccine, William Paul, head of the Office of AIDS Research at the National Institutes of Health, announced on 12 December that the NIH AIDS vaccine budget would be raised from $109.5 million to $129 million in fiscal year 1997, and that Nobel Prize-winning retrovirologist David Baltimore will head a new AIDS vaccine panel to help coordinate the effort.
Wide Use of Rabbit Virus Is Good News for Native Species
Authors: Drollette Dan
Published: July 2002

CANBERRA, AUSTRALIA
—The rabbit hemorrhagic disease virus—so far—is working exactly as Australian animal-control and health officials hoped when they released the deadly agent last fall in a controversial effort to combat a century-old plague of European rabbits. With a fatality rate of 95% in some regions, the virus is clearing the way for a rejuvenation of species ranging from the showy groundsel shrub to the western gray kangaroo.
At What Price?
Authors: Lawler Andrew
Published: July 2002

Federal belt-tightening has driven a wedge between those who favor a more aggressive approach to lobbying—rating lawmakers, rallying the troops at the first sign of danger, and raising a war chest to promote science among the corridors of power—and those who worry that such politicking will jeopardize a half-century of bipartisan support. At stake is the size of future research budgets.
Cells Count Proteins to Keep Their Telomeres in Line
Authors: Barinaga Marcia
Published: July 2002

Cells that divide repeatedly, such as cancer cells, germ-line cells, and microorganisms such as yeast, have to take good care of their telomeres, the specialized stretches of repetitive DNA at the ends of their chromosomes. Because of a quirk in the enzymes that replicate the DNA, the chromosomes shorten a little with each cell division, and for cells to keep dividing they have to add back the telomere DNA. Otherwise, essential genes could be lost. New results appearing on pages
973
and
986
now show that one way yeast cells keep track of how long their telomeres are is by counting the copies of a protein called Rap1 bound to the telomere DNA.
Atoms Take a Turn for the Better
Authors: Seife Charles
Published: July 2002

Every time a jetliner maneuvers, patterns of light and shadow in a device called an interferometer measure the change in angle. Now, photons have a rival for sensing small rotations: interfering atoms. With an atom interferometer, which takes advantage of the wavelike nature of matter described by quantum mechanics, physicists have measured rotations as subtle as a quarter of a degree per hour.
The Breast-Screening Brawl
Authors: Taubes Gary
Published: July 2002

Should regular mammography screening be recommended for women in their forties? The question has sparked a controversy that culminated last month at the National Cancer Institute, in a meeting that ended with accusations of fraud and bureaucratic chicanery. Stoking the controversy is sparse and contradictory evidence about whether screening really helps reduce breast cancer mortality in this age group, concern about false positives and unnecessary surgery, and a radical difference in outlook between the radiologists who favor screening and the epidemiologists and public health experts who urge caution.
Scientists Describe Deep-Sea Rebirth
Authors: Kaiser Jocelyn
Published: July 2002

SEATTLE
—The Annual Meeting and Science Innovation Exposition of the American Association for the Advancement of Science, held here from 13 to 18 February, opened with a panel of top science policy officials from around the world discussing inadequate research budgets and the growing R&D gap between the industrialized countries and those of the developing world. Attendees also heard a description of the remarkable resurgence of a community of bizarre creatures around deep-sea vents that had been devastated by an underwater volcano.
Update: Biological Nitrogen Fixation and Model Chemistry
Authors: Leigh G. J.
Published: July 2002

In biological systems such as plants, enzymes called nitrogenases “fix” nitrogen from the air for use by the organism. In his Perspective Update, Leigh discusses new work that examines how nitrogen is processed by simpler molecular complexes. Such studies may reveal how nitrogenases work, which would increase our fundamental understanding of plant biochemistry and could potentially lead to more efficient industrial processing of nitrogen. See also the two reports related to this Perspective by Shan
et al
. (
p. 1460
) and Fryzuk
et al
. (
p. 1445
).
Feathered Dino Wins a Few Friends
Authors: Gibbons Ann
Published: July 2002

Rumors of a Chinese fossil dinosaur with feathers sparked skepticism last fall, but the specimen is now being taken seriously by paleontologists who have actually been to China and seen it.
An Epoch Past
Authors: Birman Joseph L.
Published: July 2002

Essays of a Soviet Scientist.
VITALII I. GOL'DANSKII. AIP Press, Woodbury, NY, 1997. xvi, 303 pp., illus. $32.95. ISBN 1-56396-454-6. Masters of Modern Physics.
Globular Clusters at Low and High Redshift
Authors: Burgarella Denis
Published: July 2002

Globular clusters form homogeneous populations of stars. On the one hand, because initial conditions are homogeneous within one cluster but vary from cluster to cluster, their study can shed light on stellar evolution processes. On the other hand, globular clusters contain the oldest known stellar population in galaxies. The study of the characteristics of globular cluster systems is one way to understand parent galaxy formation and early evolution. Unfortunately, a direct observation of the time when globular clusters and galaxies formed is still out of reach for today’s telescopes, but this remains a major goal.
Clinical Trials from Close Up
Authors: Hilgartner Stephen
Published: July 2002

Between Bench and Bedside.
Science, Healing, and Interleukin-2 in a Cancer Ward. ILANA LÖWY. Harvard University Press, Cambridge, MA, 1996. vi, 370 pp., illus. $39.95 or £26.50. ISBN 0-674-06809-2.
Raising the Dead
Authors: Dodson Peter
Published: July 2002

The Science of Jurassic Park and The Lost World.
Or How to Build a Dinosaur. ROB DeSALLE and DAVID LINDLEY. BasicBooks, New York, 1997. xxix, 194 pp., illus. $18 or C$25.50. ISBN 0-465-07379-4.
Science and Technology in Foreign Affairs
Authors: Watkins James D.
Published: July 2002

With science and technology (S&T) research increasingly relying on international cooperation, there is a need for U.S. foreign policy to focus on S&T. Large collaborative research efforts, including international space and energy projects and global environmental conventions, are hindered by the U.S. government's lack of commitment, which makes potential partners in Europe and Asia hesitate at joining these projects. The U.S. government has not placed enough importance on international S&T as being integral to the United States' economic and political future.
Evolutionary Basics
Authors: Gillespie John H.
Published: July 2002

Molecular Evolution.
WEN-HSIUNG LI. Sinauer, Sunderland, MA, 1997. xvi, 487 pp., illus. $52.95 or £32.95. ISBN 0-87893-463-4.
Cells and Replicons
Authors: Newlon Carol
Published: July 2002

Eukaryotic DNA Replication.
J. JULIAN BLOW, Ed. IRL (Oxford University Press), New York, 1996. xx, 232 pp., illus. $105 or £65, ISBN 0-19-963586-2; paper, $55 or £29.95, ISBN 0-19-963585-4. Frontiers in Molecular Biology, 15.
Heroic Therapies
Authors: Löwy Ilana
Published: July 2002

A Commotion in the Blood.
Life, Death, and the Immune System. STEPHEN S. HALL. Holt, New York, 1997. xiv, 544 pp. + plates. $30 or C$41.95. ISBN 0-8050-3796-9.
A Public Scientist
Authors: Ritvo Harriet
Published: July 2002

Huxley.
From Devil's Disciple to Evolution's High Priest. ADRIAN DESMOND. Addison-Wesley, Reading, MA, 1997. xxii, 820 pp., illus., + plates. $37.50. ISBN 0-201-95987-9. Published in the U.K. in two volumes by Joseph, 1994 and 1997.
An Incipient Synthesis
Authors: Padian Kevin
Published: July 2002

Patterns and Processes of Vertebrate Evolution.
ROBERT L. CARROLL. Cambridge University Press, New York, 1997. xvi, 448 pp., illus. $85 or £70, ISBN 0-521-47232-6; paper, $39.95 or £24.95, ISBN 0-521-47809-x. Cambridge Paleobiology, 2.
Environmental Pioneer
Authors: Zuk Marlene
Published: July 2002

Rachel Carson.
Witness for Nature. LINDA LEAR. Holt, New York, 1997. xviii, 634 pp., illus., + plates. Paper, $35 or C$49. ISBN 0-8050-3427-7.
Many Faces of the Synapse
Authors: Trussell Laurence
Published: July 2002

Excitatory Amino Acids and Synaptic Transmission.
H. V. WHEAL and A. M. THOMSON, Eds. 2nd ed. Academic Press, San Diego, 1997. xvi, 388 pp., illus., + plates. $75, ISBN 0-12-746031-4.
Recreating the Brain Online
Authors: Frackowiak Richard
Published: July 2002

Neuroinformatics.
An Overview of the Human Brain Project. STEPHEN H. KOSLOW and MICHAEL F. HUERTA, Eds. Erlbaum, Mahwah, NJ, 1997. xii, 376 pp., illus., + plates. $79.95 or £60.95. ISBN 0-8058-2099-x. Progress in Neuroinformatics Research.
How the Land Turned Green
Authors: Olmstead Richard
Published: July 2002

The Origin and Early Diversification of Land Plants. A Cladistic Study.
PAUL KENRICK and PETER R. CRANE. Smithsonian Institution Press, Washington, DC, 1997. xiv, 441 pp. $55, ISBN 1-56098-730-8; paper, $27.50, ISBN 1-56098-729-4.
A Mole Brought to Light
Authors: Holloway David
Published: July 2002

Bombshell.
The Secret Story of America's Unknown Atomic Spy Conspiracy. JOSEPH ALBRIGHT and MARCIA KUNSTEL. Times Books, New York, 1997. xvi, 400 pp., + plates. $25 or C$35. ISBN 0-8129-2861-X.
Unification Not Proved
Authors: Dupré John
Published: July 2002

Consilience
. The Unity of Knowledge. EDWARD O. WILSON. Knopf, New York, 1998. x, 335 pp. $26 or C$34.95. ISBN 0-679-45077-7.
Libraries in the Digital Future
Authors: Keller Michael A.
Published: July 2002

Books, Bricks, and Bytes
Libraries in the Twenty-First Century. Stephen R. Graubard and Paul LeClerc, Eds. Transaction Publishers, New Brunswick, NJ, 1998. 379 pp. Paper, $24.95. ISBN1-56000-986-1.

Books, Bricks, and Bytes
is a collection of essays looking at the future of libraries, written on the occasion of the 100th anniversary of the New York Public Library. While defending the evolving role of librarians, most of the essays fail to grapple with potential problems such as rights to see and use information, or questions of archiving impermanent digital records.
Low-Temperature Synthesis of Zintl Compounds with a Single-Source Molecular Precursor
Authors: Beswick Michael A. , Choi Nick , Harmer Christopher N. , Hopkins Alexander D. , McPartlin Mary , Wright Dominic S.
Published: July 2002

Thermolysis of the heterobimetallic phosphinidene complex {[Sb(PCy)
3
]
2
- Li
6
·6HNMe
2
} (Cy = C
6
H
11
) at 303 to 313 kelvin gives Zintl compounds containing (Sb
7
)
3−
anions. The complex thus constitutes a stable molecular single-source precursor to Zintl compounds and provides a potential low-temperature route to photoactive alkali metal antimonates. The new chemical reaction involved, which is driven thermodynamically by the formation of P–P bonds, has implications in the low-temperature synthesis of other technologically important materials (such as gallium arsenide).
How to Make Sense of Sequences
Authors: Bult Carol J.
Published: July 2002

Bioinformatics
A Practical Guide to the Analysis of Genes and Proteins. Andreas D. Baxevanis and B. F. Francis Ouellette, Eds. Wiley-Interscience, 1998. New York, 384 pp. $149.95, £135. ISBN 0-471-32441-8. Paper, $59.95, £38.95. ISBN 0-471-19196-5.

This companion to sequence analysis provides concise overviews of many widely used methods and databases. It is intended to help readers design and implement a successful strategy for analyzing DNA and protein sequences, and to help them realize what the various methods can and cannot do.
Control of Neonatal Tolerance to Tissue Antigens by Peripheral T Cell Trafficking
Authors: Alferink Judith , Tafuri Anna , Vestweber Dietmar , Hallmann Rupert , Hämmerling Günter J. , Arnold Bernd
Published: July 2002

Self tolerance is acquired by the developing immune system. As reported here, particular properties of the neonatal tissue contribute to this process. Neonatal skin, but not adult skin, was accessible for naı̈ve CD8 T cells. In mouse bone marrow chimeras generated at different ages, recent thymic emigrants were tolerized to a skin-expressed major histocompatibility complex class I antigen only during a neonatal period but not during adulthood. Blockade of T cell migration neonatally prevented tolerance induction. Thus, T cell trafficking through nonlymphoid tissues in the neonate is crucial for the establishment of self tolerance to sessile, skin-expressed antigens.
A 3.3-Ma Impact in Argentina and Possible Consequences
Authors: Schultz P. H. , Zarate M. , Hames W. , Camilión C. , King J.
Published: July 2002

Enigmatic glassy materials (escorias) and red bricklike materials (tierras cocidas) occur at a restricted stratigraphic level (the top of the Chapadmalal Formation). Materials from one locality near Mar del Plata are attributed to a mid-Pliocene impact event with a radiometric and magnetostratigraphic age of 3.3 million years ago (Ma). An extinction of endemic fauna (including the glyptodonts and flightless cariamid birds) correlates with the unit containing the impact glasses. Moreover, the age of the glasses is coincident within dating uncertainties with a pulselike change in the oxygen isotope marine record in the Atlantic and Pacific Oceans just before the late Pliocene deterioration of the climate.
The Search for Intelligence
Authors: Bouchard Thomas J.
Published: July 2002

IQ and Human Intelligence
. N. J. Mackintosh. Oxford University Press, Oxford, 1998. 429 pp. $98, £55. ISBN 0-19-852368-8. Paper, $35, £19.95. ISBN 0-19-852367-X.

Addressing one of the most controversial subjects in science, Mackintosh offers a thorough, balanced, and thoughtful overview of measuring and explaining the general nature of intelligence.
Nota Bene: Unmasking Melodious Sounds
Authors: Voss David
Published: July 2002

The Physics of Musical Instruments
2nd ed. Neville H. Fletcher and Thomas D. Rossing. Springer, New York, 1998. 776 pp. $69.95. ISBN 0-387-98374-0.

Fletcher and Rossing revise and update their comprehensive quantitative analysis of music-making devices and provide an entirely new chapter on the materials science of instruments.
Lingua Franca
Authors: Steele Fintan R.
Published: July 2002

Tower of Babel
The Evidence against the New Creationism. Robert T. Pennock. MIT Press, Cambridge, MA, 1999. 451 pp. $35. ISBN 0-262-16180-X.

Drawing on a discussion of the evolution of languages, philosopher of science Pennock provides a restrained, patient, and thorough refutation of current creationist positions (including intelligent design and theistic science).
Do We Have to Count One by One?
Authors: Belin Thomas R.
Published: July 2002

Who Counts?
The Politics of Census-Taking in Contemporary America. Margo J. Anderson and Stephen E. Fienberg. Russell Sage Foundation, New York, 1999. 329 pp. $32.50. ISBN 0-87154-256-0.

Anderson and Fieberg provide a richly informative account of the historical and scientific context of the current controversy surrounding census-taking in the United States.
Spiraling Storm Systems
Authors: Neumann Charles J.
Published: July 2002

Hurricanes of the North Atlantic
Climate and Society. James B. Elsner and A. Birol Kara. Oxford University Press, New York, 1999. 504 pp. $49.95. ISBN 0-19-512508-8.

Elsner and Kara offer a detailed, technical reference on the nature of Atlantic hurricane activity.
Frontline View of an Invasion
Authors: Gili Josep-Maria
Published: July 2002

Killer Algae
The True Tale of a Biological Invasion. Alexandre Meinesz. translated by Daniel Simberloff. University of Chicago Press, Chicago, 1999. 376 pp. $25, £17.50. ISBN 0-226-51922-8.

Meinesz offers a personal account of the biological and political history of the spread of
Caulerpa taxifolia
after it appeared in the Mediterranean in the early 1980s. He highlights the factors that thwarted his struggles to stem the invasion.
Connections Through a Matrix
Authors: Wilf Herbert S.
Published: July 2002

Proofs and Confirmations
The Story of the Alternating Sign Matrix Conjecture. David M. Bressoud. Cambridge University Press, New York, and Mathematical Association of America, Washington, DC, 1999. 290 pp. $74.95. ISBN 0-521-66170-6. Paper, $29.95. ISBN 0-521-66646-5.

Bressoud offers an account of the search for a proof of an early 1980s conjecture on objects that generalize permutation matrices. Although this recent development in algebraic combinatorics can seem quite impenetrable, he succeeds in making it clear and provides an informative illustration of how mathematical research progresses.
Geography as Destiny?
Authors: Lang Graeme
Published: July 2002

The Great Divergence
China, Europe, and the Making of the Modern World Economy. Kenneth Pomeranz. Princeton University Press, Princeton, NJ, 2000. 392 pp. $39.95, £25.95. ISBN 0-691-00543-5.

How could some European societies come to project their power throughout the world while China and India failed to do so? Pomeranz argues that the two most important factors behind this divergence were Europe's possession of convenient supplies of coal and European's armed exploitation of other resource-rich areas.
An Emotional High for Stocks?
Authors: Stulz René M.
Published: July 2002

Irrational Exuberance
. Robert J. Shiller. Princeton University Press, Princeton, NJ, 2000. 318 pp. $27.95, £17.50. ISBN 0-691-05062-7.

In addition to arguing that the current U.S. stock market is overvalued, Shiller makes a strong case for interpreting the financial economics from a behavioral perspective that emphasizes psychological factors rather than rational choices.
How We See Things
Authors: Westheimer Gerald
Published: July 2002

Human Perception of Objects
Early Visual Processing of Spatial Form Defined by Luminance, Color, Texture, Motion, and Binocular Disparity. David Regan. Sinauer Associates, Sunderland, MA, 2000. 607 pp. Paper, $44.95, £25.95. ISBN 0-87893-753-6.

Regan's subtitle provides an accurate summary of this detailed and systematic discussion of how we see objects and discriminate their shapes.
The Context of Our Genetic History
Authors: Goldstein David B.
Published: July 2002

Genes, Peoples, and Languages
. Luigi Luca Cavalli-Sforza. North Point Press (Farrar, Straus and Giroux), New York, 2000. 240 pp. $24, £18.99. ISBN 0-86547-529-6.

Cavalli-Sforza's lively and accessible account of human genetic history also provides an excellent overview of the author's career, which has strongly influenced how we study human evolution today.
How the Brain Made Language
Authors: Ullman Michael T.
Published: July 2002

Lingua ex Machina
Reconciling Darwin and Chomsky with the Human Brain. William H. Calvin and Derek Bickerton. MIT Press, Cambridge, MA, 2000. 306 pp. $26.95, £17.95. ISBN 0-262-03273-2.

Presenting their discussion in the form of a lively dialogue, the authors integrate the different strands of language study into a consideration of the evolutionary pathways leading from ape behaviors to syntax.
Was There Life After DNA?
Authors: Weatherall David
Published: July 2002

A Passion for DNA
Genes, Genomes, and Society. James D. Watson. Cold Spring Harbor Laboratory Press, Cold Spring Harbor, NY, 2000. 270 pp. $25. ISBN 0-87969-581-1. Oxford University Press, Oxford, 2000. 270 pp. £18.99. ISBN 0-19-850697-X.

In the 25 essays in this collection, written over a period of more than 30 years, Watson offers informative and often provocative commentary on topics ranging from his early experiences to the social implications of the Human Genome Project.
From Infectious Filtrate
Authors: Rheinberger Hans-Jörg
Published: July 2002

Tobacco Mosaic Virus
One Hundred Years of Contributions to Virology. Karen-Beth G. Scholthof, John G. Shaw, and Milton Zaitlin, Eds. American Phytopathological Society Press, St. Paul, MN, 1999. 264 pp. $49. ISBN 0-89054-236-8.

This collection of classic papers on the tobacco mosaic virus and brief commentaries on their significance charts the changing interests in TMV from its role in the origins of virology to the present.
A Feast Without Recipes
Authors: Emsley John
Published: July 2002

The Cambridge World History of Food
. Kenneth F. Kiple and Kriemhild Coneè Ornelas, Eds. Cambridge University Press, New York, 2000. 2-vol. set. 2207 pp. $150, £95. ISBN 0-521-40216-6.

Over 150 experts in fields from agronomy to zoology have contributed to this international history of food and nutrition. They explore topics ranging from the diets of early humans, through a global tour of specific foods and drinks, to current food policy issues.
A Fruitful Fungus
Authors: Catcheside David E. A.
Published: July 2002

Neurospora
Contributions of a Model Organism. Rowland H. Davis. Oxford University Press, New York, 2000. 345 pp. $110. ISBN 0-19-512236-4.

Davis provides a definitive and accessible summary of the 75 years of research on this filamentous fungus, the study of which has made major contributions to a diverse range of biological problems.