bluuebunny/crossref_metadata_2025 huggingface dataset:
Performance evaluation of the commercial point of inflection thermometry substrate temperature monitor
Authors: Svensson Stefan P. , Gill David M.
Published: July 2002

One of the first commercial point of inflection thermometry (POINTTM) systems is compared to an IRCONTM ModlinePlus Series V pyrometer, and the standard noncontact thermocouple in a Mod Gen II molecular beam epitaxy system. The standard POINTTM system was modified to include a pyrometer as an integral part of the optical system. A series of temperature measurements using these three techniques were compared on GaAs and InP substrates and during the molecular beam epitaxy growth of GaSb layers on a semi-insulating, single-side polished GaAs substrate. It is possible to obtain excellent agreement between the POINTTM system and pyrometer measurements over the effective operating range of the pyrometer (∼400–600 °C). We concluded that the POINTTM system performed well in its intended mode, which consists of deposition of films with band gaps larger than that of the two substrates GaAs and InP, for which the instrument is calibrated. Furthermore, for deposition of narrow band gap materials, the integration of a transmission (POINTTM) and an emission instrument (pyrometer) provide a very powerful combination. The present limitations of the POINTTM system and recommendations for improvements will be discussed.
Cell configuration-induced strain in quaternary films
Authors: Svensson Stefan P. , Uppal Parvez N. , Gill David M.
Published: July 2002

This article describes two effects that can cause serious bending in GaSb and InAs substrates used for quaternary compounds. Understanding of both effects is required in order to produce flat wafers. We have observed a very large bending with both positive and negative curvature in wafers with mismatched films, both at growth and room temperature. We therefore postulate that misfit dislocation formation is suppressed in these materials and that the bending is due to the lattice mismatch. However, bending may also occur in wafers where the mismatch in the center of the wafer is negligible. We propose that this effect is due to a mismatch due to nonuniform mole fraction variations across the wafer and throughout the film which in turn are induced by the way the flux distributions combine to create a particular mole fraction. The conclusion that must be drawn from these observations is that production of flat wafers require the intentional introduction of a slight mismatch during the growth process.
Room-temperature chlorination of As-rich GaAs (110)
Authors: Simpson William C. , Shuh David K. , Yarmoff Jory A.
Published: July 2002

As-rich GaAs (110) is prepared by ion bombardment and annealing, followed by chlorination and reannealing. The surface is then reacted at room temperature with Cl2 gas and examined with soft x-ray photoelectron spectroscopy of the Ga and As 3d core levels. After low exposures (<5×104 L), the surface appears to passivate with half a monolayer of Cl adsorbed, primarily as AsCl. Following sufficiently large (≳5×104 L) exposures, however, the surface begins to etch, as indicated by the continuous uptake of chlorine and the formation of As and Ga chlorides. After the largest exposures, the distribution of As chlorides still favors the monochloride, whereas the Ga chlorides favor GaCl2. It is proposed that the heavily reacted surface is covered with –AsCl–GaCl2 treelike structures. The addition of Cl to form GaCl3 from GaCl2 is identified as the rate-limiting step in the overall etching reaction.
Polycrystalline silicon field emitters
Authors: Boswell E. C. , Huq S. E. , Huang M. , Prewett P. D. , Wilshaw P. R.
Published: July 2002

Field emission of electrons from polycrystalline silicon micropoint emitters has been investigated. Two process routes, wet and dry etching, were used to form emitters, and their morphologies were compared using a transmission electron microscope (TEM). TEM micrographs of the wet-etched polysilicon structures show the presence of many individual grains at the tip. Arrays were easily manufactured, using the wet-etch process, to form sharp conical micropoints. However, the dry-etch process did not allow the formation of sharp tips. Field emission current–voltage data was collected from the wet-etched polycrystalline emitters immediately after etching and showed their emission characteristics to be similar to single crystal silicon emitters. Oxidation sharpening had little effect on the field emission characteristics.
Influence of fill gases on the failure rate of gated silicon field emitter arrays
Authors: Meassick S. , Champaign H.
Published: July 2002

The influence of a variety of background gases on the failure rate of gated field emitter arrays has been investigated. The effects of argon, helium, nitrogen, and xenon were investigated, with pressures ranging from 1×10−8 to 1×10−4 Torr. The gated field emitter arrays were operated in dc and pulsed emission modes. The failure rate of gated field emitters is a very strong function of the type of background gas, its pressure, and whether the array was operated in a pulsed or dc bias mode. As expected, the failure rate for all gases increased rapidly as the background pressure increased, but was substantially different for the various gases. The failure rate of arrays increased rapidly as the electron impact ionization cross section of the background gas decreased. The large reduction in failure rates due to operation in a pulsed mode as compared to a dc mode of operation, as previously seen for experiments without a background gas, was also evident for all background gases tested.
Technology computer aided design characterization needs and requirements
Authors: Law Mark E.
Published: July 2002

Technology computer aided design (TCAD) promises predictive calculations of both structural and electrical parameters of advanced semiconductor devices. How realistic is this promise for shallow junction technology? What are the models used for predicting shallow junctions? What kind of verification and experimental support is required? Does TCAD place additional requirements on the characterization community?
X-ray induced mask contamination and particulate monitoring in x-ray steppers
Authors: Capasso C. , Pomerene A. , Chu W. , Leavey J. , Lamberti A. , Hector S. , Oberschmidt J. , Pol V.
Published: July 2002

The belief that proximity x-ray lithography is insensitive to contamination has been based on the assumption that contaminants are small hydrocarbon compounds. However, we will show that x rays may induce photoassisted processes that deposit saltlike films on the mask surface. We will also provide an explanation for the film geometry in the early stages of its growth and suggest some possible solutions to the issue.
Fabrication of x-ray masks for giga-bit DRAM by using a SiC membrane and W–Ti absorber
Authors: Marumoto Kenji , Yabe Hideki , Aya Sunao , Kitamura Kaeko , Sasaki Kei , Kise Koji , Miyachi Takeshi
Published: July 2002

Advanced x-ray masks for giga-bit DRAM require an optimization of the mask fabrication process and a stress-free absorber. In this article, we will describe the performance of the x-ray masks fabricated by a membrane process where back-etch is performed prior to electron beam writing. With other techniques such as stress control by step-annealing and electron beam (EB) multiple writing, mask-to-mask overlay was reduced to less than 40 nm. In spite of multiple EB writing, the pattern size accuracies of 0.14 μm critical dimension were about 10% and 20% for the line and two-dimensional patterns, respectively. For further improvement in the uniformity of absorber stress and resultant higher placement accuracy, a space variant annealing method is proposed, where the nonuniformity of the absorber stress is corrected by spatially variant temperature distribution during the annealing. Under this method, the uniformity of the amorphous W–Ti absorber improved to about 10 MPa in a 50 mm diam region.
Atomic wires and their electronic properties
Authors: Yamada Toshishige
Published: July 2002

Atomic wire electronics are considered, where the band structure and the resultant Fermi energy are designed by manipulating the lattice constant. Using the tight-binding theory with universal parameters, it is shown that Si wires and arrays are metallic, Mg wires are insulating, and Mg arrays have metallic and insulating phases for infinitely large, isolated cases. Structures are of finite size, and electrodes are necessary for the applications. The finite size brings about discrete electron energy levels, and electrodes will charge or discharge the structure, reflecting the work function difference, so that even the basic electronic properties may be altered. The electrodes will cause further complications such as the energy level broadening, the Coulomb interaction through an effective capacitance, or the mode-selection resistance. When the contact satisfies certain conditions, a metallic wire is predicted to show two distinct I–V patterns for small voltages. Depending on whether the highest occupied level is either partially or fully filled, the current starts to flow rapidly or does not flow until the voltage overcomes the next level, respectively.
Application of the scanning force microscope in structuring and in temperature-dependent analysis of Au nanostructures
Authors: Göbel H. , Jacobs L. , von Blanckenhagen P.
Published: July 2002

The amplitudes of one-dimensional periodic profiles were analyzed as functions of annealing temperatures to determine surface diffusion constants and activation energies with high lateral resolution. The temperature dependence of the surface self-diffusion constant was derived for temperatures between 573 and 1073 K by Fourier analysis of the profiles. A temperature-dependent study of the surface of nanocrystalline Au revealed an increase in grain size with rising temperature and the ratio of free energy on the surface and at grain boundaries.
Scanning tunneling microscopy modification of Ag thin films on Si(100): Local rearrangement of the Si substrate by Ag/Si eutectic phase formation
Authors: Memmert U. , Hodel U. , Hartmann U.
Published: July 2002

The melting, eutectic alloy formation, and evaporation, induced locally by a scanning tunneling microscope, was studied for 20 nm Ag films, deposited on hydrogen-terminated Si(100) surfaces. The Ag thin film can be locally rearranged or evaporated with a lateral resolution of 100–150 nm. For long interaction durations 50–70 nm wide and 30 nm deep, grooves could also be cut into the Si substrate. The modification mechanism can be explained by a model involving local melting, alloy formation, and evaporation.
Experimental study of matrix carbon field-emission cathodes and computer aided design of electron guns for microwave power devices, exploring these cathodes
Authors: Grigoriev Y. A. , Petrosyan A. I. , Penzyakov V. V. , Pimenov V. G. , Rogovin V. I. , Shesterkin V. I. , Kudryashov V. P. , Semyonov V. C.
Published: July 2002

The experimental study of matrix carbon field-emission cathodes (MCFECs), which has led to the stable operation of the cathodes with current emission values up to 100 mA, is described. A method of computer aided design of TWT electron guns (EGs) with MCFEC, based on the results of the MCFEC emission experimental study, is presented. The experimental MCFEC emission characteristics are used to define the field gain coefficient K and the cathode effective emission area Seff. The EG program computes the electric field upon the MCFEC surface, multiplies it by the K value and uses the Fowler–Nordheim law and the Seff value to calculate the MCFEC current; the electron trajectories are computed as well.
Strain relaxation and surface morphology of compositionally graded Si/Si1−xGex buffers
Authors: Li J. H. , Springholz G. , Stangl J. , Seyringer H. , Holy V. , Schäffler F. , Bauer G.
Published: July 2002

Systematic studies of strain relaxation were performed in a series of compositionally graded SiGe buffer layers grown without and with a subsequent constant composition SiGe layer by x-ray reciprocal space mapping techniques. The analysis of these experiments yields depth dependent strain values as well as misfit dislocation densities. The higher the grading rate (%Ge/μm) the higher the residual in-plane strain at the epitaxial surface. Atomic force microscopy studies show that the rms surface roughness increases systematically with increasing final Ge content of the graded layers and rises with increasing grading rate.
In situ controlled reactions and phase formation of thin films on GaAs
Authors: Caldwell D. A. , Chen L. C. , Bensaoula A. H. , Farrer J. K. , Carter C. B. , Palmstro/m C. J.
Published: July 2002

In situ sequential depositions and reactions are used to control a reaction sequence first to consume GaAs and then to release GaAs from the reaction product. The first reaction involves annealing in situ deposited Ni on molecular beam epitaxially grown GaAs (100) at 300 °C to form a Ni3GaAs/GaAs structure. Exposure of this structure to As4 results in a reaction which consumes the Ni3GaAs by the layer-by-layer formation of NiAs at the surface and epitaxially regrown GaAs at the Ni3GaAs/GaAs interface. The NiAs formation and GaAs regrowth are controlled by the As4 flux. Ni diffusion dominates both the Ni3GaAs formation and decomposition mechanisms. Reflection high-energy electron diffraction, Rutherford backscattering, x-ray diffraction, and transmission electron microscopy data are used to confirm the phase formation and reaction sequences.
Pattern dependent alignment technique for mix-and-match electron-beam lithography with optical lithography
Authors: Gotoh Yasuko , Sohda Yasunari , Saitou Norio , Tawa Tsutomu , Matsuzaka Takashi , Asai Naoko , Hayano Katsuya , Hasegawa Norio
Published: July 2002

An alignment technique for electron-beam (EB) lithography that corrects the writing pattern to match the pattern-dependent lens distortion of an optical stepper is proposed. In mix-and-match EB and optical lithography, precise measurement of positional distortion caused by the stepper lens is necessary. However, recent research in optical lithography has shown that the lens distortion differs depending on the pattern features. Thus, we have enhanced the measurement method to reflect the pattern-feature dependence of positional distortion in optical lithography. To measure the various types of distortions more effectively, we modified the marks used for distortion and overlay measurement. The measured pattern dependence of the lens distortion was in good agreement with our simulation results and the overlay accuracy in mix-and-match lithography was improved with this method.
Electron-optical optimization for Gaussian, high-current, high-dose columns
Authors: Mankos Marian , Veneklasen Lee H. , Garcia Rudy , Pearce-Percy Henry
Published: July 2002

This article demonstrates the electron-optical optimization of a high-current, high-dose column operating at 10 keV. The goal is to increase the available dose to the resist, which requires increasing the current density to more than 800 A/cm2. Our calculations use the MEBS Ltd. BOERSCH program. We model the complete column as a set of thin lenses, separated by field-free drift spaces. Monte Carlo simulation propagates discrete bunches of electrons through the column, taking into account the mutual repulsion between pairs of electrons. Gaussian spot size and current density in the column were calculated for three beam currents: 314, 75, and 35 nA. The results show that to achieve a higher current density, it is necessary to change the electron gun and the column. Specifically, a low aberration gun and a significantly shorter column are required. At 10 keV, the column performance at high beam currents (∼300 nA) is almost entirely dominated by electron–electron interactions. Major improvements in gun performance only yield minor improvement in total column performance, and a significant decrease in column length is required to reduce the electron–electron interactions enough to meet the design specification. A new, low aberration gun operating in an accelerating lens mode gun was chosen. A major effort was focused on redesigning the middle column to reduce electron–electron interactions. The combination of the low-aberration electrostatic gun and a shorter middle column provides the key improvement in the current density (dose) performance of the column. Results of experimental measurements on the optimized columns are in good agreement with the presented Monte Carlo simulations.
Roller nanoimprint lithography
Authors: Tan Hua , Gilbertson Andrew , Chou Stephen Y.
Published: July 2002

An alternative approach to flat nanoimprint lithography (NIL)—roller nanoimprint lithography (RNIL) is demonstrated. Compared with flat NIL, RNIL has the advantage of better uniformity, less force, and the ability to repeat a mask continuously on a large substrate. Two methods for RNIL are developed: (a) rolling a cylinder mold on a flat, solid substrate; (b) putting a flat mold directly on a substrate and rolling a smooth roller on top of the mold. Using our current roller nanoimprint system, sub-100 nm resolution pattern transfer has been achieved.
OS3: Photoemission from gold thin films for application in multiphotocathode arrays for electron beam lithography
Authors: Jiang Xinrong , Berglund C. N. , Bell Anthony E. , Mackie William A.
Published: July 2002

Photoemission is a promising approach to electron sources for electron beam lithography because of the ease with which various shapes or arrays of independently modulated sources can be fabricated. However, most high-quantum-efficiency photoemitters are extremely sensitive to even partial monolayers of contamination, and therefore require some combination of differential pumping systems and photoemitter surface protection after activation. Here we propose to use a high-power 257 nm laser in combination with the relatively high work function and low quantum efficiency of gold films to produce practical multicathode electron sources for electron beam lithography. Gold films have the offsetting advantages that their photoemission characteristics are relatively reproducible and stable even in contaminating environments. It is possible, therefore, to prepare and handle them in air as well as operate them in less demanding vacuum environments. It is shown that a back-illuminated 15 nm gold film on a quartz or sapphire substrate exhibits a quantum efficiency of approximately 10−4 at 257 nm, producing photocurrents greater than 1 μA at a laser power of under 200 mW. The quantum efficiency is very reproducible and relatively stable under a variety of environmental and operational conditions. Slow changes, by as much as a factor of 3, over time periods of several weeks following sample preparation have been observed, consistent with variations of the gold work function of approximately 0.2 eV. The results are in good agreement with a straightforward extension of existing photoemission models for bulk material.
0.18 μm KrF lithography using optical proximity correction based on empirical behavior modeling
Authors: Tritchkov Alexander , Stirniman John , Gangala Hareen , Ronse Kurt
Published: July 2002

We present the characterization of optical proximity effects and their correction for 0.18 μm deep-ultraviolet (UV) lithography processes using a semiempirically derived “behavior” model. Since critical dimension (CD) measurement data for deriving the model are taken after resist pattern transfer into the underlying layer (α-Si), the model incorporates all of the different proximity effect contributors: optics, mask, resist bake, etching, etc. The modeling technology we use allows for user defined model forms. It was empirically determined that the CD behavior could be adequately described by the diffusion of the aerial image with one Gaussian, and an adjustment to the signal threshold based on signal slope. The validity of the model for random geometry was confirmed by comparing contours drawn on Prospector™ with two-dimensional configurations of the uncorrected and corrected parts of a 0.18 μm test circuit. The model is then used for proximity effects correction of the gate level of a 0.18 μm test design and for the feasibility study for printing 0.15 μm features using deep-UV (λ=248 nm) lithography. Also, some process window enhancement techniques are evaluated in the correction recipe to enlarge the limited process window for printing 0.175 μm features.
Investigation of new overlay measurement marks for optical lithography
Authors: Saito Takashi , Watanabe Hisashi
Published: July 2002

New overlay measurement marks that consider the influence of coma aberration have been investigated. The concept behind the marks is the use of patterns that correspond to the actual device pattern rules, because the effect of coma aberration depends on the pattern size and pitch. Registration errors within one layer and overlay errors between two layers have been measured with the marks. The registration measurement results showed that the displacement of the marks with fine line patterns was different from that of the large box pattern. The difference was more than 20 nm. Then the overlay measurement marks were adapted to measure the displacement between a polysilicon gate pattern and an etched oxide layer. The results were compared to the scanning electron microscopy measurement of actual patterns and they showed good agreement. The repeatability of the marks was less than 5 nm and this is sufficient for quarter micron device fabrication. Overlay measurement marks having fine patterns can precisely measure the overlay errors of the actual fine patterns and can improve the overlay accuracy.
InP-collector double-heterojunction bipolar transistors by valved phosphorus cracker
Authors: Chin T. P. , Gutierrez-Aitken A. L. , Cowles J. , Kaneshiro E. N. , Han A. C. , Block T. R. , Oki A. K. , Streit D. C.
Published: July 2002

We report the growth and device characterization of InAlAs/InGaAs/InP double-heterojunction bipolar transistors in a solid source molecular beam epitaxy system with a valved-phosphorus cracker. Linearly graded InGaAlAs base-collector and emitter-base junctions were used. Photoreflectance characterization shows excellent growth reproducibility. The dc current–voltage characteristics of a 1.5×10 μm2 device indicate high breakdown voltage, low offset voltage, and good linearity. Breakdown voltage of an InP-collector device with compositionally graded base-collector junction is 19 V compared to 11 V for an InGaAs-collector device. By comparison, a chirped superlattice base-collector junction shows significant current oscillations due to the carrier tunneling effect. High-frequency performance was similar to previously reported InGaAs-collector devices; unity current-gain frequency and unity maximum-available power gain frequency are 75 and 140 GHz, respectively.
Heavily carbon-doped In0.53Ga0.47As on InP (001) substrate grown by solid source molecular beam epitaxy
Authors: Cai W. Z. , Lubyshev D. I. , Miller D. L. , Streater R. W. , SpringThorpe A. J.
Published: July 2002

Heavily carbon-doped In0.53Ga0.47As with hole densities between 5.6×1018 and 2.1×1020 cm−3 has been grown by solid source molecular beam epitaxy on InP. The dependence of carbon tetrabromide (CBr4)-induced lattice mismatch upon the atomic carbon concentration has been determined from x-ray rocking curve measurements. It has been found by secondary ion mass spectroscopy that the alloy composition is altered by the preferential etching effect of CBr4. After taking into account this compositional change, the “intrinsic” lattice contraction solely due to carbon incorporation has been obtained, which obeys Vegard’s law.
High-quality InAlAs layers grown on (411)A-oriented InP substrates by molecular beam epitaxy
Authors: Kitada Takahiro , Nii Keisuke , Hiraoka Tetsuya , Shimomura Satoshi , Hiyamizu Satoshi
Published: July 2002

High-quality InAlAs layers lattice matched to InP were successfully grown on (411)A-oriented InP substrates by molecular beam epitaxy (MBE). High-resolution x-ray diffraction and photoluminescence (PL) measurements of InAlAs layers grown on (411)A InP substrates revealed that crystalline quality of the (411)A InAlAs layer strongly depends on the substrate temperature (Ts), and much improved crystalline quality of (411)A InAlAs layer was achieved at a high Ts (570 °C). The linewidth of the PL (12 K) peak from the best (411)A InAlAs layer is 10.7 meV which is 16%–29% smaller than those (12.8–15 meV) of InAlAs layers grown on conventional (100) InP substrates by MBE.
Spin-on Cu films for ultralarge scale integrated metallization
Authors: Murakami Hirohiko , Hirakawa Masaaki , Ohtsuka Yoshiro , Yamakawa Hiroyuki , Imazeki Nobuya , Hayashi Shigeo , Suzuki Toshihiro , Oda Masaaki , Hayashi Chikara
Published: July 2002

We have developed the spin-on Cu metal (SOM) process to fill trenches and vias down to 0.3 μm. SOM is a liquid material that contains an organic solvent and dispersed ultrafine particles as a source of Cu. This solution was applied to a Si wafer using a spin coater to form a film. Coated wafers were baked at 623–673 K for 10 min in a reducing atmosphere. The end result is a Cu film. Contrary to the conventional deposition techniques, the SOM process is simple but advantageous to its gap filling, planarization, and cost consideration.
Outlook for 157 nm resist design
Authors: Kunz R. R. , Bloomstein T. M. , Hardy D. E. , Goodman R. B. , Downs D. K. , Curtin J. E.
Published: July 2002

We have measured the transparencies of a number of candidate resist materials for 157 nm, with an emphasis on determining which chemical platforms would allow resists to be used at maximum thicknesses while meeting requirements for optical density. Although ideal imaging is usually obtained at an optical density between 0.1 and 0.3 and values in excess of 0.5 can often result in nonvertical wall profiles, we chose to arbitrarily choose 0.4 as the maximum tolerable optical density. Using this analysis, our findings show that all existing commercially available resists would need to be <60 nm thick, whereas specialized hydrocarbon resists could be made ∼100 nm thick, and new resists based on hydrofluorocarbons, siloxanes, and/or silsesquioxanes could be engineered to be used in thicknesses approaching 200 nm. We also assess the tradeoff between these thicknesses and what current information exists regarding defects as a function of resist thickness.
Comparison of contact radius models for ultrashallow spreading resistance profiles
Authors: Hartford E. J. , Ramey S. M. , Ye C. W. , Hartford C. L.
Published: July 2002

Over the years, several methods have emerged for determining the probe contact radius in spreading resistance measurements. The methods vary from attempting to determine the physical area of the probe contact to the use of the contact radius as a variable parameter determined from calibration data. The number of different methods has led to some confusion about the applicability of the different models. In this article, we examine the validity of the different models for various ultrashallow structures typically used in current device technology. Specifically, we examine several methods of determining the physical contact area from the existing probe mark. These methods include circumscribing all visible microcontacts, determining the width of the probe mark in the measurement direction, and a summation of the contribution from all microcontacts. We further examine various electrical models for determination of the probe contact, including a calibration curve fit and a determination based on a known sample profile.
Improvement of electron emission of silicon field emitter arrays by pulsed laser cleaning
Authors: Yavas O. , Suzuki N. , Takai M. , Hosono A. , Okuda S.
Published: July 2002

A diode-pumped Q-switched Nd:YLF laser was used for the cleaning of microfabricated silicon field emitter arrays. The laser wavelength was systematically varied from infrared to visible and ultraviolet, while the emission current was measured simultaneously. Infrared (λ=1047 nm) or visible (λ=523 nm) laser irradiation did not alter the emission behavior. Ultraviolet laser irradiation at λ=349 nm, on the other hand, resulted in a significant increase in the emission current due to cleaning of the emitter tip surface. Numerical simulation of the laser induced temperature rise at the silicon surface and the wavelength dependence of the cleaning efficiency indicate that photochemical decomposition, requiring energetic photons, is the main mechanism for the removal of the contaminants. However, if higher energetic photons at λ=262 nm (fourth harmonic) are used, a temporary decrease in emission current during laser irradiation was observed. A simultaneous decrease of the vacuum level in the test chamber indicates that this unexpected behavior is attributable to the removal of ionized species from the silicon tip. Removal of the contaminants without ionization, therefore, appears to be an essential condition for efficient cleaning of the emitter tips and correspondingly for an increase in the emission current.
Requirement of Phospholipase Cδ4 for the Zona Pellucida-Induced Acrosome Reaction
Authors: Fukami Kiyoko , Nakao Kazuki , Inoue Takafumi , Kataoka Yuki , Kurokawa Manabu , Fissore Rafael A. , Nakamura Kenji , Katsuki Motoya , Mikoshiba Katsuhiko , Yoshida Nobuaki , Takenawa Tadaomi
Published: July 2002

Several phospholipase C (PLC) isoforms have been found in male and female mammalian gametes, and splicing isoforms of PLCδ4 are predominantly expressed in testis. Here we report that male mice in which the
PLCδ4
gene had been disrupted either produced few small litters or were sterile. In vitro fertilization studies showed that insemination with PLCδ4
−/−
sperm resulted in significantly fewer eggs becoming activated and that the calcium transients associated with fertilization were absent or delayed. PLCδ4
−/−
sperm were unable to initiate the acrosome reaction, an exocytotic event required for fertilization and induced by interaction with the egg coat, the zona pellucida. These data demonstrate that PLCδ4 functions in the acrosome reaction that is induced by the zona pellucida during mammalian fertilization.
Segregation of Human Neural Stem Cells in the Developing Primate Forebrain
Authors: Ourednik Václav , Ourednik Jitka , Flax Jonathan D. , Zawada W. Michael , Hutt Cynthia , Yang Chunhua , Park Kook I. , Kim Seung U. , Sidman Richard L. , Freed Curt R. , Snyder Evan Y.
Published: July 2002

Many central nervous system regions at all stages of life contain neural stem cells (NSCs). We explored how these disparate NSC pools might emerge. A traceable clone of human NSCs was implanted intraventricularly to allow its integration into cerebral germinal zones of Old World monkey fetuses. The NSCs distributed into two subpopulations: One contributed to corticogenesis by migrating along radial glia to temporally appropriate layers of the cortical plate and differentiating into lamina-appropriate neurons or glia; the other remained undifferentiated and contributed to a secondary germinal zone (the subventricular zone) with occasional members interspersed throughout brain parenchyma. An early neurogenetic program allocates the progeny of NSCs either immediately for organogenesis or to undifferentiated pools for later use in the “postdevelopmental” brain.
Impairment of Mycobacterial But Not Viral Immunity by a Germline Human
STAT1
Mutation
Authors: Dupuis Stéphanie , Dargemont Catherine , Fieschi Claire , Thomassin Nicolas , Rosenzweig Sergio , Harris Jeff , Holland Steven M. , Schreiber Robert D. , Casanova Jean-Laurent
Published: July 2002

Interferons (IFN) α/β and γ induce the formation of two transcriptional activators: gamma-activating factor (GAF) and interferon-stimulated gamma factor 3 (ISGF3). We report a natural heterozygous germline
STAT1
mutation associated with susceptibility to mycobacterial but not viral disease. This mutation causes a loss of GAF and ISGF3 activation but is dominant for one cellular phenotype and recessive for the other. It impairs the nuclear accumulation of GAF but not of ISGF3 in heterozygous cells stimulated by IFNs. Thus, the antimycobacterial, but not the antiviral, effects of human IFNs are principally mediated by GAF.
Far-Ultraviolet Imaging of Jupiter's Aurora and the Io “Footprint”
Authors: Clarke John T. , Ballester Gilda E. , Trauger John , Evans Robin , Connerney J E. P. , Stapelfeldt Karl , Crisp David , Feldman Paul D. , Burrows Christopher J. , Casertano Stefano , Gallagher John S. , Griffiths Richard E. , Hester J. Jeff , Hoessel John G. , Holtzman Jon A. , Krist John E. , Meadows Vikki , Mould Jeremy R. , Scowen Paul A. , Watson Alan M. , Westphal James A.
Published: July 2002

Far-ultraviolet images of Jupiter from the Hubble Space Telescope Wide Field Planetary Camera 2 reveal polar auroral emissions at 300 kilometer resolution and three times higher sensitivity than previously achieved. Persistent features include a main oval containing most of the emission and magnetically connected to the middle magnetosphere, diffuse and variable emissions poleward of the main oval, and discrete emission from Io's magnetic footprint equatorward of the oval. The auroral emissions are variable, exhibit magnetic conjugacy, and are visible above the planet limb. All emissions approximately co-rotate with Jupiter except the Io “footprint,” which is fixed along Io's magnetic flux tube.
Uniting Two General Patterns in the Distribution of Species
Authors: Hanski Ilkka , Gyllenberg Mats
Published: July 2002

Two patterns in the distribution of species have become firmly but independently established in ecology: the species-area curve, which describes how rapidly the number of species increases with area, and the positive relation between species' geographical distribution and average local abundance. There is no generally agreed explanation of either pattern, but for both the two main hypotheses are essentially the same: divergence of species along the ecological specialist-generalist continuum and colonization- extinction dynamics. A model is described that merges the two mechanisms, predicts both patterns, and thereby shows how the two general, but formerly disconnected, patterns are interrelated.
Giant Piezoelectric Effect in Strontium Titanate at Cryogenic Temperatures
Authors: Grupp Daniel E. , Goldman Allen M.
Published: July 2002

Piezoelectric materials have many applications at cryogenic temperatures. However, the piezoelectric response below 10 kelvin is diminished, making the use of these materials somewhat marginal. Results are presented on strontium titanate (SrTiO
3
), which exhibits a rapidly increasing piezoelectric response with decreasing temperature below 50 kelvin; the magnitude of its response around 1 kelvin is comparable to that of the best materials at room temperature. This “giant” piezoelectric response may open the way for a broad class of applications including use in ultralow-temperature scanning microscopies and in a magnetic field–insensitive thermometer. These observations, and the possible divergence of the mechanical response to electric fields at even lower temperatures, may arise from an apparent quantum critical point at absolute zero.
Local, Nonvolatile Electronic Writing of Epitaxial Pb(Zr
0.52
Ti
0.48
)O
3
/SrRuO
3
Heterostructures
Authors: Ahn C. H. , Tybell T. , Antognazza L. , Char K. , Hammond R. H. , Beasley M. R. , Fischer Ø. , Triscone J.-M.
Published: July 2002

A scanning probe microscope was used to induce local, nonvolatile field effects in epitaxial, ferroelectric Pb(Zr
0.52
Ti
0.48
)O
3
/SrRuO
3
heterostructures. Field-effected regions with linewidths as small as 3500 angstroms were written by locally switching the polarization field of the Pb(Zr
0.52
Ti
0.48
)O
3
layer; the electronic density of the underlying metallic SrRuO
3
layer was modified and the sheet resistance was changed by up to 300 ohms per square. This procedure is completely reversible and allows submicrometer electronic features to be written directly in two dimensions, with no external electrical contacts or lithographic steps required.
An Advective-Reflective Conceptual Model for the Oscillatory Nature of the ENSO
Authors: Picaut J. , Masia F. , du Penhoat Y.
Published: July 2002

Recent findings about zonal displacements of the Pacific warm pool required a notable modification of the delayed action oscillator theory, the current leading theory for the El Niño–Southern Oscillation (ENSO). Simulations with a linearized coupled ocean-atmosphere model resulted in 3- to 6-year ENSO-like oscillations, with many of the variable model parameters found to be very close to their observed values. This simple model suggests that ocean processes that are ignored or underestimated in the delayed action oscillator theory, such as zonal current convergence, zonal advection of sea surface temperature, and equatorial wave reflection from the eastern ocean boundary, are fundamental to the development of the ENSO, in particular to its manifestations in the central equatorial Pacific.
Structure, Bonding, and Geochemistry of Xenon at High Pressures
Authors: Caldwell Wendel A. , Nguyen Jeffrey H. , Pfrommer Bernd G. , Mauri Francesco , Louie Steven G. , Jeanloz Raymond
Published: July 2002

Although xenon becomes metallic at pressures above about 100 gigapascals, a combination of quantum mechanical calculations and high pressure–temperature experiments reveals no tendency on the part of xenon to form a metal alloy with iron or platinum to at least 100 to 150 gigapascals. The transformation of xenon from face-centered cubic (fcc) to hexagonal close-packed (hcp) structures is kinetically hindered, the differences in volume and bulk modulus between the two phases being smaller than we can resolve (less than 0.3 percent and 0.6 gigapascals, respectively). The equilibrium fcc-hcp phase boundary is at 21 (±3) gigapascals, which is a lower pressure than was previously thought, and it is unlikely that Earth's core serves as a reservoir for primordial xenon.
Inhibition of Invasion of Epithelial Cells by Tiam1-Rac Signaling
Authors: Hordijk Peter L. , ten Klooster Jean Paul , van der Kammen Rob A. , Michiels Frits , Oomen Lauran C. J. M. , Collard John G.
Published: July 2002

Tiam1 encodes an exchange factor for the Rho-like guanosine triphosphatase Rac. Both Tiam1 and activated RacV12 promote invasiveness of T lymphoma cells. In epithelial Madin–Darby canine kidney (MDCK) cells, Tiam1 localized to adherens junctions. Ectopic expression of Tiam1 or RacV12 inhibited hepatocyte growth factor–induced scattering by increasing E-cadherin–mediated cell-cell adhesion accompanied by actin polymerization at cell-cell contacts. In Ras-transformed MDCK cells, expression of Tiam1 or RacV12 restored E-cadherin–mediated adhesion, resulting in phenotypic reversion and loss of invasiveness. These data suggest an invasion-suppressor role for Tiam1 and Rac in epithelial cells.
Bosonic Stimulation in the Formation of a Bose-Einstein Condensate
Authors: Miesner H.-J. , Stamper-Kurn D. M. , Andrews M. R. , Durfee D. S. , Inouye S. , Ketterle W.
Published: July 2002

The formation of a Bose-Einstein condensate of a dilute atomic gas has been studied in situ with a nondestructive, time-resolved imaging technique. Sodium atoms were evaporatively cooled close to the onset of Bose-Einstein condensation and then suddenly quenched to below the transition temperature. The subsequent equilibration and condensate formation showed a slow onset distinctly different from simple relaxation. This behavior provided evidence for the process of bosonic stimulation, or coherent matter-wave amplification, crucial to the concept of an atom laser.
Association of Malaria Parasite Population Structure, HLA, and Immunological Antagonism
Authors: Gilbert Sarah C. , Plebanski Magdalena , Gupta Sunetra , Morris Joanne , Cox Martin , Aidoo Michael , Kwiatkowski Dominic , Greenwood Brian M. , Whittle Hilton C. , Hill Adrian V. S.
Published: July 2002

Host-parasite coevolution has been likened to a molecular arms race, with particular parasite genes evolving to evade specific host defenses. Study of the variants of an antigenic epitope of
Plasmodium falciparum
that induces a cytotoxic T cell response supports this view. In African children with malaria, the variants present are influenced by the presence of a human leukocyte antigen (HLA) type that restricts the immune response to this epitope. The distribution of parasite variants may be further influenced by the ability of cohabiting parasite strains to facilitate each other's survival by down-regulating cellular immune responses, using altered peptide ligand antagonism.
High-
T
c
Superconductors in the Two-Dimensional Limit: [(Py-C

n

H

2
n
+1

)
2
HgI
4
]-Bi
2
Sr
2
Ca

m
−1

Cu

m

O

y

(
m
= 1 and 2)
Authors: Choy Jin-Ho , Kwon Soon-Jae , Park Gyeong-Su
Published: July 2002

The free modulation of interlayer distance in a layered high–transition temperature (high-
T
c
) superconductor is of crucial importance not only for the study of the superconducting mechanism but also for the practical application of high-
T
c
superconducting materials. Two-dimensional (2D) superconductors were achieved by intercalating a long-chain organic compound into bismuth-based high-
T
c
cuprates. Although the intercalation of the organic chain increased the interlayer distance remarkably, to tens of angstroms, the superconducting transition temperature of the intercalate was nearly the same as that of the pristine material, suggesting the 2D nature of the high-
T
c
superconductivity.
Requirement for the Leukocyte-Specific Adapter Protein SLP-76 for Normal T Cell Development
Authors: Clements James L. , Yang Baoli , Ross-Barta Susan E. , Eliason Steve L. , Hrstka Ronald F. , Williamson Roger A. , Koretzky Gary A.
Published: July 2002

The leukocyte-specific adapter molecule SLP-76 (Src homology 2 domain–containing leukocyte protein of 76 kilodaltons) is rapidly phosphorylated on tyrosine residues after receptor ligation in several hematopoietically derived cell types. Mice made deficient for SLP-76 expression contained no peripheral T cells as a result of an early block in thymopoiesis. Macrophage and natural killer cell compartments were intact in SLP-76–deficient mice, despite SLP-76 expression in these lineages in wild-type mice. Thus, the SLP-76 adapter protein is required for normal thymocyte development and plays a crucial role in translating signals mediated by pre–T cell receptors into distal biochemical events.
Role for the Target Enzyme in Deactivation of Photoreceptor G Protein in Vivo
Authors: Tsang Stephen H. , Burns Marie E. , Calvert Peter D. , Gouras Peter , Baylor Denis A. , Goff Stephen P. , Arshavsky Vadim Y.
Published: July 2002

Heterotrimeric guanosine 5′-triphosphate (GTP)–binding proteins (G proteins) are deactivated by hydrolysis of the GTP that they bind when activated by transmembrane receptors. Transducin, the G protein that relays visual excitation from rhodopsin to the cyclic guanosine 3′,5′-monophosphate phosphodiesterase (PDE) in retinal photoreceptors, must be deactivated for the light response to recover. A point mutation in the γ subunit of PDE impaired transducin-PDE interactions and slowed the recovery rate of the flash response in transgenic mouse rods. These results indicate that the normal deactivation of transducin in vivo requires the G protein to interact with its target enzyme.
Far-Ultraviolet Imaging Spectroscopy of Io's Atmosphere with HST/STIS
Authors: Roesler F. L. , Moos H. W. , Oliversen R. J. , Woodward R. C. , Retherford K. D. , Scherb F. , McGrath M. A. , Smyth W. H. , Feldman P. D. , Strobel D. F.
Published: July 2002

Well-resolved far-ultraviolet spectroscopic images of O
i
, S
i
, and previously undetected H
i
Lyman-α emission from Io were obtained with the Hubble space telescope imaging spectrograph (STIS). Detected O
i
and S
i
lines (1250 to 1500 angstroms) have bright equatorial spots (up to 2.5 kilorayleighs) that shift position with jovian magnetic field orientation; limb glow that is brighter on the hemisphere facing the jovian magnetic equator; and faint diffuse emission extending to ∼20 Io radii. All O
i
and S
i
features brightened by ∼50 percent in the last two images, concurrently with a ground-based observation of increased iogenic [O
i
] 6300-angstrom emission. The H
i
Lyman-α emission, consisting of a small, ∼2-kilorayleigh patch near each pole, has a different morphology and time variation.
Acetogenesis from H
2
Plus CO
2
by Spirochetes from Termite Guts
Authors: Leadbetter J. R. , Schmidt T. M. , Graber J. R. , Breznak J. A.
Published: July 2002

Pure cultures of termite gut spirochetes were obtained and were shown to catalyze the synthesis of acetate from H
2
plus CO
2
. The 16
S
ribosomal DNA sequences of two strains were 98 percent similar and were affiliated with those of the genus
Treponema
. However, neither was closely related to any known treponeme. These findings imply an important role for spirochetes in termite nutrition, help to reconcile the dominance of acetogenesis over methanogenesis as an H
2
sink in termite hindguts, suggest that the motility of termite gut protozoa by means of attached spirochetes may be based on interspecies H
2
transfer, and underscore the importance of termites as a rich reservoir of novel microbial diversity.
Requirement of Type III TGF-β Receptor for Endocardial Cell Transformation in the Heart
Authors: Brown Christopher B. , Boyer Angelique S. , Runyan Raymond B. , Barnett Joey V.
Published: July 2002

Transforming growth factor–β (TGF-β) signaling is mediated by a complex of type I (TBRI) and type II (TBRII) receptors. The type III receptor (TBRIII) lacks a recognizable signaling domain and has no clearly defined role in TGF-β signaling. Cardiac endothelial cells that undergo epithelial-mesenchymal transformation express TBRIII, and here TBRIII-specific antisera were found to inhibit mesenchyme formation and migration in atrioventricular cushion explants. Misexpression of TBRIII in nontransforming ventricular endothelial cells conferred transformation in response to TGF-β2. These results support a model where TBRIII localizes transformation in the heart and plays an essential, nonredundant role in TGF-β signaling.
Moissanite: A Window for High-Pressure Experiments
Authors: Xu Ji-an , Mao Ho-kwang
Published: July 2002

We achieved a pressure of 52.1 gigapascals with moissanite anvils, which have optical, thermal, electric, magnetic, and x-ray properties that rival those of diamond. The mode-softening of D
2
O toward the pressure-induced hydrogen bond symmetrization and the Raman shifts of diamond under hydrostatic and nonhydrostatic compressions were studied with moissanite anvils in the spectral regions normally obscured by diamond anvils. Moissanite anvil cells allow maximum sample volumes 1000 times larger than those allowed by diamond anvil cells and may enable the next level of advancement in high-pressure experiments.
Crossing the Hopf Bifurcation in a Live Predator-Prey System
Authors: Fussmann Gregor F. , Ellner Stephen P. , Shertzer Kyle W. , Hairston Jr. Nelson G.
Published: July 2002

Population biologists have long been interested in the oscillations in population size displayed by many organisms in the field and laboratory. A wide range of deterministic mathematical models predict that these fluctuations can be generated internally by nonlinear interactions among species and, if correct, would provide important insights for understanding and predicting the dynamics of interacting populations. We studied the dynamical behavior of a two-species aquatic laboratory community encompassing the interactions between a demographically structured herbivore population, a primary producer, and a mineral resource, yet still amenable to description and parameterization using a mathematical model. The qualitative dynamical behavior of our experimental system, that is, cycles, equilibria, and extinction, is highly predictable by a simple nonlinear model.