bluuebunny/crossref_metadata_2025 huggingface dataset:
Deposition of indium tin oxide films on polycarbonate substrates by using ion beam processes
Authors: Cho Jun-Sik , Koh Seok-Keun , Yoon Ki Hyun
Published: October 2003

Indium tin oxide (ITO) films have been deposited on polycarbonate (PC) substrates by an oxygen ion-assisted deposition (IAD), where the PC substrates were pretreated by an ion-assisted reaction (IAR) to increase a surface energy of PC surfaces resulting in improving adhesion between a film and a substrate. In the IAD process, an oxygen ion energy and an arrival ratio were varied from 60 to 500 eV and from 0.25 to 1.50, respectively. During the pretreatment using the IAR, the PC substrates were bombarded by Ar+ ions with the energy of 1000 eV in oxygen environment. After IAR treatment, the surface energy of the PC substrates increased largely due to a polar component related to a newly formed functional group, which is identified as carbonyl group by x-ray photoelectron spectroscopy analysis. The adhesion between the film and the substrate was estimated qualitatively by a peel test using Scotch tape™ and by a water boiling test, and the significant adhesion improvement was obtained in the ITO films deposited on the IAR treated PC substrates. The surface morphology and electrical resistivity of the ITO films were significantly dependent on the bombarded oxygen ion energy, the arrival ratio and the substrate temperature. The low electrical resistivity (4.1×10−4 Ω cm) and high transmittance (≈80%) in a visible range were obtained in the 60 eV ion-assisted films deposited at the arrival ratio of 1.00 and substrate temperature of 50 °C. Based on these results, an effect of ion bombardment on the material properties of the ITO film during film growth was discussed in detail and a mechanism of adhesion improvement for the ITO films deposited on the IAR treated PC substrates was briefly proposed.
Submillimeter-wavelength plasma chemical diagnostics for semiconductor manufacturing
Authors: Benck Eric C. , Golubiatnikov Guerman Yu. , Fraser Gerald T. , Ji Bing , Motika Stephen A. , Karwacki Eugene J.
Published: October 2003

Submillimeter-wavelength linear-absorption spectroscopy has been applied to the chemical diagnostics of reactive-ion etching plasmas in a modified capacitively coupled gaseous electronics conference reactor. Approximately 1 mW of narrow-band (<10 kHz) submillimeter radiation between 450 and 750 GHz is produced using a backward-wave oscillator (BWO). The BWO is frequency stabilized to a harmonic of a 78–118 GHz frequency synthesizer. The submillimeter method offers high sensitivity for the ≈1 MHz linewidth, Doppler-broadened absorption lines typical of gas-phase molecules at a total pressure of less than 133 Pa (1 Torr). A large number of molecules can be detected, limited primarily by the need for a permanent electric dipole moment and for accurate line frequency predictions, the latter of which are often available in the literature. The capabilities of the diagnostic method have been demonstrated by the following three applications: (1) the measurement of water-vapor contamination in the reactor and in the precursor gas by monitoring a rotational transition of H2O in the reactor just prior to the initiation of the plasma; (2) the assessment of progress in the cleaning of the reactor by an O2/Ar plasma after a fluorocarbon plasma etch by monitoring the build up of the concentration of O3 and the depletion of the concentration of CF2O in the plasma; and (3) the determination of the endpoint in the etching of a SiO2 thin film on silicon by an octafluorocyclobutane/O2/Ar plasma by monitoring the decrease in the concentration of SiO in the plasma. The last observation is made possible by the large electric dipole moment for SiO of 1×10−29 C m (3.1 D), which gives a low minimum detectable number density for the radical of 2×107 cm−3 for an optical pathlength of 39 cm.
Enhanced growth of low-resistivity NiSi on epitaxial Si0.7Ge0.3 on (001)Si with a sacrificial amorphous Si interlayer
Authors: Wu W. W. , Cheng S. L. , Lee S. W. , Chen L. J.
Published: October 2003

Enhanced growth of low-resistivity NiSi on epitaxial Si0.7Ge0.3 with a sacrificial amorphous Si (a-Si) interlayer has been achieved. The a-Si layer with appropriate thickness was found to prevent Ge segregation, decrease the growth temperature, as well as maintain the interface flatness and morphological stability in forming low-resistivity NiSi on Si0.7Ge0.3 grown by molecular beam eptiaxy. The process promises to be applicable to the fabrication of high-speed Si–Ge devices.
Mechanisms of circular defects for shallow trench isolation oxide deposition
Authors: Lan Jin Kun , Wang Ying Lang , Liu Chuan-Pu , Chao Chuen Guang , Ay Chyung , Liu Chi Wen , Cheng Yi Lung
Published: October 2003

Shallow trench isolation (STI) is extensively used as the isolation method beyond 0.18 μm generation. This study explored the formation of circular defects in high-density plasma (HDP) STI deposition. Circular defects were caused by the burst flow of silane reactive gas. The defect maps were coincident with the silane flow field. Fourier transform infrared and secondary-ion-mass spectroscopy data exhibited that the silane-burst flow formed a silicon rich oxide (SRO) film. This SRO film existed between the STI oxide and liner oxide. The circular defects were easily found using optical microscopy (OM) for STI with SRO film. Scanning electron microscopy and transmission electron microscopy photographs show that these defects include bubbles and concavities. When SRO fully covers the liner oxide, bubbles easily form by delamination between SRO film and liner oxide. This correlates with the high tensile stress produced by the SRO film. Besides this, higher STI deposition temperatures yield more bubbles. When SRO discontinuously forms on the liner oxide, the concavities were induced by the variation of STI deposition rate on SRO film and liner oxide. The surface charge difference between the SRO film and the liner oxide is the driving force for the generation of concavities.
Effects of oxygen-flow rate on the characteristics of the ZrO2 dielectric layers grown by metalorganic molecular beam epitaxy
Authors: Hong Jang-Hyuk , Choi Woo-Jong , Kim Doo-Soo , Myoung Jae-Min
Published: October 2003

ZrO 2 dielectric layers were grown on p-type Si(100) by metalorganic molecular beam epitaxy. Zirconium t-butoxide, Zr(O⋅t-C4H9)4 was used as a Zr precursor for its moderate vapor pressure. The properties of the layers were evaluated by x-ray photoelectron spectroscopy, high-resolution transmission electron microscopy, x-ray diffraction, and capacitance–voltage (C–V) and current–voltage (I–V) analyses. At a low O2/Ar flow ratio, a fully oxidized ZrO2 layer was not obtained and metallic zirconium was incorporated in the layer. A higher oxygen-flow rate was required to diminish the interfacial charge effects. As the oxygen-flow rate increased, the faster change from the accumulation to the inversion state at depletion region and flatband (FB) voltage shift (ΔVFB∼0.2 V) appeared. The observed microstructure indicates that the grown layer was polycrystalline, which was the main reason for the degradation of the electrical properties. From the I–V analysis, a current density of −7.0×10−3 A/cm2 was measured at −1.5 V gate voltage. A dielectric constant of 18–19 was calculated from the C–V measurements.
Ion-cutting of Si onto glass by pulsed and direct-current plasma immersion ion implantation
Authors: Lu F. , Qiao D. , Cai M. , Yu P. K. L. , Lau S. S. , Fu R. K. Y. , Hung L. S. , Li C. P. , Chu P. K. , Chien H. C. , Liou Y.
Published: October 2003

Ion-cutting using plasma immersion ion implantation (PIII) was investigated for the integration of single crystalline Si layers on glass. In PIII, the sample is immersed in a plasma consisting of the ions of interest. A dc (direct current) or ac (alternating current) voltage is then applied to the sample to extract ions from the plasma and implant into the sample. PIII is inherently more efficient for high dose implantation. It was found that p-Si wafers implanted nominally at room temperature with H doses on the order of a few times 1016 cm−2 could be readily bonded to glass substrates with proper surface treatment similar to that used in conventional implantation for ion-cutting. The wafer surface of the as-implanted Si was converted from p-type to n-type. Upon bonding at room temperature, annealing (300 °C), and exfoliation (450 °C), the transferred Si layer on glass and the as-exfoliated surface of the implanted Si wafer remained n-type. Transmission electron microscopic examination showed a highly defective region near the top of the Si layer transferred onto glass due to H implantation. However, the crystalline quality was nearly defect-free in the deeper region of the layer, in spite of the incorporation of other impurities in the region. Annealing at sequentially higher temperatures led to the recovery of p-type conductivity at ∼600–650 °C. The thickness of the transferred layers suggested that the implanted species were mostly H3+ ions from the PIII implanter used in this study. Secondary ion mass spectrometry results showed coimplanted atmospheric impurities such as oxygen, nitrogen, and carbon that affected the electrical properties of the transferred Si layers. dc PIII is demonstrated in this study to be more superior than conventional pulsed PIII for this process and improved vacuum conditions of the implantation chamber are needed to eliminate or reduce impurities.
Failure analysis of a cascade laser structure by electrostatic force microscopy
Authors: Azize M. , Girard P. , Teissier R. , Baranov A. N. , Joullié A.
Published: October 2003

Noncontact mode electrostatic force microscopy was employed to investigate cleaved sections of a GaSb-based quantum cascade laser structure. The technique enabled us to determine the surface potential distribution, at equilibrium and under applied external field, and to locate precisely the zone which is at the origin of failure in laser characteristics when a breakdown voltage is applied to the device.
Evolution of intrinsic stress in nanocrystalline-diamond film deposited by continuous H+ ion bombardment
Authors: Gu C. Z. , Jiang X.
Published: October 2003

An in situ bending-plate method is used to measure intrinsic stress during the growth process of nanocrystalline-diamond film. Nanometer-sized diamond film is prepared by continuous H+ ion bombardment under different energies induced by applying a negative-bias voltage at the substrate relative to the grounded-vacuum chamber using the microwave-plasma chemical-vapor-deposition (MWPCVD) method. The effects of substrate-bias voltage, temperature, total pressure, and CH4 concentration on intrinsic stress during the film-growth process are investigated. The results indicate that high bias voltage and high substrate temperature are beneficial when synthesizing smooth nanocrystalline-diamond film. This film usually relates to high intrinsic compressive stress. This stress can be attributed to the high secondary-nucleation rate and grain-boundary density. The evolution of intrinsic stress presents a complicated process at different pressures and CH4 concentrations. The compressive stress of the film can be controlled by modifying the grain size at various deposition parameters.
Aluminum oxidation by a remote electron cyclotron resonance plasma in magnetic tunnel junctions
Authors: Thomas A. , Brückl H. , Sacher M. D. , Schmalhorst J. , Reiss G.
Published: October 2003

The aluminum barrier in exchange biased (Mn–Ir/Co–Fe/AlOx/Py) magnetic tunnel junctions was formed by oxidation with an electron cyclotron resonance plasma source. This technique allows, in contrast to commonly used floating substrate, an independent control of the energy of the ions bombarding the Al film by adjusting a direct current bias voltage at the sample. Here, we show that low energy ions and oxidation times between 50 and 200 s lead to optimum barrier properties and a maximum tunnel magneto resistance (TMR) ratio of 46% at room temperature and 73% at 10 K. Shorter oxidation time gives underoxidized samples with strongly reduced TMR. Ions with energy above 30 eV turn out to strongly overoxidize the sample resulting in large junction resistance and reduced TMR values.
Influence of the high-temperature “firing” step on high-rate plasma deposited silicon nitride films used as bulk passivating antireflection coatings on silicon solar cells
Authors: Hong J. , Kessels W. M. M. , Soppe W. J. , Weeber A. W. , Arnoldbik W. M. , van de Sanden M. C. M.
Published: October 2003

The influence of a short high-temperature step, comparable to the so-called “firing” of the metallization on silicon solar cells, on properties of high-rate (>0.5 nm/s) plasma deposited silicon nitride (a-SiNx:H) films has been investigated. These a-SiNx:H films are used as antireflection coating on multicrystalline silicon (mc-Si) solar cells and, after the firing process, they also induce hydrogen bulk passivation in the mc-Si. Three different types of remote plasma deposited a-SiNx:H films have been investigated: (i) expanding thermal plasma (ETP) deposited a-SiNx:H films from a N2–SiH4 gas mixture, (ii) ETP deposited a-SiNx:H films from a NH3–SiH4 mixture, and (iii) microwave plasma deposited a-SiNx:H films from a NH3–SiH4 mixture. The atomic composition and optical and structural properties of the films have been studied before and after the high-temperature step by the combination of elastic recoil detection, spectroscopic ellipsometry, and Fourier transform infrared spectroscopy. It has been observed that the high-temperature step can induce significant changes in hydrogen content, bonding types, mass density, and optical absorption of the films. These thermally induced effects are more enhanced for Si- than for N-rich films, which in some cases have a high thermal stability. Furthermore, the material properties and the influence of the high-temperature step have been related to the bulk passivation properties of the a-SiNx:H coated mc-Si solar cells. It is found that in particular the density and thermal stability of the a-SiNx:H films seem to be important for the degree of the bulk passivation obtained.
Focused-ion-beam preparation of wedge-shaped cross sections and its application to observing p–n junctions by electron holography
Authors: Wang Zhouguang , Kato Takeharu , Hirayama Tsukasa , Sasaki Katsuhiro , Saka Hiroyasu , Kato Naoko
Published: October 2003

The preparation of well-defined cross-sectional samples is critical for the quantitative analysis of p–n junctions in semiconductor devices by electron holography. A wedge is a good shape for the geometry of the cross section that is suitable for mapping and characterizing one-dimensional p–n junctions, especially those with lower doping levels. The method we used to prepare such cross sections involved focused-ion-beam milling and we describe it in detail. Following this, we could easily fabricate well-defined wedge-shaped cross sections with different given angles within a very short time. The use of such cross sections allowed us to clearly map implanted Si/Si p–n junction structures with lower dopant concentrations with off-axis electron holography.
Highly selective reactive-ion etching using CO/NH3/Xe gases for microstructuring of Au, Pt, Cu, and 20% Fe–Ni
Authors: Abe Takashi , Hong Youn Gi , Esashi Masayoshi
Published: October 2003

A highly selective dry-etch process for conductive metals (Au, Pt, and Cu) and magnetic metal (20% Fe-Ni) has been developed using a magnetron reactive-ion-etching system employing a CO/NH3/Xe chemistry. Etch selectivities of these metals to titanium are greater than 80:1 for Au, 40:1 for Pt, 30:1 for Cu, and 15:1 for permalloy (20% Fe–Ni) at the titanium-etch rate of 1.0 nm/min. The etching was conducted at room temperature. It was observed that the small addition of Xe to CO/NH3 etch gases (molar ratio=1/7) increased the etch rate of these metals while promoting nitridation of the titanium mask and achieving enhanced selectivity. The titanium can be used both as a mask for the sputter etching of noble metals and as a mask for the reactive-ion etching of magnetic metals in the plasma. By about a factor of 3, the inclusion of Xe enhanced the etch selectivities for noble metals, copper, and a magnetic metal over titanium.
Dry etching characteristics of TiN film using Ar/CHF3, Ar/Cl2, and Ar/BCl3 gas chemistries in an inductively coupled plasma
Authors: Tonotani J. , Iwamoto T. , Sato F. , Hattori K. , Ohmi S. , Iwai H.
Published: October 2003

Dry etching characteristics of TiN film have been studied in the case of using Ar/CHF3, Ar/Cl2, and Ar/BCl3 chemistries in an inductively coupled plasma. The TiN film was not etched at all without the addition of CHF3, BCl3, or Cl2 to the Ar gas flow. On the other hand, it was found that the TiN film was etched with one of the earlier additional gases. It was also found that a nontapered profile of etched TiN is obtained by Cl2 addition and a tapered profile by CHF3 or BCl3 addition. Moreover, a lower taper angle is obtained by increasing the amount of additional BCl3. X-ray photoelectron spectroscopy and Auger electron spectroscopy analyses for the etched samples of TiN show that TiF3 exists on the etched surface of TiN in the case of CHF3 addition and that BOxNy exists in the case of BCl3 addition. On the basis of these results, the effect of the gas addition to Ar on the characteristics of TiN reactive ion etching is considered as follows; under the Ar/CHF3 condition, although N in the TiN film is removed by evaporation in the form of NFx, Ti is fluorinated to form TiFx having low vapor pressure, which results in the low etching rate. Under the Ar/Cl2 condition, since NClx and TiClx have high vapor pressures, TiN is easily etched off, resulting in the highest etching rate with a nontapered profile. Under the Ar/BCl3 condition, although Cl plays the same role as it does under the Ar/Cl2 condition, B is likely to form a nonvolatile compound such as BOxNy, resulting in the deposition of the nonvolatile films on both the upper surface and sidewall of the TiN, which leads to a lower etching rate than that in the case of Cl2 addition and a lower taper angle of the etched profile.
Fabrication of metallic tunnel junctions for the scanning single electron transistor atomic force microscope
Authors: Steinmann P. , Lister K. A. , Weaver J. M. R.
Published: October 2003

Metallic tunnel junctions are important in the formation of high temperature single electron devices, which can act as the ultimate electrometer. We present a method for the fabrication of highly defined metallic tunnel junctions based on the step-edge cutoff process. Fabrication involves conventional electron beam lithography and lift-off of metallic thin films. Junctions scaling down to 50 nm linewidth have been achieved. The devices show a spread in impedance at low bias ranging from less than 10 MΩ to more than 100 GΩ. We have investigated the behavior of thin metallic films across a step forming a single tunnel junction. In the case of palladium we find that grain growth during deposition can give rise to multiple junctions across a single step. We illustrate this using one particular example of a junction, where isolated grains form a spontaneous Coulomb blockaded island with a charging energy of 20 meV at 77 K. The single and double junction fabrication process is compatible with our generic atomic force microscope probe technology, which has been shown to be capable of defining ultrasmall metallic structures on cantilevers and pyramidal tips. We demonstrate this by the fabrication of a lithographically defined device on a silicon cantilever with an integrated Ti/Au thin-film strain gauge.
Impact of chemistry on profile control of resist masked silicon gates etched in high density halogen-based plasmas
Authors: Detter X. , Palla R. , Thomas-Boutherin I. , Pargon E. , Cunge G. , Joubert O. , Vallier L.
Published: October 2003

Critical dimension (CD) control during silicon gate etching has been investigated with state-of-the-art chemistries. In particular, we have compared the etched profile of both isolated and dense gates obtained after the main etch step of a gate etch process using HBr/Cl2/O2 and HBr/Cl2/O2/CF4 gas mixtures, and study the influence of the CF4/O2 ratio in this mixture. We demonstrate that the gate etch profile is mainly driven by the passivation layer deposited on the gate and mask sidewalls during the etching. Due to aspect ratio dependant etching effect the passivation layer formation is thinner in dense than in isolated structures resulting in significant profile microloading. However, CF4 addition to HBr/Cl2/O2 strongly minimizes the difference in passivation layer thickness between dense and isolated lines thus potentially improving the critical dimension control. These results will be discussed in terms of chemical composition of the passivation layer and deposition mechanisms, based on previous studies by x-ray photoelectron spectroscopy and mass spectrometry studies. Finally, we will discuss the influence of the soft-landing and overetch steps on the final profile of the gates, and show that aspect ratio dependant etch rate during the main etch step of the process can become an additional source of CD microloading.
Ba enrichment on the surface of oxide cathodes
Authors: Weon B. M. , van Dam A. , Park G. S. , Hwang C. H. , Han S. D. , Kim I. W. , Seol S. K. , Kwon Y. B. , Cho C. S. , Je J. H. , Hwu Y. , Tsai W.-L. , Ruterana P.
Published: October 2003

We investigated the chemical structure of actual oxide cathode emission materials using soft x-ray absorption spectroscopy. High-energy resolution spectra of the Ba 3d absorption edges reveal that the Ba content significantly increases on the surface layers of oxide cathodes down to several tens of nanometers in depth, after the cathode activation process. Furthermore, we will demonstrate that the excess Ba on the surface is only slightly driven by thermal energy, but rather it is induced by the voltage difference applied during cathode activation. This result suggests that the rate controlling step of the Ba enrichment on the surface during activation is the electrolytic transport of Ba ion from the bulk powder to the interface. We assume that the Ba enrichment on the surface originates from the depletion of barium in bulk powder by the electrolytic transport.
Use of polymethylmethacrylate for pattern transfer by ion beam etching: Improvement of etching homogeneity and patterning quality
Authors: Koval Y. , Borzenko T. , Dubonos S.
Published: October 2003

We have studied the peculiar defects that appear on the surface of polymethylmethacrylate (PMMA) during ion beam etching. The quantity of defects and their type can be strongly influenced by a preparatory treatment before ion beam etching. Electron irradiation in a wide range of doses and a development procedure were used as the treatment. We have shown that high dose electron irradiation of PMMA structures before ion beam etching can noticeably improve pattern transfer. The improved homogeneity of the PMMA etching is the main reason for the effect. The obtained result is explained by a specific mechanism of ion beam etching of PMMA.
Deep dry etching of borosilicate glass using fluorine-based high-density plasmas for microelectromechanical system fabrication
Authors: Ichiki Takanori , Sugiyama Yoshinari , Ujiie Takekazu , Horiike Yasuhiro
Published: October 2003

For the fabrication of microelectromechanical system devices, deep trench etching of borosilicate glass (Corning 7740) has been investigated using SF6/Ar inductively coupled plasma. Since borosilicate glass contains metal elements which produce nonvolatile fluorides, dry etching of its smooth surface is a difficult issue. In this article, requisite conditions for etching glass with a smooth surface and high mask selectivity have been discussed on the basis of the results of a comprehensive experimental study of the effects of substrate bias power and Ar addition on the removal of involatile fluoride residues deposited via the backscattering of etch products in the vicinity of the substrate surface. Under optimized etching conditions, deep trench etching of borosilicate glass to 32 μm depth and 15 μm width has been accomplished using 3-μm-thick chrome metal masks.
Effects of high-dose BF2+ implantation on the formation of Ti-germanosilicide on polycrystalline Si/Si0.87Ge0.13/Si layers
Authors: Park Chan Woo , Lee Seung-Yun , Kim Sang-Hoon , Kang Jin-Yeong
Published: October 2003

The high-dose BF2+ implantation, which is employed for forming resistors and lowering the extrinsic base resistance in the SiGe heterojunction bipolar transistor (HBT) integrated circuit (IC) fabrication process, is shown to have strong effects on the Ti-silicidation behavior of the polycrystalline Si/Si0.87Ge0.13/Si stack layer. As the dose of BF2+ increases from 4×1014 to 4.4×1015 cm−2, the growth and C49-to-C54 transformation of the silicide/germanosilicide layer and protrusions are highly enhanced, which is consistent with previous observations on the defect-assisted nucleation of silicide grains. However, the final sheet resistance increases with increasing dose of BF2+. Such an inconsistency between the amount of C54 phase and the sheet resistance is probably due to the formation of numerous surface voids on the silicide layer from the fluorine-containing gaseous complexes. As the number of germanosilicide protrusions increases with increasing dose of BF2+, the contact resistance also increases because the protrusions are readily etched away during contact opening and leave behind cavities within the Si/Si0.87Ge0.13/Si layer. To achieve lower values of extrinsic base and contact resistances in SiGe HBT ICs, it is desirable to replace the BF2+ with B+ as well as thicken the Si cap layer on the contact region using the selective growth process of Si.
Highly selective and high rate SiO2 etching using argon-added C2F4/CF3I plasma
Authors: Ohtake H. , Ishihara H. , Fuse T. , Koshiishi A. , Samukawa S.
Published: October 2003

A high SiO2 etching rate (more than 5000 A/min) and an extremely high etching selectivity to photoresist (more than 10) have been simultaneously achieved in C2F4/CF3I/Ar plasma using a conventional dual-frequency reactive ion etching system. The etching selectivity increases with increases of Ar dilution in C2F4/CF3I. The carbon/fluorine ratio of the fluorocarbon polymer on the photoresist was drastically increased by Ar dilution and ion bombardment, which caused the etching rate of a photoresist to decrease. Under these conditions, high-aspect-ratio SiO2 contact etching (0.09 μm φ, more than 10) was achieved. These gas chemistries are promising candidates for use in nano-scale high-aspect-ratio SiO2 etching.
Redeposition of etch products on sidewalls during SiO2 etching in a fluorocarbon plasma. IV. Effects of substrate temperature in a CF4 plasma
Authors: Min Jae-Ho , Hwang Sung-Wook , Lee Gyeo-Re , Moon Sang Heup
Published: October 2003

Effects of substrate temperature on the redeposition of bottom-emitted particles to the sidewall surface and the resulting changes in the sidewall properties during SiO2 etching in a CF4 plasma were investigated. A Faraday cage and specially designed, step-shaped substrates located in a plasma etcher allowed us to observe lateral and vertical etch rates, the temperature dependence of redeposition, and resulting changes in the chemical composition of the sidewall surface. We conducted two sets of experiments under different process conditions to observe changes in the temperature effect with ion energy and plasma density. Process (I), which was carried out with a 200 W source power and a −400 V bias voltage, represented a typical reactive ion etching condition for low plasma density and high ion energy, and process (II), with 500 W and −200 V, represented an inductively coupled plasma condition of high plasma density and low ion energy. Lateral etching was more sensitive to substrate temperature than vertical etching. As the substrate temperature was raised, the redep-effect, which was defined as the difference in deposition rates between two sidewalls, either affected by bottom-emitted particles or not, was slightly decreased in process (I) but was significantly increased in process (II). The chemical composition of the sidewall surface was highly dependent on substrate temperature. The carbon content and the F/C ratio of the surface carbon-containing layer formed on the sidewall increased and decreased, respectively, with substrate temperature. The O/Si ratio of the redep-etch combined layer formed beneath the surface carbon-containing layer decreased when the substrate temperature was increased.
Wild-Type Nonneuronal Cells Extend Survival of SOD1 Mutant Motor Neurons in ALS Mice
Authors: Clement A. M. , Nguyen M. D. , Roberts E. A. , Garcia M. L. , Boillée S. , Rule M. , McMahon A. P. , Doucette W. , Siwek D. , Ferrante R. J. , Brown R. H. , Julien J.-P. , Goldstein L. S. B. , Cleveland D. W.
Published: October 2003

The most common form of amyotrophic lateral sclerosis (ALS), a neurodegenerative disease affecting adult motor neurons, is caused by dominant mutations in the ubiquitously expressed Cu-Zn superoxide dismutase (SOD1). In chimeric mice that are mixtures of normal and
SOD1
mutant–expressing cells, toxicity to motor neurons is shown to require damage from mutant SOD1 acting within nonneuronal cells. Normal motor neurons in SOD1 mutant chimeras develop aspects of ALS pathology. Most important, nonneuronal cells that do not express mutant SOD1 delay degeneration and significantly extend survival of mutant-expressing motor neurons.
Identification of a Plant Nitric Oxide Synthase Gene Involved in Hormonal Signaling
Authors: Guo Fang-Qing , Okamoto Mamoru , Crawford Nigel M.
Published: October 2003

Nitric oxide (NO) serves as a signal in plants. An
Arabidopsis
mutant (
Atnos1
) was identified that had impaired NO production, organ growth, and abscisic acid–induced stomatal movements. Expression of
AtNOS1
with a viral promoter in
Atnos1
mutant plants resulted in overproduction of NO. Purified AtNOS1 protein used the substrates arginine and nicotinamide adenine dinucleotide phosphate and was activated by Ca
2+
and calmodulin-like mammalian endothelial nitric oxide synthase and neuronal nitric oxide synthase, yet it is a distinct enzyme with no sequence similarities to any mammalian isoform. Thus,
AtNOS1
encodes a distinct nitric oxide synthase that regulates growth and hormonal signaling in plants.
Untangling Desmosomal Knots with Electron Tomography
Authors: He Wanzhong , Cowin Pamela , Stokes David L.
Published: October 2003

Cell adhesion by adherens junctions and desmosomes relies on interactions between cadherin molecules. However, the molecular interfaces that define molecular specificity and that mediate adhesion remain controversial. We used electron tomography of plastic sections from neonatal mouse skin to visualize the organization of desmosomes in situ. The resulting three-dimensional maps reveal individual cadherin molecules forming discrete groups and interacting through their tips. Fitting of an x-ray crystal structure for C-cadherin to these maps is consistent with a flexible intermolecular interface mediated by an exchange of amino-terminal tryptophans. This flexibility suggests a novel mechanism for generating both cis and trans interactions and for propagating these adhesive interactions along the junction.
Performance Monitoring by the Anterior Cingulate Cortex During Saccade Countermanding
Authors: Ito Shigehiko , Stuphorn Veit , Brown Joshua W. , Schall Jeffrey D.
Published: October 2003

Consensus is emerging that the medial frontal lobe of the brain is involved in monitoring performance, but precisely what is monitored remains unclear. A saccade-countermanding task affords an experimental dissociation of neural signals of error, reinforcement, and conflict. Single-unit activity was monitored in the anterior cingulate cortex of monkeys performing this task. Neurons that signaled errors were found, half of which responded to the omission of earned reinforcement. A further diversity of neurons signaled earned or unexpected reinforcement. No neurons signaled the form of conflict engendered by interruption of saccade preparation produced in this task. These results are consistent with the hypothesis that the anterior cingulate cortex monitors the consequences of actions.
CB1 Cannabinoid Receptors and On-Demand Defense Against Excitotoxicity
Authors: Marsicano Giovanni , Goodenough Sharon , Monory Krisztina , Hermann Heike , Eder Matthias , Cannich Astrid , Azad Shahnaz C. , Cascio Maria Grazia , Gutiérrez Silvia Ortega , van der Stelt Mario , López-Rodríguez Maria Luz , Casanova Emilio , Schütz Günther , Zieglgänsberger Walter , Di Marzo Vincenzo , Behl Christian , Lutz Beat
Published: October 2003

Abnormally high spiking activity can damage neurons. Signaling systems to protect neurons from the consequences of abnormal discharge activity have been postulated. We generated conditional mutant mice that lack expression of the cannabinoid receptor type 1 in principal forebrain neurons but not in adjacent inhibitory interneurons. In mutant mice,the excitotoxin kainic acid (KA) induced excessive seizures in vivo. The threshold to KA-induced neuronal excitation in vitro was severely reduced in hippocampal pyramidal neurons of mutants. KA administration rapidly raised hippocampal levels of anandamide and induced protective mechanisms in wild-type principal hippocampal neurons. These protective mechanisms could not be triggered in mutant mice. The endogenous cannabinoid system thus provides on-demand protection against acute excitotoxicity in central nervous system neurons.
Coherent Soft X-ray Generation in the Water Window with Quasi-Phase Matching
Authors: Gibson Emily A. , Paul Ariel , Wagner Nick , Tobey Ra'anan , Gaudiosi David , Backus Sterling , Christov Ivan P. , Aquila Andy , Gullikson Eric M. , Attwood David T. , Murnane Margaret M. , Kapteyn Henry C.
Published: October 2003

We demonstrate enhanced generation of coherent light in the “water window” region of the soft x-ray spectrum at 4.4 nanometers, using quasi–phase-matched frequency conversion of ultrafast laser pulses. By periodically modulating the diameter of a gas-filled hollow waveguide, the phase mismatch normally present between the laser light and the generated soft x-ray light can be partially compensated. This makes it possible to use neon gas as the nonlinear medium to coherently convert light up to the water window, illustrating that techniques of nonlinear optics can be applied effectively in the soft x-ray region of the spectrum. These results advance the prospects for compact coherent soft x-ray sources for applications in biomicroscopy and in chemical spectroscopy.
Thalamic Control of Visceral Nociception Mediated by T-Type Ca
2+
Channels
Authors: Kim Daesoo , Park Donghyun , Choi Soonwook , Lee Sukchan , Sun Minjeong , Kim Chanki , Shin Hee-Sup
Published: October 2003

Sensations from viscera, like fullness, easily become painful if the stimulus persists. Mice lacking α1G T-type Ca
2+
channels show hyperalgesia to visceral pain. Thalamic infusion of a T-type blocker induced similar hyperalgesia in wild-type mice. In response to visceral pain, the ventroposterolateral thalamic neurons evokeda surge of single spikes, which then slowly decayed as T type–dependent burst spikes gradually increased. In α1G-deficient neurons, the single-spike response persisted without burst spikes. These results indicate that T-type Ca
2+
channels underlie an antinociceptive mechanism operating in the thalamus andsupport the idea that burst firing plays a critical role in sensory gating in the thalamus.
Vibrational Mode-Specific Reaction of Methane on a Nickel Surface
Authors: Beck Rainer D. , Maroni Plinio , Papageorgopoulos Dimitrios C. , Dang Tung T. , Schmid Mathieu P. , Rizzo Thomas R.
Published: October 2003

The dissociation of methane on a nickel catalyst is a key step in steam reforming of natural gas for hydrogen production. Despite substantial effort in both experiment and theory, there is still no atomic-scale description of this important gas-surface reaction. We report quantum state–resolved studies, using pulsed laser and molecular beam techniques, of vibrationally excited methane reacting on the nickel (100) surface. For doubly deuterated methane (CD
2
H
2
), we observed that the reaction probability with two quanta of excitation in one C-H bond was greater (by as much as a factor of 5) than with one quantum in each of two C-H bonds. These results clearly exclude the possibility of statistical models correctly describing the mechanism of this process and attest to the importance of full-dimensional calculations of the reaction dynamics.
The Anomalous Hall Effect and Magnetic Monopoles in Momentum Space
Authors: Fang Zhong , Nagaosa Naoto , Takahashi Kei S. , Asamitsu Atsushi , Mathieu Roland , Ogasawara Takeshi , Yamada Hiroyuki , Kawasaki Masashi , Tokura Yoshinori , Terakura Kiyoyuki
Published: October 2003

Efforts to find the magnetic monopole in real space have been made in cosmic rays and in particle accelerators, but there has not yet been any firm evidence for its existence because of its very heavy mass, ∼10
16
giga–electron volts. We show that the magnetic monopole can appear in the crystal momentum space of solids in the accessible low-energy region (∼0.1 to 1 electron volts) in the context of the anomalous Hall effect. We report experimental results together with first-principles calculations on the ferromagnetic crystal SrRuO
3
that provide evidence for the magnetic monopole in the crystal momentum space.
Thoughts Without a Thinker
Authors: Mechsner Franz , Newen Albert
Published: October 2003

Being No One
The Self-Model Theory of Subjectivity. by Thomas Metzinger. MIT Press, Cambridge, MA, 2003. 713 pp. $55, £35.95. ISBN 0-262-13417-9.

In this thorough discussion of the problem of the self, Metzinger draws on contemporary neuroscience to develop a new philosophical approach to consciousness.
Production of High-Quality Particulate Methane Monooxygenase in High Yields from
Methylococcus capsulatus
(Bath) with a Hollow-Fiber Membrane Bioreactor
Authors: Yu Steve S.-F. , Chen Kelvin H.-C. , Tseng Mandy Y.-H. , Wang Yane-Shih , Tseng Chiu-Feng , Chen Yu-Ju , Huang Ded-Shih , Chan Sunney I.
Published: October 2003

In order to obtain particulate methane monooxygenase (pMMO)-enriched membranes from
Methylococcus capsulatus
(Bath) with high activity and in high yields, we devised a method to process cell growth in a fermentor adapted with a hollow-fiber bioreactor that allows easy control and quantitative adjustment of the copper ion concentration in NMS medium over the time course of cell culture. This technical improvement in the method for culturing bacterial cells allowed us to study the effects of copper ion concentration in the growth medium on the copper content in the membranes, as well as the specific activity of the enzyme. The optimal copper concentration in the growth medium was found to be 30 to 35 μM. Under these conditions, the pMMO is highly expressed, accounting for 80% of the total cytoplasmic membrane proteins and having a specific activity as high as 88.9 nmol of propylene oxide/min/mg of protein with NADH as the reductant. The copper stoichiometry is ∼13 atoms per pMMO molecule. Analysis of other metal contents provided no evidence of zinc, and only traces of iron were present in the pMMO-enriched membranes. Further purification by membrane solubilization in dodecyl β-
d
-maltoside followed by fractionation of the protein-detergent complexes according to molecular size by gel filtration chromatography resulted in a good yield of the pMMO-detergent complex and a high level of homogeneity. The pMMO-detergent complex isolated in this way had a molecular mass of 220 kDa and consisted of an αβγ protein monomer encapsulated in a micelle consisting of ca. 240 detergent molecules. The enzyme is a copper protein containing 13.6 mol of copper/mol of pMMO and essentially no iron (ratio of copper to iron, 80:1). Both the detergent-solubilized membranes and the purified pMMO-detergent complex exhibited reasonable, if not excellent, specific activity. Finally, our ability to control the level of expression of the pMMO allowed us to clarify the sensitivity of the enzyme to NADH and duroquinol, the two common reductants used to assay the enzyme.
Redefining the Role of
psr
in β-Lactam Resistance and Cell Autolysis of
Enterococcus hirae
Authors: Sapunaric Frédéric , Franssen Christine , Stefanic Patrick , Amoroso Ana , Dardenne Olivier , Coyette Jacques
Published: October 2003

The contribution of penicillin-binding protein 5 (PBP5) and the PBP5 synthesis repressor (Psr) to the β-lactam resistance, growth, and cell autolysis of wild-type strain ATCC 9790 and resistant strain R40 of
Enterococcus hirae
was investigated by disruption or substitution of the corresponding
pbp5
and
psr
genes by Campbell-type recombination. The resulting modifications were confirmed by hybridization and PCR. The low susceptibility of
E. hirae
to β-lactams was confirmed to be largely dependent on the presence of PBP5. However, against all expectations, inactivation of
psr
in ATCC 9790 or complementation of R40 cells with
psr
did not modify the susceptibility to benzylpenicillin or the growth and cell autolysis rates. These results indicated that the
psr
gene does not seem to be involved in the regulation of PBP5 synthesis and consequently in β-lactam resistance or in the regulation of cell autolysis in
E. hirae
.
Cloning and Characterization of Archaeal Type I Signal Peptidase from
Methanococcus voltae
Authors: Ng Sandy Y. M. , Jarrell Ken F.
Published: October 2003

Archaeal protein trafficking is a poorly characterized process. While putative type I signal peptidase genes have been identified in sequenced genomes for many archaea, no biochemical data have been presented to confirm that the gene product possesses signal peptidase activity. In this study, the putative type I signal peptidase gene in
Methanococcus voltae
was cloned and overexpressed in
Escherichia coli
, the membranes of which were used as the enzyme source in an in vitro peptidase assay. A truncated, His-tagged form of the
M. voltae
S-layer protein was generated for use as the substrate to monitor the signal peptidase activity. With
M. voltae
membranes as the enzyme source, signal peptidase activity in vitro was optimal between 30 and 40°C; it was dependent on a low concentration of KCl or NaCl but was effective over a broad concentration range up to 1 M. Processing of the
M. voltae
S-layer protein at the predicted cleavage site (confirmed by N-terminal sequencing) was demonstrated with the overexpressed archaeal gene product. Although
E. coli
signal peptidase was able to correctly process the signal peptide during overexpression of the
M. voltae
S-layer protein in vivo, the contribution of the
E. coli
signal peptidase to cleavage of the substrate in the in vitro assay was minimal since
E. coli
membranes alone did not show significant activity towards the S-layer substrate in in vitro assays. In addition, when the peptidase assays were performed in 1 M NaCl (a previously reported inhibitory condition for
E. coli
signal peptidase I), efficient processing of the substrate was observed only when the
E. coli
membranes contained overexpressed
M. voltae
signal peptidase. This is the first proof of expressed type I signal peptidase activity from a specific archaeal gene product.
Osmotic Adaptation of
Thermus thermophilus
RQ-1: Lesson from a Mutant Deficient in Synthesis of Trehalose
Authors: Silva Zélia , Alarico Susana , Nobre Ana , Horlacher Reinhold , Marugg Joey , Boos Winfried , Mingote Ana I. , da Costa Milton S.
Published: October 2003

Strains of
Thermus thermophilus
accumulate primarily trehalose and smaller amounts of mannosylglycerate in response to salt stress in yeast extract-containing media (O. C. Nunes, C. M. Manaia, M. S. da Costa, and H. Santos, Appl. Environ. Microbiol. 61:2351-2357, 1995). A 2.4-kbp DNA fragment from
T. thermophilus
strain RQ-1 carrying
otsA
(encoding trehalose-phosphate synthase [TPS]),
otsB
(encoding trehalose-phosphate phosphatase [TPP]), and a short sequence of the 5′ end of
treS
(trehalose synthase [TreS]) was cloned from a gene library. The sequences of the three genes (including
treS
) were amplified by PCR and sequenced, revealing that the genes were structurally linked. To understand the role of trehalose during salt stress in
T. thermophilus
RQ-1, we constructed a mutant, designated RQ-1M6, in which TPS (
otsA
) and TPP (
otsB
) genes were disrupted by gene replacement. Mutant RQ-1M6 accumulated trehalose and mannosylglycerate in a medium containing yeast extract and NaCl. However, growth in a defined medium (without yeast extract, known to contain trehalose) containing NaCl led to the accumulation of mannosylglycerate but not trehalose. The deletion of
otsA
and
otsB
reduced the ability to grow in defined salt-containing medium, with the maximum salinity being 5% NaCl for RQ-1 and 3% NaCl for RQ-1M6. The lower salt tolerance observed in the mutant was relieved by the addition of trehalose to the growth media. In contrast to trehalose, the addition of glycine betaine, mannosylglycerate, maltose, and glucose to the growth medium did not allow the mutant to grow at higher salinities. The results presented here provide crucial evidence for the importance of the TPS/TPP pathway for the synthesis and accumulation of trehalose and the decisive contribution of this disaccharide to osmotic adaptation in
T. thermophilus
RQ-1.
Restricted Translocation across the Cell Wall Regulates Secretion of the Broad-Range Phospholipase C of
Listeria monocytogenes
Authors: Snyder Aleksandra , Marquis Hélène
Published: October 2003

The virulence of
Listeria monocytogenes
is directly related to its ability to spread from cell to cell without leaving the intracellular milieu. During cell-to-cell spread, bacteria become temporarily confined to secondary vacuoles. Among the bacterial factors involved in escape from these vacuoles is a secreted broad-range phospholipase C (PC-PLC), the activation of which requires processing of an N-terminal prodomain. Mpl, a secreted metalloprotease of
Listeria
, is involved in the proteolytic activation of PC-PLC. We previously showed that, during intracellular growth, bacteria maintain a pool of PC-PLC that is not accessible to antibodies and that is rapidly released in its active form in response to a decrease in pH. pH-regulated release of active PC-PLC is Mpl dependent. To further characterize the mechanism regulating secretion of PC-PLC, the bacterial localization of PC-PLC and Mpl was investigated. Both proteins were detected in the bacterial supernatant and lysate with no apparent changes in molecular weight. Extraction of bacteria-associated PC-PLC and Mpl required cell wall hydrolysis, but there was no indication that either protein was covalently bound to the bacterial cell wall. Results from pulse-chase experiments performed with infected macrophages indicated that the rate of synthesis of PC-PLC exceeded the rate of translocation across the bacterial cell wall and confirmed that the pool of PC-PLC associated with bacteria was efficiently activated and secreted upon acidification of the host cell cytosol. These data suggest that bacterially associated PC-PLC and Mpl localize at the cell wall-membrane interface and that translocation of PC-PLC across the bacterial cell wall is rate limiting, resulting in the formation of a bacterially associated pool of PC-PLC that would readily be accessible for activation and release into nascent secondary vacuoles.