bluuebunny/crossref_metadata_2025 huggingface dataset:
Aromatic residues at position 55 of rat α7 nicotinic acetylcholine receptors are critical for maintaining rapid desensitization
Authors: Gay Elaine A. , Giniatullin Rashid , Skorinkin Andrei , Yakel Jerrel L.
Published: December 2007

The rat α7 nicotinic acetylcholine receptor (nAChR) can undergo rapid onset of desensitization; however, the mechanisms of desensitization are largely unknown. The contribution of a tryptophan (W) residue at position 55 of the rat α7 nAChR subunit, which lies within the β2 strand, was studied by mutating it to other hydrophobic and/or aromatic amino acids, followed by voltage‐clamp experiments in Xenopus oocytes. When mutated to alanine, the α7‐W55A nAChR desensitized more slowly, and recovered from desensitization more rapidly, than wildtype α7 nAChRs. The contribution of desensitization was validated by kinetic modelling. Mutating W55 to other aromatic residues (phenylalanine or tyrosine) had no significant effect on the kinetics of desensitization, whereas mutation to various hydrophobic residues (alanine, cysteine or valine) significantly decreased the rate of onset and increased the rate of recovery from desensitization. To gain insight into possible structural rearrangements during desensitization, we probed the accessibility of W55 by mutating W55 to cysteine (α7‐W55C) and testing the ability of various sulfhydryl reagents to react with this cysteine. Several positively charged sulfhydryl reagents blocked ACh‐induced responses for α7‐W55C nAChRs, whereas a neutral sulfhydryl reagent potentiated responses; residue C55 was not accessible for modification in the desensitized state. These data suggest that W55 plays an important role in both the onset and recovery from desensitization in the rat α7 nAChR, and that aromatic residues at position 55 are critical for maintaining rapid desensitization. Furthermore, these data suggest that W55 may be a potential target for modulatory agents operating via hydrophobic interactions.
A Method for Integrating Form Errors Into Geometric Tolerance Analysis
Authors: Pierce Robert Scott , Rosen David
Published: December 2007

In this research, we describe a computer-aided approach to geometric tolerance analysis for assemblies and mechanisms. A series of as-manufactured component models are generated within a NURBS-based solid modeling environment. These models reflect errors in component geometry that are characteristic of the manufacturing processes used to produce the components. The effects of different manufacturing process errors on product function are tested by simulating the assembly of imperfect-form component models and by measuring geometric attributes of the assembly that correspond to product functionality. A tolerance analysis model is constructed by generating and testing component variants that represent different manufacturing precision levels. The application of this approach to tolerance analysis is demonstrated using a case study that is based on a high-speed stapling mechanism.
Linkage Mechanisms With Cam-Integrated Joints for Controlled Harmonic Content of the Output Motion: Theory and Application
Authors: Yuan L. , Rastegar J. , Zhang J.
Published: December 2007

In a recent study, the authors presented a systematic method for the modification of the output motion of linkage mechanisms with closed-loop chains using cams positioned at one or more joints of the mechanism. In this paper, the method is applied to the design of a linkage mechanism with an integrated cam mechanism to eliminate high harmonic component of the output motion. The mechanism may be synthesized using any existing linkage mechanism synthesis technique. In the present study, a cam mechanism is synthesized to eliminate all high harmonic components of the output link motion of a four-bar linkage mechanism to illustrate the potentials of the present approach. The mechanism is then constructed and successfully tested. With the present method, selected ranges of high harmonic motions generated due to the mechanisms kinematics nonlinearity can be eliminated by integrating appropriately designed cams, thereby significantly reducing the potential vibrational excitation that the mechanism can impart on the overall system, including its own structure. Such systems should therefore be capable of operating at higher speeds and with increased precision.
Introduction of the Foot Placement Estimator: A Dynamic Measure of Balance for Bipedal Robotics
Authors: Wight Derek L. , Kubica Eric G. , Wang David W. L.
Published: December 2007

The goal of most bipedal robotics research is to develop methods of achieving a dynamically balanced gait. Most current approaches focus on maintaining the balance of the system. This paper introduces a measure called the foot placement estimator (FPE) to restore balance to an unbalanced system. We begin by developing a theoretical proof to define when a biped is stable, as well as defining the region in which stability results are valid. This forms the basis for the derivation of the FPE. The results of the FPE are then extended to a complete gait cycle using the combination of a state machine and simple linear controllers. This control system is applied to a detailed and realistic simulation based on a physical robot currently under construction. Utilizing the FPE as a measure of balance allows us to create dynamically balanced gait cycles in the presence of external disturbances, including gait initiation and termination, without any precalculated trajectories.
Prospects for nanowire sculptured-thin-film devices
Authors: Pursel Sean M. , Horn Mark W.
Published: December 2007

In this paper, we introduce a modified serial bideposition (SBD) method, asymmetric SBD, for depositing sculptured thin films (STFs) which may allow added control of the surface area, void accessibility, and optical properties of STFs. Results on using TiO2 STFs with spectral-hole filters as vapor/liquid sensors are presented. In addition, solar cell, microcavity, biological sensing, and bioabsorption devices utilizing STFs are discussed.
Fabrication of a Fresnel zone plate through electron beam lithographic process and its application to measuring of critical dimension scanning electron microscope performance
Authors: Kim J. , Jalhadi K. , Lee S.-Y. , Joy D. C.
Published: December 2007

It is important to be able to quantify the imaging performance of critical dimension scanning electron microscopes for such purposes as verifying the specification, and tracking and optimizing its performance during use. Imaging performance can be defined by parameters such as resolution, signal to noise ratio, drift, and instability under standard operation conditions. To perform tests to obtain such parameters, it is necessary to have both suitable test samples and appropriate software for image analysis. A Fresnel zone plate, as a reproducible and well characterized sample, is fabricated using direct-write electron beam lithography. A package of two-dimensional Fourier transform and analysis software, designed as a plug-in for the shareware IMAGE-JAVA program, has been developed for resolution analysis and is freely available online.
Mechanical properties of suspended graphene sheets
Authors: Frank I. W. , Tanenbaum D. M. , van der Zande A. M. , McEuen P. L.
Published: December 2007

Using an atomic force microscope, we measured effective spring constants of stacks of graphene sheets (less than 5) suspended over photolithographically defined trenches in silicon dioxide. Measurements were made on layered graphene sheets of thicknesses between 2 and 8nm, with measured spring constants scaling as expected with the dimensions of the suspended section, ranging from 1to5N∕m. When our data are fitted to a model for doubly clamped beams under tension, we extract a Young’s modulus of 0.5TPa, compared to 1TPa for bulk graphite along the basal plane, and tensions on the order of 10−7N.
Enhanced field emission from carbon nanotubes with a thin layer of low work function barium strontium oxide surface coating
Authors: Jin Feng , Liu Yan , Day Christopher M. , Little Scott A.
Published: December 2007

The authors report a field emitter structure based on barium strontium oxide coated carbon nanotubes (CNTs). This emitter consists of a thin tungsten ribbon with CNTs on the surface, and a thin layer of low work function barium strontium oxide coating on the CNTs. CNTs were grown on the surface of the tungsten ribbon by plasma enhanced chemical vapor deposition, and the oxide coatings were prepared using magnetron sputtering. This oxide coated CNT emitter was designed to combine the benefits of the high field enhancement factor from CNTs and the low work function from the emissive oxide coating. The field emission properties of the emitters were characterized. A field enhancement factor of 478 and a work function of 1.9eV were obtained for the oxide coated CNTs. As a result of the reduction of surface work function, the field emission from the oxide coated CNTs increased by a factor of 2–3 compared to the uncoated CNTs. At 4.4V∕μm, the field emission current of 23.6μA was obtained from an emitting surface of 0.012cm2.
Extreme ultraviolet lithography: A review
Authors: Wu Banqiu , Kumar Ajay
Published: December 2007

Extreme ultraviolet lithography (EUVL) was thoroughly reviewed over a broad range of topics, including history, tools, source, metrology, condenser and projection optics, resists, and masks. Since 1988, many studies on EUVL have been conducted in North America, Europe, and Japan, through state sponsored programs and industrial consortiums. To date, no “show stopper” has been identified, but challenges are present in almost all aspects of EUVL technology. Commercial alpha lithography step-and-scan tools are installed with full-field capability; however, EUVL power at intermediate focus (IF) has not yet met volume manufacturing requirements. Compared with the target of 180W IF power, current tools can supply only approximately 55–62W. EUV IF power has been improved gradually from xenon- to tin-discharge-produced plasma or laser-produced plasma. EUVL resist has improved significantly in the last few years, with 25nm 1:1 line/space resolution being produced with approximately 2.7nm (3σ) line edge roughness. Actual adoption of EUVL will depend on the extension of current optical lithography, such as 193nm immersion lithography, combined with double patterning techniques. Mask fabrication and application technologies may be the most substantial challenges. Creating a defect-free EUVL mask is currently an obstacle to its application, although a combination of removable pellicle and thermophoretic protection may overcome nonpellicle challenge. Cost of ownership is a critical consideration for EUVL; nevertheless, it has been predicted that EUVL may be in pilot production at 32nm and in large-scale production at 22nm with the capability to extend to the next technology node.
Yield improvement of 0.13μm Cu/low-k dual-damascene interconnection by organic cleaning process
Authors: Kim Nam-Hoon , Kim Sang-Yong , Lee Hyun-Ki , Lee Kang-Yeon , Kim Chang-Il , Chang Eui-Goo
Published: December 2007

Cu/low-k dielectrics are required to reduce resistance-capacitance (RC) delay and parasitic capacitance at the back-end-of-line (BEOL) interconnection. Integration of Cu/low-k dielectrics (black diamond) for BEOL interconnection in 0.13μm technology has gained wide acceptance in the microelectronics industry in recent years. In this article, the authors discuss the process-integration issues of 0.13μm Cu/low-k dual-damascene integration for static random access memory (SRAM) device yield. The same scheme of 0.13μm Cu/fluorinated silicate glass–based device was used for the full process of making a low-k based device. Black diamond was used as a low-k material with a dielectric constant of 2.95. To reduce the damage of low-k and improve the yield of a low-k based device, H2O ashing, organic cleaning, and reduced down pressure in chemical-mechanical planarization were selected for the study. Specifically, the cleaning process after the ashing process was very effective for the removal of organic residues from via, trench, and surface contaminants. There was an increase of 40.79% in SRAM device yield compared to the low-k based device without the organic cleaning chemical process. As a result, the authors successfully integrated a 0.13μm Cu/low-k dual-damascene interconnection with excellent yield performance after the improving process of organic cleaning.
C-doped semi-insulating GaN HFETs on sapphire substrates with a high breakdown voltage and low specific on-resistance
Authors: Choi Y. C. , Shi J. , Pophristic M. , Spencer M. G. , Eastman L. F.
Published: December 2007

High breakdown voltage (BV) AlGaN∕GaN heterojunction field effect transistors (HFETs) with a low specific on-resistance (ARDS(on)) were successfully fabricated using intentionally C-doped semi-insulating GaN buffers with a high resistivity on sapphire substrates. With the improvement of not only the resistivity of a C-doped GaN buffer but also the layout design near the gate feeding region, the fabricated devices exhibited a high BV of ∼1600V and low ARDS(on) of 3.9mΩcm2. This result even reaches the 4H-SiC theoretical limit and the best ever reported for the high-power GaN-based HFETs realized on sapphire substrates to the best of our knowledge.
Photolithographic synthesis of high-density DNA probe arrays: Challenges and opportunities
Authors: Pawloski Adam R. , McGall Glenn , Kuimelis Robert G. , Barone Dale , Cuppoletti Andrea , Ciccolella Paul , Spence Eric , Afroz Farhana , Bury Paul , Chen Christy , Chen Chuan , Pao Dexter , Le Mary , McGee Becky , Harkins Elizabeth , Savage Michael , Narasimhan Sim , Goldberg Martin , Rava Richard , Fodor Stephen P. A.
Published: December 2007

The continual need for increased manufacturing capacity in the production of GeneChip™ DNA probe arrays, and the expanding use of these arrays into new areas of application such as molecular medicine, has stimulated the development of new chemistries and production methods with higher efficiency and resolution. For current production methods based on contact photolithography, modifications in substrate materials and photoactivated synthesis reagents have provided significant improvements in array performance and information content (≥4×106 sequences∕cm2). An alternative next-generation manufacturing process is also in development, which utilizes photoacid generating polymer films, and automated projection lithography systems. This process has the ability to fabricate arrays with 1 micron feature pitch and smaller, providing an unprecedented sequence density of 108∕cm2 and greater.
Fabrication of zinc nanotip arrays by ion beam sputtering
Authors: Chao Liang-Chiun , Liau Chung-Chi , Lee Jun-Wei , Tsai Fu-Chieh
Published: December 2007

Zinc nanotip arrays were fabricated on polycrystalline zinc foils using capillaritron ion beam sputtering. The geometry and structure of the nanotip are found to be dependent on the ion species, beam energy, and exposure fluence. After 12keV argon ion beam sputtering, zinc nanotips with end radii less than 5nm and aspect ratios larger than 20 were obtained. Cone-shaped nanostructures with an aspect ratio of 3 and tip radius of 25nm were found after oxygen ion beam sputtering. Energy dispersive x-ray spectroscopy and scanning electron microscopy analysis indicate that the high aspect ratio nanotip formation mechanism after argon ion beam sputtering is due to differential erosion and anisotropic hardness of zinc nanocrystal, while the formation mechanism of cone-shaped nanostructures after oxygen ion beam sputtering is due mainly to the formation of ZnO on the apex, acting as an etch stop. The field emission properties of zinc nanotips are presented.
Analysis of Coulomb and Johnsen-Rahbek electrostatic chuck performance for extreme ultraviolet lithography
Authors: Sogard M. R. , Mikkelson A. R. , Nataraju M. , Turner K. T. , Engelstad R. L.
Published: December 2007

The successful implementation of extreme ultraviolet lithography (EUVL) requires the use of an electrostatic chuck to both support and flatten the mask during scanning exposure. The EUVL Mask and Chucking Standards, SEMI P37 and P40, specify the nonflatness of the mask frontside and backside, as well as the chucking surface, to be on the order of 50 nm peak-to-valley. Thus, characterizing and predicting the capability of the electrostatic chuck to reduce mask nonflatness to meet this specification are critical issues. Details describing the performance of the Coulomb electrostatic chuck have been presented in earlier publications. In this paper, the governing equation identifying the force-gap relationship for a Johnsen-Rahbek (J-R) chuck is described and compared to the Coulomb response. Using finite element techniques, numerical models of Coulomb and J-R electrostatic chucks have been constructed and evaluated for their clamping performance. The models include the effects of reticle and chuck nonflatness, surface friction, and the finite stiffness of the chuck. Modeling predictions are presented for the two types of chucks. The simulations indicate that using a reticle and chuck (Coulomb or J-R style) that meet the SEMI standards for flatness can result in a clamped reticle flatness of less than 100 nm. However, there may be a need to increase the chuck stiffness specified in SEMI P40. These results, which provide the first comprehensive comparison of Coulomb and J-R chucks, are currently being used to establish specifications for chuck geometry and to identify the range of flatness variations that can be accommodated with electrostatic chucking.
Multilayer phase-only diffraction gratings: Fabrication and application to extreme ultraviolet optics
Authors: Salmassi Farhad , Gullikson Eric M. , Anderson Erik H. , Naulleau Patrick P.
Published: December 2007

The use of phase-only diffractive devices has long played an important role in advanced optical systems in varying fields. Such devices include gratings, diffractive and holographic optical elements, diffractive lenses, and phase-shift masks for advanced lithography. Extending such devices to the increasingly important regime of extreme ultraviolet (EUV) wavelengths, however, is not trivial. Here, the authors present an effective fabrication and etch process enabling high-resolution patterning of Mo∕Si multilayers for use in EUV phase devices, providing another method for fabrication of high numerical aperture diffractive devices or high-resolution EUV phase shift masks.
Fabrication of 3D-photonic crystals via UV-nanoimprint lithography
Authors: Glinsner Thomas , Lindner Paul , Mühlberger Michael , Bergmair Iris , Schöftner Rainer , Hingerl Kurt , Schmid Holger , Kley Ernst-Bernhard
Published: December 2007

Optical lithography will reach its limits due to the diffraction effects encountered and the necessity for using complex resolution enhancement techniques like optical proximity correction, phase shift masks, and off-axis illumination [L. W. Liebmann et al., in Advanced Semiconductor Lithography (2001), Vol. 45]. The restrictions on wavelength, in combination with high process and equipment costs, make low-cost, simple imprinting techniques competitive with next-generation lithography methods. There are several nanoimprint lithography (NIL) techniques which can be categorized depending on the process parameters and the imprinting method—either step and repeat or full wafer single-step imprinting. A variety of potential applications has been demonstrated using NIL (e.g., surface acoustic wave devices, vias and contact layers with dual damascene imprinting process, Bragg structures, patterned media) [M. D. Stewart et al., Proc. SPIE 5751, 210 (2005); P. Dorsey et al., in Discrete Track Recording (DTR) Media Fabricated using Nanoimprint Lithography, NNT 1–3 December (2004)]. In this work UV-NIL has been selected for the fabrication process of 3D-photonic crystals.
Bilayer metal wire-grid polarizer fabricated by roll-to-roll nanoimprint lithography on flexible plastic substrate
Authors: Ahn Se Hyun , Kim Jin-Sung , Guo L. Jay
Published: December 2007

The bilayer metal wire-grid polarizer has several advantages over single-layer wire-grid polarizer and conventional polarizer since it provides higher polarization efficiency and can be easily fabricated. In this work, the authors demonstrate the fabrication of bilayer metal wire-grid polarizer on flexible plastic substrate by a continuous roll-to-roll nanoimprint lithography (R2RNIL) process and evaluate its performance. To fabricate wire-grid polarizer, subwavelength grating structure in epoxysilicone material is first created on a flexible PET substrate by UV R2RNIL followed by aluminum deposition. In initial measurement, extinction ratio exceeding 1000 has been achieved.
Effects and mechanisms of nitrogen incorporation into hafnium oxide by plasma immersion implantation
Authors: Wong Hei , Sen Banani , Yang B. L. , Huang A. P. , Chu P. K.
Published: December 2007

The physics and effects of nitrogen incorporation into HfO2 films were studied in detail. The authors found that only a trace amount (∼5%) of nitrogen can be introduced into the HfO2 films using plasma immersion ion-implantation technique, regardless of implantation dose. They proposed that the nitrogen incorporation is due to the filling of O vacancies (VO) and replacement of VO O neighbors in the bulk with nitrogen atoms. At the interface, the nitrogen atoms exist in the form of Hf–N and Si–N bonding, which significantly improve the interface properties of the HfO2∕Si structure. Temperature-dependent capacitance-voltage characteristics measurements indicate that both interface and oxide trap densities were greatly reduced with the incorporation of trace amount of nitrogen atoms.
Hybrid carbon nanotube-silicon complementary metal oxide semiconductor circuits
Authors: Meric I. , Caruso V. , Caldwell R. , Hone J. , Shepard K. L. , Wind S. J.
Published: December 2007

A hybrid technology is presented that combines carbon nanotube field-effect transistors (CNFET) with conventional, silicon-based complementary metal oxide semiconductor (CMOS) technology. The fabrication involves the chemical vapor deposition growth and optical characterization of carbon nanotubes, which are then transferred with lithographic precision onto a commercially fabricated CMOS substrate. In this manner, CNFET devices are fabricated on top of the interconnection network of the CMOS chip, providing a three-dimensional integration of active devices, “sandwiching” wiring, and passives. As a demonstration of this approach, a simple hybrid CNFET/CMOS inverter is fabricated and tested.
Enhanced stitching for the fabrication of photonic structures by electron beam lithography
Authors: Gnan M. , Macintyre D. S. , Sorel M. , De La Rue R. M. , Thoms S.
Published: December 2007

Large-area electron beam lithography tools pattern substrates as a series of writing fields that are stitched together. Pattern defects, termed stitching errors, can arise at field boundaries and these can have detrimental effects on device performance. These problems are exaggerated by substrate tilt. In this article, the authors demonstrate the application of a substrate tilt correction procedure to minimize stitching errors in the fabrication of photonic structures by electron beam lithography. The authors show that the magnitude of stitching errors is dependent on the position within the field boundary and is influenced by substrate tilt. Application of tilt correction procedures is shown to reduce stitching errors and give rise to a corresponding reduction in propagation losses in photonic wire waveguides. The authors show that the results of measured propagation losses arising from stitching errors are in good agreement with numerical results.
Characterizing nanoimprint profile shape and polymer flow behavior using visible light angular scatterometry
Authors: Al-Assaad Rayan M. , Regonda Suresh , Tao Li , Pang Stella W. , Hu Wenchuang (Walter)
Published: December 2007

The profile shape and the flow behavior of polymer nanoscale gratings made by a thermal nanoimprint process are precisely examined using visible light angular scatterometry. Nanoimprinted poly(methyl methacrylate) (PMMA) lines with 60–800nm width, 100–200nm height, and varied residual thicknesses of 70–400nm have been investigated using this optical approach, and insightful observations are made regarding residual stress buildup during thermal nanoimprint. In addition, a nonlinear profile model has been developed for scatterometry to monitor the “melting” behavior of PMMA gratings under annealing around its glass transition temperature. The polymer nanostructures were found to relax primarily at high stress regions.
Pixelated chemically amplified resists: Investigation of material structure on the spatial distribution of photoacids and line edge roughness
Authors: La Young-Hye , Insik-In  , Park Sang-Min , Meagley Robert P. , Leolukman Melvina , Gopalan Padma , Nealey Paul F.
Published: December 2007

Preorganized pixel-forming photoresists were prepared to investigate the effect of well-defined material structures and the spatial distribution of photoacid on line edge roughness of chemically amplified photoresists. Asymmetric poly(styrene)-block-poly(t-butylacrylate) (PS-b-PtBA) diblock copolymers, which formed PS cylinders or spheres within a PtBA matrix, were used as photoresists by adding catalytic amounts of photoacid generators (PAGs). PAGs resided only in the PtBA matrix domain, resulting in the PAG chemistry occurring only in the matrix domain. The pixelated photoresists showed a significant solubility switch after UV or x-ray exposure and postexposure bake, such that the polymer in the exposed regions dissolved in aqueous base solution. Granular structures that were matched with the domain spacing and structure of the block copolymer photoresists were observed on the edge of the patterned features. This model system demonstrated that line edge roughness is directly correlated to the structure of pixelated photoresist materials.
Nanoimprint lithography processes on 200mm Si wafer for optical application: Residual thickness etching anisotropy
Authors: Chaix N. , Gourgon C. , Perret C. , Landis S. , Leveder T.
Published: December 2007

It is well known that one limitation of thermal nanoimprint lithography is the difficulty to imprint simultaneously nano- and microstructures because of the resulting different residual layer thicknesses, which induce a very poor control of the pattern sizes during the etching steps. Line gratings with densities varying from 1 to 15 have been imprinted on 8in. wafers. The residual thickness varies from 38to158nm. Different plasma chemistries have been studied for the etching of the residual layer. The patterns have been characterized after the imprint and the etching steps by scatterometry. The results show that some chemistries are very promising for the control of the patterns during the etching step. A O2/C12/Ar process has been particularly studied, and it has been demonstrated that it presents a very high anisotropy, which allows the use of long etching times in order to remove the residual layer in gratings with various densities with no variation of the critical dimension.
Fabrication of 22nm half-pitch silicon lines by single-exposure self-aligned spatial-frequency doubling
Authors: Raub Alex K. , Li Dong , Frauenglass Andrew , Brueck S. R. J.
Published: December 2007

The relentless progression of semiconductor technology to smaller feature sizes will likely soon outstrip the theoretical linear system limits of today’s optical lithography tools (a half-pitch of λ∕4n or 34nm with a 193nm wavelength source and water immersion). We demonstrate a self-aligned process involving only a single lithographic exposure followed by spatial-frequency doubling that results a half-scaling of the original pattern and have achieved a 22nm half-pitch pattern with 193nm water immersion. A lithographic pitch of 89nm was realized with a 193nm ArF-excimer laser source and de-ionized-water immersion interferometric lithography. A self-aligned spatial-frequency doubling technique, taking advantage of the well-known anisotropic etching of silicon by KOH, was used to affect the frequency doubling. A protective layer (metal) was deposited parallel to the (110) direction of a (100) silicon wafer and the sample was immersed in an appropriate KOH solution, resulting in a series of 44.5nm opening width V-grooves terminated in 57° (111) faces etched into the silicon through the mask openings. The metal mask was removed to expose the previously protected high-etch rate (100) surface of the sample for a second wet KOH etch. This results in a pattern at twice the original spatial frequency. A frequency-doubled pitch of 44.5nm was achieved. An alternate, manufacturing friendly, processing scheme related to standard gate sidewall passivation is proposed.
Creating micro- and nanostructures on tubular and spherical surfaces
Authors: Lima O. , Tan L. , Goel A. , Negahban M. , Li Z.
Published: December 2007

The authors developed a new technique to create micro- and nanometer scale structures on curved free-standing objects by combining embossing/imprinting lithography approaches with mechanical loadings on elastic films. Embossing/imprinting generates small structures and mechanical loading determines shape or geometry of the final object. As a result, a portion of the tubes with a radius between 0.5 and 3.5 mm and a portion of the spheres with a radius between 2.4 and 7.0 mm were fabricated with grating line features (period of 700 nm) and microlens array features (lens radius of 2.5 μm) atop, respectively. It was found that both static analyses and finite element models can give good estimates on the radii of those curved objects, based on the dimension of the two layers, loading format, as well as mechanic strains. Thus, good control over shape and dimension of the free-standing structure can be achieved.
Chemical nanoimprint lithography for step-and-repeat Si patterning
Authors: Namatsu Hideo , Oda Masatoshi , Yokoo Atsushi , Fukuda Makoto , Irisa Koichi , Tsurumi Shigeyuki , Komatsu Kazuhiko
Published: December 2007

Chemical nanoimprint lithography is proposed as a new nanoimprint category. The authors investigate chemical nanoimprint utilizing an electrochemical reaction based on the anodic oxidation that occurs as a result of moisture that is present between a mold and a substrate. For stable nanoimprint patterning, the authors have developed a silicon carbide mold with low resistance. The mold also has excellent surface flatness and mechanical strength. In addition, the authors have developed the prototype of chemical nanoimprinter equipped with a step-and-repeat system. The imprinter also has a temperature-humidity controller and a mold-pressure adjustment system, in addition to a voltage supply source.
Atomic diffusion and electronic structure in Al0.52In0.48P∕GaAs heterostructures
Authors: Smith P. E. , Lueck M. , Ringel S. A. , Brillson L. J.
Published: December 2007

In order to investigate the relationship between atomic diffusion and electronic structure in the epitaxial AlInP∕GaAs system, the authors have performed cross-sectional cathodoluminescence spectroscopy and secondary ion mass spectrometry measurements of a SiOx-capped, lattice-matched Al0.52In0.48P∕GaAs double heterostructure. The authors measure atomic diffusion of over 100nm resulting from annealings ranging from 650to850°C. An ∼40meV increase in the emission energy of AlInP is observed after the highest temperature annealings. This increase is consistent with an increase in the Ga concentration of the ternary layer at the expense of In, and as a result of diffusion from neighboring GaAs layers. Additionally, the authors observe a broad, AlInP-localized feature at ∼1.98eV. The intensity of this emission relative to the AlInP band-edge emission depends sensitively on the annealing temperature and, therefore, the amount of cross diffusion, and corresponds well energetically to literature reports of P vacancies. These results clarify cross diffusion and defect emission in AlInP∕GaAs, and demonstrate that these effects can have a significant impact on the electronic structure of lattice-matched III-V heterostructures.
Multiple beam sub-80-nm lithography with miniature electron beam column arrays
Authors: Silver C. S. , Spallas J. P. , Muray L. P.
Published: December 2007

Miniature electron beam columns have the potential for high resolution, high throughput maskless lithography applications because they can be scaled in number to form high density column arrays with low fabrication costs. This is achieved using manufacturing techniques that leverage rf packaging technologies and standard bulk micromachining and integrated circuit fabrication processes to produce reliable components with repeatable performance characteristics. A 1×4 electrostatic column array designed to target the 45nm node has been built using monolithically fabricated lenses and packages. The lenses, which consist of stacks of patterned silicon and insulator, are mounted to a ceramic package. Internal to the package are traces which carry all interconnects to drive the column. Each column in the array is individually correctable. The monolithic lens design simplifies the pick-and-place assembly of high density column arrays and enables precise column-to-column registration. The design also facilitates scaling up of the column density to achieve higher throughput, and simulations presented previously suggest that the design can be extended to meet the 22nm resolution requirement. This article presents the first results from simultaneous multiple beam lithography using miniature column arrays. Independent patterns were exposed synchronously at 1keV using two columns in a 1×4 monolithic column array, resulting in 75nm features written into ZEP-520A resist. Other experiments suggest reliable high voltage lens performance and good beam current and position stability. These preliminary results from arrays of limited numbers of columns demonstrate progress toward the development of full-scale direct write lithography systems driven by miniature column arrays.
Lithography, plasmonics, and subwavelength aperture exposure technology
Authors: Ngu Yves , Peckerar Marty , Dagenais Mario , Barry John , Dutt Birendra (Raj)
Published: December 2007

This article presents the first experimental evidence that plasmonic excitation in metal films perforated with regular arrays of subwavelength apertures can produce high resolution far-field radiation patterns of sufficient intensity to expose photoresist when propagated through the optical system of a conventional stepper. The pattern fill factor (i.e., the total clear aperture area divided by the total mask area) is more than an order of magnitude smaller than the ratio of the mask clear area divided by the total mask area of a conventional mask. This could lead to a significant increase in mask making throughput. Contact window arrays were exposed with critical dimensions down to 260nm using 248nm incident radiation. While the exposure times are longer (somewhat less than three times more energy is required on the mask), the image pattern appears to be a cooperative effect of scattering from multiple apertures. If the array is defective, meaning that it contains a small number of unopened apertures, the pattern still prints as a coherent, cleared feature.
Energy dependence of effective atomic numbers for photon energy absorption and photon interaction: Studies of some biological molecules in the energy range 1 keV–20 MeV
Authors: Manohara S. R. , Hanagodimath S. M. , Gerward L.
Published: January 2008

Effective atomic numbers for photon energy absorption, , and for photon interaction, , have been calculated by a direct method in the photon‐energy region from 1 keV to 20 MeV for biological molecules, such as fatty acids (lauric, myristic, palmitic, stearic, oleic, linoleic, linolenic, arachidonic, and arachidic acids), nucleotide bases (adenine, guanine, cytosine, uracil, and thymine), and carbohydrates (glucose, sucrose, raffinose, and starch). The and values have been found to change with energy and composition of the biological molecules. The energy dependence of the mass attenuation coefficient, , and the mass energy‐absorption coefficient, , is shown graphically and in tabular form. Significant differences of between and occur in the energy region 5–100 keV. The reasons for these differences, and for using rather than in calculations of the absorbed dose, are discussed.
Sexual Selection in Males and Females
Authors: Clutton-Brock Tim
Published: December 2007

Research on sexual selection shows that the evolution of secondary sexual characters in males and the distribution of sex differences are more complex than was initially suggested but does not undermine our understanding of the evolutionary mechanisms involved. However, the operation of sexual selection in females has still received relatively little attention. Recent studies show that both intrasexual competition between females and male choice of mating partners are common, leading to strong sexual selection in females and, in extreme cases, to reversals in the usual pattern of sex differences in behavior and morphology.
Incubating Inspiration?
Authors: Whiteley Louise
Published: December 2007

Le Laboratoire
. 4 rue du Bouloi, 75001 Paris.
www.lelaboratoire.org

David Edwards established this new cultural center in Paris to show case and facilitate creativity that flows from combinations of art and science.
Dr Helen Taussig (1898–1986): pioneering American paediatric cardiologist
Authors: Dunn P M
Published: December 2007

In 1944, Helen Taussig in collaboration with Alfred Blalock initiated the first surgical treatment of cyanotic congenital malformations of the heart. She may be regarded as the founder of paediatric cardiology.
A role for doctors in assisted dying? An analysis of legal regulations and medical professional positions in six European countries
Authors: Bosshard G , Broeckaert B , Clark D , Materstvedt L J , Gordijn B , Müller-Busch H C
Published: December 2007

Objectives:

To analyse legislation and medical professional positions concerning the doctor’s role in assisted dying in western Europe, and to discuss their implications for doctors.

Method:

This paper is based on country-specific reports by experts from European countries where assisted dying is legalised (Belgium, The Netherlands), or openly practiced (Switzerland), or where it is illegal (Germany, Norway, UK).

Results:

Laws on assisted dying in The Netherlands and Belgium are restricted to doctors. In principle, assisted suicide (but not euthanasia) is not illegal in either Germany or Switzerland, but a doctor’s participation in Germany would violate the code of professional medical conduct and might contravene of a doctor’s legal duty to save life. The Assisted Dying for the Terminally Ill Bill proposed in the UK in 2005 focused on doctors, whereas the Proposal on Assisted Dying of the Norwegian Penal Code Commission minority in 2002 did not.

Professional medical organisations in all these countries except The Netherlands maintain the position that medical assistance in dying conflicts with the basic role of doctors. However, in Belgium and Switzerland, and for a time in the UK, these organisations dropped their opposition to new legislation. Today, they regard the issue as primarily a matter for society and politics. This “neutral” stance differs from the official position of the Royal Dutch Medical Association which has played a key role in developing the Dutch practice of euthanasia as a “medical end-of-life decision” since the 1970s.

Conclusion:

A society moving towards an open approach to assisted dying should carefully identify tasks to assign exclusively to medical doctors, and distinguish those possibly better performed by other professions.
Unesco’s Ethics Education Programme
Authors: Have H ten
Published: December 2007

Unesco initiated the Ethics Education Programme in 2004 at the request of member states to reinforce and increase the capacities in the area of ethics teaching. The programme is focused on providing detailed information about existing teaching programmes. It also develops and promotes teaching through proposals for core curricula, through a training course for ethics teachers and by distributing educational resources to support programmes.
Mortality risk in the French cohort of uranium miners: extended follow-up 1946–1999
Authors: Vacquier B , Caer S , Rogel A , Feurprier M , Tirmarche M , Luccioni C , Quesne B , Acker A , Laurier D
Published: December 2007

Objectives:

This paper presents the risk of death from lung cancer and from other causes of death for the French cohort of uranium miners through 1999 and estimates associations with radon exposure.

Methods:

The cohort includes men employed as uranium miners for at least 1 year between 1946 and 1990. For each miner, vital status and cause of death were obtained from the national registry, and radon exposure was reconstructed for each year. Standardised mortality ratios were computed with national mortality rates as references. Exposure–risk relationships were estimated by Poisson regression, with a linear excess relative risk (ERR) model and a 5-year lag.

Results:

The cohort included 5086 miners and 153 063 person-years of exposure. The mean duration of follow-up was 30.1 years. In all 4140 miners exposed to radon, the average cumulative exposure was 36.6 working level months (WLM). There were 1411 deaths of miners <85 years of age. The miners did not differ significantly in overall mortality from the general male population. The analysis confirmed an excess risk of lung cancer death (n = 159; SMR = 1.43; 95% CI: 1.22 to 1.68), which increased significantly with cumulative radon exposure (ERR per 100 WLM = 0.71; 95% CI: 0.29 to 1.35). The ERR per unit exposure was much higher after 1955, when the accuracy of exposure measurement improved substantially (ERR per 100 WLM = 2.00; 95% CI: 0.91 to 3.65). A significant excess of kidney cancer deaths was observed (n = 20; SMR = 2.0; 95% CI: 1.22 to 3.09), which was not associated with cumulative radon exposure. No excess was observed for other causes of death, except silicosis (n = 23; SMR = 7.12; 95% CI: 4.51 to 10.69).

Conclusions:

The analysis confirmed the excess risk of death from lung cancer associated with low radon exposure. An excess risk of death from kidney cancer was also observed, apparently not associated with cumulative radon exposure.
The occupational risk ofHelicobacter pyloriinfection among workers in institutions for people with intellectual disability
Authors: De Schryver A , Cornelis K , Van Winckel M , Moens G , Devlies G , Derthoo D , van Sprundel M
Published: December 2007

Objectives:

A cross-sectional study to evaluate the occupational risk forHelicobacter pyloriinfection, on top of other risk factors, in staff members of institutions for people with intellectual disability. In these institutions, the residents had a documented high prevalence ofH pyloriinfection (86% presenting antibodies). As a control group, the study used administrative workers from other companies.

Methods:

All participants completed a questionnaire concerning sociodemographic characteristics, medical history and employment data and they underwent a serology test.

Results:

671 staff members of the institutions and 439 subjects in the control group participated in the study. Prevalence ofH pyloriantibodies was significantly higher in the study group than in the control group (40.6% vs 29.2%; p<0.001). Crude odds ratio for occupational risk was 1.68; adjusting for the confounding effect of age, gender, body mass index, smoking, tropical journeys and number of household members during childhood resulted in an even higher (adjusted) OR of 1.98 (95% CI 1.42 to 2.69). In multiple logistic regression analysis adjusting for variables shown to be confounders, faecal contact continued to be significantly associated withH pyloriinfection. Attributable risk was 49.5%.

Conclusions:

H pyloriinfection is an occupational risk in healthcare workers working in institutions for people with intellectual disability. We identified faecal contact as an independent occupational risk factor forH pyloriinfection.
An epidemiological study of the role of chrysotile asbestos fibre dimensions in determining respiratory disease risk in exposed workers
Authors: Stayner L , Kuempel E , Gilbert S , Hein M , Dement J
Published: December 2007

Background:

Evidence from toxicological studies indicates that the risk of respiratory diseases varies with asbestos fibre length and width. However, there is a total lack of epidemiological evidence concerning this question.

Methods:

Data were obtained from a cohort mortality study of 3072 workers from an asbestos textile plant which was recently updated for vital status through 2001. A previously developed job exposure matrix based on phase contrast microscopy (PCM) was modified to provide fibre size-specific exposure estimates using data from a re-analysis of samples by transmission electron microscopy (TEM). Cox proportional hazards models were fit using alternative exposure metrics for single and multiple combinations of fibre length and diameter.

Results:

TEM-based cumulative exposure estimates were found to provide stronger predictions of asbestosis and lung cancer mortality than PCM-based estimates. Cumulative exposures based on individual fibre size-specific categories were all found to be highly statistically significant predictors of lung cancer and asbestosis. Both lung cancer and asbestosis were most strongly associated with exposure to thin fibres (<0.25 μm). Longer (>10 μm) fibres were found to be the strongest predictors of lung cancer, but an inconsistent pattern with fibre length was observed for asbestosis. Cumulative exposures were highly correlated across all fibre size categories in this cohort (0.28–0.99, p values <0.001), which complicates the interpretation of the study findings.

Conclusions:

Asbestos fibre dimension appears to be an important determinant of respiratory disease risk. Current PCM-based methods may underestimate asbestos exposures to the thinnest fibres, which were the strongest predictor of lung cancer or asbestosis mortality in this study. Additional studies are needed of other asbestos cohorts to further elucidate the role of fibre dimension and type.
SIZE REQUIREMENTS OF COMPACT SANDWICH SPECIMEN FOR TESTING OF BONE
Authors: PARUCHURU SATYA PRASAD , JAIN ANUJ , WANG XIAODU
Published: December 2007

It is well understood that bone quality deteriorates due to aging, disease, etc., and may be affected by factors at different length scales due to its hierarchical microstructure. Fracture toughness is one of the properties that assess bone quality. The compact sandwich (CS) specimen gives a better choice of bone sample size, and therefore suits a wide variety of fracture toughness testing needs and constraints. Reliable and statistically valid overall CS specimen size requirements are established in this paper; these serve as guidelines for choosing the CS specimen size. Finite element analysis (FEA) is used for simulating fracture toughness tests. Experimental fracture toughness tests are carried out to verify the FEA results. The experimental results are verified qualitatively by performing scanning electron microscopy (SEM) on the fractured specimen surfaces.