bluuebunny/crossref_metadata_2025 huggingface dataset:
Double-anchoring fluorinated molecules for antiadhesion mold treatment in UV nanoimprint lithography
Authors: Zelsmann M. , Truffier-Boutry D. , Francone A. , Alleaume C. , Kurt I. , Beaurain A. , Pelissier B. , Pépin-Donat B. , Lombard C. , Boussey J.
Published: December 2009

In this work, the authors evaluate a new type of perfluoropolyether molecule (FLUOROLINK® S10) to be used as an antisticking mold treatment in UV nanoimprint lithography. Unlike currently used ones, this molecule has two anchoring ends groups allowing two covalent grafting sites of the molecule to the mold surface. Obtained results on this molecule are compared to Optool DSX’s ones. Using contact angle measurement, x-ray photoelectron spectroscopy, and electron spin resonance, the authors carried out chemical analysis of the evolution of antisticking treatments as a function of the number of imprints. It is found that both molecules have a roughly equivalent behavior. FLUOROLINK® S10 has shown less chemical resistance, attributed to its larger number of C–O bonds in the molecule, but an improved mechanical resistance, attributed to the double grafting mechanism.
Improvement of imaging properties by optimizing the capping structure in extreme ultraviolet lithography
Authors: Jeong Chang Young , Lee Sangsul , Shin Hyun-Duck , Kim Tae Geun , Ahn Jinho
Published: December 2009

The optimization of capping structure for extreme ultraviolet lithography was conducted to minimize the mask shadowing effect. The capping structure used in this study consisted of a phase shift layer and a capping layer on the 40 pairs of Mo–Si multilayer. A phase shift layer was added below tantalum nitride (TaN) absorber pattern. The authors analyzed the effect of the following capping materials such as ruthenium (Ru), silicon (Si), and molybdenum (Mo) with thickness variation. TaN absorber thickness for out-of phase condition shifted with the capping layer thickness change. The variation in capping materials showed less of an effect compared to thickness change. The addition of phase shift layer below absorber pattern showed a significant effect on the phase difference. Ru phase shift layer with a higher δ value than TaN absorber, shifted phase difference to the positive direction, whereas Si phase shift layer with a lower δ value than TaN absorber, shifted phase difference to the negative direction. However, phase difference was not shifted by the addition of Mo phase shift layer which has a similar δ value with TaN absorber. We also calculated the horizontal-vertical overlapping process window according to Mo phase shift layer thickness using 22nm 1:1 line and space pattern. As Mo phase shift layer thickness increased, the overlapping zone in the exposure latitude of the focus-exposure plots between the horizontal and vertical features increased.
Formation of TiO2 nanopattern using reverse imprinting and sol-gel method
Authors: Yoon Kyung-min , Yang Ki-Yeon , Lee Heon , Kim Hyeong-Seok
Published: December 2009

Ti O 2 and its nanopattern fabrication have been studied intensively because of its wide band gap and photocatalystic nature. TiO2 nanopatterns can be made by conventional patterning techniques, consisting of deposition, photolithography, and etching processes. However, these processes include complicated and expensive process steps, such as photolithography. Therefore, a simpler and more economic process is needed. In this work, TiO2 nanopatterns were fabricated using reverse-imprint lithography and the sol-gel method. Ethanol based TiO2 sol was prepared using tetrabuthylorthotitanate (C16H36O4Ti) and diethanolamine (C4H11NO2). TiO2 sol was then coated on the surface of the replicated polymer mold of hard-polydimethylsiloxane and polydimethylsiloxane by spin coating and transferred to the substrate by the reverse imprinting process at 200°C. A postimprint annealing process was subsequently carried out to form the TiO2 polycrystalline phase. The x-ray diffraction and x-ray photoelectron spectroscopy results confirmed that the transferred TiO2 nanopattern was chemically pure polycrystalline TiO2.
Thermal imprinting on quartz fiber using glasslike carbon mold
Authors: Mekaru Harutaka , Okuyama Chieko , Ueno Akihisa , Takahashi Masaharu
Published: December 2009

The authors are developing an on-fiber device that uses a quartz fiber as a substrate material and a large-area display and a wearable health monitor by woven fibers with embedded electrical circuit. The electrical circuit will be formed by inserting some electroconductive material into the concave pattern by inkjet and electroless-plating after thermally imprinting on the surface of the quartz fiber. To imprint the quartz fiber, a mold should be able to withstand the high temperature of 1400°C. Therefore, a mold for quartz imprinting on quartz fiber was fabricated with a glasslike carbon substrate polished by chemical-mechanical-polishing. Mold patterns with high accuracies were processed by applying microelectromechanical system fabrication techniques such as photolithography and reactive ion etching. Precise patterns with 5μm minimum linewidths were transferred on the front surface of a 200μm square quartz fiber by thermal nanoimprint technology. The width of the imprinted quartz fibers grew from 200to296μm by the loading force, but part of the loading force was also used up in deforming the quartz fibers. Filling rates, defined as the ratio of the height of imprinted patterns to the depth of mold patterns, were calculated and then the relationship between the filling rate and the aspect ratio of mold patterns was investigated. The molding accuracy was found to be independent of the size of the mold patterns, but it did exhibit its dependency on the aspect ratio of the mold patterns. The expected overlay accuracy, which is important for making circuitry in the future, was approximately 5μm judging from the imprinted patterns on the quartz fiber.
Transparent hybrid polymer stamp copies with sub-50-nm resolution for thermal and UV-nanoimprint lithography
Authors: Schift Helmut , Spreu Christian , Saidani Menouer , Bednarzik Martin , Gobrecht Jens , Klukowska Anna , Reuther Freimut , Gruetzner Gabi , Solak Harun H.
Published: December 2009

The organic-inorganic hybrid polymer Ormostamp was successfully used for the fabrication of inexpensive, transparent working stamps to be used in nanoimprint lithography. The stamps were produced from different masters by casting and UV exposure of a viscous precursor. The cured hybrid stamp with the replicated surface relief was imprinted into several thermoplastic materials with up to 180 °C imprint temperature. In this article the authors show the effect of the imprint temperature on the structural fidelity. By using combined thermal and UV-nanoimprint lithography at 110 °C imprint temperature, a resolution down to 35 nm is demonstrated. They also investigated deterioration effects due to plasma treatment to simulate the effect of multiple recoating steps.
Ultrathin fluorinated diamondlike carbon coating for nanoimprint lithography imprinters
Authors: Fillman Ryan W. , Krchnavek Robert R.
Published: December 2009

Nanoimprint lithography (NIL) has proven to be an exceptional lithographic technique for achieving arbitrary, nanoscale features, over large areas without the use of costly step-and-repeat UV lithography tools. One requirement for NIL is to eliminate adhesion of the imprinted polymer to the imprinter upon withdrawal of the imprinter. Previous work on thick (>100nm) diamondlike carbon (DLC) layers indicates that fluorinated DLC (F-DLC) provides a durable antiwear, antistick layer. In this work, a process for depositing an ultrathin layer of F-DLC is shown for SiO2 based imprinters.
Electron beam induced deposition of cobalt for use as single- and multiwalled carbon nanotube growth catalyst
Authors: Ervin M. H. , Nichols B. M.
Published: December 2009

Electron beam induced deposition (EBID) has been investigated by many researchers for a number of applications requiring maskless deposition of material. Here, a scanning electron microscope is used to perform EBID of cobalt (Co) nanoparticles, which are then used as the catalyst for selected-area growth of carbon nanotubes (CNTs). Co nanoparticles were deposited using cobalt tricarbonyl nitrosyl as the precursor. They are oxygen plasma ashed to remove residual carbon from the deposition process prior to the growth of CNTs using a chemical vapor deposition (CVD) process. Co deposits made using different doses were found to have different catalytic properties. At sufficiently low doses, the deposits were insufficient to catalyze any CNT growth. At higher doses, single-walled CNT (SWCNT) growth was observed. Still higher doses produced deposits that catalyzed multiwalled CNT growth as well as some SWCNT growth. These differences in catalytic behavior are believed to result from nanoparticle size variations between and within the deposits. As a result, by using EBID deposited catalyst, it is possible to not only control where CNTs grow but also the kind of CNTs (SW or MW) grown during a single CVD run.
Easy mask-mold fabrication for combined nanoimprint and photolithography
Authors: Schift Helmut , Spreu Christian , Schleunitz Arne , Gobrecht Jens , Klukowska Anna , Reuther Freimut , Gruetzner Gabi
Published: December 2009

Hybrid transparent working stamps with both a surface relief and absorbing mask pattern were fabricated by replicating nanostructures in an Ormostamp film on prepatterned glass substrates. By using a combined nanoimprint and photolithography process, self-aligned mixed patterns of nano- and microstructures can be generated within one single resist layer. In this article the authors present a simple process based on the organic-inorganic hybrid polymer Ormostamp by replication on prepatterned Borofloat substrates. Using these working stamps, grating arrays with 35 nm half pitch were replicated in thermoplastic UV-curable resist. The method is easy to employ for generating mesas with nanostructures on top or the backfilling with microstructures in thermal nanoimprint lithography applications.
Bond contribution model for the prediction of glass transition temperature in polyphenol molecular glass resists
Authors: Lawson Richard A. , Yeh Wei-Ming , Henderson Clifford L.
Published: December 2009

Molecular glass resists have shown potential as replacements for polymeric resists in next generation lithography, especially extreme ultraviolet lithography. One of the main concerns about molecular resists is their glass transition temperature (Tg) which can be very low in some cases due to their small molecular size and other factors. While most of the polymeric chemically amplified resist platforms used thus far have Tg’s above 100°C, molecular resists investigated in the literature so far have shown a wide range of measured Tg’s from near room temperature to greater than 160°C. This potential for low Tg values and the current lack of ability to easily predict their Tg is a concern when designing new compounds because a molecular resist may be synthesized with a Tg value that is too low for the required processing conditions (e.g., allowing for dewetting of the resist, flow of the resist features, or excessive photoacid diffusion). To enable rational molecular resist design and overcome these problems, a quantitative structure-property relation model based on bond additivity that allows for the prediction of the Tg of molecular resists based on their full chemical structure has been developed in this work. The model shows a good coefficient of determination (R2) of 0.84 with experimental data, and a standard deviation of only 12°C for 57 compounds. It works well across multiple different levels of protection, different structural moieties, different molecular sizes, and different types of protecting groups. The model was also simplified to provide a simple heuristic for predicting Tg based on only two or three structural parameters, and this easy to use simplified model provides a similar level of quantitative agreement with experimental data to the full bond additivity model.
Direct e-beam writing of 1nm thin carbon nanoribbons
Authors: Nottbohm C. T. , Turchanin A. , Beyer A. , Gölzhäuser A.
Published: December 2009

The fabrication of 1nm thin carbon nanoribbons and nanorings is demonstrated. Aromatic self-assembled monolayers are locally cross-linked by electron beam lithography into polymeric carbon nanosheets. Annealing at 1200K in ultrahigh vacuum transforms these electrically insulating nanosheets into a conducting two-dimensional phase consisting of nanopatches of graphene with a sheet conductivity of ∼10−2Ssq. The method allows the direct writing of patterns into the monolayer, permitting the resistless fabrication of arbitrarily sized and shaped carbon nanostructures with a thickness of 1nm.
Fabrication of complementary metal-oxide-semiconductor integrated nanomechanical devices by ion beam patterning
Authors: Rius G. , Llobet J. , Borrisé X. , Mestres N. , Retolaza A. , Merino S. , Perez-Murano F.
Published: December 2009

The authors present a novel approach to fabricate nanomechanical devices integrated into complementary metal-oxide-semiconductor (CMOS) circuits. It is based on focused ion beam patterning using two different processes: (i) ion-beam-induced deposition of tethraethoxysilane and (ii) direct exposure of silicon or polysilicon surfaces. In both cases, the irradiated areas sustain a reactive-ion etching process, acting as robust masks for defining nanomechanical devices with submicron resolution. These processes are compared, in terms of throughput, with direct milling of silicon and with patterning of thin aluminum layers. Compatibility with prefabricated CMOS circuits is studied and they found that the process is entirely compatible if the proper exposure conditions are used.
Fabrication of poly(3-hexylthiophene) self-switching diodes using thermal nanoimprint lithography and argon milling
Authors: Kettle J. , Whitelegg S. , Song A. M. , Madec M. B. , Yeates S. , Turner M. L. , Kotacka Libor , Kolarik Vladimir
Published: December 2009

In this article, the fabrication of poly(3-hexylthiophene) self-switching diodes (SSDs) is described. The unique design of the SSD enables it to be fabricated from a single layer of semiconductor material with a single lithographic step using nanoimprint lithography combined with argon milling. The resultant device morphology showed good uniformity and the SSDs exhibited pronounced current rectification and wide working voltage range.
Modification of a polystyrene brush layer by insertion of poly(methyl methacrylate) molecules
Authors: Liu Guoliang , Ji Shengxiang , Stuen Karl O. , Craig Gordon S. W. , Nealey Paul F. , Himpsel F. J.
Published: December 2009

The ability to tune the wetting behavior of poly(styrene-block-methyl methacrylate) on a polystyrene (PS) brush by insertion of hydroxyl-terminated poly(methyl methacrylate) (PMMA-OH) was demonstrated. The brush properties before and after insertion of PMMA-OH were studied with goniometry, ellipsometry, near edge x-ray absorption fine structure spectroscopy, and scanning electron microscopy. The initial PS brush served as a barrier to the grafting of PMMA onto the substrate. The amount of PMMA that could penetrate through the PS brush barrier and graft onto the substrate depended on the initial PS brush thickness. As a result, the PS:PMMA ratio in the final composite brush, and therefore the brush wetting properties, could be carefully controlled. The final composition also depended on the grafting sequence of the brush molecules. This may offer a generalized approach for fabricating neutral brush surfaces without requiring the synthesis of specific random copolymers.
Defectivity issues in topcoatless photoresists
Authors: Cantone Jason , van Dommelen Youri , Jiang Aiqin , Dunn Shannon , Winter Tom , Petrillo Karen , Johnson Rick , Lawson Peggy , Conley Will , Callahan Ryan
Published: December 2009

One method currently being employed to reduce the overall lithography process complexity and cost is the utilization of a topcoatless photoresist. The development of these materials administers an additive to create the same hydrophobic characteristics as those created by advanced topcoats. The main challenge for topcoatless resists is to increase the hydrophobicity without causing too much inhibition at the resist surface which leads to bridging or residue-type defects. The key to such a design lies in creating a balance between leaching control and dissolution characteristics of the resist without degrading lithography performance and increasing defectivity. The addition of these hydrophobic additives into existing ArF photoresist systems has been shown to increase both receding contact angle and advancing contact angle in water-based immersion lithography. In this work, the authors have demonstrated that the defectivity levels of topcoatless resist are equal to or better than the industry standard of topcoat systems. This was achieved by optimizing process conditions. This article will report the influences of the develop process, postcoat apply bake/postexposure bake (PAB/PEB) temperatures, and immersion specific rinses on defect performance of topcoatless resists. It was found that pattern collapse defects along nonexposed regions for some topcoatless material can be drastically reduced by PAB/PEB temperature optimization. Complete elimination of missing pattern defects achieved by use of de-ionized water immersion specific rinses for all materials tested. Finally, the impact of the PAB temperature on surface properties will be investigated.
Hierarchical structure formation induced by dewetting in an imprinting process
Authors: Pai I. T. , Chiou D. W. , Hon M. H. , Leu I. C.
Published: December 2009

Creating an ordered three-dimensional hierarchical structure using nanoimprint lithography remains a challenge even though such structures with micro-/nanometer scale are important with technological advances in a number of applications. The controllable polyimide (PI) hierarchical structures could be obtained by using polyamic acid (PAA) precursor in γ-butyrolatone-N-methylpyrrolidone mixture solution of various concentrations (1, 2, 3, and 4wt%) through dewetting in an imprinting process. PI patterns without a residual layer are formed due to the dewetting phenomena caused by the surface tension, and thus formed patterns of different ambits are obtained due to the fluidity of the PAA solutions. This method is not restricted to a specific polymer and substrate and could be easily applied to pattern other organic materials.
Curing process of silsesquioxane in self-organized diblock copolymer template
Authors: Kihara Naoko , Takizawa Kazutaka , Yamamoto Ryosuke , Tanaka Hiroki , Hieda Hiroyuki
Published: December 2009

In the case that a self-organized diblock copolymer pattern is applied as an etching mask, one of the polymer components is required to have a high etching durability similar to that of silicon oxide. One suitable material for the purpose is a mixture of polystyrene-b-polyethyleneoxide (PS-PEO) and silsesquioxane (SSQ). After phase separation, the SSQ component is located only in PEO phase. By the following post-treatment, the polymer component was removed and residual cured SSQ structure was formed that could be available as etching mask. In this study, the authors investigated post-treatment process of SSQ in the mixed component system, comparing thermal treatment and oxygen plasma treatment. A significant difference was observed in the vertical shrinkage of the film thickness formed on a Si wafer. The plasma-treated film shrank to 72% of the baked film. By the examination of behavior of PS phase and PEO phase during post-treatment, respectively, it was found that the difference was caused by the curing behavior of SSQ in PEO. In the case of plasma treatment, the polymer component was removed before SSQ curing. As a consequence, plasma treatment gives voidless structure. Using the template as etching mask, 16nm pitch pattern was transferred to Si wafer.
Release force reduction in UV nanoimprint by mold orientation control and by gas environment
Authors: Hiroshima Hiroshi
Published: December 2009

Release force reduction is necessary for reliable UV nanoimprint. The effect of inclined mold detachment and pentafluoropropane as an ambient gas was investigated using a UV-nanoimprint stepper with a mold orientation control and a gas introduction system. The inclined release was realized by diverting the mold orientation control for directing a mold parallel to a wafer commonly used after mold exchange. A pentafluoropropane environment was generated in UV-nanoimprinting space by a gas introduction system within a UV-nanoimprint stepper. The inclined release showed a reduction in release force in comparison to parallel release at this experiment. However, the inclined release is only modestly beneficial for release force reduction. In contrast, the ambient gas in which UV nanoimprint is carried out has a significant impact on release force. Release force can be reduced to one-third of what is obtained in air by using pentafluoropropane. It is quite beneficial to use pentafluoropropane not only for bubble elimination but also for the reduction in release force.
Control of the critical dimensions and line edge roughness with pre-organized block copolymer pixelated photoresists
Authors: Kang Huiman , Kim Yun Jun , Gopalan Padma , Nealey Paul F.
Published: December 2009

Sphere-forming polystyrene-block-poly(t-butyl acrylate) (PS-b-PtBA) diblock copolymer with catalytic amounts of photo-acid generator (PAG) formulated a pixelated photoresist. In thin films with single-sphere thickness, hexagonal arrays of spheres (∼20 nm diameter on a 40 nm pitch) of PS within a matrix of PAG segregated in PtBA was obtained through solvent annealing. Upon exposure and post-exposure baking, the soluble PtBA matrix was converted to insoluble poly(acrylic acid), such that a negative pattern could be formed in the chlorobenzene developer. The concept of pixelation was demonstrated by exposing line and space patterns with increasing widths. In contrast to the width of the exposure fields that increased monotonically, the widths of the pixelated resist structures after development were quantized with respect to an integer number of rows of spheres. Furthermore, line edge roughness could be correlated with the size of each pixel (diameter of spherical domain).
Talbot lithography: Self-imaging of complex structures
Authors: Isoyan A. , Jiang F. , Cheng Y. C. , Cerrina F. , Wachulak P. , Urbanski L. , Rocca J. , Menoni C. , Marconi M.
Published: December 2009

The authors present a self-imaging lithographic technique, capable of patterning large area periodic structures of arbitrary content with nanoscale resolution. They start from the original concept of Talbot imaging of binary gratings—and introduce the generalized Talbot imaging (GTI) where periodic structures of arbitrary shape and content form high-definition self-images. This effect can be used to create the complex, periodic patterns needed in the many lithographic fabrication steps of modern semiconductor devices. Since the process is diffraction limited, the achievable resolution depends only on the wavelength, mask patterning, and degree of coherence of the source. Their approach removes all the complex extreme ultraviolet (EUV) reflective masks and optics, replacing them with nanopatterned transmission masks and makes the whole process simple and cost effective. They have successfully verified the GTI concept using first a He–Ne laser, and then demonstrated its potential as a nanolithography method using a compact table-top soft x-ray (EUV) 46.9nm laser source. These sources provide the high degree of coherence needed by diffraction-based imaging and are extendable to shorter wavelengths. They have recorded EUV GTI images up to the sixth Talbot plane, with consistent high quality good results, clearly demonstrating the ability of the GTI method to record high-resolution patterns at large distances.
Alternative developer solutions for extreme ultraviolet resist
Authors: Itani Toshiro , Santillan Julius Joseph
Published: December 2009

The use of the tetrapropylammonium hydroxide (TPAH) and tetrabutylammonium hydroxide (TBAH) aqueous developer solutions is proposed as an alternative to the tetramethylammonium hydroxide (TMAH) aqueous developer solution (semiconductor industry standard). A polyhydroxystyrene-based extreme ultraviolet (EUV) resist was utilized at a film thickness of 60nm. To confirm the effectiveness of these alternative developer solutions in improving linewidth roughness (LWR) performance, patterning exposures were carried out using the small field exposure tool with annular (σouter0.7∕σinner0.3) illumination conditions. Dissolution contrast curves of EUV resist using the TMAH, TPAH, and TBAH developer solutions have shown similar dissolution characteristics which means that the use of these alternative developer solutions might have minimal effect on the resist resolution limit and sensitivity. Imaging performance analysis results have shown negligible effect on the resolution capability and sensitivity. A 20% LWR improvement was observed with the TBAH developer solution [7.2nm at 32nm 1:1 line and space (L/S)] comparing with the TPAH and standard TMAH developer solutions (both at 9.0nm at 32nm 1:1 L/S). This improvement was perceived to be the result of the significant increase in dissolution contrast (higher Rmax and larger slope) with the use of the TBAH developer solution.
Stitching periodic submicron fringes by utilizing step-and-align interference lithography
Authors: Chen Yung-Pin , Chen Cheng-Hung , Chang Jer-Haur , Chiu Hsin-Chieh , Chen Guan-Yu , Chiang Chieh-Hsiu , Chen Lien-Sheng , Tseng Ching-Tung , Lee Chih-Hsien , Yen Jia-Yush , Wang Lon A.
Published: December 2009

The authors develop a step-and-align interference lithography system to fabricate large-area periodic submicron structures by stitching the unit exposure area step-by-step. A metal mask with a square transparent window in the center is used to intercept the quasi-flat-top region of the expanded Gaussian beam, and thus it serves as a beamshaper to approximate the ideal unit beam that has uniform intensity and spatial coherence. Two-dimensional precision dual-actuator motion stages could provide travel distance for full wafer exposure with 2nm high precision positioning capability for stitching the submicron patterns. The gratings with period of 700nm are successfully stitched along two directions on 100mm diameter wafers.
Thermal roller imprint on surface of Teflon perfluoroalkoxy inlet tube
Authors: Mekaru Harutaka , Fukushima Eri , Hiyama Yoshihito , Takahashi Masaharu
Published: December 2009

The authors succeeded in transferring patterns from a plate mold onto a cylindrical surface of a plastic tube by thermal imprinting. A roller imprint technology was selected as a pattern transfer method. A cylindrical molding material was rolled on the surface of a plate mold under an optimized contact force and heating temperature. A Teflon perfluoroalkoxy (PFA) inlet tube with an outer diameter of 1∕16in. was selected as a cylindrical molding material. This tube is often used in connecting the microfluid devices in the studies of high performance liquid chromatography. A plate mold was fabricated by employing microelectromechanical systems and Ni electroforming technologies. The minimum linewidth and depth of an electroformed-Ni mold were 5 and 2μm, respectively. Several patterns were designed to mimic microcoil and comb actuator. A Teflon-PFA inlet tube was sandwiched between an electroformed-Ni plate mold set at the bottom loading stage and a buffer material sheet mounted at the upper loading stage of an imprinting system. After applying a right amount of heat to the electroformed-Ni mold, it was moved horizontally, resulting in the rolling of the tube against the patterned surface of the mold. Using this method, three-dimensional roller imprinting was executed. A relationship among the press depth, contact force, rotation speed of a Teflon-PFA inlet tube, and the imprinted depth was investigated. As a result, it was shown that optimization of the press depth was necessary in order to avoid any slippage or stalking, impeding the rotation of the cylindrical tube.
Thermal stability of confined flip-chip laminated ω-functionalized monolayers
Authors: Coll M. , Richter C. A. , Hacker C. A.
Published: December 2009

The authors present the results of an IR study of the effect of temperature on the formation of Au-monolayer-Si molecular junctions by using a flip-chip lamination approach. Carboxylic acid-terminated alkanethiols self-assembled on an ultrasmooth gold substrate have been laminated to H–Si(111) at 0.8MPa as a function of temperature. p-polarized-back-side reflection absorption infrared spectroscopy of the alkanoic acids within the molecular junction indicates increasing disorder, likely near the carboxylic acid (–COOH) terminus, of the all-trans chain up to 60°C, followed by a propagation of these defects down the molecular length. The low frequency region of the IR spectra as a function of temperature indicates that the –COOH group is interacting with the H–Si(111) surface. The IR spectra indicate that the reaction is largely due to the availability of the COOH groups to react. Flip-chip lamination is an effective approach to form molecular junctions. Unlike direct metal evaporation, it ensures the formation of robust structures where the organic monolayer is chemically bonded to both surfaces with no signs of metal penetration.
Gold-tipped elastomeric pillars for cellular mechanotransduction
Authors: Ghassemi S. , Rossier O. , Sheetz M. P. , Wind S. J. , Hone J.
Published: December 2009

The authors describe a technique for the fabrication of arrays of elastomeric pillars whose top surfaces are treated with selective chemical functionalization to promote cellular adhesion in cellular force transduction experiments. The technique involves the creation of a rigid mold consisting of arrays of circular holes into which a thin layer of Au is deposited, while the top surface of the mold and the sidewalls of the holes are protected by a sacrificial layer of Cr. When an elastomer is formed in the mold, Au adheres to the tops of the molded pillars. This can then be selectively functionalized with a protein that induces cell adhesion, while the rest of the surface is treated with a repellent substance. An additional benefit is that the tops of the pillars can be fluorescently labeled for improved accuracy in force transduction measurements.
Iterative procedure for in situ extreme ultraviolet optical testing with an incoherent source
Authors: Miyakawa Ryan , Naulleau Patrick , Zakhor Avideh
Published: December 2009

The authors propose an iterative method for in situ optical testing under partially coherent illumination that relies on the rapid computation of aerial images. In this method, a known pattern is imaged with the test optics at several planes through focus. A model is created that iterates through possible aberration maps until the through-focus series of aerial images matches the experimental result. The computation time of calculating the through-focus series is significantly reduced by reduced optimized coherent sum, an adapted form of the sum of coherent systems decomposition. In this method, the Hopkins formulation is described by an operator S, which maps the space of pupil aberrations to the space of aerial images. This operator is well approximated by a truncated sum of its spectral components.
Low-roughness active microdisk resonators fabricated by focused ion beam
Authors: Barea L. A. M. , Vallini F. , Vaz A. R. , Mialichi J. R. , Frateschi N. C.
Published: December 2009

The authors present a new approach for the fabrication of active microdisk resonators using focused ion beam (FIB) followed by selective wet-chemical etching. This efficient technique enables the placement of the devices at any region of a sample and facilitates prototyping of monolithical integration. Also, it allows the production of very smooth walls required by the resonators. High-quality resonators with an active region based on high-gain InGaAsP∕InP quantum wells are demonstrated using this technique. Emission in the C-band at whispering-gallery modes is observed.
Experimental determination of image placement accuracy in extreme ultraviolet lithography
Authors: Raghunathan Sudhar , Wood Obert , Vukkadala Pradeep , Engelstad Roxann , Hartley John G.
Published: December 2009

Image placement and overlay error specifications in the International Technology Roadmap for Semiconductors continue to get tighter with each successive technology node. Some of the primary contributors to this error in extreme ultraviolet lithography are reticle and chuck surface nonflatness and chucking flatness nonuniformity. In this article, the authors report on results from a set of experiments that were designed to identify and separate chuck and mask contributions to image placement error (IPE). In the first set of experiments, a reticle with large peak-to-valley (P-V) nonflatness was printed to study reticle flattening and reticle thickness variation contributions to the final IPE. The experiments were designed to partition the total IPE into tool correctable and noncorrectable components. A second set of experiments was performed with a flat reticle that can be imaged in four different orientations (0°, 90°, 180°, and 270°). Both reticles have arrays of image placement fiducials that can be printed on the wafer and then used to measure the IPE.
Gallium phosphide nanowire arrays and their possible application in cellular force investigations
Authors: Suyatin Dmitry B. , Hällström Waldemar , Samuelson Lars , Montelius Lars , Prinz Christelle N. , Kanje Martin
Published: December 2009

The authors report the fabrication of gallium phosphide nanowire arrays that can be used for cellular force measurements. The nanowire positions are defined using electron beam lithography and the nanowires are grown using metal organic vapor phase epitaxy. By varying the nanowire diameter, length, and spacing from substrate to substrate, they can expect to probe cell forces over several orders of magnitude, depending on the chosen substrate. The small diameter of the nanowires allows them to densely pack the array and to achieve unprecedented spatial resolution for future cell force-array applications.
Model based optical proximity correction runtime saving with multisegment solver
Authors: Li Jianliang , Li Xiaohai , Deeth Steven , Lugg Robert , Melvin Lawrence S.
Published: December 2009

In modern photolithography, model based optical proximity correction (MBOPC) has evolved from a nice-to-have feature to a must-have feature and has been widely adopted to improve the process throughput. The purpose of MBOPC is to adjust the designed pattern on the photomask to introduce mask perturbations such that the layout printed on the wafer is as close as possible to the drawn layout. In regular MBOPC process, the polygons are dissected into segments and corrections are conducted segment by segment. While it is relatively easy and straightforward to find the optimal segment size for most one-dimensional features, it is hard for many two-dimensional features, especially line-end areas. By solving a few segments around line-end areas together, multisegment solver (MSS) showed a good contour match. However, this method is expensive on model calculation, as there is more than one segment size to be optimized and a large number of searching iterations is needed, which makes its runtime sensitive to the number kernels retained in OPC model. In this study, a novel method of computing the signal change in the MBOPC process with MSS is proposed by analyzing the optical kernel sensitivity to mask perturbation. The experimental results show that while the correction accuracy of the MBOPC process with a simplified model is maintained, the MBOPC runtime is reduced by 37%.
Negative tone molecular resists using cationic polymerization: Comparison of epoxide and oxetane functional groups
Authors: Lawson Richard A. , Noga David E. , Younkin Todd R. , Tolbert Laren M. , Henderson Clifford L.
Published: December 2009

Two molecular resists with a common molecular glass core were synthesized and characterized to compare the differences between epoxide (oxirane) and oxetane functional groups for use in high resolution negative tone molecular resists. Both resists are able to obtain at least 50nm half-pitch at a sensitivity of 75μC∕cm2 under 100keV electron-beam lithography. Due to differences in the kinetics of the cationic polymerization of epoxides as compared to oxetanes, the epoxide functionalized resist (2-Ep) was able to obtain sub-25-nm half-pitch resolution with good line edge roughness (LER) of 2.9nm (3σ) while the oxetane resist (2-Ox) was limited to 50nm half-pitch resolution and exhibited higher LER (3σ) of 10.0nm. The polymerization of the oxetane functional group has slow initiation and fast propagation which leads to reduced performance in 2-Ox as compared to 2-Ep. While oxetane functionalized molecular resists can obtain reasonably good imaging performance, epoxide functional groups show more promise for use in next generation negative tone resists that have a good combination of resolution, sensitivity, and LER.
Electrical detection of proteins and DNA using bioactivated microfluidic channels: Theoretical and experimental considerations
Authors: Javanmard M. , Esfandyarpour H. , Pease F. , Davis R. W.
Published: December 2009

In order to detect diseases such as cancer at an early stage while it still may be curable, it is necessary to develop a diagnostic technique which can rapidly and inexpensively detect protein and nucleic acid biomarkers, without making any sacrifice in the sensitivity. The authors have developed a technique, based on the use of bioactivated microfluidic channels integrated with electrodes for electrical sensing, which can be used to detect protein biomarkers, target cells, and DNA hybridization. In this article, they discuss the theoretical detection limits of this kind of sensor and also discuss various experimental considerations in the electrical characterization of our device. In particular, they discuss the temperature dependence, the impedance drift, the noise sources, and various methods for optimizing the signal to noise ratio.
The Insect Neuropeptide PTTH Activates Receptor Tyrosine Kinase Torso to Initiate Metamorphosis
Authors: Rewitz Kim F. , Yamanaka Naoki , Gilbert Lawrence I. , O’Connor Michael B.
Published: December 2009

Metamorphosis Receptor Identified

One of the challenges facing many multicellular organisms is when to change from the juvenile stage to the reproductively mature adult. In insects, this metamorphosis is activated by the brain-derived neuropeptide, prothoracicotropic hormone (PTTH), when larvae reach a characteristic weight. Almost a century after this brain hormone was discovered,

Rewitz
et al.

(p.
1403
) have identified the PTTH receptor and its signaling cascade. The PTTH receptor is Torso (a receptor tyrosine kinase that signals through Ras/Raf/Erk), which patterns the embryonic termini during early development in response to the distantly related PTTH factor, Trunk.
Promoting Interest and Performance in High School Science Classes
Authors: Hulleman Chris S. , Harackiewicz Judith M.
Published: December 2009

For the Love of Science

Which is a better predictor of a student's continued participation in science, facile understanding or personal interest?
Hulleman and Harackiewicz
(p.
1410
) designed an experiment to find out what drives high-school students. First-year high-school students were asked either to write about what they had just learned or about how what they had just learned connected to some facet of their personal lives. Connections of personal relevance were stronger than good grades for predicting interest in further science courses and future science careers. This low-cost intervention seemed to have its largest effect on students who began the class with the least amount of confidence in their abilities.
Dendritic Mechanisms Underlying Rapid Synaptic Activation of Fast-Spiking Hippocampal Interneurons
Authors: Hu Hua , Martina Marco , Jonas Peter
Published: December 2009

Dendrites Shape Interneuron Firing

Basket cells, a group of fast-spiking inhibitory interneurons, play an important part in the function of neuronal networks. The mechanisms underlying the high temporal precision and short latency of basket cell activity are unclear.

Hu
et al.

(p.
52
, published online 3 December) investigated dendrite functions in fast-spiking hippocampal basket cells and found that action potentials are initiated in the axon and propagate back into the dendrites without activity dependence but with strongly reduced amplitude. This is very different from what has been observed previously in widely investigated pyramidal cell dendrites, probably due to the high potassium to sodium conductance ratios in the dendrites of the interneurons. These dendritic mechanisms can explain the high-frequency firing and precise timing of basket cells seen in network activity in vivo.
Therapeutic Silencing of MicroRNA-122 in Primates with Chronic Hepatitis C Virus Infection
Authors: Lanford Robert E. , Hildebrandt-Eriksen Elisabeth S. , Petri Andreas , Persson Robert , Lindow Morten , Munk Martin E. , Kauppinen Sakari , Ørum Henrik
Published: December 2009

Anti-MicroRNA Antiviral

MicroRNAs (miRNAs) are small noncoding RNAs found in eukaryotes and viruses. They are critical regulators of a wide range of cellular processes. The highly conserved miRNA miR-122 is required for infection by hepatitis C virus (HCV), a leading cause of liver disease in humans. Present HCV treatment regimes can have serious side effects and are effective in only 50% of cases. In order to try to tackle HCV infection,

Lanford
et al.

(p.
198
, published online 3 December) targeted miR-122 using a complementary locked nucleic acid (LNA) oligonucleotide. Treatment of chimpanzees infected by HCV with the LNA antagonist resulted in a long-term reduction of disease symptoms without the concomitant appearance of resistant strains of the virus.
Elevated CO
2
Reduces Losses of Plant Diversity Caused by Nitrogen Deposition
Authors: Reich Peter B.
Published: December 2009

Mitigating Nitrogen Enrichment?

Nitrogen enrichment reduces the species diversity of plants in herbaceous communities. By contrast, the effects of increasing CO
2
on plant species richness is poorly documented, and the interaction of both N deposition and CO
2
elevation are unknown.
Reich
(p.
1399
; see the Perspective by

Collins

) performed a 10-year open-air field experiment in a North American perennial grassland assemblage. Reductions in plant species richness resulting from N deposition were half as large under elevated CO
2
concentrations as under ambient atmospheric CO
2
. Given that both N and CO
2
are projected to increase globally, these results provide a pointer to the types of ecological change that could be expected, at least in relatively simple plant communities.
A Crystal Structure of the Bifunctional Antibiotic Simocyclinone D8, Bound to DNA Gyrase
Authors: Edwards Marcus J. , Flatman Ruth H. , Mitchenall Lesley A. , Stevenson Clare E.M. , Le Tung B.K. , Clarke Thomas A. , McKay Adam R. , Fiedler Hans-Peter , Buttner Mark J. , Lawson David M. , Maxwell Anthony
Published: December 2009

Targeting DNA Gyrase

DNA gyrase, an enzyme that unwinds double-stranded DNA, is essential in bacteria, but missing in humans, and is thus an important antibiotic target. DNA gyrase is inhibited by the well-known fluoroquinolines and aminocoumarins antibiotics, as well as by symocyclinones—bifunctional antibiotics comprising an aminocoumarin and a polyketide group. Surprisingly, symocyclinones, unlike aminocoumarin inhibitors, do not inhibit DNA gyrase GTPase activity, but instead inhibit binding to DNA. Now

Edwards
et al.

(p.
1415
) use biochemical and structural studies to show that the two functional groups of the antibiotic bind in separate pockets on the gyrase. Each group is a relatively weak inhibitor that together potently inhibit DNA binding.
From Hydrogenases to Noble Metal–Free Catalytic Nanomaterials for H
2
Production and Uptake
Authors: Le Goff Alan , Artero Vincent , Jousselme Bruno , Tran Phong Dinh , Guillet Nicolas , Métayé Romain , Fihri Aziz , Palacin Serge , Fontecave Marc
Published: December 2009

Electrolysis at Nickel

One drawback of solar and wind power is the need for an efficient storage system to release accumulated energy when neither source is readily available (during still nights, for example). Hydrogen derived from electrolysis of water is potentially a useful medium for this purpose, but catalyzing the interconversion efficiently at large scale would currently require a substantial amount of the scarce precious metal platinum. An alternative approach would be to mimic natural enzymatic reactions, which accomplish the interconversion using hydrogenases that incorporate the more abundant metals iron and nickel. In this vein,

Le Goff
et al.

(p.
1384
; see the Perspective by

Hambourger and Moore

) have lightly modified a hydrogenase-inspired nickel complex in order to append it to a conductive carbon nanotube support. The resulting hybrid material shows promising catalytic efficiency for reversible aqueous electrolysis in a standard apparatus.
Iron Partitioning and Density Changes of Pyrolite in Earth’s Lower Mantle
Authors: Irifune Tetsuo , Shinmei Toru , McCammon Catherine A. , Miyajima Nobuyoshi , Rubie David C. , Frost Daniel J.
Published: December 2009

Spin Transitions and Mantle Phases

The extreme temperatures and pressures at depth can cause mantle minerals to undergo phase transformations. For example, it is thought that an electronic spin transition that occurs at high pressures in the lower mantle leads to the partitioning of various iron mineral phases. Using a multianvil apparatus to study a synthetic material similar in composition to the lower mantle,

Irifune
et al.

(p.
193
, see the Perspective by

Hirose

; published online 3 December) demonstrate that the spin transition occurs at lower pressures, and thus shallower depth, than suggested by earlier studies based on simpler compositions. As verification of the material's applicability in lower mantle studies, its density profile with pressure overlaps very well with those predicted by seismological models.
The Molecular Basis of Size Differences
Authors: Crickmore Michael A.
Published: December 2009

Regulation of morphogen signaling controls tissue size.
Science Goes Hollywood

Imagine Science Film Festival
Alexis Gambis, artistic director

New York. 15–25 October 2009. www.imaginesciencefilms.com.
Authors: Bohannon Cat , DeCostanzo Anthony , Requarth Tim , Dawesar Abba , Falkner Annegret , Firestein Stuart , Jung Cynthia , North Anna , Riederer Rachel , Tingley Kim , Wayne Greg
Published: December 2009

Our reviewers spread out over New York to survey the 46 short and 4 feature films that were shown at this year's Imagine Science Film Festival.
Paul C. Zamecnik (1912–2009)
Authors: Isselbacher Kurt J.
Published: December 2009

A biochemist's determination and brilliance unlocked the mystery of protein synthesis and created a new field of drug development.
The Climate in Copenhagen
Authors: King David
Published: December 2009

With just days to go before the United Nations (UN) summit in Copenhagen that is supposed to define the world's strategy regarding climate change, the news seems unremittingly bad. The rumors speak of deadlock and little or no chance of reaching the crucial agreement that will enable us to avert climate catastrophe. Though this news has apparently taken many people by surprise, it is neither surprising nor necessarily disastrous. The worst possible outcome at Copenhagen would be a weak protocol that solves nothing. The best outcome would be an agreement to delay the final protocol for another year. By the time the parties to the UN's Framework Convention on Climate Change meet in Mexico in December 2010, we could finally be in a position to set up a protocol with the power to solve the worst crisis that humans have ever faced collectively.