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Carbon-based materials exhibit distinct structures and dimensionality which allow modification of their electrical properties and enable them to be integrated in various commercial systems. One of the interesting characteristics of carbon-based materials is efficient electron field emission (FE), which makes them good candidates for displays, in electron microscopy, lithography, sensing, micro- and nanoelectronics, X-ray sources and medical applications. While nano carbon materials have been extensively studied for FE applications, their usefulness, electron emission concerns, and fundamental mechanisms for FE technologies are buried in the reported literature, and cross comparison of all nano carbon materials together is rarely explored. Here we present a comprehensive overview of fundamental and FE properties of all carbon-based materials including diamond, nanocrystalline diamond, graphite, carbon nanotubes, carbon nanofibers, carbon nanowires, carbon nanorods, graphene, and amorphous and nanostructured carbon. Some of these carbon materials, such as amorphous and nanostructured carbon, possess the added benefit of room temperature production over large areas on a variety of substrates. We have compiled an up to date summary which critically discusses the material factors, and the factors that control electron emission of these materials. We also propose unique ideas to further improve electron emission for the design of energy efficient carbon-based cold cathode materials for next generation large area electronic devices.

Lubricity, a phenomenon which enables the ease of motion of objects, and wear resistance, which minimizes material damage or degradation, are important fundamental characteristics for sustainable technology developments. Ultrathin coatings that promote lubricity and wear resistance are of huge importance for a number of applications, including magnetic storage and micro-/nanoelectromechanical systems. Conventional ultrathin coatings have, however, reached their limit. Graphene-based materials that have shown promise to reduce friction and wear have many intrinsic limitations such as high temperature and substrate-specific growth. To address these concerns, a great deal of research is currently ongoing to optimize graphene-based materials. Here we discover that angstrom-thick carbon (8 A) significantly reduces interfacial friction and wear. This lubricant shows ultrahigh optical transparency and can be directly deposited on a wide range of surfaces at room temperature. Experiments combined with molecular dynamics simulations reveal that the lubricating efficacy of 8 A carbon is further improved via interfacial nitrogen.

Friction and wear remain the primary cause of mechanical energy dissipation and system failure. Recent studies reveal graphene as a powerful solid lubricant to combat friction and wear. Most of these studies have focused on nanoscale tribology and have been limited to a few specific surfaces. Here, we uncover many unknown aspects of graphene's contact-sliding at micro- and macroscopic tribo-scales over a broader range of surfaces. We discover that graphene's performance reduces for surfaces with increasing roughness. To overcome this, we introduce a new type of graphene/silicon nitride (SiNx, 3 nm) bilayer overcoats that exhibit superior performance compared to native graphene sheets (mono and bilayer), that is, display the lowest microscale friction and wear on a range of tribologically poor flat surfaces. More importantly, two-layer graphene/SiNx bilayer lubricant (

The photocatalytic self-cleaning characteristics of titania facilitate the fabrication of reuseable templates for protein nanopatterning. Titania nanostructures were fabricated over square centimeter areas by interferometric lithography (IL) and nanoimprint lithography (NIL). With the use of a Lloyd's mirror two-beam interferometer, self-assembled monolayers of alkylphosphonates adsorbed on the native oxide of a Ti film were patterned by photocatalytic nanolithography. In regions exposed to a maximum in the interferogram, the monolayer was removed by photocatalytic oxidation. In regions exposed to an intensity minimum, the monolayer remained intact. After exposure, the sample was etched in piranha solution to yield Ti nanostructures with widths as small as 30 nm. NIL was performed by using a silicon stamp to imprint a spin-cast film of titanium dioxide resin; after calcination and reactive ion etching, TiO2 nanopillars were formed. For both fabrication techniques, subsequent adsorption of an oligo(ethylene glycol) functionalized trichlorosilane yielded an entirely passive, protein-resistant surface. Near-UV exposure caused removal of this protein-resistant film from the titania regions by photocatalytic degradation, leaving the passivating silane film intact on the silicon dioxide regions. Proteins labeled with fluorescent dyes were adsorbed to the titanium dioxide regions, yielding nanopatterns with bright fluorescence. Subsequent near-UV irradiation of the samples removed the protein from the titanium dioxide nanostructures by photocatalytic degradation facilitating the adsorption of a different protein. The process was repeated multiple times. These simple methods appear to yield durable, reuseable samples that may be of value to laboratories that require nanostructured biological interfaces but do not have access to the infrastructure required for nanofabrication.

Moth's eye inspired multiscale ommatidial arrays offer multifunctional properties of great significance in optoelectronic devices. However, a major challenge remains in fabricating these arrays on large-area substrates using a simple and scalable technique. Here we present the fabrication of these multiscale ommatidial arrays over large areas by a distinct approach called sacrificial layer mediated nanoimprinting, which involves nanoimprinting aided by a sacrificial layer. The fabricated arrays exhibited excellent pattern uniformity over the entire patterned area. Optimum dimensions of the multiscale ommatidial arrays determined by the finite-difference time domain simulations served as the design parameters for replicating the arrays on glass. A broadband suppression of reflectance to a minimum of ∼1.4% and omnidirectional antireflection for highly oblique angles of incidence up to 70° were achieved. In addition, superhydrophobicity and superior antifogging characteristics enabled the retention of optical properties even in wet and humid conditions, suggesting reliable optical performance in practical outdoor conditions. We anticipate that these properties could potentially enhance the performance of optoelectronic devices and minimize the influence of in-service conditions. Additionally, as our technique is solely nanoimprinting-based, it may enable scalable and high-throughput fabrication of multiscale ommatidial arrays.

Conventional patterning of HfO2 as a gate dielectric is a multistep complicated process that involves deposition of oxide, photolithography, and hard mask etching. In order to simplify the process of HfO2 patterning, the authors have developed photo- and electron beam-sensitive spin-coatable HfO2 resists for direct writing. They were prepared by reacting hafnium tert-butoxide with benzoylacetone in n-butanol and were found to be highly stable in air. Fourier transform infrared studies suggest that exposure to radiation results in the gradual removal of organic material from the resist and the enrichment of the resist with inorganics. This makes the exposed resist insoluble in organic solvents such as ethanol, thereby providing high-resolution negative patterns as small as ∼10nm wide. A silicon-on-insulator field effect transistor has been fabricated using sol-gel-derived HfO2 resist as a high-k gate dielectric and characterized over a range of temperatures. At room temperature a relatively high gate leaka...

A silicon on insulator field effect transistor for cryogenic operation has been fabricated using a sol-gel derived TiO2 electron beam resist as a high-k gate dielectric and characterized over a range of temperatures. The TiO2 dielectric layer allows too large a gate leakage current for good device operation at room temperature, but the leakage current is strongly suppressed at cryogenic temperatures and good transistor characteristics were observed. The temperature dependence of the gate leakage current suggests that Frenkel-Poole and trap-assisted tunneling dominates the conduction in the dielectric layer. The drain current shows peaks at certain frequencies under continuous wave microwave irradiation, which may be caused by the resonance of electrons trapped in defects at the TiO2/SiO2 interface. These resonances offer the possibility to manipulate single electrons for nonclassical information processing.

Two-photon polymerization of photosensitive materials irradiated by femtosecond laser pulses is now considered as an enabling technology for the fabrication of 3D structures, especially photonic crystals and photonic crystal templates. Depending on the topology and dielectric constant contrast of photonic crystals, their optical properties can be tailored in a desired manner. Since 1987, when the concept of 3D photonic crystal was introduced by Yablonovitch and John, photonic crystals have been a subject of intensive research. In spite of this, the fabrication of photonic crystals with a full 3D (or omni-directional) bandgap in the visible range is still a challenging task. To realize photonic crystals with a full photonic bandgap, 3D structuring of high refractive index materials is required. The high refractive index (ca. 2.4) and high transparency in the visible spectrum makes TiO2 a very promising photonic material. For many applications, it is desirable to have a simple technique for patterning this material in twoand even three dimensions. Conventionally, TiO2 is patterned by sputtering it onto a pre-patterned organic resist followed by lift-off. When thick films of TiO2 or complicated features are desired, the lift-off process does not work well. For 3D fabrication, the most attractive option so far has been to fabricate templates which were later infiltrated with a high refractive index material, followed by the removal of the original template structure. Another approach is to use inorganic–organic photosensitive materials (ormocers) for the fabrication of photonic crystals. In this case, there exists a possibility to skip the replication steps and to fabricate 3D inorganic structures directly. However, the inorganic content in these materials is not very high and the attempts to fabricate in three dimensions have resulted in porous structures. In order to eliminate the issue of making templates and their subsequent infiltration with a high refractive index material, a direct 3D fabrication of structures appears to be an attractive option. As2S3, a chalcogenide glass, was directly patterned in three dimensions by exploiting its photo-induced metastability. On the other hand, examples of direct patterning of oxides are nonexistent. In this paper, we will demonstrate a direct 3D patterning of TiO2 structures using femtosecond laser pulses. To enable such fabrication, a photosensitive sol– gel-based spin-coatable TiO2 resist was developed. The experimental setup used for the patterning is shown in Figure 1 and is similar to that used before. The TiO2 resist is transparent (refractive index = 1.68) to the femtosecond laser radiation of 780 nm wavelength, and therefore, allows focusing of laser pulses tightly into the material volume. In the focal area, where the intensity of femtosecond laser pulses is high enough to initiate multiphoton processes, bond-breaking in the TiO2 resist makes the irradiated regions insoluble in organic solvents such as acetone. This allows the fabrication of any computer-generated 3D structure by direct laser “recording” into the volume of the TiO2 resist. Because of the threshold behavior and nonlinear nature of this bond-breaking proC O M M U N IC A TI O N

We demonstrate a high yield production scheme to fabricate sub-5 nm co-planar metal–insulator–metal junctions. This involves determining the relationship between the actual gap between the metallic junctions for a given designed gap, and the use of weak developers with ultrasonic agitation to process the exposed resist. This results in an improved process to achieve narrow inter-electrode gaps. The gaps were imaged using an AFM equipped with a carbon nanotube tip to achieve a high degree of accuracy in measurement. The smallest gap unambiguously measured was ~ 2 nm. Gaps with ≤ 5 nm spacing were produced with a very high yield of about 75% for a designed inter-electrode distance of 0 nm. The leakage resistance of the gaps was found to be of the order of 1012 Ω. The entire junction structure was designed to be co-planar to better than 1 nm over 1 μ m2.

Step-and-flash imprint lithography (S-FIL) is a wafer-scale, high-resolution nanoimprint technique capable of expansion of nanoscale patterns via serial patterning of imprint fields. While S-FIL patterning of organic resins is well known, patterning of metal-organic resins followed by calcination to form structured oxide films remains relatively unexplored. However, with calcination shrinkage, there is tremendous potential utility in easing accessibility of arbitrary nanostructures at 20 nm resolution and below. However, barriers to commercial adoption exist due to difficulties in formulating polymerizable oxide precursors with good dispensability, long shelf life, and resistance to auto-homopolymerization. Here we propose a solution to these issues in the form of a versatile resin formulation scheme that is applicable to a host of functional oxides (Al2O3, HfO2, TiO2, ZrO2, Ta2O5, and Nb2O5). This scheme utilizes a reaction of metal alkoxides with 2-(methacryloyloxy)ethyl acetoacetate (MAEAA), a polymerizable chelating agent. Formation of these inorganic coordination complexes enables remarkable resistance to auto-homopolymerization, greatly improving dispensability and shelf life, thus enabling full scale-up of this facile nanofabrication approach. Results include successively imprinted fields consisting of 100 nm linewidth gratings. Isothermal calcination of these structures resulted in corresponding shrinkage of 75-80% without loss of mechanical integrity or aspect ratio, resulting in 20 nm linewidth oxide nanostructures.

Flexible palladium-based H2 sensors have a great potential in advanced sensing applications, as they offer advantages such as light weight, space conservation, and mechanical durability. Despite these advantages, the paucity of such sensors is due to the fact that they are difficult to fabricate while maintaining excellent sensing performance. Here, we demonstrate, using direct nanoimprint lithography of palladium, the fabrication of a flexible, durable, and fast responsive H2 sensor that is capable of detecting H2 gas concentration as low as 50 ppm. High resolution and high throughput patterning of palladium gratings over a 2 cm × 1 cm area on a rigid substrate was achieved by heat-treating nanoimprinted palladium benzyl mercaptide at 250 °C for 1 h. The flexible and robust H2 sensing device was fabricated by subsequent transfer nanoimprinting of these gratings into a polycarbonate film at its glass transition temperature. This technique produces flexible H2 sensors with improved durability, sensitivity, and response time in comparison to palladium thin films. At ambient pressure and temperature, the device showed a fast response time of 18 s at a H2 concentration of 3500 ppm. At 50 ppm concentration, the response time was found to be 57 s. The flexibility of the sensor does not appear to compromise its performance.

Three-dimensional hierarchical patterning of metals is of paramount importance in diverse fields involving photonics, controlling surface wettability and wearable electronics. Conventionally, this type of structuring is tedious and usually involves layer-by-layer lithographic patterning. Here, we describe a simple process of direct nanoimprint lithography using palladium benzylthiolate, a versatile metal-organic ink, which not only leads to the formation of hierarchical patterns but also is amenable to layer-by-layer stacking of the metal over large areas. The key to achieving such multi-faceted patterning is hysteretic melting of ink, enabling its shaping. It undergoes transformation to metallic palladium under gentle thermal conditions without affecting the integrity of the hierarchical patterns on micro- as well as nanoscale. A metallic rice leaf structure showing anisotropic wetting behavior and woodpile-like structures were thus fabricated. Furthermore, this method is extendable for transferring imprinted structures to a flexible substrate to make them robust enough to sustain numerous bending cycles.

We demonstrate a different approach to direct nanoimprint lithography of oxides, in particular TiO(2), using the metal methacrylate route which not only gives very high resolution ( approximately 20 nm) but also provides yields of approximately 100% over areas > 1 cm x 1 cm. TiO(2) was imprinted using a polymerizable liquid 'TiO(2) resin' consisting of a mixture of titanium methacrylate, ethylene glycol dimethacrylate, and azobis-(isobutyronitrile). The resin underwent free radical polymerization when imprinted using a silicon mold at 110 degrees C with pressures as low as 10 bar. Polymerization strengthens the imprinted structures, thereby giving approximately 100% yield after demolding. Heat-treatment of the imprinted structures at 400 degrees C resulted in the loss of organics and their subsequent shrinkage ( approximately 75%) without the loss of integrity or aspect ratio, and converted them to TiO(2) nanostructures as small as approximately 20 nm wide. Furthermore, our method demonstrates that large imprinted areas of sub-100-nm features can be achieved by sub-micron molds which translate into huge cost savings with the added flexibility of direct patterning of urinary as well as multi-component oxides.

After the cost of ownership of tool, the next significant cost involved in nanoimprint lithography is that of mold fabrication. The cost of mold fabrication is proportional to the area of pattern and follows an inverse relationship with the pattern resolution. In this work, the authors demonstrate proof-of-concept fabrication of Si and SiO2 grating molds of variable feature sizes, spacings, densities, and aspect ratios that can be generated from a single Si master mold of 2 μm line and space features. This process utilizes “SiO2 resin,” which can be imprinted via in situ thermal free radical polymerization. Heat-treatment of the patterned resin resulted in loss of organics, formation of SiOx and gave rise to known feature size reduction (∼65%). After the pattern transfer using SiOx as the etch mask, a Si daughter mold containing 0.7 μm wide gratings with 3.3 μm spacing was generated. The process of imprinting and heat-treatment was repeated using the daughter mold, which regenerated a mold that approximates the master mold feature profile. Our technique demonstrates that submicron-sized features can be achieved from Si molds containing micron-sized features and vice versa. Such flexibility may lead to substantial reduction in the cost of mold fabrication.

We report the self-assembly of single crystals of single-walled carbon nanotubes (SWCNTs) using thermolysis of nano-patterned precursors. The synthesis of these perfectly ordered, single crystals of SWCNTs results in extended structures with dimension on the micrometer scale. Each crystal is composed of an ordered array of tubes with identical diameters and chirality, although these properties vary between crystals. The results show that SWCNTs can be produced as a perfect bulk material on the micrometer scale and point toward the synthesis of bulk macroscopic crystalline material.

Polymer-based anti-reflective coatings (ARCs) on glass pose major challenges for outdoor photovoltaic applications due to their incompatible mechanical and thermal properties. Here we demonstrate durable, chemically and thermally stable polyhedral oligomeric silsesquioxane-based (POSS) anti-reflective moth's eye nanostructures on glass fabricated by double-side nanoimprint lithography. These anti-reflective nanostructures exhibited excellent broadband and quasi-omnidirectional anti-reflective properties. An optimum resist composition for nanoimprinting was obtained by mixing a methacryl POSS cage mixture with 1,6-hexanediol diacrylate in a 1 : 12 molar ratio. Thermal free radical co-polymerization during nanoimprint lithography produced a uniform array of moth's eye nanostructures on both sides of a glass substrate with yields ∼90 to 100%. The transmittance of the resulting glass was enhanced to 98.2% (reflectance 1.26%) with excellent quasi-omnidirectional transmittance observed from −50° to +50° of angles of incidence. Furthermore, a series of ASTM-based tests on the imprinted ARC structures showed strong adherence to glass, better hardness and mechanical strength with superior chemical and thermal stability, thus suggesting their strong potential for commercial applications.

Nanostructuring of Al2O3 is predominantly achieved by the anodization of aluminum film and is limited to obtaining porous anodized aluminum oxide (AAO). One of the main restrictions in developing approaches for direct fabrication of various types of Al2O3 patterns, such as lines, pillars, holes, etc, is the lack of a processable aluminum-containing resist. In this paper, we demonstrate a stable precursor prepared by reacting aluminum tri-sec-butoxide with 2-(methacryloyloxy)ethyl acetoacetate, a chelating monomer, which can be used for large area direct nanoimprint lithography of Al2O3. Chelation in the precursor makes it stable against hydrolysis whilst the presence of a reactive methacrylate group renders it polymerizable. The precursor was mixed with a cross-linker and their in situ thermal free-radical co-polymerization during nanoimprinting rigidly shaped the patterns, trapped the metal atoms, reduced the surface energy and strengthened the structures, thereby giving a ∼100% yield after demolding. The imprinted structures were heat-treated, leading to the loss of organics and their subsequent shrinkage. Amorphous Al2O3 patterns with line-widths as small as 17 nm were obtained. Our process utilizes the advantages of sol–gel and methacrylate routes for imprinting and at the same time alleviates the disadvantages associated with both these methods. With these benefits, the chelating monomer route may be the harbinger of the universal scheme for direct nanoimprinting of metal oxides.

The use of polymerization to solidify, strengthen and imprint liquid organic materials is the basis of ultraviolet (UV) nanoimprint lithography. In spite of these advantages, the use of polymerization to pattern materials in thermal nanoimprint lithography is almost non-existent. In this study, we demonstrate a facile and general method to directly imprint a host of unary metal oxides (Fe2O3, ZrO2, TiO2, Nb2O5 and Ta2O5) at a very high resolution viain situ thermal free radical co-polymerization of various metal methacrylates in the presence of cross-linker ethylene glycol dimethacrylate using a silicon mold. Polymerization during nanoimprinting rigidly shapes the patterns, traps the metal atoms, reduces the surface energy and strengthens the structures, thereby giving ∼100% yield after demolding. It was found that the higher oxidation state of metal resulted in excessive cracking of imprinted structures. This could be due to a higher degree of cross-linking of the precursor leading to shrinkage-related stress. Optimization of the resin composition by partially replacing ethylene glycol dimethacrylate with methyl methacrylate alleviated this problem. Heat-treatment of the imprinted structures resulted in the loss of organics, their subsequent shrinkage and converted the patterns to their corresponding metal oxides with line-widths as small as 25 nm.

Our study ( [1][1] ) described a new technique that allowed for the precise targeting of chemical precursors to specific surface sites with nanometer-range accuracy. One of our aims was to control both the site and growth process of single-walled carbon nanotubes (SWCNTs) by depositing controlled mixtures of C60 and metal catalyst through a moveable shadow mask, followed by annealing to form single-walled nanotubes (SWNTs), a growth process with proven efficacy. We applied the technique to a number of substrates including molybdenum grids to allow for transmission electron microscopy (TEM) and electron energy loss studies. Although anticipating that the molybdenum would further catalyze the SWNT growth, we did not anticipate the degree to which the surface chemistry of the grids would dominate the resultant structures. Shortly after the publication of ( [1][1] ), we recognized the problems associated with the Mo grids on the interpretation of our data, having carried out a detailed high-resolution energy loss and Raman study of the growth process. We reported the results of this study widely ( [2][2] – [5][3] ). The comment by Chisholm et al . ( [6][4] ) independently confirms our previous findings, and we are able to add some further detail as a result of our subsequent studies. We followed the growth process by varying both temperature and time of annealing of the C60/nickel structures, recording Raman spectra and electron energy loss spectra. The former provided the greater insight. Briefly, Raman spectra were taken with two laser energies, 2.41 eV and 1.58 eV. During the very early stages of growth after the exfoliation of the C60, all the characteristic vibrational modes expected for SWCNTs were observed. The first-order features consisted of a G peak around 1590 cm–1, corresponding to the high-energy (∼ 0.2 eV) tangential modes (TM) of SWCNTs, and a D peak around 1300 cm–1, consistent with a disorder mode in SWCNTs. The G mode was very narrow, with a full-width at half maximum (FWHM) of about 13 cm–1. The low-energy radial breathing modes (RBM) of SWCNTs were not resolvable because the chemically complex substrates gave contributions in this frequency range of the Raman spectra. Their presence was, however, indirectly demonstrated by their involvement in combination modes in the second-order spectra. Raman spectra consistent with SWCNTs were, however, observed only fleetingly during the growth process, so that the combination modes involving the RBM modes were rapidly lost, while the others—the D and G modes and their overtones—transformed into their nanocrystalline graphite (nc-C) counterparts. Thus, the resultant structures obtained on Mo grids after annealing at the times and temperatures reported in the original paper were based not on SWNTs but on a complex of molybdenum, as detailed by Chisholm et al . ( [6][4] ). The only area in which we would take issue with the Chisholm et al . comment is in the origin of the carbon edge in the energy loss spectrum as originally reported, which we would argue is at least partially residual carbon as inferred by the Raman study above. Although the shadow mask technique remains a unique method to fabricate nanostructures at controlled surface sites, including the growth of CNTs, we accept that our conclusion of the growth of single crystals containing SWCNTs was mistaken. In particular, in the case of the Mo substrates the complex surface chemistry resulting from the manufacturing process dominates the final nanostructures observed. 1. [↵][5] R. R. Schlittler et al ., Science 292, 1136 (2001). [OpenUrl][6][Abstract/FREE Full Text][7] 2. [↵][8] A. Ilie, C. Durkan, M. S. M. Saifullah, M. E. Welland, J. K. Gimzewski, paper presented at Trends in Nanotechnology, Segovia, Spain, 3 to 6 September 2001. 3. J. W. Seo, paper presented at XVI International Winterschool on Electronic Properties of Novel Materials, Kirchberg, Austria, 2 to 9 March 2002. 4. C. Durkan, A. Ilie, M. S. M. Saifullah, M. E. Welland, Appl. Phys. Lett. 80, 4244 (2002). [OpenUrl][9] 5. [↵][10] J. W. Seo, H. Siegwart, L. Forro, American Physical Society March Meeting 2003, Austin, Texas, 3 to 7 March 2003, abstract A26.008. 6. [↵][11] M. S. Chisholm et al ., Science 300, 1236 (2003); [www.sciencemag.org/cgi/content/full/300/5623/1236b][12]. [OpenUrl][13] [1]: #ref-1 [2]: #ref-2 [3]: #ref-5 [4]: #ref-6 [5]: #xref-ref-1-1 "View reference 1 in text" [6]: {openurl}?query=rft.jtitle%253DScience%26rft_id%253Dinfo%253Adoi%252F10.1126%252Fscience.1057823%26rft_id%253Dinfo%253Apmid%252F11292859%26rft.genre%253Darticle%26rft_val_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Ajournal%26ctx_ver%253DZ39.88-2004%26url_ver%253DZ39.88-2004%26url_ctx_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Actx [7]: /lookup/ijlink/YTozOntzOjQ6InBhdGgiO3M6MTQ6Ii9sb29rdXAvaWpsaW5rIjtzOjU6InF1ZXJ5IjthOjQ6e3M6ODoibGlua1R5cGUiO3M6NDoiQUJTVCI7czoxMToiam91cm5hbENvZGUiO3M6Mzoic2NpIjtzOjU6InJlc2lkIjtzOjEzOiIyOTIvNTUxOS8xMTM2IjtzOjQ6ImF0b20iO3M6MjU6Ii9zY2kvMzAwLzU2MjMvMTIzNi4zLmF0b20iO31zOjg6ImZyYWdtZW50IjtzOjA6IiI7fQ== [8]: #xref-ref-2-1 "View reference 2 in text" [9]: {openurl}?query=rft.jtitle%253DAppl.%2BPhys.%2BLett.%26rft.volume%253D80%26rft.spage%253D4244%26rft.atitle%253DAPPL%2BPHYS%2BLETT%26rft.genre%253Darticle%26rft_val_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Ajournal%26ctx_ver%253DZ39.88-2004%26url_ver%253DZ39.88-2004%26url_ctx_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Actx [10]: #xref-ref-5-1 "View reference 5 in text" [11]: #xref-ref-6-1 "View reference 6 in text" [12]: http://www.sciencemag.org/cgi/content/full/300/5623/1236b [13]: {openurl}?query=rft.jtitle%253DScience%26rft.volume%253D300%26rft.spage%253D1236%26rft.genre%253Darticle%26rft_val_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Ajournal%26ctx_ver%253DZ39.88-2004%26url_ver%253DZ39.88-2004%26url_ctx_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Actx