Oliver Hayden SIEMENS AG
Kornelius Nielsch Max-Planck-Institute of Microstructure Physics
Nina Kovtyukhova The Pennsylvania State University
Frank Caruso University of Melbourne
Teodor Veres Industrial Materials Institute-NRC
Monday PM, November 26, 2007
Room 200 (Hynes)
9:30 AM - **FF1.1
Nanoimprint Lithography for 3D Surface Nanostructuring and Photonic Devices.
C. Sotomayor Torres 1 2 3 , V. Reboud 1 , N. Kehagias 1 , M. Zelsmann 4 , P. Loveral 1 , F. Reuther 5 , G. Gruetzner 5 , G. Redmond 1 , C. Schuster 5 , M. Kubenz 5 Show Abstract
1 , Tyndall National Institute, Cork Ireland, 2 , Catalan Insitute of Nanotechnology, Bellaterra Spain, 3 , Spain and Catalan Insitute for Research and Advanced Studies ICREA, Barcelona Spain, 4 , LTM-CNRS, Grenoble France, 5 , Micro Resist Technology GmbH, Berlin Germany
Three-dimensional (3D) nanopatterning is an enabling fabrication technology with impact in several research fields and application areas . The latter includes, for example, advanced optical elements  and circuits, adaptive optics, biosensors, supramolecular chemistry, studies of cell behaviour in 3D among others.In this presentation we will review the state of the art in top-down, bottom-up and mix-and-match 3D nanopatterning methods, considering their advantages and disadvantages from the perspective of becoming a technology. Examples of combinatory approaches will be provided, for example, Reverse UV-NIL  among others. Some of the specific challenges faced in 3D nanofabrication for photonic and biological applications will be discussed. The example of a polymer photonic crystal band edge laser made by nanoimprint lithography will be presented.The support of the EC-funded project NaPa (Contract No. NMP4-CT-2003-500120), of the EC-funded project PHOREMOST (FP6/2003/IST/2-511616) and of Science Foundation Ireland is gratefully acknowledged. The content of this work is the sole responsibility of the authors.References:1. K. J . Vahala, Nature 424, 839 (2003)2. S. Y. Lin, J. G. Fleming, D. L. Hetherington, B. K. Smith, R. Biswas, K. M. Ho, M. M. Sigalas, W. Zubrzycki, S. R. Kurtz & Jim Bur, Nature, 294, 251 (1998),3. N. Kehagias, V. Reboud, G. Chansin, M. Zelsmann, C. Jeppesen, C. Schuster, M. Kubenz, F. Reuther, G. Gruetzner and C. M. Sotomayor Torres, Reverse contact UV nanoimprint lithography for multilayered structure fabrication, Nanotechnology, 18, 175303, (2007)
10:00 AM - FF1.2
Nanoimprint Lithography Molding of ``Clickable" Polymer Patterns.
Yuval Ofir 1 , Brian Jordan 1 , Bappaditya Samanta 1 , Isaac Moran 2 , Kenneth Carter 2 , Vincent Rotello 1 Show Abstract
1 Chemistry, University of Massachusetts Amherst, Amherst, Massachusetts, United States, 2 Polymer Science and Engineering, University of Massachusetts Amherst, Amherst, Massachusetts, United States
Imprint lithography techniques, including nanocontact molding, show great promise in the ability to generate nanoscale patterns in an efficient and economic fashion. These techniques are already in wide use in microelectronics, photonics, magnetic storage, and micro/nanofluidics. The traditional use of polymer patterns as sacrificial resist layers, however, does not take advantage of the chemistry available on the surface of the patterned polymer. In our research we have used the Huisgen 1,3-dipolar cycloaddition reaction, (i.e. the “click” reaction) to react functionality on the polymer patterns with a variety of chemical elements, including fluorophores, other polymers, and nanoparticles. This simple yet powerful technique combines controllable surface chemistry with an advanced patterning technique, allowing the fabrication of useful magnetic, metallic and semiconductor patterns featuring useful chemical functionality.
10:15 AM - FF1.3
Fabrication of Tunable SERS Substrates by Nanoimprint Lithography.
Kebin Li 1 , Bo Cui 1 , Liviu Clime 1 , Matthias Geissler 1 , Teodor Veres 1 Show Abstract
1 , Industrial Materials Institute,National Research Council, Canada, Boucherville, , Quebec, Canada
Since its discovery in 1974, surface enhanced Raman scattering (SERS) has proven to be a sensitive technique to detect individual molecules, and because of its chemical specificity and label-free nature, it finds increasing attention in the analytical, biomedical, environmental, as well as global and homeland security domains. Various methods were developed to fabricate the SERS substrates but most of them are still lacking in stability and/or reproducibility and usually consists of a series of expensive fabrication processes. In this paper, we will report the fabrication of the SERS substrates at low-cost, fast and reproducible way based on nanoimprint lithography (NIL) process. We will demonstrate the SERS enhancement on two model nanostructures containing Ag and/or Au nano-crescent and nano-wells. Both of them are simply created by deposition of Ag and/or Au thin film at room temperature on Si substrates which are pre-nano-structured using NIL. We have shown that the surface plasmonic resonant frequency can be tunned towards to the near infrared regime  by using NIL pre-nano-structured Si substrates. The fabricated nano-crescents and nano-wells were characterized by using SEM and AFM. The diameter of two circular arcs of the nano-crescent is about 200 nm and 300 nm, respectively. The opening of two horns of the crescent can be adjusted by controlling the fabrication process. The out diameter of the nano-well is about 120nm and the inner diameter of the well is about 60nm. The height of the well is about 100nm. Because of the special topographic structure of the nano-wells, two types of Ag nano-structure, namely the Ag nano-donuts and Ag nano-disks with diameter of about 60nm are formed in the nano-wells. The SERS effect of these Ag nano-structures is confirmed by the Raman spectra of the Rhodamine (R6G) molecule attached to the substrate. At the defect location, there is no R6G peak observable except for the peak at 520cm-1 which originates from the Si substrate. We can observe the standard R6G spectra on the patterned area with different intensities at different location which are probably due to the slightly different shape and opening of the horns of the Ag nano-crescent. The local electromagnetic field is increased with decreasing the opening of the horns of the Ag nano-crescent. SERS spectra were also observed in the structure of Ag-nano-wells. The enhancement factor of the SERS observed in these specific nano-structured Ag films is estimated to be in the magnitude order of 108. References: M. Fleischmann et al. Chem. Phys. Lett. 26, 163 (1974). S. Nie and S.R. Emory Science 275,1102 (1997). Gary A. Baker and D. S. Moore, Anal Bioanal Chem 382, 1751 (2005). Ramon Alvarez-Puebla, Bo Cui et al., J. Phys. Chem. C. 111, 6720(2007); Bo Cui, Teodor Veres, Microelectronic Engineering 84, 1544 (2007).
11:00 AM - **FF1.4
Optical Waveguides Embedded in PCBs - A Real World Application of 3D Structures Written by TPA.
Ruth Houbertz 1 , Herbert Wolter 1 , Volker Schmidt 2 , Ladislav Kuna 2 , Valentin Satzinger 2 , Christoph Wächter 3 , Gregor Langer 4 Show Abstract
1 Hybrid Materials for Microsystems and Micromedicine, Fraunhofer ISC, Wuerzburg Germany, 2 Institute of Nanostructured Materials and Photonics, Joanneum Research, Weiz Austria, 3 , Fraunhofer IOF, Jena Germany, 4 , Austria Technology & System Technology AT&S, Leoben Austria
The integration of optical interconnections in printed-circuit boards (PCB) is a rapidly growing field worldwide. There are many concepts discussed so far, among which are the integration of optical fibers or the generation of waveguides by UV lithography, embossing, or direct laser writing. However, all these technologies require complex assemblies, thus being very cost-intensive. A key issue is to identify materials and processes enabling the realization of optical interconnections in PCBs compatible to the PCB manufacturing process. This results in strong requirements for optical materials with respect to resistance against high temperatures and pressure during the PCB lamination process, or with respect to wet chemical processing. Besides, thick layers with high mechanical stability, a high refractive index step as well as low absorption losses at 850 nm are required.An innovative concept for the integration of embedded optical interconnections in PCBs is presented. In order to fulfil all requirements, nanoscaled inorganic-organic hybrid polymers (ORMOCER®s) were combined with two-photon absorption (TPA) 3D lithography, allowing one to create multimode waveguides within one and the same material. Multifunctional acrylate alkoxysilanes were used as precursors for catalytically controlled hydrolysis and polycondensation reactions, thus yielding acrylate-modified Si-O-Si units with a negative resist behavior. For UV or two-photon based cross-linking of the organic moieties, a suitable photoinitiator is introduced into the material. The latter method allows one to directly write waveguide structures into the hybrid polymer bulk in three dimensions.The hybrid polymer is casted onto a PCB substrate with a laser- and a photodiode attached to its surface. The polymer forms a thick layer on the board which completely embeds the optoelectronic components. In order to create the waveguide, a femtosecond laser is focussed in the volume of the ORMOCER® material and scanned from the laser- to the photodiode. Only within the focus of the laser, the energy density is high enough to initiate the cross-linking of the organic moieties by simultaneous absorption of two photons, while the outer focal regions are not affected. The locally confined cross-linking increases the refractive index, thus forming the core of an embedded waveguide. At the same time, the surrounding unexposed material acts as cladding layer, with no development step necessary. Subsequently, the PCB is laminated at elevated temperature and pressure, which also thermally cures the cladding. Beside the requirement for only one optical material, the TPA 3D lithography enables the in-situ coupling of two-photon written waveguides to optoelectronic components as an intrinsic part of the patterning, thus significantly simplifying the fabrication processes. The material properties and the underlying processes will be discussed with respect to the possibility of optical data transfer on PCB.
11:30 AM - FF1.5
2PP Laser Microfabrication of Ossicular Replacement Prostheses.
Aleksandr Ovsianikov 3 , Anand Doraiswamy 1 , Oliver Adunka 2 , Harold Pillsbury 2 , Roger Narayan 1 , Boris Chichkov 3 , Ravi Aggarwal 4 Show Abstract
3 Nanotechnology, Laser Zentrum Hannover, Hannover Germany, 1 Biomedical Engineering, University of North Carolina, Chapel Hill, North Carolina, United States, 2 Otolaryngology, University of North Carolina, Chapel Hill, North Carolina, United States, 4 Materials Science and Engineering, North Carolina State University, Raleigh, North Carolina, United States
11:45 AM - FF1.6
Hybrid Approaches to Nanolithography and Chemical Patterning.
Charan Srinivasan 1 , J. Hohman 1 , Mary Anderson 1 , Pengpeng Zhang 1 , Thomas Mullen 1 , Anne Andrews 1 , Mark Horn 1 , Paul Weiss 1 Show Abstract
1 Center for Nanoscale Science, Penn State University, University Park, Pennsylvania, United States
Despite the impressive pace of innovations in photolithography, this technology faces fundamental physical and economic limitations for patterning sub-30-nm features. We have combined photolithography, a top-down approach, synergistically with bottom-up chemical self-assembly to fabricate nanometer-scale features in a low-cost, scalable process – molecular-ruler nanolithography.[1,2] Here, we describe the strategies that have been developed to integrate this technique with CMOS-compatible materials and processes, patterns registered nanometer-scale features on quartz for use as the mold in nanoimprint lithography, with double the spatial frequency of features created by conventional lithographic techniques. We also use this methodology to fabricate connected device structures for ultranarrow channel length organic thin-film transistors and aligned metallic and semiconducting nanowires. One of the limitations of photolithography is its inability to pattern chemical functionality on surfaces; chemically functionalized surfaces have applications ranging from biospecific recognition to molecular electronics. To address this issue, we developed lithography-assisted chemical patterning. This technique utilizes a robust lithographic resist (LOR) that is capable of withstanding self-assembly deposition conditions to create high-quality chemical patterns. The ability to pattern chemical functionalities without intercalation and with registered, parallel processing are some of its unique advantages.[7,8]1.A. Hatzor and P. S. Weiss, Science 291, 1019 (2001).2.M. E. Anderson, L. P. Tan, M. Mihok, H. Tanaka, M. W. Horn, G. S. McCarty, P. S. Weiss, Adv. Mater. 18, 1020 (2006).3.C. Srinivasan, M. E. Anderson, E. M. Carter, J. N. Hohman, S. S. N. Bharathwaja, S. Trolier-Mckinstry, P. S. Weiss, M. W. Horn, J. Vac. Sci. Technol. B 24, 3200 (2006).4.C. Srinivasan, J. N. Hohman, M. E. Anderson, P. S. Weiss, M. W. Horn (submitted for publication).5.C. Srinivasan, J. N. Hohman, M. E. Anderson, P. Zhang, P. S. Weiss, M. W. Horn, Proc. SPIE 6517, 65171I (2007).6.Y. Xia and G. M. Whitesides, Angew. Chem., Int. Ed. 37, 551 (1998).7.M. E. Anderson, C. Srinivasan, J. N. Hohman, E. M. Carter, M. W. Horn, P. S. Weiss, Adv. Mater. 18, 3258 (2006).8.C. Srinivasan, T. J. Mullen, J. N. Hohman, M. E. Anderson, A. A. Dameron, A. M. Andrews, E. C. Dickey, M. W. Horn, P. S. Weiss (submitted for publication).
12:00 PM - FF1.7
Micro/Nano Fabrication of Surface Architectures on Polymers and Copolymers Using Direct Laser Interference Patterning.
Diego Acevedo 2 , Andres Lasagni 1 , Cesar Barbero 2 , Frank Muecklich 1 Show Abstract
2 Departamento de Química, Universidad de Río Cuarto, Río Cuarto, Córdoba, Argentina, 1 Materials Science, Saarland University, Saarbruecken, Saarland, Germany
Novel surface engineering techniques of polymeric materials are essential to produce advanced topographies which could for example serve to modulate cell and tissue response in bio-materials. Direct Laser Interference Patterning (DLIP) permits the fabrication of repetitive features and microstructures by irradiation of the sample surface with coherent beams of light. Furthermore, the most important advantage of this method is that no additional process steps are required in comparison with other top-down or bottom-up techniques (e.g. mask/mould fabrication, etching, etc.). In this study, we report a novel method for the advanced design of architectures in polymers using a single step process, as well as photo-activation of polymers with low absorption coefficient (PMMA) using a second polymer with relative high absorption coefficient (PS). Previously calculated interference patterns using the well known interference theory could be reproduced on polymeric surface. Moreover, the cross-section of the structured polymers changes depending on the intensity of the laser beams, and photomachinability of polymers is highly influenced by laser wavelength. High absorbance of the polymeric materials at specific wavelengths allows the reduction of the intensity of the laser required to achieve a determined structure depth. For PMMA/PS (60:40 %) copolymer substrate, different structures types were observed depending on the laser intensity. For moderate laser intensities, the regions at interference maxima positions inflate due to photochemical decomposition of PMMA which produces bond breakages and vaporous ablation products (such carbon dioxide). Apart from that, the copolymer PMMA/PS can be structured using the same laser fluence range of PS. If the laser fluence is increased, the subsurface formed bubbles have sufficiently energy to rise to the surface and burst, resulting in a cratered structure with a long-range order in the lateral scale given by the periodical intensity distribution of the laser beams.
12:15 PM - **FF1.8
Two-photon Engineering of Three-dimensional Micro/nano Structures: Photopolymerization, Photoreduction and Photoisomerization.
Satoshi Kawata 1 2 , Takuo Tanaka 1 3 , Nobuyuki Takeyasu 1 Show Abstract
1 , RIKEN, Wako, Saitama Japan, 2 , Osaka University, Suita, Osaka Japan, 3 , JST PRESTO, Kawaguchi, Saitama Japan
We present three-dimensional micro/nano-structures engineered by two-photon fabrication techniques. Two-photon-induced photopolymerization is demonstrated for fabricating arbitrary 3D polymer structures . Recently, a micro-lens array with 2500 lenses is used to produce a mass of structures in parallel. By using this micro-lens array system, we fabricated 800 micro-springs and micro-cubic structures by single laser scanning . Metallization techniques of fabricated polymer structures are also investigated. We successfully coated metal only on the surface of polymer by electroless metal plating, but not on the substrate . This selective coating was performed by using hydrophobic pre-coating on the glass substrates and modification of polymer surface with Sn2+-ions. With this method micro-coil array was fabricated [4,5]. In the presentation, we also propose the modification of the polymerisable resin for site-selective metal deposition . As a fabrication technique of 3D metallic microstructures, we report two-photon-induced metal-ion reduction method [7,8]. A femtosecond near-infrared laser is focused by a high-NA objective lens into a metal-ion aqueous solution such as Ag+ or Au3+. We demonstrate the fabrication of a continuous and electrically conductive silver wire whose minimum width is 400 nm. Electrical measurement shows that the resistivity of the fabricated silver wire is 5.30 × 10-8 Ωm, which is only 3.3 times larger than that of bulk silver (1.62 × 10-8 Ωm). We also discuss the resolution of our technique in terms of ions diffusion based on the Fick’s first law and the mobility of metal-ions in aqueous solution. Moreover, the realization of a self-standing 3D silver microstructure on the substrate is demonstrated. This method will become a promising technique for fabricating 3D plasmonic micro/nano structures with arbitrary shape [9,10]. In the end, we will talk about photoisomerization techniques. S. Kawata, et. al, Nature 412 (2001) 697.  J. Kato, et al, Appl. Phys. Lett. 86 (2005) 044102.  N. Takeyasu, et al, Jpn. J. Appl. Phys. Part2, 44 (2005) L1134.  F. Florian, et al, Appl. Phys. Lett. 88 (2006) 83110.  F. Florian, et al, Opt. Express 14 (2006) 800. N. Takeyasu, et al, Appl. Phys. A (submitted). T. Tanaka, et al, Appl. Phys. Lett. 88 (2006) 81107.  A. Ishikawa, et al, Appl. Phys. Lett. 89 (2006) 113102 . A. Ishikawa, et al, Phys. Rev. Lett. 95 (2005) 237401. T. Tanaka, et al, Phys. Rev. B 73 (2006) 125423.
FF2: Photonic Crystal
Monday PM, November 26, 2007
Room 200 (Hynes)
2:30 PM - **FF2.1
3D Photonic Crystals and Metamaterials: Band Gaps, Chirality, Quasicrystals, and Magnetism.
Martin Wegener 1 2 , Michael Thiel 1 , Michael Rill 1 , Martin Hermatschweiler 1 , Alexandra Ledermann 1 2 , Gunnar Dolling 1 , Geoffrey Ozin 3 , Stefan Linden 1 2 , Georg Freymann 1 2 Show Abstract
1 DFG-Center for Functional Nanostructures, University of Karlsruhe, Karlsruhe Germany, 2 Institut fuer Nanotechnologie, Forschungszentrum Karlsruhe, Karlsruhe Germany, 3 Department of Chemistry, University Toronto, Toronto, Ontario, Canada
Direct laser writing (DLW) [1,2] based on tightly focused femtosecond laser pulses has become a routine technique for the rapid fabrication of complex three-dimensional (3D) photoresist structures with lateral feature sizes down to 100 nm. Indeed, DLW has even become commercially available quite recently (see, e.g., www.nanoscribe.de ). Combined with atomic layer deposition (ALD) and chemical vapor deposition (CVD) techniques of dielectrics (e.g., SiO2 or Si) and metals (e.g., Ag), the 3D analogue of 2D electron-beam lithography is now at hand [3,4].In this talk, we review our recent corresponding work. Examples are the first realization of 3D silicon inverse woodpile structures , 3D photonic quasicrystals , polarization stop bands from 3D circular spiral photonic crystals  and heterostructures based thereupon  (thin-film polarizers, poor man’s optical isolators, optical diodes), 3D chiral layer-by-layer photonic crystal structures , or first steps towards 3D magnetic metamaterials at optical frequencies using DLW and silver CVD . The latter offers new opportunities with respect to our previous (negative-index) metamaterial work based on electron-beam lithography . S. Kawata et al., Nature 412, 697 (2001). M. Deubel et al., Nature Mater. 3, 444 (2004); Appl. Phys. Lett. 85, 1895 (2004); Appl. Phys. Lett. 87, 221104 (2005); Opt. Lett. 31, 805 (2006). N. Tétreault et al., Adv. Mater. 18, 457 (2006). M. Hermatschweiler et al., Adv. Funct. Mater., in press (2007). A. Ledermann et al., Nature Materials 5, 942 (2006). M. Thiel et al., Adv. Mater. 19, 207 (2007). M. Thiel et al., Appl. Phys. Lett., submitted (2007). M. Thiel et al., Opt. Lett., submitted (2007). M. Rill et al., unpublished (2007). G. Dolling et al., Science 312, 892 (2006); Opt. Lett. 31, 1800 (2006); Opt. Lett. 32, 53 (2007); Opt. Lett. 32, 551 (2007); Science 315, 47 (2007).
3:00 PM - FF2.2
Enabling Technology Based on Leaky-Mode Resonance Effects in Periodic Films.
Robert Magnusson 1 , Mehrdad Shokooh-Saremi 1 , Kyu Lee 1 , Debra Wawro 2 Show Abstract
1 Electrical & Computer Engineering, University of Connecticut, Storrs, Connecticut, United States, 2 , Resonant Sensors Incorporated, Arlington, Texas, United States
Leaky waveguide modes arise on photonic-crystal films when an incident light beam couples to the layer system. This results in generation of a guided-mode resonance (GMR) field response in the spectrum. The resonance effect leads to dramatic redistribution of the diffracted energy and may manifest as sharp reflection and transmission peaks radiating from the structure. The operative physical processes are understood in terms of the photonic band structure and associated leaky-wave effects near the second stop band. This effect is the basis for numerous new applications in the field of photonics and sensor technology. This paper provides computed and experimental results demonstrating its utility. In particular, use of the GMR operational principle enables highly accurate biosensors. The sensors are broadly applicable in terms of materials, operating spectral regions, and design configurations. They are multifunctional as only a surface layer needs to be chemically altered to detect different species. Since no foreign chemical labels are required in operation, unperturbed biochemical processes can be quantified in real time. Due to predicted low cost, high integratability, flexible designs, and high performance, this technology can significantly impact the pharmaceutical and homeland security marketplace. Moreover, applications in polarization control and filtering have been identified. Predicted devices include single-layer wideband bandstop and bandpass filters, wideband polarizers, and polarization independent elements. Additional functionality associated with the GMR concept is spectral tunability achievable by perturbing the structural parameters (layer thickness, refractive index distribution, symmetry). Advances in nanoscale fabrication processes enable tuning of GMR devices using nano/microelectromechanical methods. Applications such as tunable filters, variable reflectors, modulators, and tunable pixels appear feasible. It is envisioned that these devices will be useful as pixels in new, planar, ultra thin spatial light modulators for display applications as well as in other systems including tunable multispectral detectors, multispectral analysis systems, polarization discrimination and analysis systems, and tunable lasers.
3:15 PM - FF2.3
Planarization for Optical Three Dimensional Photonic Crystals and other Multilevel Nanostructures Fabricated in a Layer-by-layer Approach.
Ganapathi Subramania 1 , Yun-ju Lee 1 Show Abstract
1 , Sandia National Laboratories, Albuquerque, New Mexico, United States
Nanostructures with three dimensional architecture such as photonic crystals (PC) have become increasingly important in nanophotonics. A properly designed three dimensional photonic crystal composed of a suitable material system is capable of completely suppressing electromagnetic modes over a range of frequencies for all spatial directions (omnidirectional photonic band gap). Such a property has enormous implications for classical as well as quantum optics such as light guiding, localization, spontaneous emission, lasing and non-linear phenomena. A large number of application areas that can utilize the above aspects are in the near infrared and visible frequency regime where typical periodicity is in the range of 200-800 nm with feature sizes ranging from 80-200nm. Lithography offers an elegant way of fabricating these structures in a layer-by-layer fashion with great accuracy and reproducibility which is essential for experimental verification of theoretically predicted phenomena. However, the nanometer dimensions involved precludes the use of conventional contact photolithography and one has to resort to approaches such as electron beam lithography. In a layer-by-layer fabrication, each layer needs to be planarized to within a few percent of the layer thickness. This can prove to be extremely challenging because techniques such as chemical mechanical planarization typically used in semiconductor industry becomes impractical due to the following reasons: each layer thickness is very small ranging from 70-200nm, devices can be sparsely distributed over the wafer and are likely to be composed of non-standard materials. To address this issue we describe a planarization approach based on a combination of pre-fill-in and spin on glass application to achieve a global degree of planarization > 90% . Using this approach we will demonstrate the fabrication of 3D “logpile” photonic crystal composed of titanium dioxide rods with visible frequency omnidirectional bandgap. The planarization technique described can also be extended to large scale fabrication of PCs or other multilevel nanostructures including metamaterials and nanomagnets with little or no modification.The research at Sandia National Laboratories is supported by the US Department of Energy. Sandia is a multiprogram laboratory operated by the Sandia Corporation, a Lockheed Martin Company, for the US Department of Energy’s National Nuclear Security Administration under contract DE-AC04-94AL 85000. 1.G.Subramania , Nanotechnology, 18, 035303(2007).
4:00 PM - **FF2.4
Bi-continuous 3D Periodic Polymeric Nanostructures via Self Assembly and Interference Lithography.
Edwin Thomas 1 Show Abstract
1 , MIT, Cambridge, Massachusetts, United States
Periodic structures interact with waves (electromagnetic and elastic waves) in interesting ways when the wavelength is on the order of the structural length scale. In order to have strong wave-structure interactions, the dielectric contrast or impedance contrast needs to be high. Polymers are a versatile platform for the creation of periodic 3D structures via the self assembly of block polymers or by interference lithography using photopolymers. High dielectric contrast can be achieved by selectively sequestering high index nanoparticles in a particular component and by etching away one component. High impedance contrast can be accessed by using glassy/rubbery components or by employing bicontinuous polymer/air structures. Another way to create structures with higher refractive-index contrast or higher impedance contrast is via infiltration or CVD.Block polymers (e.g. A/B diblocks and A/B/C terblocks) can self assemble into several bicontinuous periodic structures with lattice parameters scaling with the molecular weight. However, at present there are only a small number of periodic 3D bi-continuous structures (e.g. double diamond, double gyroid etc.), moreover, due to the nature of self assembly and the low energetic penalty for imperfections, such structures always have a considerable number of undesirable defects. On the other hand, it is straightforward using the interference of multiple beams of coherent light to engineer targeted periodic structures and to fabricate essentially defect-free specimens in negative or positive photoresist polymers. Periodic 3D bi-continuous polymeric structures afford opportunities for a variety of uses in photonic and phononic applications.
4:30 PM - FF2.5
Self-assembling Process and Structures of Colloidal Crystalline Arrays in a Fluidic Cell.
Masahiko Ishii 1 , Masashi Harada 1 , Azusa Tsukigase 1 , Hiroshi Nakamura 1 Show Abstract
1 , TOYOTA Central R&D Labs., Inc., Aichi Japan
To apply colloidal crystals, which are periodically-arranged monodispersed colloidal spheres, for photonic crystals, we have to fabricate the crystals with excellent crystallinity. Recently, several methods that control the evaporation of the solvent in a colloidal suspension, such as vertical deposition, withdrawal, and physical confinement, have been explored to improve the crystallinity. However, self-assembled colloidal crystals prepared by these methods still have numerous intrinsic defects and often have striped structures. Therefore, an understanding of the ordering process and ordered structure is important for minimaization of defects.In the present study, we attempted in situ observations of the ordering process of colloidal spheres in a fluidic cell  and analyzed the ordered structure using Bragg diffraction in visible light. The observations showed that the growth direction varied with the growth rate. At an extremely low growth rate, the array grew toward the <112> direction of face-centered-cubic lattice. At a moderate growth rate, it grew toward the <110> direction. However, an extremely high growth rate induced random arrays of the spheres. We were also able to visualize the generation and/or annihilation processes of several kinds of defects. The variation of the growth direction with the growth rate was discussed on the basis of the difference in water-flow resistance in the crystalline arrays. In addition, visible light diffraction revealed that the striped structure was due to twinned structures. A color derived from the (110) plane was observed in every other lines of the striped structure. Another color due to the (113) plane was observed in another lines. From these results, we concluded that the stripped structure was caused by repeated twins parallel to the <110> direction. M. Ishii, M. Harada, and H. Nakamura, Soft Matter, 2 (2007) 872.
4:45 PM - FF2.6
Inorganic Photoresist Materials for Direct Fabrication of Photonic Crystals Using Multiphoton Phase Mask Lithography.
Matthew George 1 , Raphael Dror 2 , Matthew Highland 1 , David Cahill 1 , Bruno Sfez 2 , John Rogers 1 , Paul Braun 1 Show Abstract
1 Materials Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States, 2 Applied Materials Group, Electro-Optics Division, Soreq Nuclear Research Institute, Yavne Israel
Direct fabrication of two- and three-dimensional inorganic photonic crystals has been achieved using interference lithography and two markedly different inorganic photoresists. A conformal phase mask element was used to generate the interference pattern through a process termed ‘Proximity Field Nano-Patterning’ (PFnP). We fabricated photonic crystals of varying lattice parameter and complexity using both 1-photon UV, and 2-photon near-IR PFnP. We also demonstrate compatibility with maskless PFnP where the surface of the photoresist film is embossed via imprint lithography to form the phase mask element. Aperiodic features were added to the resulting photonic crystals through 2-photon laser direct writing. The two inorganic photoresists, one oxide based and the other a chalcogenide glass, have competing strengths. The oxide resist is based on the acid catalyzed condensation of poly(methyl silsesquioxane) end groups. After calcination, the silsesquioxane is thermally stable, allowing for infiltration with high index of refraction materials. We have used this oxide resist and silicon LPCVD to form high index 3D photonic crystals. The chalcogenide glass based photoresist is composed of As2S3. This material already has a high index of refraction, making further template infiltration and removal processing steps unnecessary. As2S3 is also very sensitive to pulsed near-IR radiation, allowing us to directly pattern high quality photonic crystals from this chalcogenide glass using multiphoton PFnP. We measure and compare the 2-photon sensitivity and resist contrast of the oxide and chalcogenide glass materials and show that both of these inorganic photoresists allow for facile fabrication of large area photonic band gap materials with embedded functional defects.
5:00 PM - FF2.7
Techniques for Fabrication of Photonic Crystals Using Silicon Nanomembranes.
R. Jacobson 1 , Frank Flack 1 , Max Lagally 1 Show Abstract
1 Engineering Experiment Station Materials Science and Engineering, University of Wisconsin-Madison, Madison, Wisconsin, United States
Photonic crystals (PhCs) show great promise for the complete control of light propagation. Control of the light propagation is determined by the geometry of the PhC, thus allowing the engineering of optical band gaps. The creation of the necessary geometries to produce these band gaps has proven to be very difficult by current methods.We have recently developed processes for the fabrication, transfer, stacking, and boding of Si nanomembranes (SiNMs), potentially allowing us to go beyond the 2D photonic crystals that have been made in thin Si so far. One of the advantages of SiNMs is that they are patternable with standard Si processing. We have already shown that we can stack SiNMs to create a Bragg mirror , effectively a 1D photonic crystal. We demonstrate, using proven electron beam lithography techniques , the patterning and stacking of SiNMs required to create a photonic diamond crystal waveguide and a woodpile waveguide. The synthesis and processing steps involved include patterning of individual membranes to create the appropriate patterns for each layer, the release and transfer of membranes, and the proper stacking and alignment to create a 3D structure.In our approach stacking is a parameter that enables precise pattern control of PhC ‘defects’, something that is crucial to engineering band gaps and optical devices. We discuss ideas relevant to this processing, including broken-symmetry models, and the use of hydrophobic/hydrophilic nanopatterning on the PhC carrier for membrane alignment. Research supported by AFOSR and DOE. 1. W. Peng, et al., [Appl. Phys. Lett. 90, 183107 (2007)]2. M. Loncar, et al., [Journal of Lightwave Technology, vol. 18, No. 10, pp. 1402-1411, October 2000]
5:15 PM - FF2.8
Making Iron Oxide Colorful: from Rational Synthesis to Highly Tunable Photonic Crystals.
Yadong Yin 1 , Jianping Ge 1 Show Abstract
1 Department of Chemistry, University of California, Riverside, Riverside, California, United States
We report the rational synthesis, self-assembly and photonic application of monodisperse colloidal nanocrystal clusters (CNCs) of magnetite with tunable sizes from ~30 to ~180 nm. These CNCs are prepared through a high-temperature hydrolysis process using polyelectrolyte as a surfactant. Each cluster is a three-dimensional aggregate of many single magnetite crystallites of ~10 nm, thus retaining the superparamagnetic properties at room temperature. The CNCs show strong responses to external magnetic field due to their much higher magnetization per particle than that of individual magnetite nanodots. The use of polyelectrolyte as surfactant in synthesis provides the clusters highly charged surfaces. The combination of superparamagnetic property, high magnetization per particle, monodispersity, and highly charged surfaces makes the CNCs ideal candidates for various important applications. In particular, we demonstrate that these specially designed nanostructures can self-assemble into three-dimensional ordered lattices in solution in response to an external magnetic field. Such colloidal lattices show photonic bandgaps magnetically tunable in the entire visible spectrum, and their optical response to the external magnetic field is rapid and fully reversible.
5:30 PM - FF2.9
Engineering Photonic Band Structures via Structural Modification in Self-Assembled 3D Photonic Crystals.
Jeremy Galusha 1 , Michael Bartl 1 Show Abstract
1 Chemistry, University of Utah, Salt Lake CIty, Utah, United States
Oliver Hayden SIEMENS AG
Kornelius Nielsch Max-Planck-Institute of Microstructure Physics
Nina Kovtyukhova The Pennsylvania State University
Frank Caruso University of Melbourne
Teodor Veres Industrial Materials Institute-NRC
FF3: Atomic Layer Deposition
Tuesday AM, November 27, 2007
Room 200 (Hynes)
9:00 AM - **FF3.1
Step Coverage in Atomic Layer Deposition (ALD) on 3D Nanostructures.
Roy Gordon 1 Show Abstract
1 Chemistry and Chemical Biology, Harvard University, Cambridge, Massachusetts, United States
ALD is usually presented as a technique that produces completely conformal coatings. In fact, ALD process conditions can be set to produce any desired degree of conformality. The conformality of ALD coatings varies according to a simple formula relating the aspect ratio approximately to the square root of the exposure to the precursor vapor. Exposure is defined as the partial pressure of a precursor vapor integrated over the time that the vapor remains at the open end of a hole or trench. Examples of the same chemistry are shown to produce either conformal coating inside holes with high aspect ratio using high exposure, or coating just at the open ends of holes under low exposure. Deviations from complete conformality can also result from non-ideal surface chemistry, such as thermal decomposition, competitive adsorption of byproducts, or etching by reactants or byproducts. Reactions showing each of these non-ideal behaviors will be reviewed. Highly conformal ALD coatings are produced commercially in DRAM memory elements, read/write heads in magnetic disk memories, in optical phase plates and polarizers, and on irregular phosphor particles. Potential future uses of conformal ALD coatings include photonic crystals, MEMS devices, and coatings of heterogeneous catalysts. Non-conformal ALD coatings can be used for sealing pores in porous dielectrics or other porous materials.
9:30 AM - FF3.2
Controlled Replication of Butterfly Wings for Achieving Tunable Photonic Properties.
Xudong Wang 1 , Jinyun Huang 1 , Zhong Lin Wang 1 Show Abstract
1 Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States
Nature provides abundant selections of micro- to nanostructures that can be used as templates for fabricating a wide range of photonic related structures. Replication is a method of using biotemplates for achieving nanostructures made of more stable, harder, and high-temperature-tolerable inorganic materials that may have some designed functionalities for practical applications. Butterfly, beetle, and sea mouse are the typical templates used for building photonicrelated structures. Inorganic structures replicated from biological templates may combine the merits offered by both the material and biological structures. For practical applications, it is, however, still a challenge to replicate not only the morphological structures of the biotemplate but also their unique property or performance. We have successfully replicated the photonic structures of a Morpho Peleides butterfly wings using atomic layer deposition at the temperature below 100 degree C. The fine structure of the wing scale of butterfly was carefully examined and the entire configuration was completely replicated by a uniform Al2O3 coating. The reflectance spectra measurement demonstrates that the replica preserves not only the photonic property of the original butterfly wing but also the tuneable color through precise control over the thickness of the inorganic layer. An inverted structure was achieved by removing the butterfly wing template at elevated temperature, forming a polycrystalline Al2O3 shell structure with precisely controlled thickness. Other than the copy of the morphology of the structure, the optical property, such as the existence of PBG, was also inherited by the alumina replica. Reflection peaks at the violet/blue range were detected on both original wings and their replica. The alumina replicas also exhibited similar functional structures as waveguide and beam splitter, which may be used as the building blocks for photonic ICs with high reproducibility and lower fabrication cost comparing to traditional lithography techniques.
9:45 AM - FF3.3
Fabrication of Large-Area Microbowl Arrays.
Jenny Morber 1 , Xudong Wang 1 , Robert Snyder 1 , Zhong Wang 1 Show Abstract
1 Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States
Recently, a novel approach has been developed in our group for large-scale fabrication of ordered nanobowl arrays, which have been successfully demonstrated as a platform for hosting and ordering spherical structures of comparable size. The process started with a highly-ordered monolayer of polystyrene (PS) spheres assembled through a water surface tension assisted self-assembly process. Atomic layer depositions (ALD), ion-milling, toluene-etching and annealing were then used to fabricate the nanobowl arrays. The size of the nanobowl therefore depends on the size of PS sphere template. Favorable sphere size for assembling a high quality monolayer by reported techniques is 300-1000 nm. Large size bowls are needed for some applications. In our previous method the highly packed arrangement of spheres is self-assembled on the water surface by “pushing” from surfactant molecules, bigger spheres are more difficult to push together to form an ordered structure, and cannot reliably be assembled in arrays [1, 2]. To address this challenge, we adopt “confinement cell” technology for making highly ordered monolayer from large PS spheres (>2μm). This technique was originally invented for making opal structures, where colloidal spheres were collected and self-assembled around the photoresist wall of a confinement cell. When the thickness of the wall was comparable to the diameter of the spheres, highly ordered monolayer could be formed. We investigated the monolayer morphology of 10 μm PS spheres with various wall thicknesses to identify the optimal confinement cell construction. Highly ordered microbowl arrays with 10 μm in diameter were then realized after ALD, ion-beam etching and PS removal. With this improved self-assembly technique, the microbowl array can uniformly cover an area of more than 1 square inch on a glass substrate and provide more than 1 million nanobowls for cell hosting. Thus, for the first time, cells can be loaded and organized in an ordered array for precise analysis. The nanobowl platform is expected to show great potential in biomedical analysis and disease detection.Xu Dong Wang, Elton Graugnard, Jeffrey S. King, Zhong Lin Wang and Christopher J. Summers " Large-scale Fabrication of Ordered Nano-Bowl Arrays", Nano Letter, 4 (2004) 2223-2226.Xudong Wang, Changshi Lao, Elton Graugnard, Christopher J. Summers and Zhong L. Wang “Large-size liftable inverted-nanobowl sheets as reusable masks for nanolithiography”, Nano Letters, 5 (2005) 1784-1788.
10:00 AM - FF3.4
Iron Oxide Nanotubes of Tunable Geometry Prepared in Ordered Arrays by Templated Atomic Layer Deposition.
Julien Bachmann 1 , Jing Jing 1 , Sanjay Mathur 2 , Ulrich Goesele 1 , Kornelius Nielsch 1 Show Abstract
1 Experimental Department II, Max Planck Institute of Microstructure Physics, Halle Germany, 2 , Leibnitz Institute of New Materials, Saarbruecken Germany
Atomic layer deposition (ALD) is particularly suitable for the creation of conformal thin films of inorganic materials on non-planar substrates. Thus, ALD can be combined with the use of a structured template in order to create nanoobjects the geometry of which is defined by the template. Application of this preparative strategy to a porous anodic alumina template yields arrays of hexagonally ordered parallel nanotubes with very smooth walls. With this approach, the length of the tubes can be tuned accurately between 1 and 50 μm and their diameter between 20 and 200 nm via the anodization conditions of the porous alumina, while the wall thickness is directly determined between 1 and 40 nm by the number of ALD cycles. For the ALD of iron oxides, several different precursor chemistries (based on organometallic, alkoxy, and carbonyl complexes) have been explored, each of which is tailored to specific applications. These preparative tools enable the experimentalist to systematically study how physical properties are affected by geometry. Of particular interest are the electrical and magnetic properties of such iron oxide tube arrays, which have been shown to strongly vary with geometry. The biocompatibility of iron oxides should facilitate future applications of such ordered or isolated hollow nanoobjects. Finally, we envision that similar methods may serve to design nanoobjects of more complex geometries, such as concentric tubes and objects of modulated diameter.
10:15 AM - **FF3.5
Deposition of Highly Ordered Complex Nanostructures Using Nanoporous Alumina.
Mats Boman 1 , Inna Soroka 1 , Marten Rooth 1 , Anders Johansson 1 , Leif Nyholm 1 , Anders Harsta 1 Show Abstract
1 , Uppsala University, Dep. of Materials Chemistry, Uppsala Sweden
Nanotubes of a wide variety of materials have been fabricated using nanoporous alumina as a template and the use of different deposition techniques. The alumina template, which was synthesized as a membrane, was made by anodization of aluminium in two steps. The inter-pore distance was typically 100 nm and the pore diameter typically 60 nm. Both the length of the pores (the membrane thickness) and the pore diameter were varied in a wide range, 0.5 to 50 μm and 10 to 400 nm, respectively. The pores were parallel and well ordered in a hexagonal pattern. Atomic layer deposition (ALD) is a gas phase method, which can evenly coat the thin pore walls of nanoporous alumina. In ALD the precursors are not mixed but are introduced into the reactor in a sequential way. This means that the chemical reactions occur sequentially on adsorbed layers. In the present paper, different metal oxide nanotubes were manufactured by ALD using nanoporous alumina as a template. Results from single layered nanotubes of Nb2O5, Fe2O3 and TiO2 will be presented as well as some preliminary results from multi-layered TiO2/Fe2O3 nanotubes.Electrodeposition is another method having a step coverage permitting filling of nanoporous alumina. By combining ALD and electrodeposition new and unique nanostructured magnetic materials have been made. Results from antiferromagnetic ferromagnetic nanotubes and low-dimensional magneto-resistance structures will be shown.
11:15 AM - **FF3.6
Atomic Layer Deposition in Preparation of Three-Dimensional Nanostructures.
Mikko Ritala 1 , Marianna Kemell 1 , Tero Pilvi 1 , Viljami Pore 1 , Santala Eero 1 , Elina Farm 1 , Markku Leskela 1 Show Abstract
1 , University of Helsinki, Helsinki Finland
This presentation gives various examples about the use of atomic layer deposition (ALD) in preparation of various three dimensional nanostructures. The unique self-limiting growth mechanism makes ALD nearly an ideal tool for coating objects that are three dimensional from macro to nanoscale. ALD provides perfect conformality and uniformity over large areas, and easy and accurate thickness control down to an atomic layer level. ALD does not come without difficulty, however. For conventional thin film applications low deposition rate has been the limiting factor but for nanostructures this appears to be of a less importance because of small film thicknesses. On the other hand, if the nanostructured substrates are macroscopic in all three dimensions, precursor transportation by diffusion in and out of the porous object may become a limiting factor. In the case of through-porous substrates the process may be speeded up substantially by a novel reactor design where the precursors are forced to flow through the substrate.
11:45 AM - FF3.7
Fabrication of Nanostructure Arrays from Metal-patterned Si-on-insulator.
Jeremy Robinson 1 2 , Paul Evans 3 , James Liddle 2 , Oscar Dubon 1 2 Show Abstract
1 Materials Science and Engineering, University of California, Berkeley, California, United States, 2 , Lawrence Berkeley National Laboratory, Berkeley, California, United States, 3 Materials Science and Engineering, University of Wisconsin, Madison, Wisconsin, United States
The fabrication of semiconductor nanostructures and their organization into functional macroassemblies and metamaterials remain a fundamental challenge in nanoscience and nanotechnology, requiring new strategies in materials processing. Here we present a simple process for the fabrication of Si nanostructure arrays from Au-patterned Si-on-insulator (SOI) . The process is based on the spontaneous, local oxidation of Si induced by Au upon exposure to air, which is selectively evaporated onto the Si surface. The Au-catalyzed oxide forms a pattern that serves as a robust mask for the underlying Si, enabling the use of simple wet chemistry to sculpt arrays of nanostructures of diverse shapes including rings, pillars, wires, and nanopores. Using a stencil mask containing windows of various geometries, we selectively evaporate Au onto SOI that has been rinsed in HF. Spontaneous oxidation enhancement occurs through two distinct processes, one occurring directly within each Au feature by the diffusion of the underlying Si through the Au to the surface where it oxidizes and the other in the immediate perimeter of each Au feature by an anodization process that is driven by the electrochemical potential difference between Si and Au. While rinsing in HF and subsequent re-exposure to an oxidizing atmosphere result in the restoration of the anodic oxide, the oxide formed over the Au does not reform. This intriguing difference between the formation of the anodic oxide and the Si oxide formed by Si diffusion through the Au allows for machining of SOI into unique nanostructure assemblies by selectively removing one oxide and not the other. For example, pillars are formed from SOI that is decorated with an array of Au squares by etching in a KOH solution, which does not attack SiO2. Rings rather than pillars are produced simply by immersing a similarly Au-patterned SOI sample in HF, which removed the oxide over the Au, prior to etching with KOH. Extensive arrays are readily detected by optical diffraction. When the Au-squares are sufficiently close to each other, the anodic oxide coronae surrounding the Au squares overlap to form a continuous surface oxide. In this case, etching with HF followed by KOH produces a Si film with a periodic array of holes through the Si device layer and terminating at the buried oxide layer. Decreasing hole dimensions at the Si device layer/SiO2 interface to less than 20 nm has been realized by decreasing the initial size of the Au-patterned features. Control over the dimensions of this nanopore is achieved through a combination of Au-feature dimension and Si device layer thickness. The remarkable simplicity of this nanofabrication process makes it widely accessible as an enabling technique for applications from photonics to biotechnology. J.T. Robinson, P.G. Evans, J.A. Liddle, O.D. Dubon, Nano Letters, in press (2007).
12:00 PM - FF3.8
3-Dimensional Al2O3 Fiber Networks using Low Temperature Atomic Layer Deposition on a Cotton Template.
Daisuke Hojo 1 , Kevin Hyde 1 , Joseph Spagnola 2 , Gregory Parsons 1 Show Abstract
1 Chemical and Biomolecular Engineering, North Carolina State University, Raleigh, North Carolina, United States, 2 Material Science and Engineering, North Carolina State University, Raleigh, North Carolina, United States
There is interest in controlling the surface properties of 3 dimensional objects by deposition of conformal coatings. We have recently utilized atomic layer deposition (ALD) to deposit metal oxide and nitride coating on a variety of fibrous surfaces including natural cotton. For this study, Al2O3 thin films were coated onto natural woven cotton samples using a binary reaction of trimethylaluminum and water at 100°C. By adjusting the number of ALD cycles, the film thickness was controlled between 50 to 175nm, as observed by transmission electron microscopy (TEM). The Al2O3 growth rate, determined from the TEM data, was estimated to be ~0.31 nm/cycle on the cotton surface, which is larger than ~0.12 nm/cycle measured under the same conditions for deposition on a planar surface. The higher growth rate on the 3D surface is ascribed to adsorption of excess water within the cotton network under the conditions utilized. Natural cotton fibers take on a complex surface structure, and TEM images demonstrate that the ALD process can readily penetrate the network and result in a highly uniform surface coating. After deposition, the coated samples were heated to 450°C in flowing air for 90 minutes to oxide and consume the woven cotton, leaving behind Al2O3 microtubules in a woven network that replicates the original cotton fibers. Energy dispersive X-ray spectroscopy and X-ray diffraction confirm complete removal of the cotton material. By measuring the mass of the Al2O3 after cotton removal for a range of ALD cycle numbers, and using an estimated value for Al2O3 density of 3.0 g/cm3, the thickness and growth rate of the conformal Al2O3 coating can be estimated independently from the TEM data. The measured mass of Al2O3 was found to increase linearly with ALD cycle number, and the slope resulted in an estimated growth rate of ~ 0.12 nm/cycle, which is less than that measured from TEM. The difference is ascribed to some non-uniformity in the film thickness across the thickness of the woven sample, and is consistent with the higher growth rate observed from TEM analysis. Results demonstrate the capability of ALD to penetrate into the complex 3D network structure of natural woven cotton to form uniform coatings at low temperature, and give insight into general understanding of methodology to translate deposition processes from a 2D surface to a 3D network to obtain a uniform coating throughout the sample network bulk.
12:15 PM - FF3.9
Microstructured Optical Fibers as 3D Templates for the Deposition of Semiconductor, Metal, and Insulator Micro- and Nanotubes and Wires.
Neil Baril 1 , John Badding 1 , Venkatraman Gopalan 2 , Pier Sazio 3 , Dong-Jin Won 2 , Adrian Amezcua-Correa 3 , Jacob Calkins 1 , Anna Peacock 3 Show Abstract
1 Chemistry, Pennsylvania State University, University Park, Pennsylvania, United States, 2 Materials Science and Engineering, Pennsylvania State Uviversity, University Park, Pennsylvania, United States, 3 Optoelectronics Research Centre, University of Southampton, University Park, Southampton, United Kingdom
Design flexibility in template materials is a highly desirable featute in any micro or nanostructure platform. Microstructured optical fibers (MOFs) are