Siegfried Bauer Johannes-Kepler Universitaet Linz
Kunigunde Cherenack Philips Corporate Technologies, Research
Barclay Morrison III Columbia University
Tsuyoshi Sekitani The University of Tokyo
R1: Novel Materials for Stretchable Electronics and Photonics
Tuesday AM, November 29, 2011
Room 308 (Hynes)
9:30 AM - **R1.1
Mechanically Dynamic Nanocomposite Materials: In Vivo Properties and Cortical Tissue Response.
Dustin Tyler 1 3 , James Harris 1 , Allison Hess 3 2 , Jeffrey Capadona 1 3 Show Abstract
1 Biomedical Engineering, Case Western Reserve University, Cleveland, Ohio, United States, 3 , Louis-Stokes Cleveland Dept of Veterans Affairs Medical Center, Cleveland, Ohio, United States, 2 Electrical Engineering and Computer Science, Case Western Reserve University, Cleveland, Ohio, United States
The neuroinflammatory response is modulated by mechanical perturbations in the neural tissue and protein response to material surfaces. The development of material substrates for neural interfaces with mechanical properties that match the mechanical properties of the brain tissue has been an active area of research for the last decade. One requirement of an interface material is that it initially needs to be stiff enough to be inserted into the neural tissue, but rapidly changes to match the mechanical properties of the brain. Inspired by the mechanical dynamics of the skin of the sea cucumber, such as Cucumaria frondosa, our team is developing nanocomposite material that is stiff for insertion into the brain and then becomes soft within 14 minutes of implant. The behavior of the material was previously well-characterized in-vitro. This behavior is now demonstrated in-vivo. The neat poly(vinyl acetate) (PVAc) matrix was not able to penetrate the pia mater of the rat cortex. A nanocomposite system that incorporated cellulose (PVAc-NC), however, was stiffened sufficiently to allow penetration. A custom-built micro-tensile measurement apparatus measured the modulus of the PVAc-NC at a series of time points following implantation and show that the in-vivo modulus of the PVAc-NC changes from 3411±98 MPa (n = 5) prior to implantation to 32±13 MPa within 5 minutes. This mimicked the behavior of the material in artificial cerebral-spinal fluid (ACSF). Further, histologic analysis of the tissue response to PVAc-NC implanted for 4 and 8-weeks compared to PVAc-coated Tungsten wire shows a significantly different profile of the response of the neurons (NeuN), microglia (IBA1), macrophages (ED1), reactive astrocytes (GFAP), vimentin (Vim), and chondroitin sulfate proteoglycans (CS-56). The NeuN intensity is higher near the PVAc-NC compared to the coated Tungsten wire at 4-weeks post-implant and the intensity is preserved out to 8-weeks. Further, the astrocyte and CSPG responses indicate that the response to the PVAc-NC is more diffuse, not resulting in a dense fibrous scar. Preliminary investigation with LPS induced changes in the inflammatory profile show changes in recording from cortical probes for different profiles. Increased, non-specific cellular density and reduced neuron populations induced by LPS result in increased impedance and loss of units recorded. These preliminary results support the hypothesis that altering the inflammatory response by using a mechanically dynamic probe substrate for cortical electrodes. Finally, MEMS fabrication techniques have been developed and demonstrated to produce stable electrode structures from the new substrate PVAc nanocomposite material. Overall, there is substantial progress in developing a new neural interface substrate material that reduces the mechanical mismatch with the neural tissue.
10:00 AM - R1.2
Conductive Composite Materials for Extremely Stretchable Electrode Application.
Sangwoo Kim 1 2 , Junghwan Byun 1 2 , Yongtaek Hong 1 2 Show Abstract
1 Electrical Engineering and Computer Science, Seoul National University, Seoul Korea (the Republic of), 2 Inter-University Semiconductor Research Center (ISRC), Seoul National University, Seoul Korea (the Republic of)
We have studied stretchable electrode by using conductive composite materials. Previous stretchable electrodes were mainly realized by separate deposition or inkjet-printing of conductive materials on elastomeric substrates. These stretchable electrodes can well sustain electrical performance for electrical device connection at relatively low strain condition (typically under 30% elongation). This limit was originated by crack formation in the conductive thin films with the strain increase. In order to realize stretchable electrodes that can well sustain electrical performance at higher strain condition (over 30% elongation), composite materials can be used.Recently, carbon nano tube (CNT) based composite materials have been reported for stretchable electrode applications. Although, this composite material showed good conductivity at high strain condition, CNT composite has cost issues and it needs a complicate fabrication method. Therefore, in this paper, we used ferromagnetic powder based composite materials due to simple patterning capability and high initial conductivity. While most conductive powder base composite materials produced relatively poor conductivity, our materials showed better conductivity after exposed under the magnetic field and well maintained electrical conduction at extremely high strain condition (over 100% elongation). When the mixture of polydimethysiloxane (PDMS) (Sylgard 184, Dow Corning) and ferromagnetic powder (150 wt%) was made into an electrode of 25mm length and 1mm width, the initial resistance was about 2 kΩ. In addition, the conductive composite electrodes showed an interesting electrical characteristic in comparison with typical conductive composite. Its resistance decreased as the applied strain increased. The initial resistance decreased to 11Ω at applied strain of 30%, and remained to 11Ω at applied strain over 100%. The magnetically treated conductive composite materials can be used for extremely stretchable electrode applications. This research was supported by the Converging Research Center Program through the National Research Foundation of Korea(NRF) funded by the Ministry of Education, Science and Technology (No. 2009-0082824).
10:15 AM - R1.3
Effect of Mechanical Deformation on the Electrical Properties of PEDOT:PSS Films.
Yoo-Yong Lee 1 , Ji-Hoon Lee 1 , Na-Rae Kim 1 , Ju-Young Cho 1 , Ki Tae Nam 1 , Young-Chang Joo 1 Show Abstract
1 Materials science and engineering, Seoul National University, Seoul Korea (the Republic of)
Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is one of the most promising materials in the field of organic-based devices for charge transport layer or electrical interconnect due to moderately high conductivity, visible light transmittance, mechanical flexibility and good film-forming properties. Among these properties, high electrical conductivity of PEDOT:PSS films is required for the good performance of devices. This electrical conductivity is strongly influenced by the morphology of PEDOT:PSS films which consist of highly conductive PEDOT-rich domains surrounded by a shell formed by excess insulating PSS. The connectivity of PEDOT-rich domains and the ratio of PEDOT and PSS determine the electrical properties of PEDOT:PSS. There have been several reported attempts to modify electrical conductivity of PEDOT:PSS by change of morphology of PEDOT:PSS, e.g., addition of solvent, pH, and, water content. As other affecting factors after deposition of the films, it can be expected that the mechanical deformation of PEDOT:PSS films transforms internal chain structure of PEDOT:PSS directly after formation of the films. In this study, we demonstrated a consistent correlation between morphological change of PEDOT:PSS films due to mechanical deformation and the change of electrical properties. PEDOT:PSS solutions were deposited onto a polyimide(PI) flexible substrate(125 um) using a spin-coat method. The spin-cast films were subsequently annealed on a hot plate at 130 °C for 15 min in N2 atmosphere glove box. Then uniaxial tensile tests were conducted on the PEDOT:PSS films in situ measuring resistance changes with constant elongation rate. The resistance changes of the PEDOT:PSS film decrease according to increasing of strain. From the result of the tensile test with 0.1 mm/sec elongation rate, the resistance of the film was reduced by 65% at 75% of the strain. The morphology of PEDOT:PSS is transformed to reduce the resistance change of the film in the direction of deformation. To understand the morphological change of PEDOT:PSS before and after deformation, the surface microstructure of PEDOT:PSS film was observed by using AFM phase images. It shows that elongated PEDOT-rich domains are aligned in the direction of deformation and effective distance of each domains are getting closer after deformation. Therefore, mobile charge hopping in PEDOT:PSS is enhanced in the direction of deformation due to improvement of the connectivity of conductive PEDOT-rich domains and alignment of PEDOT chains after deformation. Effects of addition of solvent (DMSO) are discussed to correlate morphological change of PEDOT:PSS with electrical properties due to chemical treatment as well as mechanical deformation.
10:30 AM - R1.4
Cotton-Based Organic Electronic Devices for E-Textiles Applications.
Giorgio Mattana 1 2 , Piero Cosseddu 1 2 , Beatrice Fraboni 3 , George Malliaras 4 , Juan Hinestroza 5 , Annalisa Bonfiglio 1 2 Show Abstract
1 Dipartimento di Ingegneria Elettrica ed Elettronica, Università di Cagliari, Cagliari Italy, 2 S3 nanoStructures and bioSystems at Surfaces, CNR-INFM, Modena Italy, 3 Dipartimento di Fisica, Alma Mater Studiorum - Università di Bologna, Bologna Italy, 4 Department of Bioelectronics, Centre Microélectronique de Provence, Ecole Nationale Supérieure des Mines de Saint Etienne , Gardanne France, 5 Department of Fiber Science and Apparel Design, Cornell University, Ithaca, New York, United States
In this paper we report on the fabrication of cotton-based organic electronic devices especially designed for e-textiles applications. The nanoscale modification of natural cotton fibres with conformal coatings of gold nanoparticles and a subsequent deposition of thin layers of an organic conductive polymer (namely, poly(3,4-ethylenedioxythiophene) – also known as PEDOT – and its derivatives) allowed to obtain organic electronic devices starting from plain cotton yarns. This innovative method was employed to make two classes of electronic devices: passive devices such as resistors obtained from electrically conductive cotton yarns, and two types of active devices, namely organic electrochemical transistors (OECTs) and organic field effect transistors (OFETs). We have demonstrated that thanks to this process, the resistance per unit length of cotton yarns may be reduced up to four orders of magnitude, reaching significantly low values (a few kΩ/cm); these results allowed us to successfully employ these yarns in order to electrically connect electronic devices such as LEDs or to realise the electrical connections (i.e. source, drain and gate contacts) of the cotton-made transistors. A detailed mechanical analysis performed on such conductive cotton yarns revealed that treated yarns still maintain a good flexibility. The so-obtained conductive cotton yarns were used as core elements of cotton-made transistors; PEDOT:PSS (treated with ethylene glycol) was used as active layer for OECTs, while in the case of OFETs a thin layer of parylene C and thermally evaporated pentacene were used as gate dielectric and semiconductive layer, respectively. Despite the non-optimal Ion/Ioff ratio, a transistor effect is clearly achieved in both types of devices, with charge mobilities measured for OFETs up to 10-2 cm2/Vs. Our study opens up a novel pathway for real integration between organic electronics and traditional textile technology and materials.
10:45 AM - R1.5
Nanoporous Smart-Ccutting of GaN for Inorganic Flexible Light Emitting Devices.
Benjamin Leung 1 , Yu Zhang 1 , Christopher Yerino 1 , Jung Han 1 Show Abstract
1 Yale University, Yale University, New Haven, Connecticut, United States
Despite the success of commercial GaN light emitting diodes achieved to date, there are still opportunities for increased efficiency and new unconventional modes of use, if the sapphire substrate can be removed. A simple, cost-effective method for GaN epilayer liftoff, as demonstrated in this paper, could enable viable commercialization of LEDs in the vertical device configuration, and high brightness flexible optoelectronics. The prevalent technique, laser liftoff (LLO), is costly and time-consuming, and cannot be implemented for liftoff from other technologically important substrates such as Si, SiC and HVPE GaN. Recently several other techniques have been proposed, which involve deposition of foreign metals such as W and Ta, or etching methods that are cumbersome to implement such as photoelectrochemical etching of sacrifical layers or N-polar etching from GaN grown by ELO or patterned sapphire, or other utilizes a high complexity process such as arranging silica microspheres or H+ implantation. Here, we introduce a new simple and rapid process to slice GaN from the sapphire substrate, and demonstrate its use for vertical LED and compliant optoelectronics fabrication. In this process, a 2um Si-doped GaN layer is grown by MOCVD on sapphire with a LT-GaN buffer. By electrochemical etching, the layer is porosified, consisting of vertical holes drilled through the doped film. The full range of porosity in the layer can be achieved in the potentiostatic etching of the film by changing the applied bias. High temperature processes during further growth of an LED structure reconfigures the porous layer, and with sufficient porosity, a complete airgap can be realized. This results in a weakly attached thin film LED. After growth, metal for the p-type contact is deposited, and the LED is easily lifted off by bonding to any arbitrary substrate (glass slide and PET is shown here). In conjunction with a suitable processing and interconnection scheme, this enables high brightness and efficiency blue light emitters to be used on compliant substrates.
R2: Mechanics of Stretchable Electronics and Photonics
Tuesday AM, November 29, 2011
Room 308 (Hynes)
11:30 AM - **R2.1
Stretchable Thin-Film Electronics: Direct Microfabrication of Electronic Devices on Elastomeric Substrates.
Stephanie Lacour 1 Show Abstract
1 , EPFL, Lausanne Switzerland
The main challenge for direct fabrication of electronic devices on elastomer is the disparity between the thermo-mechanical properties of the substrate and the device materials. Elastomers are visco-elastic materials with large coefficient of thermal expansion; device materials are, in most cases, brittle but very stable in a wide range of temperature. We have optimised a range of thin-film based processes that allow for the direct deposition and/or patterning of device materials onto an elastomeric substrate (silicone rubber). Typical process temperature ranges from room temperature to 150°C. Thin-film transistors (TFTs), printed conductors and antennas, and capacitive sensors directly fabricated on silicone rubber will be presented.The use of those films for stretchable electronics further requires a careful mechanical design of the macroscopic circuit. Two mechanical conditions must be fulfilled to produce elastic circuitry: the resulting strain within device materials must remain below their fracture strain, and the strain profile along the electrical interconnects running from the stiff materials to the soft elastomer should be as monotonous as possible.By engineering the silicone substrate, one can pattern locally stiff (non deformable) platforms whilst the surrounding matrix remains fully elastic. We will detail how to produce such mechanically graded elastomer membranes, and integrate them to the design and fabrication of stretchable thin-film devices. Circuits made of TFTs patterned on such substrate can sustain large and repeated macroscopic elongation (0% < strain < 20%).
12:00 PM - R2.2
Design of Stable Metal Electrode on Compliant Substrate in Repeating Tensile or Compressive Bending Deformation.
Byoung-Joon Kim 1 , Min-Suk Jung 1 , Hae-A-Seul Shin 1 , In-Suk Choi 2 , Young-Chang Joo 1 Show Abstract
1 , Seoul National University, Seoul Korea (the Republic of), 2 , Korea Institute of Science and Technology, Seoul Korea (the Republic of)
The stability of metal electrode on polymer substrate during repeated deformations has been one of the main reliability issues in flexible electronics. In the real deformation of flexible electronics, the most frequent deformation mode for flexible display or e-skin is bending deformation. The bending deformation unlike tensile deformation can cause either tensile or compressive stress on metal electrode whether the film was located in the inside or outside of bending shape. Furthermore, the electrical failure such as electrical resistance change became more critical for stable electrical connection. We investigated the electrical stability of metal electrode in various bending strain, and defined fatigue failure by in-situ monitoring the electrical resistance. The bending fatigue failures under tensile or compressive bending were also investigated. The effect of sliding distance which closely is related with the operation of flexible electronics was discussed by probability of crack initiation. The 1 μm thick Cu film was deposited on 125 μm thick polyimide using thermal evaporation. The metal film on flexible substrate was located between two outer plates and the ends of the specimen were fixed with metal grips for in-situ electrical measurement. While the upper outer plate was fixed, the lower outer plate repeated sliding motion which was related with damage zone. Cyclic sliding test was performed in 0.7 to 1.1 % strain range at 5 Hz frequency and the sliding distance was varied from 10 to 30 mm. The electrical resistance change of Cu film in 1.1 % tensile bending condition did not change and any crack was not observed in early cycles. At 6,200 cycles, the electrical resistance increased 1 % comparing to the initial resistance and defined this cycle to the failure cycle with 1 % criteria. The short cracks due to the fatigue failure by dislocation motion of Cu were observed and this cracks caused electrical resistance change. The failure cycles and the applied bending strain followed Coffin-Manson relationship and the fatigue ductility exponent was -0.18 which was similar with other report of thin film fatigue. The fatigue limit of 1 μm thick Cu was determined by 0.8 % bending strain because the film did not fail over 500,000 cycles. The sliding distance had strong relationship with fatigue life time and the power law exponent was -2.8 which meant that as the sliding distance increased the failure cycle drastically shortened due to the increase of probability of crack initiation. In the Cu only on PI structure, the failure cycle of compressive bending fatigue showed similar values with that of tensile bending. This implied that the dislocation motion of compressive fatigue affected fatigue damage similarly with tensile fatigue. However, the electrical stabilities changed in the multi-layer structure.The effects of under-layer and over-layer on fatigue damage evolution of Cu will be discussed.
12:15 PM - R2.3
Secondary Buckling of a Stiff Thin Film on a Compliant Substrate.
Jizhou Song 1 Show Abstract
1 , University of Miami, Coral Gables, Florida, United States
The compression of a stiff thin film on a compliant substrate creates periodic sinusoidal waves, which can be used to develop stretchable electronics. Further compression will induce secondary buckling: one wave grows in amplitude at the expense of its neighbours. A mechanics model is developed to study this phenomena. The results agree well with experiments and finite element simulations and therefore provide design guidelines to develop stretchable electronics in large deformations.
R3: Stretchable Electrodes and Interconnects
Tuesday PM, November 29, 2011
Room 308 (Hynes)
2:30 PM - **R3.1
Understanding the Fabrication Process: Keys to Cost Effective, Reproducible, and Reliable Stretchable Electronics.
Oliver Graudejus 1 2 , Patrick Goerrn 2 3 , Cezar Goletiani 4 , Zhe Yu 4 , Barclay Morrison 4 , Teng Li 5 , Zheng Jia 5 , Abbas James 1 , Sigurd Wagner 2 Show Abstract
1 Chemistry and Center for Adaptive Neural Systems, Arizona State University, Tempe, Arizona, United States, 2 Princeton Institute for the Science and Technology of Materials (PRISM) and Department of Electrical Engineering, Princeton University, Princeton, New Jersey, United States, 3 Lehrstuhl für Elektronische Bauelemente , Bergische Universität Wuppertal, Wuppertail Germany, 4 Department of Biomedical Engineering, Columbia University, New York, New York, United States, 5 Department of Mechanical Engineering, and Maryland NanoCenter, University of Maryland, College Park, Maryland, United States
Interconnects for stretchable electronics applications can, in principle, be fabricated in a cost effective manner using microfabrication technology. A high fabrication yield and reproducibility is required for low cost production of reliable devices. To achieve these goals, the processes to produce stretchable conductors, and their encapsulation layers need to be well understood. Gold films are often used in stretchable electronics applications, and the electrical and optical properties of these films depend heavily on their morphology. Gold films on an elastomeric substrate can adopt three morphologies: smooth, buckled, or microcracked. The desired morphology depends on the intended application. To reliably produce the desired morphology, we will provide a detailed analysis of the parameters that affect the morphology of the gold film. Many applications of stretchable interconnects require the encapsulation of the gold conductors and the opening of contact holes. This can be achieved with the photopatternable silicone (PPS) WL5150 from Dow Corning. However, the fabrication yield is often low due to the weak adhesion of the PPS to the underlying elastomeric substrate, and the features that can be patterned are much larger on an elastomeric substrate than on silicon substrates. We identify the root cause for the weak adhesion and provide remedies. We also demonstrate how 40 micrometer wide contact holes can be produced in the photopatternable silicone and demonstrate two applications of these stretchable conductors: (a) microelectrode arrays as a promising approach to “soft” neural interfaces, and (b) soft and compliant sensors for normal and shear force measurements.
3:00 PM - R3.2
Biaxially and Isotropically Stretchable Gold Films on PDMS.
Patrick Goerrn 1 , Wenzhe Cao 2 , Sigurd Wagner 2 Show Abstract
1 , Bergische Universität Wuppertal, Wuppertal Germany, 2 , Princeton University, Princeton , New Jersey, United States
We demonstrate conductors that can be stretched in any direction without losing conductance. Crack-free wrinkled gold thin films are produced on elastomeric polydimethyl siloxane (PDMS) substrates that were strained radially by up to 40% prior to deposition. Their relaxation after deposition produces isotropically wrinkled films. Such wrinkled 20-nm thick gold films are free of cracks and have a sheet resistance of ~ 10 Ohm/sq. The conductors can be stretched uniaxially in any direction, and can be stretched biaxially to the biaxial pre-strain of 40%, respectively. The electrical resistance of such conductors changes less with applied uniaxial strain than that of micro-cracked gold films and even of ideal strain gauges. Biaxial stretching to 40% causes an even smaller resistance increase of only 34%. Crack-free conductors could find use in applications that require large area continuous electrodes in stretchable thin film optoelectronics.
3:15 PM - R3.3
Inkjet-Printed Silver Electrode for Stretchable Electronics Application.
Seungjun Chung 1 2 , Jaemyon Lee 1 2 , Hyunsoo Song 1 2 , Sangwoo Kim 1 2 , Jaewook Jeong 3 , Yongtaek Hong 1 2 Show Abstract
1 Electrical Engineering and Computer Science, Seoul National University, Seoul Korea (the Republic of), 2 Inter-University Semiconductor Research Center, Seoul National University, Seoul Korea (the Republic of), 3 , Daegu Gyeongbuk Institute of Science & Technology, Daegu Korea (the Republic of)
We report technical issues in fabricating high-performance inkjet-printed stretchable silver (Ag) electrode on the elastomeric substrate. As stretchable electronics has attracted much attention, needs for the stretchable electrodes fabricated at lower cost and by simpler process are increased. Although inkjet-printing method is one of most promising candidates for low-cost flexible electronics,it has not been applied on the elastomeric substrates like poly(dimethylsiloxane) (PDMS) due to poor adhesion between metal ink and PDMS substrate. Good adhesion property is a critical factor for stretchable performance. To solve this problem, surface treatments such as oxygen plasma or UV ozone were performed to increase surface energy, resulting in better ink wetting on the substrate. However, oxygen plasma can cause PDMS surface deformation due to high energetic ions although contact angle was dramatically reduced from 116 ° to 12 °. UV ozone treatment was insufficient to obtain good metal ink wetting property. Therefore, we applied both UV ozone treatment and PDMS surface roughening for better adhesion between metal ink and the PDMS substrate. Adhesion and thus, stretching property of the printed electrodes is different for Ag ink characteristics such as its polarity or metal dispersion types. We will further discuss this issue at the conference. In order to fabricate the high-performance inkjet-printed Ag electrode, we also structured PDMS substrate. For inkjet-printed stretchable Ag electrode fabrication, nano-particle based polar ink was used. To prepare wavy PDMS substrate, mixture of PDMS from Dow corning and curing agent was poured on an aluminum (Al) mold having wavy patterns with period and amplitude of 200 μm. Surface of the Al mold was roughened by W-EDM, resulting in surface roughness of 1.05 and 5.14 μm in RMS and peak-to-peak values. This roughened surface provides an appropriate critical angle for the polar ink and improves ink spreading and adhesion of the printed electrodes. In addition, the roughened surface helps releasing built-in stress of the thick Ag electrode resulting in formation of relatively thick Ag electrodes on the PDMS substrate. This effect will be also further addressed. The inkjet-printed stretchable electrode showed comparable stretching performance with that using vacuum process even though harsher stretching conditions were applied. During slow (16.7 μm/s) stretching test, resistance of the printed Ag electrode was increased only by 3-time at 30% tensile strain. It also showed good mechanical stability during 1000-time fast (1 mm/s) cycling test with 10 % tensile strain, showing maximum resistance change of less than 3 times. Therefore, it is expected that the inkjet-printed Ag electrode can be adopted for high performance stretchable electronics applications.This work was supported by the Korea Science and Engineering Foundation (KOSEF) grant funded by the Korea Government (MEST) Grant No. I-NS07-09(0417-20090086)
3:30 PM - R3.4
Lateral Crack-Free Buckled Silver Electrodes Inkjet-Printed on 50% Prestretched Elastomeric Substrate.
Jaemyon Lee 1 2 , Seungjun Chung 1 2 , Hyunsoo Song 1 2 , Yongtaek Hong 1 2 Show Abstract
1 Electrical Engineering and Computer Science, Seoul National University, Seoul Korea (the Republic of), 2 Inter-University Semiconductor Research Center (ISRC), Seoul National University, Seoul Korea (the Republic of)
We report inkjet-printed buckled silver film on poly-dimethylsiloxane (PDMS) substrate. Inkjet-printing has many advantages such as low cost, non-vacuum process. Stretchable electronics can realize many future applications such as compliant artificial skin. Since most active materials have little strain limit (~1%), most stretchable electronics researches focus on stretchable line fabrication. One approach for better stretchable line is prestretching method. When the prestretched thin film on elastomeric substrate is released, buckles are formed like accordion bellows. This method does not require additional process on material, but just needs holding strain during film fabrication. Therefore, it is a cost-effective method for better stretchability. In the buckle formation method, previous works reported that lateral cracks are formed after releasing by Poisson’s effect since PDMS has much higher Poisson coefficient (0.5) than other materials and these cracks span the entire length once nucleated. However, since inkjet-printing needs high-temperature annealing for removing solvent, it is found that appropriate annealing process can be effectively utilized to reduce formation and span of the lateral crack. The high temperature leads to large thermal expansion since PDMS has much higher thermal expansion coefficient (310x10^-6 /°C, ΔT=100 °C occurs 3.1% tensile strain) than other materials. It should be noted that the direction of thermal expansion is opposed to the direction of Poisson’s effect, mitigating lateral crack formation caused by Poisson’s effect. Theoretically, if ΔT=180 °C, lateral crack formation in buckled silver film on PDMS substrate by Poisson’s effect can be mitigated for the prestretching strain up to 40%. Our experiment results consistently show that 200 °C annealing temperature leads to lateral crack-free buckled silver film even though we used poor mechanical performance material, higher prestretching strain (50%) than previous works which used gold film, lower prestretching strain under 30% strain.  On the other hand, without high temperature annealing, buckled inkjet-printed silver film with same prestretching strain showed similar lateral cracks. Lateral crack-free inkjet-printed buckled silver film with 50% prestretching strain showed little normalized resistance change until 15%~20% strain. We believe that optimized combination of the inkjet-printing, annealing, and prestretching will significantly improve stretching performance in the low-cost stretchable electronics applications. This research was supported by the Converging Research Center Program through the National Research Foundation of Korea(NRF) funded by the Ministry of Education, Science and Technology (No. 2009-0082824). References: C. Yu, K. O’Brien, Y.-H. Zhang, H. Yu, H. Jiang, Appl. Phys. Lett. 2010, 96, 041111 Lacour, S. P.; Jones, J.; Wagner, S.; Li, T.; Suo, Z. Proc. IEEE 2005, 93, 1459-1467
3:45 PM - R3.5
Biocompatible and Highly-Deformable Nanostructured Elastomeric Electrodes with Improving Conductivity upon Cyclical Stretching.
Luca Ravagnan 1 , Gabriele Corbelli 2 1 , Cristian Ghisleri 2 1 , Paolo Milani 2 1 Show Abstract
1 , WISE s.r.l., Milano Italy, 2 CIMAINA & Physics Department, Università degli Studi di Milano, Milano Italy
The interest for micro- and nano-manufacturing of polymeric materials is continuously increasing driven by different fields such as stretchable electronics, bioelectronics, conformable sensors, actuators and polymer-based MEMS. The need for polymer-based micro-devices requires the integration of micrometric electrodes, circuits and interconnections on soft and compliant polymeric substrates. Unfortunately, the standard approaches used for producing such structures have many drawbacks in terms of layer adhesion, electrical functionality under stretching, attainable lateral resolution, sample heating and biocompatibility of the obtained materials. Recently we developed a new method for polymer metallization: the Supersonic Cluster Beam Implantation (SCBI) of neutral metal clusters in a polymer substrate. The clusters are produced in the form of a supersonic beam by a Pulsed Microplasma Cluster Source (PMCS)  and are implanted at RT in the polymer substrate forming a metal-polymer nanocomposite layer [2, 3]. This process avoids both sample heating and sample charging, enabling the metallization of ultracompliant soft polymeric materials. Here we present the application of SCBI for the fabrication of a biocompatible elastomer-based nanocomposite materials made by gold clusters implanted in a polydimethylsiloxane (PDMS) matrix. The obtained nanocomposite is able to withstand thousands of uni-axial stretching cycles (over 50000 to 40% strain) preserving finite and reproducible electrical resistance. At odd with electrodes obtained by standard approaches, the ones produced by SCBI experience an improvement (i.e. the decrease) of the electrical resistance at maximum strain as the number of stretching cycles increases, and only a very small increase of the rest resistance (i.e. at 0% strain). Furthermore, electrical conduction is preserved also during extreme stretching, so that open circuiting is observed only when the PDMS substrate mechanically breaks.Biocompatibility tests indicate that neuronal cells adhesion and vitality improve on the nanocomposite, proving the high biocompatibility of this novel material. Finally, we demonstrated the possibility to use SCBI to pattern compliant electrodes with micrometric resolution through standard stencil mask patterning. These results indicate that SCBI can be considered a promising tool for the fabrication of complex microelectronic circuits and interconnects on stretchable and compliant supports preserving the electrical performances of the devices after extensive cycles of stretching. The devices can be efficiently fabricated on biocompatible platforms, and therefore are suitable for the production of the next generation polymer-based implantable biomedical devices. K. Wegner, et al., J. Phys. D: Appl. Phys. 39, R439 (2006).  L. Ravagnan, et al., J. Phys. D: Appl. Phys. 42, 082002 (2009). M. Marelli, et al., J. Micromech. Microeng. 21 045013 (2011).
R4: Stretchable Electronic Components and Circuits
Tuesday PM, November 29, 2011
Room 308 (Hynes)
4:30 PM - **R4.1
Ultraflexible, Heat-Resistant, Large-Area Organic Transistor Integrated Circuits for Sensors and Medical Applications.
Takao Someya 1 2 , Tsuyoshi Sekitani 1 2 Show Abstract
1 Department of Electrical and Electronic Engineering and Information Systems, The University of Tokyo, Tokyo, Bunkyo-ku, Japan, 2 , JST, ERATO, Tokyo Japan
We have successfully manufactured ultraflexible, heat-resistant, air stable, low-voltage driven, large-area organic thin-film transistor (TFT) integrated circuits. In particular, the manufactured flexible organic TFTs exhibit no detectable degradation even after the annealing at 150 °C. This becomes possible with combining heat-resistant organic semiconductor and extraordinarily highly-dense self-assembled monolayers (SAMs) as gate dielectric. By making full use of thermal stability of the novel TFTs, we have applied sterilization processes to those TFTs, realizing various kinds of novel applications including medical catheters.
5:00 PM - R4.2
Fully Deformable Organic Thin Film Transistors with Moderate Operation Voltage.
Piero Cosseddu 1 2 , Andrea Piras 1 , Annalisa Bonfiglio 1 2 Show Abstract
1 Dept. of Electrical and Electronic Engineering, University of Cagliari, Cagliari Italy, 2 S3 nanoStructures and bioSystems at Surfaces, CNR-INFM, Modena Italy
In this paper we report on the fabrication of highly flexible, free-standing organic thin film transistors (OTFTs) working at relatively low voltage, and their employment for the realization of full-swing complementary inverters. The core of the devices is a very thin, free-standing parylene C film which acts at the same time as highly flexible mechanical support and as gate dielectric. Parylene C has the great advantage to form transparent, pinhole-free, conformal coatings with excellent dielectric and mechanical properties. Parylene C thin films (with nominal thicknesses ranging from 400 nm to 1.8µm) were deposited from vapor phase on a silicon substrate with very low surface corrugation. Very interestingly, after deposition, parylene films can be easily peeled off from the silicon surface in order to obtain a final, very thin, pinhole free, free-standing film. Being accessible from both sides, such films can be patterned on one side in order to realized the gate electrode, and on the opposite one in order to realize source, drain electrodes and deposit the active layer. We have demonstrated that thanks to the excellent mechanical properties of parylene C, this approach can be employed for scaling down the operating voltage in OTFTs and complementary inverters just by lowering the final free-standing film thickness. We will show that the final thickness of the free-standing insulating films can be lowered down to 300-400nm, thus allowing obtaining fully functional OTFTs working within the range of ±15V, with mobility up to 0.1cm^2/Vs, Ion/Ioff up to 10^4 and very small leakage current (100pA), and full swing complementary inverters with gains up to 10. Moreover, it has also been found that such a structure is highly robust to mechanical stress. In fact, we have demonstrated that, since the electrical response of OFETs to mechanical deformation is mainly related to the surface strain induced by the device substrate in the active layer, these effects can be dramatically reduced (by orders of magnitude) by using the proposed substrate-free structure. We will show that the device electrical behavior is scarcely sensitive to mechanical deformation, and that devices fabricated on thin free-standing parylene films can be bent down to very small bending radii (below 1mm) without getting damaged and most importantly without giving evidence of degradation of their electrical performances. We will also show that, thanks to the extreme flexibility of the proposed structure, such patterned films can be easily transferred on whatever kind of structure like paper, fabric, or 3D structures representing a step forward to the realization of highly flexible, compliant electronics particularly suited for smart wearable applications.
5:15 PM - R4.3
Printed Stretchable Functional Circuits.
Adam Robinson 1 , Stéphanie Lacour 2 Show Abstract
1 Nanoscience Centre, University of Cambridge, Cambridge United Kingdom, 2 Laboratory for Soft Bioelectronics Interfaces, EPFL, Laussane Switzerland
We present a straightforward assembly technique for producing hybrid stretchable circuits. Printed stretchable conductors are interfaced with traditional electronic components adhered to rigid islands distributed across a stretchable substrate. The soft-to-hard interface is optimized to remove extensive peak strain along the conductors. Electrically conducting ink is plotted onto the silicone substrate preliminary patterned into an array of microscopic posts to prevent ink dewetting and ensure stretchability of the conductors. Rigid (non deformable) islands, which will host individual electronic components, are produced within the elastic substrate by embedding 50 μm thick Kapton disks, 50 μm beneath the top surface. The strain peak at the rigid/stretchable interface is further controlled by embedding a larger second disc deeper within the substrate. Strain profiles of the rigid/stretchable interface are evaluated as a function of substrate thickness and discs diameter using the COMSOL modelling software, and measured using environmental scanning electron microscopy. Electronic components, including an LED, an Op Amp and resistors, are adhered to the rigid islands and interconnected with printed stretchable conductors. The diameter of the rigid islands is adjusted to fit the geometry of the components. The circuit may be stretched and cycled to 20% strain hundreds of times without loss of performance. Combining several islands allows for the fabrication of stretchable functional circuits. A strain sensor circuit will be demonstrated.
5:30 PM - R4.4
Ultra-Compliant Rechargeable Electrochemical Dry Gel Cells for Self-Powered Stretchable Electronics.
Martin Kaltenbrunner 1 , Gerald Kettlgruber 1 , Christian Siket 1 , Reinhard Schwoediauer 1 , Siegfried Bauer 1 Show Abstract
1 Soft Matter Physics, Johannes Kepler University, Linz Austria
Flexible electronics is limited to flat substrates, but stretchable electronics can cover unusual surfaces such as curved substrates or moving parts: Stretchable electronics mimics for example the functionality and nature of human skin. Nevertheless, all electronic components like sensors, actuators and integrated circuits need to be supplied with electrical energy. Despite extensive efforts to advance stretchable electronic, including stretchable solar cells and batteries, solutions for long-term, rechargeable power storage with high energy density have so far not been found.Here we present ultra-compliant and mechanically durable rechargeable accumulators for self-sustaining stretchable electronics.An acrylic elastomer (VHB, obtained from 3M) serves as compliant matrix, embedding the chemically active pastes and gels. Textile fiber meshes with a conductive metal coating serve as low-resistivity electrodes to efficiently collect the current. The chemically active materials are Zn and MnO2 in an alkaline electrolyte, the basics of rechargeable alkaline manganese (RAM) cells. Active areas of approximately 2 cm2 are prepared with a lateral separation of 0.5 cm, to avoid intermixing of the chemicals upon stretching. The active electrodes are closed with an electrolyte gel. Such accumulators can be stretched up to 75% while being charged and discharged, without any observable change in performance compared to non-stretched cells. Periodic stretching up to 25% has been performed during 20 charge-discharge cycles, proofing the durability and mechanical stability of the accumulators when undergoing more than 700 stretch- relaxation cycles.
5:45 PM - R4.5
Corrugated Gate Thin Film Transistors.
Sanjiv Sambandan 1 Show Abstract
1 Applied Physics, Indian Institute of Science, Bangalore India
Thin film transistors (TFTs) based on non-crystalline semiconductors are of interest for large area electronics. Most often the TFT is used as an access switch in the pixel, and it is preferable to have a fast turn on and high currents to improve data access speed. We study the influence of corrugating the gate on the transfer characteristics of the TFT.The proposed corrugated gate TFT structure consists of a corrugated gate metal layer where the ridges are such that they lie along the channel length of the TFT from the source to the drain electrode. Due to the presence of corrugations on the gate, there appear a series of “sharp” and “blunt” edges along with plane regions.When the gate is set to some potential, the conductive surface of the gate requires the charge to distribute unequally such that the sharp (blunt) edges have a higher (lower) charge density compared to the plane region. Thus, the electric field normal to and just above the sharp (blunt) edge is higher (lower) compared to the plane region of the gate. Equivalently, the potential just above the sharp (blunt) edge decreases more (less) rapidly compared to the plane regions of the gate. Thus, it is possible to modulate the transfer characteristics of the TFT by the use of corrugations.We demonstrate with experimental results the improvement in the effective transconductance and hence the current in the TFT due to the presence of the corrugations. This illustrates the role of geometry in influence the transfer characteristics of the TFT
R5: Poster Session: Stretchable Electronics and Photonics
Tuesday PM, November 29, 2011
Exhibition Hall C (Hynes)
9:00 PM - R5.1
Shaping Mechanically Coupled Assemblies of Dielectric Elastomer Elements.
Yuting Huang 1 , Meghan Krupka 2 , Serguei Bagrianski 2 , Sigrid Adriaenssens 2 , Sigurd Wagner 3 Show Abstract
1 Physics, Princeton University, Princeton, New Jersey, United States, 2 Civil Engineering, Princeton University, Princeton, New Jersey, United States, 3 Electrical Engineering, Princeton University, Princeton, New Jersey, United States
Combining dielectric elastomers with thin-film solar cells opens the prospect of self-powered, smart civil structures that adapt their shape autonomously in response to external stimuli. To explore the realm of stable equilibrium forms that these Dielectric Elastomer Minimum Energy (DEME) structures can take, we numerically simulated mechanically-coupled assemblies of DEME elements. In these models elastomeric membranes are first pre-stressed across triangular frames with low bending stiffness, and then two to eleven frames are connected along their edges in various configurations. Application of voltage across the membranes’ thickness is simulated by isotropic relaxation, which may be uniform or may differ between the membranes. We find that these configurations can assume a large variety of stable shapes, some of them quite surprising. We use the following approach. First, we use a finite difference method to represent the membrane of each triangular element with a triangular mesh. Second, we employ dynamic relaxation as a numerical analysis process to solve a set of nonlinear equations based on Newton’s second law of motion. Briefly, the technique traces the motion of the dielectric membrane stretched over the bendable frame through time when loaded with pre-stress forces. In this process we iteratively update the location of every point in the triangular mesh system. During the first 200 iterations only we apply a small external force normal to the plane of the membrane (as imperfection) so that the structure will move out of plane as it does in experiment. Then we monitor the system until all out-of-balance forces have disappeared and the structure has reached a steady state. For some DEME structures we find more than one final shape. We validated our numerical results with published physical test results  and found that our simulated structures are in close agreement with those published. We will describe our goals for application of DEME structures, the simulation techniques, and results for a range of different assemblies. M.T. Petralia and R.J. Wood, “Fabrication and analysis of dielectric-elastomer minimum-energystructures for highly-deformable soft robotic systems,” Conf. Proc. 2010 IEEE/RSJ Internat. Conf. Intelligent Robots and Systems, October 18-22, 2010, Taipei, Taiwan. IEEE, New York 2010, pp. 2357-63.
9:00 PM - R5.2
Highly Stretchable Composite Conductors Made from Carbon Nanotubes and Polydimethylsiloxane.
Tae Ann Kim 1 , Hee Suk Kim 1 , Sang Soo Lee 1 , Min Park 1 Show Abstract
1 Nanohybrids Research Center, Korea Institue of Science and Technology, Seoul Korea (the Republic of)
The realization of stretchabilily in electronics is one of the most interesting challenges in materials science and engineering and makes it possible to spread electronics over arbitrary curved surfaced and movable parts. Single-walled carbon nanotubes (SWNTs) have been regarded as one of promising candidates for these applications due to their excellent mechanical and electrical properties. However, they are heavily entangled with one another and forming large bundles, which makes them difficult to process and disperse. To promote the dispersion of SWNTs, wrapping the surface of SWNTs with surfactants is an effective way. Especially, imidazolium ion-containing ionic liquids can easily exfoliate SWNT bundles; grinding SWNTs with ionic liquids in an agate mortar makes them forming physical gels where heavily entangled SWNT bundles are exfoliated to give highly dispersed, much finer bundles.In this study, SWNT/polydimethylsiloxane (PDMS) composites that can be utilized in fabricating stretchable conductors are prepared by spraying a mixed solution of ionic-liquid-based SWNT gel and PDMS onto an elastic substrate. Subsequently, the composites are exposed to nitric acid vapor. SEM and AFM images of the composites demonstrate that the SWNTs are finely dispersed, and well-connected conducting pathways are formed in the polymer matrix due to the addition of ionic liquid. Doping of the SWNTs by nitric acid can significantly lower the sheet resistance (Rs) of the composites; samples with 4 wt% of SWNT content exhibit the lowest Rs, 50 Ω/sq, which corresponds to a conductivity value of 63 S/cm. In addition, the composites maintain a high conductivity after several tensile strains are applied. Stretching the composite sample to 300% of the original length increased the Rs value to 320 Ω/sq (19 S/cm). Even after a stretch/release/stretch cycle, the conductivity remains constant at a value of 18 S/cm. These results provide a scalable route for preparing highly stretchable and conductive SWNT composites with relatively low SWNT concentrations.
9:00 PM - R5.3
Printing Flexible Electrodes onto Textured Silicon, Paper and Fabric Substrates.
Analisa Russo 1 , Bok Yeop Ahn 1 , Jennifer Lewis 1 2 Show Abstract
1 Materials Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States, 2 Chemical and Biomolecular Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States
Flexible electronics constitute a new category of devices that are highly portable, lightweight and conformal for applications including photovoltaics, displays, and wearable electronic devices. These emerging applications often require that electrodes be patterned on textured substrates such as silicon, paper, or fabric. However, most available electrode deposition techniques require etchants, high processing temperatures, or low-viscosity inks that readily permeate porous surfaces. To overcome these limitations, we have developed a new class of concentrated metallic inks for additive manufacturing of flexible circuits on textured substrates. By tailoring the ink composition and rheological behavior, we can design conductive inks for filamentary ink printing, rollerball pen writing, and drop casting. To date, we have demonstrated the construction of several flexible electronic devices including flexible photovoltaics, surface-mounted LED displays, antennas, and transparent electrodes.
9:00 PM - R5.4
Study of Boron Doped Silicon Films Directly Deposited by Cat-CVD at Low Temperature (180°C) for Flexible Optoelectronic Devices.
Sin-Young Kang 1 , Kyoung-Min Lee 2 , Ki-Su Keum 1 , Jung-Hoon Park 1 , Kil-Sun No 1 , Wan-Shick Hong 1 2 Show Abstract
1 Nano Science and technology, University of Seoul, Seoul Korea (the Republic of), 2 Nano Engineering, University of Seoul, Seoul Korea (the Republic of)
The fabrication of flexible devices recently raised up the major issue of the next-generation mobile electronics. A low processing temperature is demanded to prevent the damage of plastic substrates. We directly deposited the B-doped Si films on glass substrate by Cat-CVD at a low temperature (180°C). Silane (SiH4), hydrogen (H2) and diborane (B2H6, diluted 5 % in hydrogen) were used as source gases, and the gas flow ratio (B2H6/SiH4) was varied from 0.5 % to 5.5 %. Filament temperature, substrate temperature and process pressure were maintained at 1800°C, 180°C and 60 mTorr, respectively. As a result, the value of sheet resistance was decreased with increasing B2H6 flow rate in section (B2H6/SiH4 = 0.5 ~ 3.0 %), and the value of sheet resistance was increased with increasing B2H6 flow rate in section (B2H6/SiH4 = 3.0 ~ 5.5 %). For flexible optoelectronic devices, we fabricated p-i-n structures by Cat-CVD without vaccum break at a low temperature (180°C), and confirmed diode characteristics.
9:00 PM - R5.5
SiOX Deposition by the Prevention of the Filament Oxidation in Cat-CVD System.
Jung-hoon Park 1 , Kyoung-Min Lee 2 , Ki-Su Keum 1 , Sin-Young Kang 1 , Wan-Shick Hong 1 2 Show Abstract
1 Nano Science and Technology, Univ. of seoul, Seoul Korea (the Republic of), 2 Nano Engineering, Univ. of seoul, Seoul Korea (the Republic of)
In this study, we deposited silicon oxide (SiOX) films using the prevention method of the filament oxidation in catalytic chemical vapor deposition (Cat-CVD) system at a low temperature (< 200 °C). Cat-CVD method utilizes thermal decomposition of reactant gases at the surface of a filament at temperatures in the range of 1500~2000 °C. Because the filament is heated to high temperature, when the source gas contains oxidizing species, the filament is degraded by oxidation during the deposition process, causing unwanted influences to the process condition. We tried to avoid this problem by adding extra H2 gas to the source gas and the supplied power maintenance at a constant level. We deposited SiOX films with silane (SiH4), nitrous oxide (N2O) and hydrogen (H2) gas as source gases. Entire process was progressed at a low temperature (< 200 °C). The chamber pressure was maintained at 60 mTorr during the deposition process and the initial temperature of the filament was set to 1700 °C. The main SiO2-related Si-O bonding in the deposited films were demonstrated by Fourier transform infrared spectroscopy (FTIR). Electrical performance as breakdown field and resistivity of the SiOX film was adequate to use in gate dielectric material. We are successfully deposited SiOX films by using the prevention method of the filament oxidation in Cat-CVD system.
9:00 PM - R5.6
Surface Plasmon Resonance Based Optical Temperature Sensor Using ZnO:N Thin Film.
Kajal Jindal 1 , Monika Tomar 2 , Vinay Gupta 1 Show Abstract
1 Department of Physics and Astrophysics, University of Delhi, Delhi, Delhi, India, 2 Department of Physics, Miranda House, University of Delhi, Delhi, Delhi, India
Surface Plasmon resonance (SPR) is a highly sensitive and noninvasive surface-sensing technique for detection of chemically or physically related phenomena that can induce refractive index variations of the medium in contact with the metal surface using an electromagnetic (EM) field. Recently, doped wide band gap oxides have gathered increasing research interest for their potential applications in optoelectronics, optical waveguides etc. Nitrogen has been identified as a promising dopant in ZnO since it can reduce the threshold optical energy, which would enhance the photocatalysis or solar energy conversion effectiveness of ZnO. In the present study, we report on the development of an optical reflectance method which employs SPR monitoring in order to study the temperature dependent optical properties of ZnO:N thin film at an optical frequency (λ=633 nm). A thin film (~ 40 nm) of gold was deposited on the hypotenuse face of a right angled BK7 glass prism by thermal evaporation and was annealed in air at 573 K. ZnO:N film (~ 200 nm) was deposited on the gold coated prism by RF magnetron sputtering (50% Ar, 45% N2 and 5% O2) at a sputtering pressure of 20mTorr using a metallic Zn target (99.99% pure). The reflectance measurements were made using a simple SPR setup attached with an angle detector of accuracy 0.01 oC. A heater block was fixed on the prism table for temperature dependent studies from room temperature (RT) to 500 K. The SPR reflectance measurements were made for both the two-layer (prism-gold-air) and three-layer (prism-gold-ZnO:N-air) system as a function of angle of incidence using a p- polarized He-Ne laser incident on the film coated face of the prism.SPR reflectance curve obtained for Au-air interface as a function of angle of incidence gives a sharp reflectance dip at an angle of 44.12o. The SPR reflectance curve of the three-layer system (prism-gold-N:ZnO-air) was also recorded at room temperature (300 K) and a broad reflectance shifted dip was observed at an angle of 44.45o.With an increase in temperature from RT to 500 K, the reflectance dip was shifted from 44.45oto 45.35o. This shift in reflectance dip with increase in temperature indicates change in the optical and dielectric properties of ZnO:N thin films. The complex dielectric constant obtained by fitting the experimentally observed SPR reflectance data with theory was found to increase from 3.89+i0.04 to 3.98+i0.06 with an increase in temperature from 300K to 500K. It was found that the refractive index of ZnO:N thin film increases and the band gap shows redshift with N incorporation in ZnO, thereby tailoring the optical properties of ZnO for various applications. The corresponding increase in refractive index (1.972–1.994) and decrease in band gap with increasing temperature was observed. Thus SPR is a powerful technique which can be used as a low cost temperature sensor with a sensitivity of 1.1× 10-4 RIU/K.
9:00 PM - R5.7
Surface Plasmon Resonance (SPR) Based NOx Gas Sensor.
Shibu Saha 1 , Navina Mehan 1 , Vinay Gupta 1 Show Abstract
1 Department of Physics & Astrophysics, University of Delhi, Delhi, Delhi, India
The initial results on room temperature detection of NOx gas using surface plasmon resonance (SPR) technique are presented. The SPR response of a Au-TeO2 bi-layer with p-polarized He-Ne laser and prism-coupling method was studied. A 40 nm thin gold film was deposited on the hypotenuse face of a BK7 glass prism by thermal evaporation. Thereafter, a 130 nm thin tellurium dioxide (TeO2) film was deposited on the as-deposited Au film by radio frequency (rf) sputtering technique under optimized conditions. The experimental SPR reflectance curve of the Au film and that of the Au-TeO2 bi-layer were fitted by Fresnel’s equations, yielding the dielectric constant of the Au and TeO2 films as ε1= -12.8 + j1.1 and ε2= 4.285 + j0.01 respectively. NOx gas, in fixed concentrations, was allowed to flow into an evacuated glass sample cell attached to the coated prism face. The SPR reflectance curves of the prism-Au-TeO2 bi-layer structure shifted continuously towards higher SPR angles when exposed to increasing concentrations of NOx gas. The SPR reflectance curve became slightly broader progressively and the minimum value of reflectance also changed with increasing NOx gas concentration. The changes in refractive index of the TeO2 film due to interaction with NOx gas of different concentrations were determined by fitting the SPR reflectance curves with Fresnel’s equations, and were found to be quite linear. Alternatively, changes in SPR reflectance at a fixed incident angle (close to the SPR angle) were also measured as a function of NOx gas concentration and the detection limit of about 500 ppm was observed. The sensor was found to be reversible as the SPR reflectance curve regained its original position and shape within a relatively small time (~60s) after the removal of the NOx gas. The obtained results are encouraging and will pave the way towards realization of gas sensors based on SPR.
9:00 PM - R5.8
Diarylethene Nanocrystals for Optical Device Components: Nanocrystallization, Encapsulation by Polymer and Photochromic Properties.
Norio Tagawa 1 , Akito Masuhara 2 , Tsunenobu Onodera 1 , Hitoshi Kasai 1 , Hidetoshi Oikawa 1 Show Abstract
1 Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Sendai, Miyagi, Japan, 2 Graduate School of Science and Engineering, Yamagata University, Yonezawa, Yamagata, Japan
Photochromic nanocrystals are expected as switching component for photonic crystals and optical waveguides, because of reversible refractive index changes with photochromism. Among a lot of photochromic compounds, diarylethene (DAE) is most promising compound, because DAE has high photo-sensitivity, fatigue resistance, and response in crystal. With this background, some research group fabricated DAE nanoparticles. Unfortunately, it was difficult to control DAE nanocrystal size, and they were only amorphous nanoparticle, not nanocrystals. In this study, we tried to fabricate size-controlled DAE nanocrystals by establishing novel nanocrystallization processes based on the reprecipitation method, and to reveal size-dependence photochromic properties in nano-scale. Additionally, we encapsulated DAE nanocrystals by polymer in order to improve the size distribution and sphericity of nanocrystals for optical applications.We have fabricated DAE nanocrystals by establishing novel nanocrystallization processes based on the reprecipitation method. In these processes, we added photo-isomarized DAE molecules as a nucleating agent, or we heated nanocrystals dispersion liquid for nanocrystallization by microwave irradiation. The obtained DAE nanocrystals clearly exhibited photochromism by alternate irradiation of UV and visible light. In this measurement, we observed red-shift of characteristic absorption peak position with increasing nanocrystal size. We proposed that this peak shift was ascribed to strained structure of DAE molecules in the nanocrystal and soften of crystal lattice with decreasing in nanocrystal size.In addition, we encapsulated DAE nanocrystals by transparent polymer for monodispersed size and spherical shape. The DAE nanocrystals were covered with polystyrene by soap-free emulsion polymerization. The encapsulated DAE nanocrystals can form two-dimensional hexagonal structure due to their monodispersed size and spherical shape with a high degree of accuracy. The encapsulated DAE nanocrystals exhibited photochromism by UV and visible lights, and size-dependence photochromic properties were maintained even after encapsulation by polystyrene. The encapsulated DAE nanocrystals will be useful as components for optically functional devices.
Siegfried Bauer Johannes-Kepler Universitaet Linz
Kunigunde Cherenack Philips Corporate Technologies, Research
Barclay Morrison III Columbia University
Tsuyoshi Sekitani The University of Tokyo
R6: Soft Actuators
Wednesday AM, November 30, 2011
Room 308 (Hynes)
9:30 AM - **R6.1
Self-Sensing and Soft Artificial Muscle Motors.
Iain Anderson 1 2 , Todd Gisby 1 , Thomas McKay 1 , Benjamin O'Brien 1 Show Abstract
1 Biomimetics Lab, Auckland Bioengineering Institute, Auckland New Zealand, 2 Engineering Science, University of Auckland, Auckland New Zealand
Artificial muscles based on the dielectric elastomer actuator can be used for direct linear actuation and also rotary actuation. The rotary motion can be achieved by phasic control of antagonistic muscles within the same membrane. The muscles can turn a shaft through a crank mechanism or a central gear. For the geared motor we initially used a hard gear that drove the shaft through an orbital movement. Recently we have embedded a soft elastomer gear within the membrane, in place of the hard orbiter. Deformation of the membrane results in deformation of the gear and this can be used for not only gripping and rotating the shaft but also translating it from side to side in a soft, bearing-free all polymer motor. In a parallel development we are now investigating ways of making our soft motors self-sensing. For instance, until recently they required external electronics to control commutation of the voltage waveform from muscle to muscle. This is no longer necessary for it is now possible to fully integrate control within the membrane itself using the Dielectric Elastomer Switch; a device that will change its resistance by several orders of magnitude on stretching. To demonstrate how the DES can operate and automatically commute the motor we have produced a prototype from a pre-stretched 3M VHB4905 membrane that drives a crank. The membrane was supported in a rigid acrylic frame and DE muscles along with DES were added by painting conducting carbon grease to sectors of the membrane. DC power was supplied using a Biomimetics Lab EAP Control unit (ABI, NZ) but actuation was entirely controlled by the DES in such a way that the motor could turn the shaft.This development opens the door to fully soft artificial muscle machines with integrated control and without the need for external electronics.
10:00 AM - R6.2
Phase-Transition Actuator Inspired by Plants.
Ingrid Graz 1 , Roland Altmueller 1 , Reinhard Schwoediauer 1 , Siegfried Bauer 1 Show Abstract
1 Soft Matter Physics, Johannes Kepler University, Linz Austria
The ability for motion is common to all living beings being essential for their survival. Most animals and humans use muscles for movements. Examples of artificial muscles are dielectric elastomer actuators (DEAs) with their voltage induced deformation. However, the required driving voltages are quite large, often in the kilovolt range.Quite unnoticed, plants are also capable of motion. In contrast to animals they don’t use muscles. Instead they employ very soft actuation based on swelling and shrinking or elastic instabilities. Inspired by plants and fungi we have built hydraulic actuators. Here an elastomeric frame undergoes large deformations caused by the phase transition of an embedded liquid from the liquid to the gaseous state. The phase transition in the liquid is simply induced by electrical Joule heating. A very large deformation is feasible on the base of the huge volume changes upon the liquid gaseous phase transition. Low voltage operation is guaranteed, since the deformation relies on liquid heating, albeit with large power consumption in comparison to DEA’s.Biaxial deformations of ~100% are achieved in a 9 mm wide cell within a PDMS elastomer at a driving voltage of 10V and an input power of 1W, with a large blocking force of 5-6 N. The proposed actuator concept is easily prone to miniaturization, potentially useful in Braille readers.
10:15 AM - **R6.3
Electro-Active Skin: From Anti-Biofouling to Transfer Printing.
Xuanhe Zhao 1 Show Abstract
1 Soft Active Materials Laboratory, Mechanical Engineering, Duke University, Durham, North Carolina, United States
In this talk, we will present a polymer skin (or coating) that can dynamically change its morphology under applied electrical voltages. The working mechanism for the polymer skin is a new type of voltage-induced instability recently discovered in our group. Subject to an electric voltage, a substrate-bonded polymer film initially maintains flat and smooth. Once the voltage reaches a critical value, regions of the polymer surface locally fold against themselves to form a pattern of creases. As the voltage further rises, the creases increase in size and decrease in density, and strikingly evolve into craters in the polymer. The critical voltage, morphology, and length scale of the instability patterns can be tuned by varying the dimension and modulus of the polymer. We will discuss two examples of the electro-active skin’s applications. The voltage-induced deformation and instability of the polymer film can be used to prevent the formation of biofilms (biofouling) and/or to detach existing biofilms on the polymer surface. As another example, the electro-active skin can be used to accurately control the adhesion and release of small objects, with potential applications in transfer printing. The electro-active skin is flexible, conformal to complicated geometries, and easy to use. Large-scale fabrication of the electro-active skin is simple and cheap.
10:45 AM - R6.4
Stretchable Tactile Sensors for Various Environments.
Benjamin Chee-Keong Tee 1 , Darren Lipomi 2 , Michael Vosgueritchian 2 , Sokolov Anatoliy 2 , Gregor Schwartz 2 , Zhenan Bao 2 Show Abstract
1 Electrical Engineering, Stanford University, Stanford, California, United States, 2 Chemical Engineering, Stanford University, Stanford, California, United States
We obtained very high sensitivity for capacitive pressure sensors using micro-structured poly-dimethoxysilane (PDMS) as the dielectric in a parallel plate configuration . The method allows for simple tuning of pressure sensitivities by embossing different microstructures on the dielectric. The previous sensor was made on flexible substrates such as polyethylene terephthalate (PET). This places limitations on the types of environments that the sensor can be used. In order to apply the sensor in various environments, such as curved surfaces, elastomer substrates would be most suitable. Thus, a process to fabricate the micro-structured dielectric on elastomeric substrates was developed. We will also report on recent progress in testing the highly sensitive sensor for use in various environments, such as underwater, foldable touchscreens and prosthetic devices. 1. Mannsfeld, S.C.B. et al. Highly sensitive flexible pressure sensors with microstructured rubber dielectric layers. Nature Materials 9, 859–864 (2010).
R7: Bio-Integration with Stretchable Electronics
Wednesday AM, November 30, 2011
Room 308 (Hynes)
11:30 AM - **R7.1
Flexible and Compliant Interfaces to the Peripheral and Central Nervous System.
Thomas Stieglitz 1 2 3 , Tim Boretius 1 , Christina Hassler 1 2 , Christian Henle 1 3 , Birthe Rubehn 1 4 , Juan Ordonez 1 , Martin Schuettler 1 2 3 Show Abstract
1 Microsystems Engineering-IMTEK, Lab Miomedical Microtechnology, University of Freiburg, Freiburg Germany, 2 Bernstein Center Freiburg, University of Freiburg, Freiburg Germany, 3 , CorTec GmbH, Freiburg Germany, 4 , MedEl, Insbruck Austria
The material tissue interface between electrode arrays and the nervous tissue determines the long term stability and functionality in neural implants in the peripheral and central nervous system. Polymers, metals and semiconductors must not degenerate or corrode, respectively. Electronics must be hermetically sealed to protect the electronic circuits from water and ions. Implants must be stable and robust on one hand to survive the implantation procedure and movements of the body and on the other hand smart enough side to deliver good surface and structural biocompatibility to provoke only minor foreign body reaction and stay in a stable position with respect to the target tissue.Our group has developed two approaches for neural interfaces based on flexible and compliant substrates. Laser structured silicone rubber substrates allow medium scale integration of electrodes and interconnection tracks and help to reduce the development time towards approved medical devices for human applications. Epicortical electrode arrays for presurgical epilepsy diagnosis are the first device that undergoes investigations towards medical device approval. Large scale integration or smallest anatomical and physiological boundary conditions require even smaller feature sizes. Micromachining of thin-film metallization that were sandwiched between polyimide layers enables a wide range of designs and devices. Thread-like arrays allow stimulation of different fascicles over the cross section of a peripheral nerve with a high selectivity. Arrays in the centimeter range recorded nerve activity from the surface of a hemisphere of the brain for more than 12 months. Stiff but biodegradable coatings on the flexible substrates were investigated for intracortical neural probes. During the last years, the interest to get a more complete picture of the processes in the nervous system and to integrate electrical and chemical information led to novel neural probes with integrated fluidic and optical structures. In pilot experiments, we were able to develop polymer based neural probes as tool for optogenetic neuroscience.The more complex neural probes get, the more important is reliable and robust packaging and encapsulation of electronics in neural implants, especially on the way towards clinical application. Ceramic based hermetic packages were combined with flexible substrates and electrode arrays. Miniaturized approaches based on established technologies led to packages with about 200 hermetic electrical feedthroughs for neural implants with such a need, e.g. retinal vision prostheses and brain-computer interfaces. In vitro assessment has been promising and predicts device life-time that is beyond the requirements for neural implants.Acknowledgment: Part of the work has been funded by the German Federal Ministry of Education and Research (BMBF) ( 01GQ0830 BFNT, 01GQ0420 GoBio, 16SV3792 FutureRet) and by the European Union ( CP-FP-INFSO 224012/TIME).
12:00 PM - R7.2
Stretchable Microelectrode Arrays for In Vitro Neural Interfaces.
Woo Hyeun Kang 1 , Wenzhe Cao 2 , Sigurd Wagner 2 , Barclay Morrison III 1 Show Abstract
1 Biomedical Engineering, Columbia University, New York, New York, United States, 2 Electrical Engineering, Princeton University, Princeton, New Jersey, United States
Approximately 1.7 million traumatic brain injuries (TBI) occur annually in the US, resulting in 275,000 hospitalizations and 52,000 deaths, at a cost of $60 billion. Current studies to evaluate alterations of neuronal electrophysiology utilize microelectrode arrays (MEAs) patterned on rigid glass or flexible polyimide incapable of withstanding strains above 5%, which is necessary to induce TBI. Alternative strategies involving removal of MEAs during the injury event introduce discrepancies in pre- and post-injury recordings, resulting in problematic normalization in data analyses. Additionally, maintaining long-term culture sterility remains a challenge, limiting studies to the acute phase. To address these shortcomings, we have developed elastically stretchable MEAs (SMEAs) capable of undergoing large, biaxial 2-D stretch while remaining functional, allowing for recording before and after large stretches of up to 18% biaxial strain. Organotypic hippocampal slice cultures grown on the SMEA deform with the electrodes during mechanical stretch in our well-characterized in vitro injury model. This allows direct comparison of post-injury alterations in electrophysiological function to pre-injury baseline levels. Spontaneous neural activity was observed in hippocampal slice cultures immediately before and after injury. Post-injury, action potential firing frequency and peak-to-peak amplitude increased. In addition, bursting was observed immediately after injury, a result indicative of glutamate release caused by neuronal depolarization, possibly due to defects in plasma membrane integrity. In experiments that reflect the ability of the SMEA to stimulate tissue and record evoked responses, electrical stimuli were applied to hippocampal slice cultures immediately before and after injury to generate stimulus-response curves. Post-injury perfusion of hippocampal slice cultures with CNQX, an AMPA/kainate receptor antagonist, diminished both spontaneous activity and evoked responses. These responses recovered to baseline levels after washout of CNQX with artificial cerebrospinal fluid, and were amplified by perfusion with bicuculline, a GABAA receptor antagonist, verifying the biological origin of the spontaneous activity and evoked responses. Thus we have developed stretchable microelectrode arrays capable of withstanding large, rapid biaxial deformations while maintaining the ability to perform traditional electrophysiological measures of neuronal function, in combination with pharmacology relevant to TBI neuroscience. The convergence of these three paradigms of neurophysiology onto a single in vitro platform presents the opportunity to investigate injury mechanisms of TBI within the same brain slice culture in both acute and long-term studies. Novel TBI therapies could be identified and tested in our in vitro TBI model, greatly increasing the rate of therapeutic discovery.This work was supported by the New Jersey Commission on Brain Injury Research.
12:15 PM - **R7.3
Compliant, Bio-Integrated Electronics.
John Rogers 1 Show Abstract
1 , University of Illinois, Urbana, Illinois, United States
Hybrid combinations of hard semiconductors (e.g. silicon) and soft polymers (e.g. silicone) can yield electronic systems with excellent performance characteristics and mechanical properties matched to human tissue. We describe integrated circuits and sensors with thicknesses, effective moduli and areal mass densities matched to the epidermis. These devices can be mounted on the surface of the skin in way that is ‘invisible’ to the user, to provide various functions, including measurement of electrophysiological signals associated with activity in the heart, brain and skeletal muscles.
12:45 PM - R7.4
Tattoo-like Epidermal Electronic Systems.
Nanshu Lu 1 2 , Dae-Hyeong Kim 3 , Ma Rui 1 4 , John Rogers 1 3 Show Abstract
1 Beckman Institute, University of Illinois, Urbana, Illinois, United States, 2 Department of Aerospace Engineering and Engineering Mechanics, University of Texas at Austin, Austin, Texas, United States, 3 Department of Materials Science and Engineering, University of Illinois, Urbana, Illinois, United States, 4 Department of Electrical and Computer Engineering, University of Illinois, Urbana, Illinois, United States
We report classes of electronic systems that achieve thicknesses, effective elastic moduli, bending stiffnesses and areal mass densities matched to the epidermis. Unlike traditional wafer-based technologies, laminating such devices onto the skin leads to conformal contact, and adequate adhesion based on van der Waals interactions alone, in a manner that is mechanically invisible to the user. We describe systems incorporating electrophysiological, temperature and strain sensors, as well as transistors, light emitting diodes, photodetectors and radio frequency inductors, capacitors, oscillators and rectifying diodes. Solar cells and wireless coils provide options for power supply. We use this type of technology to measure electrical activity produced by the heart, brain and skeletal muscles and we show that the resulting data contain sufficient information for an unusual type of computer game controller.
R8: Flexible and Stretchable Photonics I
Wednesday PM, November 30, 2011
Room 308 (Hynes)
2:30 PM - **R8.1
Stretchable Transparent Composite Electrodes and Polymer Thin Film Devices.
Qibing Pei 1 Show Abstract
1 , UCLA, Los Angeles, California, United States
Both single wall carbon nanotubes and silver nanowires have been employed to fabricate transparent electrodes by an in-situ composite synthesis technique. The composite electrodes retain the high conductivity of the conductive networks and the mechanical flexibility of the polymer matrix. The electrodes can be stretched by up to 100% without significant loss of sheet resistance. The composite electrodes have a low surface roughness of less than 10 nm. Polymer light emitting diodes and solar cells fabricated on the composite electrodes show similar or superior performance compared to controls on indium-tin-oxide coated on glass substrate. Flexibility of the devices will be described, including the first intrinsically stretchable polymer light emitting devices.
3:00 PM - R8.2
Compliant, Large-Area Organic Active-Matrix LED Pixel Circuits Driven by Organic Floating-Gate Transistors.
Tsuyoshi Sekitani 1 , Tsung-Ching Huang 1 , Koichi Ishida 1 , Kazuo Takimiya 2 , Makoto Takamiya 1 , Takayasu Sakurai 1 , Takao Someya 1 Show Abstract
1 , Univ. of Tokyo, Tokyo Japan, 2 , Hiroshima Univ., Hiroshima Japan
We have demonstrated an ultraflexible active matrix organic LED pixel circuits on 13-μm thin-film polyimide for applications to medical sensors and treatments. The circuit that applies printed floating-gate organic transistors can compensate the LED brightness variations and degradation for more than 6 months. The 230×230 mm^2 printed active matrix circuit comprises 64×64 screen-printed organic 2-transistors-1-capacitor (2T1C) cells, and the periodicity is 2.5 mm. Because of 13-μm thin-film for the circuit's substrate, critical bending radii are achieved to be less than 1 mm in bending radius. By feedback controlling the threshold-voltages of the floating-gate organic transistors and the organic LED driving currents, we can realize less than 5% non-uniformity with greater than 200 cd/m^2 luminance. The active-matrix organic transistor circuit has been fabricated using screen-printing. All the electrodes are formed using screen-printed Ag pasts sintered at 80 oC, while the gate dielectric layer is by CVD parylene. Organic semiconducting channel is 50-nm-thick vacuum-evaporated dinaphtho[2,3-b:2',3'-f]thieno [3,2-b]thiophene (DNTT). Stand-alone printed transistors with bottom contact geometry exhibit mobilities more than 0.3 cm^2/Vs and on/off ratio exceeds 10^5.This study was partially supported by JST/CREST, Kakenhi (Wakate S & A), NEDO, and Special Coordination Funds for Promoting Science and Technology.
3:15 PM - R8.3
Electrical Tuning of InGaN Quantum Dots in GaN Photonic Crystal Cavities.
Alexander Woolf 1 , Kasey Russell 1 , Fabian Rol 1 , Evelyn Hu 1 , Haitham El-Ella 2 , Menno Kappers 2 , Rachel Oliver 2 Show Abstract
1 School of Engineering and Applied Sciences , Harvard University, Cambridge, Massachusetts, United States, 2 Department of Materials Science and Metallurgy, University of Cambridge, Cambridge United Kingdom
Semiconductor optical cavities offer a unique platform for the study of light-matter interactions. The ability to precisely control these interactions offers promising possibilities toward quantum computing, cavity quantum electrodynamics, and the creation of exotic states of matter like quantum dot exciton-polaritons. The large band gap and high exiton binding energy of gallium nitride (GaN) make it a candidate for such studies at room temperature. Significant challenges still remain, due to the strong piezoelectric fields in GaN and the material’s chemical inertness. Here we demonstrate the fabrication of photonic crystal cavity structures in a thin, suspended, electrically active GaN p-n junction membrane consisting of InGaN quantum dots. Historically, the lack of a selective wet chemical etch in GaN has been an obstacle in the fabrication of suspended membranes. But by utilizing a novel etch technique known as photo-electrochemical (PEC) etching, our group has recently demonstrated microdisk resonators with quality factors as high as 6,000 . In spite of clear evidence of modes in the cavity, we have not been able to measure a change in the lifetimes of the InGaN quantum dots, one signature of coupling between the emitters and the cavity. This coupling critically depends on both the resonance of the quantum dot emission and the frequency of the cavity mode as well as the strategic placement of the quantum dot at the mode’s maximum field intensity. Thus the spectral tuning of the quantum dot and the cavity mode have been essential components of achieving quantum dot-cavity resonance. In the past, spectral tuning has been achieved by a variety of techniques including temperature tuning of quantum dots and cavity deformation via oxide etching or monolayer deposition of inert gases. However, these approaches have limitations such as irreversibility or performance degradation. The internal electrical fields of GaN allow for a unique associated tunability of InGaN quantum dot emissions up to 80 meV under an applied bias of a few volts . Furthermore, such tuning is reversible and does not adversely affect device performance. Initial measurements using this technique show the feasibility of tuning quantum dots in a cavity structure . We intend to present those tuning results for a cavity. Thus we have carried out the first studies demonstrating electrical tuning of InGaN quantum dots in a material structure designed uniquely to allow the fabrication of cavities. This work should be the critical missing piece to demonstrate coupling between InGaN quantum dots and a nanoscale GaN cavity structure. These results could be pivotal in bringing fundamental science out of the lab and into to the next generation of integrateable and robust solid-state devices. Tamboli et al, Nature Photonics 1, 61-64 (2007),  Christopoulos et al, PRL 98, 126405 (2007) Jarjour et al, PRL 99, 197403 (2007)
3:30 PM - R8.4
Flexible, Self-Standing and Selective UV-VIS-NIR Optical Filters Based on Polymer Infiltration of Porous One Dimensional Photonic Crystals.
Mauricio Calvo 1 , Jose Castro 1 , Hernan Miguez 1 Show Abstract
1 Multifunctional Optical Materials, Instituto de Ciencia de Materiales de Sevilla, Sevilla Spain
Herein we present a synthetic route to attain flexible and self standing optical filters with capability of blocking electromagnetic radiation in the ultraviolet (UV), visible (VIS) and near infrared (NIR). 1 Shielding in the VIS and NIR was achieved alternating metal oxide nanoparticle layers with different refractive index to obtain a porous one dimensional photonic crystal (1DPC),2 whereas the selective filtering in the ultraviolet region was attained by changing the type of nanoparticle. Nanoparticulated layers were deposited from colloidal suspensions prepared by sol-gel and deposited following a spin coating protocol that allows to select the optical properties of the stack.3 The mechanical properties of both ensembles were acquired by the infiltration of those porous structures with polymers (PDMS or polycarbonate).4,5 The method proposed yields the uniform filling of the nanopores of the multilayer by the polymer, which allows lifting off the hybrid structure. The final hybrid material combines the photonic properties of the nanoparticle layer and the mechanical properties of the polymer infiltrated. Experimental evidence of the use of these materials as as protective films and as low-weight mirrors is also provided.References1. O. Sánchez-Sobrado, M.E. Calvo, H. Míguez J. Mater. Chem (Cover Story) 2010, 20, 8240-82462. S. Colodrero, M. Ocana, H. Míguez Langmuir 2008, 24, 44303. M.E. Calvo, O.Sanchez Sobrado, S. Colodrero, H. Míguez, Langmuir 2009, 25, 24434. M.E. Calvo, O. Sánchez-Sobrado, G. Lozano, H. Míguez J. Mater. Chem 2009, 19, 3144-31485. 5. M.E. Calvo, H. Míguez Chem. Mater. 2010, 22, 3909-3915
3:45 PM - R8.5
Organic Light Emitting Diodes with Silica/Polystyrene Diffraction Grating for Improved out-Coupling Efficiency.
Wooram Youn 1 , Won Hoe Koo 1 , Xiaohang Li 2 , Nelson Tansu 2 , Franky So 1 Show Abstract
1 Materials Science and Engineering, University of Florida, Gaiensville, Florida, United States, 2 Department of Electrical and Computer Engineering, Lehigh University, Bethlehem, Pennsylvania, United States
Through numerous efforts to improve the efficiency of organic light emitting diodes (OLEDs), the internal quantum efficiency was able to achieve the unity. Nevertheless, about 80% of light generated is trapped and wave-guided within the structure due to the total internal reflection by the mismatch of refractive indices between each layer. Many of wavelength-scale diffraction grating studies on organic light emitting diodes have been proved to extract those confined light. The periodicity, depth and directionality of the gratings are important factors to determine the out-coupling efficiency. Here, we demonstrate that the OLED with self-assembled monolayer of silica spheres semi-embedded in polystyrene (PS) layer as the grating structure can be effective and practical for the diffraction grating structures due to the properties of simple process to fabricate, and more directionality to improve the light extraction efficiency. Moreover, periodicity and depth of diffraction grating can be easily tuned using different size of silica and PS spheres. It was confirmed that varying periodicity and depth of silica grating, enhancement of current and power efficiencies was achieved maximum 70% and 120% each, compared to the OLED with the flat structure. Such convenient approach for light extraction is attractive and practical for use in lighting application.
R9: Flexible and Stretchable Photonics II
Wednesday PM, November 30, 2011
Room 308 (Hynes)
4:30 PM - **R9.1
Elastomeric Plasmonics and Photonic Crystals: Self-Assembly on the Kilometre Scale.
Jeremy Baumberg 1 Show Abstract
1 Cavendish Laboratory, University of Cambridge, Cambridge United Kingdom
New photonic properties are produced in materials which are assembled from diverse combinations of metals, semiconductors and dielectrics that are structured on the 1-100nm scale, with a wealth of potential applications ranging from communications to bio-sensing. However producing such nanomaterials on the mass-scale is far from trivial as three-dimensional structures are very hard for traditional lithographies and self-assembly has so far been a lab-scale tricky process.Here we concentrate on two types of self-assembly for producing 3D fully-ordered elastomeric photonic crystals, and plasmonics. In the latter case, gold nanoparticles are self-assembled into structures with rigid reliable 0.9nm gaps highlighting the new coupled modes that can be produced. When such nanoparticles are assembled onto elastomeric substrates, stretch tuning the nm-scale gaps results in tuning of the spectral resonances, paving the way to active metamaterials and plasmonics.When we assembly wavelength-scale dielectric spheres, a new range of structural colour nanomaterials which can be mass produced as films on the kilometre scale [3-12]. While most manmade (and natural) colours exploit dye absorption, there is strong interest in avoiding these carcinogenic and UV-bleached chemicals. Alternative structural colours are produced from periodic wavelength-scale-sized transparent components, and thus are benign, longlived, and possess new optical features. We create polymer photonics crystals made of cross-linked polymer spheres dispersed in a soft elastomeric matrix, using a novel industrially-scalable shear-based nano-assembly. Simply tuning the size of the spheres changes the colour across the entire visible spectrum, while optimised shearing creates single-domain opal films. By stretching these elastomeric photonic crystals, a phase transition from fcc to monoclinic results, breaking the traditional scattering selection rules. We demonstrate a wide variety of new optical properties based on the resonant scattering phenomena.R.W. Taylor, …, Jeremy J. Baumberg, Sumeet Mahajan, ACS Nano 5, 3878 (2011)F. Huang, J.J. Baumberg, Nano Letters 10, 1787 (2010)O. L. J. Pursianinen, J. J. Baumberg, et al., Optics Express 15, 9553 (2007). T. Ruhl, P. Spahn, G.P. Hellmann, Polymer 44, 7625 (2003). O. L. J. Pursianinen, J. J. Baumberg, et al., Advanced Materials 20, 1484 (2008).J. Sussman, D.R.E. Snoswell, J.J. Baumberg et al, Appl.Phys.Lett. 95, 173116 (2009)J.J. Baumberg, O.L. Pursiainen, et al., Phys.Rev.B 80, 201103(R) (2009)D.R.E Snoswell, J.J. Baumberg, textiles 36, 8 (2009)A. Kontogeorgos, J.J. Baumberg, et al, Phys.Rev.Lett. 105, 233909 (2010)M. Kolle, B. Zheng, N. Gibbons, J.J. Baumberg, U, Steiner, Opt Exp 18, 4356 (2010)D.R.E. Snoswell, A. Kontogeorgos, J.J. Baumberg, et al., Phys.Rev.E 81, 020401(R) (2010)C.E. Finlayson,.. J.J. Baumberg, Adv. Mat. 23, 1540 (2011)
5:00 PM - R9.2
Direct-Bandgap Infrared Light Emission from Tensilely Strained Germanium Nanomembranes.
Jose Sanchez-Perez 1 , Cicek Boztug 3 , Feng Chen 4 , Faisal Sudradjat 3 , Deborah Paskiewicz 1 , R. Jacobson 1 , Roberto Paiella 3 , Max Lagally 2 1 Show Abstract
1 Material Science Program, University of Wisconsin Madison, Madison, Wisconsin, United States, 3 Electrical and Computer Engineering, Boston University, Boston , Massachusetts, United States, 4 , Xi’an Jiaotong University, Xi'an, Shaanxi, China, 2 Material Science and Engineering, University of Wisconsin Madison, Madison, Wisconsin, United States
Silicon, germanium, and related alloys, which provide the leading materials platform of electronics, are extremely inefficient light emitters because of their indirect fundamental energy bandgap. This basic materials property has so far hindered the development of group-IV photonic active devices, including diode lasers, thereby significantly limiting our ability to integrate electronic and photonic functionalities at the chip level. Here we show that Ge nanomembranes can be used to overcome this materials limitation. Theoretical studies have predicted that tensile strain in Ge lowers the direct energy bandgap relative to the indirect one. We demonstrate  that mechanically stressed nanomembranes allow for the introduction of sufficient biaxial tensile strain to transform Ge into a direct-bandgap, efficient light-emitting material that can support population inversion and therefore provide optical gain.  J. R. Sanchez-Perez, C. Boztug, F. Chen, F. Sudradjat, D. M. Paskiewicz, RB. Jacobson, M. G. Lagally, and R. Paiella, submitted. Research supported in part by NSF and DOE.
5:15 PM - R9.3
Elastic Photonic Fibers.
Mathias Kolle 1 , Alfie Lethbridge 2 , Peter Vukusic 2 , Nicholas Gibbons 3 , Jeremy Baumberg 3 , Joanna Aizenberg 1 Show Abstract
1 School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts, United States, 2 School of Physics, University of Exeter, Exeter United Kingdom, 3 Cavendish Laboratories, University of Cambridge, Cambridge United Kingdom
Biomimetic and bio-inspired attempts to produce novel photonic structures have attracted increasing research interest in recent years. Nature offers us a wide variety of micro- and nanostructures that provide unique optical signatures including outstanding, distinctive, dynamic and tailored coloration, high reflectivity or superior whiteness. Various intriguing photonic structures have been identified on the wing scales of beetles, butterflies, the feathers of birds or in marine animals. While efforts in the study of natural structural colors have historically been focussed on photonic systems in animals, recent research suggests that many plants also employ photonic structures to tailor their interaction with light. Here, we will describe a new photonic structure found in a plant and report a bioinspired fabrication of elastic photonic fibers that mimic their natural counterpart. We present the manufacturing technique and the optical and structural characterization of the elastic photonic fibers supported by optical modeling.
5:30 PM - R9.4
Three-Dimensional Integration of Nanowire Waveguides.
Jaeyeon Pyo 1 , Ji Tae Kim 1 , Jung Ho Je 1 Show Abstract
1 Materials Science and Engineering, POSTECH, Pohang, GyeongSangBuk-do, Korea (the Republic of)
Nanowire waveguides have attracted huge interests owing to their feasibility as building blocks for photonic integrated circuit [1, 2].Propagation loss, specifically substrate-induced radiation loss, is a universal issue in nanowire waveguides [1, 3-5]. The loss is mostly caused by the coupling of the propagating light into the substrate that is in contact with the waveguide . The substrate coupling loss has been effectively reduced by suspending nanowire waveguide in the air [4, 7]. This approach is, however, not suitable for photonic integration, which is absolutely required for realizing practical devices .Here, we propose a new strategy that enables not only to significantly reduce the substrate coupling loss, but also to integrate nanowire waveguides directly into circuits. Based on accurately 3D guiding of a polystyrene meniscus by pulling a solution-filled micropipette , we demonstrate the successful fabrication of 3D nanowire polystyrene arches with controlled diameters (down to ~ 200 nm). By perfect isolation from the substrate, the propagation loss is significantly reduced. We discuss the enhanced guiding performance and the wavelength filtering effect.Email: email@example.comReferences M. Law, et al. Science 305, 1269 (2004)  CJ Barrelet, et al. Nano Letters 4, 1981 (2004) F. D. Benedetto, et al. Nature Nanotech. 3, 614 (2008) R. Yan, et al. Proc. Natl. Acad. Sci. USA 106, 21045 (2009) D. O’Carroll, et al. Nature Nanotech. 2, 180 (2007) P. Domachuk, B. J. Eggleton, Nature Mater. 3, 85 (2004) L. Tong, et al. Nature 426, 816 (2003) JT Kim, et al. Adv. Mater. 23, 1968 (2011)
5:45 PM - R9.5
Stretchable Light-Emitting Electrochemical Cells (LEECs).
Heather Filiatrault 1 , Gyllian Porteous 1 , Tricia Carmichael 1 Show Abstract
1 Chemistry and Biochemistry, University of Windsor, Windsor, Ontario, Canada
Organic light-emitting devices (OLEDs) have progressed from fabrication on rigid, planar substrates to flexible plastic substrates; there are now a few studies that report the successful fabrication of OLEDs on elastomeric substrates with stretchable interconnects. In this talk, we describe our recent work on the fabrication of stretchable light-emitting electrochemical cells (LEECs) on poly(dimethylsiloxane) (PDMS). LEECs are a class of electroluminescent devices that use ionic transition metal complexes to support charge injection, charge transport, and emissive recombination. This functionality allows these devices to be fabricated from a single layer sandwiched between an air-stable anode and cathode; this simple architecture makes these devices especially well-suited to stretchability. We describe the integration of a stretchable transparent gold anode fabricated by e-beam deposition on PDMS (an alternative to conventional brittle ITO anodes), an ionic ruthenium complex dispersed in a PDMS matrix as the emissive layer, and a liquid metal cathode to produce stretchable LEECs in which both the emissive layer and the interconnects can tolerate stretching. These devices can be stretched to ~ 27% elongation before device functionality is lost.